portable guitar amplifier cassette interface for vic20/64 · 2019. 7. 18. · 1.7351 087 19053 090...

µP- controlled frequency meterfourth in our series of measuring instruments

portable guitar amplifiertwo articles for guitar lovers

cassette interface for VIC20/64

1.2 GHz

PPCOUNTER

overcomes one of Commodore's shortcomings

11 I nnnniinn rf" uuuuuu 1.1L

TRIGGER

9GATE

SENSITIVITY

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Full rangeof 74S Et74HCseries instock.Ask forfull list.

01 sockets2426 oPPinAD OT

5507.00853

TR& ECL

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VOLTAGE REGULATORSis FIXED VOLTAGE PLASTIC TOM

EVE5.8V

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OTHER SWITCHINGREGULATORS REGULATORS53230300144379.1CL0KC70H1278905

VARIABLE1.1.0004103.41771.0017K1_1433LM263T

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110396K

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OPT() ISOLATORS

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4.504103.503.503103233200.90

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*ATTENTION*ALL PR CES ARE

SUBJECT TO CHANGEWITHOUT NOTICE

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CRTCONTROLLER

;t., 0. 1.031 CO 7.1110 27018:32 MHz 2252.03 MHz 225245763 MHz 1St

2002.5 MEM 2502_69 MHz 2503.12 MHz 1.753.276 mu 1.533.5756 MHz 1.004.03 MHz 1.404.194 MHz 1_934.43 MHz 1.004609 MHz 2534_9152 MED 2105.1300 /410. 1506 CO 0042 1.406.144 1.100 1.407.03 lAtt. 1.507 163 1.06.. 1.758031.01z 1508867 MHz 1.751060 MHz 1.70ton MHz 25010/0 1.0.10 1.501110 MHz 3.11312.50 MHz 1.5014.00 MHz 1.7534.373 14144 1.6014.75EMP.0 2501507 101-17 21:01E00 4040 2.0017.734 1.3112 2031350 7.3112 1.701600 MHz 1.70le432 1.1.14x 15019 989 MHz 1.502013301.00.2 1.7524,0:0 MHz 1500800 MHz 1.751151.04z 2.501,501033 1100

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ZENERS

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TRIALS

Mast.202V 605

EA 70400 50C. 909

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17266D 300112260 7.

DISCRETEDISPLAYS

LEDS

TEciimmATic LTD

120"RED 711203 0.12GROIN711211 0.16YELLOW111.212 020Rect LEDs111/6/10 0.3)C30 031Cs 1.03

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EIC10718BC19.980159 C6514113610185177886175BC122. LBC184: L80212,167233 L8C214.180327

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CC CONNECTORS

DISCCONTROLLERS6638272FD1771F01791FD1M3

217051797

02753D2797

W019315302143

5-032603CO202003200329 002200360332.0)15.03803

CHARACTERGENERATORS

R03 2513DC730

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1300905'04 12.031451.186783 7513

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14514411 750C07E115 5 SD47323 7.50

KEYBOARDENCODER

AY -5-2376 11.50AY53600 7.5073922 650740923 850

UHFMODULATORS6 1.00 3_758 Wiz 4,50SOUND &VI5101112 7414z 12.03

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MC63195 45001015E174A95 9530310.3432.153.53

TELETEXTDECODER

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LJARTSAy -3-10195 30055-51013P 3.00C01.3131 7 3.001.1.1632 3 CO791972 3.03

WIRE WRAPSOCXETS By TEXAS

Pen 300 18 Lea 509 24 40 75914 P. 439 2115.5 60p 213 00 100316 pn 45p 22000 650 4000 1300

16 pr,18 oo

300.350

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MAIL ORDERS TO: 17 BURNLEY ROAD, LONDON NW10 lEDSHOPS AT: 17 BURNLEY ROAD, LONDON NW10

(Tel: 01 208 1177 Telex: 922800)305 EDGWARE ROAD, LONDON W2

23 pn 40024 tin 500

TIP36CTIP4ICTIP -12401942771144771E111PE11912511929%11733E210.216021127942922242624542126462125401542E0532773044

2s Pi, 6C040 pss 900

21339203022370203713701 5237732381923366211386:244131213232E457.82E45920596324E273:512E3013 13E73

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139 76436.' 630 64%6 150920p 609 E5422. 120p

30p 441_.: 950 0:334p 355;7. 10C9 , 'Cc 160VI65

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PLEASE .1111)50p p&p &151.11V1.(Export: no VAT. p&p III Cosi)

Orders from Government Depts. & Colleges etc. vLelcome

Detailed Price List on requestStock items arc normally by return 0% post (IC

Elektor Publishers Ltd., Elektor House,10 Longport, Canterbury CT1Kent, U.K.Tel.: Canterbury (02271 454439.Telex: 965504.Office hours: 8.30 - 12.30 and 13.30 - 16.30.

Editor: P.V. HolmesAssistant editor: E.J.A. KrempelsauerUK editorial staff:R.E. Day, G.P. McLoughlin, L. SeymourOverseas editorial staff:P.H.M. Baggen, A. Dahmen, I. Gombos,P.E.L. Kersemakers, R.P. Krings,P. v.d. Linden, D.R.S. Meyer,G.C.P. Raedersdorf. J.F. van Rooij,G.O.H. Schell,Editorial secretariat:C.H. Smeets, G.W.P. VVijnen

Head of design:K.S.M. Walraven

Laboratory staff:J. Barendrecht, G.H.K. Dam, K. Diedrich,G.H. Nachbar, A. Nachunann,R.A.F.M. Sa!den, A.P.A. Sevriens,J.P.M. Steeman, P.I.A. TheunissenPublishing manager:A.J. BrialeyAdvertising manager:S. Brooks

The circuits are for domestic use only. Thesubmission of designs or articles to Elektorimplies permission to the publishers to alterand translate the text and design, and touse the contents in other Elektor publi-cations and activities. The publishers cannotguarantee to return any material submittedto them. All drawings, photographs, printedcircuit boards and articles published inElektor are copyright and may not bereproduced or transmitted in any form or byany means, including photocopying andrecording, in whole or in part without priorwritten permission of the publishers. Suchwritten permission must also be obtainedbefore any part of these publications isstored in a retrieval system of any nature.

Patent protection may exist in respect of cir-cuits, devices, components etc. described inthis magazine. The publishers do not acceptresponsibility for failing to identify suchpatent or other protection.

Elektor is also published in Dutch, French,German, Greek, Italian. Portuguese,Spanish, Turkish and lin part) Swedish inassociation with Alit om Elekuonik.

Distribution in ILK.:Seymour Press Ltd., 334 Brixton Road,London SW9 7AG.

Copyright => 1985 Elektor Publishers Ltd.,Canterbury.

Printed in the Netherlands. IABC1

Volume 11 - Number 1 ISSN 0308-308X

news, views, people 1-18

tea leaves 1-22A light-hearted look at the coming decade.

selektor 1-23Computers of the future.

Commodore cassette interface 1-25This circuit enables Commodore's VIC20 and C64 PCs to be interfaced with virtuallyany cassette recorder.

VHF/UHF modulator 1-28Improves the images obtained with PCs, video cameras, VCRs, and similarequipment.

portable guitar amplifier 1-30A project that gives colour to the basic guitar sounds for only a modest outlay.

30 watt a.f. output stage 1-36A good -quality power output stage suitable for use in the guitar amplifier.

JSR swap 1-40Makes 6502 -based computer systems more versatile by duplicating pages zero andone in RAM.

how to make your own PCBs 1-41

missing link 1-42

rumble detector 1-43Detects ultra -low frequency noise that could spoil the pleasure you get from yourhi-fi system.

µP -controlled frequency meter 1-46A highly -sophisticated do-it-yourself frequency counter that compares with pro-fessional instruments in almost everything except price.

switching radio control channels 1-60A circuit to control seven on,off functions in a radio control model that uses onlya single channel in the transmitter.

applicator 1-6420 W output amplifier based on LM1875

market 1-66

switchboard 1-71

appointments 1-76

readers' services 1-80

index of advertisers 1-82

A selection from our February issue: RLC meter gyroflashIN input stage for µP -controlled frequency meterI EPROM switchboard XL loudspeaker PCM model control

This month's front cover shows the /IP-controlled frequency meter which continuesour series of measuring instruments for thehome constructor. All instruments in theseries are designed to fit the same family ofstandard cases.

1-03

elektor january 1985 advertisement

ELEKTOR BOOKSRESI & TRANSIA series of strip cartoons in book form inwhich two enterprising characters explorethe field of electronics in their own

[ray. Their adventures are full oftension. because they often go aaainst thecurrent - whereby they encounter muchresistance - before they reach their goal.These books familiarize the reader withelectronics in an unusual way: exciting,playful, yet thorough. Part I comes com-pete with a printed -circuit board and resi-meter.Part I: Banish the Mysteries

of Electronics £6.10Part II: Hands off my Bike! .. £4.80

TV GAMES COMPUTERThis book, prov[cies a different - and, inmany ways, easier - approach to micro-processors. The TV games computer isdedicated to one specific task. as thename suggests. This provides an almostunique opportunity to have fun ratiteteeming!Price £7.10

DIGIBOOKProvides a simple step-by-step introdzc-tion to the basic theory and applicationof digital electronics and gives dearexplanations of the fundamentals ofdigital circuitry, backed up by exper-iments designed to reinforce this newlyacquired knowledge. Supplied with anexperimenter's PCB.Puce £6.30

300 CIRCUITSFor the home constructor - 300 projectsranging front the basic to the very sophis-ticated_Price L-5.80

DATA SHEET BOOKHere at last is the book that designers havebeen waiting for: the Elektor Data SheetBook. In 240 pages it gives you a CMOS.a Linear, Special Function and Audio DataBook: extensive information on 269 ofthe most imam -tam IC's A very usefuland economical reference book!Price £8.40

JUNIOR COMPUTER BOOK 1For anyone wishing to become familiarwith fmicrolcomputers, this book goesthe opportunity td build and proaram apersonal computer at a very reasonablecost.Price . . . . _ £6.90

JUNIOR COMPUTER BOOK 2Follows in a logical continuation ofBook 1, and contains a detailed appraisalof the software. Three major programmingtools, the monitor, an assembler and an&dm', are discussed together with practi-cal proposals for input and peripherals.Price £6.90JUNIOR COMPUTER BOOK 3The next, transforming the basic. singe -board Junior Computer into a completepersonal computer systemPrice . . . . . .. . . £6.90JUNIOR COMPUTER BOOK 4Book 4, the last in the senes. describes ailthe software required to operate the com-plete system. A number of peripheraldevices, such as a printer and a videoterminal, may be "hooked up' to thecomputer. During the final stage in its'growth', the machine is able to extendits linguistic skills. for a special version ofBASIC is now available on cassettePrice £6.90301 CIRCUITSThe book is a continuation of our popularand very successful 300 circuits publi-cation. It is composed of 301 assortedcircuits ranging from simple to morecomplex designs. described and explainedin straiohtforward language_Price £5.80

MICROPROCESSOR HARDWAREThis book describes a range of peripheralequipment that can be connected andused with an assortment of personalcomputers which use the 6502,6809. Z80or the 8080 CPU

JUNIOR COMPUTER VIA 6522This book deals with the wall -knownVersatile Interface Adapter IVIAI type

6522 Although it is an indispensable ad-dition to the four books already devotedto the Junior Computer, it us not aimedsolely at Junior users, but at anybody whohas a system with one or more 65Th. Itaffords a complete familiarization withthis flexible and effective component.Price £3.50

SC/MPUTER 11)Describes how to build and operate yourown microprocessor system - the firstbook of a series - further books willshow how the system may be extended tomeet various requirements.Price £5.80SC/MPUTER 12/The second book in series. An updatedversion of the monitor program (Elbug11)is introduced together with a number ofexpansion possibilities. By adding theElekterminal to the system described inBook 1 the microcomputer becomes evenmore versatile.Price £5.80FORMANTComplete constructional details of theElektor Formant Synthesiser - comeswith a FREE cassette of sounds thatthe Formant is capable of producingtogether with advice on how to achievethem.Price £6.30

33 ELECTRONIC GAMESA selection of circuits which give as muchenjoyment in building them as actuallyPlaying the games. The circuits are fasci.rating although the electronics involvedaxe not complex and therefore anyonewith a good soldering iron will find thisbook satisfying. These are electronic gamesthat do not need a TV screen, and as aresult can oa played 'UST :gout anywhere.Price £4.80

JUNIOR PAPERWARE 1Modifications of the PM/PME EPROM:Source listings, Hex dump of the Softwarecruncher and puncher (ESektor 85, May19821Price 12.10JUNIOR PAPERWARE 2Source listing of the bootstrap loader

for Ohio Scientific Floppy': Hex dumpof the EPROM LESS 515)Price £2.10

PAPERWARE 3 & 4The hardware for a Universal Terminal hasalready been described in Elektor. Itconsists basically of a VOU card and aCPU card. but, of course, to make theterminal wok some software is alsoneeded. Two new books are now availableto meet this need Paperware 3 not onlyincludes all the necessary software. butalso deals with all the 'ins' and 'outs'of the terminal Paperware 4 providesall the software and other informationfor using the Universal Terminal with theJunior Computer, either in expanded formor with DOS.Price: Paperware 3 EZ.70

Paperware 4 12.80

EXTENDED PRESET UNITFOR THE POLYPHONICSYNTHESIZERThis book is the culmination of a projectwhich was started in the October 1981issue of Elektor and to which since thenno fewer than nine articles have beendedicated. It is no exaggeration to saythat the polyphonic synthesizer can beused to its full potential only with theextended preset unit The booklet isdivided into five distinct sections: theconstruction and fitting of the variouscards, a functional description, calibrationand testing, fault-finding, and trackingof the voltage -controlled filter and taw.frequency oscillator. It is possible tobuild and test all the circuits and thenfit them all at once into the synthesizeror build and add them piecemeal. Asthe booklet is intended more as a referencework than a full instruction manual, thechapters can be read in any order. Thebooklet assurres reasonable familiaritywith computer technology.Price . E1.60

To order please use the postage paid orderca rd this issue.ADD 55p P & P U.K. [OVERSEAS £1.101

A new addition to our series of software cassettes for theTV games computer has just become available. Like itsthree precedessors, the present one, number 011, offers fif-teen games for the whole family. Snakes and ladders - reach square 100 before your

opponent(s). Molebasher - catch as many moles as you can. Snap - try to beat your opponent in deciding whether

TWO pictures on the screen are identical. Mazes - escape from the maze before your time is up. Asteroids - try to survive for as long as possible by

avoiding the asteroids. Dragster - complete nine laps in the shortest possible

time. Omega landing - land your spacecraft in a hostile

environment!

The ElektorSoftwareService(see readers' service pages) givesdetails of TV games on cassette andon software on EPROMs.

Break-out - twenty-four variations on 'bursting balloons'contained on cassette 010.

Tiny Tim - remove enough rocks and you reach thelovely girl!

Horse race/jackpot - two simple games of chance. Newton - catch as many apples as possible. Horse races - eight variations of show jumping. Painting - colour the screen without being bitten. Submarine/racing - two different games: in the first,

the submarine tries to sink as many ships as possible; inthe second, a racing car must avoid other cars on thetrack for as long as possible.

Cosmic adventure - a three-part game: first, destroytwelve meteorites; second, land under enemy fire; third,find the nuclear reactor in the underground maze.

1-04

Cirkit Making it4 bigger and better.

Cirkit stock all thecomponents, accessories andtools and the kits you're lookingfor. Designed and selected to offerthe best possible standards at thebest possible price.

lentroncsInterisce

Cirkit KitsCIRKITELEL X`60 TOOL KITContains:15W Soldering Iron 2 spare bits. heatshunt. solder, pliers. cutter.screwdriver 40-00307 1556

AUDIO FUNCTION GENERATORVersatile wavefonn generator with sine.triangular and square wave Outputs.On board mains PSU 41-01302 2700

STEREO 40W AMPLIFIERSingle board 40W per channel stereoamplifier 41-01301 38.00

STEREO VU METER5 LED per channel stereciVU meter foruse with stereo amplifiers 41.01401 1130

5W AUDIO AMPA very compact audio output stage for usein a wide range of equipment 41-01406 440UNIVERSAL AMPA universal audio pre -atop with again tN Ill 41-01604 6.45

MONO REVERBERATION UNITSingle channel. spring line rev unitto add echo effects to taperecording etc. 41-01602 1090

TONE GENERATOR AND DETECTORVery low distortion tone generatorand signal detector for circuit faultfinding 41-01603 10.45

10MHz Df'M8 Digit LED digital frequency meterand period measurement 41-01500 54.10

56MHz PRESCALERExtend the range of the 10MHz DEM to50MHz 41-01501 8351-5MHz PRE AMPLow frequency pre -amp and waveformshaper for the 10MHz DEM 41-01502 5.13

70cm PRE AMPLAW noise. minianue pre -amp for the70cm amateur band 41-01506 47870cm CONVERTER70cm to 144MHz low noise converter featuringpre -aligned helical fi !ter. schottky diode mixerand low noise transistors 41-01405 2150

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1-30V 1mA-2APSUAdjustable I -30V Power supply with pre-setablecurrent limit from lmA-2A 41-01600 37.46

5-12V IA PSUAdjustable PSU from 5-1217with currentprotection. I amp max output 41-01504 6.45

1.30V ISAPSU1.30volt adjustable PSU with protectedoutput up to 13 Amps 41.01402 10.45

3 DIGIT LED DANDVM to read up to 999 volts or configured as anammeter to read up to 999 amps 41-01403 17.00

LNTRA RED LLNKSingle channel IR Link with relayoutput 41.01300 940TEMPERATURE SENSORThermistorbased temperature sensorwith relay output 41-01303 620

LOCOMOTIVE SOUND GENERATORRealistic steam sound and whistle formodel railways 41-01304 920

LAMP DIMMERControl lamps and drill speed 41-01305 5.70

WATER LEVEL ALARMAlarm to indicate high wale r level or .

flooding 41.01601 2.70

3 NOTE CHIMEDoorbell chime with adjustabletones 41.01503 7.00

1MPRE AMPMiniature low -noise MOSFET pre -ampfor the 2m amateur band 41-01307 3.91

2MCONNERTERLow noise 144MHz-2S4Hz amateurband converter 41-01305 17.35

POWER AMP20W - 10dB gain power amplifier for the Inband. Automatic EX switch over.RXpre -amp. robust construction 41-01404 327

l(eafrCRYSTAL CALIBRATORCrystal ref erence calibrator for alignmentof receivers. outputs at 4.2. !MHZ.100.50 AND 10/31z 41-00401

CB NOISE SQUELCHImproves to mute performance of themajority of CB rigs 41-01605

CENTRON1Ci LN'TERFACF.Connect your personal computer tothe outside world via the Centronicsprinter output 41-01466

70cm PAIOW Power amp to boost the output ofhandheld and portable 70cmtransceivers 41.01506 3382

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Ram Card 40-84000 59.95ZSOA industrial controller 40-82000 54MEPROM Eraser 84T 40-EL1001 59956502 Micro Controller 40-&11320 54956802 Sficro Controller 40-6811A) 5495P82720 8058 Piero Buzzer 43-27201 03510,415A 10.7 Center Freq 20-10152 2.10111MORAA 10695 Center Freq 20.11152 3 49£CI7i LCD (freq.) 39.17700 21100C11161 LCD Clock 40-80161 8258x03- lCsocket 28.00800 0.1214 x 03" IC socket 28-14000 0.1316x03- IC socket 213-16000 0.136V KUIT-A Relay 46-8(000 0.489V KLIT-A Relay 46-80001 OAS12V KLTT.A Relay 46-80002 048CX120P COAX Relay 46.90120 1196CXS200 COAX Relay 46.90520 26,98CX5400 CO.AX Relay (EINC) 46-90540 2698

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CirkitBigger Stack_ B eHer Service

etektor january 1985

Spectrum no spectreSinclair's new computer, the Spec-trum Plus, which was launched lastautumn as a positive reaction to themarket (which had demanded a newkeyboard), is being manufactured byTimex in Scotland, A B Electronicsin Wales, and Samsung Electronicsin South Korea. Total productioncapacity for the Spectrum and Spec-trum Plus is 200 000 models permonth.Although Sinclair intends to continueselling its basic £130 Spectrum model(the basic Plus retails at £180), itforecast that the Spectrum Plus willachieve double its forerunner's UKsales. Last year the Spectrum yieldedpre-tax profits of £14 million on itsturnover of £77.7 million.Sinclair is also stepping up pro-duction of its more expensive QL to30 000 units a month, which maynecessitate the appointment of oneor more additional sub -contractors.(LPS)

Aid for the unsightedA microcomputer system that con-verts braille into print to help blindpeople at school or work has won anaward, presented by the BBC for thebest invention to help the unsighted.The winner is Dr Tom Vincent, aphysics lecturer, for his developmentof the Work Station, which enablesa person to type in braille, produce asimultaneous printed version, andthen, with the help of a voice syn-thesizer, to check the print versionindependently.Dr Vincent has also devised ancillarysoftware, which enables a blind per-son to make use of word processingfacilities, and keep personal braillerecords on floppy disks.The system has been tested for overa year in a number of UK schoolsand was demonstrated recently atthe BBC's London Headquarters by16 -year old Wendy Kirton, a Welshschoolgirl who has been blind frombirth.Dr Vincent is currently seeking com-mercial backing for the entire synthe-sizer and personal records concept,because he believes that it 'has greatworld-wide export potential. Almostany language can be incorporated'.The basic software for the conceptcosts about £1000 to set up. Existingbrand -name hardware could be adap-ted for a similar sum. (LPS)

Your rights and BritishTelecomA booklet published recently explainsto British Telecom's customers theservice British Telecom provides andgives advice on what to do if thingsgo wrong.The Consumer Code for British Tele-communications PLC has been pro-

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DES LE

duced to reflect changes in the legalrelationship between British Telecomand its customers and is a require-ment of British Telecom's licence.In addition to their normal legalrights, customers with grievancescan still choose independent arbi-

Therecommendations of the arbitratorare legally binding on both parties.Detailed advice is given in the newcode.A copy of the code is available onrequest from any British Telecomlocal office, as well as from CitizensAdvice Bureaux. The text of thecode is also to be printed in all newtelephone directories.

ANZCAN replaces COMPACThe £250 million trans -Pacific link, inwhich British Telecom International(BTI) has a significant share, andwhich was inaugurated by HM TheQueen in London recently, is one ofthe worlds longest undersea telecom-munications cables. Named ANZ-CAN, the cable runs more that15 000 km (8100 nautical miles)between Australia, New Zealand, Fiji,Hawaii, and Canada. It was largelydesigned and made in Britain. It cancarry 1380 simultaneous telephonecalls on the major route betweenCanada and Australia, and its ca-pacity is nearly twenty times largerthan the COMPAC cable it replaces.The cable's landing points are atSydney, Takapuna (near Auckland),Norfolk Island, Fiji, Oahu Island(Hawaii), and Port Alberni (Van-couver Island). It is linked to westernEurope by a microwave systemacross Canada and then through theCantat 2 transatlantic cable to

England.The cables major route, from Sydneyto Port Albemi, utilizes the STC14 MHz system which provides 1380circuits of 4 kHz bandwidth. It in-cludes more than 1100 undersea re-peaters and equalizers, spliced intothe cable at 13 km intervals.Nearly 14000 km of the cable weremade in Britain by Standard Tele-phones and Cables. ANZCAN waslaid by Cable & Wireless cable ships.More than five million phone callsare made every year between the UKand Australia and New Zealand.

Telecom Gold on high seasDirect access to Telecom Gold's elec-tronic mail service is now available toships operating worldwide. This highseas extension of Telecom Gold hasbeen made possible through BritishTelecom International's INMARSATmaritime satellite communicationservice.With suitable on -board computerequipment and the adaptation of thesatellite communications terminal(the ship's earth station), an author-ized Telecom Gold customer canaccess the full range of Gold featuresfrom any part of the world.The new service to shipping is ident-ical to that already offered by Tele-corn Gold to customers in the UK.

(or other communicating terminal) totelephone modems or acoustic coup-lers to send data and information toother terminals over the ordinarytelephone network or through BritishTelecom's Packet Switchstream dataservice.Telecom Gold's incoming and out-going telex facility enables UK -basedtelex machines to send and receivemessages from all shipping usingGold's electronic mail service.

Seconds out! Round two!British Olivetti Limited has hiredWickes Associates International Ltd(WAI), a leading public relations con-sultancy specializing in the computerand related technologies industry, tohandle press relations for the com-pany's range of IBM PC compatibleand portable microcomputers.WAI's prime task is to support amajor new marketing campaign inwhich Olivetti's M21 and M24 microswill compete aggressively against theIBM PC.According to a spokesman for WAI:'Olivetti has no option but to go forthe throat. IBM's dominance of thePC market has little to do with tech-nology and lots to do with market-ing. One look at the products andyou can see that Olivetti has wonany technical battle hands -down.Now it's 'gloves off' in the marketingarena'.

1-18

e!ektor january 1985

SCOTs for the NavyThe UK Ministry of Defence hasawarded the Satellite Communi-cations Division of Marconi DefenceSystems Limited of Stanmore,Middlesex, the largest single contractever placed with a European com-pany for satellite communicationsterminals. The order covers thesupply of nineteen Enhanced Ship -borne Communications Terminals(SCOT) to the Royal Navy.SCOT 1, the world's first and onlylightweight operational SHF ship -borne terminal, revolutionized navalcommunications planning in the early1970s by offering an immediate andsecure long-distance satellite link thatmatched the quality and reliabilityhitherto only obtainable from ter-restrial line -of -sight equipment. Vari-ous versions of SCOT 1 have nowserved as the RN's primary long -haulsatellite communications equipmentfor over ten years.Enhanced SCOT, the latest version,exploits the company's unrivalledbase of experience by providing evenhigher availability and full inter -operability with all current and plan-ned US, NATO, and UK militarycommunications satellites. A modulardesign allows the terminal to be of-fered in a number of variants, tail-ored to different classes of ship, shipfitting concepts, and operationalrequirements. Speech, telegraph,data, and facsimile transmission areall accomodated.

21st Century TechnologyAs part of the celebrations to markthe centenary of City and Guilds Col-

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lege, the engineering faculty of Im-perial College of Science andTechnology, London University, asymposium titled 21st Century Tech-nology is to be held on 27 February1985.The College has chosen as the over-all theme for the celebration 'Engin-eering for Wealth' to emphasize theenormous contribution that engineers'have made to the wealth of thecountry since the first students en-tered the College in 1885.The centenary celebrations will alsoinclude an exhibition entitled Tech-nology 2000, which will show manyof the most recent technical develop-ments at the College, with particularemphasis on the links with industry.The symposium will examine theimplications and opportunities forindustry, education, and employmentpresented by the technology cur-rently being developed and the roleof the engineer will continue to playin wealth creation.Among the many speakers, IgorAleksander, Kobler Professor inManagement of Information Tech-nology, will argue that evolutionarypressures underlying the boomingmulti -million dollar information tech-nology markets demand that ma-chines should become much moresensitive to natural modes of com-munication between people.

IDD augmentationBritish Telecom International, whichis responsible for providing telecom-munications services to 217 countriesworldwide, as well as to ships at seaand oil and gas production platformsin the North Sea, through a networkof satellite, submarine cable, andmicrowave systems, has reachedagreement with GTE Sprint of Bur-lingame, California, and MCI Inter-national, also of the USA, to operatea both -way telephone servicebetween the UK and the USA.The opening date for service willdepend on the successful completionof engineering tests.At present, BTI's international directdialling (IDD) service to the USA isprovided exclusively with AT&T Com-munications. BTI's IDD servicereaches 161 countries throughout theworld and this number is growingconstantly. IDD service is available toall British Telecom customers in theUK, and ninety-seven per cent ofinternational telephone calls from theUK are dialled direct by customers.

Automating the automatorsManufacturers of semiconductordevices that lie at the heart of thecomputer revolution are themselvesabout to undergo a wave of auto-mation. In particular, cost pressuresfrom heavily automated Japaneseproducers and the need for more

vigorous quality control is focussingmanagement attention on themaking of wafers, the sheets ofsemiconductor material on whichintegrated -circuit patterns areengraved.According to a new Frost Er Sullivanstudy 'The Automated Semiconduc-tor Wafer Fabrication Market in theU.S' (#1296), spending on the hard-ware and software that controls theaccuracy of wafer production and itsmovement through the factory willjump an average of thirty per cent ayear through 1993 to $1100 millionfrom a projected $83 million thisyear.

Towards a paperless officeA major breakthrough in computer-ized filling and reproduction of mosttypes of industrial and commercialpaperwork has been introduced byNorwegian electronics specialistEldak A/S.At the heart of the Document Man-agement System is a Digscan 9100digital scanner, developed for the USaerial and space reconnaissancetechnology. This unit optically readsevery kind of document, drawing,map, or photograph up to AO sizeand transfers the data in digital formto an E100D terminal for viewing,storage manipulation, or modifi-cation. Depending on user require-ments, the terminal can beconnected to disk and magnetic sto-rage, electrostatic plotter, internal orexternal networks, and modems forcommunication or electronic mail.Apart from offering a complete sol-ution for a company's total paperflow, the MS concept can also bereadily interfaced with existingcomputer -based systems.

Auto electronics comes ofageThe next time you see a truck andtrailer combination halted on thehard shoulder of the motorway, itscluster of hazard warning lights flas-hing away, the chances are that thisvital safety equipment was designedand produced by Thomas ElectronicsInternational Limited of Birch Valenear Stockport.This company was founded in 1963and had on its 21st anniversarygrown to a staff of fifty with a turn-over of more than a million pounds.If the direction indicators on a Minifail, the driver can continue on hisway using hand signals. When theflashers fail on a heavy goods vehi-cle, it is illegal for it to proceed fur-ther. It must stop until the lights arerepaired and this, of course, is veryexpensive in terms of lost business.To minimize the risk of such expens-ive stoppages, Thomas developedthe Teltester which checks the entireelectrical system of a truck in

1 -19

efektor january 1985

15 minutes as compared with15 hours by conventional means. TheTeltester, which was featured onBBC's Tomorrow's World as anexample of advanced technology, notonly locates existing faults but alsowarns of impending faults.

Electronic box officeOne of London's leading ticket agen-cies, Edwards and Edwards, recentlylaunched a national theatre bookingservice on British Telecom's Prestelnetwork. A wide variety of infor-mation on a range of entertainmentsis now available, along with the time-saving facility to book and pay fortickets from the comfort of home. Atits launch, the electronic box officeopened with details of fifty-two dif-ferent productions ranging fromcomedy to opera and covering majortheatres in London, Stratford uponAvon, and New York.Prestel works through ordinary tele-phone lines and offers local callaccess to ninety-six per cent of UKtelephone users. It is already beingused for home -shopping, bankingfrom home, travel agency bookings,advertising residential properties, andproviding up-to-the-minute infor-mation on stock exchange prices,currency markets, and horse racing.In addition, there are many populargeneral information services includingnews, current affaires, sport,weather, and finance.

LaserJet hits the marketAfter the introduction by Epson earlylast autumn of the LQ1500 laser printer, Electronic Printing Systems havelaunched the LaserJet. This printer isbeing manufactured by HewlettPackard, but EPS have been selectedto market the product due to theirspecialist experience in the laser mar-ket and their expertise on interfacedevelopment to suit a wide range ofhardware.Although these printers currentlycost thousands of pounds, MicroPeripherals of Basingstoke forecastthat prices are likely to fall steeplyand that in about twelve months'time there will be a laser printer onthe market at under £1000.Laser printers can operate at some180 characters per second and pro-vide features such as variable type-face with the ability to mix up tofour different fonts on a single page,the printing of charts, graphs, gridlines, raster graphics, and even digi-tized logos and signatures. And laserprinters are absolutely silent!

Vodafone on targetDetails of the coverage Racal-Vodafone is planning for its newmobile and portable public radio-telephone service in the North ofEngland and Scotland published

recently show the rapid expansion ofthe Vodafone network throughoutthe UK covering the major centres ofpopulation, motorways, and maintrunk roads. The Vodafone servicewill be available to seventy per centof the UK population within twoyears and, as the 25 -year cellularradio licence stipulates, will coverninety per cent of the population by1989.As the Vodafone service is progres-sing on schedule, trials commencedin Central London during Decemberas planned. Once the trials havebeen completed satisfactorily, theVodafone network will open forpublic service early this year.

Light under the SolentThe world's first undersea single -mode lightline - a £600 000 opticalfibre cable - has been successfullylaid by British Telecom. The cable,which is part of Telecom's hugeinvestment to provide customers withmodern digital services throughoutthe UK, will carry telephone callsand data across the Solent as pulsesof laser light.The 23 km long cable, linkingPortsmouth and Ryde, contains fourpairs of fibres. Each fibre pair worksat 140 Mbitis - a capacity of nearly2000 telephone calls at once, or theequivalent in data or other services.The system will(1300 nm) single -mode transmission,enabling light pulses to travel theentire 23 km length of the cablewithout intermediate amplification.Typically, optical fibre cables are tentimes lighter and thinner than con-ventional copper coaxial inter -citytelephone cables.

Single -mode transmission has par-ticular economic and operatingadvantages: on land networks, it will allow the

light amplifiers, known as regen-erators, to be always housed in build-ings instead of roadside manholes,making access easier and mainten-ance cheaper; in submarine systems, it will allow

regenerators to be spaced at30...50 km intervals, compared withthe current undersea coaxial cablelinks where amplifiers are neededevery 5 km or so - this provides sig-nificant circuit cost savings.The Solent crossing, though the firstunder the sea, is not British Tele-com's first underwater Lightline. InWales, 1.7 km of optical fibre cablecrosses a lake between Tywyn andCords, and the Barrow to Millomroute crosses the Duddon estuary.

Fortune keeps smiling onScotlandThree major expansion plans forScottish electronics plants have beenannounced: Honeywell InformationSystems is to increase output fromits Newhouse plant by thirty per centearly this year; Hewlett Packard is toexpand its facility at South Queens -gate with a £12 million programme;and Apollo Computer Inc. are toopen a major new European facilityin Livingston.Honeywell has been involved in elec-tronics operations in Scotland for 21years. The last two years have seena £1.5 million modernization scheme(including a £700 000 functionalboard tester) which has improved theworking environment.Principal products from Newhouseare DPS8 large-scale systems andDPS6 business micros, but the com-pany foresees a strong growth in theadd-on business in line with the mar-ket's demand for extra memory andprocessing power.Hewlett Packard's investment planswere revealed when the companyopened a new £7 million expansionwhich has already increased the fa-cility from 18 600 m2 to 27 900 m2.Under the proposed plan, £12 millionwill be spent in adding a further9300 m2 at South Queensferry. Thedecision to move straight into furtherexpansion is a response to increasingdemand for microwave and telecom-munications equipment of the typeproduced by the plant. The develop-ment should be completed early nextyear.Hewlett Packard announced at thesame time that it had been awardeda £2.8 million contract by BritishTelecom for its remote -access testequipment system. This follows anearlier £3 million order for the equip-ment, delivery of which has justbeen completed.

1-20

elektor january 1985

Apollo Computer are opening a3200 m? building which will housetraining, sales and service, and aPan -European logistics repair depot.In the longer term the companyintends to set up a manufacturingcentre.Apollo Computer Inc. is the world'sfastest growing manufacturer of pro-fessional workstations for engineeringand scientific applications. ItsDOMAIN workstations have beenaccepted as the industry standard forcomputer -aided engineering (CAE),design (CAD), and software develop-ment applications (CASD). (LPS)

PeopleMr D R Morse, C. Eng, FIEE, ChiefEngineer, External Relations (Engin-eering Division), retired from theBBC in November last after 37 years'service.Mr C Bull has been appointed to thenew British Telecom headquarterspost of Corporate Treasurer.Mr D E Fielding has been appointedDirector of Operations, British Telecom Enterprises (BTE). He will continue as Finance Director, BTE, aposition he has held since 1982.Mr N Cave has been appointedDirector and General Manager ofDowty Circuits, a division of DowtyElectronics.Following last summer's reorganiz-ation of the Marconi Group of Com-panies, Mr D Fletcher has beenappointed managing director of thenew company Marconi DefenceSystems Limited. The new companyhas already been hailed as 'the flag-ship of Europe's most powerful de-fence electronics organization'.

Silicon -on -sapphire inLincolnAs a further stage in the company'scommitment to investment in leadingedge technology, Marconi is to es-tablish a Silicon Systems Laboratoryin Lincoln. The laboratory will pro-vide advanced processing facilitiesfor 1.5 micron silicon -on -sapphire(SOS) technology. It will be fullyequipped for direct step on waferphoto -lithography, dry etching, anddedicated furnace processing,together with the associated processcontrol equipment. The high -currention implantation equipment recentlyinstalled in the adjacent MEDL ICfabrication area will be available forSOS processing to provide a com-plete facility for the 1.5 micron technology.The advantages of SOS as anenhanced CMOS technology areimproved speed or reduced powercombined with a high logic packingdensity and proven radiation resist-ance. The technology is suitable forall applications where power con-sumption and heat dissipation must

he minimized whilst still achievingvery high logic throughput rates. Aparticularly important application isfor electronics in satellites where thecost of providing electrical power ishigh and the electronic circuits areexposed to many years of continuousnatural radiation.

Balancing act resolvedProblems of connecting a receivingor transmitting balanced aerial to anunbalanced radio receiver or trans-mitter with coaxial cable or otherunbalanced transmission line havebeen solved at Exeter University.According to Mr P May, senior lec-turer at the university's Departmentof Science Engineering, the variousdevices such as transformers andcoaxial transmission line halunswhich have been used so far to over-come the problems are often inef-ficient and, in the case of transmit-ting aerials, there is also a seriousheat dissipation problem.Mr May's solution, which has beenpatented, is to produce a balancedaerial with an active element to anunbalanced transmission line withtwo conductors. The basic principleadvocated is that the coaxial cableshould enter the aerial system insidean earth plane, the zero potentialsurface of the aerial. The path of thecoaxial cable should only be allowedout of this zero potential plane if itforms an integral part of an elementof the aerial system.When this principle is applied to aYagi aerial, the coaxial cable forms asimple loop which is, in fact, half ofthe folded dipole in the Yagi array.The technique can be used withdouble or triple folded dipoles, half -wave folded dipoles, full wave ortwo -third -wave dipoles, and in widebandwidth applications. (LPS)

British computer for SwissnewspapersSwiss newspaper publisher GasserAG, who publish several Germanlanguage newspapers, including thedaily Bunder Zeitung, have ordered af330 000 CS7-15 Series 2 editorialtext management and typesettingsystem from Ferranti ComputerSystems.The equipment includes six Argus700GL processors with 4 Mbytes ofmain memory, two 160 MbyteWinchester disks, twenty-nine VDUs,two page make-up terminals, fourprinters, system control consoles,and the latest multiprocessor oper-ating system.Direct input of the wire service provided by the Schweizerische Depe-schenagentur (SDA) provides around the clock supply of world-widenews. This is stored in CS7's mag-netic disk memory which can beedited as required on VDU terminals.

-144F14M

n common with many newspaperpublishers in Europe, Gasser have anactive general printing requirementand the extensive page make-up,tabulation, and automatic paginationfacilities of CS7 are of particular

those areas. (LPS)

Events

Electronic Displays 84 Exhibition andConference28 30 November 1984Kensington Exhibition Centre,London

Cellular Radio National Conference7 ..8 February 1985Marriott Hotel, London

Defence Components & EquipmentExhibition and Conference14 .16 May 1985Metropole Hotel, Brighton

POWER 85 Exhibition and Con-ference21.. 23 May 1985Metropole Hotel. Brighton

COMPETA 85 (computers 5.peripherals! Exhibition and con-ference4 . 6 June 1985Kensington Exhibition Centre,London

Euromicro 85 Symposium onmicroprocessing and programming3 6 September 1985Brussels

1-21


tea leaves.Looking in our tea cups, we didnot feel like starting the new yearwith reflections on super -chips orsolid-state audio, but decided towait and see how last year's tea -leafpatterns in this respect will fare.So, what would we like to museover? Well, the first point is thestate of technological development.This is still accelerating at anincreasing rate: the super -chip oftoday is the standard chip of tomor-row. We regularly receive letterswith cries for help like: "Help! Istopped my subscription two yearsago, but because of withdrawalsymptoms I have recently recom-menced it. But I don't understandthe circuits any more!.."If we give free rein to our gaze intothe future, we must assume thatintelligent machines, far-reachingminiaturization, and affordableprices will become the norm.The second point is: where will wefind ourselves in 1985? One thing iscertain: new devices and equip-ment no longer amaze us. The

housewife will have amicroprocessor -controlledmicrowave oven which automati-cally weighs the food and sets theappropriate temperature. All shehas to do is to indicate that she isputting in a chicken and the ovendoes the rest. Or does it? The firsttime the oven is being used, youhear cries from the kitchen "Whyis that stupid thing not working? Itis program three...chicken...well then, why don't you start? Oh,the door was not closed properly.Sorry!" ClickSo, we are no longer overwhelmedwith wonder, but we do remaincritical. If a 'stupid thing' does notdo what we expect it to do, it's nofun any longer.

Utensils and crazesWhen something is new and nottoo expensive, it sells. With someluck (and a lot of publicity) it maybecome a craze. Or a fashion. Or anormal utensil for everyday use.

What's the difference?Why were newton's marbles, thehula hoop, and the rubik cubecrazes? Why were the charleston,the mini skirt, and aluminium lug-gage racks in fashion? Why aretelephones, automatic washingmachines, and zips utensils? Thedifference appears to lie in theuser -friendliness. Utensils are just,well, handy. They make it possibleto do something you wanted to doin an easy manner. They have apurpose, they meet a need. Crazesand fashions are, initially, exciting,but after a while the novelty wearsoff - and all of a sudden they areno longer useful, or user-friendly;just plain dull.Which brings us to the home com-puter. Gaze or utensil? As they arenow, we would say: craze. They areaffordable, exciting - even addic-tive. If you manage to work withthem you continue doing so.Sometimes until two or three in themorning. But why? And here's thecrux of the matter. Because those

1-22


'stupid things' do not understand -and therefore don't do - what youwant. They are not user-friendly.And that's why most computerowners get fed up with theirmachines. The standard games areboring and the 'family memory'was far more accessible when itwas contained in the telephonebook. Home programming is not sohot either. So?In nine out of ten cases, the com-puter is put away in a cupboard.Nice when you have visitors, butfor the rest... In the remainingone case, some interest remains.Elektor readers are prominenthere. They want more. For them thecomputer is a hobby, not a utensil.For that, it is not yet sufficientlyuser-friendly.

The futureBack to the tea leaves. What canwe expect? Which crazes willcome and go? What utensils willcome and become 'normal'?As we said, the cheap home com-puter appears to have all thehallmarks of a craze. The new MSXsets promise to become one hell ofa craze: they are almost 'real', thereare promises of much software, andthey are not too expensive.But...user-friendly? No, not really.Do they meet a real need? No, notreally.What about that pocket -diary -in -a -wristwatch recently launched bySeiko? There is some doubt here.An 'old-fashioned' diary is cheapand convenient, and you can enteror alter information in it withoutFirst having to read the operatinginstructions. And yet, a watch isalways with you, while a diary mayaccidentally be left at home.What are our real needs; in what

computers of the futureIt is not all that long ago that com-puters worked only from a bunch ofpunched cards which could not beproduced at home. Nowadays, com-puters are generally operated from akeyboard but this is still a long wayfrom the desired goal of voice -actuated machines. Keyboards arehighly restrictive because they meanthat if a user wants to communicatewith a computer he or she has tolearn to write programs. As the mainuses of computers will become cen-

direction should we look for futureutensils? Let's see: Peace and quiet. A noise

eradicator would be verydesirable. Built into your easy chair,or at the head -end of your bed.Technically, it is quite feasible, butas yet very expensive. Communication, but selective.

This is a wide field, but to nameone aspect that is definitelytechnically possible: a new BritishTelecom telephone service. Johnindicates on his phone that hewould like to speak to his brother.All subscribers indicate when theydon't want to be disturbed; forinstance, by a switch on theirphone. On the first occasion bothJohn and his brother are free andavailable, the computer makes theconnection. Information. Assuming that

you're interested in internationalnews, chess, cartoons, andtechnical news, which paper doyou read? Why, your own, per-sonalized one, of course - orderedfrom a fully automated publishingcompany. Each morning your veryown paper rolls from your ownprinter - no sports results, nostock exchange news, no gossip. Literature: books and

magazines, for relaxation orlearning. Currently, these havemany advantages: they are easy touse, legible, and relatively cheap.A computer screen is definitely notan improvement! And yet, the elec-tronic system has its good points:the information is distributed easilyand cheaply, and the 'covers' maybe very compact - mini cassetteor mini floppy. So, what do weneed? A handy, not too expensive,battery -operated reading book witha clearly legible screen. Put in thecassette and on you go with your

tred more and more on office auto-mation, data communications, andhome work stations, it is extremelyunlikely that more than a small pro-portion of users will be prepared tolearn how to program - and whyshould they?No, computers will have to comeinto much closer contact with theuser to become a real tool of humanthought. This means that computershave to become much cleverer thanthey are.In essence, a computer is nothing

novel. When you've finished it, youcall for a new 'book' - bytelephone, of course! Now, that willbe user-friendly! Physical aids, for healthy as well

as for (lightly) handicapped peo-ple. Better hearing aids, forexample, but also night glasses(with light amplifier), which aremuch more convenient andeconomical than torches. Or amuscle -enervating massage belt toenable you to lose those poundsduring breakfast - now, that couldbecome a craze (and, like its cur-rent mechanical counterpart, itwould be quite useless!). Elektor. What sort of articles will

we publish in Elektor in the1990s? Using the same criteria astoday - practice -oriented, usingmodern technology, broadly deal-ing with all aspects of electronics- the contents are bound to bequite different. Or are they?We will publish audiopreamplifiers, but with a 32 -wayinput bus for those new audioROMs.And we will combine those newMbyte memory ICs with thoseridiculously cheap AID and D/Aconverters to make a guaranteed -reproducible echo unit.We will make a de luxe housetelephone exchange for connectionto the normal telephone network:this will be allowed by then.We will make a 'music searcher'which tunes the radio (yes, that willstill exist) to a transmitter thatbroadcasts.the music of our likingand no advertising!We will...well, we'll see... In anycase, we'll make it interesting! 114

but an array of interfacing units: atthe centre the microprocessor,swathed in software - machinecode, compilers, assemblers,operating systems, languages, appli-cation programs, printers and/orscreens. This is, of course, an unfor-tunate arrangement because anychange at the user's end will nor-mally affect all these peripherals, andtherefore the very design of thecomputer.Of course, even users of personalcomputers now have other devices at

1-23

their disposal for communicatingwith the computer. For example, themouse is a small pointing devicewhich when rolled along a desktopcauses a pointer to move across thescreen in a corresponding direction.Originally the mouse was operatedthrough a pair of wires, but modernversions are cordless and communicate with the computer by infra-red signals. The mouse is also usedto select icons, which are smallgraphic representations displayed onthe screen to illustrate a computerfunction.These are but first steps towards per-sonalization of the computer, that is,giving the user facilities for mouldingthe operations more to his ownrequirements. The next steps willprobably have to wait until the 32 -bitmicroprocessors (such as Motorola's68020S, Intel's 80386, Zilog's Z8000,or National Semiconductor'sNS32032) and very large, inexpensivememories have become available inthe course of the next few years. Itis true, of course, that there are32 -bit computers on the marketalready, such as Apples Lisa andMacintosh, both of which useMotorola's 68000 microprocessor.Unfortunately, the 68000 has only a16 -bit bus, so to the user these com-puters do not seem much faster thanIBM's 16 -bit PC. True 32 -bit chipswith a full-size bus will enabledesigners of PCs to give users muchmore flexibility: they can executebetween two and three millioninstructions per second, that is asfast as many main-frame computers,and can process software programsmore than three times as fast as the68000.Power requirements of these newchips are the same as that of the68000 although they contain threetimes as many transistors. This lowpower consumption, whichminimizes heat problems, and thehigh speed coupled with a largememory mean that very small butvery powerful computers can bebuilt. As a result, highly complexmathematical and engineering prob-lems can be executed by a desktopcomputer and up to twenty peoplecan work on the same computer filesimultaneously.Personalized computers have recentlybecome available in the USA fromMetaphor. These machines arecustomized for groups of users, suchas accountants. Metaphor expectsusers, untrained in programming, totake it from there and write furtherapplications for themselves. So. hereis already an example of what cannowadays be done by the user

himself that had to be done byspecialized programmers only a fewyears ago.The two important developments are,however, the use of natural insteadof man-made language (such asBASIC or FORTH) and graphics. Theability to speak into a computerinstead of having to sit down at akeyboard will increase the uses ofcomputers vastly. Basically, what isrequired for this is an interfacebetween the user and the computer:a device such as a voice -actuatedtypewriter (vat) that can transcribespeech without having to understandit.As the problems facing designers ofautomatic speech recognition (ASR)systems are enormous, large pro-grammes, many government spon-sored, have been initiated in Britain(the Alvey programme, named afterJohn Alvey who chaired the commit-tee that established the programmein 1982); in Europe (the EuropeanStrategic Programme on Research inInformation Technology -- ESPRIT);in the USA (Defence AdvancedResearch Projects Agency -DARPA; -- Microelectronics andComputer Technology CorporationMCC - the civilian counterpart ofDARPA; and Semiconductor .

Research Cooperative - SRC); andin Japan (Institute for new -generation Computer Technology -ICOT - and the NationalSuperspeed Computer Project).Several of the world's big computercompanies have been working onautomatic speech recognition (ASR)for some time. A few months ago,IBM announced that it had producedan experimental system with aninety five per cent recognition ratefor a 5000 -word business vocabulary.There are two approaches to ASR,of which one relies on a templaterecognition system. Templates aredigital patterns used by a recognitionalgorithm to identify words. Theother is based on pattern analysis ofthe forty phonemes that make upspoken English, and the 1600 transi-tions possible between each adjoin-ing pair of them.All the signs are that by the year2001 we will be able to emulate HAL(but only as far as its positiveaspects!) and command computersthrough natural language, becausethat is, and will remain, the mostefficient and subtle, though com-plicated. instrument for human com-munication.Visual representation is virtuallyuseless to convey certain kinds ofinformation. But when it comes toshow the relation between, say,

elektor fanuary 1985

forecast and actual sales, picturescome into their own.Unfortunately, many companies havebeen frightened by the experience ofMindset. This Silicon Valley companymakes an IBM compatible PC thatproduces high -quality graphics. Afterthis set had been hailed by the pressat its launch early last year, itflopped. Although there were marketreasons for this, the main disappoint-ment was that the idea that goodgraphics would create its own marketamong general business users waswrong. None the less, most con-sultants are forecasting that thecomputer graphics industry isheading for a huge boom, with agrowth rate of more than forty percent per year for the remainder ofthe 1980s.Good graphics will be possiblebecause PCs are becoming powerfulenough to use bit mapping, a tech-nique in which each pixel can becontrolled individually. The mostimpressive PC with a bit -mappedhigh resolution screen is Apple'sMacintosh, while in the businessmarket it is IBM's 3270PC/G (which,incidentally, also has a mouse).Finally, two new printingtechnologies are becomingeconomically available. Up till now,there have been three basic types ofprinter: daisywheel, producing goodquality print slowly and loudly; dotmatrix, which uses a row of fineneedles shot forward by electricalpulses to form the shape of lettersand figures and is faster but lessclear than the daisywheel; and heattransfer, which also uses needlesbut, instead of moving, these heatup momentarily.But the future will almost certainlybelong to laser and LCD (liquidcrystal display) printers, both ofwhich are fast (6. 7 pages of A4per minute), noiseless, and give aprint quality where you do not noticeany dots (pixels). Printers usingthese techniques are still veryexpensive, although market forecastsare that there will be a laser printeron the market for under £1000 inabout a year's time.

1-24

Commodore cassetteinterfaceelektor january 1985

Commodore cassetteinterfaceNecessity being the mother of invention this circuit was destined tobe designed. The 'necessity' here is Commodore's insistence that theVIC 20 and C64 computers can only be used with a special cassetterecorder supplied by ... Commodore. One of our designers baulkedat the idea of buying a cassette recorder only for his computer whenhe already had a perfectly good audio recorder. Some kindly souldirected his outraged energy towards the nearest soldering iron andso was born THE Commodore cassette interface by Elektor.

As in many home computers, the data out-put by the VIC 20 and C64 via thecassette interface is in the form of asquare wave signal with an amplitude of5 Vpp. The information input to the com-puter has the same form. The cassetteconnector also contains a so-called 'senseinput' that enables the computer to checkif the recorder's PLAY button is pressed.The Commodore will only activate itsmotor output if this is the case. The com-puter itself switches the recorder motoron and off and we will see later how thisis actually done. First, however, we mustsee what happens if the computer wantsto save a file on cassette.

THE interface in detailThe program to be saved appears in theform of pulses with an amplitude of 5 Vppon the write output of the connector. This

amplitude is, of course, much too large tobe saved directly on the tape so thesignal is first reduced to about 200 mV byvoltage divider R13/R14. This signal is thensuitable for recording on the tape.The procedure for loading a program issomewhat more involved. The signal sup-plied by the recorder via a DIN orloudspeaker output socket is nowherenear square in shape and its amplitude isalso much too small, at about 200 to300 mV. The signal must therefore beamplified and its shape improved. Asingle op -amp (Al) increases the signal'samplitude by about six times. The offset ofAl, and consequently of A2, is set to halfthe supply voltage by means of R3 and R4.The second op -amp is set up as a schmitttrigger which takes the signal from Al andforms it into a clean square wave signalwith an amplitude of 5 Vpp. The computercan now load the program via the connec-

THE alternative

1-7R

Commodore cassetteinterfaceelektor january 1985

Figure 1. Looking at howsimple this cassette inter-face is, you may wonderwhy Commodore found itnecessary to insist on aspecial recorder. We did!

Figure 2. This is thelayout used by the six -way edge connector onboth C64 and VIC 20 com-puters.

049 ce I°-1

5V

CZ

5V

0R5

C3

224 16V

5V

R14

C4=1M

Toon

A2

051

I=1 Z114

, 4148V

T2R15

Al,A2 = ICI = LM 387

SL A = AUTOB MAN

SI 0

0 A

1312 C

D4

Ti

BC5478

5V0

VIC 64

60

O

4

C5

100nRIO

3-0

all 3

1N4148

O

0

SENSE

WRITE

READ

MOTOR

GROUND

Imo 1 o

2

Commodore edge connector(tool

2 3 4 5 6

A B C D E F

1

234

6

GND5 Vmatzerm.!*muw -as

25010-2

tor's read input. A LED (D4) has beenincluded in the circuit to show that this isactually happening. It will only light whentransistor T1 is caused to conduct by a '1'appearing on its base but the logic levelsswitch far too fast to be seen with thenaked eye. When data is being transferredthe LED appears to be continually on.One obvious advantage of this LED is thatit simplifies finding the start of a program.The motor in the cassette recorder mustbe switched on and off at the right timesby the computer. Naturally enough this isdone via a relay (Rel) instead of directly.When pin 3 of the connector goes hightransistor T2 is switched on and causes

the relay to operate. First of all, however,the computer must be made to think thatthe PLAY button is pressed. This conditionis simulated by connecting the senseinput to ground, which is exactly whathappens in the Commodore data recorderwhen this button is pressed. If the senseinput is connected straight to ground, aswe have done, we can then simply forgetabout it. The power supply for the inter-face is very kindly provided by the com-puter. As figures 1 and 2 show, pins 1 and2 of the cassette connector are GND and+5 V respectively. This makes a separatesupply for the circuit unnecessary.

The interconnectionsBefore any data can be transferred all theelectronics must be constructed and allinterconnections must be made. A total ofsix links are needed at the computer sideand the most important point here is toensure that none of these are inter-changed. The computer would not bevery pleased with this so have a look atfigures 1 and 2 to see where everythingbelongs before soldering any wires. Thecassette recorder is more tolerant ofwrong connections but it is far better if

1-26

the circuit works correctly first time.Again make sure to solder the right wiresin the appropriate places. The layoutusually used for a cassette recorder's DINsocket is illustrated in figure 3. The twoterminals for the relay contacts (points Rand S in figure 1) are linked to therecorder's remote input via a jack plug. Ifthe tape recorder in question does nothave any remote input this is no reason forpanic; simply connect R and S in series inone of the voltage supply lines to themotor.

Installation and useAll the components must be fitted to theprinted circuit board shown in figure 4and when this is done a suitable casemust be found for the circuit. Alterna-tively, it may be possible to include itwithin the cassette recorder case.Whichever of these is chosen there is onepoint to bear in mind: the connectingwires must not be made too long. Aspecial connector is needed to link theinterface to the computer's cassetteinput/output lines. This is a six -wayprinted circuit board connector with aspacing of 3.96 mm (0.156") between thepins. The wires can also be soldereddirectly onto the printed circuit board.We will be very brief in our instructions

3

pLoyback

DIN socket

ound rtoord

55010.3

on using the circuit: refer to page 18 ofthe C64 user's manual.The function of S1 in the circuit is clear. Itis used to switch the motor on and off,which is very handy for winding the tape.If an error message is generated duringloading the volume control on the cassetterecorder is probably not correctly set.When reading tapes that you have notrecorded yourself it may be necessary tore -align the record/playback head. If ourexperiences with this interface areanything to go by, however, errors willrarely occur, even when 'turbo' loading. N

4

Commodore cassetteinterfaceelektor January 1985

Figure 3. Here is thearrangement most com-monly used when acassette recorder has aDIN socket forinput/output.

Parts list

Resistors:RI, R2 = 4k7R3, R4 = 2k2R5, R8 = 22 kR6, R11, R16 = 47 kR7, R10, R15 -= 10 kR9 = 220kR12 = 220 QR13 = 100QR14 = 1k5

Capacitors:Cl = 10 nC2 = 22 nC3 = 22 p/16 VC4... C7 --- 100 nC8 = 10p/16 V

Semiconductors:D1, D2 = AA119D3, D5 = 1N4148D4 --- LEDT1, T2 = BC54713ICI = LM387

Miscellaneous:Ref = relay, 6 V PCB -mounting type (MSComponents - part no.8055)

Si = single -pole toggleswitch

6 -way PCB edge connectorwith pin spacing of3.96 mm (0.156" -order no. FG248)

Figure 4. Constructing thecircuit is simply a matterof assembling the com-ponents on this printedcircuit board. Make sureno wires are switchedwhen making the inter-connections.

1-27

VHF/UHF TV modulatorElektor january 1985

Computers, video games, videocameras, games computers; all ofthese produce video signals thatmust be displayed via a televisionset. If the TV receiver in questiondoes not have a video input andits owner is reluctant to vandaliseit in order to fit one then thissort of modulator is the obvioussolution. It is a simple circuitthat processes video signals toenable them to be fed straightinto the TV set's aerial input.

VHF/UHFTV modulator

for any TV setwithout a videoinput

Figure 1. A TV modulatoris, in fact, a small TVtransmitter. In this casethe transmitter consistsof a modulatable (AM)oscillator followed by aharmonics generator.

A 'TV modulator' is really no more than atransmitter. It is a very small transmitter,admittedly, but none the less that is whatit is. What does a modulator actually do?In general - and this design is no excep-tion to the rule - it is a simple oscillatorthat generates a frequency somewhere inthe VHF or UHF region. The oscillator ismodulated with the video signal and themodulated carrier wave thus generated isfed into the TV set's aerial input via acable. Then all that remains to do is tunethe TV to the correct frequency.

The layoutThe whole business is not quite as simpleas we have just suggested, of course, asthe mini transmitter must meet certainrequirements. The frequency stabilitymust be very good as, indeed, must thequality of the display. The required fre-quency stability is achieved by the use ofa crystal oscillator. A well thought out

1

0

choice of component values takes care ofthe display quality: the modulator allows aresolution of 80 characters per line, as thisis a value that is often needed.A very important feature of the circuit thatmust be decided is the transmission fre-quency. If this is only a single -channel, assuggested above, it gives rise to somepractical problems. Different users willwant different channels, the carrier wavecan become somewhat difficult to locate,and unless the frequency is exactly spoton no signal will be received. A muchbetter idea is to ensure that the HF signalcontains a large number of different fre-quencies. This makes it much easier totune the TV set to one of the frequenciesas there will surely be one to suit everyuser.The block diagram of figure 1 shows howthis is achieved. The TV modulator ismade up of two parts, namely amodulatable crystal oscillator and a har-monics generator. The oscillator operatesat a frequency of 27 MHz, which is quitelow so inexpensive crystals are readilyavailable. The harmonics generator con-verts the oscillator signal into a sort of fre-quency spectrum containing all themultiples of 27 MHz up to about 1800 MHz.The TV modulator's output signal is madeup of a large number of little peaks, eachof which is a complete transmitter signal.At least one of these will always be inband I (VHF channels 2...4), one in bandIII (VHF channels 5...12) and many ofthem will be in bands IV and V (UHFchannels 21...69).

The circuit diagramLike the block diagram, the circuit (shownin figure 2) is very straightforward. Thecrystal oscillator is based on a very fastHF transistor, T1 (BFR91), which performsthe amplitude modulation. Apart from thisthere is little to be said about the oscil-lator except, perhaps, that it is essential touse the correct values for the componentssurrounding T1. This is, of course, simplycommon sense in this sort of HF circuit.The harmonics generator is formed by twoSchottky diodes, DI and D2. These diodesmust switch very quickly in time with the27 MHz signal so they provide strong har-monics up into the gigahertz range.The modulation depth can be set with P1,while the oscillator's d.c. value can bevaried by means of P2. The combinationof these two presets enables either posi-tive or negative amplitude modulation tobe selected. This is essential as the har-monics produced vary in this respect. Wewill discuss the calibration of PI and P2later in this article.The power for the circuit can be providedby either an unstabilized 8...30 V or astabilized 5 V. The latter could be takenfrom a computer's power supply and inthis case ICI is not needed.

ConstructionThe tiny printed circuit board designedfor this circuit is shown in figure 3. It is

1-28

2 5V

not double -sided as this was found to beunnecessary. Construction is therebysimplified and readers who do not buythe board through our EPS service (tut -tut)will find it easier to make themselves.Building the circuit is simply a matter offitting the components onto the printedcircuit board. The coils, often a source ofmuch teeth -gnashing and hair -pulling, willnot be a problem in this case. Two ofthem, Ll and L2, are made by winding 31/2turns of enamelled copper wire (about0.2 mm thick) on a 3.5 mm ferrite bead.Another, IA, is just one turn of copperwire (0.8...1 mm thick) air -wound with adiameter of 8 mm. The fourth inductor, L3,can simply be bought.Any third overtone crystal with a fre-quency of between 25 and 30 MHz willwork in this circuit. A number of suitablevalues are advertised in this issue.The only parts that might prove difficult tofind are diodes D1 and D2. The onesstated in the pans list are available at themoment but do not give up hope if yourcorner shop does not have them. The onlyimportant thing is that they must be UHFSchottky diodes; the actual type numberis of little consequence.

CalibrationCalibrating the modulator calls for a cer-tain degree of care as it involves morethan just 'set the presets to mid -position'.The setting depends, in fact, on the har-monic to which the circuit is tuned. Cali-bration should be carried out as follows:I Set the TV receiver to maximum

brightness and contrast. Feed a video signal into the modulator

(a video recording of a test card, or alink to a computer's `TV' socket, could

be used) and connect the circuit's output

OMB.. 1 menCuLlJSMG19..211

UHFIF VHF

85002-2

to the TV's aerial input.IN Set P2 to mid -position and PI to

minimum resistance (fully anti-clockwise).

Tune the TV receiver to a harmonic,preferably one of the VHF bands (chan-

nels 2...12). The tuning is correct whenthe 'snow' on the screen disappearsand/or the screen becomes dark.III Turn P1 very slightly until 'something'

becomes visible. Calibrate P2 to give the best possible

quality image. If the result is not verygood the wiper of P1 can be moved a bitmore and P2 again trimmed to give a bet-ter image. If this still fails to provide an acceptable

result tune the TV to the next harmonic.This must give a decent image. 14

VHF/UHF TV modulatorElektor january 1985

Figure 2. In this circuitdiagram we see that the27 MHz oscillator is basedon transistor T1 and theharmonics are generatedby Schottky diodes DIand D2.

Parts list

Resistors:RI, R2 = 4k7R3, R4 = 56 QP1 = 100 Q presetP2 = 500 Q preset

Capacitors:Cl = 4p7/16 VC2 = 10 pC3 = 220 pC4 = 47 pC5 = 47 n, ceramicC6 = 100 nC7 = 330 n*

Inductors:L1, L2 = turns of0.2 mm (SWG 35 or 36)CuL on a ferrite bead ofabout 3.5 x 3.5 mm

L3= 1 pHL4 = 1 turn of 0.8...1 mm(SWG 19...21) CuL, air -wound with a diameter of8 mm

Semiconductors:D1, D2 = 1N6263(Ambit/Cirkit)

D3 = 1N4148T1 = BFR91 (Ambit/a/kidIC1 = 7805'

Miscellaneous:X1 = crystal, 27 MHz_j3rdovertone) or other 3ruovertone crystal between25 and 30 MHz

* = not needed if thecircuit is powered from astabilised 5 V supply

Figure 3. Fortunately theprinted circuit board forthe modulator is onlysingle -sided. The largecopper surface acts as aground plain.

1-29

portable guitaramplifierwith a host offacilities

Apart from output power and thechoice of valves or transistors asactive elements, there is notmuch to distinguish themultitude of commercial guitaramplifiers on the market. All thatmost of them offer is a three -channel equalizer for bass, mid-range, and high frequencies, anda built-in reverberation spring:this does not give the musicianmuch scope for experimentation.Yet, even for only a modestoutlay is it possible to bringsome colour to the monotony ofthe basic sound of the strings.This is made possible by avoltage -controlled filter - surelyno stranger to our musicalreaders.

The controls for bass, mid -range, and highfrequencies on most commercial guitaramplifiers may be compared with thoseon a hi-fi installation. Unfortunately, theydo not change the basic character of thesounds produced by a guitar string: to doso, many more additional units arerequired: phaser, chorus, flanger, fuzz box,and so on In marry cases, these unitsreally do mellow the harsh notes pro-duced by the guitar. The amplifierdescribed here does not, and is notintended to, replace such additional unitsentirely. However, several of the add-onunits are based on similar principles andcan be imitated fairly easily, and well, bythe voltage -controlled filter on which thedesign of the present amplifier is based.Mixing the outputs of a voltage -controlledfilter (VCF) allows the continuous transitionfrom all pass to notch mode. Furthermore,the signal from the integral fuzz circuitmay be added to the outputs of the VCF,so that with only four potentiometers awhole spectrum of tone colour variationsbecomes available.

Voltage -controlled filter (VCF)The VCF is a simplified version of thatused in the Formant synthesizer (seeElektor December 1977, page 12-27). It isbuilt from opamps A2, A3, and A4 asshown in figure 1, which function as highpass, band pass, and low pass filterrespectively. Stereo potentiometer P3enables the setting of a specific turnoverpoint, that is, the centre frequency of theband pass filter.

Overdrive (fuzz) circuitEither the direct or the filtered signal fromthe guitar may be fed to opamp A5 byswitch SI. The gain of the amplifier can beset within wide limits by P2: this is vitalbecause the stage following A5 needs athreshold to function as limiter and so pro-vide the required amount of distortion.The use of three pairs of diodes results ina smoother onset of limiting, that is, a pro-gressive increase in distortion, which pro-vides a tone reminiscent of valveamplifiers. The operation of the overdrivecircuit is clarified in figure 2.

MixingPotentiometers P6... P9 allow the mixingof the outputs of the filter and the dis-tortion generator. the wipers of all four areconnected to the inverting input of opampA7. Preset P10 enables the setting of therequired feedback factor: the higher itsvalue, the greater the gain of A7.

Reverb(eration) unitReverberation springs have been awelcome addition to guitar amplifiers for along time. Although they do not performmiracles, they add to the fullness of thesound.The principle on which they work is thatthe sounds to be reverberated aremagnetically coupled to one or two metal

1-30

1C2

HIGH

25 V 15 V

25V VII 15v

Al...A4 = ICI = TL074= IC2 = 71074

I portable guitar amplifieris vv elektor ianuary 1985CD-

CIT0 min 0(Cl y IC2

C 14 CrO

C}-15 V

to

springs. Because of the elasticity of thesprings, the mechanical waves to whichthe signals from the guitar have been con-verted take a certain time to reach theother side of the spring where they arereconverted to electrical signals. Inte-grated a.f. amplifier IC3 drives the inputcoil: a standard opamp would not be ableto provide sufficient energy, that is, outputcurrent.Opamp A8 is a mixer in which the directand the reverberated signals are addedtogether. Potentiometer P12 enables con-tinuous adjustment of the level of theecho. The relatively low value of R17, com-pared with that of feedback resistor R19,provides a fiftyfold gain of thereverberated signal.

CalibrationThe potentiometers are all brought out atthe front panel and their setting will bediscussed under 'operation and settingup'.Depending on the type of pick-up used,the peak value of the signals produced byan electric guitar vary widely. Preset PIdetermines the gain of input amplifier Al.To start with, set the wiper of this controlto the centre of its travel. Then connectthe output of Al (pin 7) to the outputamplifier, and connect an electric guitarto the input of the circuit. If the 30 -watt a.f.output stage described elsewhere in thisissue is used, set the potentiometer, P13,between Al and that amplifier to maxi-mum. Also, set the volume control on theguitar to maximum.

The maximum required volume can nowbe set with P10, but only after P6... P8have been turned open (wipers at outputof opamps A4, A3, and .A2 respectively),P3 and P4 have been set to the centre oftheir travel, and P9 and P12 so that theirwipers are at earth potential. The settingof P2 is immaterial. When all this is done,the basic sound of the guitar, without dis-tortion and reverberation, should be heardin the loudspeaker. If the sound is dis-torted, it probably means that Al isoverloaded. The remedy is to reduce itsgain with Pl. If you have an oscilloscope,check that the signals at the output (pin 7)of Al are not being limited.It may also be that the output stage isoverloaded; in that case, reduce its gainwith P13 until the sound is fairly soft.If there is still distortion, A7 or A8 may beoverloaded: the remedy for this is to

walk111117

$

n.4fi

Figure 1. Circuit diagramof the pre -amplifier.

Figure 2. A clean sinewave la) at the input ofthe overdrive (fuzz) circuitappears flattened (b) atthe output if its peakvalue is equal to. orexceeds, the thresholds,Q1...03. of the threepairs of limiting diodes.At x the first diode pairstarts to conduct, at y,the second also, and at zall diodes conduct.

portable guitar amplifierelektor January 1985

Figure 3. If a compositesignal (a) is distortedthrough limiting, thehigher frequencies maybe chopped (b, 21 or notbe affected at all lb, 1). Amore pleasant soundensues if first only thehigh frequencies arelimited and then superim-posed onto the lowerones (c).

Figure 4. Suggested con-struction of the housingfor the complete ampli-fier. Note the chassis towhich the front panel isfixed: the whole may con-veniently be slid into andout of the case.

reduce the gain of A7 with P10. Again, ifyou have an oscilloscope, the output of A7(pin 8) or of A8 (pin 14) may be checkedfor clipping. It is, however, very unlikelythat there is overloading of these stages.

Setting the reverberationThe level of the signal applied to thereverberation exciter coil is determined bypreset P11. To find the correct level, firstset P12 to maximum. Next, move the wiperof Pll slowly from earth potential and sim-ultaneously pluck one of the guitarstrings. If everything is all right, the echo

3U IV)

U (VI

841284

should become clearer and clearer.However, at a certain point, that is, whenthe output level of IC3 becomes too high,the echo becomes muffled and suffersfrom frequency -dependent distortion. Toavoid this happening even when the guitaris plucked vigorously, carry out this testwith firm plucking of the string. If theecho is too weak with Pll and P12 at maxi-murrl, it may be enhanced with P10, eventhough this also increases the level of thedirect signal.

Operation and setting upPlaying without overdrive (fuzz): set P9 tozero (wiper at earth) and with P6...P8choose the desired bass, mid -range, andtreble response. It is important that thesetting of each of these controls is com-patible with that of the others. When allthree are set for identical gain, the outputof the guitar sounds virtually natural.Potentiometer P4 is of considerableimportance to the operation of the VCF: itdetermines the quality, Q, that is, theslope of the pass band of the filter. Whenthe Q is high (steep slope) it is possible toproduce artificial resonance peaks in theband-pass characteristic which give thesound a distinct colouring. This is alsoaffected to some extent by the setting ofP3.Varying P3 (imagine this control fitted in afoot -operated swell) with Q high and onlythe low-pass filter section operatingcauses a wa-wa effect. With a low Q andthe mid -range frequencies attenuated,slowly altering the crossover frequencygives rise to a phasing effect.When the wiper of P4 is at earth potential,the VCF functions as an oscillator and it istherefore necessary that PS is adjusted sothat with maximum Q the filter just doesnot oscillate.Playing with overdrive (fuzz): whenswitch SI is in position I, the entire soundfrom the guitar becomes overdriven.Unlike many other guitar amplifiers, thepresent one allows the continuous mixingof the original and overdriven sounds: thismay be arranged by a foot switch con-nected to jack socket S (see figure 1). Ifonly the overdriven sound is wanted,potentiometers P6... P8 must be turned offcompletely (wipers at earth).The degree of overdrive may be set withP2 to individual taste.When Si is in position 2, only those fre-quencies that lie above the crossoverpoint set by P3 will be overdriven. If youmix the fuzzy high frequencies with theoriginal low ones, a very pleasant, hoarsesound ensues that cannot be produced bya traditional fuzz box (see figure 3).Because of space considerations, we can-not describe all possible sound variations,but hope that the examples given willspur you on to further experimentation.

Power output stageA low -weight, portable guitar amplifier ofmodest dimensions requires a power out-put stage that is small, reliable, efficient,

1-32

5 portable guitar amplifierelektor January 1985

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and yet provides sufficient power to pre-vent the audience reaching for their hear-ing aids! To cut a long story short, wehave opted for the 30 -watt output stagedescribed elsewhere in this issue. Thecomplete set-up gave very satisfactoryresults during tests and operation in smallto medium-sized halls; it would probablynot be quite suitable for use in largerspaces.

Power supplyPower for the pre -amplifier is derived fromthe supply of the 30 -watt output stage: theprinted circuit of that stage is already fit-ted with appropriate take -off terminals.If you do not use the 30 -watt output stage,you need a supply that is capable of pro-viding +18... +25 V at 35 mA (positiveline) and 22 mA (negative line).

In

N

CO

Figure 5. View of the topof the chassis and therear of the front panel. Itis important to adhere tothe wiring layout to pre-vent earth loops. Do notforget to insulate allsockets from the frontpanel!All dashed lines indicatescreened cables. Screensmust only be connectedto earth where shown orat the front panel.

1-33

portable guitar amplifierelektor january 1985 6

Figure 6. Suggested frontpanel of the guitaramplifier. It is, unfor-tunately, not availableready-made from ElektorPublishers.

FILTER

-

CHARACTER

vik

MIXER

84128-6

LoudspeakerNever use a loudspeaker designed for usein hi-fi installations for the followingreasons. The amplitude of a vibratingguitar string is not particularly large: inthe case of the top strings, it is hardlypossible to see with the naked eyewhether they are vibrating, especially ifplucked only lightly. The amplificationconsequently required to make them aud-ible is quite considerable.If, however, a string is plucked vigorously,because of the type of music or thetemperament of the player, it is deflectedquite a distance from its rest position. Theinstantaneous voltage then induced in thepick-up coil reaches a very high peakand, in modern hi-fi equipment, this isfaithfully transferred to the loudspeakerwhich in consequence may easily bedamaged or destroyed. Fortunately, thereare loudspeakers available which havebeen specially designed for use withelectric guitars. They are characterized bya very rigid suspension of the cone andtheir ability to cope with the widedynamic range of electric musicalinstruments.Basically, the loudspeaker should be ableto handle not less than 50 watts (sinewave) and have an input impedance of 8ohms or 4 ohms. Note that mid -range andtreble speakers are not just superfluousbut unwanted! After all, we are not look-ing for linear transfer of the guitar sounds:it is the unfaithfull reproduction thatmakes the music of electric guitars sopopular!

ConstructionThe complete amplifier, includingloudspeaker, may be housed in a case assuggested in figure 4. The shape cor-responds closely to current market trends.Dimensions are primarily dependent uponthe loudspeaker unfortunately, we havenot been able to find a suitable speakerthat would make it possible to house theamplifier in a truly portable case.The top compartment of the wooden caseoffers ample space for the pre -amplifier,output stage, and power supply.The best material to use is 19 mm (3/4 inch)chipboard. The various panels should befastened together with dowels and wood

glue: if you must, chipboard screws mayalso be used.The completed case may then be coveredin, say, black leatherette and the cornersprotected by suitable metal corner piecesto give the whole a near -professionalappearance.The electronic circuits are best mountedonto a chassis which is fastened to thefront panel so that the whole may be slidin and out of the upper compartment. Thefront panel should be fastened to the casewith suitable chipboard screws. It is wiseto fit two runners at the underside of thechassis so that it does not lie direct on thewood: this has the advantage that any fix-ing screws for the transformers, PCBs, andso on may protrude from the underside ofthe chassis without causing any problems.

Some useful hintsIf the wiring to the potentiometers, thepower lines, and the wires connecting thepre -amplifier to the output stage are notplaced with careful thought, it may easilyhappen that hum is audible from thespeaker even when all potentiometers areturned off. One of the prime causes of thisis that the earth connections to variousparts are not radial but form a loop. Ifsuch a loop lies in a stray field, a voltagemay be induced in it which is thensuperimposed onto the signal. Careshould also be taken that signal paths andwires (including PCB tracks) carryingunsmoothed alternating currents neverhave a common return. It is for thesereasons strongly recommended to adhereto the interconnection wiring layout infigure 5.When fitting the reverb unit, care shouldbe taken that the output coil is not tooclose to the mains transformer. Thescreened housing of the unit does notoffer all that much protection against thestrong electro-magnetic field existing inthe immediate vicinity of the transformer.It is also best not to fit the unit rigidly tothe chassis to prevent any mechanical vi-brations from the loudspeaker and mainstransformer being transferred to it. This iseasily accomplished with a felt washer fit-ted between the chassis and the unithousing: it is wise to glue the washer inplace.

1-34

portable guitar amplifierelektor January 1985

Parts list

Resistors:

R1 = 470 kR2,R5,R33 = 1 MR3 R17 R22 R29 = 2k7R4,R7,R12,R13,R18,R19,1134 = 100 k

R6,R25,R28 = 220 QR8,R9 = 47 kR10,R11,R20,R31 = 10 kR14.R15 = 22 kR16 = 10 QR21,R32 = 3k3R23,R26 = 150R24.R27 = 270 QR30 = 8k2P1 = 50 k preset, PCB typeP2 = 10 k potentiometerlog.

P3 = 100 k potentiometer,stereo, lin.

P4 = 100 k potentiometerlin.

P5 = 25 k preset, PCB type136,P7,P8,P9,P12 = 100 kpotentiometer, log.

P10 = 500 k preset. PCBtype

P11 = 10 k preset. PCBtype

Capacitors:

C1,C2,C4,C,8.C10 = 47 nC3,C5,C15.C16,C21 = 10 y/35 V

C6,C7 = 3n3C9,C17,C18,C19.C20 = 100 n

C11 = 220 p/25 VC12 = 47 p/25 VC13,C14 = 330 nC22 = 2412/10 V

Semiconductors:= 1N4148

T1 = BC 547T2 = BC 557IC1,1C2 = TL 074 ITL 084)IC3 = LM 386IC4,1C6 = 7815IC5 = 7915

Miscellaneous:

Si = SPST switch2 jack socket, 6.3 mm,mono, without switch

1 jack socket, 6.3 mm,mono, with switch

printed circuit board 84128

Figure 7. The printed cir-cuit of the pre -amplifier.

1-35

The input of the device is formed by dif-ferential amplifier T2/T3 whose emitterresistance consists of current sourceTI/DI/D2. The output of the amplifier isfed to driver T6 whose collector resist-ance is formed by current source T4.

Transistor T5 provides a constant bias volt-age for the output transistors: the biasallows a quiescent current of about 50 mAthrough these transistors. The output tran-sistors are arranged as quasi -complemen-tary darlingtons: T7 and T9 form an n -p -ndarlington; T8 and TIO are the com-plementary pair. Any asymmetry of T8/T10is negated by diode D5.

Circuit descriptionThe amplifier circuit, shown in figure 2, isdesigned for operation from a ± 25 V

symmetrical power supply. The full 50 V,decoupled by C4 and C8, is applied tothe output transistors, pins 6 and 8, in theSTK077. The supply for the input anddriver stages is decoupled by R3/C3 andR5/C7 respectively and applied to pins 10and 4. Feedback is arranged by connec-ting the output, pin 7, to the invertinginput of the differential amplifier, pin 3,via R6.

The gain, A, is determined by the feed-back factor, that is, the ratio R6:R4 -A = (R6 + R4)/R4.

When planning the power output stage for the guitar amplifierdescribed elsewhere in this issue, we came across an interestinghybrid IC made by Sanyo: the STK077. In contrast to a monolithic ICwhere all the components are manufactured into or on top of a singlechip of silicon, a hybrid IC consists of several separate componentparts, attached to a ceramic substrate, that are interconnected by anappropriate metallization pattern or by wire bonds. Hybrid ICs arefrequently encountered in medium power (30...60 W) hi-fi equipment.They are, however, also eminently suitable for use in home-

constructed amplifiers, because they are more reliable and smallerthan circuits built up from discrete components, and are not sovulnerable and susceptible to oscillation as monolithic IC stages.Hybrid ICs are generally available with power ratings up to 70 W andare normally reasonably priced.

30 watt a.f. output stagebased on a newhybrid IC

The STK077 is a 30 watt hybrid IC that isideal for use in small mono a.f. amplifiersor medium power stereo equipment. It isalso of interest to those who want a smallamplifier for fitting into an activeloudspeaker box.The innards of the STK077 form a fairlyconventional a.f. amplifier circuit as canbe seen from figure 1. Note that the powertransistors are mounted direct on the cool-ing area of the device to ensure betterheat dissipation.

With values shown this amounts to nearly27 dRThe input signal is applied to the non -inverting input (pin 1) of the differentialamplifier. DC zero potential is ensured byresistor R2, which carries the base currentfor T2. Pin 2 is the earth terminal which isinternally connected to the metal base ofthe STK077.

Stability of the output transistors is ar-ranged by various methods. On boardthere is a Miller capacitor between base

1-36

and collector of driver T6, while externallycapacitor C5 is connected between pins 3and 5. Capacitor C9 and resistor R7 at theoutput, pin 7, ensure a defined load athigh frequencies and this enhances thestability under no-load conditions. Finally,the input has been provided with an RClow-pass filter (R1/C1) which increases therise time of the input signal and soreduces the transient intermodulation dis-tortion (TIM).The power supply, with the exception ofthe mains transformer, is housed on thesame printed circuit as the amplifier. Itconsists of an unregulated circuit: fourstandard diode rectifiers, and two electro-lytic smoothing capacitors each shuntedby a foil capacitor.When a mains transformer with 2 x18 Vsecondary is used, the direct output volt-age under no-load conditions is of theorder of 25 V, falling to about 22 V when anormal load is connected. A 1 A trans-former can be used for output powers upto 20 W.

More powerWith a ± 20 V power supply, the STK077provides 20 watts into 8 ohms, or 30 wattsinto 4 ohms. In the latter case, both thethird harmonic distortion and the currentconsumption are somewhat higher than inthe former. If you want higher power, oneof the series STK078...STK083 may beused: the printed circuit board remainsunchanged, but it is, of course, necessaryto use an appropriate mains transformerand higher rated electrolytic capacitors.Data for these are given in table 2.

Practical tipsThe mains transformer may have a singlecentre -tapped secondary or two separatewindings. In the latter case, proceed asfollows: connect one of the terminals ofsecondary 1 with one of secondary 2 andmeasure the a.c. voltage between the twofree terminals. If this is 0 V, the terminalsof ONE of the secondaries must bechanged over so that across the free ter-minals an a.c. voltage of twice the ratingof one of the secondaries is measured.The interconnected terminals become theequivalent of the centre tap which is con-nected to earth as shown in figure 2.

2

Fl

100 ,.A

1 2 3 4 5 6 7 8 9 10

!!IIIIIIR

Tr.I

2: 1811.1 A

R3

4 x 1N5401

D2

C12 C13I=1 mos

.25V

30n..259

30 watt a.f. output stageelektor january 1985

Figure 1. The circuit ofthe STK077. Note that thepower transistors are con-nected in a quasi -complementary dar-lington arrangement.

Figure 2. Circuit diagramof the amplifier and itsunregulated, symmetricalpower supply.

25 V

25 V

25 V

35031-2 25V

1-37

30 watt a.f. output stageelektor january 1985 3

Parts list

Resistors:

R1 = 1 kR2,R6 = 56 kR3,R5 = 100 QR4 = 2k7R7 = 4Q7P1 = 100 k logarithmicpotentiometer

Capacitors:

Cl = 470 pC2 = 1 p/16 VC3,C7 = 220 p/35 VC4,C8 = 10 p/35 VC5 = 1p8C6 = 47 p/16 VC9 = 47 nC10,C12 = 4700 p/40 VC11,C13 = 330 n

Semiconductors:D1...04 = 1N5401IC1 = STK077 (orSTK078...STK083)

Miscellaneous:S1 = DPST mains switchTrl = mains transformer,secondary 2 x 18 V/1 A

F1 = fuse, 100 mA, slowblow

F2 = 1 A (8 Q loudspeaker)or 1.6 A 14 Q loudspeaker)slow blow (2 seconds)

Heat sink - temperaturerise 1.7 K/W

Printed circuit board 85001

Figure 3. The printed cir-cuit board is not only foruse with the STK077 butalso with other membersof the family,STK078...STK083, whichgive output powers of notless than 24...40 wattinto 8 ohms, dependingon which member isused.

085001

0

0

Failure of one of the power lines duringoperation of the amplifier would destroythe IC. It is, therefore, vital to ensure thatboth power lines are connected properlyat all times. Furthermore, under no cir-cumstances should either the positive orthe negative line be protected by a fuse. Itis, of course, also important that the

voltages across the two secondaries aswell as capacitors C10 and C12 areidentical.The value of the thermal rating of the heatsink stated in the parts list and table 2applies to the amplifier being driven hard.If the amplifier is intended for domestic(music) use only, the value may be

Table 1

Supply voltage, Ub - maximum- recommended

Case temperature - maximumShort-circuit duration - maximumLoad resistance - recommended

- minimumQuiescent current - maximum

- typicalPower into 8 ohms - minimum*Bandwidth - at 1 W into 8 Q

- at 20 W into 8 QOutput direct voltage - maximumInput voltage (rms) - for 20 W into 8 Q

- for 30 W into 4 QInput impedanceCurrent consumption - at 20 W into 8 Q

- at 30winto40

± 32 volts+ 22 volts

85°C2 seconds8 ohms4 ohms100 mA50 mA20 watts10 Hz...100 kHz10 Hz...30 kHz±70 mV600 mV500 mV50 kilohms1A1.5 A

Table 1. Brief technicalcharacteristics of theSTK077.

1 -38

in range 20 Hz...20 kHz, THD = 0.3%, Ub = + 22 V

somewhat lower. It may be useful to drillout the fixing holes in the heat sinkslightly to avoid mechanical stress duringits installation. The use of silicone heattransferring grease is strongly rec-ommended.If the amplifier is used for mono appli-cations, a fuse may be fitted in theloudspeaker lead: this is shown in dashedlines in figure 2. The fuse should be of themedium -slow (about 2 seconds) type.Values for use with other ICs in the seriesare given in table 2.The heat sink and printed circuit boardshould be fixed to a chassis with the aidof an aluminium angle piece as shown infigure 4, since the terminals of the IC can-not support the PCB.As always in a.f. amplifiers, the wiringlayout should be thought out carefully. Onthe premiss that any wires may causeproblems, we reduced the amount of wir-ing by designing the power supply andthe amplifier on one PCB. The only wiresconsequently required are three to themains transformer, two to the loudspeaker,and a screened one for the input signal.If two amplifiers are built for stereoapplications, it is possible to use onemains transformer of twice the ratingstated in the parts list. Separate powerlines should then be connected to each ofthe PCBs. Separate earth return lines foreach loudspeaker are also required: thismeans that each PCB is connected to theappropriate loudspeaker by a two -corecable.If you want to use a 4 -ohm loudspeaker,the mains transformer should be capableof providing a secondary current of 1.5 A:alternatively, a transformer with lowersecondary voltage (2 x15...16 V) may beused. The heat sink should also beadapted to the higher dissipation, forinstance, 1.5 K/W instead of 1.7 K/W. Theonly other difference between the 4 -ohmand 8 -ohm versions is that the former hasa slightly higher third harmonic distortion(THD) factor than the latter, as shown infigure 5. N

Table 2 30 watt a.f. output stageelektor january 1985

STK078 STK080 STK082 STK083Supply voltage - max. V + 35 + 39 + 43 ± 46- recommended V ± 25 ± 27 + 30 ± 32

Load resistance- recommended Q 8 8 8 8

Output power into 8 52- minimum W 24 30 35 40

Secondary transformervoltage - recommended V 2 x 20 2 x 22 2... 25 2 x 27

Transformer rating- recommended VA -Z.50 --60 -75 -90

Rating of electrolyticcapacitors V 35/40 >=50 >=50 >=50(C3,C4,C7,C8,C10,C12)

Fuse rating(8 -ohm loudspeaker) A 1.2 1.6 1.6 2

Heat sink - temperaturerise K/W <=1.5 <=1.4 <=1.2 <=1

5

THD

a1

2 Ub= Z211.111

I.e1%1 7

7

0.1

LD

- 7JSCHZ

2 s

power output (WI

2 3 S

85001-5.

THD

1%1 10

01

b

i MINIIIMO MOM111 -!!":;:..O

o t iIII.uUmin=An..amt..r.__ I mop=a-,;-_-_,.sumlINNIIIIA1111111fir"- 1.....411.7.11INE

0I 2 7 10 a

-is. power Grope IWI

ID

135001.5b

Table 2. Variations inratings if higher powerICs from the STK seriesare used.

Figure 4. To avoidmechanical strain on theIC terminals, the printedcircuit board. heat sink.and IC should be fittedtogether as shown.

Figure 5. Third harmonicdistortion vs outputpower in the STK077: in5a with 8 -ohm load and- 22 V supply: in 5b with4 -ohm load and ±20 Vsupply.

1-39

JSR SWAPe!ektor january 1985

software tointerchangepages 0 and 1in a 6502 -basedsystem

Table 1. The processorleaves the SWAP routine(which it entered usingJSR) not by RTS but byJSR! The return addressis 'stacked' at the start ofthe routine, then cor-rected (return address =address left - 1) andthen placed after thejump instruction ident-ified by the labelJMPINS.

Whenever two (or more) large programs must exist at the same timein a 6502's memory there is bound to be a conflict as regards page 0and the stack (page 1). The situation could arise if a BASICinterpreter and a DOS (disk operating system), or both of these and avideo handler, are being used simultaneously. One of the acceptedmethods of solving this problem involves reserving two areas inrandom access memory where these pages are 'duplicated, giving,for example, E000...EOFF for page 0 and E100...E1FF for the stack.Every time the computer changes from one program to the other thecontents of these areas of RAM are swapped with the appropriatecontents of pages 0 and 1. This removes any possibility of corruptingthe pointers on page zero or the contents of the stack.

JSR SWAPOne of the notable characteristics of the6502 microprocessor is the way it usespages 0 and 1. The 256 bytes from0000HEX to 0OFFHEX can be addressedusing commands specific to this zone.This is known as page zero addressing;the most significant address byte is notspecified as it is implicit in the operationcode. The same 256 bytes can be used as16 -bit pointers for indirect indexedaddressing of the rest of the memory. The256 bytes from 0100HEX to 01FFHEX formthe 6502's stack. This is a registergenerated by the processor itself toenable it to store certain information. Itoperates on the principle of 'last in firstout' so the processor can only work withthe last item stored on the stack. Aninternal stack pointer continually indicatesthe address of this last item.It is obvious that the slightest careless

8048: 80***0eau: *SWAP*8868: 8188880078:8888:8898: SWAP PAGE 8 AND PAGE 1 WITH E000 AND 21888188:8118:8120:0132: E280 P2 10800 PAGE ZERO8148: E280 STACK I 18100 STACK AREA6158: (288 SPZ 8E880 SWAPPED PAGE ZERO8160: EZ02 SSTACK 8E180 SWAPPED STACK AREA8170:0188:8198:8288: (208 IS SWAP CLC0218; (281 a8 PLA8228: (282 .69 et ADCIM Sel PUT RETURN ADDRESS0232: (284 a7 2C E2 STA JMPINS .01 JUST BEHIND A JUMP OP-CODE824e: E287 68 PLA8250: E288 AA TAX0260: 8209 98 el BCC SW8278: (288 ES INr8280:0298: E28C SE 2D (2 SW STX JMPINS .82838e: E20F A2 ee LEIXIM 188 RESET INDEX8310:8328: (211 BD ee OS SWAPST LDAX STACK GET BYTE FROM PAGE 1

033E: E214 EC 08 El LDYX SSTACK GET BYTE FROM SWAP AREA8340: E217 9D 88 El STAX SSTACK SAVE BYTE FROM PAGE 1 IN SWAP AREA8352: E21A 98 TYA8360: E218 90 00 01 STAR STACK SAVE BYTE FROM SWAP AREA IN PAGE 1

8378: E21E 85 08 LOAX P2 GET BYTE FROM PAGE 08380: (228 BC 08 Eft LOY% SPZ GET BYTE FROM SWAP,AREA8398: E223 90 88 Ea STAX SPZ SAVE BYTE FROM PAGE 8 IN SWAP AREA0488: (226 94 88 STYZX P2 SAVE BYTE FROM SWAP AREA IN PAGE 88418: E220 ES INX BUMP THE OFFSET0420: E229 D8 Ed BNE SWAPST NOT DONE. KEEP ON8430:0440: E228 4C FF FF JMPINS JMP $FFFF SELF MODIFYING CODE'.!0450s

change of the parameters saved on thesetwo pages will upset the operation of aprogram that is being run - usually withno possibility of correcting the error.When two programs are run in parallel itis essential that they do not destroy eachother's page 0 and 1 parameters. This isan extra worry for the programmer, par-ticularly as it can be an insoluble prob-lem. As soon as the programs that arebeing run reach a certain size it is betterto find a way to break away from theshackles governing the use of pages 0and 1.The routine proposed here is used tomove the contents of page zero and pageone to another area of RAM where theycan be changed at will. At the same timethe contents of the RAM area in questionis transferred to pages 0 and I. The nameof the routine is SWAP, for obviousreasons.Using this routine means that the program-mer no longer has to worry about the con-tents of pages zero and one when leavingone program to carry out another. All hehas to do is run the SWAP routine. Pagezero (0000HEX-OOFFHEX) and page one(0100HEL -01FFHEX) of the first programare saved at E000HEx...E1FFHEX, andthe contents of pages 0 and 1 for the sec-ond program, which had been stored atE000HEX...EIFFHEX. are transferred to0000HEX...01FFHEX. When returningfrom the second to the first program theSWAP routine is again executed and thesame procedure is carried out again toreturn the two pairs of pages zero andone to their original locations. The lo-cations we have used to store pages 0 and1 (E000HEX...E1FFHEX) can, of course,be changed to suit the system with whichthe SWAP routine is used, provided thearea reserved is in random accessmemory. Similarly the SWAP routine itselfmust be run in RAM. A look at the lastline of the listing will show why this isnecessary. Indexing and swapping are thetwo procedures that make this routinepossible so bear this in mind.

1-40


anodizingaluminium(September 1984,page 9-56)We have been advised by areader that caustic soda lyeCAN be stored in glas bottles,provided they do not use aglass stopper: fitted with ascrew plastic cap or rubberstopper they are perfectly sa-tisfactory. If a glass stopper isused, carbon dioxide is gra-dually absorbed from the at-mosphere (because thestopper is a poor seal) and thecontents are eventually con-verted to sodium carbonate

(washing soda). Furthermore,if caustic soda solution getsonto the ground glass of theglass stopper, this again isconverted to sodium carbo-nate which can make thestopper quite unremovable ina matter of weeks.

elabyrinth(March 1984. page 3-34)The last address and data(800: FFI in the hexdump intable 1 should be deleted.

direct -coupledmodem(October 1984, page 1048)It appears that the missinglink in our November issue isstill not the complete solutionto FF3 setting inadvertentlyon switch -on. A satisfactorysolution is to connect a470 pF capacitor betweenpins 7 and 13 of 1C7 and toensure that C21 in positionsTELEPHONE and MODEM isconnected to earth via one ofthe unused sections of switchS2.

funny bird(summer circuits,page 7-68)Ti is drawn erroneously as anNPN type, whereas it is, ofcourse, a PNP type.

1-41


How to make your own PCBsYou require an aerosol of 'ISOdraft'transparentizer (distributors for the UK:Cannon & Wrin, 68 High St., Chislehurst,Kent, 01 467 0935, who will supply thename and address of your local stockist onrequest), a mercury vapour lamp, sodiumhydroxide (caustic soda), ferric chloride,positive photo -sensitive board material(which can be either bought or homemade by applying a film of photo -copyinglacquer to normal board material). Wet the photo -sensitive (track) side of

the board thoroughly with thetransparant spray. Lay the layout cut from the relevant

rumble detector

the board thoroughly under running water. After the photo -sensitive film has been

developed in a sodium hydroxide solu-tion (about 9 grammes of caustic soda toone litre of water) for no more than21/2 ... 3 mins at 20°C, the board can beetched in ferric chloride (500 grammes ofFeC13 to one litre of water). Then rinse theboard (and your hands!) thoroughly underrunning water. It is advisable to wear rub-ber or plastic gloves when working withcaustic soda or ferric chloride solutions. Remove the photo -sensitive film from

the copper tracks with wire wool anddrill the holes.

commodore cassette interface

oroas

vhf/uhf modulator

DANGER! Ultra -violet light is harmful to your eyes, so when working witha mercury vapour lamp, wear some form of effective eye protection.

page of this magazine with its printedside onto the wet board. Remove any airbubbles by carefully 'ironing' the cut-outwith some tissue paper. The whole can now be exposed to ultra:

violet light. The exposure time is dependent upon

the ultra -violet lamp used, the distanceof the lamp from the board, and the photo-sensitive board. If you use a 300 watt UVlamp at a distance of about 40 cm from theboard and a sheet of perspex, an exposuretime of 4 ... 8 minutes should normally besufficient. After exposure, remove the layout sheet

(which can be used again), and rinse

03 -controlled frequency meter (crystal oscillator)

30 watt a.f. output stage

1-42

A very large low -frequency range is notnecessarily a good thing. Often when arecord is played at a reasonable volumethe woofers occasionally 'strike' far furtherthan the normal (acceptable) distance.This is usually due to undesirable dis-tortion in the range of about 1 to 10 Hz.This phenomenon is limited only to rec-ord players; it is not noticed with compactdisc players, radio tuners or tape players.The reason is that these last three have ahigh-pass filter of about 20 Hz fittedsomewhere in the electronics or in thesignal source. As far as this circuit is con-cerned, therefore, we are only interestedin the record player.For most people a record player is still thebest source of high -quality soundreproduction. (The CD - compact disc -system may be technically better but is farless popular.) A lot of attention is paid tothe MM (moving magnet) and MC (movingcoil) inputs in 'reasonable -quality'amplifiers as the best results are possibleby making use of these inputs. A goodamplifier must nowadays have a frequencyrange right down to (practically) d.c.values - the merit of which we will notdiscuss - but when combined with aturntable this can make life difficult forloudspeakers. In order to remove theproblem, however, we must first of allknow how it arises.

Resonance and warped recordsMost subsonic problems are caused by

rumble detectorManufacturers of audio equipment are constantly competing againsteach other by improving the quality of their products. As a resulteven inexpensive amplifiers now have an extremely good frequencyrange, especially at low frequency. A lower cut-off point of a fewhertz is certainly no exception and some actually go right down tod.c. This is all to the good as far as the quality of sound reproductionis concerned but it is also disadvantageous to a certain extent.Subsonic noise can be passed on to the loudspeakers and could evendamage them. Murphy's Law of Acoustics comes into play here, ofcourse: as this noise is subsonic it cannot be heard so how do youknow that it is there? That can be very difficult ... unless you buildthis rumble detector, which indicates, by means of a LED, when thesubsonic part of an output signal becomes too great.

resonance in the turntable and pick-uparm. It all starts at the point where the armpivots, its fulcrum in other words. The armalways pivots on some sort of elastic struc-ture to allow the needle to move freely inthe record grooves. Because there is areaction between the mass of the arm andthe elasticity of the mounting theassembly will have a resonant point. Thefrequency at which resonation occursdepends on the mass of the arm and thetype of material on which it pivots. The

extent of the resonance depends mainlyon the inherent damping of the fulcrumand any damping intentionally built in.When choosing a cartridge to fit to anarm, or vice versa, care must be taken tobe sure that the resonant frequency of thecombination is not in the audible range.By the same token the resonant point mustnot be so low that it is triggered by warpsin the record or by a vibrating floor. Aresonant frequency of about 10 Hz is gen-erally considered to be optimal, although

traces ultra -lowfrequencysignals

1-43

1rumble detectorelektor january 1985

Figure 1. The filters in therumble detector only passfrequencies below about10 Hz. When this sort ofsubsonic noise isdetected LED D1 lights toshow that the signal isnot very healthy for thewoofers.

I pr

330n 220n

R2 R6

47

C6 C8

180n 27n

1C37915

18 ... 30 V 15V

CI

Re R12

00k 100k

RIO C14 CI6

en 1 ra

in practice a value between 5 and 15 Hz isacceptable. Unfortunately it is usuallyimpossible to predict beforehand what theresonant frequency will be if a new armor a new cartridge is bought. The onlything to do is to put your faith in anexperienced audio shop. Most of usalready have a certain combination of armand cartridge and unless this gives ter-rible results we are not likely to change it.The next problem is that of resonance inthe chassis. Like the arm, the chassis willprobably be mounted on springs or someother elastic assembly. Understandably,this also has a resonant point. In a well -designed turntable the resonant frequencywill be about 2 to 4 Hz so that it cannotinfluence the resonance of the arm. Theturntable is then relatively immune tosounds in the room (such as somebodywalking around) and the arm can copewith warped records. If the chassis is notmounted on an elastic assembly there isone less resonant point to worry about,but this sort of turntable is more sensitiveto outside interferance, like those sameheavy footsteps and feedback from theloudspeakers.If a record that is being played has abump in it or is warped there is quite a

1N4148

R14

15V

0R%7

3

71

;I13 (Ire

C17- RI6 fl478

D2 15V

Al ... A4 = IC1 = TL 084

84109

likelihood that the pick-up arm will start toresonate. The result is a subsonic 'spike'that will be strengthened by the amplifierand fed through to the loudspeakers.Even if the resonant point is well dampedthis will still happen. When somebodyforgets to tread softly their heavy footfallscan cause the chassis to resonate, with thesame result. The loudspeaker cones againthump out a note that nobody hears.Clearly subsonic noise can very easily beproduced by a turntable but it is not soeasy to get rid of it. A good steep sub-sonic filter with a cut-off frequency of 15to 20 Hz is ideal .for this but such a filter israrely included in an amplifier. If a filter isprovided it is usually a rather impreciseaffair that also removes some of the lowfrequency sounds which should be heard.That does not seem to leave any optionsopen, but the situation is not by anymeans hopeless. Provided theloudspeakers do not deflect too much thesubsonic signals in themselves will causeno damage. That idea was the inspirationfor this circuit, which monitors the sub-sonic content of the signal at an ampli-fier's loudspeaker outputs and lights aLED to signal when it becomes too great.The listener can then take appropriatemeasures. This may involve reducing thevolume setting, examining the record forbumps or warps or mounting the turntablemore firmly, for example. Whatevermeasures are needed the rumble detectorwill not effect the quality of the hi-fisystem as it does not involve connectinganything in the signal line.

The circuitThe circuit has a very simple layout, con-sisting of only a low-pass filter for eachchannel (left and right) followed by a com-mon LED for the indication. The filter roll -

1-44

2 rumble detectorelektor january 1985

off characteristics must be very steep toprevent the circuit from reacting to bassfrequencies that are acceptable for theloudspeakers. This is the reason for using24 dB/octave fourth -order Butterworthfilters. (For detailed information about thisand other types of filters refer to thearticle 'active crossover filter' published inthe September 1984 issue of Elektor.) Theactual multiple -feedback arrangementused for the filters makes them very stableand that is more than enough justificationfor their relative complexity. Each filterconsists of two 12 dB/octave sections -A1/A3 and A2/A4. The component valueschosen set the cut-off frequency to about10 Hz so signals up to about 12 Hz can bedetected. The output signals from thefilters are half -wave rectified and thenadded together. The resultant signalcharges capacitor C17 quickly. When thevoltage on this capacitor reaches about2.5 V transistor Ti conducts and causesthe LED to light. After the subsonic signalhas passed the LED remains lit for a cer-tain time, dependent upon the dz. voltageacross C17.

Power for the circuit is provided via twovoltage regulators, IC2 and IC3. The maxi-mum input voltage to this power supplysection is 30 V. This can be supplied by asmall transformer (2 x 15 V/50 mA, forexample) in combination with a bridgerectifier and two electrolytic capacitors(such as 470 y/25 V). If the amplifier has asuitable symmetrical 15 V from which atap -off can be taken the componentsmarked with an asterisk in the parts listcan be left out. The current consumptionis a mere 20 mA so this will not prove anexcessive burden to an amplifier.The last thing to be done is to connectthe circuit in parallel with the amplifier'sloudspeaker outputs and the detector isready for use. N

Parts list

Resistors:R1... R6 = 47 kR7...R12 = 100 kR13, R14 = 100 QR15 = 33 kR16 = 10 kR17 = 1k

Capacitors:Cl, C2, C21*.C22` = 330 n

C3, C4 = 220 nC5. C6 = 180 nC7, C8 = 27 nC9, C10 = 470 nC11, C12 = 150nC13, C14 = 39 nC15, C16 = 1n8C17 = 47 µ/16 VC18_ ..C20 = 100n

Semiconductors:D1, D2 = 1N4148D3 = LED, redT1 = BC549CIC1 = TL084IC2* = 7815IC3 = 7915

= not needed if asymmetrical 15 V supply isused

Figure 2. Voltageregulators are among thecomponents found on theprinted circuit board. If a

and -15 V supply canbe tapped off the ampli-fier these two stabilisersare not needed.

Filter component values:

Butterworth 4th order(24dB/octave)

C5 C7 = C6 + C8 =1.85/6 a fR

C1 C3 = C2 ÷ C4 =3/3.7 Tr fR

where R = R1 = R2 =R3 = R4 = R5 = R6

C13 + C15 = C14C16 = 0.77/6 it fR

C9 C11 = C10 + C12 =3/1.54 Ti fR

where R = R7 = R8 =R9 = R10 = R11 = R12

(All values are given in Q,Hz and F)

1-45

:I 1' C Otit4 T B- INPLIT

-PERI .B ? r PE QUI- :4 r

P L : :; ? POS. SLOPE PEP. O. 00000 SEC

microprocessor -controlledfrequency counter

accurate, fast,user-friendly andpractical

Technical specifications: Frequency range:

0.01 Hz . . .1.2 GHzII Period time measure-

ment: 10 ns...100 s Pulse time measure-

ment: 0.1 ps...100 sIII Event counter: 0...10'

pulsesIII User -selectable accuracy

to 6 or 7 digits Measuring time for fre-

quency measurements:<0.2 s (6 digits) atf>20 Hz

<2 s 17 digits) atf>2.5 Hz

I Auto -ranging in all ranges 16 -digit alphanumeric

display with interactiveoperation

Sensitivity:input A: 10 mVrms(2 Mg)

input B: TTL, CMOSlevel (25 kg)

input C: 10 mVrms150 41

with prescaler(>100 MHz):100 mVrms (50 0)

Superlatives simply have to be used when describing this frequencycounter, but we will try not to let it get out of hand. We think it isonly natural to feel a certain amount of pride, however. Here, at last,is a do-it-yourself frequency meter whose capabilities, features andease of use are comparable to much more expensive ready-made(professional) equipment. This is a tribute to the Elektor designerswho continually burned the midnight oil working on the design. Theiradvice to anybody who is thinking of building or buying a newfrequency counter is to read this article and study the circuit diagramfirst. The chances are that this will be your next frequency meter.Many of our readers regard micropro-cessors as a scourge and something thathas no place in a respectable 'electronic'circuit. Even having read the title on thispage we hope that you have none the lessread this far because we are now going toentreat you to bear with us and read theremainder of this article. This frequencycounter does contain a microprocessorbut for all intents and purposes it can beconsidered as just another 'black box'. Itsuse does. however, allow the design to bemade more versatile and totally removesthe need for a user's manual. Surely this isenough reason to turn a blind eye to thefact that this test instrument is 'cursed'with a microprocessor.Let us look at the frequency counter'sfeatures one by one, starting with the auto -ranging possibility. In most meters thiswould have required a handful of com-ponents but in this design the 'calculator'does all the work.The second point is the measuringmethod used, which was mentioned in theintroductory article published in lastmonth's issue. This so-called reciprocalmeasuring is only possible with the aid ofa microprocessor as there are a lot ofcalculations to be made. The advantagesof this method are maximum accuracywith a very short measuring time. It is

used both for frequency and periodmeasurements. A secondary benefit is thatmulti -position rotary switches areunnecessary as simple push buttons aresufficient.If the circuit has a microprocessor anywaywhy not use an alphanumeric display?This, again, is easier to use. The fre-quency meter plays a game of questionand answer with the user, who thenmakes a choice of the function desired bypressing a YES or a NO button. Thedisplay always shows what is beingmeasured and what the units are: such as'FREQ. 1.234567 KHZ' or 'PER.8.61059 MSEC'. The price of the alpha-numeric display and the associated con-troller IC is comparable to that of a set ofgood 7-segThent displays plus drivers socost does not enter into the equation.Extensions and modifications can easilybe included in this frequency counter;usually this is a matter of changing pan ofthe software. This line of thought couldlead to such things as an IEEE output orfeeding in offset frequencies.Finally, we draw your attention to the frontpanel foil with built-in low-pressure mem-brane switches. This gives the project avery professional appearance andsimplifies fitting it into the case.

1-46

The measuring principleIf the frequency counter electronics areconsidered in the form of blocks a firstrough sub -division leaves us with thethree parts shown in figure 1: the micro-processor, the counter hardware and thedisplay controller. The microprocessorsection consists of a standard 6502 systemwith RAM (6116), EPROM (2732) and PIA(6821). The microprocessor works with theprogram stored in the EPROM and usesthe RAM memory as a notepad and tostore data. Communication with the otherhardware is via the PIA (peripheral inter-

. face adapter). The display controller willbe described in next month's issue so wewill not deal with it now. The counter sec-tion makes up most of the circuit so wewill look at that in detail, using blockdiagrams and timing charts, to give a bet-ter understanding of the operation of thewhole circuit.All the hardware is complied by themicroprocessor. with the aid of a pair ofmultiplexers to select the various measur-ing procedures. Each of the possibilitieswill be discussed in detail on the basis ofa timing chart and a block diagram con-taining only the components appropriateto a particular function. The multiplexersare considered as straight -through links.First, however, we must see how all themeasurements are made.

A lot of calculationThe article in the last month's issue (called'pan 0' because it was only an introduc-tion, intended to whet your appetite)skimmed over the frequency counter'smodus operandi. The microprocessorstarts by setting the programmable dividerto its lowest value. This means that the div-ider stops the measurement after a singleperiod of the input signal. This is a test toprepare for the actual measurement sothat the right division factor can beselected. The period time is worked outfrom the test and the processor thencalculates which multiple of this period

can be stored in the counter within thedesired measuring time. Based on this theprogrammable divider factor, which isalways a power of 2, is set. The measuringtime is then defined by: 2' x T, where T isthe period time measured and n is thenumber selected for the divider. Thenumber of period times that are countedis always a power of 2 so the measuringtime for different frequencies can alsovary by a factor of 2. As an example,assume art accuracy of 6 figures isselected. The gate time (measuring time)for this accuracy is at least 0.1 s. If the fre-quency to be measured is 5 kHz its periodtime will be T = 200 pS. After the testmeasurement the microprocessor quicklymakes the following calculations:

x 200 x 10-2_0.1, so 2"2_500, givingn = 9 and 2' = 512.The last number is the factor for the pro-grammable divider. The gate time is then:512 x 200 x 10 = 0.1024 s.If the frequency were 2.6 kHz the periodwould be: T = 385 tts.

x 385 x 10-'2_0.1, whereby 2'2_260,_which gives n = 9 and 2" = 512.The same division factor is selected butthe gate time is now:512 x 385 x = 0.197 s.At 2.5 kHz the gate time does becomeless as the division factor is then 2' = 256.The measuring time is given by:2' x 400 x 10 = 0.1024 s.When the 'real' measurement has beenmade the contents of the counter (X) isread out by the processor. The result isthe gate time multiplied by 107 (the refer-ence frequency of 10 MHz). The gate time.is 2' x T, so X = 107 x 2" x T. Taking theexample of f = 2.6 kHz again we see thatT = 1/2600 s. This givesX = 10' x 512 x 1/2600 = 1969230. Basedon this figure and the division factorselected the microprocessor can calculatethe frequency or period time, whicheverthe user has chosen.f = (10' x 2')/X = 2.60000 kHz

1 counter -hardware

FREQ.12.3456 KHZ

display -controller

8097.1

microprocessor -controlledfrequency counterelektor January 1985

Figure 1. The blockdiagram for the frequencycounter in vastlysimplified form. Themicroprocessor controlsvirtually all the rest of theelectronics.

1-47

2amicroprocessor -controlledfrequency counterelektor january 1985

IC44!ICI VI I

cw 10532 -bitcounter

bINPUT

n-631;1

a Oar. OaA Dal, a0 1111111

1.

START

D

FF1CLK

0

FF4[LC

o FF11241 r

1C3L

UCLK IC3

-2.74'

Er.k0

CLK IC4

I I

READY

STADT

CNT

Figure 2. These are thecomponents that play apart in test measurementsfor the frequency orperiod functions. The tim-ing chart shows whathappens to the relevantsignals.

Figure 3. This arrange-ment is used for actualfrequency or periodmeasurements.

TEIDT1-2.

T = X/(102 x = 384.615 AsThat, basically is how the frequency andperiod time are calculated. We will nowlook at the electronics needed to achievethis.

Frequency and periodmeasurementsThe set-up used for the frequency andperiod 'test' measurements is shown infigure 2a. The output signal of FF1 is fedto N4 and the Q output of IC3 is con-nected to FF4's clock input (via amultiplexer in each case). The sequenceof events is shown in the timing chart(figure 2a). First the 32 -bit counter is resetand the hardware is enabled by means ofthe START signal. The lowest possible div-ision factor, 22, is selected for IC3. Thenext rising edge of the input signal makesFF1's Q output high so N5 can then feedthe input signal to IC3. At the same timethe CNT input of IC5 goes low so it startscounting 10 MHz pulses. The second ris-ing edge of the input signal causes the Qoutput of IC3 to go high. (This outputbecomes '1' after the 2:'-'th rising edge ifa division factor of 2° is selected.) The

READY line then becomes zero and resetsFF1. This flip-flop's Q output then goes lowwith the result that IC5 stops counting.Even though IC3's division factor was setto 4 the output becomes high after asingle input -signal period. The contents ofIC5 is the result of counting 10 MHzpulses for one period and this figure isused to decide what division factor has tobe set for the actual measurement.For the actual measurement FF3's Q out-put is connected to N4 and the 0 outputto FF4's clock input (see figure 3a). Themicroprocessor then sets IC3 to the div-ision factor that it has selected. The firstrising edge after the START signal takesFF1's Q output high so N5 can then passthe input signal on to IC3. After 2n-i risingedges the output of IC3 becomes '1'; thissignal clocks FF3 and only then can IC5start counting 10 MHz pulses. The nextclock pulse for FF3 comes after exactly 2°periods and FF3 then flips and stopscounter IC5. At the same moment theREADY line is taken low by FF4 to informthe processor that the measurement iscompleted. The counter's contents andIC3's division factor are then used tocalculate the frequency or period. When

3a

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this is done the result is passed to thedisplay and the circuit is then ready tostart the next measurement.

Pulse timePulse time is measured on the basis of thecircuit seen in figure 4. The signal is inputvia an EXOR gate (N1) to enable the micro-processor to define whether the '1' or the'0' time is measured. The timing chart offigure 4b assumes that Ni does not invertthe signal so the '1' time is measured.Once the hardware is STARTed the Q out-put of FF1 goes high with the inputsignal's first rising edge. The 32 -bitcounter is triggered via N5 and stopsagain at the input's falling edge. At thefalling edge a clock pulse is fed to FF4via FF2 and N2. The READY line (whichgoes low) then informs the processor thatthe measurement is complete and FF1 isalso prevented from reacting to any moreinput signals. The contents of the counteris then equal to the pulse time in tenths ofmicroseconds (as 10 MHz pulses werecounted). This makes further calculationsunnecessary.The width of the pulses that are counted(1/107 = 0.1 µs) means that the resolution

for pulse -time measurements is also 0.1 µsand the result displayed takes this intoaccount. A number shown in micro-seconds on the display will never havemore than one figure after the decimalpoint. The shorter the time measured thefewer figures will appear on the display.

Counting pulsesThis is the easiest function so its blockdiagram (figure 5a) is also the moststraightforward. Again Ni enables themicroprocessor to choose whether thecounter reacts to a rising or falling edgeat the input. The input signal is then usedto clock counter IC5 directly (so the10 MHz reference frequency is no longerconnected to the counter's ALT.CNTinput). The microprocessor regularlyexamines the contents of the counter andoutputs the result to the display.The actual components used for each ofthe frequency counter's functions weregiven in each of the block diagrams sothey can be more or less ignored in theactual circuit diagram. This is a distinctadvantage as the circuit's complexitymakes it difficult to see directly whichparts relate to which function.

5a b

IUPUT

CUT

Figure 4. Pulse times aremeasured using thelayout seen here and theappropriate signalchanges are indicated.

Figure 5. Very few com-ponents are needed forthe event counter func-tion, which uses thisset-up.

11

O 1 2 I 3

00117,6i

P

1-49

microprocessor -controlledfrequency counterelektor january 1985

The frequency counter circuit

SFFIF

saes!OFF

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RAM

Figure 6a. The processorsection of the circuitcomprises the micropro-cessor itself and twomemory chips, a ROM(EPROM, actually) and aRAM. The power supplyis also shown in thisdiagram.

Table 1. These are theconnection details for thethree connectors in thefrequency meter circuit.

The circuit diagram is divided into twoparts: the processor section (figure 6a)and the counter hardware section (figure6b). The power supply has been includedin the drawing of figure 6a.There is little need to say anything aboutthe 6502, 2732 and 6116 in the processorsystem, especially as they are beingtreated as 'black boxes' in this circuit. Theaddress decoder, IC8, and PIA, IC7, alsobelong to the processor section but theyhave been drawn in figure 6b because ofthe large number of connections betweenthese ICs and the hardware section.A break -down of the addressing ranges isgiven in the margin here as we must say

something of the address decoding. Thedecoding method used is very wasteful ofmemory space but its great advantage isits simplicity as it requires only a singleIC. Furthermore it works very well in thisapplication, even leaving a block of 8 Kfree. The clock signal for the 6502 is takenfrom the 10 MHz reference via decade div-ider IC18. The circuit can cater for eithera 2732 or 2764 EPROM (IC16) so there isroom for software expansion. The systemis reset on power -up by means of C5, R50and N13.Many of the components found in figure6b are already known from the blockdiagrams. The display and its controller

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Figure 6b. The remainderof the circuit consistsmainly of the counterhardware. Some of the

components do notactually belong here: IC7and 1C8 are part of theprocessor section and thedisplay with its controlleris really a separate sub-section all of its own.

1-51


Figure 7. The LS7060 is adedicated counter IC,which means that it isquite expensive, but notin terms of what itprovides.

axe also shown in this section but we willnot deal with them until next month. Allthe 'boxed -in parts of this diagram arefound on the display printed circuit board.A number of points about this main circuitdiagram must now be clarified.At the input is the pair of four -bit multi-plexers found in ICI. One of these multi-plexers is used for choosing an input -A, Bor C/I6. If a prescaler is included in thecircuit (this will be published next month

.with the input amplifier) the C/512 inputcan also be used. The prescaler is de-signed to handle the frequency rangefrom 100 MHz up to 1.2 GHz. If link PR isfitted the circuit 'knows' that the prescaleris not fitted and the menu published lastmonth applies. If, on the other hand, theprescaler is included points P and R mustbe linked with a wire bridge. An extrachoice is then included in the menu.Choosing FREQUENCY and C -INPUTwould normally be followed by the ques-tion 6 DIG. PRECISION? Instead the querydisplayed is: FREQ.<100 MHZ? If the replyis NO the counter then asksFREQ.>100 MHZ? Depending on theanswer to this question the inputmultiplexer chooses input C/16 or C/512.The other section of ICI drives LEDsD14...D16 via N9 and N10.The TRIGGER LED, D1, is driven bymonostables MMV1 and MMV2. This LEDalways flashes if there are active edges atthe input. If the input signal frequency islow, 2 Hz, for example, Dl flashes witheach active edge. At higher frequenciesthe LED simply flashes at a constant easilyvisible rate but there is then no distinctionmade between a frequency of 100 Hz andone of 10 MHz. This does not matter, ofcourse, as the only intention of the LED is

to show the user that the counter is beingtriggered.The SCRL and CNTRES signals (scanreset/load and counter reset, both ofwhich come from the address decoder)are synchronized to 4)0 by means of FF5and FF6 to remove any spikes that mightbe present. This brings us to the heart ofthe. circuit, the LS7060, whose internallayout is shown in figure 7. This is adedicated counter IC containing a 32 -bitbinary counter complete with latch,multiplexer and three -state data outputs,all of which is microprocessor -bus com-patible. To achieve the same result in TTLwould require about 15 ICs so ICI's price.is not as exorbitant as it might seem.The contents of the 32 -bit counter isstored in the latches as soon as the SCANRESET/LOAD input goes from '0' to '1'. Atthe same time the scan counter is resetand the left -most multiplexer feeds theeight least significant bits to the data out-puts. If an ENABLE pulse is now fed tothe IC (CNTR goes low) these eight bitsare placed on the data bus by the outputdrivers so that they can be read by themicroprocessor. Should the E line returnhigh the contents of the scan counter isincreased so that the next eight bits aresent to the output drivers. The next Epulse places these eight bits on the databus so after four enable (CNTR) pulsesthe processor has read all 32 bits. A logiczero of at least 1 ps on pin 37 of the ICRESETs the 32 -bit counter. This is takencare of by the CNTRES line in the circuit.The microprocessor generates the signalby simply placing the address for theCNTRES block momentarily on theaddress bus. In this way output '4' ofaddress decoder IC8 is activated and this

7

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1-52

TEST CCITT 134e37-7

signal is passed via FF6 to ICS's R input.The LS7060 IC also has two clock inputs,COUNT and ALT COUNT. One of these isused as the clock input while the otherserves as the enable input. We will notdeal with the remaining pins of IC7 hereas the TEST COUNT, SCAN andCASCADE ENABLE are not used in ourfrequency counter circuit.The gate LED, D2, indicates the time dur-ing which a measurement is made, andwill light if there is a '1' on line PBS or onoutput Yl of IC4. We have already seenfrom the block diagrams that the Y1 out-put defines the 32 -bit counter's measuringtime for frequency and periodmeasurements. When the event countermode is selected the input is connectedto Yl and IC5 counts the incoming pulses.The circuit is then measuring continu-ously, even if a lot of the time is spentwaiting for a pulse, so the gate LEDshould light continually. For this reasonthe processor places a '1' on the PBS line.For pulse width measurements either the'1' or the '0' part of the signal is measured.A long pulse time (0.5 s, for example) caneasily be seen on the LED but this is notso if the measured time is short (a repe-tition frequency of 1 kHz and a pulse timeof 200 la, for instance). A delay built intothe software takes care of the problem.After taking a measurement the processorwaits for about 200 ms before starting tomeasure again. The LED is driven by PB5for a few milliseconds so that it flashesvisibly. The software delay also works onthe display, and in this way the last digitdoes not keep changing from one value toanother (if, for instance, the pulse time isbetween 200.0 pes and 200.1 us).The gate LED makes one short and onelong flash during frequency and periodmeasurements of signals below about100...200 Hz. The short flash is the test,while the actual measurement is madeduring the long flash. The LED onlyflashes once when very low frequencysignals are being measured as the maxi-mum measuring time is then shorter thanthe signal's period. In this case the 'test' isthe actual measurement.Finally there is STPLED, D5, whichindicates that the display is frozen and thatno more measurements are being carriedout. This LED is linked to output '5' of theaddress decoder and lights if the relevantmemory block is addressed. The pro-cessor must then run through a loop inwhich the LED is constantly addressed.This is the only thing the processor has todo in the HOLD state. The display con-troller (IC6) ensures that the read-outremains fixed.The display section is a completelyindependent pan of the circuit. The ASCIIdata that must be displayed is sent to thecontroller IC by the processor. This infor-mation is then stored by IC6, which alsotakes care of driving the display. The pro-cessor only intervenes by transmitting newdata if the displayed information has to bechanged.

8

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The power supply section seen in figure6a shows that several different voltages areneeded. A heating voltage of 6 V a.c. isfed to the fluorescent display from one ofTrl's windings. The same transformer pro-vides a zenered -24 V d.c. that is alsoused for the display. The remainder of thecircuit is powered by the regulated 5 Vline. Two more supply voltages (U -F and-5 V) are needed for the input stage. Thediagram shows a single mains transformerwith a total of three secondary windingsbut the same effect can be achieved withtwo or with three separate transformers.

The crystal oscillatorThe crystal oscillator is a very importantpart of the frequency counter as it deter-mines the accuracy to a large extent. The .

design used is shown in figure 8. Thecrystal is in series resonance as thisguarantees quite good stability. Both sidesof the crystal are terminated into a lowimpedance in order to prevent its Q factorfrom being unnecessarily reduced. TheMOSFET at the output acts as a bufferbetween oscillator and frequency meter.This oscillator circuit has been fitted to aseparate small printed circuit board, andthere is a good reason for this.The oscillator shown is quite acceptablebut a very precise, temperature -stablecrystal oscillator is needed to achieve anaccuracy of six or seven digits. A cautiousestimate gives the oscillator of figure 8 astability of at most 10 ppm (parts permillion) in a temperature range of 15 to35 °C. This means that the accuracy is farfrom optimal but it is good enough for theaverage hobbyist especially as thetemperature within the case will settledown to a constant value within quite ashort time. Some people will, of course,demand that measurements be accurate tosix or seven digits. This can be achievedby substituting a special temperature -compensated oscillator in place of theone shown here. Such an oscillator will beexpensive but it can easily be incor-porated into this frequency counter.


5V

C5

TOO n

0(52508)

114097-8

Figure 8. The circuit forthe crystal oscillator isstraightforward. Two tran-sistors, T1 and 12, lookafter the low -impedanceterminations for thecrystal and a third one,T3, acts as a buffer.

1-53


A self -testing circuit

5V

The frequency meter is made up of threeprinted circuit boards:- the main board, which is double sided

with through -plated holes- the display board, and- the crystal oscillator.The first to be built is the crystal oscillator(if it is used). The series capacitanceindicated in figure 8 is needed if thecrystal has a capacitance of 30 pF. Thecapacitor and trimmer will have to bechanged if different crystals are used.(Keep the trimmer as small as possible toprevent deterioration caused by its poortemperature stability.) The circuit is con-nected to a regulated supply and tested tosee if the oscillator is supplying a 10 MHzsignal. The output is probably distortedbut this does not matter as it is caused bythe capacitive load of the probe. A 10 MHzoscilloscope is needed during construc-tion of the frequency counter so this issomething you will have to get your handson.The next part to be tackled is the mainprinted circuit board, starting with thediscrete components. Some of thecapacitors and resistors (and one diode)must be mounted vertically. Sockets(preferably low -profile types) should beprovided for all ICs, which must not be fit-ted yet. The eight lines indicated as K3can be fitted with soldering pins. One ofthe voltage regulators, IC21, is connectedto the board by means of three thick flex-ible leads about 10 or 11 inches long(roughly 25 cm). A pair of capacitors, Cl2and C13, solder directly to the IC's pins.This regulator is not fitted with a heat sinkbut rather mounts straight onto the backpanel of the Verobox. The heat generatedis conducted through the metal plate andto aid this process silicone grease shouldbe applied between voltage regulator andback panel. The photographs show whereand how this IC must be fitted.

The mains transformer possibilities havealready been mentioned but one point tonote is that the case recommended doesnot leave a lot of room to play with. Thefewer and the smaller the transformers thebetter they can be fitted into the availablespaCe. The 10 V winding is first solderedto the board and the output of IC20 ismeasured. This should be 5 V. The 24 Vwinding is now connected and theappropriate voltages measured: -5 V atpin 7 of K3 and -24 V at pin 19 of K2.The oscillator board can now be mountedon the main board. Be particularly carefulto prevent short circuits between the 5 Vcopper track and the ground connectionto the oscillator board. The Urt., connec-tion is not used by the Elektor oscillator. Itprovides an unregulated 9...12 V d.c. forcrystal oscillators that need more than the+5 V we have used.Two of the ICs, IC18 and IC19, are now fit-ted to their sockets. A square wave of1 MHz should be present at pin 12 of IC18.Hexadecimal number $AA must then beset on the data bus by means of eight 10 kresistors as shown in the margin here.The resistors are temporarily soldered toconnector K1 and the 6502 can then beinserted into its socket. When the poweris switched on again there should be asquare wave of 250 kHz on address lineAO, 125 kHz on Al, 62.5 kHz on A2, and soon down to 7.6 Hz on A15. This is easilychecked with the oscilloscope as theperiod doubles each time. All addresslines are available at connector K1. If thefrequencies are not correct or if they aresimply not present check pin 40 of IC15(RES), which should be '1'. Similarly NMIand IRQ should be '1. On pin 39 (P132) thereshould be a (rounded) 1 MHz square wave.If there are signals on the address bus,but not the correct ones, it is possible thatthe 10 k resistors are not properly con-nected and that something other than $AA(10101010) is present on the data bus. Afurther, ever-present, possibility is that anaddress line may be shorted to anotherline.The resistors are left where they are andIC8 and IC14 are fitted. Outputs ofIC8 should then in turn become logiczero for 16.4 ms. Pin 9 of IC14 mustbecome '0' at the same time as pin 4 ofIC8 and the same applies for pin 5 of IC14and pin 5 of IC8. If this checks out the10 k resistors can be removed.Now we move on to the display sectionbut first the heating voltage for the fila-ment must be measured. Connect 330 Qacross the transformer's 6 V winding andmeasure the a.c. voltage across theresistor. It will usually be a little higherthan 6 V. The series resistance needed togive a voltage drop of 5.8 V across the330 Q resistor can be calculated from theformula: R = u x 57 - 330, where u is thevoltage measured. Divide the result bytwo and use the nearest El2 or E24 value

9 microprocessor -controlledfrequency counterelektor January 1955

o© C13I

®®LEIEl El ESmu MISO 0 0ID 01O0 000 0

/"--. 0 00 CM 00 0 WI11:00

11:1

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00 0=/0

0 0 0 011111511

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Figure 9. Due to spaceconsiderations the mainprinted circuit board forthe frequency counter isshown here at 70% offull-size. Note that C3. C5,C6. C11, C14, C15, D13and some of the resistorsmust be mounted ver-tically.

1-55


Figure 10. The displaysection is fitted on thisprinted circuit board. The16 -digit alphanumericdisplay is solderedstraight onto the boardand only bent back aftertesting is complete.

for R9 and R42 on the display board.The display board can now be assembledexcept that the display itself and 106should not yet be fitted. Do not use asocket for 106. Note that the tops of the

LEDs should extend 12 mm above theboard and that transistor T2 is laid flat ontop of the board. Use as thin a capacitoras possible for C4 or fit it on the reverseside of the printed circuit board. The

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Parts list

- Main board and displayboard

Resistors:RI, R2 = 100 kR3, R47, R59 = 390R4, R5, R51...R54,R57 = 2k2

R6 = 5k6R7, R8 = 220R9, R42 = *R10...R41 = 100k, 1/8WR43 = 22 kR44... R46, R50 -= 1 kR48, R49, R56, R58 = 10 kR55 = 680 St

Capacitors:Cl. C2 = 0.47 p/10 V TaC3, C14 = 47 p/10 VC4 = 10 j.r/25 VC5 = 100 p/10 VC6 = 470 p/40 VC7...C10 = 47 nC11 = 1000 p/25 VC12, C13 = 4.7 p/25 V TaC15 = 47 p140 VC16, C18...C23 = 100 nC17 = 10 y/10 V Ta

Semiconductors:D1 = LED, 5 mm yellowD2. D5, D14_ _.D16 = LED.5 mm red

D3 = 15 V/400 mW zenerD4 = 5V6/400 mW zenerD6, 08...012 = 1N4001D7 = 24 V/1 W zenerD13 = 10 V/1 W zenerT1 = BC547T2 = BC557IC1, IC4 = 74LS153IC2 = 74LS221IC3 = 74LS292IC5 = LS7060 (LSOIC6 = 10937-50 (Rockwell- available fromRegisbrook/

1C7 = 6821IC8 = 74LS42IC9 = 74LS86IC10 = 74LS08IC11 = 74LS1321C12...IC14 = 74LS74IC15 = 6502IC16 = 2732IC17 = 6116IC18 = 74LS90IC19 = 74LS1321C20 = 78051C21 = 7905

Miscellaneous:F1 = fuse, 100 mA slowblow

LD1 = Futaba 16 -digitalphanumeric fluorescentdisplay, type number16-SY-03(Z) (available fromRegisbrook)

S1 ...S5 = membraneswitch in front panel foil

S6 = miniature double -polemains switch

TR1* = mains trans-formerls) 6 V/?;50 mA,10...12 800 mA) and24 V/>150 mA

heatsink for 1C21connector for cablefrom front panel foil 17 -wayright angled, 2.54 mm/0.1"centres)

Verobox no. 075-014110(dimensions205 x 140 x 75 mm)

front panel no. 84097-F

= see text

1-56

cable from the membrane switches in thefront panel clips into the connectorbetween R4 and K2. A length of 20 -wayribbon cable about 7 inches (17 cm) longis soldered directly into the holes for con-nector K2 on the reverse side of thedisplay board. The other end of the cableis then soldered directly to the mainboard (do not use soldering pins at eitherend). The numbers linked by each wire inthe cable must, of course, be the same onboth boards.With the power switched on the voltageson the display board can be checked.There should be +5 V at pin 1 of IC6 and-10 V on pin 18. The d.c. voltage on thecommon line for R9... R41 should be-24 V. Switch the power off and solderIC6 directly onto the board. The pins ofthe display are pushed through the boarduntil they extend by about 1 mm and arethen soldered. Do not bend the displayparallel with the board yet; until testing iscomplete it is left standing straight outlike this. Returning to the main boardIC16, complete with its program, isinserted into its socket. Switch the poweron again and then touch the NMI line (pin4 of Kl) to ground for an instant. The self -test program in the EPROM then starts.The first function of this program is to testif it is itself correctly stored in IC6. If it isstop LED D5 lights for about 1 s to showthat all is in order. If the LED remains outthe EPROM is probably incorrectly pro-grammed or one of its pins is not makingproper contact. This assumes, of course,that the LED is fitted properly and that thewiring between the two boards is alsocorrect.After D5 has lit up the power can beswitched off to enable IC7 to be fitted intoits socket. The power is turned on againand the '0' pulse is again applied to theNMI line. Each of connections PA0...PA7then goes high for 1 s in turn so LEDs D2,D14, D15 and D16 start flashing (on for 1 sand off for 8 s). There is also a '1' runningthrough lines PB0...PB6 (except for PB4).Provided the 'l's keep running and theLEDs flashing the circuit is correct so far.Otherwise check ICI's socket to ensurethat all the pins of the chip are insertedcorrectly. Next it is IC17's turn to be fitted.Substitute a wire bridge for S3 on thedisplay board so that the circuit thinks thatthis push button is pressed continuously.Power is again applied to the circuit andthe NMI line momentarily grounded. Thegate LED should light for a short time. Ifthis does not happen there is somethingwrong in (or with) the RAM. The gat?, LEDmay also fail to turn off and the stop LEDmay light and if this happens it indicates aproblem, probably a programming error,in the EPROM.It may be an advantage at this stage to seeexactly what the test program does. Ifswitch S3 is closed (or bridged) and NMIreceives a short '0' pulse the programtests itself and lights the stop LED forabout one second. The microprocessorthen examines PB7. If this line is '1' the

PIA is then tested but if it is '0' (as it iswhen S3 is bridged) the RAM test pro-cedure is started. This involves copyingthe contents of the EPROM to the RAMand then comparing what is stored inboth. Assuming this test gives a positiveresult the gate LED lights briefly. Immedi-ately after this the EPROM is tested: allthe bytes are summed and a checksumbyte is added. The result must be $cia Anyother result indicates one or more faults inthe EPROM and the stop LED then lights.The power can now be switched off andthe short circuit for S3 removed, as canthe wire used to provide pulses to theNMI line. Connect the 6 V winding of themains transformer to the display board.When the power is now switched on thedisplay shows the text OVERFLOW,PLEASE RESET or FREQ. X.XXXXX HZ.This is an indication that the display boardis correct. If nothing appears on thedisplay the connections to the displayboard from the main board and from thetransformer should be checked. Test alsothat the 6 V a.c. is present. Remove thepower again and install the remaining ICsinto the main printed circuit board. Thecable from the front panel can also beplugged into its connector. (This cable isactually a thin plastic 'tail' with the wiresfrom the front panel's switches embeddedinto it.) Treat the ICs carefully, especiallythe 74LS292 which is very sensitive.Once again the power is applied to thecircuit. The display should show FREQ.0.000000 HZ. Press the menu button onceand the NO button three times. Thedisplay is now EVENT COUNT? Press theYES button three times and the displaywill indicate TOTAL 0. Apply a squarewave (about 1 Hz) at Tri.. level to pin 2 ofK3 and measure if this signal is also present on pin 9 of ICI, pin 3 of IC9, pin 7 ofIC4, pin 8 of IC9 and pin 1 of IC5. Bothpin 6 of IC9 and pin 2 of IC5 should bezero.If the circuit is working correctly eachincoming pulse will be added to the totalshown on the display. The trigger LEDshould also flash with each pulse and thegate LED should light continuously. If thisdoes not happen the problem is almostcertainly to be found in or around IC5.All the frequency meter's functions shouldnow operate properly. Doubting Thomasescan check this by comparing signals atvarious points in the circuit with theappropriate timing charts.

Casing the circuitBefore any part of the circuit can be fittedinto the case the necessary ventilationholes must be drilled in both upper andlower sections. Assuming the rec-ommended type of box is used the mainprinted circuit board will fit snugly insideparallel to the bottom and can be fixed tothe mounting bosses with self -tappingscrews. An insulating ring must be placedunder the bolt beside Kl. The mountingboss at the front left-hand corner of the


11

Figure 11. The small sizeof the printed circuitboard for the crystaloscillator belies itsimportance. This is whatmakes the micropro-cessor tick.

Parts list

- Crystal oscillator

Resistors:R1, R6 = 2k7R2. R3 = 220 QR4 = 33kR5 = 3k3

Capacitors:Cl = 330 nC2' = 22 pC3' = 20 p trimmerC4= 1nC5 = 100 n

Semiconductors:Tl. T2 = BF494T3 = BF900, BF905, BF907,

BF961, BF981

Miscellaneous:Xl' = 10 MHz crystal with30 p series capacitance

' = see text

1-57


8409743

top of the case must be removed so thatthe surface here is completely flush.The attractive finished appearance andcorrect operation of the meter can onlybe assured if the front panel foil availablethrough Elektor's EPS service is used. It isan essential part of the circuit as it con-tains the membrane switches used to con-trol the frequency counter. This foil isquite thick so the slots provided in thecase to accomodate the metal panel sup-plied with the box will be too thin toaccept both of these at the same time. Forthis reason a sheet of aluminium about1 mm thick and with the same dimensionsas the front plate supplied must be usedinstead. Use the template provided withthe front panel foil to drill all thenecessary holes in the new front plate.The display board can be fixed to theplate by means of four countersunk boltsor with four bolts stuck to the inside ofthe panel. The locations for these holes orbolts are indicated by the template and itis important to note that the bolts may notprotrude by more than 15 mm. The holesfor the BNC sockets are drilled undersizeand then filed to the right shape and size.One side of each hole is flat so thesockets cannot turn. The slot for the frontpanel cable must also be cut and then afinal check made to make certain thateverything fits as it should. The backingpaper can now be taken off the frontpanel foil. Pass the cable through the slotand then stick the foil carefully andaccurately onto the aluminium front plate.Any excess foil should now be cut offwith a sharp knife. There is a thin layer ofprotective plastic on the front of the foilthat can be removed when the case iscompletely finished.The wires to the mains switch can now besoldered in place. Note that they must risestraight up from the switch as otherwisethey might foul the capacitors on the

display board. (The sketch in the marginhere indicates what we have in mind.)Insulate the connections very well, withshort lengths of heat -shrink tubing, forexample.All the components must now be fixed tothe front panel. A 10 k potentiometer mustbe fitted to the hole left in the displayprinted circuit board. The type usedshOuld ideally have small dimensions andan insulating washer must be used at thecopper side of the board. This poten-tiometer will be used later - when theinput stage is added to the meter.Bend the display carefully towards theboard and over IC6. Do this correctly andthe display will fit exactly in the windowin the front panel. Fix the display board tothe front panel by means of the boltsalready discussed.The mains transformer is now fixed to therear panel of the case so that its mountingbracket is about 2 mm below the top ofthe box. Fit the transformer above IC15.IC7 and IC17 in order to leave room forthe input stage next month. Also fitted tothe back panel is IC20 and in this casesome heat -conducting paste must be usedbetween IC and metal. The mains cable.naturally enough, feeds through the backpanel, preferably by means of the chassisplug and socket arrangement normallyused for laboratory test instruments.Before screwing the top onto the case aheatsink must be fitted onto IC21.The oscillator in the circuit can only becorrectly calibrated with reference toanother (accurate) frequency counter.Measure the frequency at pin 1 of 1C18and use the trimmer to set this to exactly10 MHz. Fit the top onto the case andleave the meter on for about half an hour.Measure the frequency again and ifnecessary re -trim C3.The constructional details of this fre-quency counter have been dealt with inmuch more detail than is usual in our cir-cuits. We felt that this was necessary as itis a very important test instrument and theinstructions given should enable any hob-byist to build a working example. Nextmonth we will describe the input ampli-fier with the prescaler. All of the counter'sfunctions are self-explanatory and selec-tion is simplicity itself but it is alwaysuseful to familiarise yourself with any newequipment by experimenting with it 14

Table 2. This hexdump isthe program that tests,drives and controls thefrequency counter circuit.

1-58

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,

switching RIC channelseleIctor January 1985

G. Seegers

switching R/C channels

seven on /offswitches forradio control,operated by asingle (uni-directional)joystick

This is a time of year that could be considered 'quiet' for most radiocontrol and modelling enthusiasts. That is not to say, of course, thatthey completely forget about their hobby just because there is a force10 blowing outside. On the contrary, it provides a breather in whichto repair damaged models, build new ones or to update and modifyequipment. The circuit we will describe in this article falls into thelast category. It consists of a relatively uncomplicated design thatenables up to seven functions to be switched from the R/Ctransmitter using just one joystick.

The vast majority of radio control transmit-ters have at least one thing in common:they are fitted with joysticks. Thesejoysticks enable the user to proportionallycontrol various functions on his model,such as ailerons, rudder and throttle set-ting. The more sophisticated transmittersalso provide a number of switching func-tions. This makes the model behave morerealistically by allowing the user to switchlights on and off, raise and lower under-carriage and even drop bombs or firetorpedos. Desirable though these func-tions are, the transmitters that providethem are often out of the price range ofmany enthusiasts (including impoverishedElektor designers).One common solution is to fit a micro -switch inside the model and operate it bymeans of a servo. In this way one servochannel is needed to switch one function.Other methods involve making somechanges to the actual transmitter. Neither

of these methods particularly attracted usso we approached the problem from acompletely different angle. In our finaldesign the advantages are manifold: nochanges have to be made to the transmit-ter, up to seven functions can be switchedusing a single proportional channel andoperation is simple.Moving a joystick switches the functions;forward for 'on', backward for 'off. Thejoystick is moved the same number oftimes forward (or back) as the number ofthe function that is to be switched.Pushing the joystick four times forwardturns on the function connected to 'chan-nel' number four. and if the stick is movedthree times backward the function con-trolled by 'channel' three switches off. Afurther advantage of this circuit over othertypes is that it 'remembers' the joystick'slast movement so the relevant functionremains on after the suck returns to the(neutral) mid -position.

1-60

One input pulse, seven outputchannelsEach proportional channel in a PWM(pulse width modulation) radio controlreceiver continually outputs pulses with awidth of between 1 and 2 ms. The pulsesappear 50 times per second and theirwidth depends on the position of theappropriate joystick in the transmitter. Thisis illustrated in figure la; mid -position ofthe joystick corresponds to an outputpulse of 1.5 ms at the receiver, oneextreme (forward, for instance) gives a2 ms pulse, the other extreme causes apulse of 1 ms to be output. Lest there beany misunderstanding, let us clarify whatis meant by a joystick pulse. We havereferred to 'a pulse' but this is not strictlycorrect. In fact the 'pulse' in question is a

la

__.1 L

MID_ POSITION

15,,

SS017-12

2 L

lbMMV1

1

OR

12 on

RSflipflop

MMV3 MMV4

CLK P LATCH

AO

COrc5T)ER A, LATCH BUFFER -P'(IC6) (IC7) -0

-0W AS -1-510-.7A

55017.15

pulse train in which all the pulses havethe same width. For the purposes of thiscircuit the only joystick pulses that interestus are those that fall into two bands:1.0...1.2 ms and 1.8...2.0 ms (as shown infigure 2a).The block diagram of figure 1 and timingchart shown in figure 2 give an insight intothe operation of the circuit. The joystickpulses that are output from the R/Creceiver must first be detected. Pulsesgreater than 1.8 ms are detected by MMV1,those smaller than 1.2 ms by MMV2.Depending on which of these conditionsis met the R/S flip-flop is set or reset. Ineither case MMV3 will be activated andits output pulse will subsequently clockthe counter and trigger MMV4.The counter counts the number of outputpulses given by MMV3, which is the sameas the number of joystick pulses. Eachpulse input to MMV4 retriggers it so itsoutputs remain active until about2.5 seconds after the last MMV3 pulse.(This time can be made longer or shorterat will by changing the value of R6.) Theeffect of this is that about 21/2 secondsafter the last joystick movement the eight -way latch (IC6) is enabled by MMV4.When this happens the information fedinto the data input from the flip-flop isplaced in the latch selected. Which latch

is selected depends on the counter out-put and this, as we have seen, is deter-mined by the number of joystick pulsesinput to the circuit. The information in thelatch is then fed via the buffer to the out-put so one of the seven lines is switchedon or off. The counter is now reset byMMV4.

From joystick to switchesThe complete circuit diagram is shown infigure 3. The R/C transmitter need not bechanged at all to allow this switching func-tion to operate but the circuit doesmonopolise the channel for one joystick,which means that one less servo isavailable. When the joystick is moved fromone extremity to the other (from fullybackwards to fully forward, for example)the pulses output from this channel in thereceiver vary from 1...2 ms.If the pulses are less than 1.2 ms wideMMV2 detects this and makes the outputof flip-flop N5/N6 high. Ultimately this willmean that a '1' will be fed into latch IC6.If, on the other hand, the pulses aregreater than 1.8 ms the Q1 output ofMMV1 makes pin 4 of N6 go low so a '0'will be fed into ICS. Any noise that mightbe present in the signals is removed byR3/C3 and R4/C4 as otherwise it couldcorrupt the data in the flip-flop and trigger

switching R/C channelselektor january 1985

Figure la. When thejoystick is moved fromone end of its travel tothe other the width ofthe corresponding outputpulses in the R/C receivergo from 1 ms to 2 ms.

Figure lb. The joystickpulses are input to thecircuit whose main partsare seen here. There aretwo pu/se detectors.MMV1 and MMV2, thatdetermine the data storedin a flip-flop. The counteris incremented every timethe joystick is moved toone end and the finalnumber stored deter-mines into which of thelatches in IC6 the infor-mation from the flip-flopis loaded. The outputs aredriven from the latch viathe buffer.

1-61

switching R/C channelselektor january 1985 2a

Figure 2a. The joystickpulses that interest us forthis circuit are located intwo bands: 1.0...1.2 msand 1.8...2.0 ms. One ofthese bands is used toswitch functions on. theother to switch them off.

Figure 2b. When thejoystick pulses are inputto the circuit the signalsat various points are, ofcourse, effected. Here wesee how the most import-ant signals react to thetwo conditions thatinterest us.

A

JOYSTICKPULSE

1.2 ma 1.8 ms1 rrcs MID_POSITION2 ms

END ENDPOSITION POSITION

ON puIttdetftted

OFF pLtIseefunictad

135017-2A

2br12

e

1.3 ,A

MMV1 61

N1040

ft

IYINIV2 02 12 er''

N3p10

N604(FF)

N4.1:111

1 <2

0

1.3

53017.2

MMV3.Whether the joystick pulse is long or shortit must still be added to the contents of105 as it is the number of times that thejoystick is pushed to one extremity thatdetermines the count stored in the 4029.When the output of N4 goes low it trig-gers MMV3. The rising edge of thismonostable's output pulse clocks IC5(once for every time the joystick is moved)and triggers MMV4. When the channel tobe selected is reached the joystick is nolonger moved so MMV4 is not retriggeredafter this. About 2.5 seconds later itsmonostable time elapses and its Q2 outputtakes the enable input of latch IC6 low.This is a very unusual latch. When pin 4 istaken low the data presented to pin 3(Data) is input to whichever of the eightinternal latches is selected via the addressinputs, A0...A2. The lowest latch willnever be selected because this is taken asthe base level, to which the IC returns onreset. (Incidentally, all the flip-flops in thelatch are reset on power -up by means of

C8 and R9.) Outputs 01...Q7 of the 4099are linked directly to the inputs of bufferIC7. The outputs of the ULN2003 dar-lington array are used to drive the variousswitching functions.At the same time as MMV4 latches IC6 itsQ2 output returns high and resets counterIC5 (after a slight delay incurred via N7and N8).

The outputsEvery one of the outputs, pins 10...16 of1C7, can be used to switch one functionon and off. All the outputs are the sameand the layout used is shown in the 'blow-up' in figure 3. Each consists of a dar-lington that can handle a maximum cur-rent of 500 mA and a maximum voltage of30 V.If the outputs drive inductive loads, suchas relays, the internal diodes in the buffermust be used in order to suppress theinductive transients. This simply involvesconnecting pin 9 to the positive voltagesupply line.

Construction and calibrationThere is little involved in constructing thiscircuit. All the components fit quite easilyon a smallish piece of Veroboard. Theinput can then be linked to the radio con-trol receiver in place of one of the servos.After calibration the outputs are con-nected to the functions that they willswitch.Before the circuit can be calibrated presetP1 must be set to maximum resistance,preset P2 to minimum resistance and amultimeter (10 V d.c. range) must be con-nected between pin 6 of 1C4 and ground.The R/C transmitter is then switched on,followed by the receiver. The output ofpin 6 is low so the meter indicates zerovolts. Move the joystick to half -way between

centre position and fully forward. TurnP2 until the meter deflects. This indicatesthat the output of pin 6 has gone high. Release the joystick and it returns to

mid -position. The meter should againindicate zero volts.

1-62

3 switching R/C channelsetektor january 1985

4V8

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Move the joystick to half -way betweencentre and fully backward. Turn PI until

the meter again deflects to indicate thatpin 6 has gone high.I When the joystick is released it returns

to mid -position and the meter indicateszero volts. The calibration is nowcomplete.

Switching with the joystickIn use this circuit will soon show itsworth. Admittedly the method used is notthe quickest imaginable way of switchingfunctions using R/C equipment but it isfast enough for many non -critical appli-cations. The most important functions in aboat or plane or whatever need to be pro-portional in any case so they could notsimply be switched on and off with this,or any other, circuit.Whatever the functions are used for it isvery important to remember what is con-trolled by each 'channel'. It could come assomewhat of a surprise if you move thejoystick forward three times expecting toswitch on the lights in your boat, forexample, only to find the anchor suddenlylowering itself. Apart from that using thecircuit is very simple. Move the joystick Xtimes towards you to switch channel X on,or Y times away from you to turn chan-nel Y off. That is all there is to it!

p

Figure 3. The photographsat the start of this articleand below shows theprototype of this circuit.the diagram of which isshown here. Clearly it issmall enough to be easilyconstructed on a piece ofVeroboard. The currentconsumption in the cir-cuit is neglegible becauseCMOS ICs have beenused throughout.

1-63

Output amplifier ICType LM 1875The LM 1875 from National Semi-conductor is a monolithic outputamplifier that can provide up to20 watts audio power of excellentquality. It is housed in a TO -220encapsulation in which you wouldnormally expect no more than asmall voltage regulator.Maximum output power is 35 wattsinto 8 ohms, but the distortion atthis level is no longer acceptable forhi-fi purposes. At 20 W, however, theharmonic distortion is only 0.05% at1 kHz. The bandwidth is a veryreasonable 70 kHz, while the slewrate of 8 V/pes is excellent for this

type of IC. Other plus points are thevery good hum suppression of94 dB, the thermal protection circuit,and the short-circuit protection.Further characteristics are given inTable 1.The LM 1875 has five connectingpins: two for the supply voltages(positive and negative), one for theoutput, and two for the inputs(inverting and non -inverting).Two possible circuits are given infigure 1: one with a symmetricalsupply (a) and the other for use withan asymmetrical power supply (b).Figure la is noteworthy for theminimal number of additional com-ponents required: two diodes, D1


and D2, for the protection of theoutput transistors, high-pass filterC5/R5, input filter Cl/R1, negative -feedback network R2/R3/R4/C2, anddecoupling capacitors C3 and C4.The gain, A, is determined byA = 14-R4/R3.The characteristics in figure 2 showthe total harmonic distortion, THD,versus power output and frequencyand the power output versus thesupply voltage.Because of its small dimensions, thequality of the output, and the smallnumber of external componentsrequired, this IC is eminently suitablefor use in active loudspeakersystems.

Table 1

Absolute Maximum Ratings

Supply VoltageInput VoltageOperating TemperatureStorage TemperatureJunction TemperaturePower Dissipation (Note)Lead Temperature (Soldering, 10 seconds)

Electrical Characteristics

4- 30 V-VEE to VCC0°C to ,70°C

-65°C to --150°C150°C30 W

300°C

TO -220 Power Package (T)

0 ----) OUTPUT

- NI

f13.03T VIE*

Pt

VCC = 30 V. -VEE = -30 V. TTAB = 25°C, RL = 8 Q, AV = 32 (30 dB), fo = 1 kHz, unless otherwise specified.

Parameter Conditions Min Typ

1

Max Units

Supply CurrentI POUT = 0 W 60 100 mA

DC Output Level 0 V

Output Power THD = 1% 30

THD POUT = 20 W 0.05POUT = 20 W. fo = 20 kHz 0.2 0.4ROUT = 30 W 0.1

ROUT = 30 W. fo = 20 kHz 0.4 1.0

ROUT = 2° W, RU = 4Q 0.06POUR = 20 W, RL = 4 Q, fo = 20kHz 0.3 0.6

Offset Voltage -30 ÷ 5 ' 30 mV

Input Bias Current -5 -2 5 MA

Input Offset Current -1.5 0 1.5 MA

Input Sensitivity POUT = 20 W. fo = 20 kHz 400 450 mVrms

Open Loop Gain 90 dB

PSRR VCC, 120 Hz, 1 Vrms 52 93 dB-VEE, 120 Hz, 1 Vrms 52 95 dB

Max Slew Rate 8 V/j4 s

Current Limit 3 4 A

Equivalent Input Noise Voltage = 600 Q, CCIR 3 pVrms

Note: Assumes TTAB to 60°C max. For operation at higher tab temperatures and at ambient temperatures greater than 25°C.the LM 1875 must be derated based on a maximum 150°C junction temperature. Thermal resistance depends upon device moun-ting techniques.

Table 1. Absolute maximum ratings and electrical characteristics.

1-64


-11cr

la

84104 -la

Figure 1. Two possible circuits for an output amplifier based on the LM 1875- one for use with a symmetrical power supply(a) and the other for an asymmetrical supply (b).

b

2a ,0

10

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0 01 0 1 1 0 10 100

POWER OUTPUT 1W)

b0

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0.02

00120 50 1E0200 500 1k 21 5t 101 205

PREGUENCY 11121

35

30

25

20

15

10

5

00 5 AD 15 20 25 30

SUPPLY VOLTAGE 1 Y1

FIL =811TOD = 1% -4---

40

35

30

25

20

15

10

00 10 20 30 40 50 60 70 80

-MIEIENT TEMPERATURE rti

III1/1111,117E NEAT 5151 I I 1

St/WI-1E4T 5154

10.0 /W HEAT SUVA

1

I I I

Figure 2. Total harmonic distortion versus power output (a): total harmonic distortion versus frequency (b); power output ver-sus supply voltage lc): internal dissipation versus ambient temperature Id).

I

L'S

84104-3b

Figure 3. Printed -circuit layout of the two suggested circuits of figure 1: (a) withsymmetrical and (b) with asymmetrical power supply.

Literature:National Semiconductor:Preliminary ApplicationNote on the LM 1875

National Semiconductor addresses:United Kingdom:301 Harpur CentreHome LaneBedfordPhone: (0234/ 47147

Denmark:Bianco Lunos Alle 11868 Copenhagen VPhone: (01) 213211

Southern Europe:Via Solferino 1920121 MilanoItaliaPhone: (02) 6596146

Spain/Portugal:c. Agustin de Foxa 27 (9 diE -Madrid 16EspaiiaPhone: (01) 7332954

Northern Europe:Postadress Box 2016S-127 02 SkarholmenSverigePhone: 08-970190

Outside Europe:2900 Semiconductor DriveSanta ClaraCalifornia 95051USAPhone: (408) 721-5000

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Power reed relayNew from Hamlin Electronics Europe Ltd is ahigh -power reed relay with a one -make con-tact. Designed for screw mounting, the devicehas 0.25 inch male quick connects for coil andswitch terminals. It is housed in a flame-retardent plastic encapsulation to UL-90-VO.Maximum switching capability is 15 A at250 V a.c. or 30 A at 110 V a.c. Maximumswitching voltage is 600 V a.c. With a requiredcoil power of 0.5 W, the relay is ideal forswitching lamps, motors, heating elements,electromagnetic contactors, and valves forindustrial and -domestic equipment.Hamlin Electronics Europe LtdDissNorfolk 1P22 3AYI0.7791 44/1 (3017 MI

New versions of StripblocNew versions of the Stripbloc CEE 22 a.c.outlet are now available from Rendar Limited_Moulded in rugged black ABS plastic, thismulti -power -outlet uses BEAB accepted com-ponents and meets the requirements ofBS 5733 and the European CEE 22 standards.Ideal for rack mounting, the panel -mountedStripbloc is capable of providing up to six con-nections from one power source. Optionalfeatures include a neon indicator and fuse,which take up one of the socket positions,and, on the free-standing variants, a standard

CEE22 inlet, and a filtered inlet. This last ver-sion is particularly suited to sensitive equip-ment.Render WKR LimitedDurban Road Industrial EstateBognor RegisWest Sussex P022 9RL102431 825811 (3020 M)

ZEN assembly code systemKuma Computers have confirmed their stand-ing as the leading software house for MSXproducts in Europe by commencing deliveriesof their ZEN Assembly Code System to soft-

ware houses on time as promised. ZEN is acomplete Z80 assembler, editor, debugger, anddisassembler, enabling machine code pro-grams to be developed on MSX micros. Itensures that there will be a wide range of soft-ware available for the MSX machines whenthey are launched. ZEN will retail at £19.95.Kuma Computers Limited12 Horseshoe ParkHorseshoe RoadPangbourneBerkshire RG8 7JW(07 3571 4335 (3025 M)

ZIF socketsNo force is required to insert or remove ICsfrom the new range of IC sockets from Dage.The sockets have a hinged base with fingersthat protrude by approximately 1.5 mm ateither end. After the IC is inserted, a littlepressure on the fingers will cause the hinge to

click over and lock the legs of the IC in place.Four versions are available, for ICs with 24, 28,40 and 48 pins. All are low -profile style with aheight of 5 mm. The contacts are made ofcopperberyllium with either tin -lead or selec-tive gold plating.The sockets are stackable, side -to -side, forhigh density printed circuit board layouts. Alead-in entry point ensures easy IC insertion,with the point of contact located 0.8 mm fromthe top of the socket.Dage EurosemRabans LaneAylesburyBucks HP19 3 RGTelephone:102961 33200 13045 M)

New mains suppressionchokeslskra has introduced a new range of PCBmounted mains interference suppressionchokes, the EDT series.Originally developed for applications in con-sumer equipment, the new filters are designedto suppress incoming and equipmentgenerated low frequency and medium fre-quency conducted RFI. A typical applicationwould be the protection of microprocessingequipment controlling electrical pumps, fansor motors and all other units having a potentialfor producing mains interference. The chokeconsists of two inductors symmetricallywound on a common ferrite ring core. Induct-ance values of each arm of the two windings(which are electrically isolated from one

elektor january 1°b5

another) range from 12 mH to 27 mH butother values can be supplied to special order.Typical resistance values per winding are: 0.6ohms for the 12 mH version increasing to 0.7ohms for the 27 mH version. Current rating is1 A at rated voltage of 250 V AC and the filterswill withstand 2000 V a.c. 50 Hz test voltage(applied between windings). This device canbe an efficient custom built transient filterwhen used in conjunction with the lskra KNBseries 'X' and 'Y' capacitors.Overall dimension are 33.5 m x 36.5 x 18 mand the housing is made of a self extinguishingplastic material to UL94VO.lskra Ltd.,Redlands,Coulsion,Surrey CR3 2H7:Telephone: 01 668 7141. (3088 Ml

Video head replacementand maintenance kitThe average video head needs replacing everytwo or three years and can cost over £100 inrepair charges. The Monolith ElectronicsCompany Limited, specialist manufacturerand supplier of magnetic tape heads andsystems, has now introduced their VMC-02video head replacement and maintenance kitwhich contains everything the homeenthusiast needs to reduce this expensesubstantially. Included in the kit are a novelhead -concentricity gauge for the alignment ofBetamax heads to an accuracy better thanthree thousandths of a millimetre, a strobo-scopic tacho disc which verifies the head rota-tional speed on VHS machines, a pair ofhandling gloves, a cross -head screwdriver, aninspection mirror, a can of air -blast dust

remover, an anti -static cloth, cleaning fluid,shaped spatulas, replacement service labels,and a quality mains -operated soldering ironwith solder. A set of step-by-step instructionsand a stock list of heads available from Mono-lith are provided and all customers can makefree use, by telephone, of Monolith's advisoryand service department. The total cost of thekit, including VAT, is £19.95 plus £1.50 p&p bymail order. The kit may be used repeatedly forroutine maintenance and head replacements.The Monolith Electronics Company Ltd5-7 Church StreetCrewkemeSomerset TA18 7HR104&1) 74321 (3014 MI

1-66


'Impak' small instrumentcaseImhof has introduced a re -styled version of itspopular Impak packed -flat small instrumentcase featuring casing panels with attractivebevelled edges, and an easy assembly system.Designed specifically to provide a good-looking stand alone enclosure for small desk-top instruments, the new design hassuperceded the established range. Assemblingthe case is a quick and simple operation, usingplastic bushes in threaded inserts which effec-tively rivet the parts together when the screwsare tightened. The construction system givesthe case good strength and rigidity.

PP"'""'"Wwrrimmappempimpig

Available with an oatmeal finish on the body,and bitter chocolate rear panel, Impak smallinstrument cases range in size from overallheight of 76 mm, width of 204 mm, and depthof 152 mm, up to 159 x 432 x 197 mm. Stan-dard sizes are available through the company'sExpress Catalogue service, and other sizes canbe manufactured to order.

Imhof-Bedco Standard Products Limited,Ashley Works,Ashley Road,Uxbridge,Middlesex.Telephone: 0895 37123 (3089 MI

Subminiature D -connectorsfor PCB mountingSubminiature D -connectors from the 420Series offer five choices of contact numberfrom 9 to 37 -ways, with rightangled receptaclefor PCB -mounting.The 420 connectors feature all -plastic con-struction and offer a standard footprint on thereceptacle half for PCB mounting. The con-

nector is moulded from UL94V-0 insulator, andinserted with contacts having gold-platedcopper -alloy contacts in the connector body,and tin -lead plated tails. A large cavityfacilitates insertion of the male connector. The423 connectors provide a metal shell over its UL94V-0 insulator body. Contacts are copper -alloy with selective gold plating. The recep-tacle component features a short footprint forincreased circuit density.Dage IGB) Ltd,Eurosem Division,Rabans Lane,Aylesbury,Bucks HPI9 3RG.Telephone: 0296 33200. (3084 MI

New prototyping boardPROTOCARD is a new board for easy con-struction of prototypes. Six 16 -pin DIL socketshave their pins brought out to large solderpads allowing components to be easily tackedonto the board. Each IC is marked with a pinlocation and supply tracks, signal tracks, etc.run the full length of the board.PROTOCARD can be used as many times asrequired by simply removing all componentsfrom the board.

Each PROTOCARD is supplied with a pack ofplanning cards which enable the componentlayout to be planned, as well as with solderand instrument wire.PROTOCARD measures 210 x 100 mm and ispriced at £8.50 post paid (UK only).E & H electronics33 North StreetKeigh/yWest YorkshireBD20 3SLPhone: 105.35144103 (3071 MI

Electronic glue gunThermoplastic adhesives are finding everincreasing uses within industry as well as thehobbyist's workroom. They can be used onPVC, Plexiglas. Perspex, minirals, asbestos,cement, paper, glass, brass, aluminium, steel,concrete, softwood, and hardwood. Anaccurate chart of bonding strength is availableon application. Supply voltage is 100 to 250 V.heating -up time is 7...10 min, and meltingtemperature is controlled electronically at260°C. The Glue Matic 3000 for constant useis fitted with a trigger to feed in the 200 mmlong sticks of glue. Electronic glue guns,together with over 3000 other tools and pro-duction aids, can be found in the Toolrange1983/84 catalogue.Toolrange LimitedUpton RoadReadingBerkshire RG3 4.JA107341 22245 13010 Ml

Precision d.i.y. enclosuresystemAnyone requiring small rumbers of enclosuresto their precise specification, can now producethem 'in-house using the new Varidesignsystem from Frepar. Manufactured in WestGermany, the d.i.y. kit comprises three com-ponents - two alumium extrusions, plus cor-ner pieces. Together with the front sections,the side sections form the frame of the case.The corner pieces are manufactured in black,glass -fibre reinforced maclaron, and the extru-sions in E6/EV1 are supplied in one metrelengths. lnfill panels are supplied by thecustomer who is therefore not restricted in hischoice of material. Material up to 2,5 mmthick is accepted by the extrusions.The system is put together rather like a cubicpicture frame, the panels being slid into placebefore the corner pieces are pressed in. Endpanels are srewed in, the extrusion having abuilt-in duct to accept self -tapping screws.The front extrusion has, as part of its profile,facility to hold a p.c.b. or mounting -plate.

(1) Cuur± piece(2) Side section(3) Front section(4) Front and rear p&nels(5) Top, base &nd sides(6) Fixing screw

This Varidesign system complements theexisting Frepar range which includee 12, 16, 19and 25 way plug-in enclosures. A new quickrelease DIN rail -mounting connector is nowavailable for this range.Frepar Electronics Limited,119 Newland Street,Witham,Essex CM8 1BE. (3087 M)

1-67

advertisement'elektor January 1985

PRINTERS -7DOT MATRIX

All printers have centronic parallel interface unless otherwisestated. All printers have hires dot addressable graphic mode.

Please send SAE for full details.

EPSONFX80 160CPS 10" wide friction & pin feedFX100 160 CPS 15- wide friction & tractor feedRX8OFTT 100 CPS 10" wide friction & tractor feedRX80 100 CPS 10" wide tractor feedRX100 FIT 100 CPS friction & tractor feed8143 RS 23 Interface for FX and RX printers8148 RS 232 Interface with 2K buffer x on x offRibbon Cartridge for RX8OFX80& MX80Ribbon Cartridge for FX100& MX100

STARGemini 10X120 CPS 10' wide friction & tractor feedGemini 15X120 CPS 15" wide friction & tractor feedGemini RibbonSEIKOSHABP 420 designed for the business world. 420CPS indraft mode. 110CPS in NLQ mode. £1095

SMITHCORONAFastext 80: 80 col, 80CPS. Friction feed standard

TAXAN KAGA160CPS 10 wide 27CPS NU) 24 x 16matrix16OCPS 15' wide 27CPS NLO 24 x 16 matrix

CANONPW1080A160CPS NLOmode. 27CPS. 10"wide friction &tractor feed£299 + VAT £344PW1156A160CPS NLQmode. 15' widefriction & tractorfeed£379 + VAT £436

COLOUR PRINTERSSeikosha GP700A 7 colour 50CPS printerCanon PJ1080A 7 colour 40CPS ink jot printer

DAISYWHEELJUKI 6100II PRINT20 CPS Bi-Directional Logic seeking 10 12 15 CP1+ PS spacing 2K buffer best selling DaisywheelSinger sheet feeder unitTractor UnitRS 232 InterfaceSpare Daisywheel

BROTHER HR -1513 CPS Bi-directional 10. 12. 15 CP1 + PSKeyboard UnitSingle Sheet Feeder UnitTractor Unit

QUENDATA20 CPS Unidirectional 10 12 15 CP1

£347 + VAT £399£499 + VAT £574£239 + VAT £275£199 + VAT £229£385 + VAT £443£39 + VAT £45£60 + VAT £69£5 + VAT £6£7 + VAT £8

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All our printers have 1 year warranty

MONITORSPHILIPS7001 Kgn Res Green Screen with sond input

£65 + VAT £75

GM1211GM1211 18 MHZ High Res MonochromeMonitor with tilt and swivel stand available ingreen or amber etched antiglare screen

89e9seSPecrtycolOur £86 + VAT £99

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£86 + VAT £99DM2112 12' Green

screen 15MHZ£66 + VAT £75

MICROVITEC CUB1431 MS 14 P.09 t4c,,,a, Fes C.;

£173 + VAT £1991451 MS 14' RGB Medium Res Colour

£251 + VAT £28914.41 MS 14* RGB High Res Colour

£417 - VAT £479

MICROVITEC FOR QL1451 14' Mc-:: 7 -'es OaiGur. Speciallydesigned fors U39 + VAT £275

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DISASSEMBLER: This is 6502 machine code disassembler DUP: To copy and rename a file on disc' FORMAT: Formating progam for 40 & 80 tracks FREE: This utility provides a disk usage analysis MDUMP: Enables you to display and modify any part of

BBC memory' MERGE: Merge a number of text files into one file RELOCATE: Downloads a basic program to &E00

SDUMP: Screen dump for EPSON In all graphic modes VERIFY: Verifies every sector on a disk MENU: A flexible menu program

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3.ATAR1 1010 PROGRAMRECORDER - £34: For low cost storage and rebte,al caps:cad). C-; - a- -s :n band Storage capalufity100K bytes on a sixty minute cassette. Track configuration four track, two channels (ctc,:a 3). Auto reconlipLayback/pausecontrol,un,que. sconothrough facility. Also included is built in accidental erasure prevention o -at: shutoff after each pograrn aswea as a 3 riga tape counter.

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MI In ME Ell IN IM =I MI I=To: SILICA SHOP LTD. Dept EK 0185, 1-4 The Mews. Hatherley Road,

Sidcup. Kent, DA14 4DX Telephone: 01-309 1111LITE_toATU:-IE AEC:JEST:

El Please send me your FREE colour brochures and 16 page price 1,51 on Alari Computers.LI I own a Videogame

Mr fart Ms: IniUals:

Address:

I own a Computer

Surname

Postcode:ORDER REQUEST:

Please Send me: EOOXL 62K Computer £169O BOO 48K Computer £99O 1010 Program Recorder £34O 1050 127K Disk Drive £199

O I enclose Cheque/PAX payable to Silica Shop Limited

O 1020 4 Colour Printer £99O Leiter OttaBly Printer £249O Touch Tablet Cartridge £49O Trek Ran E19.95O Super Controller £9.95

Tor the lobtieing amount

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The amazing Maplin Catalogue is here again!The new edition is packed with hundreds andhundreds of new electronic components to bringyou right up to date with all the latestdevelopments. As all home constructors agree(and a good many professionals too) the MaplinCatalogue is the one essential piece of equipmentthey really need. And now with all our prices onthe page the Maplin Catalogue is better valuethan ever.

On Sale From 10th November 1984.

Pick up a copy as soon as it's published at anybranch of W.H. Smith or in one of our shops. Theprice is still just £1.35, or £1.75 by post from ourRayleigh address (quote CAO2C).

Post this coupon row for your copy of the 1985 catalogue.Price £1.35 40p post and packing. If you live outside the U.K.send £2.40 or 11 International Reply Coupons.I enclose £1.75.

Name

Address

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nivapionM n Electronic Supplies1.74410rder: P.O. Box 3, Rayleigh, Essex SS6 8LR.Tel: Southend (0702) 552911. Shops at:159-161 King Street, Hammersmith,London Wb. Tel: 01-748 0926. 8 Oxford Road, Manchester. Tel: 061-236 0281. Lynton Square. Perry Barr, Bilminghant Tel: 021-356 7292.282-284 London Road, Westcliff-on-Sea, Essex. Tel: 0702-554000.

ELECTRONIC SUPPLIES LTD 46-48 Bevois Valley Road, Southampton. Tel: 0703-25831. All shops dosed all day Monday.

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