popular hobbyists handbook -...

Projects you can build! GERNSBACK SPECIALTY SERIES L 49604

;;;; ELEC RONICSPopular HOBBYISTS

Electmnies®handbook TM

COMMUNICATIONS Aviation -Band

Receiver 4 -Element,

2 -Meter Quad Receiver

Preamplifiers Active Antenna

AUTOMOTIVE Smarter

Gas Gauge Turn Signal

Reminder

FUN PROJECTS Electronic Gong Beverage Cooler Digital Bowl Box Non -Serious Circuit

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What Do These PrestigiousCompanies Have In Common?

AerovoxDC Film and RFI Suppression Capacitors,

AC Oil Capacitors, EMI Filters

AMPElectrical/Electronic

IC Sockets,Connectors,

PCB Switches

WAX CORPORATION OCER. CAO,C0Hr

MLC, Tantalum and Thin FilmCapacitors, Resistors,Networks, Trimmers,

111-Z Oscillators, Resonators, Filtersand Piezo Devices

CAROL I I " 4:4 III- CommunicationsTubing, Conduits, Hose Sleevings. Splices,[ARO!, CAB. COMONr II Instruments, Inc.

Electronic and Electrical Wire and Cable Insulation and Cable Harness Productsand Power Supply Cords Relays and Solenoid Relays

CORNELLDUBILIER

Capacitors -AluminumElectrolytics, Mica, AC Oil, Film,

MICA Paper and Relays

'111. P BLICATION

Electronics Now Magazine

A

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A COMPANY OF

Dale Electronics, Inc.Resistors, Networks, Oscillators, Displays,

Inductors & Thermistors

PPM, EPriVEMURATA ERIE NORTH AMERICA

Monolithics, Discs, Variable Capacitors,

Oscillators, Potentiometers, RFI/EMI Filters,Microwave, Surface Mount Capacitors

ROHMRohm Electronics Division

Resistors, Ceramic Capacitors,

Transistors/Diodes,Opto Components and IC's

INDUSTRIES,J INC.BATTERIES, Computer, Cordless

Phone, Scanner & R /C.ANTENNAS, Cordless Phone (metal &

rubber), Scanner Bumpers,Grommets and Stik-On Feet

MAN SPEER ELECTRONICS, INC.Resistors, SMT Tantalum Capacitors Inductors,

Resistor Networks, SMT Thermistors

AlWNTE ELECTRONICS, INC.A WONLAWIN PINVIATION FOR PART NINO AN) atm

Semiconductors, Resistors,Capacitors, Relays

c:DISEIECTA

Switches, Relays, Terminals,

Indicator/Pilot Lights, LED Indicators,Test Clips, Test Leads, Cable Ties and

Heat Shnnkable Tubing

A CO PANT OF

BERGELECTRONICS

High Density and Industry Standard an FC I CompanyConnectors/Subsystems

Electronic Connectors

4E4 BURNDY

BeldenMulti Conductor, Paired, Coaxial, Flat, BussmannFiber Optic, Instrumentation/Process Fuses, Fuseholders, Fuse Blocks,

Control, LAN, Special Application Cables,and Fuse Accessories

Power Supply Cords & Molded Cable

Assemblies

DEARBORNMr 1 Mr ANIS CABLE L. X,

MALLORYNorth American Capacitor Company

Tantalums, Aluminums, Sonalerts°Ceramics, Films and AC's

Philips ECGA North American Philips Company

Semiconductors, rest Equipment.Relays. A /V Parts and

Chemicals

Tantalum Capacitors, Wet & FoilCapacitors, Resistor Networks,

Resistor Capacitors Networks, Filters

SvatteltaraftA Ilayilimm Company

Switches. Connectors. Jacks, Plugs.Jackftelds & Audio Accessories

E NEaton Corporation, Commercial& Military Controls Operation

Switches, Relays, Displays and Keyboards

NA-tronQuartz Crystal Clock Oscillators

and Special Hybrid Products

Loudspeakers and Commercial SoundProducts

Non-CFC Cleaners/Degreasers,

UV Cured Compounds, Swabs, Wipes,

Brushes, Wick, Cleanroom Supplies, andStatic Control Products.

They sell through distributors.They belong to the E.I.A.

They belong on your vendor list.Leadership in electronics is not just a matter of designing products bet-

ter and manufacturing them better, but also of marketing them better. Andthe sponsors of this message understand that better service to customersrequires effectively involving distributors as part of their marketing teams.

Distributor involvement means lower prices, quicker deliveries, betterservice over-all. The Buyer wins. . . the Seller wins.

Distributors help achieve marketing leadership. So does the manufac-turer's involvement in the Components Group of the Electronic IndustriesAssociation. EIA fosters better industry relations, coherent industry stan-dards, and the sharing of ideas, which helps one another and servescustomers better.

In choosing your component supplier, look for the marks ofleadership -

availability through distribution membership in the E.I.A.

Electronic IndustriesAssociation/Components Group2001 Pennsylvania Avenue, NW. 11th FloorWashington, D.C. 20006Phone: (202) 457-4930 Fax: (202) 457-4985

Committed to the competitiveness of theAmerican electronics producer

AMAZING Electronic andScientific Products

MysteryLevitatingDevice!Remember War of the World? Objects float ih air and move to the

touch. Defies gravity, amazing gift, conversation piece, magic trick or

great sdence project.

ANT1K Easy to Assemble Kit! Plans $19.50

Laser Ray Gun

DANGERitiv,smE USER RADATION

AMC Ell OR SARI EXPOSLRETO 014V OR SCATTER RADIATION

CLAM IV LASER PRODUCT

Acvarced proect produces a burst of right erergy capable of burning

holes ^ most materials. Hand-held device uses rechargeable batteries.

500 jollies of flash energy exdte either a neodynium glass, yag or other

siitabie 3" laser rod. This is a dangerous CLASS IV project (individual

Darts as sem DI les available).

LAGUNI Plans $20.00

LAGUN1K Kill Plans ........ Price on Request

Extended PlayTelephone AOC)Recording SystemREADY TO USE Autorhaticady cohtrois and records on our X-4

extended play recorder, tap ng broth s ces of a telephone conversation.Intended for order entry verification. L.;neck your local laws as some

states may require an alerting beeper.

TAP2OX Ready to Use System . . $129.50

Shocker Force Field/Vehicle Electrifier .-

Neat little device a lows you to raxe nanc anc rock balls, shod(

wands and electrify objects, charge capacitors. Great payback fo

those w!se c..ys who have wronged you!

SHK1KM Easy to Assemble Electronic Kit $24.50

Blaster PulserPocket -sized wand produces 100,000 watts cr power for personal

defense, fed and lab use, etc. BLS3 Plans $10.00

BLS3K Kit! Plans $69.50

Homing / Tracking TransmitterBeeper device. 3 m!t ,ange

HOD1 Plans ..... 14001K Kit / Plans.._ $49.50

Listen Through Walls, FloorsRph-y sens t:ve stethoscope ihrAe

STETHI Plans.........$8.00 STETHIK KitPlans $44.50

NEW!

Telephone Line Grabber /Room MonitorALL NEW! The Ultimate in Home or Office Security 6 Safely!S rhpie to Use! Call your home or office pnone, push a secret tone on

your telephone keypad to access either: A. On premises sounds and

voices; or B. Existing telephone conversation with break in capability for

emergency messages. CAUTION: Before assembly or use, check

legalities with your state Attorney General's office as you may require

*beepers' or other 3rd party alerts.

TELEGRABI Plans Only $10.00

TELEGRAB1K Kit Plans $99.50

Ultrasonic BlasterLaboratory source of acoustical shock

waves. Blow holes in metal, produce

'old' steam, atomize liquids. Many

deaning uses for PC boards, jewelry, -coins, small parts, etc.

ULB1 Plans..... ...... 410.00 ULB1K Kit/Plans....469.50

100,000V Intimidator /Shock Wand ModuleBuild an electrical device that is affective up to 20 feet. May be

enclosed for handheld, parade `field or laboratory applications.

ITM2KM Easy -to -Assemble

ITM2 Plans only, credit -able to kit $10.00

/,

Ion Ray GunProjects charged ions that induce shocks in people and objects without

any connectionl Great science project as well as a high tech party

prank. 10G3 Plans $8.00

1003K Kit/Plans $69.50

Invisible Pain $))Field Generator §

Shirt pocket size electroric

device produces time variant

complex shod( waves of intense directional acoustic energy, capabie of

warding off aggressive animals, etc.

IPG7 Plans IPG7K Kit/Plans _.$49.50IPG70 Assembled $74.50

SUPER

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SPECIAL INTRODUCTORY OFFER! WOW! Over 500 items - the

argest smoke assortment we have! Each super giant assortment

drains at least 500 pieces - enough to last you a long time. All

this at a special price - less than 12 cents per item. Guaranteed value

at east 50 percent more than you pay! SMOKE 25 $59.50

TV & FM Joker / JammerShy Doc,re!oevice allows you to :01.3 y control at remotey disrupt TV

or tao a receD: on. Great gag too ay c^ 'am iy or friends. Discretion

rec., 'en EJKIKM Easy to Assemble Electronic Kit $2430

Visible Beam LaserH gh prigntness red HeNe aser v.sib e 'or m es

Produce your own light show! Projects a vsoe beam of red lite deary

visible in most circumstances. Can be used to intimidate by projection

of a red dot on target subect Also may be used to listen in using our

aser window bounce method #1.1.1S1 below. Easy to build module

makes A working visible laser'

LAS1KM Kit wilmw Laser Tube, Class II. 469.50LAS3KM Kit w2.5mw Laser Tube, Class II1A $99.50

"Laser Bounce" Listener SystemAl Nis you to hear sounds horn an area via a lite beam reflected from a

w ndow or other similar objects. System uses our ready -to -use LATR1

Laser Terminator gun site as the transmitter. The receiver section is

sop ed as an easy -to -build kit, including our cushioned HS10

eacsets. LLIST2 Plans $20.00

LLIST1K Kit of Both Transmitter and Receiver $199.50

LLIST20 Assemble with Laser Gun Site 429950

*5mw Visible Red Pocket LaserUtilizes our touch DOwer control!

VRL5KMX Kit Plans 4119.50

Fantastic ALL NEW Dative -Tel effect for auto. motorcycle, bicycle, etc.

Use one per wheel SIMPLE TO USE LWMIRLY $950

Pocket Sized Night V iewerUses Low Level Starlightto See in the Dark! Low Cost Ultra -Hi Lite Amplification!

Auto Brightness Control

Limited Amount Available

Made in USA Night s,,rve ante Animal studies, etc.Can be used to fly an airplane or drive a car!PKV7 Plans $15.00

PKV7K Easy to Assemble Kit $1,295.00

PKV70 Ready to Use $1,595.00

(f)

I2

00(TO

rri

rn

33

Wireless MicrophoneSubminiature! Crystal dear, uitra sensitive pickup transmits voices and Pi)

sounds to FM radio. Excellent for security, monitoring of children or

rvalids. Become the neighborhood disk jockey, or go 'under cover 0using our sunglasses FM radio (see catalog). FMV1 Plans ... $7.00 ce,3

FW1K Kit and Plans $3950 -<

SUGL10 Sunglasses with built in FM Radio $29.50 u_24

Telephone Transmitter - 3 MiAutomatically transmits both sides of a telephone conversation to an FM z

radio. Tunable Frequency Uhaetectable on Phone Easy to Build

oandUse Up to 3 Wile Range Orly transmits during phone use.

VWPM7 Plans $7.00 0VWPM7K Kit/Plans S39.50

3 Mile FM

liONNLIMITEDMC, VISA, COD, Chocks accepted Meese add $5.00 Shipping & Handling

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Peltier Effect Beverage Cooler(See page 43)

Receiver Preamplifiers(See page 34)

Battery Butler(See page 93)

Solar Power Supplies(See page 89)

Reduce Home Heating Costs2 (See page 25)

PoPlar SPRINGElectronics®

1994Contents

HIGH -VOLTAGE ELECTRONICS

200,000 -Volt Van de Graaff Generator 58Enjoy hours of high -voltage experimenting

Solid -State Tesla Coil 61An updated version to spark -a -mania!

Jacob's Ladder 65You see it in "crazy scientist" movies

FABULOUS PROJECTS

Build a Smarter Gas Gauge 14Build intelligence into your car's gas -measuring system

Turn -Signal Reminder 23A musical reminder to hit the lever when you forget!

Reduce Heating Costs with the Fuel Miser 25Tame home -heating cost and keep warm, too!

Wire Tracer 30Follow out -of -sight wires hidden in walls and ceilings

Configurable Power Supply 32Delivers 1.2 to 33 volts DC up to 1.5 amps

Receiver Preamplifiers that You Can Build 34Design a front-end for your SW/VHF/UHF receiver

An Electronic Gong 38A civilized way to signal

Build a Four -Element, Two -Meter Quad 41Inexpensive to build and has great performance

Peltier Effect Beverage Cooler 43Keep your soda cool and taste buds happy

Digital Bowl Box 47A must project for "College Bowl" players

Dog Bark Inhibitor 52A humane way to de -bark a woofer

As a service to readers, Popular Electronics Spring 1994 Electronics Hobbyists Handbook publishes available plansor information relating to newsworthy products, techniques and scientific and technological developments. Because ofpossible variances in the quality and condition of materials and workmanship used by readers, we disclaim anyresponsibility for the safe and proper functioning of reader -built projects based upon or from plans or information publishedin this magazine.

ELECTRONICSHOBBYISTShandbook

A Non -Serious Circuit 55A lot of fun and it's educational

Freeze Fighter 68Power control in sync with the weather

Active Antenna 72Boost those hard to hear 3-3000 MHz signals

Build an Ion Detector 75Zero in on high -voltage leakage and static build-up

Build the Water Tap 78Who knows-maybe fish can talk?

Aviation -Band Receiver 80Tune in the chit-chat from the high flyers

Experimenting with Shaped Memory Alloys 85Discover a new hobbyist project adventure

Solar Power Supplies for Portable Radios 89Cut down on battery expense

Battery Butler 93Restore and charge Ni-Cd batteries as never before!

Making the Connection 99Cut antenna losses with the correct connection

DEPARTMENTS

Editorial-About this issue 4

New Products 6

Literature Library 12

Free Information Card 56A

Classified Advertising 111

Advertisers' Index 111

Advertising Sales Offices 112

Since some of the 'equipment and circuitry described in Popular Electronics Spring 1994 Electronics HobbyistsHandbook may relate to or be covered by U.S. patents, we disclaim any liability for the infringement of such patents by themaking, using, or selling of any such equipment or circuitry, and suggests that anyone interested in such projects consult apatent attorney.Popular Electronics Spring 1994 Electronics Hobbyists Handbook is published semi-annually by GernsbackPublications Inc. All rights reserved. Printed in U.S.A. Single copy price $3.95. Canadian G.S.T. Registration No.125166280. Canada $4.50. OGemsback Publications Inc., 1994.

AA -7POWER

RE' GAIN OUT/HEIN/VHF

411? ACTIVE AN. NA lib

Active Antenna(See page 72)

Aviation -Band Receiver(See page 80)

A Non -Serious(See page 55)

Wire Tracer(See page 30) 3

,;;; ELECTRONICSDIpAm: HOBBYISTSElect"le'S handbook .

Larry StecklerEHF. CET

Editor -In -Chief and Publisher

Julian S. MartinHandbook Editor

POPULAR ELECTRONICSEDITORIAL DEPARTMENT

Carl LaronEditor

Robert A. YoungAssociate Editor

John J. YaconoAssociate Editor

Teri ScadutoAssociate Editor

Evelyn RoseEditorial Assistant

Marc SpiwakEditorial Associate

PRODUCTION DEPARTMENTRuby M. Yee

Production Director

Karen S. BrownProduction Manager

Kathy CampbellProduction Assistant

Lisa RachowltzEditorial Production

ART DEPARTMENTAndre Duzant

Art Director

Injae LeeIllustrator

Russell C. TruelsonIllustrator

Jacqueline P. Cheeseboro(initiation Director

Michele TorrilloBookstore

BUSINESS AND EDITORIAL OFFICES

Gernsback Publications, Inc.500-B Bi-County Blvd.

Farmingdale, NY 117351-516-293-3000

Fax: 1-516-293-3115

President: Larry Steckler

Advertising Sales Offices listed on page 112

Cover photography byRuth Carey

Oak Ridge, TN

Composition byMates Graphics

Since some of the equipment and circuitry described in1994 ELECTRONICS HOBBYIST HANDBOOK may relateto or be covered by U.S. patents, 1994 ELECTRONICSHOBBYIST HANDBOOK disclaims any liability for the in-fringement of such patents by the making, using, or selling ofany such equipment or circuitry, and suggests that anyoneinterested in such projects consult a patent attorney.

There's a name missing from ourmasthead this issue. We've lost agood editor and a longtimefriend-Byron G. Wels. Byron wasa very unusual friend and co-worker. This brief editorial cannothope to unveil his gloriouscharacter or even the humorousadventures that life gave to himand he gave to us.

Editorial

I met Byron in September, 1958,when I was the Managing Editorof Popular Electronics (then aZiff -Davis publication) and Byronwas an author specializing inaudio -stereo stories at that time.He had a knack for opening doorsto the big audio mavens at H. H.Scott, Fisher, EICO, Heath, Arkay,Marantz, Garrard, Rek-o-kut,Knight and many others. Nameslike Pioneer, Sony, Sansui andothers were not household namesthen.

Byron's fame came from themany diverse free-lance jobs heheld, I remember he undertook afeature story for a famous houseorgan. He reported on an indoorski training technique that used asloping, moving -carpet machine.Yep, Byron tried it and broke hisleg. He sky dived for a story longbefore many of our readers wereborn.

That was no feat, because earlierhe bailed out over the BurmaRoad during WWII. That was atrue story, but each time he told itthe derring-do and the rescuefollow-up got better and better.

Most of all, Byron loved to writeand talk. His office here at

Gernsback Publications was ameeting place for the staff. That'swhere everyone took a coffeebreak. He loved people andpeople loved him. He retired toFlorida and continued to work forthe company. His phone callswere welcome breaks in theworkday.

Finally, the Grim Reaper cameand took Byron. I can't help butthink that Byron put a smile onthat apparition's face. God blessyou, Byron, for being a part of mylife.

However, life and editorialscontinue on!

We find it difficult to repeat aneditorial, but portions of the lasteditorial are repeated here todescribe the function of the"Project Time Evening" ratings.We found the ratings for projectsto be a confidence builder fornovice project builders. Manyreaders' letters said that theratings for two or three eveningprojects should have beenreduced. Most of the letters werefrom first-time or novice builders.That was heartening.

Many editors are involved in thegeneration of ElectronicsHobbyist Handbook articles, sowhen the editorial "we" is used,believe me when I say that Ispeak for a crowd of dedicatededitors, who, by the way, areacomplished project builders.Here are their views on theproject rating system.

We consider the project's

construction time to begin after allthe parts are available, and thatincludes the printed -circuit board.Although there are modernmethods for adding resistpatterns to the copper -cladsurface of a board, even that timeis an indeterminate quantity. So,the gun fires to start the clockwhen all the parts are on theworkbench and you plug in thesoldering iron.

Projects that require tuning,alignment or adjustment have thetime interval thus required addedto the total time. The making ofsimple boxes, cabinets, etc., andother minimal cosmetic taskssuch as nameplates, dialmarkings, paint jobs, etc., areincluded in the total time. Aspreviously stated for the parts,materials and equipmentnecessary for the task to becompleted must be on theworkbench or available nearby soas not to interrupt the flow ofwork.

We assume that most of the workwill be done in the evenings afteryour normal work day, so that atypical one -evening project takesabout three hours. Expect a give -or -take of one hour dependingupon your skill and the qualityand availability of tools andequipment on your workbench.For example, we consider that atleast one solder connection mustbe redone for whatever reason. Ifyou have a "suction -tip" de -soldering iron, add 30 seconds tothe task. If you use a copperbraid to sap off the solder, addtwo minutes. If you let the tip ofthe iron do the job, add five

minutes. (Of course, the lattertechnique should not be used!)

A small drill press, power jig saw,desk -top illuminated magnifyinglens, electric screw -nut driver, andother convenient hand toolsspeed up most hobbyist'sprojects. Also, what many readersfail to do is study the text carefullybefore they begin to build aproject. Know what you have todo, then do it. Don't look for shortcuts or redesigning efforts as youassemble the project. It's best tostop all work and seriously thinkout and plot out what you want todo and how to do it. In mostcases, it is wiser to complete theproject, get it working, thenredesign for a specific purpose.

Now you know the time -evaluation system, look for the"Project Time" label for eacharticle. (See above.) The editorswould like to know if this systemwas of value to you, so drop us aline and tell us what you think andwhat you experienced.Remember, your reports are oureyes. Happy project building.

Confidence in building projectsbuilds confidence to undertakebigger and larger projects. If so,you may be interested inElectronics Experimentershandbook, Summer 1994 issueon sale April 6, 1994.

Julian S. MartinHandbook Editor

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Nine -RangeBatteryTester

6

NEW PRODUCTSA compact battery tester fromL-com, the DX2OBT, acceptsany standard carbon -zinc, al-kaline, mercury, silver -oxide,lithium, or nickel -cadmium bat-tery. When the selector switch isset to the desired battery type,the meter will provide a true testof its condition with an actualload imposed. Test results areshown on three colored meterscales for regular, lithium, andnickel -cadmium cells.

The DX2OBT featu-es perma-nent, built-in test leads toprevent signal loss. A specialadjustable clamp holds all typesof button cells, making the testfast and simple. Dual contactbuttons on the top panel accept9 -volt batteries, eliminating theneed for test leads in 9 -volttests. The tester also features a"neg" contact button to test anysize single cell, so that only thered test lead is required forthose tests. The case iselevated for easy reading.

The DX2OBT nine -range bat-tery tester costs $18.50 insingle units; quantity discountsare available. For further infor-mation, contact L-com, Inc.,1755 Osgood Street, North An-dover, MA 01845; Tel:800-343-1455 or 508-682-6936;Fax: 508-689-9484.

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PC -BASED CALLER ID

Most products designed to pro-vide security against intrusioninto telecommunications equip-ment automatically answer

incoming calls and wait for thecaller to enter an access codeor password. Such systems areeasily thwarted by hackers andinconvenient for authorizedusers. According to Pewee Val-ley Innovations, however, theirPC Receptionist, a PC -basedCaller ID accessory, eliminatesany chance for a hacker to gainaccess to the system, whileallowing the user to completelyblock calls from unauthorized,"privatized," or unknown num-bers, or to pass only calls fromparticular numbers. The deviceis transparent to outgoing calls.

The PC Receptionist usesCaller ID to determine whetherto pass or block the ring signal.When a call comes in, fore-ground computer activity istemporarily suspended and adisplay pops up on the screen,showing the phone number ofthe caller and, if previously en-tered into the system, thecaller's name. The user canenter a one -line memo regard-ing the call. Previous consumeractivity is restored with a singlekeystroke, or after a user -spec-ified time period. At the end ofthe call, the device saves thecall record and memo alongwith a date and time stamp andthe length of the call. The call

record can be called up at anytime, and can be imported intomany popular databases. Withthe included software for man-aging a digital pager, youneedn't give out your pagernumber. Incoming calls can berouted to an answering ma-chine, with only calls from pre -specified numbers forwarded toyour pager.

The package includes aneasily configured, 8 -bit adapter

card for IBM PC -compatiblecomputers, a DOS -based soft-ware package on 3.5 and 5.25 -inch diskettes, a modular exten-sion cord, and a user's manual.The user must subscribe toCaller ID from the local tele-phone company.

The PC Receptionist packagecosts $149.95; for Windowssoftware, add $30. For moreinformation, contact Pewee Val-ley Innovations, Inc., 6601 OldZaring Road, Crestwood, KY40014; Tel: 502-241-4295.


DIGITAL AC -LINEMONITOR

Well suited for such applicationsas high -end consumer elec-tronics, laboratoryinstrumentation, and other prod-ucts requiring accurate AC -linemonitoring, DetersDMS-20PC-1-LM is a self-con-tained, 3 -digit LED display thatmeasures AC -line voltages from85-265 VAC (47-63 Hz). Noexternal components or auxili-ary power are needed. Whenthe device is plugged into anywall outlet or PC board, it in-stantly measures line voltages.Using half -wave sinusoidal aver-aging techniques, typicalaccuracies of -±1 VAC areachieved over the full input spanof the meter. The AC -linemonitor is packaged in a0.88 x1.38 x 1.00 -inch red filtercase with an integrated bezel.The 0.37 -inch high LED is easy

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STANDARD SERIESS-1325 25MHz $349S-1340 40MHz $495S-1365 60MHz $849

ELENCO OSCILLOSCOPES

DELUXE SERIESS-1330 25MHz $449S-1345 40MHz $575S-1360 60MHz $775

Features: Features:

MI High Luminance 6' CRT II TV Sync Delayed Sweep Dual time bas e

lmV Sensitivity 2 - x1, x10 Probes II Automatic Beam Finder Illuminated in ternal

X -Y Operation Complete Schematic Z Axis Modulation gradicule

Voltage, Time, + Frequency differences displayed II Built-in Component Test

on CRT thru the use of cursors (S-1365 only) Plus much, much more

Plus all the features of the "affordable" serie

Hitachi Compact Series Scopes

V-212 - 20MHz Dual Trace $399V-525 - 50MHz, Cursors $995V-523 - 50MHz, Delayed Sweep $949V-522 - 50MHz, DC Offset $895V-422 - 40MHz, DC Offset $795V-222 - 20MHz, DC Offset $649

V-660 - 60MHz, Dual Trace $1,149V -665A - 60MHz,DT, w/cursor $1,325

V-1060 - 100MHz, Dual Trace $1,395V -1065A - 100MHz, CT, wicursor $1 649V-1085 - 100MHz, QT, w/cursor $1,995V -1100A - 100MHz, Quad Trace $2.495V-1150 - 150MHz, Quad Trace $2,395

B&K OSCILLOSCOPES2120 - 20MHz Dual Trace $3892125 - 20MHz Delayed Sweep $5391541B - 40MHz Dual Trace $6952160 - 60MHz Dual Trace, Delayed Sweep,

Dual Time Bash $9492190 - 100MHz Three Trace Dual Time Base,

Delayed Sweep $1,3952522A - 20MHz / 20MS/s Storage $875

Digital Capacitance MeterCM -1550B

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to read under virtually any light-ing conditions.

The DMS-20PC-1-LM digitalAC -line monitor costs $45. Foradditional information, contactDatel, Inc., 11 Cabot Boulevard,Mansfield, MA 02048; Tel:508-339-3000; Fax:508-339-6356.


RANGEMASTERMULTIMETER

Extech's 380280 Rangemastermultimeter has nine functionsfor monitoring and testing, anda large 31/2 -digit LCD readout foreasy viewing. The rotary range -selector switch lets you monitorDC and AC amps in four(ranges from 2 mA to 20 A), DC

volts in five ranges (from 200mV to 1000 V), AC volts in fiveranges (from 200 mV to 750 V),resistance in six ranges (from200 ohms to 20 megohms),capacitance in five ranges (from2 nF to 20 and frequencyin four ranges (200 Hz to 200kHz). Other functions include atransistor test. diode check, andcontinuity tester with buzzer.Ideal for field work, the ruggedRangemaster features full over-load protection and low -batteryand over -range indicators. Itcomes complete with built-in tiltstand, a rubber holster, testleads, and a 9 -volt battery.

The 380280 Rangemastermultimeter costs $79. For addi-tional information, contactExtech Instruments Corpora-tion, 335 Bear Hill Road,Waltham, MA 02154; Tel:617-890-7440; Fax:617-890-7864.


DIGITAL SPECIAL -EFFECTS GENERATOR

Although it is targeted primarilyat the semi-professional "pro-sumer" market, small produc-tion facilities and home -videoenthusiasts can use Sony's XV-

D1000 digital special -effectsgenerator to obtain profession-al -like results. The easy -to -usecomponent lets you combinemultiple video and audiosources, create dramatic scenetransitions, add spectacular vid-eo effects, and quickly programeffects sequences. Designed towork with professional editingdecks, the effects generatorfeatures VISCS and GPI inter-faces for use with computerizedediting systems, three AN in-puts and two A/V outputs formultiple -source editing andpost -production effects ses-sions, and an S -Video input/output.

The XV-D1000 features a dig-ital frame synchronizer forprecise combination of two dis-tinct video sources, a double -frame memory for high -resolu-tion images, and 77 differentwipe patterns. It allows you tosize and insert one image intoanother, fade to white or black,zoom in on a particular area,divide the screen into nine pic-ture areas, stop the action atsuccessive points and displayeach point in a nine -image ma-trix, and freeze the full -screenimage without ghosting or track-ing lines. A ten -programmemory lets you store effects.

The XV-D1000 digital special -effects generator has a sug-gested retail price of $2600. Formore information, contact SonyElectronics Inc., One SonyDrive, Park Ridge, NJ 07656.

CIRCLE 103 ON FREEINFORMATION CARD (More on page /0)

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WeatherPort's WS -12 WindSta-tion is a data -acquisition systemfor measuring and logging windspeed, wind direction, and tem-perature on a personalcomputer. The device interfacesvia the parallel port of an MS-DOS -based computer. Mea-surement data can be displayedon screen, stored as disk files,

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MULTI -PURPOSETESTER

If you're worried about elec-tromagnetic radiation, poorantenna performance, or EMI/RFI, I.C. Engineering's Digi-Field field -strength meter canhelp put you at ease. With itsfrequency response of DC up to12 GHz, it readily detects poten-tial electromagnetic radiationhazards. Digi-Field can easilyfind 60 -Hz AC -line interference,

as well as RFI, EMI instrumenta-tion -disrupting setups. Thehandheld instrument can alsobe used to check antenna gain/loss and polarization patterns.All measurements are displayedon the unit's 31/2 -digit LCD read-out, allowing the user to makequick visual checks of radiationgain or loss, antenna patterns,garage -door opener transmit-ters, microwave oven leakage,and cellular and portablephones, and to locate transmit-

ters. The battery -powered meteralso has a detector output jackfor AM monitoring. The Digi-Field can be used with its owntelescoping antenna or with anexternal one with a PL 259connector. Typical calibrationcurves in dBm are available.

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BENCH -STYLE DIGITALMULTIMETER

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From Not-Workinto Networking!TroubleshootingLocal -Area Networks!

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Gain a fuller knowledge of networkfundamentals and how theydeveloped from the early days ofmain frames, from XNS to Ethernettechnology, the OSI stack forinterconnecting different computers,basic and specialized test instruments, etc. Severaltough LAN case histories bring from theory to thepractical side of troubleshooting.

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diode and continuity checks.Frequency measurement ex-tends to 1 MHz, with up to 1 -Hzresolution, and capacitancemeasurement is to 40 pf withup to 1-pF resolution. TheModel 2835 features autorang-ing or manual ranging operationand a high -contrast back -lit LCDreadout with 42 -segment bar -graph.

Designed for bench or fielduse, the instrument offers AC orbattery operation, with batterylife rated at 1800 hours. Thecompact unit has convenientbuilt-in storage for test leadsand AC power cord. High-ener-gy fusing, overvoltageprotection, and an impact -resis-tant case provide protectionagainst accidental misuse. TheDMM comes with test leads,power cord, hand and neckstraps, and user's manual.

The Model 2835 digital multi -meter costs $270. For furtherinformation, contact B + K Preci-sion, Maxtec InternationalCorporation, 6470 West Cor-tland Street, Chicago, IL 60635;Tel: 312-889-9087; Fax:312-794-9740.


SURGE SUPPRESSOR

Tripp Lite's Spike Bar Super 7surge suppressor features threediagnostic indicators that light toshow the presence of wiringfaults, status of protection cir-cuitry, and loss of AC power.The indicators warn of any ab-normalities before equipment isturned on, assuring completeprotection of connected equip-ment. The UL -listed Spike BarSuper 7 also has seven spike -and noise -filtered AC outlets, aseven -foot AC line cord, and asafety circuit breaker. In addi-tion, "Ultimate LifetimeInsurance" protects both thesurge suppressor and any con-

nected equipment from surgedamage, including direct light-ning strikes, for up to $5000.

The Spike Bar Super 7 has asuggested retail price of $49.95.

For additional information, con-tact Tripp Lite, WO NorthOrleans, Chicago, IL60610-4188; Tel: 312-329-1777;Fax: 312-644-6505.


HIDDEN WIRE TAPE

Today's speakers are gettingsmaller and less conspicuous,but there's still the problem ofunsightly wire runs between thespeakers and the audio or videocomponents. Wire Tape, de-signed to replace any 18 -gaugewire for speakers or burglaralarms, is just ten thousandthsof an inch thick. Its resemblanceto a strip of tape is compoundedby its pre -applied adhesivebackjng that allows you to sim-

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IMCIRCLE 21 ON FREE INFORMATION CARD

ELECTRONICS LIBRARYINSIDE YOUR SHORTWAVE RADIO

by Ted Benson, WA6BEJ

Written in a clearly understand-able style, this book explainshow your shortwave radioworks, beginning with radio re-ception and taking readersthrough the inner workings of atypical superhet shortwave re-

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about shortwave receivers andtheir use.

Inside Your Shortwave Radiois available for $14.95 plus$2.00 shipping and handling($3.00 outside the U.S.) fromTiare Publications, P 0. Box493, Lake Geneva, WI 53147.


VOODOO WINDOWS:Tips & Tricks With anAttitudeby Kay Yarborough Nelson

Although the appeal of Micro-soft Windows, with its intuitiveinterface and friendly flexibility,is obvious, many Windowsmanuals obscure the programsattributes with excess informa-tion and technical language.This book helps remove theconfusion by reducing eachWindows function to its simplestingredients, and limiting thosefunctions to the most accessi-

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ble, quickest, and easiest. Thebook demonstrates techniquesfor teaching your mouse newtricks, customizing Windows forfun and productivity, and avoid-ing common pitfalls. It providestips on starting, switching, andexiting Windows; and on copy-ing and pasting. It revealsProgram Manager secrets forinstallation, creating newgroups, and multitasking, alongwith File Manager hints for se-lecting, moving, copying, andrenaming files; deleting files anddirectories; and using the Viewmenu. The book also coversprinting pointers; accessoriesincluding Calendar, Calculator,Notepad, Paintbrush, Cardfile,

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THE ELECTRICITYBOOK:The Junior Technician'sDiscovery Guideto How Electricity Worksby Gene McWhorter

This book aims to "spark" theyoung reader's imagination andinterest in electricity-for a hob-by, a science -fair project, oreven a future career in electricalengineering. With easy -to -readtext and clearly illustrated ex -

(Continued on page 77)

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Does your VCR have a "Head Cold?"Probably not! However, through constant playing and using of degrading dryor wet cleaners, the output of your video tapes has slowly diminished to anunacceptable level and the VCR plays as if it has a head cold! The culprit ismost likely clogged and dirty video and/or audio heads.

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13

BUILD ASMARTER

GAS GAUGEBY JONATHAN GORDON

Whether you have a 1930-1950's vintage car, a 1960-1970's stock car that's been

rebuilt into a musclecar, or a modern1980-1990's car that has an enginecomputer, the Smarter Gas Gaugedescribed in this article will accuratelymonitor the changing gas level in thetank-without affecting the operationof your factory installed gas -gauge inany way. Although your car may al-ready be equipped with an in -dashlow -fuel indicator, sometimes calledan idiot light (which uses a factorypreset, gas -level -sensing switch), suchswitches offer no manual control overthe fuel level at which the idiot -lightilluminates.

But, that's not the case with theSmarter Gas -Gauge. The Smarter GasGauge lets you electronically set thefuel -level trip point to 3/ / / full,4,12, 1, 4 al-most empty, or any level in between.And the trip point that you set remainsvalid, even during periods of extremeagitation like when you quickly accel-erate or take a tight turn. When thegas level reaches your preset trip -point, the low -fuel indicator illumi-nates.

Build intelligence into your car'sfuel -measuring system byinstalling an indicator lamp thatflashes when your fuel supplyfalls to a user -defined level.

But before we get into the opera-tion of the circuit, a quick discussion offuel -level indicators is in order.

Fuel -Gauge Systems. There arethree types of fuel gauges found onautomobiles: The magnetic, bal-anced -coil fuel gauge, the bimetal-lic, heated -coil fuel gauge, and anelectronic fuel -level bargraph or dig-ital display.

Figure 1 shows the magnetic fuel -gauge system that's used in a 1972Olds Cutlass convertible, which, inci-dentally, acted as the test platform forthis project. The car's original gas -gauge was working fine but had be-come blocked from the driver's viewby a modified steering -wheel col-umn.

Inside the magnetic gauge is a setof balancing coils labeled L1 and L2,which are electromagnetic inductorsthat are wound around a plastic coreat right angles to each other. Thegauge needle is attached to a metalarmature on which the two elec-tromagnetic coils act. A series DC cur-rent flows through limiting -coil L1, thenthrough operating -coil L2, and finallyto ground.

Limiting -coil L1 exerts a constant

magnetic pressure on the gas -gaugeneedle that pulls it toward the empty -tank position; while operating -coil, L2exerts a variable magnetic pressurethat pulls the gauge needle towardthe full -tank position. In such systems,the direction of the needle's move-ment depends on how much currentis shunted away from L2 to ground viatank -rheostat R1 (which is usuallycalled a sender).

Because coil L2 has more windingsthan coil L1, a small resistor, R2, is add-ed to the winding resistance of L1 sothat the resistance between the twocoils is balanced.

Now let's suppose that ignition -

switch S1 is turned on and sender R1 isin the full -tank position. Most of thecurrent flows to ground through thegas gauge via coils L1 and L2; minimalshunt current flows to ground throughthe high -resistance path of sender R1,which is in parallel with coil L2. Oper-ating -coil L2 builds up a strongermagnetic field than limiting -coil L1,and the pointer is pulled to the fullposition.

Now suppose that sender R1 is in theempty -tank position. Most of the cur-rent flows through the gas gauge viacoils L1, and the low -resistance path

LIMITING COIL L1HAS CONSTANT FIELD

MEASURE Vgas VOLTAGEAT SENDER WIRE

IGNITION SWITCH

R2

200BALANCING

RESISTOR

"III 1/2\ 111111'S

CHASSISJ

No00/ '... i 1 ...'... VI' GROUND

+12V CARBATTERY

+11 I

-e.r. CAR -CHASSIS

- GROUND

SENDER R1 ISTHE GAS -TANK RHEOSTAT

ARMATURE

.*------- FLOAT ARM

-LCAR -CHASSIS

GROUND

OPERATING COIL L2HAS VARIABLE FIELD

POLE PIECE

FULL TANK POSITION: 80-300 OHMS

EMPTY TANK POSITION: 3-30 OHMS

Fig. I. There are two types of magnetic balanced -coil gauge systems; the one shownhere uses a set of electromagnetic coils, LI and L2, and a sender, RI, that shunt's coil

LIMITING COIL L1HAS CONSTANT FIELD

_L CHASSISGROUND

IGNITIONSWITCH

1-1-----11-!- 12V CAR+BATTERY

CAR -CHASSISGROUND

T-POLE

PIECE

ARMATURE

FIXED -POLE SHOE


OPERATING COIL L2HAS VARIABLE FIELD

FULL TANK POSITION:

3-30 OHMS

EMPTY TANK POSITION:

80-300 OHMS

FLOAT ARM

v.-. CAR -CHASSISGROUND


Fig. 2. Here is the second type of magnetic balanced -coil gauge system; this one usesa set of electro-magnetic coils LI and L2, and a sender RI, as with the previous one.But, instead of the sender shunting L2, the sender is in series with coil L2.

to ground through sender R1, whichshunts current around coil L2. Limiting -coil L1 builds up a stronger magneticfield than operating -coil L2, and thepointer is pulled to the empty position.

Figure 2 shows another version ofthe magnetic, balanced -coil, fuel -gauge system. In this version, limiting -coil LI exerts a constant magnetic

pressure that pulls the gauge needletoward the empty position. Operat-ing -coil L2 exerts a steady magneticpressure that pulls the gauge needletoward the full position, but the mag-netic strength depends upon theamount of current flowing through theseries circuit formed by coil L2 andsender R1. When R1 is in the empty

position, the resistance is high, whichreduces the series current, so that themagnetic pull developed by coil L2 isweak. When sender R1 is in the fullposition, the resistance is low, whichincreases series current, so that themagnetic pull developed by coil L2 isstrong.

The magnetic fuel -gauge systemsin Figs. 1 and 2 work differently. Thegauge in Fig, 1 uses a shunt circuit,consisting of operating -coil L2 andsender R1, while the one in Fig. 2 usesa series circuit of operating -coil L2and sender R1. In addition, sender R1in Fig. 1 has a low resistance in theempty position and a high resistancein the full position; while sender R1 inFig. 2 has just the opposite, a highresistance in the empty position and alow resistance in the full position.

Figure 3 shows another type of fuel -gauge system; a bi-metallic, heated -coil type. In that system, sender R1 in-fluences the series current flow by wayof a coiled heating element that'swound around a bi-metallic bar in thegauge. When the tank is full, sender R1has a low resistance, allowing max-imum current to flow through thecoiled heating element, whichcauses it to heat. As the bi-metallicbar heats, it begins to bend because

A BRIGHT IDEA

The author wishes to thank Bob Man -ford of SK Technologies, Inc.. BocaRaton. FL, who is an expert on 1972Cutlass convertibles in particular andmusclecars in general It all startedwhen Bob asked the author to designan instrument that would flash a lightwhen his car was in need of fuel Theauthor admits that the whole ideasounded a lot like the idiot light (thatmost cars already had in abundance)that flash to signal everything from analternator malfunction, low fuel, batteryproblems. door atar you name it ButBob wanted no ordinary idiot light: whathe want was a smarter light The oldfashioned idiot light trat Lust illuminateswhen the gas gauge reads near emptywasn't good enough Bob wanted tomanually set the light's trip point for anygas needle position. from empty to fullAnd the light had to be an extremelybright incandescent lamp, an LED justwouldn't do. That s how the bright ideafor the Smarter Gas Gauge got startedand one week later the author's pro-totype was installed in Bob's 1972 OldsCutlass. The Smarter Gas Gauge hassince become a fool -proof warning sys-tem and a conversation piece for every-one who comes along for a ride



CAR -CHASSISGROUND

BI -METALLICARM

CURRENT HEATSCOIL U1

VOLTAGE

REGULATOR

12V CAR

BATTERY

CAR -CHASSISGROUND

FLOAT ARM FULL TANK POSITION: 3-30 OHMS

EMPTY TANK POSITION: 80-300 OHMSFig. 3. The bi-metallic heated -coil gauge system uses a heating coil wound around ahi -metal bar, and a sender (RI) that's connected in series with the heating -coil wire.

of the difference in temperature ex-pansion properties between the twobonded metals. Consequently, thegauge needle moves to the full posi-tion. When the tank is empty, senderR1 has a high resistance so minimumcurrent flows through the coiled heat-ing element. The bi-metallic barcools, bending back to the originalposition, and the gauge needlemoves to the empty position.

Voltage regulator U1 assures thatany changes in current through thecoiled heating element is caused bychanges in resistance originating atthe sender. Because the bi-metallicstrip heats and cools slowly, suddenfuel -level changes caused by fuelsloshing in the tank are dampened sothat a steady reading of the averagefuel level in the tank is indicated. Thatis in contrast to the magnetic, bal-anced -coil gauge, which responds tosloshing fuel and gives a noticeableswing to the gauge needle.

Figure 4 shows an electronic fuel -

level gauge that uses a bargraph dis-play (digital readout). Notice that thegas -tank rheostat R1 (sending unit) isthe same as that used by the elec-tromechanical needle -type gauges.The sender consists of a float arm andvariable resistor. As the fuel levelchanges, the sender's resistance alsochanges, which, in turn, places a vary-ing voltage across the sender.

The electronic control module (orECM) senses the voltage across the

sender and converts it into a bar -

graph or digital readout that indi-cates fuel -gallons remaining. Forexample, a typical General Motorssender has 90 ohms when the tank isfull and 0 ohms when empty. There-fore, every decrease of 6 ohms woulddecrease the display one segment if itis equipped with a 16 -segment bar -

graph gauge and a 16 -gallon tank.Figure 5 shows how a typical send-

ing -unit is situated in the fuel tank. Therheostat assembly works just like a po-tentiometer. The resistive element is in-side a metal housing that is loweredinto the tank. The float arm is attachedto a brush that contacts the resistiveelement. As the fuel level changes,the float arm moves and the rheostatthen converts that linear up-and-down motion into a changing resis-tance. That varies the current flowthrough the fuel gauge so that thepointer needle moves.

Typical sender -resistance valuesare: 0 -ohm empty to 90 -ohms full formost GM vehicles; 73 -ohms empty to8- 12 -ohms full for Ford and Chrysler;240 -ohms empty to 33 -ohms full forAMC, Stewart Warner senders, andmarine applications.

Now that we've established that thesender resistance depends on thefuel level in the tank, it stands to rea-son that by measuring the voltageacross sender R1 a unique voltage isrecorded for each fuel level in thetank from empty -to -full.

In fact, a table can be created bymeasuring the voltages-which we'llcall Vgas -at various fuel levels. Table 1shows the Vgas voltage rising as thetank is being filled for the fuel gaugein Fig. 1. Tables 2 and 3 show Vgaslevels falling as the tank is being filledfor the fuel gauges in Figs. 2 and 3,respectively. By monitoring the Vgaslevel, we'll always know exactly howmuch fuel is in the tank. Now let's gothrough the procedure to measureV90, and record the data.

Measuring Vg. To measure theVgas level, you'll need to perform thefollowing steps: Turn the ignition switchto the on position (powering up thefuel -gauge system); disassemble thedash to locate the fuel -gauge plug;and hookup a DVM to measure theV905 voltage that's across the sendingunit.

A typical ignition switch with fourpositions- -LOCK, ACC, ON, and START-iS

GAS -GAUGE

R1 SENDER

FULL

'/2

EMPTY

ELECTRONICCONTROLMODULE


CAR -CHASSIS

0-OHM EMPTY GROUND

90-OHM FULL

FLOAT ARM

Fig. 4. This electronic, fuel -level,hargraph-display system UR'S anElectronic Control Module (ECM), a lb -segment LED display, and a sender RI.

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17

FUEL CAPPICKUP

PIPE

FLOAT ARM

VAPOR LINE

FUEL FILTER

FUEL LINE

RHEOSTATSENDING -UNIT WIRE

GROUND WIRE

R1FUEL TANK

GAS -TANK

RHEOSTATALSO CALLED

SENDING UNIT

Fig. 5. The sending unit is effectively a rheostat that is controlled by a float arm.which senses the gas level in the fuel tank.

TABLE 1-DATA FROM FIG.1 GAS GAUGE

Fuel Level Vga,

Full 7.76.7

1/2 6.21/4 5.2

Empty 4.5

TABLE 2-DATA FROM FIG. 2 GAS GAUGE

Fuel Level Vga,

Full 4.13/4 5.21/2 6.0IA 6.7

Empty 7.5

TABLE 3-DATA FROM FIG. 3 GAS GAUGE

Fuel Level Vga.

Full 1.53/4 2.81/2 3.91/4 5.3

Empty 6.4

shown in Fig. 6. The first step is to startthe engine by turning the ignitionswitch to the START position. Release thekey when the engine turns over. Withthe engine running, the alternatorand DC regulator supply the elec-trical power necessary to operate the

ON

Fig. 6. Most ignition switches have fourpositions: WCK. Acc (accessory), ON. andSTART, as shown here.

fuel gauge and other instrumenta-tion.

The ignition switch may also beturned to the ON position without start-ing the engine. In that case, all thehigh -current electrical systems (likethe fuel gauge, heater, and wind-shield wipers) will function normallyexcept the battery will be supplyingall the power. If left in the ON positionfor a lengthy period, the battery canbecome discharged.

When the ignition switch is in the ACCposition, only the low -current devices(such as the radio and some of thewarning buzzers, like door ajar willfunction), but the high -current de-vices (like the fuel gauge) will not besupplied with power.

For now, it's important to understandthe ignition switch so that you can

take Vgas voltage measurements withconfidence. Begin by turning the igni-tion switch to the ON position to powerthe fuel -gauge system. The next step isto disassemble the dash and removethe instrument cluster to get to the fuelgauge plug. In the 1972 Olds Cutlass,that means that the fuel-oil-gen-tempcluster gauge must be removed.Connected into the back of the clus-ter gauge is the fuel -gauge plug.

The third step is the most difficultbecause you'll have to locate thesending wire that is surely among sev-eral dozen other wires that all lookalike. Turn on the ignition -switch andhook a voltmeter's positive lead to thewire coming from the sender, and thevoltmeter's ground lead to the carchassis. If you don't know which wire inthe fuel -gauge plug comes from thesender, don't be intimidated. Take agood look at the back of the clustergauge: locating the fuel -gauge plugwill be obvious.

Just study the plug and take an ed-ucated guess as to which wire comesfrom the sender. The wire is oftencolor -coded green, brown, or striped.Now stick the voltmeter probe into theterminal (wire) you've picked. Theprobe's tip should be ground to apointy spike that can be jabbed intothe insulation of a harness wire.

There are just so many wires in theplug and sooner or later you'll hit onthe right one. Make a splice into thesending wire and you're ready to takesome measurements. Be advised,however (if you don't already know),that even shop manuals (like Chilton,etc.) are poor references when itcomes to plug -connector diagrams.

A fool -proof method for locatingthe sending wire is to assemble a jab-bing test -probe like that in Fig. 7. You'llneed a sharp sewing needle or hatpin, a 10 -watt, 10 -ohm resistor, somehook-up wire, and an alligator clip.The probe's lead length should beseveral feet. The idea is quite simple.Hook the alligator clip to ground, turnthe ignition switch to the ON position,and start jabbing the sewing pin intoone wire at a time while watching thefuel gauge. When you hit the sendingwire, the gas -tank rheostat (sender)will now be shunted by a 10 -ohm re-sistor. Because any two resistors in par-allel will reduce the total resistance,the fuel gauge thinks the rheostat re-sistance has changed and the gauge

needle will swing. It's fast, it's simple,and it works every time.

When your tank is about empty,drive to a gas station and have theattendant fill up your car. While theattendant goes for the gas hose, youshould turn the ignition -switch to the

SOLDER

BLACKELECTRICAL

TAPE

10f1, 10 -WATTRESISTOR

SOLDER

ALLIGATORCLIP

LARGESEWING -PIN

HOOK-UPWIRE

4 -FOOT

HOOK-UPWIRE

Fig. 7. A home-made test probe-likethis one made from a 10 -ohm, 10 -wattresistor, a large sewing needle, analligator clip, and some hook-up wire-can be used to locate the lone sendingwire amongst the jumble of wires behindthe dashboard.

+12V CARBATTERY

ON position to power up the instrumentgauges; but do not start the engine.As the tank is being filled, watch thefuel -gauge pointer move toward thefull position, and record the voltagemeasured for each 1/4 tank of gas.

There are three reasons why youmight not get a Vgas voltage reading;two of which are bad news. One badreason could be that the fuel gauge iscompletely inoperative and burntout-no current can flow through thegauge to get to the sender. The otherbad reason might be that the senderis broken, or maybe the connectingwire is broken or intermittent. In eitherevent, you'll have to do some elec-trical checking to diagnose whythere's no Vgas voltage.

The third reason isn't so bad andmay even surprise you. When thegauge is lifted out of the dash onsome musclecars, the electricalground is lost and the gauge be-comes inoperative; the Vgas voltagemay also be lost. The fix for that is sim-ple: Use hook-up wire to jump thegauge's ground wire or terminal to thecar chassis.

Circuit Theory. A schematic di-agram for the Smarter Gas Gauge is

shown in Fig. 8. In that circuit, a singleop -amp, U1 -a-1/4 of an LM324Nquad op -amp, configured as a com-parator-is used to compare the Vgasinput to a reference voltage (Vref).Switch S1 is used to reverse the Vgasand Vref inputs to U1 -a, depending onwhether Vgas rises from empty -to -full

as in Table 1, or falls from an empty -to -full as in Tables 2 and 3.

Let's take a look at two examples:Suppose Vgas rises in the manner indi-cated in Table 1. In that instance, Vgasgoes to pin 2 (the inverting input) andVref goes to pin 3 (the non -invertinginput). Let's set the indicator lamp toilluminate when the tank is 1/4 full.

According to Table 1, Vgas is 5.2 volts,so Vref-which serves as the trippoint-should be manually set to 5.2volts via potentiometer R2. When thetank is more than 1/4 full, the Vgas levelwill be above 5.2 volts, causing U1-a'soutput at pin 1 to be driven to ground.The output of U1 -a, which is fedthrough S2, reverse biases transistorQ1, causing lamp 11 to stay off. How-ever, when the tank is less than 1/4 full,the Vgas dips below 5.2 volts, causingU1-a's output at pin 1 to swing to thepositive rail, forward biasing Q1 andturning 11 on.

Now let's suppose that Vgas falls asindicated in either Tables 2 or 3; in thatcase, the Vgas level is fed to U1-a's non -inverting input at pin 3 and Vref isrouted to U1-a's inverting input at pin2. Let's set the indicator lamp to illumi-nate when the tank is 1/4 full. Accordingto Table 2, V905 is 6.7 volts, so Vrefshould be manually set to 6.7 volts (thetrip point for this example) via potenti-ometer R2.

When the tank is more than 1/4 full,Vgas will be below 6.7 volts and U1-a'soutput at pin 1 will be driven toground, which reverse biases tran-sistor Q1, causing 11 to stay off. How -

S1 -a S1-bL

o-- o

VgasFROM o

SENDER

CARCHASSIS

GROUND

I

R1

100C1

R210K

$ VietTRIP

THRESHOLDCONTROL

Mci10

D1

1N4739A9.1V

1WATT

U1 -a

11

S2 -a

1/4 LM324N

D21N4001

C210

11

12V100mA

R55K

IVY VIAR3

50KLAMP

DIMMERCONTROL

R41MEG

SLOSH pg-TIME-OUTCONTROL

2

v.r

Fig. 8. At the heart of the Smarter Gas Gauge, is a single op -amp (UI-a) that'sconfigured as a comparator. The output of the op -amp toggles high when the gas tankneeds to be refilled, which forward -biases transistor QI, causing II to light.

+91VA

U2 -a 14/4 CD4093

34

2N4400

Fig. 9. When the car accelerates, gasoline within the fuel tank begins to slosh around.The float arm follows the gasoline, causing the gas -gauge needle to move tmvardempty, giving a false indication. Some float arms have a calibrated friction brake toprevent gasoline wave -motion from oscillating the float arm.

ever, when the tank is less than 1/4 full,Vga, rises above 6,7 volts, causing U1-a's output at pin 1 to swing to thepositive rail. That forward biases Q1,which, in turn, causes 11 to light.

Switch S2 can route U1-a's output ineither of two directions. In one direc-tion, the output of U1 -a is fed straightto the base of Q1 (as we've just seen).In the other direction, the output of U1

is routed to an RC, gas -sloshing, time-out circuit (comprised of R4/C2).

Let's discuss how the time-out circuitfunctions. When the gas level is at thecomparator's trip point and the caraccelerates, the sloshing gas causesVgas to oscillate above and belowVruf. That causes the output of U1 -a atpin 1 to also oscillate high and low.When the output goes high, capaci-

PARTS LIST FOR THESMARTER GAS GAUGE

SEMICONDUCTORSU I-LM324N quad, low -power (T-

amp, integrated circuitU2-CD4093, quad 2 -input NAND

Schmitt -trigger, integrated circuitQ1 -2N4400 small -signal, general-

purpose NPN silicon transistorDl-IN4739A 9.1 -volt, I -watt, Zener

diodeD2 -1N4001 general-purpose silicon

rectifier diode

RESISTORS

(All fixed resistors are 1/2 -watt, 5%units.)

RI -100 -ohmsR2 -10,000 -ohm linear -taper

potentiometerR3 -50.000 -ohm linear -taper

potentiometerR4-1 megohm linear -taper

potentiometerR5 -5,000 -ohm

ADDITIONAL PARTS ANDMATERIALS

Cl. C2 -10-11F, 35-WVDC, tantalumcapacitor

11 -12 -volt. 60-175-mA incandescentlamp

SI, S2-DPDT slide switchPrinted -circuit materials, enclosure

(optional), 2 -amp 3GA-type fuse,crimping tool and connectors, in -line fuse holder, hookup wire, wireties, solder, hardware, etc.

Note: The following items areavailable from Jonathan Gordon.74 Berkshire, Apt. C. West PalmBeach, FL 33417; a kit of partscontaining the printed -circuit boardand all components (except anenclosure) for $49.95; the fullyassembled and tested Smarter GasGauge for $69.96. Please add

$4.(X) to all orders for shippingand handling. Florida residentsplease add 6% sales tax.

tor C2 charges through resistor R4 (to-gether R4 and C2 form an RC timeconstant).

The voltage across C2 rises only forthe time that the output of U1 -a is high,which is usually for less than a second.Eventually, the slosh reverses itself andthe output of U1 -a goes low, whichimmediately discharges C2 throughdiode D2. The C2 charging -cyclemust now start all over again. Notice

that Vcps can now swing above andbelow Vr yet the indicator lamp re-mains off When C2 has chargedenough to trigger U2 -a (1/4 of a 4093quad CMOS NAND Schmitt -trigger), 11illuminates.

There are two reasons for using aCMOS Schmitt -trigger for U2: CMOSgates offer a high input -impedancethat won't interfere with the chargingrate of C2, and because the voltageacross C2 is slow -rising voltage, that'sfar too long a time for most digitalgates. Digital gates like fast rise -timeinputs (at the least a few milliseconds)or they'll get confused and the outputwill oscillate while trying to figure out ifthe input voltage is actually rising orfalling past the gate's trip -point.

A Schmitt trigger has two separatetrigger points one for rising voltagesand another for falling voltages-andcan, therefore, toggle on the slowly -rising voltage across C2 without os-cillating.

The circuit is powered from a 12 -voltsource that is tapped off the vehicle'sbattery. The 9.1 -volt power source forthe IC's is provided through a conven-tional Zener-regulator circuit consist-ing of D1 and its current -limitingresistor, R1.

Slosh Time -Out. When the 1972Olds Cutlass (mentioned earlier) ac-celerates from a stop, the gas -gaugeneedle swings toward empty. In Fig. 9,when the tank is about Y2 full and thecar lurches forward, there's plenty ofroom in the tank for the gas to sloshback -and -forth like an ocean surf.When the float arm that's attached tothe rheostat rides the surf to the tank'sbottom, the rheostat thinks the tank isempty and the gauge needle swingsall the way to "E" (empty).

The Vas voltage will vary with therocking gas -tank sender every timethat the car accelerates quickly, takesa tight turn, or hits a road bump. Thatpresents no problem until Vg0, ap-proaches the comparator's triggerpoint (the Vro voltage). Points a and bin Fig. 10 show that every time Vgasoscillates above and below Vref, U1-a'soutput toggles (as shown in Fig. 10 atpoint c), which causes the lamp toflash (see point c4.

If U1-a's output is routed to the sloshtime-out circuit, C2 charges on thepositive pulse (see Fig. 10, point e).Because there is not insufficient time

SECONDS I I I

v,

Vgal

SLOSHINGGASOLINE

4.1VOLTFULLTANK

7.7VOLTEMPTYTANK

U1 -a

OUTPUTLAMP OFF

LAMPWITHOUT

SLOSHCONTROL

C2CHARGING

LAMPWITH

SLOSHCONTROL

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16I I I I I I I III

FLASHING FLASHING

C2 CHARGING THROUGH R4

LAMP STAYS OFF

LAMP STAYS ON

7.7 VOLTEMPTYTANK

DATA FROMTABLE 2

DATA FROMTABLE 1

4.5VOLTEMPTYTANK

U2 -a TRIGGERPOINT

C2 DISCHARGINGLAMP STAYS ON

THROUGH D2

Fig. /0. The low fuel indicator flashes when gasoline within the tank sloshes aroundthe threshold trip -point. The RC circuit (R4IC2 in Fig. 8), operating in much the samemanner as a switch-debouncer, prevents the lamp from flashing as gas sloshes about

the fuel tank.

1431/4 INCHES

Fig. 11. The author's prototype was assembled on a small printed -circuit board thatmeasures about 31/4 by 19/16 inches. A full-size template of that printed -circuit pattern isshown here.

J1 I I

LAMP, YLWU1 J J U2

I

LAMP, YLWI

Cl

12V RADIO, RED R11174-4121

GRN 0 --SENDER,

S1 L:-.1 S2GROUND, BLK DID IN III

R4

-C2

41:-]

Fig. 12. Here's the printed -circuit board's parts -placement diagram. Carefid attentionshould be paid to component orientation, which will prevent most construction errors.

to charge C2 to U2-a's trigger point, driving for some time, the tank gets sothe lamp remains off. Ultimately, after low that the float arm cannot swing

CARCHASSISGROUND

LAMPDIMMERADJUST

GAS GAUGE

WIRE TAP -IN

CONNECTORGREEN -WIRE SENDER

E

+12VDC 2A FUSE

cr P

FUSE

BOX

RED -WIRE

YELLOW-WIRE.

YELLOW -WIRE

0 0 0

R2

Si

2 3 5

1

7

J1

vlIC1

14

S2

7

R3

IC2

14

TAIL SIG

HEAT GLASSOHORN

HEAD LT

-11 IRADIO

HEATERUUFT -WIPERO

P/WINDOW

HAZARD

MEMA/C

SENDINGWIRE

C\ DASHBOARDIDIOT -LIGHT

THRESHOLD ADJUST

SLOSHTIME-OUTADJUST

CAR -WIRING BUS

SMARTER GAS -TANK

GAS GAUGE SENDER

Fig. 13. Here's the musclecar hook-up diagram. To make installing the Smarter GasGauge a bit easier, use a different color wire for each connection: It's also a good ideato plan your installation carefully before starting.

high enough to oscillate Vgas around\ire,. When that happens, C2 has timeto charge (see Fig. 10 point 1, andtrigger U2 -a, which causes M to turn oncontinuously (see point g).

There is, of course, always the pos-sibility that a wild screeching turn willrock the float arm enough to pushVgas to the Vre, level. That causes U1-a'soutput to go low, discharging C2.When that happens, M turns off, andrequires another 5 seconds or so be-fore turning on again. But the lamp willnot flicker or flash.

A flashing lamp sure gets your at-tention though, possibly because theflash rate is somewhat non-re-petitive-sometimes flashing quicklyand at other times quite slowly-de-pending on how the gas sloshes in thetank. Although for many, a flashinglight that goes crazy when the caraccelerates is a perfect attraction,

not everyone loves a flashing light.And if you prefer a lamp that justcomes on and stays on when the gaslevel exceeds the trip threshold, thenthe answer is to use the slosh time-outcircuit.

Construction. The Smarter GasGauge was assembled on a smallprinted -circuit board that measuresabout 31/4 by 19/16 inches. A full-sizetemplate of that printed -circuit pat-tern is shown in Fig. 11, with the corre-sponding parts -placement diagramappearing in Fig. 12. The electroniccomponents are simple and shouldtolerate all but the most severeabuses.

There are no delicate oscillators ortouchy amplifier feedback loops toworry about, no ultra -fast computerclocks that wreak havoc with everywire that comes near them, and no

delicate transistor betas to worryabout when the temperature gets toohot or too cold.

What you should do, however, is tomake absolutely sure that U1 and U2,D1 and D2, Q1, and C1 and C2 areinstalled with the proper orientation. IfZener diode D1 is put in backwards,the 9.1 -volt power source used to op-erate U1 and U2 just won't be avail-able. Remember, reverse -biasedZener diodes act like regular rectifierdiodes. The means that if D2 is in-stalled backwards, R4 will be shortedout and the R4/C2 time constantwon't function at all-C2 will chargeand the lamp will be lit continually.

If the voltage at U1 -a pin -1 is highand the lamp isn't lit, check Q1, makesure that R3 is wired correctly, andcheck the continuity through switchS2.

Once assembly is complete, care-fully inspect your work for solder shorts(bridges) between pads and lands,cold solder joints (characterized bydull blobs of solder). Finally, label allwires going to the car as either G forground, S for sender, or + 12V for bat-tery.

Installation. First we'll take a look atthe original prototype installation inthe aforementioned 1972 Olds Cut-lass. For a proper installation, you'llneed the right tools and the knowhow to do the following: disassemblethe dash; drill a hole here or there; runa wiring harness up and around cor-ners; find the sending wire in the backof the dash at the fuel -gauge plug;make good splice connections usinga crimping tool or soldering iron; knowhow to take voltage measurementsusing any DVM or VOM; and use metalbrackets and other hardware for asecure installation. Also, be preparedto treat minor cuts and scrapes shouldyou be careless and thrust your fingersin blind corners under the dash.

Before beginning your installation,study the car's dash and decide whatkind of installation you want. If yourdash has a low -fuel "idiot" light, you'llhave to disconnect the Iwo wires fromthe lamp's socket. That usually meanscutting the wires unless there's a sim-ple crimp terminal to pull off. Just tuckthose wires away. Now wire the in-

dash light to the appropriate pads onthe Smarter Gas Gauge's printed-cir-


Have you ever mer-ged onto an inter-state highway from

an on ramp and severalmiles down the road realizedthat your turn signal neverwent off as you entered traf-fic? Suddenly, you realizethat there are 16 cars slightlybehind you in the left lanethat have been refusing topass for several miles, fear-ing that you may really in-tend to change lanes. Youturn off the signal, and asthose vehicles fly past you,their drivers give you a lookthat, as they say, could kill!

Well, the Tune -Signal de-scribed in this article whichis designed to set off a musi-cal chime-- will prevent thatfrom happening by alertingyou when your signal hasbeen left on a little too long.The circuit uses a small, inex-pensive, pleasant -sounding,musical chime, rather thanan irritating buzzer; youprobably already haveenough irritation while drivewithout adding more irrita-tion to it.

TURN -SIGNALREMINDER

BY JIM STEPHENS

If you often neglect to turn off your car'sturn signal, then perhaps this easy -to -build reminder is just what you need!

About the Circuit. A schematic di-agram of the Tune Signal is shown inFig. 1. The circuit consists of U1 and U2(a 4093 quad two -input NAND Schmitttrigger and a 4040 12 -stage ripple -carry counter/divider, respectively),Q1 (a TIP42 PNP silicon power tran-sistor), B71 (the aforementionedchime module), and a handful of sup-port components.

The input to the circuit -a series ofpulses plucked from the load (or out-put) wire of the auto's flasher mod-ule immediately divides along twosignal paths. In one path, the signal isapplied to gate U1 -d, which is config-ured as an inverter. The output of thatgate is fed through diode D1 andused to charge C2, a 470-11; capaci-tor. The charge on C2 is applied toboth inputs of U1 -c (also set up as aninverter), pulling its output low, ineffect, enabling U2.

In the second path, the signal is fedto U1 -a, which squares the appliedsignal in preparation for its applica-tion to the clock input of counter U2.The squared -up pulses applied to U2's

clock input cause the counter to ad-vance one count for each clock pulsereceived. When both pins 3 and 4 (the05 and 07 outputs, respectively) arehigh at the same time, the output ofU1 -b is pulled low. That low is appliedto the base of Ql, causing the tran-sistor to turn on. With Q1 turned on,power is applied to the chime mod-ule (BZ1), causing it to sound, Thechime module which puts outenough volume to be heard over theroad noise -will chime twice, wait afew seconds and chime again if thecircuit is not reset.

After the chime has sounded, andthe turn signal is switched off, thecharge stored in C2 is bled off throughR3. With C2 no longer charged, theoutput of U1 -c goes high, resetting U2.When U2 is reset, its outputs (at pins 3and 4) go low. That low, which is ap-plied to the base of the transistor,causes Q1 to turn off, removing powerfrom the chime module.

The number of flashes that the cir-cuit counts depends on which two ofU2's outputs are connected to U1-16.With the circuit wired as shown in Fig. 1,about 70 flashes are allowed to occur

before the chime sounds.The number of flashes thatthe counter counts beforetriggering the chime can bealtered by connecting pin 6of U1 -c to another of U2's out-puts. For example, con-necting pin 13 (the ! output)of U2 to pin 6 of U1 -b, ratherthan to pin 4, directs the cir-cuit to count 144 flashes before sounding the chime.Even greater counts can beachieved by connecting tothe higher c.! outputs (say. the

and Qt! outputs, at pins 15and 1, respectively) of U2 topins 5 and 6 of U1 -b.

Power for the circuit is

taken from any keyed(switched) power line at thevehicle's fuse panel, so thatthe circuit receives poweronly when the ignition key isin the on position. Fuse Fl isincluded in the circuit incase of a wiring error orshort.

Circuit Assembly. The au-

Signal was hard -wired on asmall section of perfboard. Use Fig. 1as a guide when assembling your unit.It is recommended that sockets beprovided for the two integrated cir-cuits (U1 and U2). That will preventthermal damage to the IC in theevent that a component is miscon-nected to an IC pin. The IC's, beingCMOS units, are highly susceptible todamage due to heat and elec-trostatic discharge.

The chime module (EMI) was notmounted to the perfboard along withthe other components, but was in-stead mounted to the front panel ofthe enclosure in which the circuit washoused. You could, however, mountthe chime module remotely in someother position that allows it to beheard. The circuit was housed in asmall plastic enclosure with a metallid. The only enclosure preparation re-quired is to make a hole (or slot) in theenclosure for the wires that connectthe circuit to a keyed (switched) 12 -volt power source, ground, and theflasher's load wire, and (as appropri-ate) a cutout for the chime module ora second hole for the connectingwires between the circuit and a re-

Yoe

(KEYED POWER) "4-114:1-11-F1

TO R1 1A"LOAD" WIRE 22K

ONFLASHER ],MODULE

C1

5

12

13

D111 1N4000

-04

14

2

R2 U1 -a1000 1/4 4093

8

U1 -d

1/4 4093 R3 C210K 470

Fig. I. As shown by this schematic diagram, the circuit consists of LI and 1?.? to 4093quad two -input NAND Schmitt trigger and a 4040 /2 -stage ripple -carry counter/divide.respectively), QI (a TIP42 PNP silicon power transistor). VI (the chime module), anda handful of support components.

0

11

Vcc

CLK

U24040

05

)t) 11RST 07

GPID

V4 4093 8

U1 -b

3 51/4 4093

..4.4

01-1TIP42

t R447012

RED

Here is the author's petjboard assembly. The chime module can he installed in acutout in the front panel of the enclosure, and secured in place with silicon cement, asshown here, or mounted remotely in some other convenient location within earshot.

Here's the completed unit just prior toinstallation.

motely located module.Note that fuse Fl (a fast -blow unit) is

not mounted to the circuit board, butis instead an in -line unit that should beconnected to the far end of the cir-cuits power -supply line (near the + Vfeed point) to minimize the chancethat a short could occur between thefuse and the connection.

Installation. The first step in installingthe circuit is to locate the vehicle'sflasher module. Connect the project'spositive -supply line to a switchedpower source (the 12 -volt power linethat feeds the flasher module is ideal)and the negative line to ground (pref-

PARTS LIST FOR THETUNE -SIGNAL

SEMICONDUCTORSUI-4093 quad 2 -input NAND Schmitt

Trigger, integrated circuitU2-4040 12 -stage. ripple -carry,

binary counteridiyider, integratedcircuit

QI-TIP42 PNP silicon, powertransistor

DI-IN4006 $00 -Ply.rectifier diode

RESISTORS(All resistors are Vs -watt. 5(1 units.)RI -2200 -ohmR2 -1(X) -ohmR3-I0,000-ohmR4-470 ohm

CAPACITORS

25-WVDC. electrolyticC2 -470-µf, 25-WVDC, radial lead

electrolytic


FI-I-amp, fast -blow fuseBZI-Chime module (Radio Shack

270-071)Perthoard materials, enclosure, in -

line fuse holder, snap -onconnectors, wire, solder, hardware.etc.

erably somewhere on the chassis).Then connect the Tune Signal's inputwire to the load (or output) of the vehi-cle's turn -signal flasher module. Thesignal and power connections canbe simplified by using small "self tap"snap connectors.

To test the operation of the circuitsimply turn the vehicle ignition on,and activate the turn signal (any di-rection will do). After a predeterminednumber of flashes, the circuit shouldactivate the chime. Let the turn signalremain on for a while. The module willchime, wait a few seconds, and theunit should chime again if the circuit isnot reset. If the circuit works as out-lined, you can turn off the turn signal,and mount the unit near the bottomof the dash so that sound will be di-rected into the car and not up into thedashboard. The author used Velcrofasteners to attach the unit to the un-derside of the dash. That allows theproject to easily be removed should itbecome necessary to service the unit.

That's all there is to it. Once the Tune -

Signal is intalled, you and your fellowdrivers should enjoy safer and sanermotoring.

The price of everything is stead-ily going up these days. Andone of the major drags on most

household budgets is home heatingcosts; be it gas, oil, or electric. That'sbecause a properly designed heat-ing system operates with a 100% dutycycle, meaning that the burner is ei-ther 100% On. producing possibly80,000 to 120,000 BTU's of heat energyfor each hour of operation- -or 100%off at any given time. Unfortunately,there is a flaw in that type of opera-tion; the thermostat knows nothing ofthe amount of heat that has built up inthe heat exchanger, which can trans-fer just so many BTU's of heat. Thus, theburner can run and run until the tem-perature set -point is reached, and soa great amount of heat is simplywasted. Not a very efficient method ofoperation, to say the least.

Some thermostats have a "heat an-ticipator" feature that shuts off theburner before the thermostat set -point temperature is reached. Thathelps somewhat; but a significantamount of heat (fuel) is still wasted. Ofcourse, there are other ways to re-duce heating -fuel consumption, in-stalling better insulation and/or lower-ing the thermostat settings, forinstance. But what can be done afterthose measures have been taken?

Reduce HeatingCosts

with theFuel

MiserBY ANTHONY J. CAR ISTI

Tame home -heating costs by installingour super -efficient furnace controller

That's where the Fuel Miser de-scribed in this article comes into play.

Miser, which is designed to beconnected to the thermostat circuit ofa heating system, takes control of thesystem and meters out a selectedamount of fuel, as we'll soon see.

How It Works. The Fuel Miser, a solid-state, optically isolated, duty -cyclecontroller, is connected in series withthe thermostat wiring of a heating sys-tem. Without regard to the thermostatsetting, the Fuel Miser allows the fur-nace burner to operate at selectableduty cycle increments of 10% of up to100%. There is no apparent loss ofcomfort level because the Fuel Miser,while keeping the burner cut off, al-lows the heat normally trapped andwasted in the exchanger to be dis-tributed, thereby enhancing fuel effi-ciency.

Gas- and electric -heating systemsrespond well to short bursts of fuel de-mand. For gas- and electric -heatingsystems, the Fuel Miser is designed sothat each 10% of duty -cycle time isjust 45 seconds, and a complete on -off cycle takes 450 seconds or 71/2minutes. Oil systems are more restric-tive in their cycling requirements be-cause the system must be allowedtime to cool down before it can be

restarted. For oil systems, the Fuel Mis-er's duty cycle is 31/2 minutes for each

of duty cycle, thus afull on -off cycle (100% duty cycle)takes 35 minutes.

The Fuel Miser's duty cycle is set by aspecific value of timing capacitorone value for gas and electric systemsand another for oil -fired systems. Thecircuit's duty cycle is instantly adjusta-ble at any time by means of a 10 -position rotary switch. An optoisolator/Triac circuit is used to interface theFuel Miser to the heating system.

About the Circuit. Refer to the sche-matic and timing diagrams in Fig. 1 In

the schematic diagram (Fig. 1A), U1 (a555 oscillator/timer) is configured asan astable multivibrator (or free -run-ning oscillator), whose operating fre-quency is determined by R1, R2, andC2. The value of C2 (the timing ca-pacitor) must be selected for the typeof fuel used by the system; gas, elec-tric, or oil. For gas and electric systems,U1's operating frequency should be to0.02 Hz; for oil systems, it should be setto 0.005 Hz.

The output of U1 at pin 3 Is fed to theclock input of U2 (a CD4017B decadecounter/divider with 10 decoded out-puts) at pin 14. That causes U2 to ad-vance one count for each low -to-

01

1N4004

9T015 II -

VOLTS DCINPUT

4701

U1

LM555CN

11

R1

' 1MEG

1416 3 2 4 7 10

-0

-0

516

100%

si 010%

9?9 11

R21MEG

6

C2*

COUNT I 0

U2PIN 14CLOCK

U2PIN 3100%

1UN22

90°A

U2PIN 480%

U2PIN 770%

U2

U2CD4017B

13 8

'C2 -22µF FOR GAS AND ELECTRIC SYSTEMSC2=1000 FOR OIL SYSTEMS

1 1 2 3 4

A

'WR41K

U3 -a

1/4 CD40018

START

12 STOP

C3

.01

R5150f24As* 0

2 4U4

MOC3011

LED10

0183170

1.8,9,10,11,12,13

U3 -bI/4 CD4001B

7'R3

100K

51 6 1 7

I 81 9 1 0 1 1

PIN 12I00-4

U3PIN 3DUTY

CYCLEI

STARTB

Fig. 1. Here are the schematic and timing diagrams for the Fuel Miser. The Fuel Miseris comprised of a 555 oscillator/timer (U1), a CD4017B decade counter/divider (U2),half of a CD4001 quad two -input NOR gate (U3), an MOC3011 optoisolator/coupler(U4), a BSI70 N -channel, enhancement, TMOS field-effect transistor (QI), a T2322DTriac, and a handful of support components.

high transition of the clock input, se-quentially forcing one of U2's ten out-puts high, as illustrated in Fig. 1B.

An eleventh output at pin 12 (thecarry output) goes high when outputpins 3, 2, 4, 7, and 10 (the 0, 1, 2, 3, and4 counts, respectively) go high. WhenU2's outputs at pins 1, 5, 6, 9, and 11(which correspond to counts 5-9, re-

spectively) go high, pin 12 goes low.The output of U2 at pin 12 is fed to oneinput (pin 1) of a bistable latch, com-prised of U3 -a and U3 -b (1/2 of aCD4001 quad two -input NAND gate).The U2 output selected via S1 is fed tothe other input of the latch at pin 6.Together, those two U2 outputs areused to start (set) and stop (reset) the

STOP

MT2

MT1

TR1

T2322D

OUTPUT

latch, which in turn determines theduty cycle of the circuit.

Now, let's assume that S2 is set to the80% duty -cycle (U2 pin 4). When pin 4(which corresponds to a count of 2)goes high, the latch sets, causing itsoutput at pin 3 to go high and pin 4 togo low. The latch remains in that stateuntil U2 goes from count 9 to count 0.

At that point, a positive -going signalappears at pin 12 of U2 and is appliedto pin 1 of U3, causing the latch toreset. The latch remains in the resetstate until U2 again reaches a countof 2, and the cycle repeats.

Note that the output signal appear-ing at U3 pin 3 has a duty cycle of80%, which is the setting selected byS1. One can see that if S1 is set to anyof the other nine decoded outputs ofU2, the resulting duty cycle at U3 pin 3will respond accordingly.

The signal appearing at U3 pin 3 isused to bias Q1 (a BS170 N -channel,enhancement, TMOS field-effecttransistor) on and off. The drain of Q1 isconnected through LED1 to the cath-ode end of U4's internal LED. When Q1turns on, current flows through U4 (anMOC3011 optoisolator/coupler),causing LED1 to light and U4's Triac-driver output stage to turn on. With U4activated, the Triac-driver appliesgate current to TR1 (a T2322D), caus-ing it to conduct. At that point, operat-ing power is fed through thethermostat wiring of the heating sys-tem, permitting the burner to operate(provided that the thermostat is call-ing for heat).

When the signal at U3 pin 3 is low, Q1is cut off and no current flows into U4,so TR1 remains off and the heating -system burner is prevented from oper-ating during the off -time of the FuelMiser. However; heat continues to flowfrom the heat exchanger into the sys-tem, maintaining the comfort level,without consuming fuel.

The Fuel Miser can be set to 100%duty cycle at any time; that restoresthe heating system to its normal oper-ating state. When S1 is set to any of theother positions, the circuit provides afuel savings that depends on the se-lected duty cycle.

The Fuel Miser can be poweredfrom any 9 -15 -volt DC power source(although the author's unit waspowered from a common wall adapt-er). Any ripple voltage generated bythe power source is filtered out by C1.Diode D1 is included in the circuit toprotect against accidental reversepolarity connections.

Construction. There is nothing crit-ical about the construction of the FuelMiser. In fact, if you choose, the circuitcan be built on perfboard usingpoint-to-point wiring techniques.

31Vie INCHES

Fig. 2. The author's prototype Was built on a small printed-circuit board. measuring

about 3%, by 13/4 inches: a full-size template o/ that printed -circuit pattern is shown

here. You can etch your own board from the pattern shown or purchase one ,from the

supplier listed in the Parts List.

01

--101-- R1 -R3--R2-

C1

TO

9-15VOLT

DC

SOURCE

U1

C2 +

C3

U2

-84- -R5-MT2 TR1

FU4MT1 111

CD®LED1 6

TO

THERMOSTATCIRCUIT

U3

r .70% /0

80% nno,

100%

50%40%

30% 20%0

10%

Fig. 3. Assemble the prim ted-circuit hoard using this parts -placement diagram as a

guide. Note: It is recommended that sockets be provided for all of the IC's.

However, the author's prototype wasbuilt on a small printed -circuit board,measuring about 313/46 by 13/4 inches;a full-size template of that printed -cir-cuit pattern is shown in Fig. 2. You canetch your own board from the patternshown or purchase one from the sup-plier listed in the Parts List.

Once you've obtained all the nec-essary parts and the printed -circuitboard, construction can begin. As-semble the printed -circuit boardusing Fig. 3 as a guide. It is recom-mended that sockets be provided forall of the ICs. The use of sockets allowsfor ease of troubleshooting and ser-vicing of the circuit should it ever be-come necessary. If you do not have 6 -or 8 -pin sockets on hand (for U4 andU1, respectively), they can be simulta-neously fabricated by carefully cut-ting a 14 pin socket into two pieceswith a small hacksaw.

After the sockets are installed,place and solder all the passive corn-

ponents (resistors, capacitors), exceptthe timing capacitor (C2). Follow thepassive components with the activecomponents. Be sure that all of thepolarized components (electrolyticcapacitors and all semiconductordevices) are properly oriented; all it

takes is one misoriented polarizedpart to render the circuit inoperative.That error can also cause parts to bedamaged.

Timing -Capacitor Selection. Asmentioned earlier, the Fuel Miser's tim-ing circuit (U1) must be set for the typeof fuel-gas and electric or oil-that isused by the heating system. It doesnot matter what kind of heat is pro-duced by the system . . hot water,warm air, or steam . . . the Fuel Miserwill operate properly when the cor-rect value of timing capacitor (C2) isinstalled. For gas (either propane ornatural gas) and electric systems,make C2 a 221.1,F unit. For oil burners,

use a 100-p5 unit. Low -leakage elec-trolytic capacitors are a must to en-sure timing accuracy.

Note. If an oscilloscope is available,the Fuel Miser can be put through arapid test by temporarily using a 1000-pF (0.001-11F) 50 -volt, ceramic -disccapacitor in place of the specifiedC2 values to temporarily increase U1'soscillating frequency. (We'll discussthe rapid test procedure later.)

Final Assembly. When the board isfully populated (excluding C2), in-spect it carefully for any possibleshorts, especially between closelyspaced conductors. All solder jointsmust be shiny, smooth, and filleted.Any that appear as dull blobs of solder(known as cold solder joints) must becorrected by removing the old solderand redoing the joint. It is far easier tocorrect such faults at this stage of thegame than attempting to do so laterafter you've discovered that the proj-ect is inoperative.

The Fuel Miser's circuit board canbe housed in the furnace enclosure orplaced in a small plastic enclosure ofits own, and installed next to the ther-mostat, furnace, or anywhere youchoose. A suitable enclosure is sug-gested in the Parts List. LEDI, whichprovides a visual indication of the FuelMiser's operation may optionally beplaced on the front of the cabinet orfurnace where it can be seen.

The rotary switch may be installed inany convenient location near the cir-cuit board, with the positions marked10%, 20%, etc., (in 10% increments) upto 100%. That allows you to instantlychange the Fuel Miser's duty cycle atany time. When wiring S1 refer to Fig. 3,which illustrates the location of theconnections.

Power for the author's prototypewas provided by a 9 -15 -volt DC walladapter (but any power supply withan output voltage within the specifiedrange will do just fine). Be sure tocheck your power source with a DCvoltmeter to be sure that its outputvoltage is within the specified range.Connections between the powersupply and the Fuel Miser can be hardwired, or made through a miniatureplug and jack arrangement. In anycase, be sure to observe proper po-larity

When installing the Fuel Miser in a28 cabinet, a pair of binding posts or a

PARTS LIST FOR THEFUEL MISER

SEMICONDUCTORSUl-LM555CN oscillator/timer,

integrated circuitU2-CD4017B decade counter/

divider, integrated circuitU3-CD4001B quad 2 -input NOR

gate, integrated circuitU4-MOC3011 optoisolatorIcoupler

with Triac-driver output. integratedcircuit

QI-BS170 N -channel, TMOSenhancement -mode FET

TRI-12322D 4 -amp. 400 -Ply TriacDI -1N4004 or similar I -amp, 4(X)-

PIV silicon rectifier diodeLEDI-2-volt, 20-mA, light -emitting

diode

RESISTORS

(All fixed resistors are 1/4 -watt. 5Yunits.)

RI, R2-l-megohmR3 -100.000 -ohmR4--1000-ohmR5 -150 -ohm

CAPACITORSC1 -470-µ,F, 25-WVDC, electrolyticC2--22- or 100-02 25-WVDC,

electrolytic (timing capacitor, see

C3 -0.01-11..F, ceramic -disc


SI-SPIOT rotary switch IRS275-1385 or similar)

Printed -circuit hoard materials,enclosure (RS 270-231 or similar).IC sockets, binding posts, 9- to 15 -

volt DC. 20 mA or more, walladapter (RS 273-1431 or similar)wire, solder, hardware, etc.

Note: The following parts areavailable from A. Caristi. 69 WhitePond Rd., Waldwick, NJ 07463:PC hoard for $10.95; UI, U2, U3,U4 for $2.25 each; Q1 for $2.(X);Q2 for $3.50; C2 low -leakagecapacitor (specify value) for $1.50.Please add $3.00 postage/handlingto all orders.

two -wire connector should be used tobring TR1's MT1 and MT2 terminal con-nections out to the heating system.The polarity of those wires does notmatter. Once those terminals are in-stalled, do not connect the Fuel Miserto the heating system until instructedto do so, which will come later, afterthe checkout procedure.

Checkout. Since the Fuel Miser's tim-ing circuit operates at a very low fre-quency (0.02 Hz for gas and electricsystems and 0.005 Hz for oil systems), aDMM or VOM with an input imped-ance of 1 megohm or more and aclock or stopwatch can be used tocheckout the circuit. If, on the otherhand, an oscilloscope is available, amore rapid checkout procedure canbe performed by temporarily sub-stituting, as mentioned previously, a1000-pF capacitor for C2 and observ-ing the output waveform's duty cycle.In addition, if a 24 -volt step-downtransformer is available, it can beused to check the Triac output of thecircuit.

Begin the checkout procedure byconnecting a 9 -15 -volt DC powersource to the circuit, and after makingsure that the source voltage is prop-erly polarized, apply power. Checkthe signal at pin 3 of U1. A normalindication is about a 67% duty cycle(high level 2/3 of the time and low level1/3 of the time). The period of the signalshould be about 45 seconds (gas/electric systems) or 31/2 minutes (oilsystems) with the specified value ofC2 installed. With a 1000-pF unit in-stalled, the period (as observed onthe oscilloscope) should be about 2milliseconds.

If you do not obtain the correct sig-nal at U1 pin 3, troubleshoot the circuitbefore proceeding. Check the powersupply voltage and its polarity. Checkthe orientation of D1, U1, U2, and C2.Check the values of R12, R2, and C2. Ifeverything looks correct, try a new555 oscillator/timer (U1).

Set S1 to the 50% position, and ob-serve LEDI or examine the scope dis-play of the signal at pin 3 of U3. Afterthe circuit has gone through one on -off cycle, the duty cycle should, there-after, be 50%. With the specified valueof C2 for gas and electric or oil sys-tems in place, the off and on times ofthe LED should be either 33/4 minutesor 171/2 minutes each, dependingupon which timing capacitor hasbeen installed in the circuit. With the1000-pF test capacitor installed, theoff/on times should be 10 millisecondseach.

Try different positions of S1, and ver-ify that the duty cycle can be set from10% to 100% (in increments of 10%) byobserving LEDI and/or the scope dis-play of the signal at U3 pin 3. If the LED

GAS VALVEOR RELAY COIL

9 -T015 -VOLT DC

INPUT

117VAC

Fig. 4. When the circuit is workingproperly, the output circuitry can bechecked using a 24 -volt step-downtransformer, a lk resistor, and an LED.Together those components simulate theload that the Fuel Miser sees duringnormal operation.

EXISTING24V FURNACE

TRANSFORMER

WALL FUEL

ADAPTER MISER

Fig. 5. This drawing shows the FuelMiser connected in series with thethermostat of a two -wire gas furnacethat's powered by a 24 -volt transformer.

THREE WIREEXISTING r- - - - - "THERMOSTAT

24V FURNACETRANSFORMER

WALLADAPTER

FUELMISER

EXISTINGFURNACE

RELAY

Fig. 6. Some oil -fired systems use three -wire thermostats to control the operationof the burner motor and ignition systemby activating a relay. This is a typicalinstallation for such systems.

does not flash on and off as indicatedor the duty cycle is incorrect, checkthe orientation of U2, U3, U4, Q1, andLED1. Check C3, R3, and R4. Checkthe wiring to S1. Examine the circuitboard carefully for any possible shorts,opens, or cold solder joints. Try newchips for U2, U3, and U4.

When the circuit is working properly

THERMOSTATEXISTING

24V FURNACETRANSFORMER

WALLADAPTER

AC

LINEPOWER

0

1 01

EXISTINGFURNACE

RELAY

FURNACEHEATINGELEMENT

Fig. 7. Dec ric-heating systems may or mar not use a relay in the thermostat circuit.Those that do have a relay can he controlled by the Fuel Miser hr wiring its outputcircuit in series with the relay coil connections as shown here.

240VAC LINEPOWER

OUTPUT

WALL FUEL

ADAPTER MISER

.L-7.1

(f)L__ _THERMOSTAT

K1

ADDEDHEAVY DUTY

RELAY ORCONTACTOR

FURNACEHEATINGELEMENT

Fig. 8. Electric -heating systems that do not contain a low -current thermostat (as in the

previous installation), use a heavy-duty thermostat that directly feeds current to the

heating element.For such systems, it will be necessary to install a heavy-duty relay WIin this example) to control the heavy heating -element current.

the output circuitry can be checkedusing a 24 -volt step-down transformer,a 1k resistor, and an LED as illustrated inFig. 4. Together those componentssimulate the load that the Fuel Misersees during normal operation. Beforemaking this test, however, install thecorrect C2 value (assuming that therapid test was performed).

With power applied to the circuitand the 24 -volt transformer ener-gized, allow the Fuel Miser one on -offcycle to initialize itself. Then verify thatthe test LED flashes off and on at theduty cycle set by S1, and that it's syn-chronized with LED1. Check that thetotal time for one complete cycle (offand on) of the test LED is either 7Y2minutes for gas and electric systems,or 35 minutes for oil systems for anysetting of S1.

If the test LED does not light, checkthe orientation of TR1 and the wiringassociated with it. Also check R5 and/or try another optoisolator/coupler forU4 and/or another Triac For TR1.

Installation. As previously stated, theFuel Miser can be installed directlyinto the furnace enclosure, on the wallnext to the thermostat, or in any desir-ed location where the thermostat wir-ing is accessible. Be sure to turn offpower to the furnace before attempt-ing the installation.

Figure 5 shows the Fuel Miser con-nected in series with the thermostat ofa two -wire gas furnace that's pow-ered by a 24 -volt transformer that islocated inside the furnace enclosure.The polarity of the connections fromthe Fuel Miser to the furnace circuit isnot important. The thermostat directlycontrols the gas valve, which oper-ates at 24 -volts AC and draws about 1 -ampere of current. The Triac in theFuel Miser switches current off and onin the thermostat circuit.

Three -wire thermostats are used insome oil -burner systems to control theoperation of the burner motor andignition system (by activating a relay).


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29

In these difficulteconomic times,many home own-

ers are opting, wher-ever possible, to dotheir own home re-pairs and remodeling.Do-it-yourself homerepairs often entailspending many hourstrying to trace the ACwiring through wallsand junction boxes.Remodeling, such asadding a new windowor door to your home,often requires that youcut a section out of awall. When hackingthrough a wall, youhad better know thelocation of the elec-trical wiring or it's lightsout.

A simple solution tothose and other similarwire -tracing dilem-mas -such as tracinga signal through yourautomobile's elec-trical system ---can befound in the McTrakwire -tracing circuit de-scribed in this article.The McTrak can turn ajob that might other-wise require hours ofcutting, whacking,and pulling into child's play (well al-most), cutting your work time from afew hours to only a few minutes.

The McTrak is easy and inexpensiveto build, and best of all, there isnothing difficult about using the unit.All you have to do is connect theMcTrak to the wire of interest and,using a portable AM receiver, trace asignal (put out by the McTrak) to itsfinal destination.

oN OpEti LOOT'

CLOSFD LOOP

OFF(-(' 1.OFF

IRETRACER

Cut those

How It Works. A schematic diagramof the McTrak is shown in Fig. 1. At theheart of the circuit is a 567 tone de-coder. The tone decoder (U1) is con-figured as a simple astable, square-

wave oscillator, operating at about250 Hz. The 250 -Hz output of thesquarewave oscillator, at pin 5, is fedto the base of 91 (a 2N3904 general-purpose NPN transistor), which in thisapplication, functions as a bufferstage. The alternating output of U1

seemingly insurmountable wire -tracingjobs down to size

BY CHARLES D. RAKES

causes 01 to switch on and off in timewith the drive signal.

The output of 01, taken from its col-lector, is fed through capacitor C2 to02 and 03--a second 2N3904 NPNunit and its companion 2N3906 PNPtransistor, respectively --which form acomplementary pair. Together, thosetransistors alternately amplify bothhalves of the applied signal; e.g.,when one transistor is off the otherone is on. That pair of transistors pro-vides a low output -impedance signalsource that can be used to drive ei-ther an open- or closed -loop circuit.

The output of the complementarypair (02 and 03) splits along Iwopaths; in one path, the output of thecomplementary pair is applied to C5,causing the 250 -Hz output of thecomplementary pair to be inducedinto the AC wiring and radiated

throughout the wiringsystem. The circuit's250 -Hz squarewaveoutput, which is rich inharmonic signals thatreach into the AMbroadcast band, al-lows the signal to betraced through thehouse or other wiringwith an inexpensiveAM transistor radio. Theradiated signal, whendetected by an AM re-ceiver, produces abuzzsaw-like sound inthe receiver's speaker.

In the other path,the signal goesthrough C4 and is de-livered to output jackJ1 (the open -loop out-put); the signal alsocontinues on through47 -ohm current -limit-ing resistor R6 (which isused to protect thetracker's output fromoverload) to J2 (theclosed -loop output).

output jacks,along with J3 (com-mon), are used whenconditions are lessthan optimum. (We'llgive examples of howand when to use thosejacks at the appropri-

ate time later in this article.)

Construction. Building the McTrak issimple and the parts layout is not crit-ical, so just about any constructionscheme will suffice. However, the au-thors prototype of the circuit was as-sembled on a printed -circuit board. Atemplate for that printed -circuitlayout is shown in Fig. 2. If you optto gothe printed -circuit route, follow theparts -placement diagram shown inFig. 3.

As usual, start by installing the pas-sive components (resistors, capaci-tors, etc.) followed by the semicon-ductors. double-checking all partlocations and their orientations asthey are installed on the board. Oncethe electronic components havebeen installed, connect a 9 -volt bat-tery connector to the board at thepoints indicated in Fig. 3. Be sure thatthe proper polarity is observed.

C1

.068

6

R1

47K

5

R410K

R3 t1K

R2

U1

567

4.7KC24.7

R510K

2N3904

032N3906

C3 ?S1 1°--11---147 + 9V

C5

.01

C4

47

R64712

C6.01

o J1OPEN LOOP

o J2CLOSED LOOP

J3° COM.

PL1117V

Fig. 1. At the heart of the McTrak is a 567 tone decoder, configured as a simple squarewave

oscillator, operating at about 250 Hz.

[01---- 1 IM INCHES --01Fig. 2. The author's prototype of the cir-cuit was assembled on a printed -circuitboard, the template for that printed -cir-cuit layout is shown here full size.

Si

o-

- R1--C1 -

111

C3-+

-R2 - Ot

C2R3 +

-R4-

side and prepare the enclosure.The author's prototype was housed

in a 45/e x 2°A6 x 19/16 -inch plastic

project box (available from RadioShack and other sources) that is slot-ted to hold small circuit boards inplace. The circuit board was sized to fitthe case's internal slots.

It will be necessary to drill holes inthe enclosure for the off -board com-ponents: S1 (along with its mountinghardware), J1 -J3, and PL1. Note thatalthough the author used a slideswitch for S1, there is no reason that atoggle or even a locking pushbutton(push on/push off) switch could not besubstituted. Mount switch S1 to oneside of the cabinet, and the three out-put jacks on the opposite side. Then

PARTS LIST FOR THEMCTRAK

SEMICONDUCTORSUl-LM567 tone -decoder, integrated

circuitQ1, Q2 -2N3904 general-purpose

NPN silicon transistorQ3 -2N3906 general-purpose PNP

silicon transistor

RESISTORS(All fixed resistors are 1/4 -watt, 5%

units.)R1 -47,000 -ohmR2 -4700 -ohmR3 -1000 -ohmR4, R5 -10,000 -ohmR6 -47 -ohm

CAPACITORSC1- O.068 -µF, 100 -volt MylarC2-4.7-p.F, 16-WVDC, electrolyticC3, C4-47 p.,F, 16-WVDC,

03

02

C6

C4+ -C5

-R6 -

J3COM

J1

---0 OPENLOOP

J2--o CLOSED

LOOP

Fig. 3. Follow this parts -placement diagram when assembling McTrak's printed -circuit

board. As usual, start with the passive components, followed by the semiconductors.double-checking the part's location and orientation as it is installed.

After all of the on -board compo-nents have been installed, check yourwork for potential problems-solderbridges, cold solder joints, and so on.

When you are satisfied that the circuitboard contains no errors (of thenature usually associated with hob-byist projects), place the board to the

electrolyticC5, 500-1000-WVDC

ceramic -disc


B1 -9 -volt transistor -radio batterySI-SPST slide switchJI-13-See textPrinted -circuit materials, enclosure

(Radio Shack #270-222), moldedAC power plug with line cord. 9 -volt battery holder and connector.wire, solder, hardware, etc.

Note: The circuit board and all of theparts that mount on it are availablefor S14.95, plus S1.00 shippingand handling from: Krystal Kits.P.O. Box 445, Bentonville, AR72712. Arkansas residents pleaseadd appropriate sales tax.

using hook-up wire, connect theswitch and the three jacks to the cir-cuit board at the appropriate points.

Once that is done, mount an ACplug with line cord to one end of theenclosure. That can be accomplishedby first passing the plug's line cord thethrough a 1/8 -inch hole in one end ofthe enclosure, and then clipping offthe excess cord length and con-necting the line cord to the circuitboard as shown in Fig. 3. After that isdone, the plug can be secured to theenclosure using hot -melt glue.

Check Out and Use. To check theoperation of the McTrak, first install a


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power supplies are not some-thing that we think aboutoften-we usually take them

for granted. But when you think aboutit, where would electronic projects bewithout them? And for that matter,where would this magazine be with-out them? The fact is, we don't usuallythink about power supplies until weneed one.

Usually a power supply is built spe-cifically for a certain project, and in-corporated right into the project itself.However, general-purpose powersupplies can be even more useful,lending themselves to all sorts of ap-plications. So, what we've got here is avery basic power supply that can beadapted to almost any project. The12 -volt power supply that we came upwith was actually built for poweringcar radios indoors, but it is useful forany 12 -volt accessory. With just a fewpart substitutions, the supply can havean output of from 1.2 to 33 volts-which should be good for nearly any-thing you can think of. If you'd like tobuild one of these no-nonsensepower supplies, then read on.

Adjustable Voltage Regulators.The adjustable voltage regulators thatare readily available today are agreat boost to hobbyists buildingpower supplies. Unlike fixed reg-ulators, adjustable units can be pro-grammed to output any voltagewithin their operating range. (The min-imum and maximum output voltagevaries from model to model and man-ufacturer to manufacturer.) Further-more, the devices come in positiveand negative 'flavors" to suit any rea-sonable application.

Our power supply uses .an LM317positive -voltage adjustable regulator.It can produce an output voltageranging from around 1.25 to 33 volts.We buy these units in place of stan-dard regulators (5 -volts, 9 -volts, 12 -volts, etc.) simply because they canprovide any voltage required to suitmost needs. As long as one or two ofthose devices are around, there'snothing to stop us from building anyproject we desire.

As regulators go, adjustable unitscy)

°2 provide excellent ripple rejection and2 have a neat short-circuit shut-off fea-E ture: If you short the regulator's output,u) it shuts down and automatically turns32 back on when the short is removed.

CONFIGURABLE

POWER SUPPLYAn inexpensive, configurable power supply to suit anydevice in need of 1.2 to 33 volts at up to 1.5 amps!

BY JOHN YACONO AND MARC SPIWAK

They also shut down if they becometoo hot.

To add to their value, adjustableregulators are easy to use. In Fig. 1A apositive adjustable regulator is shownwith its two programming resistors inplace. A negative adjustable reg-ulator is shown in Fig. 1B. For the sakeof discussion, we'll talk about positiveregulators, but keep in mind that theexact same rules apply for negativeregulators; the only difference is thatthe input and output voltages fornegative regulators are, of course,negative.

Resistor R1 is usually chosen to bearound 240 ohms to provide optimalperformance, but we often use 220 -ohm resistors without the least bit oftrouble. While the value of R1 is prettystandard, the value of R2 determinesthe output voltage of the regulator

according to the relation:

Vout = 1.25(1 + R2/R1) + R2lad1

where ladj (the adjustment current, asit's called) is usually between 40 and50 p.A. That amount of current is sosmall that you can often disregard itand use this abbreviated equation:

Vout = 1.25(1 + R2/R1)

Since you usually know the voltageyou want, lets rearrange the equationto find R2 based on Vow:

R2 = R1(VouT/1.25 - 1)

There are just three restrictions thatyou should bear in mind when usingan LM317. First, the supply to the reg-ulator should be filtered to supply atleast 3 -volts rms more than the desir-ed V0uT. That fact will help you to de-termine the secondary voltage of the

Vow

POSITIVEFILTERED

PULSATINGDC

NEGATIVE

FILTERED

PULSATINGDC

- Vout

Fig. I. Adjustable regulators are easy to use. Whether you need a positive (A) or anegative (B) output voltage, you just have to add two resistors and a filtered source ofpulsating DC.

ADJUSTMENT

BR12A

50PIV-7 7 71

+1

CASE IS OUTPUT

(T0-3)METAL CAN PACKAGE

BOTTOM VIEW

D1

1N4001

+ (RED)

(BLACK)

Fig. 2. The adjustable supply can easily be reconfigured by altering the value of R2and beefing up some other components as necessary.

Because the case size was chosen for the size of the transformer. theft- room

inside for the board.

PARTS LIST FOR THECONFIGURABLE POWER

SUPPLY

SEMICONDUCTORSUl-LM317 adjustable positive -

voltage regulator, integrated circuitBR1-2-amp, 50-P1V, full -wave

bridge rectifier (see text)DI-IN4001 I -amp, 50-PIV rectifier

diode

RESISTORSAll fixed resistors are 1/4 -watt, 5c4

units.)R1--240-ohmR2 -2200 -ohm

CAPACITORSCI -1000-µF 50-WVDC electrolyticC2 -0.l -µF, ceramic -disc


F1 -0.4 -amp fast -blow fusePLI-3-terminal molded AC power

plug with line cordSI-SPST toggle switchT1 -125 -volt primary, 12.6 -volt, 2 -

amp secondary, power transformer(see text)

Perfboard, case, rubber grommets,heat sinks, fuse holder, wire,solder, hardware, etc.

transformer that you should use tosupply the LM317 in your design. Sec-ond, make sure the the difference be-tween the input voltage to theregulator and the output voltage fromthe regulator is less than 12 volts rms.That will guarantee at least a 1.5 -ampoutput at the rated voltage, with apossible maximum current of 3.4 -amps with good heatsinking. Third, ifsubstantial current (more than 1/4 -amp) is to be drawn from the reg-ulator Ilse a heat sink.

One last thing to be aware of is thefact that adjustable regulators havedifferent pinouts than constant -volt-age models. In a similar vein, positiveand negative adjustable regulatorsdon't have the same pinouts as oneanother. That's enough theory for now,let's get to the real circuit.

The Circuit. The transformer's pri-mary in the power supply (see Fig. 2) isconnected to the AC line via S1 andFl. The value of Fl has been selectedto prevent the secondary (yes, thesecondary) from experiencing toomuch current.


Receiver Preamplifiers

Design and build a "front end" for your shortwave or VHF/UHF receiver

Receiver preamplifiers, whichare used to boost weak signalsbefore they are applied to a

receiver's input terminal, come in Iwobasic forms: tuned and untuned. Thetuned version, also called a preselec-tor, passes only one frequency at atime. The untuned version, on theother hand, is designed to pass a

8 wide range of frequencies at thecoO same time.

Until very recently, the task of de-= signing and building very widebandcn(17i amplifiers was daunting. Stray induc-

tances and capacitances, as well asCD

0CO the limitations of the active devicesm (usually transistors) in the circuit, con-

spired to thwart success. While thereE were a lot of circuits laid out in print, itix wasn't until monolithic microwave in-1--

tegrated circuit's (MMIC's) came onLu

Li,-1 the scene that very wideband pre-

amplifiers became easy for elec-0) tronic hobbyists to build.

Although MMIC's had been aroundzE for a while, they were previously lim-can iced by price to high -cost equipment.34 Today, however, hobbyists can easily

obtain MMIC's at low cost. The MAR -xseries of MMIC's (available from Mini -Circuits, PO. Box 350166, Brooklyn, NY,11235-0003) are some of the mostuseful for projects like the preamplifiercircuits that will be discussed in thisarticle.

MMIC. Figure 1 shows the MAR -xpackage outline. On the surface, itlooks like any UHF/microwave tran-sistor. The leads (radiating outwardfrom the body of the unit) are notwires, as with other devices, but flatstrips that reduce inductance (aprime limiting factor in VHF and higherfrequency amplifiers).

As shown, MAR -x devices have onlyfour leads, two of which are grounds(leads 2 and 4) terminals. The reasonfor two grounds is to distribute ground-ing, thereby reducing the inductanceof the leads. The other two terminalsare the RF input (lead 1) and the RFoutput (lead 3). Note that lead 1 is

marked in two ways: the end of thelead is beveled, and there is a colordot next to it.

MAR-x's come in several varieties(which are designated by a numberreplacing the "x" in the dummy typenumber above). The MAR -1 can oper-ate from DC to 1000 MHz (1 GHz), andprovide gains of up to 18.5 dB, whileproviding a noise figure of 5 dB. Otherdevices (carrying suffixes 2, 3, 4, 6, 7, or8) operate to 2,000 MHz, with noisefigures as low as 2.8 dB. Thus, the MAR -x series can fulfill the requirements of alarge number of applications.

Table 1 lists several MAR -x devicesalong with their capabilities and theunique color dot that indicates the RF-input terminal; the color of the dotindicates the MAR -x version.

An interesting aspect of the MAR -xseries is that the input and output im-pedances of the device are inher-ently 50 ohms. There is no need tomatch impedances if the source andload impedances are 50 ohms. Thatsingle fact makes MAR -x devices ex-tremely interesting to use, becausemuch of the complex and finicky cir-cuitry associated with RF amplifiers isfor impedance transformation.

GROUND

4

COLOR DOT

1

(RF IN

BEVEL

2.15mm(0.085IN.)T

1 3 1

11 68mm

RF OUT (0.460 IN.)

2GROUND

Fig. I. The package outline of MAR -xseries MM/C looks, on the surface, likeany UHF!microwave transistor, with itsflat leads radiating outward from thebody of the unit. The leads (flat strips)help to reduce inductance, a primelimiting factor in VHF and higherfrequency amplifiers.

Fig. 2. In the basic MAR -x -basedcircuit, shown here, both the input andoutput are comprised of a single DC -blocking capacitor (CI and C2 for theinput and output, respectively). The DCpower -supply network (comprised of LIand RI) is attached to the MAR -x via theRF-output terminal (lead 3).

Basic MAR -x Circuit. Figure 2shows a bare bones, MAR -x -based cir-cuit that works well in nearly all cases.Note that both the input and output ofthat circuit consist of a single DCblocking capacitor (C1 for the inputand C2 for the output). For frequen-cies up to 100 MHz or a little higher, C1and C2 can be ceramic -disc units,but above 100 MHz, they should bechip capacitors. (Digi-Key -PO. Box

677, Thief River Falls, MN, 56701-0677;Tel. 1-800-344-4539- -sells Panasonic -brand, type 0805 and 1206 chip ca-pacitors in 100 -unit quantities.) In mostcases, C1 and C2 should be 0.001-gunits, although for HF (below 30 MHz)circuits, 0.01-µF units are more suit-able. For projects that are strictly forabove 100 MHz, 100 -pr or smaller ca-pacitors are used.

TABLE 1-MAR-X CAPABILITIES

DEVICE MAX. FREQ.(MHz)

GAIN (100/50/1000 MHz) N.F. COLOR

MAR -1 1,000 18.517.515.5 5 Brown

MAR -2 2,000 13:12.8.12.5 6 5 Red

MAR -3 2,000 13'12.812.5 6 Orange

MAR -4 1,000 8.2'8.28 7 Yellow

MAR -6 2,000 20.1916 2.8 White

MAR -7 2.000 13.5 13.1 12.5 5 Violet

MAR -8 1.000 33:28 23 3.5 Blue

There is also a DC power -supplynetwork, comprised of L1 and R1. TheDC power -supply network is attachedto the MAR -x via the RF-output termi-nal (lead 3). The basic componentneeded in that network is current -lim-iting resistor R1, with an RF choke (L1)being used in some cases. The resistoris used to limit current to a designedoptimum value, which for the MAR -1 is15 mA. The value of the resistor de-pends on the value of the V + and thedesired current level, as follows:

R1 = (V + ) - M/I

where V + is the power -supply volt-age, V is the voltage at the RF-outputterminal of the MAR -x device, and I is

the current. Consider this example forthe MAR -1 operating from a 12 -volt DCsupply, and providing + 5 volts DC forV

R = ( + 12) - (5)/0.015

R = 7/0.015 = 467 ohms

Because the standard value of 470ohms is close to 467 ohms, that valueis selected instead. (Note: A 5% toler-ance 470 -ohm resistor may well havean actual resistance of 467 ohms,anyway!) The power dissipation of theresistor is 0.105 watts, so a quarter -watt resistor is sufficient. The resistorselected for R1 should be a non -in-ductive type such as carbon com-position or metal film. No form of wire -wound resistor should be used in thecircuit, not even those touted as non -inductive because they are non -in-ductive only in the audio -frequencyrange.

The optional RF choke (L1, which isused in many practical circuits) hastwo purposes: Choke L1 is used to pre-vent the RF output of the MAR -x fromgetting into the power -supply circuitor vice versa. The choke's other pur-pose is to act as a peaking coil toimprove the circuit's upper -frequencyresponse. The latter purpose is fulfilledbecause the load impedance seen

by the MAR -xis the combination of theinductive reactance of L1 and the re-sistance of R1. Because L1's reactanceincreases with frequency, the load im-pedance is also higher at higher fre-quencies.

Now that we've got the basic cir-cuit, let's put it together and make aworkable project. I selected two proj-ects. The first is a shortwave -band(high -frequency) preamplifier, andthe other is a VHF/UHF preamplifier formonitors and scanner receivers.

HF SW Receiver Preamplifier.Figure 3 is an HF preamplifier that isdesigned to be used in front of short-wave receivers. It can be used toboost weak signals or to form a basickind of active -antenna circuit (moreon that later).

The input to the circuit consists of abroadband toroidal transformer thatwas made by winding 3 turns of #26enameled wire on an Amidon Associ-ates (FO. Box 956, Torrance, CA 90508)T-50-2 (red) core for L1 -a, and thenwinding 10 turns of #26 enameledwire on the same core for L1 -b.

From there, the signal is fed to acomplex LC network comprised of a1600 -kHz, high-pass filter and a 32 -MHz, low-pass filter. Those filters areused to limit out -of -band signals. AMbroadcast -band signals (less than1600 kHz) are usually very strong atmost locations, and can easily drivethe preamplifier into saturation, caus-ing big problems. The high-pass pi -filter (which is comprised of C1 -C3, L2,and L3) is designed to attenuate sig-nals below the 1600 -kHz point, reduc-ing their effect on the amplifier.

Inductors L2 and L3 can be madeby winding 26 turns of #26 enameledwire over an Arnidon Associates 1-50-2(red) toroidal core. However, I used aToko adjustable core (available fromDigi-Key). The Toko 332PN-T1018Z (Digi-Key part no. TK5136) is a good bet (Iactually used a retuned 5.60 version

1600 kHzHIGH-PASS FILTER

J1 C1 C2 C3

INPUT .002 .001 .002

32 MHzLOW-PASS FILTER

L4 L5 C6.3µH .301 ATTN1 .01

L3 C4

3.31.tH 100pF

J2TO

RECEIVERINTERFACE

BOX

100pF

-m C7ATTN2 .01

TO EXT.POWER

(SEE TEXT) C9.1

irta

R1

150f1

L61mH

C8.1

Fig. 3. The HF SW Receiver Preamplifier is comprised of a broadband toroidaltransformer (LI-a and LI-b), a complex LC network (comprised of a I600 -kHz, high-pass filter and a 32 -MHz, low-pass filter), L2 and L3 (26 turns of #26 enameled wirewound on an Amidon Associates T-50-2, red, toroidal core), a pair of resistiveattenuators (ATTNI and ATTN2), and of course, the MAR -x device.

R1

6.211IN OUT

R2 R3

910fI 910C2

Fig. 4. Shown here is the composition ofthe basic I -dB pi -network resistorattenuator used in the circuit of Fig. 3.

J3TO

PREAMP

rSHIELD

C901 E

TOJ4

R2 RECEIVER1200

L7

1mH B19V C\Sc;o1

+ 4O L_0

Fig. 5. The purpose of this receiver-° interface circuit is to pass RF to thereceiver through capacitor C9, whileadding DC power to the feedline throughR2 and RE choke L7.

T -

co of the same coil in the model I built= and tested for this article, but that isct)O not an optimum choice). The capaci-

o tors are NPO ceramic -disc units.cr The two -section 32 -MHz low-pass fil-es - ter is designed to attenuate local VHF/-I UHF signals, but pass HF-shortwaveL.L1

a)r signals. The capacitors can be NPO2? ceramic -disc or silvered -mica (theO former are preferred) units. InductorsEE L4 and L5 (0.3-µH units) were made bycb winding 9 turns of #26 enameled wire36 on Amidon T-50-6 (yellow) cores.

REGULARSHORTWAVE

ANTENNA

COAXIALCABLE

PREAMPLIFIER

make them from ordinary 1/4 -watt,carbon -composition or metal -film re-sistors.) Figure 4 shows a basic pi -net-work attenuator pad that will drop thesignal 1 -dB with 50 -ohm input andoutput impedances.

The output of ATTN1 is fed to U1. Thatportion of the circuit is essentially thesame as the basic circuit of Fig. 2, witha 1-mH RF choke and a 150 -ohm re-sistor supplying the DC power. Thepower supply end of the resistor isconnected to the coaxial connectorthat carries signal to the receiver. TheMAR-x's input and output capacitors(C6 and C7) are 0,01-g ceramic -discunits.

In order to improve performance athigher frequencies, it is necessary tostrip the leads of those capacitors ofthe ceramic material that flows downonto them during manufacture. A pair

INTERFACEBOX

SHORTWAVERECEIVER

.1_

Fig. 6. In this set up, the preamplifier is used with an ordinary SW antenna (such as arandom -length wire, vertical, or dipole) in the conventional manner.

WHIP ANTENNA

PREAMPLIFIER

_10-OPTIONALGROUND

COAXIALCABLE

V INTERFACEBOX

SHORTWAVERECEIVER

Fig. 7. In the active antenna setup shown here, the SW antenna from the previoussetup is replaced by an 18 -to 30 -inch whip antenna.

From the 32 -MHz filter, the signal isfed to the first of two 1 -dB, 50 -ohmresistive attenuators (ATTN1 andATTN2) used in the signal line at the RFinput and output of the MAR -x. Thoseattenuators are used to swamp outimpedance variations in the sourceand load. Those impedances canvary considerably, and the at-tenuators help level them out as far asthe MAR -x device is concerned. (Iused Mini -Circuit's AT -1 1 -dB shieldedattenuators for the project. But if youdon't want to purchase those parts, orcannot for some reason, then you can

of long -nose pliers will crush the ce-ramic overflow so that it can be re-moved.

The preamplifier circuit can beplaced remote from the receiver; i.e.,mounted on the antenna mast orother support structure. That remotecapability is possible because the cir-cuit sends DC power up the samecoaxial -cable feedline that's used bythe RF signals. Sometimes, a decoup-ling capacitor is used at the junctionof L6 and R1 to limit the load imped-ance to the reactance of L6 (a 1-mHToko choke, Digi-Key part #TK4312).

SHORT BIPOLE ANTENNA

PREAMPLIFIER

INTERFACEBOX

SHORTWAVERECEIVER

Fig. 8. Here the preamplifier is modifiedto unground the input coil (LI-a in Fig.3) so that a bipole (a small. two -element) antenna can connected.

r

J1

TO ANTENNA

SHIELD

route it to the external power source. A0.01-µF decoupling capacitor isneeded in that case.

The preamplifier should be built intoa shielded metal box, either die-casttype, or a sheet -metal box with over-lapped edges between the top andbottom covers. That type of box pre-vents RF leakage into or out of the box.Flush -fit boxes are not well shieldedand should be shunned for RF proj-ects.

Receiver Interface. A receiver inter-face for the preamplifier is shown inFig. 5. The purpose of the interface isto pass the RF signal to the receiverthrough capacitor C9, and to add theDC power to the feedline through R2and RF choke L7. The DC power sup -

J2TO

RECEIVER

INTERFACEBOX

Fig. 9. Here's a VHF/UHF version of the preamplifier. The VHF/UHF preamplifier issimilar to the basic' configuration shown Fig. 2. while using the DC power -supply, feed

system used in Fig. 3.

5mm 5mm

8mm

2.75mm

4mmTOP ANDBOTTOM

H17mm__d

-- 3mm9mm

17mm

1-4-10m8mm

11mm

4mmALL

AROUND -0 -EXCEPT

WHERE NOTED

Fig. 10. The circuit can be assembled on perfboard, using adhesive backed copper foiland following the pattern shown here. The back of the board is a solid copperfoilground plane.

If you wish to use the preamplifiercloser to the receiver, with a DCpower source that is not fed throughthe coaxial cable, then break the DCpower line at point X in Fig. 3 and

ply is a 9 -volt transistor -radio battery.As a precaution, an AC -derivedpower source is not recommendedbecause the preamplifier is oftenused outdoors. Switch S1 (an SPST unit)

is used to turn the preamplifier on andoff.

The project can be built on a sec-tion of perf board. There is some point-to-point wiring on the bottom side ofthe board, although the MAR -x con-nections are on the component side.Large ground -plane areas are madefrom adhesive -backed copper foil.(The foil material is sold in electronicparts stores for those who want tomake pseudo -PCB's.)

Figures 6-8 show three differentways that the preamplifier can beused in shortwave -receiver systems.Figure 6 shows the conventional man-ner, in which the preamplifier is usedwith an ordinary SW antenna (such asa random -length wire, vertical, or di-pole).

An active antenna setup is shown inFig. 7. In that setup, the SW antennafrom the previous setup is replaced byan 18 -to 30 -inch whip antenna. Intesting that setup, I had good short-wave reception from my dining roomtable, using a 20 -inch telescopingwhip antenna that was soldered tothe center conductor of a coaxialconnector. The original antenna wasintended as a portable radio re-placement type.

Another active antenna setup isshown in Fig. 8. In that setup, the pre-amplifier is modified to unground theinput coil (L1 -a in Fig. 3) so that abipole antenna can connected to it.So what's a bipole antenna? I coinedthat word for a small two element an-tenna, similar to a dipole. It is not adipole because the antenna is of sim-ilar size to the whip used in Fig. 7. Aregular dipole for shortwave bandswould be at least 16 -feet long for tenmeters, and as much as 150 -feet longat the lower bands.

VHF/UHF Preamplifier. Figure 9shows the schematic diagram of aVHF/UHF version of the preamplifier.The VHF/UHF preamplifier is similar tothe basic configuration shown Fig. 2,while using the DC power -supply,feed system shown in Fig. 3. The ca-pacitors for the RF input and outputmust be 100-pF or 0.001-µF chip ca-pacitors. In this circuit, the RF choke(used in Fig. 3) has been replaced byan Amidon Associate FB-43-101 ferritebead, which is more suitable for VHF/UHF applications.

(Continued on page 108;

Replace that raspy sounding mechanical buzzer with apleasant -sounding electronic substitute.

Iwas awakened one morning forthe umpteenth time by the loudrasping noise produced by our

bedside tea -making machine. Mywife and I would hate to be withoutour morning resuscitator. However, Ithought that it deserved a more civi-lized sounding device than an elec-tro-mechanical buzzer. So, I decidedto replace it with a less crude alter-native-the Electronic Gong de-scribed in this article.

Circuit Operation. Figure 1 shows ablock diagram of the ElectronicGong, which is comprised of a powersupply an oscillator, an active filter,and an audio -output amplifier.

Figure 2 shows a full blown sche-matic diagram of the ElectronicGong. Power for the circuit is providedby a 12 -volt stepdown transformer (T1)coupled with a fullwave bridge rec-tifier (BR1). The power supply providesa non -critical DC voltage, which is fil-tered by capacitor C1, and is used topower the rest of the circuit.

Application of power causes anasymmetrical astable multivibrator oroscillator (formed around U1 -a andU1 -b) to begin generating pulses, Re-sistor R1 is included in the oscillatorcircuit to minimize voltage depen-dency. Components R2 and D1 pro-vide a fast alternative discharge path,causing the circuit to produce a seriesof very sharp output pulses, about 12seconds apart.

One requirement of simple CMOSastables is that the timing capacitorbe non -polarized. For short periodsthat's not a problem, since the valueof capacitance would be low (e.g.,below 1µF). The timing period (1) inseconds is roughly equal to 0.7RC,where R is resistance in megohms andC is capacitance in microfarads. Thatmeans that the capacitance wouldhave to be about 1.4T/R.

Unfortunately, for periods of morethan, say, 5 seconds, with the value ofR kept below 5 megohms, the value ofthe timing capacitor would have tobe greater than 1.4µF. That would nor-

mally call for an electrolytic unit. How-ever, that problem is easily circum-vented by using a pair of equal value,back-to-back electrolytics in series(C2 and C3 in Fig. 2). That producesan effective capacitance that's halfthe value of the individual units, whileat the same time, doubling the effec-tive voltage rating; in effect, the volt-age ratings of the two units areadditive. (Incidentally, the capacitorsdo not have to be equal in value,however, equal values make the cal-culation simple.)

For any two values given C2 andC3, the resulting capacitance is cal-culated like resistors in parallel, from 1/C = 1/C1 + 1/C2. (That can also bequite a handy dodge when you haveno capacitor on hand with a highenough voltage rating; just use twoback-to-back units and treat the resultas having twice the rating.)

The output of the oscillator (at pin 4of U1 -b) is coupled via C4 to the baseof Q1 (a BC108 NPN silicon transistor),causing it to briefly conduct. With Q1

_L.

117VAC

POWERSUPPLY

TRIGGERPULSES

ACTIVE FILTERON VERGE OFOSCILLATION

AUDIOAMPLIFIER

0 OPTIONAL OUTPUTTO EXT. AMPLIFIER

Fig. I. This block diagram shows the various subassemblies that combine to form the

Electronic Gong.

117VAC

R510K

+V

Ti12V

100mA

Fl200mA

BR1

1A50PIV

C1

330

R1

1MEG

2

1/4 4001

1

R2 R3

3.3K' t 4.7MEG

D1

3 1N4148 5

R7

220K4/6k

C7

.0015

C6.003

R9100K

R1022K

R8

220K

C8

" .0015

2

R6 C5 =10K 39 Tw.

+V

U2

7

6

C9.01

LM741

6

1/4 4001

R4

10K

14

C2" 6.8

C3

6 8

4

7 - C422pF

K

6

LM380

R147K

14

U3

1

BC108

EXTERNALAMPLIFIER

8 FL -

C12330

)Fi-- -C10 SPKR1 [:(10

Fig. 2. The Electronic Gong is comprised of a power supply (made up of a 12 -voltstepdown transformer coupled with a fulltivve bridge rectifier), an oscillator (builtaround half of a 4001 quad 2 -input NOR gate), an active twin -T filter (built around anLM741), and an audio -output amplifier (consisting of an LM380 low -voltage audio -power amplifier).

conducting, pin 2 of U2-a 741 gener-al-purpose op -amp, which forms theheart of the active twin -T filter circuit-is pulled close to ground which is allthat is needed to strike the gong.

The twin -T filter configuration, seeFig. 3, is normally used as the basis fornotch filters (or sometimes as a sine -wave generator). In our application,however, the filter it is set up to be onthe threshold of oscillation. In the twin -T circuit, two separate T -filter ele-ments-lowpass (Fig. 3A) and high-pass (Fig. 3B) filters-combine toproduce a bandpass filter. Figure 3C

shows the basic configuration for thetwin -T filter used in the ElectronicGong. Also shown in that figure is therelationship between the compo-nents values of the Iwo filter elements.The bandpass frequency of the circuitis given by:

f 1/27rRC

where f is frequency in Hz, R is resis-tance in ohms, and C is capacitancein farads.

Table 1 gives the bandpass fre-quency of the filter network base on afixed capacitance (in our case, 1500

PARTS LIST FOR THEELECTRONIC GONG

SEMICONDUCTORSU I -4(8)1 quad 2 -input. sso< gate.

integrated circuit112-1.,M741 general-purpose up -

amp. integrated circuit1.1.3-LN1380 low -voltage, audio -

power amplifier. integrated circuitDI-IN4148 general-purpose. small -

signal, silicon diodeBRI-1-amp. 50-PIV, fullwave-bridge

rectifier

RESISTORS(All fixed resistors are 1/4 -watt. 5(4

units.)RI-1-megohmR2 -3300 -ohmR3-4.7-megohmR4-R6-10.000-ohmR7. 128 -220.000 -ohmR9 -100,t/00 -ohmR10 -22,000 -ohm, potentiometerRI I -47,000 -ohm. potentiometer

CAPACITORSCI -330-11F, 16-WVDC, radial -lead

electrolyticC2. C3-6.8-p.F, 10-WVDC, radial -

lead electrolyticC4-22-pF, ceramic -discCS -39-µF. 10-WVDC, radial -lead,

electrolyticC6 -0.003-µF, polystyreneC7, C8 --0.0015-µF, polystyreneC9 -0.01-µF, ceramic -discC10 -10-µF, 16-WVDC, radial -lead

electrolyticC11-0.l-p.F, ceramic -discC12-330-m.F, I6-WVDC.

electrolytic


TI -12 -volt, 100-mA. stepdowntransformer

FI-200-mA PC -mount fuseSPKR1-Speaker, see textPerfboard materials, enclosure, AC

power source, IC sockets,grommet, stand-offs, wire, solder,hardware, etc.

pF) and various resistor values. For ex-ample, if you want to try for a bass -drum sound, you might try replacingR7 and R8 (220k, respectively) with 1-megohm (1000k) resistors. You wouldadditionally have to alter the values ofR9 and R10 so that their combinedresistance could be adjusted to about500k; that could probably be bestachieved by making R9 a fixed 470kunit and presetting R10 to 47k. (Natu-

A

R7=R

C

Fig. 3. The filter network is comprised of two separate T -filter elements-lonpass, A.and highpass, B, filters-which combine to produce a bandpass filter. The basicconfiguration for the twin -T filter used in the Electronic Gong is shown in C. Alsoshown is the relationship between the components values of the two filter elements.

B

Fig. 4. The prototype of the Electronic Gong was assembled on a printed -circuithoard, measuring approximately 41/4 by 4who inches. Here's a template of that foilpattern.

TABLE 1-BANDPASSFREQUENCY RANGE

Resistance Capacitance Frequency(k ohms) (pF) (Hz)

4756

100180220390470560680

10001200

15001500150015001500150015001500150015001500

226018901060590480270230190160110

90

rally, if you are using a miniaturespeaker as specified in the basic cir-cuit, then don't expect it to do justiceto your drum.)

The output of the twin T -filter circuit(at pin 6 of U2) is fed to the invertinginput of U3 (an LM380 audio poweramplifier) at pin 6 through C9 and thewiper of R11 (which serves as a volumecontrol). Any speaker impedance ofgreater than 8 ohms is suitable and itsselection is mainly a question of whatmaximum volume you need; thelower the speaker's impedance, thelouder the output at any given R11setting. The author used a 64 -ohm unitin his prototype.

Construction. The author's pro-totype of the Electronic Gong was as-sembled on a printed -circuit board,measuring approximately 41/4 by 410/16inches. A template of that foil patternin shown in Fig. 4. Once you've etchedyour printed -circuit board andgathered the parts construction canbegin.

A parts -placement diagram for theauthor's printed -circuit layout is shownin Fig. 5. It is recommended that sock-ets be provided for the IC's. For themost part, the component values arenot critical; the only exception is thatthe twin -T resistors (R7 and R8) andcapacitors (C7 and C8) are within atleast 5% of each other. Note that inthe area of C2 and C3, the author hasprovided extra pads to accommo-date capacitors slightly larger thanthe subminiature units used in the pro-totype.

Begin construction by first installingthe IC sockets, followed by the passivecomponents. Afterwards, install all


Build aFour -ElementTwo -Meter

Quad

.0.11111.-1101h-J11011Lil LJED1U1

D OD

Ireally enjoy my work in the Elec-tronics Technology Program at theSno-Isle Skills Center where I

teach. The Center is a vocational highschool with twenty-two programs ofinstruction. During the second se-mester of each year, I teach amateurradio to junior and senior high schoolstudents. As part of their instruction, I

have each of my students build anAM/FM superheterodyne receiver.

Of course, we also cover antennadesign. So as a group, we had alsoconstructed a half -wave dipole forIwo -meters. Two -meters gave us thecompact size and also allowed me todemonstrate .vertical and horizontalpolarization.

As I explained the half -wave dipoleantenna to my students, they ap-peared puzzled as if to ask "how canthat work?" After the demonstration,some of these bright young mindscame to life and started to ask ques-

S

o

6390/NOW11,1 Aim

1111,,;),.Or 1,7 AS IIIIV """w

;0;r:.:16:3:111147:

tiligt:/m/#/wir 11#/#0A

igargii=drialimallmmllal

4 " is/ mys/sysimorisomf

r.204,..011,/ SON/MWOMMYRA.

wg NtrizzAtiz,WN/N/0 N/S/MYIAN,

- ';.;.- -

You can easily build aninexpensive transceiverantenna that's both fun

and educational.

lions out loud:,"How can a full wave fitinto a half -wave length of wire?" "If agallon of milk is a gallon of milk andwe drink a glass is it still a gallon?" Myexcitement increased with eachquestion; they were obviously very in-trigued by antennas.

So it Started. Since antennas wereobviously a point of interest to theclass, I searched for my ARRL AntennaBook (my personal favorite) and start-ed to look for a two -meter quad an-tenna that could be easily con-structed with little cost to the students.With the book in hand, I went to thefaculty lounge to discuss my quad -antenna project with some of thestaff.

I showed our welding instructor thedrawings of a portable 144 -MHz, 4 -element quad. It turned out that hewas the right man to speak to as hehad a large quantity of Ys -inch braz-

BY LARRY R. LUCHI, W7KZE

ing rods that we could use for theloops. (For your information, No. 8 alu-minum ground wire will work just aswell, but using the brazing rods keptstudent cost to a minimum.) Our plas-tics instructor had the needed PVCsupports (spreaders) and a PVCboom. Our machine -trades instructorsuggested he have his students drill allof the holes needed in the PVC sup-ports and boom.

Now I would have to do somenumber crunching before we wentfurther. The element spacing for quadantennas found in literature rangesfrom 0.14X to 0.25X (where X is thewavelength). Factors such as thenumber of elements in the array andthe parameters to be optimized(frront/back ratio, forward gain band-width, etc.), determine the optimumelement spacing within this range.

The other characteristics obeythese relations:

00co

z

rn

U)5-

0

0

0w-J

Ea_ As each brazing rod was added to a givenCI) loop, its ends were simply soldered to42 those already in place.

Reflector length = 1046.8/fmN,Driven element = 985.5/fmHz

Directors = 937.3/fmHz

where fmHz is the frequency of interestand the lengths are measured ininches. The 4 -element quad we builtin class was designed for 146.58 -kHzoperation, so the reflector was 86 -inches, the driven element was 81 -

inches, and the directors were 77 -

inches. With that out of the way, it wastime for the students and Ito roll up oursleeves and get to it.

Building the Quad. Construction be-gan with two, 10 -foot, 1/2 -inch PVCpipes. From that stock, the boom wascut to 42 inches in length with al-lowances given for two PVC tees to befitted at each end (see Fig. 1); one forthe reflector and one for the first di-rector. Those tees were not perma-nently installed at that time.

Construction of the elements be-gan by cutting the PVC stock for thespreaders and drilling 1/8 -inch holes inthe ends of each piece to accommo-date the brazing rods. The reflectorspreader was initially cut to be 221/2inches long, with holes drilled to be103/4 inches from the center of theboom. The driven spreader was firstcut to 211/4 inches long with holesdrilled so that they'd be 101/8 inchesfrom the center of the boom. The di-rectors were then cut to 201/4 incheswith holes drilled to place them 95/8inches from the center of the boom.

At this point, each spreader was cut

CENTER OFBOOM

16

10'/4

0

REFLECTORSPREADER

103/4

13

0

101/8

101/8

DRIVEN -ELEMENTSPREADER

(ALL DIMENSIONS IN INCHES)

Fig. 1. This is the boom/spreader assembly for the quad antenna. Note that the locations ofthe holes are measured from the center of the boom.

13

95/8

9/8

MACHINE BOLTS ANDWASHERS

Yr PVC CROSS CEMENTEDTO 'I2" PVC BOOM

Jt / 0

DRIVEN -ELEMENT

1/e" BRAZING ROD

Fig. 2. A Plexiglass strip was used as asupport for the feed point. It was cementedto the driven -element spreader.

1" x 12"PLEXIGLAS CEMENTED

TO SPREADER

in half (i.e., the reflector was cut at 11-1/4 inches). Then the reflector and first-

director spreaders were glued (usingNova Weld P cement) to their tees,which were in -turn glued to the endsof the boom. The driven -element andthe middle -director spreaders wereglued into two PVC crosses that hadbeen cut in half and glued to theirmeasured places on the boom.

The driven element required extrapreparation as the coax feed -point

0

10 DIRECTORSPREADER

0

2" DIRECTORSPREADER

MATERIALS LIST FOR THE 4-ELEMENT 2 -METER QUAD

2 10 -foot lengths of /2 -inch PVC1 x 12 -inch Plexiglass plate2 pounds of V8 -inch oxy-acetylene bra-zing rodsPVC cementRTV cement2 Solder lugs for No. 8 hardware2 No. 8 nut/bolt pairs2'/ -inch PVC tees5 1/2 -inch PVC crossesA length of 52 -ohm feedline

needs to be adequately supported.We used a 1 x 12 -inch Plexiglass plateto support the coax feed line, asshown in Fig. 2. One end of the Plex-iglass plate was cut to fit around theboom, where it was expoxied. At theother end of the Plexiglass plate wedrilled two holes 3/4 of an inch apart.

To begin making the feed -pointconnections, a 52 -ohm coax feedlinewas terminated in solder lugs. Thentwo brazing rods were taken and aloop was formed in one end of each.A bolt was passed through each loop,solder lug, and hole in the Plexiglassand secured with a nut. The junctionswere then soldered and sealed withRTV cement. From there, the cablewas routed directly to the mast anddown.

Three more brazing rods (two of(Continued on page 107)

PeltierEffectBeverageCoolerBY JAMES MELTON

Keep your soft drinks cool, evenduring a sweltering summer heat wave'

There are several reasons whyelectronics hobbyist elect tobuild projects; for example, it

can be fun as well as educational.However, there is a practical side tothe hobby; hobbyist often must buildthings that they cannot afford to buy,or those that are simply not commer-cially available. The Peltier Effect Bev-erage Cooler described in this articlefalls into the latter category. The Solid -State Beverage Cooler, as its nameimplies, is a project that is designed tokeep a soft drink or other beveragecold. That is, if a canned drink isplaced in the cooling chamber, it willbe kept cool indefinitely.

About the Project. The Solid -StateBeverage Cooler is built around acooling module that makes use of the"Peltier effect," which is similar to theeffect used in thermocouples; how-ever, the effect is applied in reverse.What that means is that instead of atemperature difference between twojunctions causing a current to flow, acurrent flow is used to cause a flow ofheat.

A thermocouple is formed whentwo different metals are joined to-gether. You can make your own ther-mocouple for experimental purposesby screwing two pieces of copperwire on either end of an aluminumstandoff, as shown in Fig 1. If a volt-meter is attached to the copper wires,

and one of the copper/aluminumjunctions is placed in proximity to aheat source (such as a candle flame),the meter will register small amount ofvoltage. The hotter the heat source,the higher the voltage. Similarly, thecooler the cold end gets, the greaterthe voltage.

With a crude thermocouple like theone shown in Fig. 1, of course, you'llnot be able to power any equip-ment-it does, however, demonstratethe thermoelectric effect. It also simu-lates the Peltier effect. If a current ispassed through the copper/alumi-num junctions, one of the two junc-tions will experience a temperaturerise, while the other junction will expe-rience a temperature decrease. Butthat effect will be so slight on thiscrude model so as to be virtually un-detectable.

Modern solid-state Peltier junctionsare formed from various metals, whichare doped like semiconductors. De-

pending on the doping, the metal willeither have an excess of electrons (P -type material) or holes (N -type mate-rial) in its atomic structure. The metaljunctions formed from the two types ofdoped material act kind of like a ther-mocouple, but are much more effi-cient.

Figure 2 illustrates the make up of acommercial Peltier cooler junction. Ina commercial junction device (cool-ing module), more than 50 junctions

are series -connected electrically andparallel -connected thermally. That re-sults in a device with an impedancethat's high enough so that the coolingmodules can be connected directlyto a 12 -volt power supply.

The Cooler. The cooler itself was builtusing almost every available meansto make it easy, fast, and fun, The cool-ing module was bought commer-cially. (I have included the addressesof two places that sell cooling mod-ules in case you have trouble locatingone; see the Materials List.) Most of theconstruction of the cooling module/heat -sink combination was done withepoxy adhesive. That leaves the top ofthe unit clean in appearance, andhelps a little more with the heat trans-fer efficiency.

The power for the circuit is providedby a commercial (surplus) 12 -volt DC,3 -amp power supply that was origi-nally intended for computers. Such aregulated power supply is requiredbecause a "brute force" supply willhave too much ripple, which will pro-duce excessive heat that must be dis-sipated somehow. For the con-venience of using the cooler in mycar, I attached a 12 -volt cigarette -lighter power adapter to the unit'scord,

The heat sink has two major require-ments: it must be big (far larger thanyou might think) and it should not

LEADS TO VOLTMETER

COPPER WIRES

COLD END HOT END

,cialninEBV=06M121WWWANNVI"li,

THE COLDERYOU CAN KEEP

THIS ENDTHE MORE EMF

YOU CANGENERATE

ALUMINUM STAND-OFF

HEAT SOURCE(CANDLE

SOLDERING IRON,ETC.)

Fig. I. Modern solid-state Peltier devices are formed by joining two dissimilar metals,which are doped in the same vein as semiconductors to form junctions. Depending onthe direction of the applied current, one junction will experience a temperatureincrease, while the other will experience a temperature decrease.

TOP PLATE COLD SIDE

-cf" 41JUNCTION

JUNCTION

P P

PP P

P

P P

N N

NN

NN

N

N N

P P

PP P

PP

P pP

N N

N NN

NN

N

P P

P pP

P p

PP

P p

BOTTOM PLATE HOT SIDE

POWERSOURCE

Fig. 2. This illustration shows the make up of the commercial Peltier cooler junction.In a commercial junction device (cooling module), more than 50 junctions are series -connected electrically and parallel -connected thermally.

12V CIGARETTE -LIGHTER PLUG

PELTIER JUNCTION

MUFFINFAN

O0

Fig. 3. A small muffin fan is connected in parallel with the cooling module, and inseries with the power supply so as to increase the amount of cooling available from theheat sink by several degrees.

MATERIALS LIST FORTHE PELTIER EFFECTBEVERAGE COOLER

Thermoelectric cooling module(Melcour CPI.4-71-06L orequivalent)

12 -volt DC miniature muffin fan12 -volt DC power source (see text)Large heat sinkDouble -walled soft drink containerPower supply (see text)Enclosure, wire, solder, epoxy,

hardware, etc.

Note: Cooling modules can beobtained from Melcour, 1040Spruce Street, Trenton, NJ 08648Tel. 609-393-4178; and AmericanScience and Surplus, 601 LindenPlace, Evanston, IL 60202.Contact the companies directly forcurrent pricing, shipping, etc.

have any holes at all in the areawhere the cooling module is to bemounted. That last requirement mightbe a little hard to meet with generaljunkbox materials, however, it is essen-tial that you have the best heat trans-fer to the heat sink obtainable.

As shown in Fig. 3, a small muffin fanis included in the project so as to in-crease the amount of cooling avail-able from the heat sink by severaldegrees. The lowest temperature ofthe cooling module, after the excessheat of the soft drink has been re-moved, depends on the lowest tem-perature that can obtained on theheat sink. In the design presentedhere, the lowest possible obtainabletemperature is approximately 30°Fbelow the ambient temperature.

You need a soft-drink container ofthe type typically sold in gas stations.Such containers are double walledand are ideal for the cooling cham-ber of this project.

Construction. Begin construction ofyour cooler with the base (or en-closure), which will hold the coolingmodule/heat-sink combination andthe muffin fan. Obviously, there isnothing critical about the dimensionsor layout of the base-it merely has tohave sufficient room to accommo-date the cooler components.

The cooling module by itself is veryineffective, so you have to help it outevery step of the way. To that end, ahole, about 2 inches in diameter, must

Fig. 4. Here is the cooling module priorto installation in the project. Unmarkedunits can be tested by attaching a D -cellbattery to the cooling module's two leadsto determine the hot and cold sides 1fthe device. Under power, one side of themodule will be hot while the other willbe cool.

be made in the top of the base toexpose the heat sink. Cut the holecarefully; the cut -away portion of thehole will be used later. Then flip thebase over, cut another circular hole inthe bottom of the base for the fan. Thematerial from this cut-out will also beused.

After cutting the holes, mount theheat sink inside the enclosure, cen-tered under the 2 -inch top hole andflush to the inside surface of the base,using epoxy-the epoxy makes for thebest heat transfer possible and alsoleaves the top of the box smooth.

Figure 4 shows the cooling module.While irs free of its enclosure, attach aD -cell battery to its leads-red topositive and black to negative. Feelboth sides of the cooling module todetermine the hot and cold side; thenmark the hot side with an "H" using asoft pencil. That helps to orient thedevice in the cooler later.

After the epoxy holding the heatsink has cured, place the coolingmodule on top of the heat sink, andmark appropriate holes in the heatsink for the leads of the cooling mod-ule to go through. Then drill and de -burr the holes. Next mount the muffinfan. The muffin fan should bemounted so that it blows out of thebottom (as the author did) or the sideof the base. However you mount the

Fig. 5. Using the pieces of aluminum left over from the holes in the base, make aplatform (which consists of two pieces) for the soda can. A rectangular aluminumpiece. which rests against cooling module, lifts the top circular platform piece into the

chamber where it can contact the beverage can.

towc.itosto12ttAliO4--

Fig. 6. With the top plate and insulationin place. allow the epoxy to cure, beforemoving on to the final phase the

cooling chamber construction.

Fig. 7. Here is the business end of heSolid -State Beverage Cooler.

fan, make sure that the flow of air isunobstructed. (I cannot stress enoughthat the amount of air flow and thesize of the heat sink will have a majoreffect on the final temperature of thecooler.)

Place the cooling module back ontop of the heat sink and pre -form theleads so that there is no strain whenthe cooling module is epoxied inplace. After forming the leads, epoxythe cooling module to the smooth topsurface of the heat sink. Pass the leadsthrough the heat -sink holes. While theepoxy is curing, clamp or weight thecooling module to ensure that therewill be a good strong bond.

Using the pieces of aluminum thatyou saved when making the holes inthe top and bottom of the base,make a piece that will serve as a plat-form for beverage cans. The platform,which consists of two pieces, is shownin Fig 5. The rectangular piece, whichrests against cooling module, lifts thetop circular piece into the chamberwhere it can contact the beveragecan. The rectangular piece alsoleaves room for some foam insulationbetween the cool top plate and thehot bottom plate. I used the bottomfrom a foam drink keeper for the in-sulation.

(Continued on page 108) 45

computers...

"That's very odd, Mr. Stnitch, your monitorreads, 'Viewer Discretion Advised!'"

mipAtiE ayooaa IFromm.% TELLING

ICRYSTAL eM2iN6TVA LEAVE REARM*

"You know, Mr. Mark, this PC gadgethas definite possibilities!"

gOIAGMfia WINal[EVWCMg.

"But enough about me-how about you?"

'11

.71

O

14

ByErnie

Brown

"We're confident, Larry, that this new modelwill help kids become computer literate."

ASA MISSION CONTROL---- 1 1

FM'

Iprj

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[email protected]

'4 SALESMAN

CIMUST BE

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COMPUTERLITERIT.

f=1r-1 ==

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Karl Young has.finallv found his niche in life!

DIGITALBOWLBOX

BY WILLIAM L. CALL

This circuit brings the old "College Bowl" concept of first -responseanswers to a moderator's questions into the `90's.

Many contests and gameshows are based on the old"College Bowl" concept of

first -response answers to a moder-ator's questions. Usually Iwo teams areassembled, typically with four con-testants each; a question is read, andthe first person to respond gets theopportunity to answer the question.Middle and High Schools have gotteninto the action with Math Bowls andAcademic Bowls; even churcheshave gotten into the act with "BibleBowls." In individual classrooms, manyteachers have used the Contest Bowlidea to build excitement into class-room activities.

A key component of the ContestBowl is an impartial judge to deter-mine which participant respondedfirst. Usually each contestant is given apushbutton switch that is connectedto an electronic device that deter-mines which button was pushed first.Such a system can be quite elaborate(incorporating large and colorful dis-plays, impressive sound effects, etc.)and complex. The system presentedhere, on the other hand, was de-signed to be compact and inexpen-sive. Since the heart of the electronicsystem is a digital IC often used incomputer circuits, the unit has beendubbed the Digital Bowl Box.

Circuit Description. Figure 1 shows

a schematic diagram of the DigitalBowl Box. At the heart of the circuit is a74LS373 low -power Schottky octal (oreight -input) transparent latch, U1. Atpower up, U1's output -enable (aE) ter-minal at pin 1 is held low via pull -downresistor R2 and the latch -enable (LE)terminal at pin 11 is high, via pull-upresistor R1-i (part of a 9 -resistor net-work). That allows any signal pre-sented to U1's data -input (Do- D7)terminals to be passed to its respec-tive output. Since all of the data inputsof U1 are held high via pull-up resistors(R1 -a -R1 -h), each output of U1 is high.That reverse biases LED1-LED8 so all ofthem remain dark; only LED9 is illumi-nated.

Let's say that S1 is the first switch toclose. That low pulls U1 pin 3 low, caus-ing its corresponding output (pin 2) togo low. The low output on pin 2 for-ward biases LED1, causing it to light. Atthe same time, a voltage drop de-veloped across R8 (as a result of cur-rent flow through LED1), turns Q1 on,which then causes Q2 and Q3 to turnon.

When transistor 02 turns on, pin 11(LE) of U1 is pulled low, latching U1 in itspresent state, keeping LED1 on, identi-fying the contestant who respondedfirst, while locking out all subsequentrespondent signals. With 03 turned onBZ1 sounds. The 74LS373 and tran-sistors have a response time of a few

nanoseconds, making it highly un-likely (though not impossible) that a"tie" could occur.

After noting which contestant re-sponded first, the moderator momen-tarily presses RESET (S9), which pulls pin 1

(aE) high, clearing U1. That causes thehighs presented to the data inputs ofU1 (as a result of the pull-up resistors) toonce again be passed to their corre-sponding outputs. As before, the LED'sare now reverse biased, so no voltagedrop develops across R8. That re-moves the bias from 01, which causesQ2 and 03 to turn off, turning off BZ1and deactivating the latch.

Power for the circuit is provided by atraditional transformer, rectifier, andvoltage -regulator system. As de-signed, the Digital Bowl Box supportsup to eight contestants. An expansionjack (J3) is included in the circuit, al-lowing you to daisy -chain two DigitalBowl Boxes together for up to 16 con-testants (eight for each team). The ex-pansion jack parallels the LE controlsignals of the Iwo Boxes. Only one LEDwill light, corresponding to the firstswitch depressed; full lockout of allother switches remains in affect. Theexpansion jack could be omitted ifthat option is not desired.

Construction. The majority of theDigital Bowl Box's circuitry was as-sembled on a printed -circuit board,

RED

TEAM

S4 S3 S2 S1

-7- Z.-

GOLDTEAM

S8 S7 S6 S5

_I_

+5V

PL1

PL2

S10S10POWER

T1

18VCT300mA

J2

o o -S9

RESET

D2

1N4004

R1 -b1K

S RI -a1K

+ 5V

R1 -e

1K

R1 -f R1 -h

1K 1KR1 -e $ R1 -g1K o' 1K

i R22.2K

+ 5VR1 -d

1K

7

3

14

17

18

DO

D1

D2

00

01

02

D3 03

U1

7413373

05

D6

D7

04

05

06

7

61 LE

GND Vcc10 20

+ 5V

RED ® LED1

\\ 0 LED2

5\\ 0 LED3

LED4

6 \\4

9 \\4

YEL 0 LED5

\\A 0 LED612

15\A\ 0 LED7

LED8

\4\

16

19

+12V +5V J3EXPAND

C3220

R91800

LED9GRN

\4\4

Fig. 1. At the heart of the Digital Bowl Box is a 74LS373 low -power Schottky octal (oreight -input) transparent latch, UI. Note that instead of 9 -individual lk resistors, thecircuit uses a 10 -pin 1k x 9 SIP bus -type resistor network.

415he INCHES

+ 5V

R1 021K 2N3904 R4

2.2K

t R32.2K

R62.2K

012N3908 R7

2.2K

R5 t 032.2K 2N3904

Fig. 2. Most of the Digital Bowl Box's circuitry was assembled on a printed -circuitboard, measuring approximately zPsho by 27/s inches. A template for that printed-circuit layout is shown here full scale.

R8

12011

BZ1

V

+ 5V

+12V

PARTS LIST FOR THEDIGITAL BOWL BOX

SEMICONDUCTORSU I-74LS373 low -power Schottky,

octal D -type latch, integratedcircuit

U2 -7805T 5 -volt, I -amp voltageregulator, integrated circuit

Q1 --2N3906 general-purpose PNPsilicon transistor

Q2, Q3 ---2N3904 general-purposeNPN silicon transistor

LED1-LED4--Red light -emittingdiode

LED5-LED8-Yellow light -emittingdiode

LED9-Green light -emitting diodeDI, D2-IN4004 I -amp, 400-P1V

rectifier diode


units, unless otherwise noted.)RI -1000 -ohm x 9 SIP bus -type

resistor networkR2-R7-2200-ohmR8-I20-ohmR9-I80-ohm

CAPACITORSCl, C2 -0.01-µ,F, 1000-WVDC.

ceramic -discC3-2201.11, 25-WVDC, radial -lead

electrolyticC4 -100-1.1,F, I0-WVDC, radial -lead

electrolyticC5 -0.1-µF, ceramic -disc

SWITCHESSl-S9-SPST momentary -contact,

pushbutton switchesS10--SPST toggle switch


BZI-12-volt buzzer (Mouser251-(X)12)

Fl--0.125-amp fuseJI, J2-Panel-mount 5 -conductor,

DIN jackJ3-Panel mount, RCA phono jackPLI, PL2-5-conductor DIN plugPL3-3-conductor, molded AC power

plug with line cordT1 -18 -volt, center -tapped, 300-mA,

transformer (Mouser 41W.1300)Printed -circuit board materials,

enclosure, strain reliefs, fuseholder, LED mounting clips, #6x 1/2 -inch sheet -metal screws,#6-32 x 1/4 -inch BH machinescrews, 20 -pin IC socket, 2 x 6 -inch pine wood (see text),aluminum sheet metal, threadedaluminum #6-32 x 1/2 -inch

standoffs, #24 4 -conductorshielded cable, wire, solder,hardware, etc.

LED7LED2 cv..LED1

LED40/170111\LED80\\9\

LED9/7/ /0( LED3 U2

C4

-R9- +1 111 C3I+

DI

D2 -C

BZ1

-R2-

R6

03

S.S9

RESET

J1

PL1

U1

R1

LED5

T1

C2

Cl

F1

S10POWER

Fig. 3. In this parts -placement diagram for the printed -circuit board, note that the

power transformer (TI) and the buzzer (BZI) are mounted directly to the board. That

means that due to physical space tolerances, the vendor-referenced components

specified in the Parts List are required.

measuring approximately 415/la by 27/8inches. A template for that printed -circuit layout is shown in Fig. 2. A parts -placement diagram for the printed -circuit board is shown in Fig. 3.

Note that the power transformer (T1)and the buzzer (BZI) are mounted di-rectly to the board, eliminating inter-connecting wires. Although thatsimplifies construction, it also requires(due to space tolerances) that thevendor -referenced componentsspecified in the Parts List be used.Non -vendor -referenced parts are notcritical. The switches, cabinet, switchwiring, and switch housings should berugged enough to withstand therigors of constant use.

Start by mounting a socket where

U1 is indicated. Follow that by install-ing the passive components. Notethat R1 is a 10 -pin SIP bus -type resistornetwork, which is available from Digi-Key Electronics (701 Brooks Ave., POBox 677, Thief River Falls, MN56701-0677; Tel. 800-344-4539) aswell as other sources.

After the passive components,mount and solder the active compo-nents to the board as indicated in Fig.3. Once that's done, attach the trans-former to the board with #6-32 x 1/4 -inch screws and 1/2 -inch threadedmetal standoffs; the transformermounting holes double as the board -mounting holes. Install screws andstandoffs at the other mounting holes.After first tightening the mounting

NI

9/le 11/16

- 3/49/16

3/4 id-_

3

9/1e I 9/1e 9/isIN 4 N

,9-0-0 0 27/8

0 0-0-0-015/8

6

A

8

518

J1

13/32 x 15/32

RESETCORD

5/8

J2

1/4

J3

15/32 X 17/32

LINECORD

1/4

S10

.4--13/16 -01

13/4

223/32

319/32

INN

415/32

57/32

6

B

Fig. 4. Holes must be drilled in the front and rear panels of the enclosure toaccommodate the off -board components; A shows the front panel layout while B showsthe rear panel layout. You can layout your enclosure's front and rear panels in asimilar manner, or follow any scheme that you choose.

27 a

screws to the stand-offs, solder thetransformer terminals to the appropri-ate circuit -board pads. After that sol-der 4 -inch lengths of pre -strippedhookup wire for the LED's, jacks, andpower switch to the board.

The printed -circuit board assemblyis now complete.

PCB Endosure. Before the boardcan be mounted in its enclosure, it willbe necessary to do a little preparato-ry work; e.g., holes must be drilled inthe front- and rear -panels of the en -

ALL DIMENSIONS IN INCHES

closure to accommodate the off -

board components. Figure 4 showsthe front and rear panel layouts for theauthor's unit. You can layout your en-closure's front and rear panels in asimilar manner, or follow any schemethat you choose.

In any event, prepare the enclosureby punching or drilling nine Y4 -inchholes in the front panel for the LED's. Topromote the team concept, red LED'swere used for one group of four out-puts, and yellow for the other. (Thecorresponding switches, which we'll

get to shortly, were mounted on platesthat were painted red or yellow.) TheLED's and switches can be labeled1-8 or red 1 through red 4 and gold 1through gold 4. If the application is forindividual contestants rather thanteams, like -colored LED's and platesmight be preferable. The cabinet waslabeled with embossed tape labels.

Mount the LED's into the front panelusing plastic LED -mounting clips, andconnect the anodes of all but LED9(the power indicator) together withbare bus wire. Run the reset andpower cords loosely through theircabinet holes and solder their ends tothe board. Maneuver the board intoposition in the cabinet, and install thebottom mounting screws into theother end of the standoffs. Installclamp -in strain -relief bushings on thereset and power cords, and then in-stall a pair of DIN jacks and the powerswitch.

Now the final soldering can becompleted. The easiest way to solderto the LED's is to first melt some solderonto the end of the connecting wireand then separately to the LED lead.After that, reflow-solder them to-gether. The switch jack terminals workwell with this method too. Once theprinted -circuit board has beenmounted, and the connections be-tween the circuit board and the off -

board components have been com-pleted, move on to the final phase ofthe projects construction.

Contestant Switches. Figure 5shows one unit of the four -contestantswitch arrangement used in the au-thor's prototype. The contestantswitches were housed in wood blocks(approximately 21/2inches square)that were cut from 2- x 6 -inch pinelumber using a table saw. However, ifyou happen to have some scrap 2 -by -4 lying around, that can be used aswell. The blocks were then drilled outusing a drill press. A router with a 0.25 -

inch veining bit was used to cut agroove into the wood to hold theswitch wiring snugly clamped under ametal, switch -mounting plate.

The switch -mounting plates werefabricated from 1/4,5 -inch sheet alumi-num, and cut just slightly smaller thanthe wood blocks. A hole was thenpunched in the center of eachmounting plate for the switches, andsmaller holes in each corner for the

Fig. 5. Shown here is one unit of the four -contestant switch arrangement used in the author's prototype, which was wired together

using an approximately 14 footlength of 4 -conductor shielded cable for each team. Each switch within that arrangement has one

terminal connected to one of the color -coded inner wires of the cable. The other switch terminal is connected to the cable

After connecting the contestant switches to the cable, a heavy-duty DIN plug was connected to the free end of the cable.

plate's mounting hardware. Once themounting plates are complete,mount the switches in position. Notethat the recommended switches re-quire a small notch in their mountingplate. tf desired, small plastic en-closures could be substituted for thehomemade switch boxes, using suit-able strain reliefs on the wires.

The four -contestant switch arrange-ment (see Fig. 5) was wired togetherusing an approximately 14 -foot lengthof 4 -conductor shielded cable foreach team; that arrangement is lessprone to tangling than individualswitch cables. Shielded cable wasused to lessen the chances of staticdischarges causing false triggering.

Prepare the cable by removingabout 1.5 -inch of insulation at threelocations (each switch should beabout 24 inches apart) along themulti -conductor cable. The fourthswitch connects to the very end of themulti -conductor cable. Strip onecolor -coded inner wire for eachswitch. The color -coded wire is thensoldered to one switch contact, andthe bare shield wire is looped out andsoldered to the other contact. A

Here's the authors completed prototype shown along with one unit of the four -

contestant switch arrangement.

heavy-duty DIN plug was then con-nected to the other end of the cable.

Conclusion. The design that hasbeen described is the result of manysuccessive improvements over theyears. The Digital Bowl Box was de-veloped in response to requests bylocal school systems for an afford-

able, compact, easy -to -use quiz -bowlapparatus, and nearly 100 similar sys-tems are now in use in our area.Needing to build so many in a part-time operation, considerable atten-tion was given to easy assemblymethods. The unit reportedly has metits need well, and helps make con-testing very exciting.

Although it may seem quitedistant now, summer is ap-proaching with the antic-

ipation of backyard games, bar-becues, and the dog next doorbarking incessantly. If you happento be the owner of the irritating,barking dog next door, then neigh-borhood harmony is at risk. But,worry not.. for in this article, we'regoing to show you how to build aDog Bark Inhibitor that will restoreneighborhood harmony by hu-manely stopping your dog frombarking.

Commercially available dogbark inhibitors (electronic devicesbuilt into a dog's collar) that arecurrently on the market are bothexpensive and can in some circlesbe considered inhumane. Withsuch devices, every time the dogbarks an electrical charge is sentto the dog's neck. While that stopsthe dog from barking, it can alsoturn a dog into a cowering animalafraid of its own shadow.

However, the Dog Bark Inhibitordescribed here is inexpensive andhumanely stops the dog from bark-ing by actuating a buzzer every timethe barking begins. The buzzing isused to give the dog negative feed-back that he'll associate with his barki-ng, causing him to refrain from thatannoying tendency.

Circuit Description. Figure 1 showsa schematic diagram of the Dog BarkInhibitor. At power up, a one-shot mul-tivibrator, consisting of one-third of a40106 hex Schmitt trigger (U4 -c andU4 -d), resets U2 and U3, keeping thebuzzer (BZ1) cut off. At the same time,resistors R1 and R2 set the trigger levelof U1 -a, U1 -c, and U1 -d (3/4 of an LP324

quad op -amp) to 2.5 volts. Op -ampsU1 -a and U1 -d are configured as in-verting comparators with hysteresis,while U1 -c is configured as a voltagefollower,

The voltage follower (U1 -c) providesa standing DC bias voltage for anelectret microphone (MIC1). WhenMIC1 picks up the dog's barking (seethe waveform diagram in Fig. 2A), thebias voltage applied to MIC1 fluctu-ates, and the output of U1 -c follows.Fluctuations in the microphone's biasvoltage are applied to U1 -d, whichamplifies the signal and feeds its out-put to U1 -a. The overall sensitivity of

Dog -BarkInhibitor

Give yourself and yourneighbors some peace

and quiet with thistraining aid

BY ROBERT J. GAFFIGAN JR.

the circuit is determined by the gainsprovided by U1 -a and U1 -d. The hys-teresis provided by those two op -

amps helps to keep backgroundnoise out of the signal applied to U1 -b,which is setup as a low-pass filter. Thatlow-pass filter is used to remove fre-quencies from the signal that are notin the range of a dog's bark.

From the filter, the signal (see Fig. 2B)is made compatible with digital cir-cuitry by U4 -a (1/a of a 40106 hex invert-ing Schmitt trigger), which also invertsthe input signal. That signal is againinverted by U4 -f and output to the fol-lowing circuitry as a train of negative -

going pulses. Those pulses are pro-duced each time that the soundpicked up by the microphone fallswithin the low-pass range of the filter(see the waveform in Fig. 2C).

The output of U4 -f divides along Iwosignal paths: in one path, the signal isfed to the clock input of U2 (a 404012-

stage ripple carry binary counter); inthe other path, the signal is applied tothe trigger input of U3 -a (1/2 of a 556dual oscillator/timer). The negativepulses trigger U3 -a, whose output, inturn, enables U2, causing it to countthe number of times that the soundfalls within the low-pass range of the

filter. The purpose of U2 and U3 -ais to reject spurious sounds thatfall within the filter's range and toallow the dog a period of freebarking.

If the counter (U2) counts 256bark pulses within eight seconds,its output goes high. That high isinverted by U4 -b and applied tothe trigger input of U3 -b at pin 8,forcing its output at pin 9 high.The high output of U3 -b is appliedto the base of Q1 (an MPSA12Darlington transistor), causing it toconduct. With Q1 conducting, BZ1(a 6 -volt electronic buzzer) acti-vates for about half a second. Atthe same time, the ripple counter(U2) is reset via an oa gate, madeup of D1, D2, and R11.

If, on the other hand, U2 countsfewer than 256 pulses within that8 -second period, the counter re-sets, and awaits the next barkingsession.

The circuit is powered by a 9 -

volt transistor -radio battery. Be-cause of that, the semiconduc-tors used for this circuit werechosen for their low -current re-

quirements-the circuit draws ap-proximately 0.9 microamps of quies-cent current, and 15 mA with thebuzzer on-and should not be sub-stituted unless swapped for lower -

power components.

Construction. Although the author'sprototype was built on a section ofperfboard, using point-to-point wiringto interconnect the circuit elements,the final version was assembled on aprinted -circuit board, measuringabout 3 x 2 inches. A template of theprinted -circuit layout is shown in Fig. 3.You can etch your own printed -circuitboard from the template shown in Fig.3, or you can order a printed -circuitboard and the parts (separately) topopulate it from the supplier listed inthe Parts List.

Once you have obtained theboard and the parts that go with it,construction can begin. Figure 4shows the parts -placement diagramfor the author's printed -circuit layout. Itis recommended that IC sockets beprovided for all of the DIP units (U1 -U4).The regulator, U5, is housed in a TO -92style package. Begin construction byinstalling the DIP sockets and thejumper wires. Once that is done, install

MIC1

+5V

R1

100K

R2100K

C1

2.2 13

R31K

12U1 -d

's&R4

39K

14

1/4 LP324N

10

+ 5V

4

U1 -c8

LP324N

11

BZ1

S1

R1210K

)1 NA,* C2 3

.047

9

R575K

U1 -a

'/4 LP324N

U3 -b

1/2 L558

12

+5V -R 6 t t4046_4,100K

R151MEG *C.18

07-1MP3Al2

13

8 3

Ana=- R9

39K

R6 R7 R82.2K 11K 11K

U4 -b10 1/640108

- C3-*%

C4

.01

Lt R10

56K

1/4 LP324N

U1 -b

C5

01

16+ 5V -1--

4

CLKU2

4040RST

088 13

SOUND- -12

U4 -a U4 -f1/6 40108 Ye 40106

SOUND

10D- + 5VU4 -e

1/6 40100 114

11

D21N914

01

1N914

4444R11

100K

10

+ 5V

14

7U3 -a

1/2 L558

4

+ 5VSOURCE

6

U4 -c

1/6 40106

5 8

U4 -d

1/6 40108 R141MEG

NYkt +5V

-I-_ C7I

2 + 5V

R13 t1MEG

C6

8.2 T

Fig. I. The Dog Bark Inhibitor is comprised of an LP324 quad op -amp (UI), a 4040 12 -stage ripple carry binary counter (U2), anLM556 dual oscillator/timer (U3), a CD40106 hex inverting Schmitt trigger (U4), an LM2931A 5 -volt series, low -dropout, voltageregulator (U5), an MPSAI2 Darlington transistor (QI), two IN914 general-purpose, small-signal silicon diodes (DI and D2) and a

handful of additional components.

RF1

GND

ti

Me-

II

CH1

GND -4-

CH2GND .-

I rl

A

PIN 14 U1 -d

B

PIN 7 U1 -b

C

PIN 12 U4 -f

Fig. 2. Shown in A is the waveform produced at the output of U1 -d when the dogbarks; B shows the same waveform after it has undergone filtering: and C shows howthe waveform looks after being processed for application to the digital circuitry thatfollows.

the passive components (resistorsand capacitors).

After the passive components havebeen installed, mount the activecomponents (excluding the DIP IC's,

they will be installed in their respectivesockets later), and connect a 9 -voltbattery connector to the appropriatepoints on the board. In the author'sprototype unit, the microphone

(MIC1) was mounted directly to thecircuit board, although it might ap-pear otherwise in the parts -place-ment diagram.

It will be necessary to prepare theenclosure that is to house the circuitboard and the off -board compo-nents. The author's unit was housed ina plastic project box with a metal lid,measuring about 31/4 x 21/8 x 1

inches. Begin preparing the en-closure by first placing the circuitboard into the enclosure to deter-mine where the microphone will belocated when it is permanentlymounted. Mark that position on thewall of the enclosure, and drill severaltiny holes at that location.

Next, on the same side of the en-closure, drill two holes (one near eachend), which will be used to mount anylon web strap (dog collar) to theproject box. Then make two cutouts atopposite ends of the enclosure for thebuzzer (BZ1) and the slide switch (S1);the cutouts should be approximately7/5 x 5/8 inches for the buzzer, and the

PARTS LIST FOR THEDOG BARK INHIBITOR

SEMICONDUCTORSC1-1_13324 micropower quad op -amp

(National), integrated circuitU2-CD4040 12 -stage ripple carry

binary counter, integrated circuitU3-LM556 dual oscillator/timer,

integrated circuitU4-CD40106 hex inverting Schmitt -

trigger, integrated circuitU5-LM2931A 5 -volt series, low -

dropout. voltage regulator,integrated circuit

QI-MPSA12 Darlington NPNsilicon transistor

DI, D2 -1N914 general-purpose,small -signal silicon diode

RESISTORSfixed resistors are 1/4 -watt, 5c4

units.)RI. R2, R11, R16 -100,000 -ohmR3 -1000 -ohmR4, R9 -39,000 -ohmR5 -75,000 -ohmR6 -2200 -ohmR7, R8 -11,000 -ohmR10-56 ,000 -ohmR12 -10,000 -ohmR13-R15--1-megohm

CAPACITORS16-WVDC, tantalum

C2 --0.047-µF, monolithicC3 -0.1-µE monolithicC4, C5-0.01-p.F. monolithic

16-WVDC, tantalumC7, C8 -1-µE 16-WVDC, tantalumC9 -22-µF. 16-WVDC, miniature

electrolytic


S1---SPST slide switchMICI-Electret microphoneBZ1-6-volt electronic buzzer (RS

#273-054)B1 -9 -volt transistor -radio batteryPrinted -circuit materials, enclosure,

is X 24 -inch web strap, adhesivebacked cushion feet, battery holderand connector, wire, solder,hardware, etc.

Note: The following items areavailable from Futronics. 22524Millenbach. St. Clair Shores. MI48081. A complete kit of parts,S29.95; printed -circuit board only,59.95. Please add $3.00 forshipping and handling. Michiganresidents please add appropriatesales tax.

27/e INCHES

Fig. 3. The final version of the circuit was assembled on a printed -circuit board,measuring about 3 x 2 inches. A template of that layout is shown here full size.

R5

81211;z

R91C41 1C31R6

c5I R71 1R8

RIO

D

R4

U1

J -

MIC1

-CI -+R11 fir

-R3 -

R11

J

J J

Di* *02

U4

B1

U2

111, 6

C71 1R4---'01

BZ1

U3

1113

C8

R15

C6

Fig. 4. Once you've obtained the board and the parts that will populate it (either onyour own or by ordering them from the supplier listed in the Parts List), use this parts -

placement diagram to locate and install the components in their proper positions.

other approximately 5A6 x 1/4 inchesfor the slide switch.

Connect short lengths of hook-upwire to the buzzer and the switch, con-nect the wires from the off -boardcomponents to the appropriatepoints on the printed -circuit board.Mount the printed -circuit board,switch, and buzzer to the enclosure,and then secure the nylon web strapto the side of the enclosure using apair of 4/40 screws and nuts. The strap-ping used to secure the project to thedog's neck is available at most sportsand army surplus stores.

Cut off any excess strap length aftersizing it to the dog's necic, the free endof the strap should be melted to avoidfraying. Finally, install the IC's in theirrespective sockets, install a 9 -volt bat-tery, and close up the project box.

Operation. Using the circuit is easy.Simply strap the Dog Bark Inhibitor toyour dog's neck (be sure to orient theunit so that the microphone is up), turnthe unit on using St Any long durationor repeated barking by the dog willcause the buzzer to sound for one halfsecond. If greater sensitivity is desired,increase the value of R5.

A longer free -barking period canbe achieved by increasing thenumber of counts U4 allows beforeturning on the buzzer (that can bedone by cutting the trace to pin 13 ofU2 and moving the wire to the Q9output pin 12 or the Q10 output pin 14).The project has been used on the au-thor's dog for more than a year andhas stopped the dog's nuisance barki-ng and has restored neighborhoodharmony.

Every reader of this magazine isfamiliar with the difference be-tween a parallel circuit and a

series circuit. The parallel circuitshown in Fig. 1A allows independentcontrol over each lamp: S1 turns M onor off independent of S2, while S2 op-erates 12 without regard to the posi-tion of S1. In the series circuit shown inFig. 1B both switches must be closed inorder to light the lamps, and if either isopened, both lamps go out. There isno independent control of the lamps.

That's where the Non -Serious Circuitcomes in. The unit consists of twocolor -coded switches (one yellow,one red), and two bulbs of corre-sponding color. Since the compo-nents and wiring are clearly visiblethrough the clear plastic box they arein, you can see that the switches andlamps are wired in series.

However, if you plug the unit in andflip a switch, only its like -colored lampis affected! Flip the other switch andthe other lamp goes off. At this pointyou'd be wondering what's going onhere? As an experiment you might tryswitching the bulbs, but to no avail;the red switch still operates the redbulb, and the yellow switch controlsthe yellow bulb.

Very astute readers may have al-ready figured out the circuit. If you

A NON -SERIOUSCIRCUIT

BY D. DEREK VERNER

Is it a parallel circuit or isit a series circuit? You'll have

loads of fun watching your, friendstry to figure it out for. themselves.

haven't yet, don't feel toobad, this circuit has been

known to confuse and mystifyelectronically sophisticated en-

gineers. I built the first version of itwhen my son was studying paralleland series circuits in a technologyclass in junior high school. He broughtit into class and asked his teacher whyit didn't work properly. Believe me, theteacher almost went crazy trying toexplain it. The secret is that each lampand switch contains a concealedcomponent.

How it Works. As can be seen in Fig.2, the concealed components arerectifier diodes connected as shown.With both switches open there can beno current flow because the diodeswired across them block current inboth directions.

Let's suppose we close S1. Let's alsoassume that during the first half -cycleof the power line's waveform currentflows in a clockwise direction aroundthe circuit. At 11 the current encountersD1, which blocks it so it travels throughthe lamp (M) instead, lighting it (at halfpower). Next the current approaches12, where D2 effectively shorts out thelamp. At S2 the current passes readilythrough D4 and on through S1, whichis closed.

On the next half cycle when thecurrent attempts to travel counter-clockwise through the circuit it is sim-ply blocked by D4. The overall effect isthat lamp M appears lit and 12 is out.When S2 is closed as well, the current

is AC and each lamp lights during theappropiate half cycle.

Parts Selection. You probably haveall the parts necessary to build theNon -Serious Circuit in your junkbox.Any clear plastic box large enough tohouse the components will serve forthe enclosure. The lamps can be anylow -wattage AC bulbs with an inter-mediate -size brass base. Most Ameri-can -made bulbs these days aremade with aluminum bases that arenot suitable for this project because itis hard to solder to the shell. If you useChristmas -tree bulbs, as I did, choosered and yellow ones as they light withmore apparent brightness than blueor green when fed half -wave AC.

Although your hardware store prob-ably also stocks a large selection ofintermediate -size lamp sockets, thebest choice is the brass shell removedfrom a composition -type Christmas -light string. That is because the shellscannot be "gimmicked" in any waythat wouldn't be readily apparent.

The toggle switches must be of atype that can be easily disassembled.The ones shown are held togetherwith two small screws. Although no -longer listed in their current catalog, itmight be possible that your local Ra-dio Shack has them still on the shelf asitem 275-602 or in their toggle -switchassortment as item 275-322. However,any SPST switch that can be neatlydisassembled and re -assembled willdo.

The diodes can be 1N4002's or any

PL1 11

s ,S S2

A

Fig I. The operation of a normal parallel circuit (A) or straightforward series circuit(B) is easy to figure out if you have a little knowledge of electronics.

PL112

PL1

I1

D1

1N4002L

r

S1 1

I

L_ t crAPo__9_4

D31N4002

T

12

S2

oS1 S2

D21

I 1N4002L--------J

-1

D4

1N4002

Fig. 2. This is the Non -Serious Circuit. If you follow each alternation of the AC linecurrent around the loop for various settings of SI and S2 you'll soon see how confusingthe circuit would appear to the unsuspecting.

The components of the circuit can be clearly seen through the transparent enclosureNote the clear -plastic strip holding the socket shells in place beneath the box's cover.

others rated at least 1 amp at 100 PIV.These are generally available in theDO -14 size, which is less than aquarter -inch long. The smaller sizemakes it easier to conceal the diodesin the switches and lamp bases.

If you opt for the brass shells fromsome Christmas lights, you will have todevise a way to mount them so thatthe shell is not exposed (presenting ashock hazard). I epoxied mine into

suitably countersunk holes in a smallstrip of acrylic plastic mounted insidethe box by means of 6-32 screws.Slightly smaller holes in the top of thebox allow the bulbs to be inserted, butprevent the shells from protruding out-side the box.

To remove the bases from thelamps, you will need a propane torchand a pair of gas pliers. Wrap the bulbin a cloth with the base exposed and

PARTS LIST FOR THE NON -SERIOUS CIRCUIT

SEMICONDUCTORSDI-D4-IN4002 100-PIV,

rectifying diode (see text)


II, l2-Christmas-light bulbSi. S2-SPST power switch (see

text)linecord and plug

Clear -plastic case, two Christmas -light sockets, wire, solder, etc.

put on a pair of goggles. (Although Ihave never had a bulb break duringthis operation, it is always better to besafe than sorry.) Heat the base of thelamp in the flame of the torch, andwith the pliers keep testing the bondby twisting it slightly. It shouldn't takemuch heat before the base loosens.As soon as it is free, turn off the torchand set the bulb down to cool. If thebase and the bulb are still connectedby wires soldered to the center con-tact and to the shell, carefully un-solder the connections.

With a penknife, scrape out theremnants materialfrom the base of the lamp and fromthe interior of the shell. The material isbrittle and can be easily removed.Clean the Iwo exposed copper wirescarefully by scraping or using finesandpaper. Tinning the wires willmake the next operation easier.

Clip the cathode lead of the diode(usually marked with a band), leavingabout Y4 inch of lead. Wrap one of thewires from the lamp around the short-ened lead close to the body of thecomponent. Also wrap the lead with ashort length of bare, tinned, solidhookup wire, Using a heat sink on thediode, solder the connection. Insertthe stubby length of lead into thespace between the evacuation tubeand the remainder of the bulb. Takecare not to fracture the fragile glassevacuation tube. Slip a small piece ofspaghetti over the other wire from thelamp and solder it to the anode of thediode.

Examine the brass shell and locatethe point on its rim where the wire waspreviously soldered. File a small notchin the rim large enough to clear thepiece of hook-up wire installed in theprevious step. Check the center con-tact and make sure that no solder is

blocking the small hole in it.Apply a liberal coating of epoxy to

the inside of the shell and install it onthe base. The uncut lead from the di-ode goes through the hole in the endcontact and the short length of hook-up wire through the small notch in theshell. Clamp the assembly togetherand allow the epoxy to set with thebulb in a base -up position.

When the adhesive has cured, sol-der the diode lead to the end contactand cut it off flush. With your goggleson, clip off the other lead so thatabout 3/46 of an inch is exposed, bendit over, and solder it to the shell. Re-peat the operation with the otherlamp, but this time the cathode end ofthe diode should be left long for con-nection to the end contact.

Open up the toggle switches and,by pushing them out from the back,remove the contacts. If you use thesame switches the author did, drill asmall hole in the left-hand contact forone lead of the diode, and tin thearea of the right-hand contact wherethe other lead will go. Reassemble thecontacts into the switch housing and,with its leads cut short, solder the di-ode to the contacts. In one switch, thecathode should face to the left, in theother, to the right.

If you are using a different type ofswitch or you cannot locate any di-odes small enough to fit, you canprobably find some space for the di-ode somewhere else in the switchhousing. A motor tool with a small burrbit can be used to rout out space atthe end of the housing opposite thecontacts. Small wires can be used toconnect the diode to the contacts.

Reassemble the switches, makingsure that the slot in the mountingbushing is on the side opposite thecontacts. This assures that the on -offnameplates will read correctly.

Mount the components in the boxback in Fig. 2. Install the lamps andpaint the switch handles to corre-spond to the colors of the bulbs.

Using the Unit. The best way to pres-ent the Non -Serious Circuit to a friendis to pretend to be confused. Explainthat you'd like his help-it seems thatyou wired up this circuit and it is oper-ating in a very strange manner. Youcan probably build the unit in oneevening with parts already on hand,so I hope you'll give it a try.

BONUS SECTION

117Y!)j,e

200,000-volt Van de GraaffGenerator

Solid -State Tesla Coil

Easy to build Jacob's Ladder

Just turn the pageto High Voltage Excitement

57

The first known electrical gener-ator was built in 1660 by theGerman experimenter, Otto von

Guericke (also known to historians asthe inventor of the air pump). ThoughGuericke's generator consisted of littlemore than a revolving ball of sulfur, thatfrictional device was capable of de-veloping a very strong charge of staticelectricity.

The generator's ball was made bypouring molten sulfur into a sphericalglass container "about the size of achild's head." When the sulfur cooled,the glass was broken open, and theglobe removed and equipped with aniron axle. The assembly was thenmounted on a wooden frame that al-lowed the ball to spin freely. When a dryhand was applied to the rotating sulfursphere, the ball would become elec-trified, attract small objects, make acrackling sound, and glow faintly in thedark.

Van de Graaffs Generator. Otto vonGuericke's machine quickly becameobsolete, but the triboelectric princi-ples that allowed that generator to op-erate did not. It is an elementaryphysical fact that extremely high volt-ages can be generated by the repeat-ed contact and separation of dissimilarsubstances, a process that is otherwiseknown as friction.

In 1927, New Zealand physicist ErnestRutherford voiced the need for "a copi-ous supply of atoms and electrons ...transcending in energy the alpha andbeta particles from radioactive sub-stances." He was talking about an ac-celerator. Rutherford's wish inspired ayoung American scholar by the nameof Robert J. Van de Graaff.

Van de Graaff knew that chargedparticles could be moved to highspeeds by high voltages. He also knewthat conventional methods of elec-trical transformation might not providethe necessary energy. But the elec-trostatic characteristics of the atomicnucleus gave him an idea. Van de

200,000 -VoltVan de Graaff

Generator

Have hours of high -voltagefun when you experiment

with this working high-

voltage generator.

BY STANLEY A. CZARNIK

Graaff decided to find some way ofgenerating high electrostatic voltagesin order to, as he phrased it, "meet theatom on its own terms."

The first Van de Graaff generator wasbuilt at Princeton University in the fall of1929. Van de Graaff built the machinefrom scrap: a silk ribbon, a small motor,and a tin can. The silk had to be pure;there is a story about how Van deGraaff would visit local fabric shopsand set fire to silk samples to see if thecloth was tainted. Van de Graaff's primi-tive static device developed about80,000 volts. The high -voltage outputwas restricted by corona dischargefrom the edges of the can.

The public became aware of Van deGraaffs new technology in 1931. That'swhen he demonstrated the creation of

volts between the spher-ical terminals of two belt -driven gener-ators. Following that, general interest inthese magnificent machines grew veryquickly.

Giant Generators. The early successof Van de Graaff's creations was en-couraging. Immediately, researchersbegan making plans for a much, muchbigger generator. The size of the ma-chine was to be limited only by the sizeof the building found to keep it in. Asuitable structure was located on theestate of Colonel E.H. Green at SouthDartsmouth, Massachusetts. It was thebiggest enclosure anyone could find. Itwas a hangar built originally to house adirigible, or blimp.

Engineers built two separate ma-chines: one for the positive charge, andone for the negative. The spherical ter-minals, about 15 feet in diameter, weremade of welded aluminum andmounted on two large tubular in-sulators, each 24 feet high and 6 feetacross. The generators were carried onrailway track. That allowed techniciansto vary the distance between the elec-trodes. The giant Van de Graaff systemwas capable of generating nearly ten -million volts.

nro dt. Graall gellerai(11 built in .11(1\\ the

early 19.41.A. machine was capable of developing nearly ten million volt, I Ihlarge .sirucnv in the background was, originally, a hangar built for a blimp.

A Working Model. With a kit of partsfrom Analytical Scientific, a laboratorysupply company in Texas, you can buildyour own 200,000 -volt Van de Graaffstatic generator in about one hour. (Seethe Parts List for ordering information.)

The fully assembled machine isabout 18 inches high. The spherical alu-minum terminal, mounted on top of aheavy plastic tube (PVC pipe), is about7 inches in diameter. The generatorruns on 117 VAC and comes completewith a small electric motor and all thenecessary hardware; there's even aspare rubber belt. It's a classic designand an excellent addition to anyhome -experimenter's workshop.

Building your Model. Once you'veobtained the kit, begin by attachingthe three rubber feet to the round met-al base. Now locate the L-shaped

WARNING!! This article deals with andinvolves subject matter and the use ofmaterials and substances that may behazardous to health and life. Do not at-tempt to implement or use the informationcontained herein unless you are experi-enced and skilled with respect to suchsubject matter, materials, and sub-stances. Neither the publisher nor the au-thor make any representations as to theaccuracy of the informaton containedherein and disclaim any liability fordamages or injuries, whether caused byinaccuracies of the information. misin-terpretations of the directions, misapplica-tion of the information, or otherwise.

motor bracket and the lower brush,which is the short.length of strandedwire that's connected to a solderinglug. Push three small screws (8-32 x 1/2 -inch) up through the bottom of thebase and the motor bracket. Place lockwashers on the screws and secure theassembly with three 8-32 hex nuts. Thelower brush goes on the screw furthestaway from the 90 -degree bend in themotor bracket. The brush should point

towards the vertical section of thebracket. Handle the brush carefully as itis delicate.

The next step is to find the electricmotor and mount it by passing the twothreaded studs plus the armature shaftthrough the three remaining holes inthe motor bracket. Place lock washerson the threaded studs and secure themotor with a couple of hex nuts.

Now look for the white plastic pulley.Push the pulley over the armature shaft.If you have trouble, tap the end of thepulley very gently with a small hammeror the handle of a screwdriver. Thepulley should not come into contactwith the motor bracket.

The plastic pipe is held against theupper portion of the motor bracket witha large U -bolt, a metal strip, and twolarge hex nuts. One end of the pipe hasa couple of semi -circular notches cutinto it. That end of the pipe should beup; the plain end should be down. Thelower end of the pipe should extendabout 5/8 inch below the U -bolt. Thenotches on top should line up with thepulley at the bottom. To check thealignment, simply look straight downthrough the center of the pipe.

Next, locate the rubber belt and slip itover the metal pulley. Place the pulleyinto the two notches on top of the in-sulator and allow the belt to fall throughthe tube. Pull the lower end of the beltdown and place it over the lowerpulley. Try to avoid handling the belt too

cr.

z

coco

mr-m

330z

O03CO

-4

z

cn

co0

1I](, 1, ;wit. the inside of your Van de look 11/1 / 0aluminum!, shell is placed over the round metal base. Note the arrangement ol the strand( dwire brush, the rubber belt, and the pulley assembly. 59

60

much as skin oils can reduce its effec-tiveness.

Now, very carefully, adjust the lowerbrush so that it just barely touches therubber belt. Spread the strands of wiregently so that as many of them as possi-ble are touching the rubber.

Find the collector support and up-per -brush assembly. That's the shortlength of stranded wire soldered to a V-shaped piece of stiff wire. Push the V-shaped wire into the two small holes atthe upper end of the insulator (PVCpipe). And here again, adjust thestranded wire brush so that it just barelytouches the rubber belt.

Return to the bottom of the gener-ator and hook up the 117 -VAC line cord.Use the wire nuts provided with the kit.The line cord is held in place with aplastic strain relief. Don't forget to con-nect the little green ground wire. Boththe strain relief and the ground wire areattached to the base of the generatorwith a small screw and a hex nut.

Finally, lower the cylindrical alumi-num shell over the plastic tube andpush it down over the base. Then placethe spherical terminal over the collec-tor support. It should balance perfectly.Now stand back and admire your newVan de Graaff generator. Ifs a work ofelectromechanical art!

Testing. Plug your generator in and

upper brush and upper terminalsupport fit into the upper end of thetubular insulator. Note how the wire brushis positioned to make contact with therubber drive belt.

The

This photograph illustrates the creaion of what is sometimes called an "electric wind."Tape one end of a narrow metal rod to the top of your Van de Graaff generator. Turn onthe machine and light an ordinary household candle. Now bring the candle close to thefree end of the rod. As molecules of ionized air rush from the metal tip, the flame is blownto one side.

the motor should turn. If it doesn't, re-move the upper spherical terminal andgive the pulley a little spin in the rightdirection. That should start the gener-ator. Replace the aluminum sphere im-mediately.

Wait a few moments for a charge tobuild up on the terminal. Now ap-proach the sphere with a large fluores-cent tube. When the tube is three orfour inches away from the sphere, themachine will discharge, and the tubewill flash. If that doesn't happen, or if theflash isn't very bright, your generator isnot working properly.

Unplug the unit and remove the up-per terminal and the lower shell.(Please be careful. A small staticcharge may be waiting for you whenyou touch the aluminum sphere.)Check the belt and the pulleys fordirtand moisture. They should be cleanand dry. Then check the brushes. If thewire strands are too far away from thebelt, the generator will operate verypoorly, or not at all.

Finally, check both the upper termi-nal and lower shell for dust and lint.They, too, must be very clean. I was ableto improve the performance of my ownVan de Graaff generator by cleaningboth the shell and the terminal with abit of good quality metal polish and asoft cloth. That seemed to make a bigdifference in the machine's operation.In fact, it might be a good idea to polishthe aluminum sections before puttingthe machine together.

MATERIALS LIST FOR THE VANDE GRAAFF GENERATOR

EXPERIMENT

Van de Graaff generator kitAluminum -foil strips, very thinCandleFluorescent tubeFoam plastic packing materialMetal polishMetal rod, 8 to 10 inches longTapeThe Van de Graaff generator kit is

available from Analytical Scientific,Post Box 198, Helotes, TX 78023,Tel. 210-684-7373. The catalognumber is N1LE-10-065 and the priceis $137.75. Include $5.00 for shippingand handling within the continentalU.S. The Analytical catalog is $3.00,which is refundable with first order.TX orders must include appropriatesales tax.

Theory of Operation. Here's how yourVan de Graaff generator works: Theelectric charge originates with the fric-tion of the rubber belt moving over thelower plastic pulley. The plastic pulleyacquires a negative charge that ap-pears on the outside of the belt while apositive charge appears on the inside.The negative charge is picked up bythe ionized air around the lower brush.The positive charge is carried to theupper brush by the belt where it is trans-ferred to the aluminum sphere.


SOLID-STATETESLA COIL

Build an updated versionof Nikola Tesla's most -

famous experiment.

By Charles D. Rakes

N!KOLA TESLA IS CONSIDERED BY SOME TO BE THE

greatest inventor of our modern electrical age, andmany experts consider him to be the true father of

radio. However, today he is best remembered for his fascinat-ing wireless power -transmission experiments, using his fa-mous Tesla coil.

The high -frequency air -core, oscillating Tesla coil is just asexciting today as it was back in 1899, when he used it tosuccessfully transmit electrical energy over 25 miles, withoutwires, to light a large number of incandescent lamps. TheTesla coil is ideal for demonstrating and exploring the un-usual phenomena that occur with high -frequency high -volt-age energy.

Most Tesla coils designed for educational and experimen-tal purposes use a line -operated, step-up transformer --insetups like that shown in Fig. 1 --to generate the high voltageneeded for the coil's primary circuit. While there's nothingtechnically wrong with that approach, it can place the oper-ator in harm's way if the coil's primary circuit is accidentallytouched. A shock from the high -voltage winding could proveextremely dangerous and may be fatal.

Our version, the Solid -State Tesla Coil (see photos), elimi-nates the line -operated, high -voltage transformer, making it asafer project to build and to experiment with. Even so, wiseoperators will keep their digits out of the wiring while the coilis under power.

Solid -State Tesla CollThe schematic diagram for the Solid -State Tesla Coil is

shown in Fig. 2. In that updated version of the Tesla experi-ment, an 18 -volt, 2 -ampere transformer (T1), a bridge rec-

r

117VAC <

STEP-UPTRANSFORMER

PRIMARYCOIL

SECONDARYCOIL

Fig. 1-Shown here is a basic design for a Tesla Coil cir-cuit, using a line -operated, step-up transformer to gen-erate the high voltage needed for the coil's primary.

tifier circuit (consisting of 1)1-1)4), and titter capacitors (Cland C3) supply operating power for the cud circuitry..

A 555 oscillator -timer R.I1 is configured as a self -oscillat-ing pulse: -generator circuit. Resistors RI end R2 make up avoltage -divider network., whi,:h is used to lower the 24- voltDC output of the power supply to a sale operating level forUl. The 555's narrow output pulse at Fir. 3 supplies drivecurrent to the base of Ql. Transistor Q2 supplies sufficient

Here is the author's prototype of the Solid -State Tesla Coilwith the 9-Tch circular deck removed. The twc heavy wiresrunning the length of the top and bottom of the board serveas the ground and V bus.

PL1

117

VAC

F1

1A

S1

SPST

PRI.

T1

18VJ01

1N5408

licSEC.

D31N54128

D21N5408

+1 Cl

D41N5408

2200

V

C3

.47

t R2".1K

R310K R4

10K

7

U1

555OSC./TIMER

2 3 al__C4

RI .33

470S-2

C2

^ 47

R6 R710K IK Q2

PAJE34

012N3908

R52.2K

R81K

C5* SPARK1500pF GAP

Fig. 2-Our updated version of the Tesla experiment uses an18 -volt, 2 -ampere transformer (T1), a full -wave bridge rec-tifier (consisting of D1 -D4), and fitter capacitors (C1 andC3) to supply operating power for the Coil's circuitry.

current to transistors Q3 and Q4 to drive those componentsinto full saturation.

The primary winding of T2 (an automobile -ignition coil) isconnected in series with Q3 and Q4, and across the powersupply. Transistors Q3 and Q4 operate like a toggle switch,connecting the coil across the power source at the rate and on -time set by Ul.

That high -current pulse generates a rising and collapsingfield across the primary winding of T2. The field causes acurrent to be induced in the secondary winding of T2. Thesecondary output of T2 is fed across three 500-pF, 10 -kilovoltdoorknob capacitors (collectively designated C5) that areparallel connected and tied across the high -voltage output ofT2 as an energy -storage device. Those capacitors charge upto Ti's secondary voltage and are then discharged through thespark gap and the primary (LI) of the Tesla coil, producinghigher voltage in the secondary of the coil (L2).

The secret of producing a successful Tesla coil is in thetuning of the primary coil to the natural resonance frequencyof the secondary coil. Because variable 10 -kilovolt capacitors

are about as common as Condor eggs, some other meansmust be used to tune LI. The simplest method is to tap theprimary coil on every turn and select the tap that produces thegreatest voltage at the hot end of L2.

Pertboard AssemblyThe author's prototype was built breadboard style on an 11

X 11 x 1 -inch wooden cutting board (see photos), but anysimilar non -conducting material (perhaps plastic) will do.The majority of the small components, as shown in thephotos, were mounted on a 3 x 5 -inch section of perfboard,and point-to-point wiring techniques were used to completethe connections. Refer to the schematic diagram (in Hg. 2)and the photos for wiring and general parts -layout details.Note: Components T1 and T2, C5, Q3 and Q4, Fl, and SI arenot mounted to the perfboard (see photos).

Figure 3 shows the positioning of the perfboard and off -board components on the baseboard. Mount the fully -popu-lated perfboard assembly to the baseboard using four 1/4 -inchplastic spacers and wood screws. The location of the sub-assemblies on the baseboard isn't too critical, so long as thegeneral layout is followed. Keep all wire leads as short aspossible, especially around the high -voltage circuitry.

A 21/2 x 2 -inch piece of aluminum is formed into an "L"bracket, which is used to hold SI and Fl (see photo), and ismounted on one corner of the baseboard. A 5 x 3 -inch pieceof aluminum mounts to the opposite corner and functions asthe heat sink for the two power transistors (Q3 and Q4). Asimple band is formed from aluminum to hold T2 in place.

Recall that C5 is really three 500-11F doorknob capacitors.

PARTS LIST FOR THESOLID-STATE TESLA COIL

SEMICONDUCTORSU1-555 oscillator/timer, integrated circuitQ1 -2N3906 general-purpose PNP silicon transistorQ2-MJE34, ECG197 (or similar) audio -frequency PNP

silicon power transistor03, Q4 -2N3055 NPN silicon power transistorD1 -D4 --1N5408 3A, 100-PIV silicon rectifier diode

RESISTORS(All resistors are 1/2 -watt, 5% units, unless otherwise

noted.)R1 -470 -ohmR2, R7, R8 -1000 -ohmR3, R4, R6 -10,000 -ohmR5 -2200 -ohmR9-R12-100-ohm, 1 -watt resistor

CAPACITORSC1 -2200-µF, 50-WVDC electrolyticC2 -47-µF, 25-WVDC electrolyticC3 -0.47-µF, 100-WVDC mylarC4 -0.33-µF, 100-WVDC mylarC5-1500-pF, 10K-WVDC (three parallel -connected

500-pF doorknob capacitors, see text)

ADDITIONAL PARTS AND MATERIALSF1 -1 -ampere fuse, 3AGL1, L2-see textS1-SPST miniature toggle switchT1 -117 -volt primary, 18 -volt 2 -ampere secondary

stepdown transformerT2-Automobile-ignition coil (Ford #6S25, or similar)Perfboard, #12 wire, #26 wire, aluminum, Fahnestock

clips, spacers, solder, hardware, etc.

Q3 & 04ON ALUMINUMHEAT SINK

MOUNTINGSTRAP

NO. 12 SOLID COPPER WIRECONNECTS TO L1 GND

Fig. 3-The author's prototype was built breadboard styleon an 11 x 11 x 1 -inch wooden cutting board, and most of thecomponents were mounted on a 3 x 5 -inch piece of perfboard.

Two brass strips, about 3/8 -inch wide by 3 -inches long, areused to tie the three high -voltage capacitors together. Ifdoorknob capacitors cannot be located (often they can besalvaged from older black -and -white TV's), a substitute canbe made from window glass and aluminum foil.

To fabricate C5, take a 10 -inch square piece of glass, likethat of a picture frame, and glue a 9 -inch square piece ofaluminum foil to the center of the glass on both sides, leavingan equal border around each aluminum plate. Cut two 6 -inchlengths of #22 insulated stranded wire. Strip about 3 -inchesof insulation from one end of each wire and tape the strippedend to each of the aluminum plates.

Shown here is the 9 -inch circular deck supported by fourdowel rods, and an end cap positioned at its center.

The DeckFigure 4 and the photos show the top deck of the author's

prototype, where the two air -core coils (Ll and L2) aremounted. The top deck consists of a 9 -inch diameter circlecut from 1/2 -inch thick fiber board. Four 31/4 -inch lengths of 3/8

-inch dowel hold the 9 -inch coil base above the perfboard.Select a drill bit slightly smaller than the dowel rod's

diameter and drill the four mounting holes in the 9 -inch circleto match the illustration. Position the 9 -inch circle on thebaseboard at about the center, and mark the location of eachhole. Drill each location on the baseboard with the same bit toa depth of about 1/2 -inch.

If the two -layer Tesla coil seems like too much bother to

0I

HOLEFORGROUND ROD

DOWELHOLE

A1/2

SPARK GAPMOUNTINGHOLE

5- /2

9 -INCH DIAMETER, 1/2 -INCH THICKFIBER OR WOOD CIRCLE


Fig. 4-Shown here is the general layout of the top deck ofthe author's prototype, which supports coils L1 and L2. Four33/4 x Ve-inch wooden dowel rods hold the 9 -inch circularbase above the perfboard and other components.

Here is what L1 (left) and L2 (right) should look like oncecompleted. Although winding L2 may appear difficult, it canbe done in an hour by hand or in 15 minutes by lathe.

duplicate, then build a single -level unit on a larger woodenbase to suit your own needs. Actually, any good layoutscheme that respects the dangers of high voltage should doquite well.

Winding the Primary CoilThe primary -coil (L1) is wound on a form cut from a 4 -inch

diameter, plastic sewer pipe to a length of five inches (see Fig.5). Take a 27 -foot piece of #12 insulated solid -copper wireand strip away a Vs -inch section of insulation at about every 12inches, continuing for one-half the length of the wire (12times total). Those stripped areas serve as tap points fortuning the coil.

3/8

TURN 25

TURN 13

START

1-1/4

o

25 TURNSNO. 12 SOLID o

4,---- COPPER (WITHPLASTIC INSULATION)

TAPON 13 ANDALL TURNSABOVE

/TURN 1

COIL FORM (4 -INCH DIAMETER PLASTIC SEWER PIPE)ALL DIMENSIONS IN INCHES

Fig. 5-The form on which L1 is wound is a five -inch lengthof four -Inch diameter, plastic sewer pipe. A 27 -foot lengthof #12 insulated solid copper wire (with 12 quarter -inchsections of insulation stripped away at intervals of aboutevery 12 -inches) Is then wound onto the form.

Wind the coil starting at the top of the coil form (see Fig. 5)with the end that has the 12 tap points. In other words, turn 25is the first winding to be made. That gives a tap on every turnfrom turn number 13 to turn number 25. Drill two small holesin the coil form where the winding starts and ends. Thoseholes are used to secure the ends of the windings (see photos).

Winding the Secondary CoilThe secondary coil form (see Fig. 6) is cut from a section of

11/2 -inch diameter, plastic water pipe (which actually mea-sures 17/8 -inches in diameter). So when selecting your second-ary coil form, take a ruler with you and be sure to come homewith the correct -diameter pipe. You'll also need two plasticend caps that snugly fit the ends of the tubing.

Make a mark on the coil form about one inch from eachend. That sets the starting and ending points for the winding.Fill the space between marks with a neat solenoidal windingof #26 enamel -covered copper wire. Winding the coil byhand shouldn't take over an hour, and if a lathe is handy, youshould be able to complete the job in about 15 minutes. Leave

NO. 26 SOLID -COPPERWIRE

1 14-START WINDING

14-

6/ENNENESS NERESS)/8

LAST WINDING

24


Fig. 6-Using #26 enamel -coated copper wire, L2 is woundon a 24 -inch length of 11/2 -inch diameter, plasticwater pipe, either by hand or (If available) using a lathe.

about 6 -inches of wire at both ends of the winding for makingconnections.

Spray several coats of Krylon clear #1301 acrylic on thecoil for added insulation and protection against moisture.Always let each coat dry completely before applying the next.Two or three coats are sufficient.

It's Coming TogetherMount one of the 11/2 -inch, plastic end caps to the center of

the 9 -inch circular deck with a 1 -inch long #8-32 screw,washer, and nut. Take two small metal "L" brackets andmount the primary coil centered around the end cap on the 9 -inch base. Drill a small hole through the end cap and base-board near the rim of the cap. Take the secondary coil andpush one end of the coil's lead through the hole in the end cap,and then set the coil in the end cap.

INSULATEDALLIGATORCLIP FORTAPPINGCOIL (1.1)

5/8DOWELROD

9 -INCHLENGTHOF TESTWIRE

FAHNESTOCK

NO. 12 COPPERCLIP

WIRE

1.-1-3/4-01

RINOF9 -INCH 6-32 SCREWSCIRCLE

1 7/8

NO. 26 OR 28SOLID WIRE

1/2

TO C5

ALL DIMENSIONS IN INCHESFig. 7-The spark gap is formed by mounting two fahnestockclips to the 9 -inch circular deck; one tied to the maingrounding point, and the other connected to an alligatorclip, which is used to change taps on L1.

Take the other end cap and drill a hole in the center to cleara #8-32 screw, and mount a feed -through insulator (seephoto) on top. Select a #8-32 screw long enough to stickthrough the top of the insulator by about 1/2 -inch, and grindthe end to a nice sharp point. Connect the top end of thesecondary coil to the bottom of the #8-32 screw with a smallsolder lug and tighten in place. Place the cap on top of thecoil.

The spark gap is shown in Fig. 7. Two holes are drilled toclear a #6-32 screw to match the drawing in Fig. 4. Two


JACOB'SLADDER

A climbing electric arc has heldthe imagination of science -fiction fansas the symbol for an eerie laboratory!

JAMES, NICOLE, and DWIGHT PATRICK, Jr.

IN MANY SCI-FI AND HORROR FLICKS, ESPECIALLY THE STOCK "FRAN-kenstein" variety, along with weird sound effects and the like,movie producers always feature the fantastic visual effects pro-duced by Tesla coils, van de Graaff generators, and Jacob'sLadders. Of those three devices, the Jacob's Ladder is the easiestto build. With a low -current neon -sign transformer, a convertedflyback transformer, converted auto spark coil, or other similartransformer, you can whip together your own Jacob's Ladder inless than an hour. Because the ladder is so simple, there's noneed for a detailed parts list or a schematic. We tell you how tobuild one as we reveal the theory of operation.

Getting startedAs we can see in Fig. 1, a Jacob's Ladder provides a fantastic

visual effect. A beautiful electric arc hisses its way up twodiverging wires, providing a fascinating and downright scaryeffect. The arc starts at the smallest distance between the veeelectrodes (Fig. 1-a), and "walks" up the widening gap towardthe top of the electrodes (Fig. 1-b).

Why does the arc walk up the vee electrodes? You wouldexpect that when the arc starts to jump across the narrow gap atthe bottom of the electrodes, that it would stay there where theelectrical resistance between the electrodes is lowest. Whatactually happens is that the arc heats the air it passes through,causing it to rise. Because the heated air is ionized by the high -voltage arc, it provides a very low -resistance path, so the currentpath (the arc) rises with the warm air.

Eventually the arc reaches the top of the ladder (the elec-trodes) and bows upward creating an electrical path that getslonger and longer. At the point where the resistance at thebottom of the electrodes is less than that of the arc -path, theupper arc stops, and a new arc begins at the bottom of the ladder.Thus, what is seen is a continuous climbing arc that disappearsat the top of the ladder and reappears at the bottom. It's all a lotof fun to watch, providing that you don't poke your fingerbetween the electrodes or get your nose too close.

To build a Jacob's Ladder, you need a high -voltage source that

FIG. 1-HERE IS A TIME-EX0OSED PHOTOGRAPH showing the development of an arc atthe bottom of the ladder as it climbs to the top. Display Jacob's Ladder in a darkened roomfor best viewing.

FIG. 2-NOTICE HOW NEAT THE WIRINGIS. RTV cement is used around the high -voltage connection points. -he line cord'sthird lead is used to ground the case.

can deliver around 10 kilovolts at 30milliamperes or more-such as a neon -sign transformer or high -voltagepower -supply transformer. The lowerthe current output, the less chancethere is for building a fatal shock haz-ard. The higher the voltage, the largerthe separation you'll be able to makeat the top of the ladder's electrodes.

The high -voltage source should beplaced in a well -insulated case or cab-inet. If the case is metal, it should beadequately grounded. In the pho-tograph in the opening of this article,a 7 -kilovolt transformer was placed ina 1/4 -inch Plexiglas case with the pri-mary winding connected via fuse andswitch to the 117 -volt AC input. Theoutput of the transformer was con-

nected via high -voltage TV anodehook-up wire to two pieces of no. 12copper wire used for the vee-shapedelectrodes that protrude from por-celain insulators. When removing theinsulation, be sure not to nick thewire. The connections between thetransformer's secondary and the bot-tom of the insulators must be kept asshort as possible and void of sharpbends (see Fig. 2). Exposed high -volt-age points were given a coat of RTVsilicon rubber to prevent any arcinginside the enclosure.

Adjustment and operationThe last step in getting your Jacob's

Ladder to work is the adjustment ofthe vee electrodes. DO NOT MAKEANY ADJUSTMENTS WHEN THEUNIT IS TURNED ON. The unitshould be turned off and unpluggedwhen making adjustments, to preventaccidental electrical shocks.

The electrodes must be closeenough at the bottom to establish thespark or arc -over, with the wires gent-ly angling away from one another toform the "V." The initial distance atthe base to start the spark will varywith the voltage applied, humidity,altitude, etc.; so, it's pretty muchdone by trial and error. Start with thewires at the base about an inch apartwhen using 10 kilovolts or more, andmove them closer in small incrementsuntil an arc is established. But re-member to kill the power before eachadjustment.

When the distance is correct, thearc should start. On the other hand, if

the ladder arcs at the initial setting,move the wires apart until an arc isjust sustained. Placing the wires tooclose together will ruin the trans-former over time. When you have es-tablished the arc, if it does not moveup between the two diverging wires,they must be adjusted in or out.

Better safe than sorryOnce your Jacob's Ladder is up and

running, a clear Plexiglas or acryliccylinder around the entire unit willprevent the unthinkable from happen-ing (see Fig. 3). The clear plastichousing should have vent holes at thetop and bottom to allow heated gassesto escape, but not so large that thesmallest child in the family can get hisor her mitts or anything else inside.Generally, such cylinders can be pur-chased from most plastic -supplyhouses rather cheaply, and are wellworth the added protection.

You do have to keep in mind that suchhigh voltages are extremely dangerous,and you certainly don't want to come incontact with them.

FIG. 3-A PLASTIC SHIELD SHOULD BEUSED to prevent inquisitive people fromaccidentally touching the arc or the elec-trodes. Be sure to include a vent hole atthe top and bottom of the shield so thatgasses produced by the arc are allowed toescape.

SOLID-STATE TESLA COIL(Continued from page 64)

fahnestock clips are mounted to the board on V2 -inch alumi-num spacers, using #6-32 hardware. A 13/4 -inch length of#12 solid -copper wire is fitted in one end of a 13/4 -inch pieceof dowel rod to produce the adjustable terminal of the sparkgap. The other gap wire must be made from a #26 or smallerwire for the gap to perform properly.

Place the four dowel rods in the baseboard, position the 9 -inch deck on top, and press down until all four dowel rods areeven with the top of the circle. Connect the bottom of LI,using a short length of #12 wire, to the main grounding point(see Fig. 3). Also connect the bottom end of L2 to the samepoint.

A separate vertical ground rod can be positioned on thedeck (see photos) for additional experimenting. The verticalground was made from a 29 -inch length of 1/4 -inch threadedrod, and covered with a section of aluminum tubing to give aneat appearance. At the top, a binding post was mounted forversatility. That allows the ground rod to accept a number ofdifferent experimental items.

Checking It OutBefore we start this stage of construction, a word of warn-

ing is in order:Do not touch or make any adjustments while power is

applied to the Solid -State Tesla Coil. Remember thatyou'll be dealing with high voltages, so caution is thewatchword.

With the power off, set the spark gap for a 1/4 -inch gap and

connect the tap clip to turn 15 or 16. Plug in the power cordand turn SI on. A loud electrical discharge should be heard,and a blue brush discharge should be seen at the top of thepointed screw that's connected to L2.

Turn the power off and move the tap wire (that's connectedto LI) up or down one turn at a time until the greatest bluedischarge is obtained at the top of L2. Form a 11/2 to a 2-inchvertical gap between the ground rod and the top of the coil toaid in tuning up the coil. When the Tesla coil is properlyadjusted, it should produce a 2 -inch arc between the top of L2

and the ground terminal.The coil discharge is most dramatic in a darkened room,

and you should be able to light a fluorescent lamp at adistance of about two feet from the secondary coil. A clearincandescent lamp moved to within a few inches of thesecondary coil will produce a beautiful blue lightning arrayfrom the lamp's filament to the outer edge of the glassenvelope. Neon lamps glow around the coil without wires.Experimenting with the coil can be an almost endless adven-

ture. But remember, always put safety first!

VAN DE GRAAFF(Continued from page 60)

A powerful static charge builds up onthe spherical terminal. In a dark room,you will be able to see long, thin, bluishbolts of artificial lightning jump be-tween the upper terminal and thebase. It's a fantastic sight!

Experiments. Gaseous tube illumina-tion and spark production are only twoof the many interesting things you cando with your Van de Graaff generator.Here are just a few of the others: Obtain some foam plastic packingmaterial and break it up into smallpieces. Turn on your generator and al-low it to run for a few moments. Now,drop the plastic bits, one by one, on topof the spherical terminal. They land onthe aluminum, sit there for a second,and then shoot off! Some of the plasticmay fly for a distance of one or two feet.When the material makes contact withthe terminal, it picks up an electriccharge. Since like charges repel, theplastic is thrown off the surface . Find some very thin aluminum foiland carefully cut it into strips about 1/4 -to 1/2 -inch wide and about 8 incheslong. Tape the strips to the top of theterminal. Make sure the foil is makinggood electrical contact with the alumi-

num sphere. Turn on the generator. Thestrips will be repelled from the terminaland from each other. Now approachthe sphere slowly with the palm of yourhand. The strips will be attracted mag-ically to your fingers! You can also use your generator tocreate what is sometimes called an"electric wind." Locate a narrow metalrod about 9- or 10 -inches long. Tapeone end of the rod to the top of thespherical terminal. Make sure that thisend of the rod is entirely covered withtape, and, once again, check for agood electrical contact. Turn on themachine. Next, light a household can-dle and approach the free end of therod with the candle flame. As mole-cules of ionized air rush from the metaltip, the flame will be blown to one side.

These experiments just scratch thesurface of what you can do with yourgenerator. The book, Nature's Electricityby C.K. Adams (Tab Books, Blue RidgeSummit, PA 17294) contains many otherinteresting experiments that can beperformed with your Van de Graaffgenerator, as well as other static -elec-tricity experiments.

A word of CAUTION: When you workor play with high voltages, you can beinjured or killed. Always proceed withcaution. If you are a minor, obtain theassistance of an adult.

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67

Abroken water pipe can be anexpensive repair job. The re-pair leaves you with walls torn

apart, floors ripped up, and wehaven't even mentioned the waterand construction damage to rugsand furniture. In Texas where I live, thenumber of times during the winter itfreezes hard enough to break pipescan be counted on the fingers of onehand. However, only one mishap isenough to cost significant money.Also, since freezing weather is some-thing we Texans normally let the folksup north deal with, most of our houses(and the plumbing in them) are notreally designed to withstand theweek-long plunges below 20 de-grees. For example, I have a few out-side faucets that insist on freezing atevery opportunity. Putting covers overthem works for a short time, but inextended freezes, they freeze-up sol-id. Letting them drip is often a surecure, but after a week of dripping, alot of water is wasted and somemighty respectable ice cones havebuilt up.

While there are many things youcan do to winterize your house in gen-eral (see the boxed text entitled "AWinter Arsenal") I wanted a solution tothis yearly nuisance in particular. Thesolution had to be simple, reliable,and able to work totally unattended.My solution was to build a circuitcalled the Freeze Fighter that auto-matically warms outdoor faucetsonce the temperature drops to thefreezing point.

The Design Process. I wanted to goon vacation, leave the house, and letthe system handle any "blue norther"that might blow in. Therefore I neededa device to sense temperature andtake appropriate action. Fortunately,National Semiconductor makes an in-tegrated circuit that is designed tosense temperatures and turn deviceson or off with changing temperatures.This IC is the LM3911; an 8 -pin devicecontaining a voltage reference, atemperature sensor, and an op -amp.With the addition of a few resistors, thisIC can be configured into a completetemperature controller that will switchan external load with rising or fallingtemperatures. Now I had to figure outhow to take the on/off signal gener-ated by the controller and use it tokeep the faucets warm.

FREEZE FIGHTERKeep your outdoor faucets warm in cold weather,and control your air conditioner in the summer.

BY DAVID H. PENROSE

Luckily, very little energy is neededto keep a faucet from freezing. A fewwatts of power should keep most fau-cets cheerfully warm. I decided tostrap a 50 -ohm, 10 -watt resistor to thefaucet using a hose clamp, and thenapply enough voltage to produceabout five watts of heat. I determinedthat a 13 -volt, AC -to -AC adaptor,which will result in about 4 watts whenterminated in the 50 -ohm resistor,would be adequate. A 50 -ohm re-sistor with 13 volts across it is going topull about 300 milliamps. The adaptoris rated at 800 milliamps so the adapt-er was chosen with that current rating.I do not recommend using a DCadaptor for any extended period,since in a wet environment, a platingeffect could occur which would even-tually destroy the connections at theresistor.

The only problem left to solve washow to take the small control voltageavailable from the controller, and useit to turn the 13 -volt supply on and off.

The application notes on the LM3911show a method of controlling a relayor similar device using a transistorswitch. This would work fine if there wasjust a single faucet to protect, but myhouse has three that are vulnerable tofreezing. I didn't want to string wirefrom one to another and use multiplecontrol relays, nor did I want to pro-duce three copies of the control cir-cuit.

Radio Shack's universal interface fortheir "Plug'n Power" home controllersprovided a solution. The interface willaccept almost any kind of signal on itsinput, and will activate any number ofremote modules through the housewiring when the signal is received.Adding a matching remote-con-troled appliance module or a specialwall outlet (both available from thesame source) completes the system.Figure 1 illustrates the major compo-nents of the system and how theymight be used to protect two faucets.Note that both a controled outlet and

CONTROLLEDOUTLET 1":"/ \

=2'

d=. Et

UNIVERSALINTERFACE

TEMPERATURECONTROLLER

13VTRANSFORMER

A10 -WATT

RESISTOR

12VDCADAPTER

APPLIANCEMODULE

13VTRANSFORMER

10 -WATTRESISTOR

Fig. I. A few components must be added to the temperature controller to complete theFreeze Fighter. This illustration shows two options for the remote devices: a remote-controled outlet and a plug-in controller.

an appliance module are shown toindicate how both are connected.Before discussing the Freeze Fightercontrol circuit, it would be wise to ex-plain a little about the operation ofthe LM3911 and the interface mod-ules, so I'll deal with them next.

All -in -One Temperature Control-ler. As mentioned, the heart of theFreeze Fighter is an LM3911 Tempera-ture Controller IC. As you can see inFig. 2, this clever IC incorporates avoltage reference, a temperaturesensor, and an op -amp all in one 8 -pin package. The voltage referenceallows this chip to operate over awide temperature range and also al-lows the unit work with accuracy overa wide power -supply range. The refer-ence is a 6.8 -volt active shunt reg-ulator connected between pins 1 and4 of the IC. In order to operate prop-erly, this reference must be wired inseries with an external current -limitingresistor. The selection of this resistorand the input voltage determines inpart how much power is dissipated bythe package. The application infor-mation on the LM3911 recommendsvalues ranging from 3.5k to 12k de-pending on the application.

The sensor incorporated in the ICproduces an output voltage that is di-

rectly proportional to temperature indegrees Kelvin at 10mVPK. The sensoris powered by the internal referenceand feeds the positive input of the on-board op -amp. If the output of thisop -amp is tied back to the feedbackinput on the package, the 10mVrKwill be available for external use.

FEEDBACKINPUT

03

1.16.8V

SENSOR

4o V+

2()OUTPUT

Fig. 2. There are only a few buildingblocks inside the LM391I: a voltagereference, a sensor, a comparator, and apull-up network.

The internal op -amp can also beconfigured as a comparator. This isthe mode used for the Freeze Fighter.To use this mode, the feedback inputpin is supplied a voltage that corre-sponds to the desired temperaturesetting. The internal op -amp thencompares this voltage to the voltage

being generated by the sensor andswitches high or low if the tempera-ture is lower or higher than the setpoint. The passive output of the op -amp is pulled high by an internal re-sistor and series diode.

Remote -Control Using House Wir-ing. The universal interface controllerand the remote -controlled outlet orappliance module used in the FreezeFighter are only a few selections froma wide array of different home -auto-mation devices available from RadioShack, Heathkit, and other suppliers.The devices all use an interface ad-hering to the X-10 standard to sendcontrol signals over a home's AC -power lines. These devices have ex-isted for a number of years and havegone through a number of refine-ments to make them more reliableand flexible.

The universal interface controller isa remarkable device in that it allowsalmost any type of control input togenerate command signals to otherdevices in the house. The controllercan accept a switch closure, or a low-level AC or DC signal at its input. It canthen turn on one or more devices thatmatch the address set through switch-es on its faceplate. The control inputscan be momentary or continuous,and the controlled devices can beturned on or flashed.

This device was obviously designedas an interface for alarm circuits, but itis also perfect for computer control. Acomputer can easily generate theoutput signals required to control re-mote devices. Granted, the devicecan only address devices corre-sponding to its switch settings, but thisis usually not a major limitation. For thepurposes of the Freeze Fighter, theController works perfectly.

The remote -control devices comein a number of different packageswith a variety of functions. The devicesrecommended in this article are de-signed to be used to turn an appli-ance on and off. Other units that aredesigned for incandescent lights canvary the brightness of the light over anumber of steps. These devices arenot appropriate for the Freeze Fighter,and can cause the user significantproblems if accidentally connectedto fluorescent lights or other devicesthat allow only on/off control.

Little difficulty should be encoun-

tered in using the devices, since mostof them just plug in. In some cases,devices plugged into different legs ofthe house's power line may not beable to communicate with eachother. However, some means do existto correct this problem. One methodis to place capacitors across the dif-ferent legs of the power line at thehouse's junction box. If you encounterthis problem, I would recommendthat you search around for outlets thatdo share a common supply leg,rather than paying an electrician toinstall the capacitors. I would neverrecommend attempting to installthese capacitors yourself.

Winterizing.

The Freeze Fighter is only one weaponin the war against winter. A homeownershould be prepared with both activeand passive defenses against freezingtemperatures

One of the best passive tools is pipeinsulation Sections of foam tubes canbe bought that easily wrap around ex-posed pipes This wrap helps trap theheat of the water and thus prevent freez-ing during mild freezes A properly de-signed house will have all exposedpipes covered with this tubing or someother form of pipe insulation Housesdesigned to withstand the killer freezesof the northern climates will have all thepipes protected within the warm core ofthe house Faucet extensions allow thewater carrying pipes to be inside theinsulated walls while the controis andoutlets are on extensions that are ac-cessible from outside the house Anideal configuration has a separate sys-tem for pipes that are in danger of freez-ing so that this system can be turned offand drained during winter In milder cli-mates. these precautions are overkill,and most of the time a foam bonnet onthe exposed faucets prevents disaster

Active defense systems consist of theFreeze Fighter described in this articleand the electrical heating tape that canbe wrapped around pipes This tape ispowered by house current and can bepurchased in a number of differentlengths, with or without built-in ther-mostats This tape is an excellent de-fensive measure for those houses withexposed pipes that are prone to freez-ing This tape should be used in accor-dance with all the instructions thatcome with it Tape which is improperlyused can destroy plastic pipes or evencause fires The tape should not beplaced in walls or other enclosedspaces. nor should it be overlapped onitself Power consumption is minimalthe cost of warming pipes is consider-ably less than that of replacing themafter they break

The Circuit. The LM3911 requiresvery few external components to im-plement a full -function temperaturecontroller. Figure 3 illustrates thesimplicity of the Freeze Fighter circuit.The resistor network consisting of R1,R2, and R3 is used to provide the set -point voltage for the feedback inputof the LM3911.

R1

15K

R210K

Fig. 3. The LM39I I requires only a fewresistors and a capacitor to turn into afull -function temperature controller.

PARTS LIST FORTHE FREEZE FIGHTER

RESISTORS(All fixed resistors are 1/4 -watt, 5e4.

units.)R1 -15,000 -ohmR2 -10,000 -ohm miniature trimmer

potentiometerR3 -24,000 -ohmR4 -7,500 -ohmR5 -10,000 -ohm

ADDITIONAL PARTS AND MATERIALSCI -0.1µE ceramic or Mylar capaci-

torUl-LM3911 temperature controller,

integrated circuit (Digi-KeyLM391lN)

Universal interface module (RadioShack 61-2687), a 12 -volt DC adapt-or, a case with perfboard, jacks andplugs if desired, wire, solder, etc.For each faucet you'll also need a 13 -volt, 800-mA power transformer, a50 -ohm, 10 -watt resistor, a hoseclamp, and an appliance controller(Radio Shack 61-2681 or 61-2684) orremote -controlled outlet (RadioShack 61-2685).

Resistor R4 limits the current throughthe internal voltage reference of theLM3911 and can be selected from awide range of values. I chose 7.5k,which is specified in most of the ap-plication notes.

Resistor R5 pulls the output of the IChigh when the temperature is belowthe set -point. The internal 50k resistorprobably would have been sufficient

for this project, but I included the ex-ternal 10k resistor just to be safe. Theinternal resistor is in series with a diodethat allows a switching voltage up to35 volts to be used with the device. Forthe Freeze Fighter, 12 volts is ade-quate.

If ultimate reliability is required, dis-pensing with R2 is a good idea. To dothat you should wire the circuit asshown, calibrate R2 with the pro-cedure that follows a little later, re-move R1 -R3 from the circuit, andinstall larger values for R1 and R3 toaccount for the absence of R2 basedon the calibration setting of R2.

Capacitor C1 is placed across thewiper of the variable resistor to limitnoise that may be present. These fewcomponents complete the circuitand provide the interface required bythe universal interface module. If theapplication had required switching avoltage on with a rising temperature,an additional transistor would havebeen required on pin 2 of the IC toinvert the output.

Construction. Any typical methodof construction (point-to-point wiring,wire-wraping, or PC -board mounting)is suitable for this project. I chose touse point-to-point wiring on a perf-board that comes with its own plasticcase. If you choose to do the same,clean the perfboard well with somesteel wool or other cleansing agent toinsure that the copper pads are freeof all oxidation. I soldered the IC di-rectly to the board rather than using asocket to avoid the potential corro-sion problems that may developwhen the circuit is used outside overextended periods.

One additional caution when work-ing with this IC: the positive voltage isattached to the bottom leg of thepackage (pin 4) where most other IC'shave the ground attached. Theground on this IC is attached to pin 1which is the top pin. Confuse thesepins and the temperature -controllerIC becomes a fuse.

Once you have your own tempera-ture controller mostly built, you mustdecide on a power source. I poweredmy circuit from an AC adaptor I hadavailable. If you don't have one inyour junkbox, purchase a small 12-15volt DC unit. The circuit draws very littlecurrent, so any adaptor rated at asuitable voltage will do.

I mounted the perfboard in thecase with the components facing theplastic rather than the aluminum faceplate, and drilled a number of holes inthe side of the box to insure that thesensor was exposed to ambient air.Use caution when drilling these holesso as to not drill through the supportsfor the PC board, which are at thecorners of the box. Power is suppliedthrough a DC coaxial jack and theoutput is terminated in a 2 -conductorminiature phone jack. These jacks arenot necessary and could be re-placed with direct connections. I in-cluded them because it makes iteasier to string the power and signalconnections through small openings.

Calibration. Now it's time for calibra-tion. The relationship between thevoltage at pin 3 of U1 and the desiredtemperature set -point is 10mV/°K.Since absolute zero Kelvin is equal to-273.4°C, a temperature of 0°C willresult in an output voltage from thesensor of 2.734 volts. The resistor net-work values were chosen so that thesame amount of voltage is obtainedwith the wiper of variable resistor R2near its mid -point, so start by settingR2 to its middle position.

You will be required to check thevoltage set by R2 shortly. However, becareful when measuring this valuebecause the IC is not looking for avoltage referenced to ground, but in-stead is looking at the difference be-tween the voltage at pin 4 and thisset -point voltage. That seems simpleenough until you fall back on old hab-its of connecting the black lead of themultimeter to ground and then mea-suring the voltage at pin 3. It took me afew minutes to realize that the circuitwas working properly but that I wasn't.

That said, connect the black probeof your meter to pin 3 and the redprobe to pin 4. Apply power and ad-just R2. As you adjust the voltage youshould find a point at which the circuitjust switches on or off. At normal roomtemperature that should happen atabout 2.98 volts, which is 250 millivoltsabove the zero point of 273 volts, Thepresence of 250 millivolts at 10mV/°Kwould indicate a room temperatureof about 25°C. Now adjust R2 until youget as close as possible to 2.734 volts.This should calibrate the unit for thefreezing point.

You can verify the calibration with

NIGHTLIGHT

MULTI -TAPADAPTER

5052

10 WATTS

13 VOLTAC

ADAPTER

A

LED tiB

Fig. 4. If you want to monitor theoperation of one of the faucet stationsyou could augment it with a cubeadapter and a night light (A), or aresistor and LED (B).

just a little extra work. First place thesensor in your refrigerator and verifythat it does not switch on, move it toyour freezer and in a few minutes itshould switch on.

Set Up. On the Plug'n Power inter-face connect the terminal labeled" + " to the output from pin 2 on thetemperature controller. Connect the" " terminal to the ground connec-tion of the temperature controller.Make sure you have set the modeswitches on the interface for an on/offcontrol of the addressed device ("in-put select" to 1 and "mode select" to3), then select the house code andunit code settings you wish to use forall the devices. The remote units mustbe set to the same house and unitcodes.

I placed the controller outside neara window and ran the wire betweenthe window and the frame. The sealson my windows allowed this. If thiswon't work on your window, you'll haveto find some other way of exposingthe controller to the outdoor temper-ature. If you must drill through the wall,plug the opening with caulk to keepthe bugs out, and put a loop in theportion of wire that is outside to keepthe rain from following it in.

Plug a 13 -volt transformer into eachremote module and run its leads out-

side as you did for the temperaturecontroller. Use common sense in plac-ing the resistor's transformers (and thusthe remote modules); they can getwarm when operating and should nothave any drapes or flammable mate-rial near them. Connect each trans-former output to its intended high -wattage resistor and cover the jointswith high -temperature tubing. Avoidplastic that could melt at the elevatedtemperature. Physically attach each10 -watt resistor to its faucet with ahose clamp and you are done.

Improvements. I put foam coversover the faucets and taped a temper-ature sensor from an electronic ther-mometer (Radio Shack 63-842) to thefaucet to monitor the effect of theheater until I was comfortable with it.You might do the same, and then ad-just R2 until the desired effect isachieved. If a you wish to have anoperation indicator for each faucetstation, you can put a multi -tapadaptor on the remote unit and in-clude a small night light to indicatewhen the unit is activated (see Fig. 4A).An even more fool -proof device is il-

lustrated in Fig. 4B. There, the currentflowing through the load resistor in-duces a voltage drop in a monitoringresistor. The voltage drop can be usedto power an LED. Make sure the wat-tage of the monitoring resistor is largeenough so if the load resistor shorts -out, the full load current will not causeany damage.

Summertime. This same controllerwith minor modifications can be usedin the summertime to help control theair conditioner in your house. To usethe controller in that way, rewire it toinclude an inverting transistor on theoutput lead. Mount the heating re-sistor under the air conditioner's ther-mostat and set the thermostat to ahigh temperature. Now when the out-side temperature exceeds the max-imum you program via R2, theheating effect of the resistor will turnon the air conditioner. This will takesome careful adjustment of the re-sistor because eventually you wantthe air conditioner to turn off.

The Freeze Fighter can be used inmany more applications around thehome and in the car. Let your imag-ination work, and see what you cancome up with.

If you have a shortwave orhigh -frequency receiveror scanner that is strug-

gling to capture signals with ashort, whip antenna, andyou'd like the kind of perfor-mance that a 60 -foot long-wire antenna can provide butlack the space to put one up,consider building the AA -7 HF/VHF/UHF Active Antenna dis-cribed in this article.

The M-7 is a relatively sim-ple antenna that is designedto amplify signals from 3 to3000 megahertz (MHz), in-cluding three recognizedranges: 3-30 MHz high -fre-quency (HF) signals; 30-300MHz very -high frequency(VHF) signals; 300-3000 MHzultra -high frequency (UHF) sig-nals. Those bands are typicallyoccupied by shortwave, ham,government, and commer-cial radio signals.

ACTIVEANTENNA

Active Antennas. In its sim-plest form, an active antennauses a small whip antennathat feeds incoming RF to apreamplifier, whose output isthen connected to the anten-na input of a receiver. Unlessspecifically designed other-wise, all active antennas areintended for receive -only operation,and thus should not be use with trans-ceivers; transmitting into an active an-tenna will probably destroy its activecomponents.

A well -designed broadband activeantenna considers field strength ofthe desired signal (measured in mi-crovolts per meter of antenna length),atmospheric and other noise, diame-ter of the antenna, radiation resis-tance, and antenna reactance atvarious frequencies, plus the efficien-cy and noise figure of the amplifiercircuit itself.

Circuit Description. Figure 1 showsa schematic diagram of the M-7,which contains only two active ele-ments; Q1 (an MFE201 N -channeldual -gate MOSFET) and Q2 (a2SC2570 NPN VHF silicon transistor).Those transistors provide the basis oftwo independent, switchable RF pre-amplifiers. Two double -pole double -throw (DPDT) switches play a major

Lift hard -to -hear signalsout of the mud with

this handy receiver accessory.

BY FRED BLECHMAN

role in the operation of the M-7.Switch S1 is used to select one of theIwo preamplifier circuits (either HF orVHF/UHF). Switch S2 is used to turn offthe power to the circuit, while coup-ling the incoming RF directly to theinput of the receiver. That gives thereceiver non -amplified access to theauxiliary antenna jack, at J1, as well asthe on -board telescoping whip an-tenna.

With switch S2 in its power -on posi-tion, the input and output jacks aredisconnected and B1 (a 9 -volt tran-sistor -radio battery) is connected tothe circuit. With switch S1 in the posi-tion shown in the schematic , incom-ing RF is directed to the HF preampcircuit built around Q1 (an MFE201 N -channel dual -gate MOSFET). The HFpreamp operates with an excep-tionally low noise level, and is ideal forcopying weak CW and single -side -band signals.

When S1 is switched to the otherposition, the captured signal is cou-

pled to the VHF/UHF preampbuilt around Q2 (a 2SC2570NPN VHF silicon transistor),which has excellent VHFthrough microwave charac-teristics. With the on -boardwhip antenna adjustable toresonance through much ofthe VHF -UHF region (length infeet = 234 divided by the fre-quency in MHz), the VHF/UHFmode is ideal for indoor andportable use with VHF scan-ners and other receivers.

Either mode can be usedwhen tuning 3 -30 -MHz HF sig-nals. The VHF/UHF preamp of-fers higher gain that the HFpreamp, but also has a highernoise level. You can easilychoose either amplifier forcopying any signal of inter-est-just try both S1 positions.The RF gain control (R5) canbe used to trim the output ofeither amplifier.

Caution: The M-7 is not in-tended for transmitting oper-ations (be it ham, maritime, orCB); If it is used with a trans-ceiver of any kind, make sure itis not possible to transmit byaccidentally pressing a mikebutton or CW keyer. Transmit-ting RF into the M-7 is likely toruin one or both of the tran-

sistors in the circuit.

Construction. The M-7, which canbe built from scratch or purchased inkit form from the supplier listed in theParts List, was assembled on a printed -circuit board, measuring about 4 by413/46 inches. A template for theprinted -circuit board is shown in Fig. 2.You can either etch your own boardfrom that template, or purchase thecircuit board or a complete kit ofparts (which includes a printed -circuitboard and all parts).

The kit comes with a 16 -page kitassembly and instruction manual thatgives step-by-step assembly instruc-tions and contains additional infor-mation not covered in this article. Kitassembly time, working slowly andcarefully, should take less than anhour.

Most of the parts specified in theParts List are standard componentsand can be procured through con-ventional hobby electronics suppliers.

ANTI

J1

AUX.ANTENNA

C2.01

S1 -a R6HF/VHF 100K

C3

100pF

022SC2570

01MFE201

G2

R1

1MEG

B1 ii+0

ON/OFF I9V I

S2 -b

+ 9V

D

R3100K

S1 -b

S2 -a C5

.01

C6 J2.01 RECEIVER

0

Fig. I. The AA -7 Active Antenna contains only two active elements; Q1 (an MFE201 N.channel dual -gate FET) and Q2 (a 2SC2570 NPN VHF silicon transistor), whichprovide the basis of two independent, switchable RF preamplifiers.

4 INCHES

Fig. 2. The AA -7 was assembled on a printed -circuit board, measuring about 4 by4u/to inches. A template for the printed -circuit board is shown here.

PARTS LIST FOR THEAA -7 ACTIVE ANTENNA

SEMICONDUCTORSQI-N1FE201. 3N204. or SK3991 N -

channel, dual -gate MOSFET (seetext)"'

Q2 2SC2570, 2N5I79, or SK9I39NPN VHF silicon transistor (seetext)°

RESISTORS(All fixed resistors arc 1/4 -watt. 5(4

carbon units.)RI-- I-megohmR2 -220,000 -ohmR3. R6 -100.000 -ohmR4 -1(X) -ohmR5--10.0(X)-ohm potentiometer*

CAPACITORSCl. C2, C5, C6 0.01-µF. ceramic -

discC3-100-pF ceramic -discC4-4.7 to 10-µF, 16-WVDC.

radial -lead electrolytic


B1 -9 -volt transistor -radio batterySI, S2-DPDT PC -mount

pushbutton switch*ii, .12-PC-mount RCA jack*ANTI-Telescoping whip antenna

(screw mount)*Printed -circuit materials, enclosure.

battery holder and connector, wire.solder, hardware, etc.

Note: The following items areavailable from Ramsey Electronics,Inc. (793 Canning Parkway, Victor,NY 14564; Tel. 716-924-4560): Acomplete kit of parts (order#AA-7BP), including printed -circuit board, $24.95. etched anddrilled printed -circuit hoard only(order #AA-7PCBP), $10.00:special parts kit, containing allitems marked with an asterisk (*)in the Parts List (order#AA-7SPKBP), $14.50; customcase and knob set (order #CAA -BP), $12.95. Please add $3 fororders under $20, and $3.75 forpostage: handling. New Yorkresidents, please add appropriatesales tax.

However, some parts- - J1, J2, S1, S2,and R5- have particular physicalmounting dimensions; the board isdesigned to accept those parts. Inaddition, Q1 and Q2 can be hard tofind; however, it is possible to makesubstitutions provided that you canfind a supplier. Suitible replacements

for Q1 and Q2 are given in the PartsList.

The telescoping whip antennascrew -mounts to the board; the screwprovides contact between theprinted -circuit board traces and theantenna. To save lime and trouble lo-cating and ordering hard -to -findparts, a Special Parts IGt is also offeredby the supplier listed in the Parts List.

A parts -placement diagram for theM -7's printed -circuit board is shown inFig. 3. When assembling the circuit, beespecially careful that transistors Q1and Q2, and electrolytic capacitorC4, are oriented as shown.

Although not shown in the sche-matic (Fig. 1) or the parts -placement(Fig. 3) diagrams, an optional LEDpower indicator can be added to thecircuit. Adding a power indicator tothe circuit allows you to tell at aglance if the circuit is on; leaving thecircuit on, even though the AA -7draws only about 0.7 mA, will even-tually discharge the battery. Ofcourse, adding an LED will increasethe current drain by about 7 mA, butthe red glow makes it obvious whenthe unit is on.

If you decide to include the indica-tor in your project, power for the in-dicator can be easily taken from theswitched 9 -volt DC terminal of S2(center terminal, right side, looking atthe top of S2). Simply connect thepositive voltage to the anode (longerwire) of the LED and connect thecathode lead through a current -limit-ing resistor of about 1000 ohms to aground point on the printed -circuitboard, or as the author did from theframe of R5. Mount the LED at any

TYPES OF ACTIVE ANTENNAS

The RF preamplifier section of an activeantenna may be of several differentstyles. A fixed -tuned preamplifier hasthe greatest gain for the specific fre-quency of operation. but is limited toonly that frequency A variable -tunedamplifier can be peaked within a rangeof frequencies. but the circuitry is morecomplex and expensive. and tuning re-quires constant resetting whenever thereceiver frequency is changed. Abroadband preamplifier doesn't requireany tuning, making it very versatile andeasy to use, but has less gain at anyspecific frequency The AA -7 describedhere, for simplicity and low cost, is of adual broadband design.

ANTI"

R6

J1

R5

-J--R4 -

-C6-

C2 -05-

-R1- +C4

S2

J2

ANTENNA RECEIVER

Fig. 3. When assembling the AA -7's printed -circuit board, he especially careful thattransistors QI, and Q2, and electrolytic capacitor C4, are oriented as shown in thisparts -placement diagram.

convenient point near the switch.Although not supplied with the kit, a

custom plastic enclosure (with frontand back panels, and knobs for theswitches and gain control) is offered inthe Parts List. The enclosure comespre -drilled and silk-screened with theappropriate legends for all the circuitcontrols and connectors, but is notequipped with holes for the whip an-tenna or the LED (if you include one).

Use. Prepare a coaxial cable to connect the RF output of the AA- 7 to theantenna input of your receiver orscanner. One end of the intercon-necting cable must be terminatedwith an RCA phono plug; the otherend connector depends on the tar-

get receiver. With some receivers, theonly practical connection is to clip theoutput of the AA -7 to the receiver'santenna, although that connectionmethod won't be as effective as con-ventional (ground -return type) coup-ling.

To increase signal strength, es-pecially for the lower frequencies, youcan connect a simple supplementaryportable antenna of any design (adipole, a random -length wire withEarth ground, a bigger vertical whipof some kind, etc.) to the circuit. Justuse a small -diameter coaxial cableterminated in an RCA plug for matingwith J1.

No alignment is required, If you're(Continued on page 112)

Iions are defined as electricallycharged atoms. Positivelycharged ions have a deficiency

of electrons, and negatively chargedions have a surplus of electrons. An ioncan also be classified as an atom ormolecule with an electrostaticcharge. Another classification of anion is a charged particle that isformed when one or more electronsare taken from or added to a pre-viously neutral atom or molecule.

The Ion Detector described in thisarticle can be used to detect thepresence, and indicate the relativeamount, of free ions in the air. The Ion

Detector, a handheld unit about thesize of a pack of cigarettes, is de-signed to indicate ion emissions fromion generators, high -voltage leakagepoints, static -electricity sources, elec-tric -field gradients, and in other situa-tions where the presence of ions or ameasurement of their relative fluxdensity is required.

The front cover features, a sensitivitycontrol with on -off switch, a high -fluxindicator lamp, and a panel meter. Anantenna, mounted on the top of theunit, serves an external ion collector. Astrip of metallic foil on the outside ofthe plastic enclosure touches theusers hand and is used to ground theunit. For fixed applications, the stripcan be replaced by a wire con-nected to ground.

Circuit Description. Figure 1 showsa schematic diagram of the Ion De-tector-a rather simple circuit consist-ing of three transistors, (two PN2907PNP units, and a single PN2222 NPNunit), three resistors, an antenna, andan LED.

In that circuit, a telescoping anten-na is used as the pickup. In the pres-ence an ion field, ions accumulate onthe antenna, causing a minute nega-tive current to flow to the base of 01.Capacitor C1 and resistor R1 form anRC network, whose function is to elimi-nate any rapid fluctuations. Once thenegative current becomes largeenough, it causes Q1 to turn on, con-necting the negative terminal of bat-tery B1 to the base of Q2. That forwardbiases Q2, causing it to turn on. That, inturn, couples the base of 03 to thepositive terminal of the battery, for -

Buildan

Ion Detector

ward biases Q3-whose collector is inseries with current -limiting resistor R2and meter -sensitivity control R3-causing it to conduct.

With Q3 turned on, meter M1 indi-cates (in a non-linear manner) the rel-ative level of ion flux, while LED1(which is connected in series with 03'semitter) lights to give a visual indica-tion of strong ion fields. It should benoted that in order for the unit to oper-ate properly, some sort of ground isusually required.

Metallic tape is used in the pro-totype to provide a convenient con-tact for the users hand, therebyproviding a partial ground. If possible,such as when the unit is used as amonitor at a permanent location, thedetector should be grounded to awater pipe, or some other convenientgrounding point.

The detector is set up to detectnegative ions. It can be made to de-tect positive ions by simply reversingthe polarity of the transistors that com-prise the circuit; i.e., PNP units becomeNPN units, and the NPN transistor isreplaced by a PNP unit. It should notethat the performance of the detectoris seriously affected by high humidity.Damp or moist air tends to impair thecircuit's ability to detect ion flux.

The Ion Detector can be used togive a quick indication of the pres-ence of a negative ion field, aid inidentifying its source, and indicate itsrelative strength, but it is not designedto provide an absolute measurementof flux intensity. The circuit can also beused to aid in making adjustments toion sources, by noting the meter'sneedle deflection as you attempt toincrease or decrease ion emissions.The Ion Detector can also be used toferret out residual ion fields, check forion leakage (in shielding tests, for ex-ample), or to test for static charges (inpeople's clothes, fluorescent lighting,

BY VINCENT VOLLONO

This simple circuit lets you track down sourcesof high -voltage leakage, static build-up, and more.

ANTI

The author's prototype of the IonDetector was housed in a small plasticenclosure, measuring about zIct, by 2f/Nby Pim inches. Note the strip of taperunning along the side of the enclosure.which is used to ground the circuit viathe user's hand contact. The strip can besupplemented or replaced by a wireconnected to the same point in thecircuit and terminated at the other endwith an alligator clip.

plastic containers, certain winds, etc.),along with a host of other applica-tions.

Construction. The author's pro-totype of the Ion Detector was as-sembled on a section of perfboard,using point-to-point wiring for inter -component connections. Pay closeattention to the orientation of the po-larized components (diodes, tran-sistors, electrolytic capacitors, etc.), aswell as the polarization of the DCsource that will power the circuit,when assembling the circuit. It is veryimportant that you verify all your inter-connecting wiring.

It is highly recommended that thecircuit be enclosed in a plastic projectbox. Once the circuit is completed, a1/2 -inch wide strip of aluminum is at-tached to the side of the enclosure,and is then connected to the circuit

R1

100MEG1/2W 1

01

PN2907

ci7±170pF

ALUMINUM TAPEOR

EARTH GROUND'

02PN2907

"SEE TEXT

03PN2222

R2

LED1

Si.o -

10K M1r - - - - 100mA

R3'5K

B1 I9V

Fig. I. The !on Detector is a rather simple circuit consisting of three transistors, (twoPN2907 PNP units, and a single PN2222 NPN unit), three resistors. a telescopingantenna (which is used as the ion pickup), and an LED.

PARTS LIST FOR THEION DETECTOR

Q I Q2-PN2907 general-purposePNP silicon transistor

Q3-PN2222 general-purpose NPNsilicon transistor

LEDI-Light-emitting diodeR 1-100-megohm, v:! -watt, 5(4

resistorR2 -10.(X0 -watt,

resistorsR3-5(XX)-ohm potentiometer I see

text)C1 -470 -ph ceramic -disc capacitorMI-100-mA panel meterB1 -9 -volt transistor -radio battery.SI---sce text


F'erfboard materials, plasticenclosure, 9 -volt battery holderand connector, wire, solder,hardware. etc.

board (at the junction of C1, thepositive lead of the panel meter, andthe positive terminal of the battery) asshown in Fig. 1. The aluminum stripserves as the circuit's grounding point.That grounding strip can be replacedor supplemented by a wired alligatorclip for connection to a "true" earthground (a water pipe, for instance),

The author used a telescoping an-tenna as the ion pickup in his pro-totype unit; however, a piece of stiffwire (a wire hanger, for example)would also work. In either case, theantenna must be electrically isolated;i.e., it should not be connected to

ground in any way. Note that S1 (theon -off switch) is piggy -backed to po-tentiometer R3 (a 5k potentiometerthat serves as a the meter's sensitivitycontrol). You can also use a potenti-ometer with a piggy -back switch oruse two separate components.

For meter M1, the author used asmall 100-mA panel meter; using ameter with a rating other than thatspecified may effect the perfor-mance of the unit. It is alsoto remember that any leakagearound the input of Q1 will reduce thecircuit's sensitivity. To help prevent (orat least reduce) leakage, the circuitcan be coated with a high -qualityvarnish. If you decide to coat the cir-cuit, make sure that the unit is com-pletely clean and dry before apply-ing the varnish.

Use. To demonstrate the unit's sen-sitivity, run a plastic comb throughyour hair, and place it near the anten-na of the Ion Detector. Making surethat the unit is grounded (either by theuser touching the aluminum strip or byconnecting an earth ground to thecircuit), bring the comb near the an-tenna. As the comb is brought nearthe antenna, you'll note a needle de-flection on the meter (indicating thepresence of ions), and LED1 lights. Asthe detector is brought closer to theion source, the meter needle shoulddeflect harder. If the needle deflectstoo hard (pegs), R3 can be adjustedto bring the meter reading on scale.

That's all there is to it. While the IonDetector is not a precision instrument,it can come in handy in yourworkshop or laboratory.

ELECTRONICS LIBRARY

(Continued from inige 13)

The JuniorTechnician'sDiscovery Guideto HowElectricity Works

by Gene McWhorter

- ftylltr,

amples, the book guides junior -high and older students throughthe principles of electricity. Top-ics covered include atoms,protons, electrons, and neu-trons and how their chargesattract or repel one another;motor action and how it is pro-duced; voltage, current, andresistance; and magnetic fields.Each chapter includes applica-tions for various projects andexperiments, and ends with aself -test for what the studenthas learned about electricity.Bold two-color graphics areused in the book and are de-signed to hold a the youngreader's interest.

The Electricity Book costs$14.95 and is published byPrompt Publications, Howard WSams & Company, 2645 Water-front Parkway, East Or,Indianapolis, IN 46214; Tel:317-298-5710; Fax:317-298-5604.


THE MODERNCONVERTER ANDFILTER CIRCUITENCYCLOPEDIAby Rudolf F Graf

This book contains a large as-sortment of ready -to -use circuitssure to meet the converter andfilter needs of engineers, techni-cians, students, and hobbyists.Representing state-of-the-arttechnology, the circuits includeanalog -to -digital and digital -to -

analog converters; current -to -voltage and frequency -to -volt-age converters; temperature -to -frequency converters; frequencyconverters; and band-pass,high-pass, low-pass, notch,noise, and state -variable filters.For easy reference, the circuitsare arranged alphabetically byapplication. Each entry includesa schematic and a brief expla-nation of how the circuit works.

the modern

CONVERTERAND

FILTER CIRCUITENCYCLOPEDIA

RUDOLF F GRAF,

The Modern Converter andFilter Circuit Encyclopedia costs$12.95 and is published by TabBooks Inc., Blue Ridge Summit,PA 17294-0850; Tel:800-233-1128.


1994 CATALOGfrom Radio Shack

Radio Shack calls its largestcatalog ever an "encyclopediaof electronics." Within its close -to -200 pages, are featured morethan 75 electronic "BuzzWords," brief definitions ofterms. In several product cate-gories, helpful hints for smartshopping also are included, andcharts make it easy to makefeature -by -feature comparisonsof each product offered. A pageof money -saving coupons isalso included.

The full -color, perfect -boundcatalog features more than3000 performance -tested prod-ucts that fall into suchcategories as audio, video,computers, telephones, do-it-yourself, automotive, communi-cations, and home and family.New products include such in -

Radio Mae*

novative items as America's firstDigital Compact Cassette(DCC) recorder and the TandyZ-PDA Personal Digital As-sistant, as well as the OptimusProfessional Series of audiogear, Optimus home -theaterequipment, two stereo satellitesystems, a mobile CB radio withdigital signal processing, andtwo multimedia personal com-puters (MPC).

The 1994 Catalog is availablefor $2.95 at more than 6600participating Radio Shackstores nationwide. For more in-formation, contact Radio Shack,700 One Tandy Center, FortWorth, TX 76102.


REPAIRING IBM PCsAND COMPATIBLES:An Illustrated Guideby Michael F Hordeski

Written for anyone who uses,manages, maintains, or repairsPC's, this book is based on thephilosophy that the better yourunderstanding of your comput-er's design and operation, theeasier it is to discover when andwhy they are not working cor-rectly. With that aim in mind, thebook thoroughly explains thearchitecture of the IBM-PC fam-ilies and compatible computers.defines common buzzwords

airing IBM PCsnd Compatibles

Illustrated Guide

and acronyms, and detailseffective troubleshooting tech-niques.

By learning how to maintainyour system, you can reducedowntime and its inherent costs.Packed with time- and money-saving diagnostic and repairtips, the book explains themany ways that a PC can fail,how to detect those failures,and how to make the appropri-ate repairs. Data disasters aswell as hard -drive difficulties are

covered.Repairing IBM PCs and Com-

patibles: An Illustrated Guidecosts $19.95 and is publishedby Windcrest/McGraw-Hill, BlueRidge Summit, PA 17294-0850;Tel 1-800-233-1128; Fax:717-794-2103.


RIDING THE AIRWAVESWITH ALPHA & ZULUby John Abbot

If you'd like your children to gettheir Amateur Radio Novice orNo -Code license but couldn'tget them to finish reading alicense manual, this book couldbe the answer. Taking a freshapproach to teaching the ama-teur -radio question pool, it usesa family of "Phonetico" cartooncharacters that review everyquestion contained in the pool.Graphics and drawings areused in place of endless pagesof text.

Each cartoon episode is oneor two pages long and is fol-lowed by a mini exam designedto test reader comprehension.Additional teaching tools pro-vided in the book include wordsearches, crosswords, andother fun puzzles. EachPhonetico character is namedafter a letter in the Phoneticalphabet, and their bodies aremade up of the appropriate Mor-se code dits and dahs for thatletter. Youngsters and adultsalike will enjoy following thePhoneticos adventures as theyexplore and discuss the excitingworld of amateur radio.

Riding the Airwaves with Al-pha & Zulu costs $14.95 and ispublished by Artsci Inc.. P 0.Box 1428. Burbank, CA 91507:Tel: 818-843-4080: Fax:818-846-2298.


TH

WAIEETimitA PAdd the dimension of sound to your fish

tank with this one -evening

project.

BY MARC SPIWAK

Ideas for projects don't grow ontrees-usually they're the result ofwanting to do something that

can't be done without some uniquegadget. That's exactly how the ideafor this project came about. You see, Ihave a rather large freshwater fishfrom the Cichlid family known as a"Jack Dempsey" (in Latin it's calledCiclasoma octofasciatum). The fish isof a rather violent nature, even moreso than most Cichlids (hence thename Jack Dempsey). He can't bekept in a community aquariumamong peaceful fish, so he has hisown tank.

Besides being able to swallowsmaller fish whole, the Jack Dempseycan also swallow whole food pellets.These food pellets are "crunchy"when dry, and "Jack" swallows themas soon as they hit the water. One day

mwhile feeding him, I could swear Io heard a sort of "crunch, crunch"

sound just after he swallowed a pellet.

cn Now although the pellets seem like(Fn. they would be hard for a fish with no5: teeth to pulverize, apparently he canCO

03 do just that.oI Thinking about the faint yet strange2 o sounds, I wished that I could somehow

0z amplify them. I had an amplifier cir-II cult1-

cuit with an electret microphone at-(-) tached to it, but electret microphonesLu

cd shouldn't be placed underwater. IfTr only there were some easy way to wa-cr)

°2 terproof the microphone, then ito would be easy to amplify the under -E water sounds-or to at least to test theci_ca idea.78 So I wrapped the microphone in

cellophane, plunked it into the fishtank, and powered up the amp. Itworked, but at first all I heard was thefilter bubbling muchlouder than usual. After shutting offthe filter, it sounded very much likewhat you hear when you swim under-water. So then I dropped in a foodpellet, and there was that crunchingsound, loud and clear.

After listening for a while, static start-ed to replace the nautical theme. Theproblem was that the cellophanehad somehow leaked, and the micro-phone was actually exposed to water.

R3

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Clearly the microphone wouldneed better waterproofing. Let's dis-cuss the method I used to protect themicrophone, and the amplifier circuitin greater depth so you can build yourown.

The Water Tap. The amplifier circuitis shown in Fig. 1. It's based on a 2 -wattTBA820M op -amp, but as you can seefrom the Parts List, there are a fewother chips that are pin -for -pin com-patible replacements for it. The circuitis powered from a 9 -volt battery. In-stead of making a PC board for the

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Fig. I. The amplifier circuit is based on a 2 -watt audio op -amp, and powered from a 9 -volt battery. Perfboard and point-to-point wiring was used to make the circuit.

TELEPHONE WIRE

(POWER IN, AUDIO OUT)

LID

HOT -MELTGLUE

FLOATING CASE

GLASSTUBE

ELECTRETMICROPHONE

HOT -MELT GLUE

SPEAKER

LID

AMPLIFIERBOARD

PROJECTCASE

Fig. 2. The microphone and amplifier board are mounted in one floating project case,and the battery, speaker, and on/off switch are mounted in another case.

project, simple perfboard and point-to-point wiring was used.

The microphone was connected tothe circuit with a 3 -inch shielded ca-ble. The amplifier is so sensitive that,during the initial tests, the speaker hadto be attached to the cable via a 2 -foot wire-otherwise the circuitsquealed uncontrollably with feed-back. Fortunately the wire can beshortened for the final Water Tap de-sign.

It was decided that the micro-phone and amplifier board would bemounted in one floating project case(since the microphone's shielded ca-ble shouldn't be too long), and thatthe battery, speaker, and on/off switchwould be mounted in another projectcase that could be stuck to the side ofthe fish tank with a suction cup.

Figure 2 shows how the two sections

are interconnected. Since four wiresare needed to connect the two sec-tions together, a piece of 4 -conductortelephone wire a little over a foot longwas used. You can use four separatewires twisted together, but telephonewire has a neat finished appearance.

A glass test tube was used as a wa-terproof case for the microphone. Itwas reasoned that glass would prob-ably result in better sound pickup thanplastic, but you can experiment ondifferent microphone covers if youlike. The test tube was included in afish -tank ammonia test kit. If you can'tfind a suitable test tube, or somethingsimilar, buy a cheap test kit (theyshould only cost two or three dollars)from an aquarium -supply store anduse the one that comes with it.

The figure also shows how the float-ing case is laid out. A hole exactly the

9 -VOLTBATTERY

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% , HANGING CASE

PROJECTCASE

DOUBLE -SIDEDTAPE

same size as the test tube must bedrilled in the bottom of the case. Thetube then hangs out of the bottom ofthe case, making a tight fit in the hole.The joint between the case and thetest tube must then be sealed withhot -melt glue or R1V (room -tempera-ture vulcanizing) silicone to ensure acompletely watertight seal. The mi-crophone then slides down to the bot-tom of the tube, and more hot -meltglue or R1V silicone plugs up the top ofthe tube to further isolate the micro-phone from the outside air. Anotherhole is drilled in what is now the top ofthe case for the telephone wire topass through. Make the hole as smallas possible-seal the hole if Ws muchwider than the wire to help preventwater from getting inside the case.The circuit board is then centered

(Continued on page 107) 79

Aviation -Band ReceiverJoin a growing throng of listening enthusiasts who regularly tune in

commercial air -to -ground and ground -to -air aeronautics communications.

If, like many scanner enthusiastsand ham operators, you are inter-ested in listening in on all the ex-

citement manifest in aeronauticcommunication, but lack the equip-ment to pursue your interest, then per-haps the Aviation Receiver describedin this article is for you. The AviationReceiver, designed to tune the118 -135 -MHz band, features excep-tional sensitivity, image rejection, sig-nal-to-noise ratio, and stability. Thereceiver is ideally suited to listening inon ground and air communicationsassociated with commercial airlinesand general aviation.

Powered from a 9 -volt transistor -ra-dio battery, it can be taken along withyou to local airports so that you won'tmiss a moment of the action. Andeven if you're nowhere near an air-port, this little receiver will pick-up theair -to -ground and ground -to -air com-munications of any plane or groundfacility within about 100 miles!

Circuit Description. Figure 1 showsa schematic diagram of the AviationReceiver-a superhetrodyned AM(amplitude modulated) unit builtaround four IC's: an NE602 double -balanced mixer (U1), an MC1350 lin-ear IF amplifier (U2), an LM324 quadop -amp (U3), and an LM386 audioamplifier (U4).

In operation, an antenna that plugsinto J1 picks up the AM signal. Thatsignal is then coupled through C1 to athree -section, tuned -filter network,

BY FRED BLECHMAN

consisting of L1 -L5 and C2 -C6. Sig-nals in the 118 -135 -MHz VHF (very highfrequency) range are coupledthrough C7 to a VHF transistor (9i),where the signals are amplified. Fromthere, the signals are fed through C8to the input of U1 (the NE602 double -balanced mixer), which in this ap-plication serves as a local oscillator. Avariable inductor (L6) and its associ-ated capacitor network set the local -oscillator frequency at 10.7 -MHz high-er than the incoming 118 -135 -MHzsignals. A tuning network, consisting ofvaractor diode D1 and potentiometerR1, allows the local -oscillator frequen-cy to be tuned across about 15 MHz.

The 10.7 -MHz difference betweenthe received signal and the local -os-cillator frequency (i.e., the intermedi-ate frequency or IF) is output at pin 4of U1 to a 10.7 -MHz ceramic filter (FIL1).The filter is used to ensure a narrowpass band and sharp signal selec-tivity.

The output of FIL1 is amplified by Q2and then fed through C16 to U2 (anMC1350 IF amplifier), which, as con-figured, also offers automatic gaincontrol (AGC), as we'll see shortly. Theamplified 10.7 -MHz IF signal is peakedusing variable transformer T1. The AMaudio is then demodulated by diodeD2. After that, the audio is fed in se-quence through the four sections ofU3 (an LM324 quad op -amp).

Note that a portion of U3-a's outputsignal is fed back through resistor R25to the AGC-control input of U2 at pin 5.

That signal is used to automaticallydecrease the gain of U2 when strongsignals are present or to automaticallyincrease U2's gain for weak signals.That keeps the output volume of thecircuit within a comfortable listeningrange regardless of the strength of theincoming signals.

The receiver circuit also contains asquelch circuit that is controlled bypotentiometer R3, which is used to killrandom noise below a selectedthreshold level. When properly set, thesquelch control virtually eliminatesbackground noise, so that all you hearare incoming signals that can bebrought up to a usable level. Potenti-ometer R2 controls the overall volumefed through C26 to U4, an LM386 low -voltage audio -power amplifier. Dueto the overall design and squelchcontrol, the audio output is quite lowin background noise, and yet it's ca-pable of driving simple communica-tions speakers or earphones toexcellent volume levels.

Construction. The Aviation Receiverwas assembled on a printed -circuitboard, measuring about 4 x 43/4inches. Figure 2 shows a full-size tem-plate of that printed -circuit board'slayout. A kit of parts (which includesan etched and pre -drilled, printed -circuit board, but no case) is offeredby the supplier listed in the Parts List.

Although most of the parts for thisproject are commonly availablethrough conventional electronic-

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Fig. 1. The Aviation Receiver-a superheterodyne unit, built around four IC's-isdesigned to receive AM signals in the 118 -135 -MHz frequency range.

All of the components for the AviationReceiver (including the 9 -volt transistor -radio battery that powers the circuit)mount on a single printed -circuit board.

components suppliers, a source forsome of the more difficult to find partsis given in the Parts List for those whoprefer to do their own shopping. If youopt to gather your own parts or you

plan to use what you have on hand,keep in mind that the circuit -boardlayout was designed to accommo-date components of specific dimen-sions in some cases; jacks J1 and J2,switch S1, transformer T1, and all threepotentiometers, for example. To easethe pain of obtaining those parts, a"Special Parts Kit" is also availablefrom the listed source.

Also note that either of the Siemensparts specified in the Parts List forvaractor diode D1 will work, but bothmay be difficult to find from hobbyistsources. However, the second unit(BB505) is available from Allied Elec-tronics.

However you go about collectingthe parts for this project, don't eventhink about building the receiver cir-cuit without the printed -circuit board.

R2

10K

VOLUMER1333K

At the frequencies involved, theplacement of every wire and part,and every part value is critical for trou-ble -free performance.

Once you've obtained all of thecomponents and the board for theAviation Receiver, construction canbegin. A parts -placement diagram isshown in Fig. 3. When assembling theproject, take special care that polar-ity -sensitive components (electrolyticcapacitors, diodes, and transistors)are installed properly. Just one partinstalled backwards can cause griev-ous harm!

Begin by installing the passive com-ponents (jumper wires, resistors, ca-pacitors, and inductors). Follow thatby installing the active components;diodes, transistors, and IC's. Once theactive components have been in - 81

consider the enclosure that will houseyour receiver.

The receiver's circuit board can behoused in any enclosure that youchoose. However, if you prefer, an op-tional case and knob kit for the re-ceiver is available from the supplierlisted in the Parts List. The optionalcase is supplied with neatly letteredfront and rear panels, knobs, rubberfeet, and mounting screws.

If you choose a case other than theone available from the listed supplier,it will be necessary to drill holes in thefront and rear panels of the enclosureto accommodate the controls (S1, R1,R2, R3) and the jacks Wand J2). Oncedrilled, the front and rear panels of theenclosure can be labeled using dry -transfer lettering.

The antenna for the Aviation Re-ceiver can be as simple as a 21 -inchlength of wire, or you can get a fancyroof -mounted aviation antenna. Ifyou are near an airport, you'll getplenty of on -the -air action from thewire antenna, but if you're more thana few miles away, a decent roof -mount antenna offers a big improve-ment.

Alignment and Adjustment.Aligning the Aviation Receiver consistsof nothing more than adjusting theslug in the local -oscillator coil (L6) forthe center of the desired tuningrange, and peaking the IF transformer(T1). The receiver can be calabratedusing a VHF RF signal generator, fre-quency counter, or another VHF re-ceiver by setting R1 to its mid -position;remember that you want to set thelocal -oscillator frequency 10.7 -MHzhigher than the desired signal orrange to be received. Then, using anon-metallic alignment tool-a met-al tool of any kind will drastically de -tune the coil, making alignmentalmost impossible-adjust 1.6 (the LOcoil) until you hear aircraft or airportcommunications.

Once you are receiving aircraft orairport frequencies, adjust T1 for thebest reception. Typically, T1 is adjusted2-3 turns from the top of the shieldcan. If you don't have any signal -refer-ence equipment for alignment, andare not yet hearing airplanes, yourbest bet is to pack up the receiver and

stalled, check your work for the usual nents, solder bridges, etc. Once the necessary alignment tools, andconstruction errors: cold solder joints, you've determined that the circuit has head for the nearest airport! If the air -misplaced or misoriented compo- been correctly assembled, it's time to port has no control tower, visit a gen-

F 4 INCHES

Fig. 2. Here's a full-size printed -circuit pattern for the Aviation Receiver. The printed -circuit board can be purchased as part of a full-blown kit or separately from thesupplier listed in the Parts List.

The Aviation Receiver's printed -circuit hoard fits neatly into this optional 5.25 x 5.25-x l.5 -inch custom cabinet (which comes with knobs, hardware, silk-screened frontand back panels, us well as rubber mounting feet).

No matter where you live, you will beable to receive at least the airborne sideof many air-traffic communications. If

you know where to tune, you can hearany aircraft that you can see, plus plan-es a hundred miles away and more,since VHF signals travel "line of sight."An airliner at an altitude of 35,000 feetand in the next state is probably stillline -of -sight to your antenna.

Similarly, whatever ground stationsyou may hear are also determined bythe line -of -sight character of VHF com-munication. If there are no major obsta-cles (tall buildings, hills, etc.) betweenyour antenna and an airport, you'll beable to hear both sides of many kinds ofaviation communication. Be preparedfor them to be fast and to the point, andfor the same airplane to move to severaldifferent frequencies in the span of a fewminutes!

At most metropolitan airports, pilotscommunicate with the FAA on a "Clear-ance Delivery" frequency to obtain ap-proval or clearance of the intended

WHAT YOU CAN EXPECT TO HEAR

flight plan, which is done before con-tacting ground control for taxi instruc-tions.

From the control tower, ground move-ments on ramps and taxiways are han-dled on the Ground Control Frequency,while runway and in-flight maneuversnear the airport (takeoffs, local -trafficpatterns, final approaches, and land-ings) are on the Tower Frequency. ATIS,or Automatic Terminal Information Sys-tem," is a repeated broadcast aboutbasic weather information, runways inuse, and any special information suchas closed taxiways or runways. Such abroadcast offers an excellent steadysignal source for initial adjustment ofyour receiver, if you are close enough tothe airport to receive ATIS.

Approach Control and DepartureControl are air-traffic radar controllersthat coordinate all flight operations inthe vicinity of busy metropolitan -airportareas. When you hear a pilot talking with"Jacksonville Center" or "IndianapolisCenter," these are regional ATC (Air Tref-

fic Control) centers. The aircraft is reallyen route on a flight, rather than just leav-ing or approaching a destination. A pilotwill be in touch with several differentRegional Centers" during a cross-coun-try flight.

Airports without control towers rely onthe local Unicorn frequency for strictlyadvisory communications between pi-lots and ground personnel, such as fuelservice operators. The people on theground can advise the pilot what theyknow about incoming or outgoing air-craft, but the pilot remains responsiblefor landing and takeoff decisions. Typ-ical Unicorn frequencies are 122.8 and123.0 MHz.

The FAA's network of FSS (Flight Ser-vice Stations) keeps track of flightplans. provides weather briefings andother services to pilots. Some advisoryradio communication takes place be-tween pilots and a regional FSS. If thereis an FSS in your local area, but no air-port control towers, the FSS radio fre-quency will stay interesting.

PARTS LIST FOR THE AVIATION RECEIVER

SEMICONDUCTORSUl-NE602 double -balanced mixer,

integrated circuit (Digi-Key)U2-MC1350 linear IF amplifier.

integrated circuit (Allied 858-3011)U3-LM324 quad op -amp, integrated

circuit (Digi-Key)U4-LM386 low -voltage audio -power

amplifier, integrated circuit (Digi-Key)

Ql-2SC2570 or 2N5179 NPN UHFtransistor (Allied 858-1041)

Q2 -2N3904 general-purpose NPNsilicon transistor (Digi-Key)

Dl-BB405 or BB505 varactor diode(Siemens. Allied 586-0610)

D2 -1N270, 1N34, or similargermanium diode

D3 -1N914 silicon diode


units.)R1 -R3 -10,000 -ohm PC -mount

potentiometerR4, R9, R15, RI6. R20. R21, R24-

47,000 -ohmR5, R7, RII, RI8, R25, R27 -1000 -

ohmR6, R28 -270 -ohmR8, R12, R17, R23 -10,000 -ohmRIO. R14-1-megohmR13, R22 -33.000 -ohm

R19 -100,000 -ohmR26 -22,000 -ohm

CAPACITORSCl, C7. C8, C13, C16 --0.001-µF,

ceramic -discC2, C4, C6-82-pF, ceramic -discC3, C5-3.9-pF, ceramic -discC9, C17, C19, C20, C28, C30-

0.01 -µF, ceramic -discC10, C15, C21, C25. C26, C31--4.7-

to 10-µF, 16-WVDC, electrolyticC11-10-pF, ceramic -discC12. C14-27-pF, NPO ceramic -discC18. C27, C29-100- to 220-µF, 16-

WVDC, electrolyticC22 -0.47 -RE 16-WVDC,

electrolyticC23, C24 0.1 -RE ceramic -disc

INDUCTORSLI, L3, L5 -I1/2 -turns #24 to #30

gauge wireL2, L4-0.33-1111, inductor (Digi-

Key M9R33-ND)L6 -0.1-11H, 31/2 -turn, slug -tuned

coil (Digi-Key TK2816)TI -10.7 -MHz, shielded transformer

(Mouser 421F123)


FL1-10.7-MHz ceramic filter (Digi-

Key TK-2306)Sl-SPST switch, PC mountJI-RCA jack, PC mountJ2 -Subminiature phone jack. PC

mountB1 -9 -volt transistor -radio batteryPertboard materials, enclosure. AC

molded power plug with line cord,battery(s), battery holder andconnector, wire, solder, hardware.etc.

Note: The following items areavailable from Ramsey Electronics.Inc.. 793 Canning Parkway, Victor.NY 14564; Tel. 716-924-4560: Acomplete kit of parts (AR-IBP),including printed -circuit board (butnot the case or control knobs),$24.95; an etched and drilledprinted -circuit board only(AR-1PCBP). $10.00; a SpecialParts Kit (AR-1SPKBP) containingall semiconductors, R1 -R3, allinductors. SI, .11 and J2. and FILL$14.50; Custom case and knob set

(C-AR-IBP), $12.95. Please add$3 for orders under $20. All ordersare subject to $3.95 postage,'handling charge. New York Stateresidents, please ad appropriatesales tax.

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R3

-R20--J--R24- CJ8

-J-C221 1

i -R18-R19+ R1711 R16 64I I C23 "

I 1

-R25- +C211

+C31U2

-C17 --R26 -

T1

-C1-

[.1 J1

ANTENNA

C12 L11

F1127

-R12--C30-

D2

C26+

U4

J2SPEAKER

+C27

-C28-

+

C9

""'""Nr"--

U3

S1

-C24-

R22 I -R21-1R23

1

vv)

B1

Fig. 3. Use this parts -placement diagram as a guide when assembling the printed -circuit board

eral aviation service center on theairport grounds, and ask which arethe most active frequencies. Then ad-just L6 and R1 until you hear the action.

A ground -service operator or pri-vate pilot may be willing to give you abrief test transmission on the 122.8 Uni-corn frequency. Remember, also, thatif your airport has ATIS transmissions,you can get a steady test signal assoon as you are within line -of -sight ofits antenna. (See the sidebar for ex-planation of Unicorn and ATIS.)

Use. Plug an antenna into J1 and a 4 -to 8 -ohm speaker or earphone intoJ2. Turn on the Aviation Receiver byclosing S1. You may or may not hearbackground noise. Turn R2 (the SQUELCHcontrol) fully counterclockwise. Thenrotate R2 clockwise until you hear a"pop" and some background noise;

then back it off slightly (counterclock-wise) past the pop. You are now insquelch mode.

With pilots and controllers talking sobriefly, you will need to get used totuning your receiver. As you sweepacross the band (via R1), listen for asound, then rock back and forthslightly to tune it in clearly.

Troubleshooting Suggestions. If

the receiver does not work at all, care-fully check the obvious things first; bat-tery polarity, soldering of the batterywires and switch, and the connectionsto the speaker jack. Also, be sure tocheck that you've correctly installedall of the Jumpers. If the circuit's opera-tion is erratic, a solder connection isusually the culprit, or there could be abreak in the antenna or speaker wire.

Pay special attention to the orienta-

PILOT AND CONTROLLERTALK

Don't blame the Aviation Receiver if allyou hear are short bursts of words thatdon't make a lot of sense at first. Avia-tion communication is necessarilyquick and brief, but clear and full ofmeaning. Generally, pilots repeat ex-actly what they hear from a controller, sothat both know the message or instruc-tions were correctly interpreted If youare listening in, it's hard to track every-thing said from a cockpit, particularly inbig city areas. Just to taxi, takeoff, andfly a few miles, a pilot may talk with 6 or 8different air -traffic -control operationswithin a few minutes, all on different fre-quencies.

Here's the meaning of just a few typ-ical communications.

"Miami Center, Delta 545 heavy out ofthree -zero for two -five " Delta Flight 545acknowledges Miami Center's clear-ance to descend from 30,000 feet to25,000 feet The word ''heavy" meansthat the plane is a jumbo let, perhaps a747. DC -10, or L-1011."Seneca 432 Lima cleared to outermarker. Contact tower 118 7." The localApproach Control is saying that thePiper Seneca with the N -number, or "tailnumber" ending in "432L" is cleared tocontinue flying an instrument approachto the outer marker (a precision radiobeacon located near the airport), andshould immediately call the airport ra-dio control tower on 118.7 MHz Thatmessage also implies that the controllerdoes not expect to talk again with thataircraft

"Cessna 723, squawk 6750, climband maintain five thousand." A control-ler is telling the Cessna pilot to set theairplane's radar transponder to code"6750." climb to and level off at the al-titude of "5000 feet."

"United 330. traffic at 9 o'clock, 4miles, altitude unknown." The controlleralerts the United Airlines flight of radarcontact with some other aircraft off tothe pilot's left at a "9 o'clock" position.Since the unknown plane's altitude isalso unknown, both controller and pilotrealize that it is a smaller private planenot equipped with altitude -reportingequipment.

tion of all IC's, transistors, diodes, andelectrolytic capacitors. Also, be surethat C11 and C12 in U1's oscillator cir-cuit are of the right values. Local -os-cillator operation can be verified witha simple VHF receiver or frequencycounter. Remember that the local os-cillator should be set to a frequency10.7 MHz above the desired listeningrange. If the oscillator works, only adefective or incorrectly installed partcan prevent the rest of the receivercircuit from functioning.

Experimenting WithShaped Memory AlloysLearn about Shaped Memory Alloys and how they work, then perform some

hands-on experiments with these fascinating materials

BY JOHN (OVINE

Shaped Memory Alloys (SMA)are alloys of two or more met-als that have some interesting

properties. One property of the mate-rial is that it contracts when heated.This is analogous to the contraction ofmuscle tissue; note that this effect isthe opposite of standard metals,which expand when heated andcontract when cooled.

Another property of these alloys iscalled the Shaped Memory Effect(SME). Simply put, this material will,when heated to a critical tempera-ture, return to a shape that it has beentrained to "remember" In short thismatrial could be twisted, bent andfolded, but when heated it will returnto its original shape.

History. In 1932, Arne Olander, aSwedish researcher, discovered theShaped Memory Effect in a gold -cad-mium (AuCd) alloy. In 1951, two re-searchers, L.C. Chang and T.H. Read,analyzed the crystal structure andchanges of the Shaped MemoryEffect in the AuCd alloy, and in 1958those two researchers made a cyclicweight -lifting device to be displayedat the Brussels World Fair.

In 1961, William Beuhler working atU.S. Naval Labs discovered SME in analloy of titanium -nickel. At the time,Beuhler and his team were looking todevelop a heat and corrosion resis-tant alloy. In any case, the alloy theydiscovered was, by far, cheaper andsafer to work with than any SME alloy

to date. The team named the newalloy Nitinol, pronounced night -in -all.The material's name is representativeof its elemental components andplace of origin. The "Ni" and "Ti" arethe chemical abbreviations for nickeland titanium, and "NOL" stands for the"Naval Ordnance Laboratory" whereit was discovered.

In later years, other alloys were dis-covered that exhibited SME. In 1985,Dr. Dai Homma of Japan's Toki Corpo-ration announced n improved ver-sion of Nitinol. That improved versionof Nitinol is sold in this country underthe name trade name BioMetal. ACalifornia company, Mondo-Tronics,sells Nitinol wire under the trade nameof Flexinol.

There are many interesting ap-plications for this material. NASA hadproposed using Nitinol to make spacecraft antennas that would deploywhen heated by the sun, or a second-ary heating unit. More down to earthventures are its use in eyeglass frames,dental -alignment material, pumps,blood filters, solenoids, and an ar-tificial heart.

How it Works. The properties ofNitinol rely upon the crystal structureof the material. That structure is sen-sitive to both external stress and tem-perature. Before we discuss the actualmechanics involved, we must definethe temperature phases of the mate-rial.

Parent Phase refers to a state thatexists above the transition tempera-ture, the temperature where the wirecontracts or returns to a previously de-fined shape. In this phase, the crystalstructure is cubic. The transition tem-perature depends upon the exactcomposition of the material. For theNitinol wire we will be working withlater on in this article, the transitiontemperature is 100-130°C(190-260°F).

Martensitic Phase refers to statethat is below the transition tempera-ture. The crystal structure is needle -likeand is collected in small domains.Within each domain, the crystals arealigned. The material is cool and canbe bent or formed into other shapes.That external stress transforms thecrystal structure of the material. It is

sometimes called stress -inducedmartensite.

The Annealing Phase occurs at atemperature where the material willreorient its crystal structure to re-member it's current shape. The an-nealing phase for the material we areworking with occurs at a temperatureof 540°C.

With those definitions under ourbelt, we can discuss how the materialworks: When a cooled wire is bent ortwisted, the crystal structure is trans-formed. If the wire is then heatedabove its transition temperature (Par-ent Phase), the crystal structurechanges from needle -like to cubic.Since the cubic crystals don't fit intothe same space as the needle -likecrystals, they are formed under strain.To relieve this strain they move andchange their positions to relieve the

strain. This "least strain" position hap-pens to be the original shape (or theannealed shape) of the material.

Where the wire hasn't any stress -in-duced transformations, the crystalstructure still changes, but thatchange results in no net movement.

Properties. Nitinol metal can gener-ate a shape -resuming force of about22,000 -pounds -per -square -inch. Inour experiments later on, we will beusing a 6 -mil wire. Even so, a 6 -mil wire(.006 inch diameter) can generate acontractive force of 11 ounces. If youwant more pull, simply multiply thewires till you reach the contractiveforce you require.

Nitinol wire, as stated previously, issold under the trade name of Flexinolby Mondo-Tronics. The wire diameteris given in micrometers as a numbersuffix of the name Flexinol. So Flexinol150 is a Nitinol wire with a diameter of150 micrometers. To convert microm-eters to Inches multiply by .00003937.Doing that, we find the diameter ofFlexinol 150 is 6 mils (.006 inch).

The wire can contract up to 10% ofifs length. To extend the life of a givensample (greater than 1,000,000 cy-cles), you should restrict the con-traction to only 6% of its length.

Reaction time can be quite short,measured in milliseconds. In addition,full strength is developed at the be-ginning of the cycle.

The Nitinol material is stronger thanmany steels. The 6 mil wire has abreaking strength of about 6 pounds.

Activating Nitinol Wire. The easiestway to heat the wire is by passing anelectric current through it. The wire'sresistance to the current heats thewire and causes it to contract. The

CRIMPCONNECTOR

FLEXINOLWIRE CUT LINE

Fig. 1. Soldering directly to the Nitinolwire could adversely affect it. Thesupplier mentioned in the articlesupplies crimp terminals that get aroundthat problem.

PARTS LIST FOR THENITINOL DEMONSTRATION

U1-4011 quad SANE) gate, integratedcircuit

QI-IRF511 MOSFET transistorR1 -15,000 -ohm, 1/4 -watt, 10% resistorC1 -1-µF, 35-WVDC, tantalum

capacitorB1 -9 -volt transistor -radio batterySI, S2-SPST toggle switchNitinol wire, pertboard or plastic,

hardware, rubber hand, enclosure, etc.The following are available from Mondo-

Trnnics. 524 San Anselmo Ave.,#107, San Anselmo, CA 94960; Tel.415-455-9330, 800-374-5764: ShapeMemory Wire Guidebook and SampleKit (part no. 3-074), $29.90; 40inches of Flexinol 151) (part no.3-072), $14.95. Please add $4.00 forshipping in the U.S.; internationalorders add $9.00. California residentsmust add 8.25% sales tax.

volume of the wire doesn't changeduring contraction, so as the wire de-creases in length, it diameter in-creases by a proportional amount,keeping the volume the same. Theactivation temperature of the wire is

to 130°C (or 190-260°F).Care should be taken not to over-

heat the wire or its properties will de-grade. The wire has an electricalresistance of a little less than 1 -ohm -per -inch. Flexinol wire is supplied withcrimp terminals (see Fig. 1). These ter-minals are used to make connectionsto the material because the Nitinolwire should not be heated to the tem-perature that would be required forsoldering.

Direct Electric Heating. Nitinol wirecan be activated using low voltage,such as a 9 -volt transistor -radio bat-tery. A simple circuit can be built usinga battery, switch, and a small length ofNitinol (see Fig. 2).

Again, care must be taken not tooverheat the wire. In addition, con-nections to the Nitinol will draw heataway from the ends of the wire. Thatresults in the center of the wire heat-ing faster than the ends. So althoughdirect electric heating works, a bettermethod is pulse -width modulation.

Pulse -Width Modulation Heating.In this technique, a squarewave froma simple circuit is used to turn theelectric current on and off. Depend-

NITINOL WIRE

Fig 2. While this is the simplest way toactivate Nitinol wire, it has someimportant limitations.

ing upon the frequency and duty cy-cle of the squarewave, we can adjustthe amount of contraction and main-tain the wire in a contracted con-dition for a longer period of time.Because of the rapid on and off ac-tion of the waveform, the wire hastime to distribute the heat, which re-sults in a more uniform heating. That isthe method that we shall use in ourexperiments.

The Circuit. The circuit we shall use(see Fig. 3) is designed around a 4011quad NAND gate. The NAND gate is con-figured as a squarewave generator.The circuit can be operated manuallyusing a switch (S1), or it can be inter-faced to any computer by deletingthe switch and connecting the circuit(via pin 1 of U1) to a port line that canbe brought high and low under pro-gram control. The 4011 can't handlethe current requirements of the Nitinolwire, so the wire is interfaced to therest of the circuit via an IRF511 MOSFET.

Nitinol Demonstrations. To dem-onstrate the potential of this material,we need to build a small mechanicaldevice. If you're like me, you'll wantthe simplest unit to start with. To makeour electric "muscle," the materialsyou'll need are 3 machine screws withsix nuts, a piece of perfboard or plas-tic, a small rubber band, and, ofcourse, a length of Nitinol material.

Look at Fig. 4. Three machinescrews are arranged in a triangularpattern in the perfboard or plastic asshown. The Nitinol wire is connectedto the two top screws. The rubberband is looped around the bottommachine screw, with the Nitinol wirelooped through the top of the rubberband. Begin by drilling two holes toaccommodate the top two screws. Todetermine the location of the third(bottom) machine screw stretch therubber band from a position that isparallel with the top screws and

.

15K

- C11 4

5

6

7

U1

401111 G

10

9

01IRF511

NITINOL WIRE

J

Fig. 3. This circuit produces a squarewave outp 41 and provides a much better way toactivate the wire. It can be manually controlled as shown, or, with some simplemodifications, can be interfaced to a computer.

TO CIRCUIT

NITINOL

WIRE

RUBBER BAND

COOL

POSITION

SHEET OF PLASTIC ORPIECE OF PERFBOARD

TO CIRCUIT

Fig 4. This simple demonstration is easy to build, and shows off the basic properties ofthe Nitinol wire.

down. Remember the Nitinol has apull of about 11 ounces so don't makethe rubber band so tight that theNitinol isn't able to contract and moveupwards, although it should be tightenough for it to take up the slack ofthe Nitinol wire when it is relaxed. Drillthe third hole and build the assembly

as shown. Finish up by connecting theNitinol wire to the circuit of Fig. 2.

When the unit is activated, the wiregets hot, contracts, and pulls up therubber band. When the unit is deacti-vated the wire cools, elongates, andlowers the rubber band into its restingposition.

PLASTICOR

PERFBOARD

NITINOLWIRE

WOOD BLOCKSTAND

Fig 5. Another simple demonstration, this time showing how the Nitinol wire can beused to move a lever.

3 -HOLE SOFTRUBBER TUBING

A

NITINOLWIRE

CRIMPTERMINAL

COPPERWIRE

A

Fig. 6. This simple one -digit flexor can be bent to the left or the right depending on88 how power is applied to the three leads.

POWER CONNECTIONS

B

CB

NITINOLWIRE

B

I also built a second Nitinol demon-strator, shown in Fig. 5. That unit showshow you can amplify the mechanicalmotion of the wire using a lever. Thelever pivots on screw A. The Nitinol wireis attached to the lever and screw E.The wire is threaded around screws B,C and D. When activated, the leverrises.

The lever can be made from wood,plastic, or metal. If you use a metallever, you can make the electricalconnections to the wire throughscrews A and E. If the lever is madefrom a non-conductive material, usescrews B and E for the electrical con-nections.

Going Further. We have justscratched the surface of the potentialof this material. It is quite possible tobuild a realistic android hand. As anexample, consider the simple single -digit flexor that is illustrated in Fig. 6A.That unit is built using a three -hole soft -rubber or silicone tube. The Nitinolwire is threaded in a loop through thetwo outer holes. A copper wire isthreaded up through the center hole.The loop of Nitinol wire and the end ofthe copper wire is crimped in a smallterminal. By applying current be-tween the copper wire and one endof the Nitinol you can make the tubeflex right (A -C) or left (B -C), as shown inFig. 6B. Or by applying power to theIwo ends of the Nitinol wire the tubewill flex backwards.

Heat engines are another fertilefield for experimentation and de-velopment. One company sells a toyboat powered by Nitinol wire. Theboat has a small cargo bay for ice.The difference in temperature be-tween the ice and the water the boatrests in powers the toy boat.

You may want to attempt to train apiece of Nitinol wire to a particularshape. You can do this by bending thewire to the shape you want, clampingit in position and heating it to about540°C. You also might want to try di-rect electric heating of the wire toreach the annealing temperature.

Mondo-Tronics sells a book titledWorking with Shaped Memory Wires,which shows various actuators anduses of this material. Several Nitinol-wire samples with various diametersare included with the book. It is aworthwhile investment if you plan ondoing any experimentation.

Solar Power Supplies

for PortableRadios & Cassette Players

If you make extensive use of porta-ble radios or cassette players, youare well aware of the high cost of

replacement batteries. Besides beingexpensive, batteries tend to expireright in the middle of your favorite mu-sic. The Solar Power Supply describedin this article is designed to addressthat problem by providing a low-costalternative to purchasing batteries,assuming that much of your listening isdone during the daylight hours and inplaces where sunlight is available.

To accommodate different types ofportable electronic equipment, twosystems will be described; a switching(step-up) regulator and a linear (step-down) regulator. Each of the regulatorcircuits is used in conjunction with asolar -cell array, which converts lightinto electrical energy. The outputs ofthe circuits remain constant even withvarying degrees of light intensity.

For special low -light operation, thebuilder can add more cells in series

BY ANTHONY J. CARISTI

Build an environment -friendly, money -saving

power supply for radios,cassette players, and

more!with the solar -cell array to compen-sate for that condition. For night-timeor indoor use, if the solar array isplaced close to bright lighting, the So-lar Power Supply will be able to pro-vide sufficient power to operate mostportable devices.

Switching Regulator. Figure 1 showsthe schematic diagram of the switch-ing regulator, which can be config-ured to output 7.2 or 4.8 volts ofregulated DC, depending on the re-sistor value selected for R1. By making

R1 453k, which produces an output of7.2 volts, the circuit can be used tooperate radios that are normallypowered from a 9 -volt battery. Bymaking R1 274k, which produces anoutput of 4.8 -volts, the circuit can beused to operate devices that are nor-mally powered from a 6 -volt source(i.e., two M or C cells).

At the heart of the switching -reg-ulator circuit is an MAX630CPA (Harris)micropower switching regulator (U1),which is designed to deliver 7.2 voltsat 15 mA with an input of 3 volts. Theswitching regulator is fed from a solar -array, consisting of eight, 0.5 -volt pho-tovoltaic or solar cells, which output 4volts. The 8 -cell solar -array ensuresthat the circuit can provide sufficientpower to operate the connected de-vice when less than full Sun intensity isavailable.

With a typical load current of 15 mAat 7.2 volts, the power output of thecircuit is 108 mW. Assuming that the

PC1

PC2

PC3

PC4

}C2 VREG

1000 OUT

PC5 PC6 PC7 PC8

Fig. 1. Powered from an 8 -cell solar array, the switching regulator can be configuredto deliver 7.2 or 4.8 volts of regulated DC. At the heart of the circuit is anMAX630CPA micropower switching regulator (U1), a chip that's designed to deliver7.2 volts at 15 mA with an input 43 volts.

PC1

PC2

PC3

PC4

VREG

OUT

PC5 PC6 PC7 PC8

Fig. 2. This linear regulator circuit has at its heart a low -power op -amp, whichcontrols a PNP transistor that's connected as a high -side switch between the array andthe load.

circuit has an operating efficiency of70%, power input is 154 mW. With aninput of 3 volts, the solar -cell arraymust be able to deliver 51 mA topower the regulator circuit. With thespecified resistor value, the circuit canprovide 4.8 volts at 115 mA with aninput of as little as 3.3 volts.

The calculations for a typical loaddriven by the circuit are as follows: Acassette player that draws 115 mA ofcurrent at 4.8 volts requires an inputpower of 552 mW. Using a con-servative figure of 70% efficiency forthe switching regulator, the current re-quired from the solar -cell array is 239mA. For this application 250- or 300-mA cells would be a good choice. Ifnecessary, one way to attain greatercurrent ratings than can be obtainedfrom one solar cell is to connect two ormore in parallel.

Linear Regulator. Some portablecassette players use two M cells as

the power source, and require an op-erating current of typically less than125 mA. Although a step-down switch-ing regulator can be designed for thisapplication, a linear circuit is moreefficient. Such a circuit is illustrated inFig. 2. The heart of that regulator is alow -power op -amp, which controls aPNP transistor that's connected as ahigh -side switch between the cell ar-ray and load. The circuit's input/outputvoltage differential just 0.3 volt, whichis lower than most fixed linear -reg-ulator chips.

In the linear circuit, the negative in-put of the op -amp is biased at a refer-ence voltage of 0.7 volts by means ofR5 and D2. A voltage divider, com-posed of R3 and R4 and connectedto the positive input of the op -amp,monitors the output voltage of theregulator. The output of the op -ampacts as a current sink for the base ofQ1, and draws sufficient base currentto maintain a relatively constant out-

put voltage with variations in solar -cellvoltage and load current.

As the output voltage of the solar-

cell array changes with varying de-grees of Sun intensity, the voltage atpin 1 of U2 moves up and down ac-cordingly As a result, the output of thesupply remains at or close to 2.4 volts.

As discussed earlier, the current sup-plied by the solar -cell array is essen-tially equal to the current demandedby the radio or cassette player. Formost 3 -volt portable cassette players,the current is usually in the 125-mArange. One way to obtain a solar cellwith that capacity is to parallel 100-mA cells with 50-mA cells, whichwould provide an extra margin ofpower to the system.

Construction. Both of the regulatorcircuits are extremely simple to buildand can easily be hardwired on asmall section of perfboard. But for amore professional look, you may wishto use printed -circuit construction. Theboard(s) can either be etched fromthe full-sized, printed -circuit tem-plates shown in Figs. 3 and 4 (theswitching and the linear regulators,respectively), or purchased from thesource given in the Parts List.

0.1

"roof

11/4 INCHES

Fig. 3. The switching regulator wasassembled on a small printed -circuitboard. This full-sized, printed -circuittemplate can be used to etch your ownboard.

kg- 1112 INCHES-01Fig. 4. The linear regulator was alsoassembled on a small section of pr'nted-circuit board. Here is a template of thatfoil pattern.

\\4PC1

PC2

PC3

PC4

L.1

-R1-

U1

C1 C31

PC5 PC6 PC7 PC8

J5,0r").0 0

+

D4 C2

VREG

OUT

PARTS LIST FOR THESWITCHING REGULATOR

SEMICONDUCTORSUl-MAX630CPA switching

regulator (Harris Semiconductors).integrated circuit

DI -1N5819 Schottky diode

Fig. 5. When gathering the components for the switching -regulator board, be sure touse the parts specified in the Parts List, including the use of metal -film resistors wherecalled for, and a Schottky diode.

PC2

PC3

PC4

C41

D2

-R5-

U1

(0)

PC5 PC6 PC7 PC80060:\ *\

I 1

R4 R3C5

YRE,

OUT

Fig. 6. Here is the parts -placement diagram for the linear -regulator circuit. Whenassembling this, as well as any other electronic project, make absolutely sure that allof the polarized components are properly oriented.

When gathering the necessarycomponents, be sure to use the partsspecified in the Parts List. That includesusing 1% metal -film resistors wherecalled for, and a Schottky diode in theswitching regulator. The inductor mustbe rated for twice the load current ofthe supply, and have a resistance ofless than 5 ohms. The use of alternatecomponents will result in less than op-timum operation. Be very careful toorient all polarized componentsproperly; just one part placed back-wards on the board will render thecircuit inoperative and may causecomponent damage.

Once you've obtained the spec-ified parts, construction can be begin.Parts -placement diagrams for Figs. 3and 4 are shown in Figs. 5 and 6, re-spectively. It is recommended that asocket be used for the DIP IC in eachcircuit. The use of sockets makes trou-bleshooting or servicing much easiershould either ever be necessary.

When the circuit is completely as-sembled and wired, inspect it verycarefully for shorts, opens, and coldsolder joints (which may appear asdull blobs of solder). Any suspect jointshould be redone by removing theold solder and applying new solder. Itis far easier to correct constructionproblems at this stage than it is to doso later on should you discover thatyour project does not work.

Solar Cell Selection. In order to se-lect the correct -size solar cells for thedesired application, the current drawof the device to be operated must beknown. That can be determined byactually measuring the current drawnby the device to be powered, with aDMM set to read DC milliamps, whilethe radio or cassette player is oper-ated from a set of batteries or an ACadapter.

Using batteries as the power sourceis the preferred method for determin-


units, unless otherwise specified.)R1 -453,000 -ohm or 274,000 -ohm,

metal -film (see text)R2 -100,000 -ohm, carbon, 5%

CAPACITORSCI -1004th 10-WVDC, radial -lead

electrolyticC2 -1000-µF, 10-WVDC, radial -lead

electrolyticC3--100-pF. 50-WVDC, ceramic -

disc


PC1-PC8-0.5-volt photocell (seetext)

L1-1-mH. 200-mA choke. DCresistance 5 ohms or less

Printed -circuit materials, enclosure.wire, solder, hardware. etc.

ing load current since it will provide amore accurate reading. While mak-ing the measurement, play the unitwith the highest volume that you in-tend to use.

The easiest way to make this mea-surement is to obtain a power -adapt-er plug that the fits the external powerjack of the unit to be powered, anduse an external power source (bat-teries or AC adapter) to operate theunit. A DMM connected in series (asillustrated in Fig. 7) with one of thepower leads and set to 200 mA DC willindicate the current drawn by the unit.

Because there is no standardpower -supply connection schemefrom one manufacturer to another,one must be very careful aboutpower -supply polarity when perform-ing this test. One way to check polarityof the jack on some units is to connecta pair of wires to the adapter plug,insert the plug into the jack, and use aDC voltmeter to check the polarity ofthe battery voltage appearing acrossthe wires. That test requires batteriesto be in the unit to provide voltage atthe power jack, and will work if theplug does not automatically discon-nect the batteries.

PARTS LIST FOR THELINEAR REGULATOR

SEMICONDUCTORSU2-LM358N dual low -power op -

amp, integrated circuitQ1 -2N3906 general-purpose PNP

silicon transistorD2 -1N4148 general-purpose silicon

diode

RESISTORS(All fixed resistors are 1/4 -watt, I%

units, unless otherwise specified.)R3 -26,100 -ohm, metal -filmR4 -10,000 -ohm, metal -filmR5 -1000 -ohm, carbon, 5%

CAPACITORSC4-100-10, 10-WVDC, radial -lead

electrolyticC5 -1000-µF, l0-WVDC, radial -lead

electrolytic


PCI-PC8-0.5-volt photocell (seetext)

Printed -circuit materials, enclosure.wire, solder, hardware, etc.

Note: The following parts areavailable from A. Caristi, 69 WhitePond Road, Waldwick, NJ 07463:PC board (specify linear orswitching regulator), $5.00; Ul,$11.50; U2, $2.75; Ll, $5.50; DI.$2.00; metal -film -resistor kit(specify values), $2.00. Please add$3.00 postage/handling. NewJersey residents please addapplicable sales tax.

Another way to verify polarity (if anAC adapter for the unit in question isavailable) is to plug the unit into a 117-

Ovolt AC receptacle and check the DC

co voltage at the output of the plug withz a DC voltmeter.

Table 1 gives the approximate cur-cn rent drawn by several types of corn-

>-mon portable radio and cassette

co equipment. Note that "radio only" op-alo eration requires significantly less cur-=cn rent than cassette operation. That

because the motor does not runo when simply playing the radio. For 3 -

volt devices, the linear regulator cir-c..)Lu cuff is the best candidate. For that-Jw type of circuit, the solar -cell array'scr) output current should equal that ofcr)

the unit to be powered.For 6- and 9 -volt devices, the step -

dc0. up switching regulator in Fig. 4 is thepreferred circuit. In that case, the re -

92 quired solar -cell current capacity

TEST

BATTERY-II II

MILLIAMMETERJACK

-1) )=11-t

ADAPTERPLUG

RADIO ORCASSETTE PLAYER

Fig. 7. The solar cell used in this project must be selected according to the currentdraw of the device to be operated. That can be determined by actually measuring thecurrent drawn by the device using a DMM set to read DC milliamps, in a setup likethat shown here.

TABLE 1-TYPICAL CURRENT REQUIREMENT FORPORTABLE RADIO AND CASSETTE PLAYERS

Power Source/Drive Volts Mode Load Current

2 AA cells/Walkman 3 Radio 25 mA2 AA cells/Walkman 3 Tape 125 mA4 AA/C cells/Radio S. cassette 6 Radio 25 mA4 AA/C cells/Radio 8 cassette 6 Tape 115 mA9 -volt battery 9 Radio - 15 mA

POSITIVEOUTPUT

WIRE

SOLDERTO BACK

SIDE I.

(-,

4,)

CELL

in"-(" NEGATIVEe TERMINAL

ON FRONT

SET OF 8 CELLS

NEGATIVE

OUTPUT*-1 WIRE

Fig. 8. This illustration shows the proper way to wire solar cells in series. Theconnections are made from the back of the cell (positive terminal) to the silver coloredband on the front of the cell (negative terminal). The free ends of the 8 -cell string is theconnected to the circuit as shown in the schematic diagram.

must be calculated, using two simpleequations. First calculate the radio/tape player power input in milliwatts:

mW = V x mA

where V is the nominal regulated sup-ply voltage (4.8 or 7.2 volts) and mA isthe device's load current, which wasmeasured previously.

Next calculate solar -cell currentusing a conservative estimate of 70%(0.7) for switching -regulator efficiency,and a minimum solar -array outputvoltage of 3 volts under hazy sunlight:

Solar -array current = mW/(0.7 x 3)

where mW is the power input pre-viously calculated. For example, for atypical cassette player that ispowered by 4 M cells and draws 115-mA load current:

mW = 4.8V x 115 mA = 552

and:

Solar -array current = 552/(0.7 X 3) =263 mA

For the above example, a set ofeight solar cells (rated at 300 mA)connected in series will be ideal forthis application.

Solar -Cell Assembly. Solar cellsmay be obtained individually, or ingroups connected in series to form anarray. A typical solar cell, rated at 300mA, is available from Radio Shack(part number 276-124). Another goodsource for solar cells is Edmund Scien-tific Co. (101 E. Gloucester Pike, Barri-ngton, NJ 08007).


Eliminate frequentrechargeable Ni-Cdbattery replacement

with a chargingcircuit that can also

restore batteries thathave developed

a "memory"

BATTERY BUTLERWith the widespread use offast -charging, nickel -cad-mium (Ni-Cd) battery

chargers supplied with many con-sumer products, many consumershave found that the convenience ofrapid charging has not offset the highcost of replacing destroyed batteriesin their telephones, handheld trans-ceivers, remote -control model cars,and planes. The replacement cost ofthe batteries that power such porta-ble and cordless gadgets can rangefrom 25 to 75 dollars. On top of that,with regular use, some types of fastchargers can reduce the useful life ofa rechargeable battery to 20% to50% of its normal life.

Further reducing the useful life oftheir Ni-Cd batteries, consumers, es-pecially portable cellular telephoneusers, fail to let their batteries fully dis-charge before recharging them. Thatcan cause the battery to developwhat is known as a "memory"-whichis caused by repeated partial dis-charge of the Ni-Cd battery. Eachtime the battery is partially dis-charged, prior to a normal rechargecycle, the battery demonstrates anapparent loss of capacity. However,most of the incurred loss is recovera-ble by subjecting the battery to a fewdeep -discharge cycles.

Operating and charging Ni-Cdbatteries at elevated temperaturesalso reduces their useful life. Most Ni-Cd batteries give their best perfor-

mance at temperatures between18°C and 30°C. The high internal tem-peratures of Ni-Cd batteries duringfast charging, often near 50°C, accel-erates cell electrolyte -seal and sepa-rator deterioration and increases theprobability of internal shorting. Elec-trolyte venting, due to high internalpressures, occurs more often at ele-vated temperatures. The loss of cellelectrolyte, due to continuous cellventing, results in a net loss of cell ca-pacity.

The Battery -Butler, described in thisarticle, solves the common problemsassociated with the maintenanceand operation of Ni-Cd batteries. TheBattery -Butler, by initially discharginga Ni-Cd battery to a preset point, re-duces the possibility of the "memory"effect occurring. Once discharged, abattery is then usually charged at25% or less of the fast -charge rate.Charging at a lower rate will typicallyreduce the internal cell temperaturerise by 25% and reduce the internalcell pressure increase by 40% ormore. Once the battery is fullycharged, a trickle charge is providedto maintain the battery in a fullycharged state. The Battery -Butler cir-cuit can be bypassed, and the exist-ing fast -charger used, if needed.

Circuit Description. A schematic di-agram of the Battery -Butler is shown inFig. 1. When power is first applied tothe circuit and S1 is in the off position,

BY LARRYLANPHER

C2 is held discharged. At the sametime, pin 14 of U3 -f is held low via R2,forcing U3-f's output at pin 15 high. Thehigh output of U3 -f divides along Iwopaths. In one path, U3-f's output is fedto U3 -b at pin 5 through D3, causingthe output of U3 -b at pin 4 to go low.The logical -low output of U3 -b is fed tothe base of Q4, keeping it turned off.

In the other path, the high output ofU3 -f is applied to the input of U3 -c atpin 7, forcing its output low, which inturn holds C1 in a discharged statethrough R4 and D2. That keeps theoutput of U1 -b (at pin 9) high, whichkeeps LED1 dark. The reset signal(taken from pin 6 of U3 -c), being low,forces both R/S latches (comprised ofU4-a/U4-b and U4-c/U4-d) to return totheir respective reset states. Once in areset state, pin 4 of U4 -b and 10 of U4 -c go high, and pin 11 of U4 -d remainslow, indicating a discharge cycle. Thelow output of U4 -d at pin 11 forces pin2 of U3 -a high, turning Q2 on. Thatpulls the ADJ pin of U7 low, which holdsthe output off.

When S1 is flipped to the SLOWposition, pin 15 of U3 -f goes low, forc-ing pin 6 of U3 -c high, while at thesame time reverse biasing D3, so nocurrent flows through that unit. With D3reverse biased and pin 11 of U4 -d low,pin 4 of U3 -b goes high, turning on Q4.The battery then starts to dischargeinto R39 through Q4. Zener diode D7provides overvoltage and reverse -voltage protection for 04.

J1

05

194001R35820

DC INPUT SLOW11.5- 15VDC si

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2A

DC OUTPUT12VDC/1A

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DISCHARGE

LEVEL

SEE TEXT

+ 12V

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Fig. I. The Battery -Butler is comprised seven IC's-an LM556 dual oscillator/timer,an MC14040 CMOS 12 -stage binary counter, an MC14049 CMOS hex inverting buffer,an MCI4011 quad CMOS NAND gate, an LM339N quad comparator, an LM78M05 5 -volt, 500-mA, voltage regulator, and LM3/7T 1 -amp, adjustable voltage regulator-along with their support components.

Pin 6 of U3 -c, which is now high,allows C1 to begin charging. Thecharge on C1 is applied to the thresh-old input of U1 -b at pin 12. The highoutput of U4 -b at pin 4 is applied tothe reset input of U1 -bat pin 10. Thosetwo signals, being high, cause U1 -b tobegin oscillating, which in turn flashesLED1. The displayed color of LED1 isselected by the state of pin 10 of U4 -cand 11 of U4 -d. With pin 11 of U4 -d low,LED1 flashes red.

The Ni-Cd battery's voltage is ap-plied to the circuit and divided by R6and R7, and is monitored by U5 -a.When the voltage at a pin 5 of U5 -adips lower than the reference voltageat pin 4 of U5 -a, pin 2 of U5 -a goes low,indicating that the battery has beendischarged. Note that the dischargecycle can last from seconds to hours,depending upon the type and con-dition of the battery. The low output ofU5 -a is fed to one input of an R/S latch(consisting of U4 -c and U4 -d), forcingpin 10 low and 11 high, which, in turn,causes the red section of LED1 to turnoff and the green section to turn on.indicating that a charge cycle hasbegun. The high output of U4 -d at pin11 forces the output of U3 -a at pin 2low, turning Q2 off. That allows the ADJterminal of U7 to float high, whichturns the output pin on and allows cur-rent to flow to the Ni-Cd battery.

Since the initial reset cycle, pin 4 ofU4 -b has been high, generating thehi -rate signal. The hi -rate signal (in ahigh -logic state) turns Q1 on, whichturns Q3 on. With Q3 conducting, R34sets the regulator's constant -currentoutput at the higher charging rate.

The Ni-Cd battery's charge voltageis divided by a resistor network com-prised of R22, R23, and R25, and ap-plied to a track -and -hold circuit,which is used to monitor the chargevoltage. The track -and -hold action isinitiated when the reset input of U2 atpin 11 drops low at the start of thecharge cycle. That allows U2, clockedby U1 -a, to begin counting. Oncecounting, U2, combined with R11 -R20.produces a ramp voltage at pins 8and 10 of U5 -c and U5 -d, respectively.That voltage continually increases un-til the voltage at pin 8 of U5 -c is great-er than that at pin 9, at which time, thereset input of U1 -a at pin 4 goes lowinhibiting the clock.

As the battery continues to charge,the voltage at pin 9 of U5 -c increases

PARTS LIST FOR THEBATTERY BUTLER

SEMICONDUCTORSUl-LM556 dual oscillator/timer,

integrated circuitU2-MCI4040 CMOS 12 -stage

binary counter, integrated circuitU3-MC14049 CMOS hex inverting

buffer, integrated circuitU4-MCI4011 quad CMOS NAND

gate. integrated circuitU5-LM339N quad comparator,

integrated circuitU6--LM78M05 5 -volt, 5(X)-niA,

voltage regulator. integrated circuitU7-LM3I7T I -amp, adjustable

voltage regulator, integrated circuitQI, Q2 -2N2222 general-purpose

NPN silicon transistorQ3-TIP30 PNP Darlington power

transistorQ4-TIP120 NPN Darlington power

transistorDl-Not usedD2, D3-IN4148 or IN914 general-

purpose silicon, switching diodeD4-IN5819 or equivalent Schottky.

diodeD5 -1N4001 I -amp. 50-PIV rectifier

diodeD6, D7-IN4746A 18 -volt, I -watt,

Zener diodeLEDI-Bi-color (3 lead) light -

emitting diode


units, unless otherwise' noted.)RI -68,000 -ohmR2, R3, R6-R9, R22-R24. R32,

R37 -47.000 -ohmR4, R5 -220 -ohmR10 -25,000 -ohm, cermet trimmer

potentiometer (Bourns 3386P)R11 -6040 -ohm, 1/4 -watt, 2%R12 -12010 -ohm, 1/4 -watt, 2%R13 -24030 -ohm, 1/4 -watt, 2 %RI4-48700-ohm. 1/4 -watt, 2C/eRI5-97600-ohm 1/4 -watt, 2 %R16 -191.000 -ohm. 1/4 -watt, 29R17 -383.000 -ohm, 1/4 -watt, 2%

R18 768,000 -ohm, 1/4 -watt. 2 %R19 1.5-megohmR20, R21-3-megohmR25 -5000 -ohm cermet trimmer

potentiometer (Bourns 3386P)R26-Jumper wire, see textR27-No connection, see textR28. R29, R38--4700-ohmR30. R36 -1800 -ohmR31 -330 -ohmR33 -1000 -ohmR34-6.8 ohm 1/2 -watt. 5%R35 -82 -ohmR39 -10 -ohm 10 -watt, 5% ceramicR40 -15,000 -ohm x 5 SIP resistor

network

CAPACITORSCl. C8. C9, C11 -10-µE 25-WVDC,

electrolyticC2. C3, C14 -1-µE 25-Vv'VDC,

electrolyticC4-C6. C13 -0.01 -RE ceramic -discC7. C12-0.1-1.LE ceramic -discCIO 47-µF, 25-WVDC. electrolytic


F1 -2 -amp, 125 -volt, 5 -mm x 20 -mm fuse

J1 -5.5 -mm x 2.1 -mm DC powerjack

SI-SPDT center -off toggle switchPrinted -circuit board materials. 51/2-

x 5- X I1/2 -inch plastic enclosure,battery -output cable, DC -outputcable, LED bezel, grommets,TO -220 heat -sink, fuse holder,wire, hardware, etc.

Note: A kit containing a PC hoard,plastic enclosure, and all parts forthe Battery -Butler is available fromPeripheral Products (P.O. Box19278, Tampa FL, 33686-9278:Tel. 813-835-80881 for $49.95.plus $4.5() shipping and handling.Florida residents please addappropriate sales tax.

proportionately with the increase Inbattery voltage. When the voltage atpin 9 of U5 -c is greater than that pin 8.the reset input of U1 -a at pin 4 pulledhigh, causing it to oscillate. The outputof U1 -a at pin 3 is fed to the clock inputof U2 at pin 10. As the charge cyclecontinues, the track -and -hold circuittracks the battery's reference voltageat pin 9 of U5 -c, which is slightly lessthan the voltage at pin 11 of U5 -d. That difference can be adjusted viaR25.

As the Ni-Cd battery approachesfull charge, the voltage across thebattery terminals begins to decrease.Since the voltage at pin 8 of U5 -c andpin 10 of U5 -d is held slightly below thepeak V,,, voltage, the circuit can de-tect when the decreasing voltagecrosses the lower limit, and hence de-tect that the battery is approachingfull charge.

Once falls below the voltageat pin 10 of U5 -d, pin 13 drops low,causing the high -rate signal at pin 4 95

of U4 -b to go low. That signal turns Q1off, which, in turn, turns Q3 off. With Q3turned off, R35 sets the regulator'sconstant -current output at the lowercharging rate. The high -rate signalbrings pin 10 of U1 -b low, inhibitingLED1 from flashing; LED1 remains asteady green until S1 is returned to theoFF position or DC power is lost.

If the battery Is disconnected dur-ing discharging or charging, the leak-age current through U7 will causeVim,,,, to exceed the threshold voltageat pin 7 of U5 -b, causing pin 1 of U5 -bto go low. That low signal, which indi-cates a high level at the battery termi-nals, sets pin 1 of U4 -a low, forcing theready state as previously described.That function also detects overcharg-ing conditions and functions as asafety feature.

Construction. The authors pro-totype was assembled on a double -sided, printed -circuit board. The foilpatterns for the two sides of the boardare shown in Figs. 2 and 3 for thosewho wish to etch their own board. Theboard is also available separately oras part of a complete kit from thesupplier listed in the Parts List. Notethat, in any event, it will be necessaryto solder the circuit elements to bothsides of the board.

Once you have the board and allthe components, construction canbegin. A parts -placement diagramfor the project's double -sided board isshown in Fig. 4. It is wise to socket all ofthe DIP IC's, as some are CMOS de-vices and as such are static sensitive,Note: To make socket installation sim-pler, it is recommended that you usewire -wrap DIP sockets, elevating themslightly so that the leads can be sol-dered to the top, as well as the bot-tom, of the board. Once the socketsare in place, install the passive com- R28

ponents (resistors, capacitors, fuse,etc.), followed by the active compo-nents (diodes, and non -socketed IC's).Be sure and use heat sinks on both U7and Q4.

The Battery -Butler may be built withan internal DC power supply, allowingoperation directly from the 117 -voltAC line, or an external adapter maybe used. The circuit, as described, re-quires 11.5-15.0 volts DC at 250 mAduring charging, and less than 80 mAduring discharging and when in theready state.

4 INCHES

Fig. 2. The author's prototype of the Butter -Butler itus assembled on a double -sided,printed -circuit board, measuring about 4 by 41/2 inches The Pit pattern fin- copperside of the board is shown here full-scale.

U7

Note that in the author's prototype, a jumper wire has been plate in the R26 positionand R27 (just below it) has been omitted. Also note that (.17 and Q4 have heat sinksmounted to them.

4 INCHES

Fig. 3. This full-size template shows the circuit board traces for the components sideof the Battery -Butler's double -sided, printed -circuit board. If you decide to etch yourown board, be very sure that the too traces are properly aligned before the etchingprocess is begun.

Modifications and Limitations. Asdescribed, the circuit has been de-signed to operate a six-cell -a 7.5 -volt DC, 1.2 amp/hr Ni-Cd battery,commonly used in several models ofportable cellular telephones. In theunit used by the author, access to thebattery is provided through thehands -free interface modular tele-phone jack on the rear of the charg-ing stand. When using a standardRJ-11 plug and four conductor wire,the red wire is the battery's negativelead, the black lead is the battery'spositive lead, and the yellow andgreen wires are not used.

The charging stand may be usedwith the 12 -volt DC auxiliary output ofthe Battery -Butler. By connecting thatoutput to a 5.5 mm x 2.1 mm DCpower plug (polarized for positive tip)and inserting the plug into the DCpower jack on the charging stand, thefast charger can be used normally byplacing S1 in the FAST position. Someusers have reported good success

even with occasional use of the fastcharging mode.

The circuit may be adapted for usewith any Ni-Cd battery within therange of from 4.8 to 8.8 volts at 500 mAwith a capacity of up to 2 amp/hrs.The charge and discharge charac-teristics can be easily adjusted to suitthe battery. The rate of discharge is setby the value of R39. The dischargelevel is set by the combination ofR8 -R10. The high -rate charge currentis set by R34 and the low -rate chargecurrent is set by R35. The output over -voltage limiter threshold is set by R26and R27. (Note that in the version forthe 7.5 -volt DC/1.2-amp/hr batterydescribed in this article, those resistorsare replaced by a jumper and anopen circuit, respectively; i.e., theovervoltage limiter threshold is equalto 5 volts.)

The infinite range of battery types,voltages, and current ratings make itdifficult to address all possible config-urations, but by experimenting and

Shown here is the wiring interlacebetween the battery -charging stand andthe Battery -Butler

using simple calculations, the propersetting for those resistance values canbe determined.

Table 1 lists modifications to the cir-cuit for various battery voltages andnumber of cells. For example, for abattery with two cells and a voltageranging from 2.40 to 2.50 volts, R6should be replaced by a jumper wire,R7 is not installed, R9 goes from 47k to12k, R22 is replaced by a jumper wire,R23 goes from 47k to 82k, R26 (which,in the author's configuration, is ajumper wire) becomes 47k, and R27(which is omitted altogether in the au-thor's unit) is now 68k. In addition, thevoltage measured at pin 4 of U5should be around 1.80 volts, with nomore than a 0.06 -volt deviation.

The discharge rate can be con-trolled by changing the value of R39. Ifthe battery's rated full -charge voltageand the desired discharge rate areknown, the new value for R39 (inohms) can be determined using thefollowing formula:

R39 = (Vban - 0.7)/'discharge

where Vb is the battery voltage, and

'discharge is the discharge current inamperes. For example, if Vbatt is 7.5volts and 'discharge is .68 -amps (680mA), then:

R39 = 7.5-.7/.68

= 6.8/.68 = 10 ohms

which is the R39 value used in theauthor's prototype unit,

OUTPUTTO BATTERY

UNDER CHARGE

11 IF

C9

D4

Ot

El-R34 --R35 --R31 --R30 --R33-R32 --R28 --R29 -

U5

C5

I -C4-

R25

12VDCAUX OUTPUT

03

FAST

04

D7

-R36-

C14

C31 1 1C2

+ + +

R10

-R21 --R23 -- R22 ---R26-R27 --R7--R6--R8--R9--R15 --R16 --R11 --R14 --R13 --R17 -

-C13- -R12 --R18 --R19 --R20 -

R39

D J1

C10-+

U4

R3

R40

U2

-C6-

D6

-R38-R2 --R1--C12-

R24

U3

D3

D2

F1

R4

-R3- + C1

U1

-R5-LEDI

+-C11

Fig. 4. Assemble the Battery -Butler's printed -circuit board guided by this parts -placement diagram. Note that whether you purchase a board or kit from the supplierlisted in the Parts List or etch your own board, it will be necessary to solder the circuitelements to both sides of the board. It is also wise to socket all of the DIP IC's. assome are CMOS devices, and as such are static sensitive.

TABLE 1 -RESISTOR VALUE CHANGES AND VOLTAGE ADJUSTMENTS

No. of

Cells Battery

(V) R6 R7 R9 R22 R23 R26 R27

Pin 4

U5

(V) - dV

2 2.40 - 2.50 JW NI 12K JW 82K 47K 68K 1.80 0.063 3.60 - 3.75 JW NI 43K JW 82K JW NI 2.70 0.084 4.80 - 5.00 15K 47K 47K 15K 47K JW NI 2.70 0.085 6.00 - 6.25 33K 47K 47K 33K 47K JW NI 2.60 0.086 7.20 - 7.50 47K 47K 47K 47K 47K JW NI 2.70 0.107 8.40 - 8.75 68K 47K 47K 68K 47K JW NI 2.60 0.108 9.60 -10.0 82K 47K 47K 82K 47K JW NI 2.60 0.10

JW = Jumper Wire

To charge seven- and eight -cell(8.40 - 10.0 volt) batteries, the circuitmust be supplied from a 16 -18 -voltDC power source. That voltage mustbe regulated (via an LM317 or equiv-alent device). Resistor R34 -whichnormally ranges from 2 to 47 ohms at

NI = Not Installed

1/2 watt -sets the high -rate chargecurrent. Resistor R35 -which normallyranges from 47 to 120 ohms at 1/4watt -sets the low -rate (trickle)charge current.

Testing and Adjustments. Set S1 to

the OFF position. Connect the com-pleted circuit to a 12 -15 -volt DC sup-ply. Measure the voltage at pin 3 ofU5. That voltage should be at, or near,5.0 volts DC. If either of those voltagesare not within the specified ranges,remove the DC voltage source andrecheck the connections.

Measure the voltage at pin 4 of U5with a high input -impedance digitalvoltmeter (DVM). That voltage can beset by adjusting R10. The recom-mended voltage at pin 4 of U5 can bedetermined by the following:

0.90M x (number of cells)/2

For example, if a 6 cell, 7.5 -volt Ni-Cdbattery is used, the voltage at pin 4should be adjusted to:

0.90 x 6/2 = 2.70 volts DC

That adjustment sets the level to whichthe battery will be discharged. Notethat the battery will discharge totwice this present voltage:

Battery Discharge Level =pin 4 of U5 x 2

= 2.70 VDC x 2 = 5.40 VDC

If the Ni-Cd battery is not dis-charged low enough, the battery willlose its ability to hold a full charge. Ifthe Ni-Cd battery is discharged toolow, it is possible that the cells withinthe battery may reverse and the bat-tery will lose its ability to take acharge.

Connect a fully charged 7.5 -volt,1.2 amp/hr Ni-Cd battery to the prop-er terminals on the Battery -Butler. Beaware that reversing the battery con-nection will cause the battery to im-mediately begin discharging throughD7 and R39; that should not damagethe Battery -Butler.

Again using a high input -imped-ance DVM, measure and record thevoltage at pin 5 of U5. Measure thevoltage at pin 9 of U5. The recom-mended voltage at that point can bedetermined by subtracting 0.10 voltDC from the voltage noted earlier atpin 4 of U5. The proper voltage can beset by adjusting R25.

If the voltage at pin 9 of U5 is within.02 volts, or greater than the voltageat pin 5 of U5, the circuit will return tothe ready state too soon, and the Ni-Cd battery will not reach a fullcharge. Note: If the voltage at pin 9 ofU5 is 0.30 volts less than the voltage at


Making TheConnectionMake the right connection between a wireantenna and your rig.

There is large amount of infor-mation on wire antennasavailable to receiver users.

However, Iwo related topics that seemlacking in coverage, or at leastjumbled up with other material, areantenna -construction and termina-tion. In this article, we will take a lookat both topics. As we proceed, keep inmind that the information applies tonearly all wire antennas, not just thetypes mentioned.

Types of Wire Antennas. The vari-ety of wire antennas around is mindboggeling, but they fall into two basiccategories. One group is like the Mar-coni -style antenna, shown in Fig. 1A,consisting of a single -wire radiator,usually made of insulated or uninsu-lated No. 14 or No. 12 wire placedhigh in the air. The antenna is typicallysupported by a set of end insulatorsand rope supports. One end of theantenna is connected to a piece ofinsulated wire (called the "down -lead"), which is connected to the rig(receiver, transmitter, or transceiver).

Related antennas include the ran-dom -length wire antenna, long-wireantenna (both resonant and nonreso-nant types), windoms, Tee -antennas,and top -hat antennas to name a few.They are all different, but have onesimilarity: they consist of a single radi-ator element connected to a single -wire downlead that is connected tothe radio rig.

Someplace before the downleadenters the house, a protective light-ning arrestor is connected to the cir-cuit. The lightning arrestor is used tobypass as much of a lightning strike aspossible to ground. The ground wireconnected to the lightning arrestor ismade of heavy wire or braid cut asshort as possible, and is connected atthe other end to a ground rod driveninto the ground. Always follow localelectrical and safety codes for the

BY JOSEPH J. CARR

ground rod, which in most casesmeans you should use an 8 -foot cop-per -clad steel rod. Those little 4 -footground rods are not terribly good forlightning protection, so don't dependon them.

The downlead is connected di-rectly to the rig's antenna terminal. Asecond ground, which may go to thesame ground lead as the lightning ar-restor ground, is used to improve theRF performance of the radio antenna.

The other basic type of antenna isshown in Fig. 1B. That antenna is adipole. Such antennas consist of twowire radiators fed by a two -conductorcable such as twin -lead, twisted -pairor, most commonly, coaxial cable.When coaxial cable is used, the cen-ter feed point may be either a specialcenter insulator or a BALUN (BAL-anced UNbalanced) transformer.Again, end insulators and rope sup-ports hold the antenna in the air. Aswith all antennas, a lightning arrestoris used to protect the house and rig.

End and Center Insulators. End in-sulators are used to electrically isolate

the wire radiator from the supportrope. In addition, they provide a cer-tain amount of mechanical strengthin the connection between the radi-ator wire and the rope supports. Theymay be made of glass, glazed ce-ramic, or a synthetic material such asnylon or Teflon.

Figure 2 shows one popular shapeof the classic ceramic end insulator.Most of those sold in stores today aremade of synthetic material, althoughused ceramic and glass insulatorscan be frequently seen at hamfests.

Two synthetic end insulators areshown in Fig. 3. The larger one showncan be used for high -power ham -ra-dio transmitter antennas as well asgeneral -receiver antenna use. It pro-vides a much larger degree of isola-tion between the wire and thesupports (which presumably reducesend effects). The smaller unit is usedfor smaller transmitter antennas, andgeneral shortwave -receiver anten-nas.

A pair of popular center insulatorsare shown in Figs. 4 and 5. The typeshown in Fig. 4 has an SO -239 UHF 99

ANTENNADOWNLEAD

LIGHTNINGARRESTOR

RECEIVERGROUND

#12 OR #14WIRE

CENTER INSULATOR

OR BALUN

COAX TO RECEIVER

A

#12 OR #14WIRE

#12 OR #14WIRE

LIGHTNINGARRESTOR

RECEIVER

B

Fig. I. The two most common antenna types-the Marconi -style antenna (A) and theHertzian "balanced" antenna (B)-are shown here. Note the additional radiator in B.

Fig. 2. End insulators come in differentstyles. Here is a "classic" end insulatormade of glazed ceramic. Some can stillbe found at ham shows today.

Fig. 3. The modern end insulators aretypically made of a synthetic materialsuch as nylon. That makes them fairlyresilient

coaxial connector, that can mate di-rectly with the PL -259 coaxial con-nectors used on many antennafeedlines. The radiator elements areconnected to heavy-duty, solid -cop -

100 per wire "pigtails" protruding out each

end of the center insulator. (Connec-tions for this type of center insulatorwill be discussed later.) A differentform of center insulator is shown in Fig.5. In that type of insulator, a hollowbody of PVC -like plastic material con-tains connections for the SO -239coaxial cable. The wires are con-nected to, and supported by, a pair ofscrew/eye terminals on either side.

Some center insulators contain BAL-UN transformers. For ordinary dipolesuse 1:1 BALUN transformers; for foldeddipoles use 4:1 BALUN's.

Using Insulators. There are twogoals to keep in mind when makingconnections to either end insulators orcenter insulators. First, you want astrong, reliable mechanical connec-tion that won't come loose under thebuffeting the antenna will receive.Winds and weather can take a terri-ble toll on wire antennas, so a good,reliable connection is mandatory. Thesecond goal is to make a good elec-trical connection-after all is said anddone, the antenna is still an electricaldevice connected to an electroniccircuit.

A minor point to make is to avoidkinks. Radiator wire is either hard -drawn copper wire or copper -cladsteel wire (e.g., Copperweld), so keep

Fig. 4. Some center insulators have"pigtails" on each side that theradiators need to be soldered to. Theantenna's downlead attaches to theconnector at the bottom of the insulator.

Fig. 5. This type of center insulator hascrimp -on lugs for a good electricalconnection. These center insulatorssometimes contain BALUN transformers.

in mind that it kinks up very easily. Infact, experienced antenna erectorsclaim that gremlins or RF demons existwhose main function in the universe isto put permanent kinks in wire. Whenthe wire kinks, it is nearly impossible toget the kink out of the wire so that itlooks good again. The antenna will stillperform well, but the spot where thekink occurred will always remain.

Let's deal with end insulators first.Figure 6 shows how to make a con-nection to an end insulator. Althoughonly one style insulator is shown here,the method for the other styles shownearlier is identical.

The first step in connecting the an-tenna wire to the insulator is to passthe wire through one of the holes inthe insulator. Leave 6 to 8 inches offree wire. Next, double the free end ofthe wire back on itself, and wrap itaround the main body of the wire sixto eight times; leave about 3/4- to 1 -inch of loop to permit the insulator tomove freely. If a downlead is required,as it will be on one end of a Marconi -style antenna, then strip away about 2inches of its insulation, and then wrapthe bare downlead wire around themain antenna wire four to eight times.

The final step is to solder all the con-

Fig. 6. To make a connection to an endinsulator, you first insert some wire intoan eyelet, twist it over on itself 6-8turns, and then solder.

nections. The purpose of the solder isnot to add mechanical strength, butto ensure the electrical connection inthe face of potential corrosion. Useeither 50/50 or 60/40 lead/tin resin -core solder. Use solder marked "resincore," "radio/Mr or "electronic" solder.Under no circumstances use acid -core solder! That solder will eat theantenna wire away. It is marked"plumber's" solder, or something sim-ilar. Also avoid coreless solder. It canonly be used with separate acid -coreflux, and is useless to wire -antennaconstructors.

Use at least a 150 -watt solderingiron or soldering gun. A small pencil -type iron (typically less than 75 watts)is not suitable for this purpose. Heatthe joint thoroughly, and then applythe solder so it completely coats thewire of the support splice and thedown!ead splice. You may find thatthe area where you apply the iron willturn out well coated with solder, butother areas aren't wetted at all, so besure to turn the wire over and solder allsurfaces.

Apply caution when soldering.Solder must be very hot to melt, andthe wire junction and its vicinity (eventhe insulator) will try to "sink" the heat,so don't touch it with your bare hands!It can cause painful first- and second-degree burns. Handle the wire andthe insulator with insulated pliers, orsome other heat -handling tool.

The procedure for connecting acenter insulator depends on the typeof center insulator that is used. Figure7 shows the use of an ordinary endinsulator as a center insulator for adipole or other balanced antenna.The two wire radiators are splicedonto the insulator in the normal man-ner for end insulators. The coaxial ca-ble is stripped such that its centerinsulator and conductor are each

INSULATOR

INNERCONDUCTOR

INNERINSULATION

BRAID(OUTER CONDUCTOR)

Fig. 7. The split -coax method of making center connections shown here is notadvisable, as the connection is prone to corrosion.

routed to one of the antenna radi-ators, while the braid (outer conduc-tor) is routed to the other. Both arespliced to their respective radiator el-ements. One popular method is touse the pigtails left over from makingthe two support splices as electricalconnections for the coaxial cable.

In some cases, the body of thecoaxial cable is wrapped around thecenter insulator and tied off withstring, cord, or fishing line in order toprovide mechanical support for theconnections. If you use the "split coax"method, then a strain relief is essential.

The method shown in Fig. 7 is notrecommended. It is mechanicallyweak, and open to the weather. It iscommon to find water infiltration intothe coaxial cable, which deterioratesits performance. It is better to use aregular center insulator or a BALUNtransformer.

The type of center insulator shownback in Fig. 4 has heavy, solid copper -wire pigtails protruding from inside theinsulator. Before beginning the splice,you must tin the pigtails. That is, heatup each one with a soldering iron andspread a thin coating of solder overthem. They should look silver platedand smooth after they are tinned.

The antenna wire is laid alongsideeach copper pigtail, and in contactwith it, and is then passed through thehole in the insulator, doubled back onitself, and then wrapped around boththe pigtail and its own main body sixto eight times. It thus resembles anordinary end insulator support splice,except for the pigtail in the core. Fi-

nally, using a soldering iron or gun,solder the splice thoroughly in thesame manner as for support splices.

The method for connecting theother type of center insulator (shownback in Fig. 5) is similar to the tech-nique for an end insulator. You passthe antenna wire through an eyelet,and leave about 8 to 10 inches of wirefree when you pass it through. Thenwrap the wire back on itself until youhave about 5 -inches of the free endleft. The end left over is then con-nected to the terminal lugs fastenedto the eyelet. It is prudent to pull thelug away from the body of the in-sulator so it can be later crimped andsoldered without melting the plasticbody. Pass the end of the wire all theway into the terminal past both sets offlanges, and then crimp the flangesover the wire with long -nose pliers inorder to form a good mechanicaljoint. Next, solder the terminal andwire together.

The Rig End. There are a variety ofconnectors used for connecting an-tennas to receivers and transmitters. Ifthe connector on your antenna com-pliments the one on your receiver, youjust have to plug them together. If thetwo connectors do not mate, youcould just buy an adapter to bridgethe connection.

Some receivers are equipped witha Iwo- or three -station screw terminalinstead of a connector. On a two -screw terminal block, one screw(often labeled "ANT" or "A") is for theantenna and the other (labeled

Fig. 8. The rear panel of this shortwavereceiver can accept coax, lug -terminal,or bare -wire downlead terminations. Ina pinch, a banana plug could be pushedinto the 50 -ohm socket for single -wireantennas.

"GND," "GRND," or "G") is for theground connection.

The screws on units equipped withthree -terminal antenna blocks aretypically labelled "Al," A2," and "G."Those sets can use a balanced trans-mission line, such as twin -lead, paral-lel line or twisted pair line, but are mostoften connected to a single -wire line.When a single line is used, the inputcan be converted into an unbal-anced one by connecting a wirejumper between terminals A2 and G(i.e., by strapping one side of the an-tenna connector to ground).

The method of choice for con-necting any such wires is through theuse of neat cable -ends, or spade lugs.However, if you must use iuRt the ex-

posed wire, take the time to strip theend of the downlead about 3/8 inch,and then form it into a loop that has adiameter slightly larger than the bodyof the screw terminal. If the wire isstranded, then tin the stripped end toprevent it from fraying and shorting tothe adjacent terminal. Place the loopunder the screw in the direction oftightening for the screw (clockwise).The idea is to cause the loop to closeon itself under the screw when thescrew is tightened. If you place theloop under the screw in the coun-terclockwise manner, then it will openwhen the screw is tightened.

Figure 8 shows the rear panel ofone of my shortwave receivers. Thereare three connections present: 50 -ohm antenna, "Hi -Z" antenna, andground. The 50 -ohm antenna input isan SO -239 UHF connector for coaxial -cable fed antennas, while the Hi -Z in-put is for single -wire downleads. Inmany cases, it is found that the twoare connected together inside the re-ceiver, so which one to use is a mootpoint. However, if needed, it is possibleto connect a single -wire antenna di-rectly to an SO -239 coaxial connectorby placing a banana plug on the endof its downlead. If the "Hi -Z" terminal isused, then use a spade lug on the end)f the downlead.

These connectors are commonly used to link the downlead to a receiver or transmitter.From left to right they are the PL -259 UHF coaxial connector, the BNC coaxialconnector, the banana plug, and the alligator clip. The coaxial adapters in theforeground are a PL -259 -to -SO -239 male -to -female right-angle adapter (left) and an

102 SO-239-to-BNC adapter (right).

TELESCOPINGWHIP ON

A PORTABLE

TOROIDCOIL

GROUNDLEAD

Fig. 9. This method of coupling a single -wire antenna to a portable shortwaveradio equipped with a telescoping -whipantenna sometimes works. Other times,it just overloads the receiver

A means for connecting a single -wire antenna to a portable shortwaveradio is shown in Fig. 9. Of course, youcould use an alligator clip on the endof the downlead, and connect it di-rectly to the whip antenna of the ra-dio. But that may cause damage tothe radio if static charges build up onthe antenna. The method shown usesinductive coupling to avoid that.

The coil is wound on a toroidal corethat has an inside diameter that willjust fit loosely over the bottom portionof the whip antenna when the coil iswound. That usually means a T37 orT50 core. For low bands (less than 7MHz), use about 20 turns of No. -26enameled wire over the core; forhigher bands (greater than 7 MHz),use 8 to 10 turns of No. -26 enameledwire. Connect one end of the coil tothe downlead, and the other to theground lead.

Be careful when adding an externalantenna to a portable shortwave ra-dio. Some of them already providecompensation for their small tele-scoping whip antennas. If an externalantenna is used, then signal levelsmay prove excessive causing the ra-dio to overload.

SMARTER GAS GAUGE(Continued from page 22)

cuit board. An incandescent lampcan be connected directly to the cir-cuit board. If, however, the in -dash idi-ot light is an LED, it will be necessary touse a 1000 -ohm current -limiting re-sistor in series with driver transistor Q1and the LED. (Check to see if there isn'talready a limiting resistor.)

If your car is an early model, thenyou might not have an idiot light thatwas factory installed and integral tothe instrument cluster. In that case,You'll want to install your own idiotlight.

Although you could mount all threepotentiometers (trip threshold, lampdimmer, and slosh control) in the dash,the trip -threshold potentiometer is theone that you'll be adjusting the most.The other two controls can be left onthe circuit board, adjusted once, thenleft alone.

The grounding wire should be ter-minated with an eyelet (ring lug) andattached to the car chassis anywhereunder the dash using a sheet -metalscrew or rivet. It's better to ground thecircuit directly to the car chassis ratherthan to another wire that seems to begrounded. Very often, wires that seemto be grounded are actually discon-nected when the ignition switch is inone position or another; going di-rectly to the chassis ground takes mostof the guess work out of the installa-tion procedure.

The 12 -volt wire should go to theradio fuse in the car's fuse box, eithersolder the joint or use a mechanicaltwist connector. Also, don't forget toplace a 2 -amp, in -line fuse in serieswith the positive supply lead of theSmarter Gas Gauge. If you're in a rush,just jam the Gas Gauge's positive leadwire against the radio fuse and pushthem both into the fuse box. The fuseclip will hold the wire pretty tightly. It'sfast and it works.

Lastly, the Vgas lead wire should beconnected at the gas gauge to thesending wire using a wire tap -in con-nector.

Quick connect, snap -n -splice, orwire tap -ins are trade names for aconnector that's designed to makean electrical connection betweentwo wires without having to cut, twist,or solder them together. First select

The author's finished prototype of theSmarter Gas Gauge, though small, isuncluttered.

the wire -tapping connector of theappropriate wire gauge for your in-stallation. Place the sending wire andconnecting wire into the wire -tapconnector, then fold and squeezewith pliers until the metal insert bot-toms out; that will force the metal in-sert to pierce the insulation of bothwires thereby making electrical con-tact without cutting the conductors.

What if your gas gauge is broken?Maybe the gas needle is stuck in thefull or empty position. If so you can stilluse our Smart Gas -Gauge, but you'llhave to bypass your broken gauge.That's because series current mustflow from the battery through the gasgauge then through the sender toground. Any broken wire internal tothe gauge will open the series circuitand no current will be able to reachthe sender.

The idea is to disconnect the gaugewiring and install a 100 -ohm, 10 -watt,bypass resistor (such as Radio Shack'sP/N 271-135 wire -wound resistor). Youcan leave the gauge in place to re-tain the dash aesthetics.

Calibration. Here's one method tocalibrate the threshold at which thegas level in the tank turns 11 on. Driveyour car until the gas tank is well be-low 1/4 tank and pull up to a gas pumpat any gas station. Turn the ignition keyto the ON position, which will leave thefuel -gauge system on, but the engineoff. For the calibration to work you'llneed to watch the gas -tank needlemove as the tank is being filled. Whenthe gas -station attendant starts thepump, adjust R2 (the TRIP -THRESHOLD CON -

ma) so that the lamp is illuminated.The second the gas gauge shows ex-actly 1/4 tank, back off on the tripthreshold until the lamp extinguishes.

That's all there is to it. Now you've setthe lamp to come on when your tankis 1/4 full. Then adjust R3 (LAMP DIMMER CON-

TROL) to achieve the desired lampbrightness.

You could also fill up the tank your-self to the exact gasgauge indica-tion, say 1/2 full, then go back into yourcar and adjust the trip -threshold po-tentiometer so that the lamp just turnson. Any additional gas pumped intothe tank will immediately turn thelamp off, as the tank fills up.

The bi-metal, heated -coil, fuelgauge requires a minute or so toaccurately reflect the gas level in thetank. That's because the bi-metaltakes that long to heat up and bendto the correct position. So give thegauge a minute to stabilize beforeadjusting the trip threshold. Magnetic -type gauges, which display the cor-rect gas level in the tank right away,don't have that problem.

Even though bi-metal gauges taketheir time to respond to the correctgas -level reading, the Smarter Gas -Gauge reads the sender voltage im-mediately and is therefore imme-diately accurate.

the trip threshold whiledriving on the open road is easy, too.When the gas tank reads about 1/4 full,adjust the trip -threshold potentiome-ter so that the lamp just comes on.When you adjust the trip threshold,you're actually adjusting Vref. As thegas sloshes in the tank, Vgas variesabove and below Vref and that willcause the lamp to flash while you'redriving. You, therefore, might want tore -adjust the trip threshold severaltimes until you get a feeling for thelamp's flashing rate.

Accelerating quickly by steppingdown hard on the gas peddle orturning tight corners at screechingspeeds may also light the lamp, again,because the gas is rolling in the tank. Asteep hill or incline may also turn onthe lamp. Stopping the lamp fromflashing is easy: Adjust potentiometerR4 (the SLOSH TIME-OUT CONTROL) until the

lamp stops flashing, then tweak R4 alittle more in the same direction forgood measure.

Of course, the beauty of theSmarter Gas -Gauge is that you canadjust the lamp to illuminate at anygas level in the tank; whether 3/4 full, 1/2full, 1/4 full, almost empty, or anywherein between. MI

cn

z(0CD

m

rn

0zcn

00707

C-7)

z

cn

00700

103

104

SOLAR POWER SUPPLIES(Continued from page 92)

A solar cell will deliver about 1/2 voltinto its rated load when exposed tofull sunlight; a set of eight connectedin series will deliver 4 volts for use withthis project. The current capability of acell may be estimated by noting itsarea. A rule of thumb for solar -cell cur-rent rating is 40 mA for each squarecentimeter of cell area, when ex-posed to full sunlight.

Refer to Fig. 8, illustrating the properway to connect solar cells in series.The connections are made to theback of the cell (positive terminal),and the silver colored band on thefront of the cell (negative terminal).One must be extremely careful whensoldering wires to the cells, which areextremely fragile and will break if sub-jected to excessive force. Use a low -power soldering iron and very fineflexible wire to make the connections.

The assembly of cells should beplaced into a frame that's made ofwood or some other suitable insulat-

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ing material. The cells can be held inplace by sandwiching them betweena piece of glass or clear rigid plasticand the frame. A 1/8 or 1/4 -inch thickpiece of flat foam rubber makes agood cushion to prevent excessiveforce on the fragile parts.

The regulator circuit itself may beplaced into the frame, or a pair offlexible wires can be brought out ofthe solar panel to allow connection tothe circuit.

Checkout. The regulator circuits canbe checked out using either the solar -cell array placed in full sunlight as thepower source or using a well -filteredadjustable DC supply that can pro-vide 3 to 4 volts at 250 mA. Using apower supply is the preferred methodas it will demonstrate that the reg-ulator circuit will operate properlywith the minimum specified input volt-age.

The radio or casseffe player thatyou intend to power from the circuitcan be used as the load, but it wouldbe more convenient to calculate itsrepresentative load resistance anduse a fixed resistor instead. The loadresistance (R1) is equal to the regu-lated output voltage (Vreg ow) of thesupply divided by the required loadcurrent (I,,) in amperes. Be sure touse a resistor with a sufficient powerrating; about 1 watt should do.

Testing the circuit will require a DCvoltmeter with an input resistance of 1megohm or more. A typical DVM orVOM is satisfactory. Before applyingpower to the circuit, check the polar-ity of the input and output connec-tions to be sure they are correct. If acurrent -limited power supply is usedfor power, set it to limit the current toslightly more than the circuit require-ment.

Apply about 3.5 volts to the reg-ulator circuit while measuring the reg-ulated output voltage. It should bewithin 0.1volt of the nominal rating, 2.4(for the linear circuit), 4.8. or 7.2 volts(for the switching circuits). Vary the in-put voltage to the circuit by partiallyshielding the solar cells from the Sunor adjusting the DC power source.Note that the output voltage of theregulator circuit remains relativelyconstant as the input voltage variesfrom about 3 to 41/2 volts.

If the supply is operating as de-scribed, remove the load resistor and

connect the radio or tape player tothe output of the regulator. Verify thatthe circuit will properly drive the unit,delivering a minimum of 2.4, 4.8, or 7.2volts DC (depending of the type andregulator configuration you'vechosen to build. Replace the powersupply (if one was used) with the solar -cell array; place solar cell in full sun-light, and verify radio or casseffe op-eration. That completes the checkout.

If the circuit does not work as de-scribed, examine it very carefully forproper component values, and cor-rect orientation of the IC, electrolyticcapacitors, and diodes. Inspect thewiring for inadvertent short circuits,open circuits, and bad solder joints.Check the input and output connec-tions of the supply to be sure the po-larity is correct.

Check the output voltage of the so-lar -cell array to be sure it is delivering4 volts in full sunlight. If the output volt-age of the regulator is not within 0.1volt of nominal, check the values ofR1/R2, or R3/R4 to be sure they arecorrect.

Using the Solar Power Supply.When using the Solar Power Supply,the batteries should be removed fromthe radio or tape player. The easiestway to connect the power supply tothe unit to be powered is via that unit'sexternal power supply (AC -adapter)jack. Units that do not have an exter-nal power jack can easily be modi-fied by connecting a pair of wires tothe positive and negative contacts inthe battery compartment and bring-ing the wires out to the output termi-nals of the Solar Power Supply.

The solar panel should be exposedto direct sunlight for best perfor-mance. If the sun is very bright, thepanel may simply be placed in a hori-zontal position during most of daylighthours. On hazy or cloudy days, it maybe necessary to position the panel sothat it is perpendicular to the rays ofthe Sun to achieve maximum perfor-mance.

If the switching Solar Power Supply isto be used for AM radio reception,some interference from the radiatedswitching -frequency harmonics maybe experienced. That may be coun-teracted by placing the supply somedistance from the radio, and usingadditional filtering and/or shielding tominimize interference.

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SPI4PV1 105

AN ELECTRONIC GONG(Continued from page 40)

semiconductors (BR1, D1, and Q1) ex-cept the IC's. Follow that with trans-former T1. In the prototype, T1 wasmounted to the board using a coupleof nuts and bolts. Ned, you must de-cide on a location for SPKR1. Themounting location for the speaker de-pends on the circuit's intended useand housing. (In the author's case, thespeaker was fastened inside the baseof the tea -maker using a self -tappingscrew.)

Once you've mounted SPKR1, con-nect short lengths of hook-up wire be-tween the circuit board and thespeaker. Finally connect, a 117 -volt ACsource to the appropriate points onthe circuit. In the author's prototypeinstallation, the AC source wastapped directly from the tea ma-chine's internal wiring.

Check Out. Before applying powerto the circuit, it is wise check the as -

117VAC

Fl

I I

P

sembly for construction errors, such assolder bridges (shorts) betweentraces, cold solder joints, misplacedand misoriented components, etc.Once you are satisfied that the circuitcontains no errors, it time to put thecircuit through its paces. Install the IC'sin their sockets, making sure that theyare properly oriented.

With a project that's powered by theAC line, it is often a good idea to firsttest the circuit using a regulated, low -voltage DC power supply. The circuit isin no way fussy about the supply volt-age, and will operate on any voltagefrom about 9 volts (below which theLM380 does not perform reliably) to 15volts (above which CMOS IC's like the4001 tend to get zapped).

With power applied, adjust R10 untilthe twin -T network is just about to oscil-late; working from there, decreaseR10's resistance until the circuit oscil-lates steadily. After that, increase R10'sresistance until the oscillations fade tosilence (as shown in Fig. 6). If R10 is setto its maximum resistance, there willbe fast decay, or perhaps even no

BR1

Ti 0

R1

+C2 R2

+ C3

C4

R4

I 1

Ul

01

R5

R6C5

+ +

I ci ICll

R9

CcC8

I I

U2 C9

TO

EXT.

AMP

SPKR1

Cl 2

U3

C10

Fig. 5. This diagram shows the component locations for all of the circuit elements,both on -board and off -board. It is recommended that sockets be provided for the IC's;two 14 -pin units for Ul and U3, and an 8 -pin unit for U2.

AMPLITUDE

TIME

Fig. 15. With power applied, adjust RIOuntil the twin -T network is just about tooscillate; working from there, decreaseRIO's resistance until the circuitoscillates steadily. After that, increaseRIO's resistance until the oscillationsfade to silence, as shown here.

oscillation. With R10 at the other endof its rotation, oscillation should beconstant, i.e., no decay.

The preferred setting will be influ-enced by the triggering period. Withthe RC component values used in theoscillator circuit (U1 -a and U1 -b), thedelay between pulses was about 12seconds. With R10 set very critically, formaximum decay and reverberation,the sound may not have completelydisappeared when the next triggerpulse arrives. Finally R11 should be ad-justed to give the required volumelevel.

Other Uses. I have used essentiallythe same circuit in a car -alarm unit toprovide a repetitive warning alert dur-ing the exit and re-entry periods. it isalso triggered to give between oneand four chimes on detecting variousconditions such as low fuel, low wash-er fluid, and icy temperatures.

I've also built a little electronic -per-cussion unit with 11 switchable soundsacross the frequency spectrum, whichwas fun to make and play with. Lots ofother possibilities come to mind, suchas using it in a prowler alarm, a prox-imity detector, or (with some chal-lenging logic circuitry) as a clockchimer.

PET5 AND SUPPLIES

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TROPICAL aFISH 8

"This usually brings them out of hiding-

QUAD ANTENNA(Continued from page 42)

which were snaked through thespreader holes) were used to com-plete the driven -element loop andsoldered together. The other loopswere assembled in the same fashion,feedpoint not withstanding.

An electrician's copper -wire clampplaced on the reflector was used totune the quad. We pointed the reflec-tor toward a handheld two -watt trans-ceiver and tuned for minimum signalinto the transceiver.

The antenna provided very goodperformance, with a reasonable SWRover the entire 144 -MHz band. Weused a watt meter to measure thereflected power, and found that with100 watts of output, less than a 1/2wattwas reflected.

So my students now know the dif-ference between a full -wave andhalf -wave antenna. Our next class-room project is to build a PVC -basedten -meter quad. Hope to work you onten meters.

BUILD THE WATER TAP(Continued from page 79)

over the tube so that the assemblyfloats as level as possible.

The other section contains the 9 -volt battery with the power switch inseries, which supplies power to thefloating section via two strands of thetelephone wire. The battery is held inplace inside the case with a piece ofdouble -sided tape. Holes are drilledin the lid of the case for the speakersound to pass through. The speaker isthen secured to the lid with hot -meltglue. The speaker is connected to theamplifier board with the two remain-ing telephone wires. The telephonewire exits the top of the case. A suctioncup is mounted on the back of thecase to hang it on the outside of thefish tank.

When the adhesive (hot melt glueor RTV silicone) is completely dry, theWater Tap is ready to listen in on yourfish. You can probably think of manyother unusual uses for this bizarregadget.

PARTS LIST FOR THEWATER TAP

RESISTORS(All resistors are 1/4 -watt, 5% units.)RI -1 -ohmR2 -10 -ohmR3 -2200 -ohmR4 -4700 -ohmR5 -10,000 -ohm

CAPACITORSC1-270-pF, ceramic -discC2-0.01-1LE ceramic -discC3, C4-0.1-ji,F, ceramic -discC5 -33-µF, 10-WVDC, electrolytic

10-WVDC, electrolyticC7. C8-220-ji,F, 10-WVDC,

electrolytic


Ul-TBA820M audio -amplifierintegrated circuit, (SN76001,MCE820, NTE1294, or equivalent)

MIC1-Electret microphoneSPKR1-8-ohm speaker

Shielded cable, telephone wire, 9 -volt battery and clip, glass testtube, two project cases, suctioncup, hot -melt glue or RTVsilicone, double -sided tape, wiresolder, etc.

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POWER SUPPLY(Continued from page 33)

If you choose to use a transformerwith a different current rating than the2 -amp unit we used, then you willhave to compute the value of the fuseto suit your needs. Most transformersare rated by their primary voltage,secondary voltage, and secondarycurrent. You will need to know themaximum current to permit in the pri-mary that will not damage the sec-ondary. Here is a simple relation youcan use to determine that maximum:

1p = Is(Vs/Vp)

where 1p is the primary current, Is is thesecondary current, Vp is the primaryvoltage, and Vs is the secondary volt-age.

You may wish to select a slightlylower value for added safety. How-ever, since some of the power pro-duced by the primary is lost in thetransformer's iron core, not all of itreaches the secondary. Opinions may

vary, but that provides a margin ofsafety that has proven itself sufficientover the years.

The bridge rectifier BR1 is used toturn the secondary's AC into full -waverectified, pulsating DC. While we useda 2 -amp bridge, you should use onethat will handle the maximum currentthat you expect to draw, plus a 25%safety margin.

Capacitor C1 filters the pulsatingDC of the rectifier into a more man-ageable form for the adjustable reg-ulator. The capacitor at the regulator'soutput (C2) helps to eliminate de-structive transients or other noise thatmay occur on the power leads.

Of course, R1 and R2 program theregulator for the desired 12 -volt out-put in the fashion mentioned earlier.Note that a diode (D1) has been add-ed to the circuit. It steers any currentthat might be coming from the deviceunder power around the regulator toprevent the regulator from beingdamaged. Such reverse currents usu-ally occur when devices are powereddown.

Construction. Building the powersupply is easy since so few compo-nents are required. We mounted theparts on a piece of perfboard andused point-to-point wiring to com-plete the interconnections. The size ofthe cabinet was chosen mainly for thesize of the transformer, which wouldn'tfit in a smaller cabinet. The trans-former and circuit board aremounted to the bottom of the caseusing some drywall screws and scrapsof perfboard as "nuts." While standardhardware could also be used, drywallscrews cost much less and perfboardscraps are essentially free. To use thedrywall screws, all you have to do iscountersink the holes on the bottomside of the case and drill a starter holein the perfboard "nuts." To make thepower supply as versatile as possible,we put simple binding posts on thetop of the case for the output. We alsoput the on/off switch there.

The power supply should only takea couple of hours to build. However,we're sure you'll find uses for it formany years to come.

BEVERAGE COOLER(Continued from page 45)

Figure 6 shows the top plate, insula-tion, and a soda can all in place whilethe epoxy cures. The last part of thecooling chamber construction is thechamber itself. My chamber is madefrom a doubled -walled drink con-tainer, which are available virtually ev-erywhere. If you buy one specificallyfor this project (rather than using oneyou have on hand), try to find one thatis insulated. That prevents you fromhaving to stuff insulation into void ofthe double -walled container (coolingchamber).

Prepare the cooling chamber bycutting off the bottom 2 inches or soof the drink container. If you are fortu-nate, you'll find insulation betweenthe walls. Obviously, the one I used inthe prototype only had air betweenthe walls, so I had to stuff it with theinsulation from the soft-drink keepermentioned earlier. You absolutelyneed to insulate the chamber for sat-isfactory results.

Once the drink container has beenprepared, epoxy it in place over the

108 cooling module assembly. Just put a

decent layer of epoxy all around thebottom, and press it into place. Let theepoxy cure with a weight on top of it.

To finish the chamber, put a singlelayer of weather stripping around thetop of the cooler, on the inside. Thatseals the chamber from outside air asmuch as possible. Your soda canshould just fit inside the chamber, withabout one inch of can sticking out thetop. Figure 7 shows the business endof the cooler.

The Hookup. As shown in Fig. 3, thecooling module is wired in parallelwith the fan, and both are connectedto a 12 -volt DC power source. If youare not comfortable soldering theconnections, you can use wire nuts.Your car's battery works well as asource of DC to test the unit. (I now usethe power supply from my ham -radioequipment to power the cooler.) Re-member, the power source must beclean (free of ripple) and capable ofdelivering a full 3 amps without over-heating.

That all there is to it. I hope you haveas much fun building and using thecooler as I did. And don't be surprisedif you are ask to build several forfriends!

RECEIVER PREAMPLIFIERS(Continued from page 37)

The circuit can be assembled onperfboard, using adhesive -backedcopper foil and following the patternshown in Fig. 10. The back of the boardis a solid copper foil ground plane.The preamplifier works better if theperfboard is replaced with the G-10epoxy fiberglass type of board, andeven better yet (to 2000 MHz) withPTFE woven fiberglass board.

Conclusion. Monolithic microwaveintegrated circuits, like the MAR -x,make it possible to build well be-haved receiver -preamplifier circuitsthat will operate to 1000 MHz in somevarieties, and up to 2000 MHz in someothers.

Note: For a limited time after pub-lication of this article, I am preparedto sell an MAR -1 MMIC chip and two0.001-g or 100-pF chip capacitors for$6.00, postpaid. You can get themcheaper from Mini -Circuits, but mayrun into a minimum order problem. Ifyou are interested, contact me, JoeCarr directly (at P.O. Box 1099, FallsChurch, VA 22041).

BUILD A WIRE TRACER(Continued from page 31)

9 -volt battery, then connect a cliplead to the closed -loop output, J2,and power up the circuit. Turn on asmall AM receiver and position it closeto the clip lead. Tune the radio untilyou hear a buzzsaw-like sound, andthen adjust the tuning for maximumsignal strength. (The maximum trans-fer of energy occurs when the radio'sinternal ferrite loop is positioned per-pendicular to the wire).

Once that is done, connect the op-posite end of the clip lead to thecommon output, J3, and note the in-crease in signal strength. The increasein signal strength is due to circulatingcurrent within the closed loop. (Any-time a closed loop can be used, thesignal will be greater and, in mostcases, easier to track.)

Now plug the McTrak into a 117 -voltAC outlet and try to trace the McTraksignal through the AC wiring using theAM receiver. If the wiring happens togo behind a metal panel in the wall oris run through a metal conduit, themetal will attenuate the signal, possi-bly making it too weak to follow. Whenthat happens (or if the signal is dimin-ished for some other reason), try con-necting the open -loop output (J1) tothe conduit and see if the signal canbe traced along the conduit.

Using McTrak to trace your auto'selectrical wiring is just as easy. With allof the electronics in today's cars, it'salmost impossible to visually trace awire from one location to anotherwithout going through a maze of ca-bles, and possibly becoming side-tracked. But McTrak can handle thattask as well.

To trace your auto's wiring, connectthe McTrak's J2 output to the wire youwant to follow. Then track the signal bymoving the radio along the path thatproduces the strongest signal. If thereceiver's signal is too weak, connectthe common lead (J3) to the car'sground system (negative battery ter-minal or chassis in most vehicles) toincrease the signal strength. Sincethere are some circuits in a car's elec-trical system that could be effectedby the full output of the Tracker, itwould be better to always use theclosed -loop output when workingwith automotive electronics.

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THE BATTERY BUTLER(Continued from page 98)

pin 5 of U5, the circuit will never returnthe ready state and the battery will beovercharged. The total amount ofcharge that the Ni-Cd battery re-ceives can be adjusted by R25. Themaximum charge level can be deter-mined by starting with the voltage atpin 9 of U5 near the level of voltage atpin 5 of U5 and adjusting R25 to ob-tain a greater voltage differenceeach time the battery is cycled, butstill allowing the circuit to come to theready state. Note that as a Ni-Cd bat-tery ages, its ability to hold a com-plete charge will decrease and R25may have to be reset to compensatefor the aging battery.

Set S1 to the SLOW position. LED1should begin flashing red, indicatingthat the battery is being dischargedvia R39. In a few minutes, transistor Q4and resistor R39 should be warm tothe touch; that's normal. Connect theDVM across the battery terminals, and

note that the voltage should begindecreasing towards the present dis-charge limit. Once the voltage acrossthe battery is at the discharge level,LED1 should begin flashing green andthe voltage across the battery shouldrapidly start moving up.

Depending on the type of battery,the circuit will reach the ready state,which is indicated by LED1 being in asteady green state, in 4 to 5 hours. If itdoes not, adjust R25 to bring the volt-age at pin 9 of U5 closer to the volt-age at pin 5 of U5.

The battery can remain connectedto the Battery -Butler for prolongedperiods without damage to the bat-tery. A 20-mA trickle charge is main-tained across the battery after theunit returns to the ready state. How-ever, it is recommended that the bat-tery, once charged, be removed fromthe circuit if the charger is to beturned off. The input circuit load willdrain a small amount of current fromthe battery over extended periods.

The Battery -Butler can hold a bat-tery on a trickle charge to offset the

internal losses of Ni-Cd batteries in-curred during storage. To use that fea-ture, apply power to the circuitwithout a battery connected. PlaceS1 in the sLow position. LED1 should im-mediately go to a steady green state.The Ni-Cd battery may now be con-nected. A 20-mA trickle charge will bemaintained across the battery untilthe circuit is reset.

Operating Tips. Avoid making or dis-connecting DVM connections to thecircuit or the battery once a charge/discharge cycle has started. The cir-cuit detects very small changes involtage in the comparator section,and DVM connections and other ex-ternal noise sources can cause erraticcircuit operation. Operate andcharge your Ni-Cd batteries at nor-mal room temperatures. Avoid ex-treme heat and cold. Ni-Cd batterieswill recover from occasional dips tonear -freezing temperatures. However,extreme heat (above 40°C) will dryout the seals of most Ni-Cd batteries,resulting in electrolyte loss.

FUEL MISER(Continued from page 29)

Such thermostats have two sets ofcontacts that close at slightly differenttemperatures, and are wired so thatthe burner can start only when bothsets of contacts are closed. That typeof system is shown in Fig. 6. To installFuel Miser in such systems, simply con-nect the Fuel Miser's output terminalsin series with one of the relay coil con-nections, as shown.

Electric -heating systems may ormay not use a relay in the thermostatcircuit. Those that do have a relay canbe controlled by Fuel Miser by wiringits output circuit in series with the relaycoil connections as shown in Fig. 7.Electric -heating systems that do notcontain a low -current thermostat (asin the previous installation examples),use a heavy-duty thermostat that di-rectly feeds current (as shown in Fig. 8)to the heating element, without theuse of a relay or contactor. For suchsystems, it will be necessary to install aheavy duty relay (as shown in Fig. 8) tocontrol the heavy heating -elementcurrent. The voltage and current rat-ing of the relay must be equal to or

greater than the electrical require-ment of the furnace.

Final Test. After installing the FuelMiser, apply power to both the heat-ing system and the Fuel Miser. Set theduty cycle (via S1) to 100%, and checkthe furnace for normal operationwhen heat is called for by the ther-mostat. At the 100% duty cycle setting,the heating system should operatenormally-as it did prior to the installa-tion of the Fuel Miser.

If all is well, set S1to 10% and turn thethermostat up as high as it will go toforce the system to call for constantburner operation. Time the operationof the burner for at least Iwo com-plete Fuel Miser cycles. For gas sys-tems the valve should be powered forabout 45 seconds and be off forabout 7 minutes. (The gas flame maystart and stop after a time lag). For oilsystems, the burner should operate for31/2 minutes and be off for 31%minutes.

That completes the checkout of theFuel Miser, and it is ready to controlyour heating costs. A good startingpoint for the Fuel Miser's operation isat the 70% duty -cycle setting; try thatsetting for a day or Iwo. Remember, try

to keep a constant thermostat settingduring the test period to see how theFuel Miser operates in your system.

With some experimenting, you'll beable to determine which duty cycle isbest. Remember, the lowest duty cy-cle that still provides sufficient comfortwill provide the greatest savings.

"Those are the company archives?"

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BUILD AN ACTIVE ANTENNA(Continued from page 74)

using the whip antenna, simply con-nect the output of the M-7 to yourreceiver, with the unit turned off (that'sthe bypass position) and the RF gaincontrol (R5) turned fully counter-clockwise. Turn on the receiver andtune -in a weak station. Switch S2 on,and adjust the gain control clockwiseto increase the output signal. ToggleS1 back and forth to see which settinggives you the best results. Don't be sur-prised if the gain control overloadsthe receiver; if so, back it off.

There are other characteristics orphenomena associated with pre-amplifiers and active antennas thatdoes not mean that your the circuit ismalfunctioning. For example, if youhave strong AC hum in the HF setting,the antenna is too close to an AC cordor power line. HF signals may be clear-er at the VHF/UHF setting than at the HFsetting. Why? Although either preampmay be used for HF, the signal strengthwill be greater with the VHF/UHF pre -amp. However, the HF signal-to-noiseratio is better with the dual-gate-MOSFET-based preamp. Try both anduse the best for your particular receiv-ing conditions.

Although not shown in the schematic or the parts -placement diagrams, an LED can beadded to the circuit so that you can tell at a glance if the circuit is on. In his own unit.the author accomplished that by connecting the LED (with a series -connected current-limiting resistor) between a terminal on the power switch and the grounded frame ofthe gain control (R5).

Troubleshooting. The fact that thereare two independent preamplifiers inthe M-7 makes faults easier to diag-nose than with many other devices. Ifa problem occurs, only at one settingof S1, concentrate on that part of thecircuit. If the problem is common toboth settings, the components andconnections common to both pre -amps should be checked. Make surethe jumper wires are in place.

Some portable receivers not en-closed in metal cases may break intooscillation when connected to any RFpreamplifier. Try reducing the M -7'sgain and make sure that goodgrounds are provided with the inter-connecting coax cables. A pre-amplifier will intensify any problemsdue to poor receiver design: over-loading, images, or any problems withselectivity and image rejection.

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Standard Features - AC & DC VOLTAGES DC CURRENT RESISTANCE TRANSISTOR CONTINUITY TEST - Buzzer DIODE TEST 3 1/2 Digit LCD 10M ohm INPUT IMPEDANCEBATTERY TESTTRANSISTORDC CURRENT10 Amp

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$2995

FREO COUNTERup to 20MHz

TRANSISTORCAPACITANCEfrom 1pF to 20uF

AC/DC CURRENT

10 Amp

200 LEStock # 990123

$4995

INDUCTANCEResomico l uHFRED COUNTERUp to 20MHzCAPACITANCEfrom 1p F to 200uFAC/DC CURRENTDUTY %20 Amp

400 LEStock # 990124

$7995Deal ned to meet IEC-348 & UL -1244 safe a IfIcatIona

2 Year Warranty (Parts & Labor)

KELVIN 94LCR

"Not only does theKelvin 94 boast alot offeatures ... the featuresgo the extra distance."

"If we had to run into aburning building to dosome emergencytrouble -shooting andcould carry in only onepiece of equipment, theKelvin 94 would be it!"

Popular ElectronicsReviewed - May 1993

The Ultimate MeterdBm True RMS

TRUE RMS PLUS

#990111

*See Standard Features

Logic Probe

ENGINEANALYZER PLUSModel 95 #990112

$ 1 9995A Must For

Auto Mechanics

Standard Features plus -TEMP, TACHOMETER &DWELL ANGLE TESTER,DUTY CYCLE, 10M OHMIMPEDANCE, ANALOG BARGRAPH, K -TYPE TEMPPROBE, ALLIGATOR CLIPTEST LEADS, INDUCTIVEPICKUP CLIP, 6' TEST LEADS& DELUXE CARRYING CASE

* Standard Features - Models 94 & 95 DC/AC VOLTMETERS AC/DC CURRENT OHM METER DATA HOLD RELATIVE MOD FRED COUNTER to 4 MHz (Model 95) AUDIBLE CONTINUITY TEST DIODE TEST MAX/MIN AVERAGE MEMORY RECORD 10A HIGH-ENERGY FUSE PROTECTION

A T PWER SFF

KELVIN100 Basic# 990087

$ 1 995 AC & DC 4'0VOLTAGES DC CURRENT RESISTANCE CONTINUITY TEST -Buzzer 3 1/2 Digit LCD LOW BATTERY INDICATOR DIODE TEST BATTERY TESTCAPACITANCE METERKELVIN250 LE# 990126

$5995 ACCURACY:

0.5% RANGES:20mF,2000uF,

200uF, 20uF, 2uF, 200nF,20nF, 2000pF, 200pF

Zero Adjust Safety Test Leads Test Socket for Plug-in

Come I nentsAUTO -RANGE METERKELVIN300 LE# 990125

$4995AUTO -RANGE

ACV & DCV DC CURRENT RESISTANCE CONTINUITY TEST DIODE TEST 31/2 Digit LCD 10M ohm INPUT IMPEDANCEINSTRUMENTS

.017:7E7111=1:13.1.111

'to 4-

20 MHz SCOPEDual Trace 2 Yr Warranty -Parts 8 Labor

Stock No. 740085 538540 MHz SCOPE 2 yr WarrantyDual Trace with Delayed Sweep

Stock No. 740086 5655

TEST ACCESSORIESSCOPEPROBES60 MHz, X1 8 X10

SPECIAL

700072 .... 896150 MHz, X10700073

-.wen.,

IC CLIPS cr"

SPRING LOADEDlliSOLDER TYPE

sew No. COLOR COST 25+ Qty990104 BLACK .65 ea.' .50 ea990105 RED .65 ea.'.50 ea

Established 1945

MIC & VISA '20 MinimumOrder

KELVIN CATALOG 53Stock No. 6504 12

DC TOY MOTORSDC Toy MotorStock No. 850647'.80 ea5.75 ea / 50+ Qty 6V DC High SpeedSolar Motor Stock No. 850646

.60 ea 1.5V DC8.55 ea / 50+ OtySolar Cells 3 3/4" L x 2 9/16" WStock No. 260099 1000mA .45V'5.95 ea$

. 0 ea / +

DIGITAL TRAINER

Laptop Digital Trainercomes with 100page instruction manual, power supply,built-in 1 digit true Nexadecimel display,two independent clocks with useradjustable freq & duty cycles, 4 data L-2switches and 4 LED displays. AssembledStock No. 840460 599e5

BINARY QUARTZCLOCK w/Alarm

ORIGINAL DESIGN -24 Hr. BinaryQuartz Accurate Clock with 2 colorLED's. Built-in Alarm and AlarmDisplay in binary code. DESIGNEDFOR LEARNING about dig taicircuitry & binary code. Built withindividual IC components. BatteryMemory Loss Prevention. Comeswith rechargeable battery, DC walltransformeranddetailed instructionmanual. Advanced Level KitStock No. 840589 67995

ElectronicVOICE PAD

An electronic note pad, ableto record your message &replay it later. It has a built-inphoto cell & as soon as it senses yourpresence, it will automatically playbackthe message left for you. Thecomponents are PC mounted. The ICcan record a message up to 20 seconds& no mechanical parts or tape - only adigital integrated circuit.

Intermediate Level KitStock No. 840606 549"BREADBOARDS

Stock No. Post Contacts . yOUli COST

680093 0 500 5 4."680097 0 840 $ 5.95

680098 2 1330 511.75680100 4 2390 522.95WIRE JUMPER KITPre-cut, Pre -Stripped330289 140 Piece Set $ 4.14330290 350 Piece Set $ 8."

COMPONENTSWHOLESALE PRICES!

(10 Pc. Min.)Stock No. TYPE YOUR COST600021 555 TIMER '.29 ea

600029 556 DUAL TIMER '.40 ea

600039 LM566 PPL '.60 eaFUNCTION GENERATOR

600018 Tr. ST1ECR Fi1APL-LA( M

sC PENSATED"

600026 1458 OP -AMP .35 eaDUAL 741C OP -AMP

630041 2N2222 '.20 ea

630383 PN2222 '.08 ea

600023 7805 Voltage Reg '.38 ea

SILICON CONTROLLED RECTIFIER(Sieve,. to GE C10661) 4.0 amp, 100PIV600014 ... $.89 ea $.79 ea/10+

THERMISTER - 100 ohm110097 $1.35 ea '1.00 ea/20+THERMISTER 10K ohm110097 '1.35 ea '1.00 ea/20+

PROJECT PARTSProjectSpeaker2", 8 Ohm, .1 WattStock No. 350009

59ProjectBUZZER3 9 Volt DC 80 db

68Stock No. 0089H.59 ea$1.39 ea / 10+ Qty

SolderingIRONwith STANDLONG LIFE T112Stock No. 990098'3.95 ea

LED T 1 3/4Stock No. Color 100+ Oh 1000+ ON

260020 RED '.05 as '.045 ea260027 GREEN 1.08 ea $.07 ea260026 YELLOW '.08 ea .07 ea260078 2 COLOR s.32 ea .29 ea

RED/GREEN

XENON STROBEStock NO. TUBE260050'3.25 ea$2.95 ea 120+ Qty

TRIGGER COILfor XenonStrobe TubeStock No. 320037'1.25 ea$.89 ea 20+ Qty

INFRARED LEDIR Pair, LED Infraredtransmitterand receiverStock No. 260061

51.95 ea

NEON LAMPNE2, 2" LeadStock No. 260003'.15 ea$.12 ea / 100+ OW

PHOTO CELLPhoto Cell 450 ohmStock No. 260017$.65 ea .45 ea /20+ QtyPhoto Cell - 1.5K ohmStock No. 260018

.65 ea 8.45 ea /20+ Qty

PUSH-BUTTON SWITCHPUSH -ON. PUSH -OFFStock No. 270021'.55 ea$.49 ea / 100+ City

SUB-MtNIATURE MOMENTARYSWITCHStock No. 990002'.35 eav.28 08/100f City

MINIATURE TOGGLE SWITCHStock No. 270034.90 ea Type SPST

$.79 eat 50+ Qty

?if


CountersurveillanceNever before has so muchprofessional information on the artof detecting and eliminatingelectronic snooping devices-andhow to defend against experiencedinformation thieves-been placedin one VHS video. If you are aFortune 500 CEO, an executive inany hi -tech industry, or a noviceseeking entry into an honorable,rewarding field of work incountersurveillance, you mustview this video presentation againand again.

Wake up! You may be the victim ofstolen words-precious ideas that wouldhave made you very wealthy! Yes, profes-sionals, even rank amateurs, may be lis-tening to your most private con-versations.

Wake up! If you are not the victim,then you are surrounded by countless vic-tims who need your help if you know howto discover telephone taps, locate bugs, or"sweep" a room clean.

There is a thriving professional servicesteeped in high-tech techniques that youcan become a part of! But first, you mustknow and understand CountersurveilanceTechnology. Your very first insight intothis highly rewarding field is made possi-ble by a video VHS presentation that youcannot view on broadcast television, sat-ellite, or cable. It presents an informativeprogram prepared by professionals in thefield who know their industry, its tech-niques, kinks and loopholes. Men whocan tell you more in 45 minutes in astraightforward, exclusive talk than wasever attempted before.

Foiling Information ThievesDiscover the targets professional

snoopers seek out! The prey are stockbrokers, arbitrage firms, manufacturers,high-tech companies, any competitiveindustry, or even small businnesses in thesame community. The valuable informa-tion they filch may be marketing strat-egies, customer lists, product formulas,manufacturing techniques, even adver-tising plans. Information thieves eaves-drop on court decisions, biddinginformation, financial data. The list is

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what was to be an embassy and privateresidence into the most sophisticated re-cording studio the world had everknown. The building had to be torndown in order to remove all the bugs.

Stolen InforniationThe open taps from where the informa-

tion pours out may be from FAX's, com-puter communications, telephone calls,and everyday business meetings andlunchtime encounters. Businessmen needcounselling on how to eliminate this in-formation drain. Basic telephone use cou-pled with the user's understanding thatsomeone may be listening or recordingvital data and information greatly reducesthe opportunity for others to purloinmeaningful information.

rCLAGGK INC. HHSP.O. Box 4099 Farmingdale, NY 11735

Please rush my copy of the Countersurveillance TechniquesVideo VHS Cassette for a total cost of 553.95 each (whichincludes 54.00 postage and handling).

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All payments in U.S.A. funds. Canadians add 54.00 per VHScassette. No foreign orders.

The professional discussions seen onthe TV screen in your home reveals howto detect and disable wiretaps, midgetradio -frequency transmitters, and otherbugs, plus when to use disinformation toconfuse the unwanted listener, and thetechnique of voice scrambling telephonecommunications. In fact, do you knowhow to look for a bug, where to look for abug, and what to do when you find it?

Bugs of a very small size are easy tobuild and they can be placed quickly in amatter of seconds, in any object or room.Today you may have used a telephonehandset that was bugged. It probablycontained three bugs. One was a phonybug to fool you into believing you found abug and secured the telephone. The sec-ond bug placates the investigator whenhe finds the real thing! And the third bugis found only by the professional, whocontinued to search just in case there weremore bugs.

The professional is not without histools. Special equipment has been de-signed so that the professional can sweepa room so that he can detect voice -acti-vated (VOX) and remote -activated bugs.Some of this equipment can be operatedby novices, others require a trained coun-tersurveillance professional.

The professionals viewed on your tele-vision screen reveal information on thelatest technological advances like laser -beam snoopers that are installed hun-dreds of feet away from the room theysnoop on. The professionals disclose thatcomputers yield information too easily.

This advertisement was not written bya countersurveillance professional, but bya beginner whose only experience camefrom viewing the video tape in the pri-vacy of his home. After you review thevideo carefully and understand its con-tents, you have taken the first importantstep in either acquiring professional helpwith your surveillance problems, or youmay very well consider a career as a coun-tersurveillance professional.

The Dollars You SaveTo obtain the information contained in

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