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You should see Ambit's new Autumn Catalogue...

OiP2) 1E011717022.

Another milestone incomponent supply...If you've been wonderingjust what's been going onat Ambit lately, we arenow taking the wraps offthe most advanced andimaginative concept incomponent, tool, andinformation distributionsince we launchedWR&E last year.

We have included newitems and information toplug a few gaps, and weare just starting toimplement a newinteractive computerisedsystem of service andinformation thatsimply cannot beoverlooked by anyoneinterested in thecommunications,electronics, video andcomputing business.

* Price on the page*24 Hour response

-Guaranteed* Low prices* High quality* Export a speciality

AMBITINTERNATIONAL'S

WORLD13,ADIOC.

LECTRONICSCONCISE PARTS CATALOGUE

WR&E

Some of the newitems from this

issue...

Weller/Cooper:Soldering Irons

& ToolsRpm t:mt:

* TCP series* Tips & spares* Cutters/pliers* Toolkits

MotorolaRF Power:

mesa.* 1W 130MHZ to* 80W/150MHz* ..& beyond

Test equipmentA AO* too*. ear

* Auto DMMs

* 'Scopes* Bananas (?)* Sig gens

TOKO inductorsRM assemblies

Intelligent LCDsUfli Crystal Filters

Coaxial relaysMicros &memoriesLinears

KeyswitchesPanelwareHardware

128 Pages of the broadest component range in the business

24 HOURS A DAY, 7 DAYS A WEEK

AUTUMN '82 W EZ1 70pAT YOUR NEWSAGENT - OR DIRECT FROM

kREE3E7 EM7ME2Hk7ECHk1 BRENTWOOD ESSEX CM14 4SGTelephone (02771230909, telex 995194 AMBITG, data RS2321300 baud (0277)230959'

*Dial (0277)230959, hook in your low cost modem and terminal (most personal computerscan be configured to access REWTEL, details are being published in R&EW over the nextfew months) and REWTEL will give you access to up to 5000 pages of background to theWR&E catalogue, equivalents, news, updates, hot off -the -press product news, information,jobs being advertised in the industry. It's computing at its most versatile and worthwhile:why be satisfied with a 64K MCU, when you can gain free access to the 70MByte + of the

REWTEL computer ??

PROJECTS* HE MICROLOG 9The analog computer strikes back.* STEREO NOISE GATE 20Taking the hiss out of audio.* HE TV AMP 25Clearer sound for the slightly deaf.* PHASE FOUR 37A four stage audio phaser.* POP AMPS No. 1 52A single op -amp microammeter.* SLIDE -TAPE SYNCHRONISER 56Audio visuals with added bleep.* POP AMPS No 2 62Voltage follow -and -hold for meters.* LOW COST ALARM 70A security alarm that won't cost everything you've got.* HE LOFTY 74Don't hide your loft lights - turn them off!* THE BIG EAR 80An electronic eaysdropper for nature lovers.

FEATURESFAMOUS NAMES 33J. M. E. Baudot.RADIO RULES 43Single sideband.

COMPONENTS FOR COMPUTING 46Part 1 gets into (and out of) I/O Ports.HC6010 DMM 65Digital multimeter reviewed.

Monitor 6What's On Next 18Points of View 31Buylines 34Clever Dick 51HE Book Service 46HE Backnumbers 74PCB Service 63PCB Printout 65Classified Advertisements 81

Editor: Ron KeeleyEditorial Assistant: Helen ArmstrongAdvertisement Manager: Gary PriceAssistant Advert. Manager: Jolyn NiceManaging Editor: Ron Harris BScManaging Director: T.J. Connell

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Hobby Electronics is normally published on the second Friday of the month prior to the cover date.Hobby Electronics, 145 Charing Cross Road, London WC2H OEE, 01-437 1002. Telex No 8811896. Published by Argus Specialist Publications Ltd.

Design and Organisation by MM Design and Print Ltd, 145 Charing Cross Road, London WC2H OEE, 01-437 1002.Distributed by S. M. Distribution Ltd, 16/18 Trinity Gardens, London SW9 8DX.

Printed by QB Ltd, Colchester. Covers printed by Alabaster Passmore.Notice: The contents of this publication including all articles, designs, plans, drawings and programs and all copyright and other intellectual property rights therein

belong to Argus Specialist Publications Limited. All rights conferred by the Law of Copyright and other intellectual property rights and by virtue of internationalcopyright conventions are specifically reserved to Argus Specialist Publications Limited and any reproduction requires the prior written consent of the Company. All

resonable care is taken in the preparation of the magazine to ensure accuracy, but Argus Specialist Pulications Ltd cannot be held responsible legally. ©Copyright1982 Argus Specialist Publications Ltd. Member of Audit Bureau of Circulation.

Hobby Electronics, December 1982 3

Size 5 Savbit£1.15 Per pack I zmnda

Ersin MulticoreErsin Multicore, solder contains 5 cores of non-corrosive flux, instantly cleaning heavily oxidisedsurfaces. No extra flux is required.Comes in handy dispensers and tool box reels in twodifferent alloys 40/60 tin/lead for general purposeelectrical soldering and 60/40 tin/lead ideal forsmall components and fine wire soldering.

Size 3 40/60 tin/lead£4.37 Per reel 1 bmmda

Size 10 60/40 tin/lead£4.37 Per reel 071mmtha

Size PC115 60/40 tin/lead£1.38 Handy pack 0 028rnm dsa

Multicore SavbitMulticore Savbit, solder increases the life of yoursoldering bit by 10 times, for better solderingefficiency and economy.Comes in two handy dispensers and tool box reels.

Size 12 Savbit£4.37 Per reel I2mmdm

.474.

Size 19A 60/40 tin/lead£1.15 Handy pack I22rnrnd..3

Size SV130 Savbit

Multicore Alu-Sol £1.73 Per pack 004*,,,,,

Multicore Alu-Sol. solder contains 4 cores of flux,suitable for most metals especially aluminium.Comes in handy dispensers on tool box reels.

Size AL150 Alu-Sol£2.07 Per pack 04Srnm d.

Size 4 Alu-Sol£7.82 Per reel

All prices inclusive of VAT.Available from most electrical and DIYs stores. Ifyou have difficulty in obtaining any of these productssend direct with 50p for postage and packing. Forfree colour brochure send S.A.E

Multicore Solder WickMulticore Solder Wick, absorbs solder instantly fromtags and printed circuits with the use of a 40 to 50watt soldering iron.Quick and easy to use, desolders in seconds.

Size AB10 Solder Wick£1.43 Per pack

Multicore Tip KleenMulticore Tip Kleen, soldering iron tip wiping pad.Replaces wet sponges.

Size 2 Tip Kleen£0.92 Per pack

Bib Wire strippers and cuttersWire strippers and cutters, with precision groundand hardened steel jaws. Adjustable to mostwire sizes. With handle locking -catch and easy -gripplastic covered handles.

Size 9 Wire Strippers£2.69 Per pair

Bib Audio/Video Products Limited(Solder Division), Kelsey House,Wood Lane End, Hemel Hempstead,Hertfordshire, HP2 4RQ.Telephone (0442) 61291Telex 826437

4 Hobby Electronics, December 1982

WATFORD ELECTRONKS 74,371:L747400 i74027403

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7404 i1371

7405 y6

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7407 20

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16244° m7441 ii2442,244. 907444 %7445 557446 607447 357448 44-7450

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4074153 40

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74157 3374159 8074160 6074161 4874162 4074163 4074164 40

487744112

4474167 15074170 12574172 25074173 54174174 5474175 5074176 4074177 4574178 8074180 4074181 5074182 6074184 9074185 9674186 47074188 25074190 4874191 46

74192 4674193 4574194 4674195 4674196 4874197 4674198 8474199 84P1221 54

LS124 go

LS126LS125 24

35

LS132 seLS133 30

LS136 26

LS138 25

LS139 aLS145 70

LS147 100LS108 70

LS151 40

LS153 40

LS155 30

LS157x)LS158v

LS160 32

LS161 37

LS162 37

15163 37LS164 43

LS165 50

LS166 52

LS170 7019173 56

LS174 50

LS175 40LS181 90

LS190 36

LS191 36LS192 36

LS193 37

LS194 33

10195 33

LS196 45

LS197 46LS221 55

LS240 56LS241 55

LS244 55

LS245 70

LS25715261 100 1

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604053 504054 954055 954056 854057 19154059 4354060 454061 11954062 9954063 %4066 244067 2454068 144069 134070 134071 134072 134073 134075 134076 504077 134078 154081 134082 134085 504086 604089 1254093 204094 704095 754096 704095 no4097 1904098 754099 1904160 751161 994162 994163 994175 1%4194 1064408 7904409 7904410 7254411 MO4412 7904415 0804419 2804422 7704433 7704435 8504440 9994450 3504451 3504490 3504500 6754501 284502 604503 354504 754506 354507 354508 130 .

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AY -1-5051 180AY3-8910 43385-5-1230 460AY -5.1350 350CA3018CA3020 210CA3028 96CA3035 256CA3045 366CA3046 70CA3048 220CA3059 336CA3075 213CA3080E 70CA3081 190CA3085 96CA3089E 200CA3090AQ 375CA3123E 150CA3130 90CA3140 40CA3160 95CA3161 160CA3189 296HA1336W 240017106E 750

17107 97518038CC 300M7204 560

CM7216A 1960M7224 7%

CM7555 80M7556 150

183350 250LA4031 300LA4032 29eLA4400 440LC7120 X0LC7130 340LC7137 395LF347 150LF351 48LF353 50LF355 66LF356 96LF357 110LF359 96LF398 475LM301A 24LM308 96LM311 70LM318 150LM319 215LM324 30LM339 471M348 64LM349 115LM358 60LM377 175LM379 480LM380 75LM381 146LM382 115LM384 140LM386 90LM387 120LM389 95LM393 100LM394 290LM733 70LM1458 30LM2917 1%LM3302 75LM3900 50LM3909 85LM3911 125LM3914 200LM3915 200LM3916 250

S7220 210MC1303 68MC1304P 260MC1310 160MC1455 150MC1458 %MC1469 300MC1488 40MC1489 55MC1495 350MC1496 70MC1596 225MC1648 290

MC3302MC1709G 9090

MC1710 79

MC3340P 123MC3360 P 120MC3401 85MC3403 75MFC6040 75M 650398 635ML924 275MM5303 635MM5307 1275MM5387 47NE529 225NE531 140NE543 225NE544 210NE555 16NE556 46NE560 325NE561 398NE562 410NE564 420NE565 120NE566 156NE567 140NE570 410NE571 4006E5534 150RC4136 139

0C4556 45p5566E1 225SA83209 425SA63210 3255863271 486SAB4209 5865576013 360S676023 350SN76477 420S676488 4805576660 120SL490 350568629 299TA7120 150TA7204 200TA7205A 90147222 150TAD100 159T134120 70164641 290TI3A800 80TBA810 95TBA820 80TCA965 1207081004 2907801008 3107081022 4997081024 11511341490 325TDA2004 4%TDA2020 320TL061 ao11063 807107106 24

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11072 4611074 100TL081 24TL082 4511083 75TL084 90uAA170 170UAA180 170

120002211XR06 300

22 575Z80CPU 299Z804 CPU 300Z804 CTC 260Z80 CTC 250280610 2802808610 2752N414 8025424E 130ZN425E 345ZN426E 30076427 59025428 410ZN429 210251034E 200251040E 675

35c CARDIFF ROAD, WATFORD, HERTS, ENGLANDMAIL ORDER, CALLERS WELCOME. Tel Watford 40588

L . , , s 1 A - ' ,DESPATCHED BY RETURN OF POST. TERMS OF BUSINESS: CASH /CHEQUE/P.OsOR BANKERS DRAFT WITH ORDER. GOVERNMENT AND EDUCATIONALSTITUTIONS' OFFICIAL ORDERS ACCEPTED. TRADE AND EXPORTWELCOME. P&P ADD 50p TO ALL CASH ORDERS. OVERSEAS ORDERSAT COST. AIR/SURFACE. ACCESS ORDERS WELCOME.

VAT AN Prices exclusive of VAT. Please odd 15% VAT to the total cost incl.We stock thousands more ierns. It pays to yr. us. We are situated behind Watford FootbelNearest underground/BR Station: Watford High Street. Open Monday to Saturday: gam to 6pm

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IN-ENQUIRYPOSTAGE

PfsPGround.

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POLYESTER CAPACITORS, Axial Lead T ype4005: 10F, 105, 2n2, 3n3, 4n7, 6n8 11p; 10n, 15n, 18n, 22n 12p: 33n, 47n. 68n 15p; 100n, 150n 20p: 220n389; 330n 42p: 470n 52p; 680n 130p; 7µF 68p; 2,2 82p; 4,7 86p.160V; lOnF, 12n, 100n 1116 150n, 220n 17p: 330n, 470n 30p: 680n, 311p; 10F 42p: 1v5 45p: 2p2 48p.1000V: 1nF 17p; 100F 30p; 15n 40p; 22n 36p; 33n 42p; 47n 48p; 100n 50p; 470n 99p.

POLYESTER RADIAL LEAD CAPACITORS: 250V,1006, 15n, 22n, 27n 6p; 33n, 47n, 68n, 100n 7p: 150n, 220n 10p.;330n, 470n 13p; 680n 19p; 1µF 23p: 1,5 40p; 2,2 45p; 4a7 (60p.

ULTRASONIC TRANSDUCERS40kHz 325p/pr

ELECTROLYTIC CAPACITORS: (Values are in vn 500V- 10 520: 47 760; 2505: 100 56p; 83V: 0.47, 1.0,1.5, 2.2, 2.5, 3 3 6p: 4.7 9p; 6.8. 10 10: 15, 22, 12p; 33 15p; 47 12p; 100, 19p; 100, 19p; 1000 7p. 50V, 47120; 68 20p; 220 24p. 470 32p; 2200 90p. 40V: 4.7, 15, 22 9p: 3300, 90p; 4700, 120p; 25V: 1.5, 6.8. 10, 2280; 33 9p; 478p: 100 11p: 150 12p; 220, 150; 330 22p; 470 26p; 680, 1000, 34p; 2200, 50p; 3300, 76p; 470092p: 16V, 40. 47, 100 96 125, 12p; 220 13p:470, 20p: 680 34p: 1000 27p: 1500, 31p; 2200 380: 3300 74p,4700 79p.TAG -END CAPACITORS: UV: 2200 139p; 3300 19816 4700 246p 50V: 2200 110p; 3300 154p; 40V: 4700190p; 25V. 2200 90p, 3300, 4000, 4700 960; 10,000 320p: 15,000 345p; 16V: 22,000 350p.

TANTALUM BEAD CAPACITORS35V: 0.1µF, 0.22. 0.33 16p: 0.47, 068,10 F, 1.5 16p: 2.2, 3.3 18p; 4.7, 6.822p; 10AAF 213p: 16V: 2.2, 3.3 16p; 4.7aF,6.8.10 160; 15, 360; 22 300; 33, 47 40p; 10075p; 220 88p: 10V: 15, 22, 213p, 33, 47350: 100 55p: 81/: 100 42p.

OPTOELECTRONICSLEDs with ClipsTIL209 Red 11100,10211 Grn 14747011L212 Yel 14390..2' Red 121000,

SILVER MICA (Values in pFl2, 3.3, 4.7, 6.8, 8.2, 10, 15, 18, 22.27, 33, 39, 47, 50, 56. 68, 75, 82, 85,

120, 150, 180pF 15p each200, 220, 250, 270, 300, 330, 360.

470, 600, 800, 820 21p each1200, 1800, 2200 30p each

60p

7453 1!7454 '7460 3108

7472 247473 ?4,74747475 257476 257480 007481 120

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704041 404042 404043 404044 ao4045 1,4046 464047 404048 40

25- -

POTENTIOMETERS: Rotary, Carbon,Track. 0.25W Log Et 0.5W Lin.

.2" Yell or GrnSquare LEDs 149 R/G 851

3300, 4700pF each I

--'-High5000. 160 8 260 I Linear only) Single

Gang 30p569-2MOSingle Gang 30p560-2M0 Single Gang 0/P Switch 790560-2190 Double Gang 85p

-ColourBi-Colour G/Y 761Tri-colour R/G/Y 85OCP71 120

ORP12 78255777 06

RESISTORS - Carbon FilmStability. Low Noise. MiniatureTolerance 5%.

RANGE VAL 199 100-

-1

SLIDER POTENTIOMETERS0-25W log and linear values 60mm560-50060 single gang 700'10613500Kit dual gang 11001Self Stick Graduated Bezel 40p

10271 46.SFH205 91

11L32 52

T1L78 541TIL38 66TIL100 00

1W 202.4M7 E24 2p 1pIW 202-4M7 012 2p 1p1W 202-10M E12 5p 4p2% Metal Film 100IM 6p 4p1% Metal Film 5111-19 Oct Sc100 -A- once applies to Resistors of each

MYLAR FILM CAPACITORS 7 Segment Displays value not mixed.100V: 1nF, 2, 4, 4n7, 10 6p; 15nF, 22n,30n, 40, 47 7p; 56. 100n, 200 9p;470n/50V 129

1

TIL321 .5 CA 1151111_322 .5 CC 115'DL704 .3 CCth 99

CERAMIC CAPACITORS 50V. 0-5pFto lOnF 4p: 22n to 47n 5p. 100n 7p.

fMINIATURE TYPE TRIMMERS,...2-8 F, 2-10pF, 2-25 F, 5-56pF 30p

01707.3 CA 99)

.3 Green CA 120DL747 CA 193,

GAS Et SMOKE DETECTORSTGS812 or TGS813 775p

`COMPRESSION TRIMMERS340pF; 10-80pF 20p; 20 250pF 28p;100-580pF 360; 400.12500F 41111.

.6650357 120FND500 90MAN3640 175

ACCESS ORDERSJust phone your order through

and we do the rest

ICs211412 962708 725

2254116 70

(BBC) 225390

6502 3256522 3206800 125709C 8 pin 35733 90741 B pin 14747C 65748C 36753 185810 159B1L.S95 80811596 80811597 809400CJ 350AY11320 225AY1-5050 99

PRESET POTENTIOMETERSVertical Et Horizontal0.1W 50 M 5 MOMindture 7p0.25W 100 M-3.3 MI1 horn. 10P0.25W 200 M-4.7 MO vert 10p

10 Sag Bargraph 225LCD 3) Digits 525Isolators1174 4611074

BBC MICROUpgrade kit now available16-K RAM (8 x 4816 API

E18.00

VOLTAGE REGULATORSx-1A T03 ve - ve

5V 7805 146p 7905 220p kJ.,12V 7112 146p 7812 n°P **.i15V 7815 1459 -18V 7818 1459 -1A 10220 Plastic Casing5V 7805 40p 7095 45p

12V 7812 40p 7912 46p155 7815 400 7915 466

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185 7818 40p 7918 45p24V 7824 40p 7924 46p

100mA 1092 Plastic Casing5V 78L05 30p 791_05 60p .6V 78L62 30p8V 781_82 30p

SWITCHESTOGGLE: 2A/250V SLIDE: 240VSPST Standard 33 IA SPST 13

DPDT Standard 44 i44 06131 13

SUB -MIN TOGGLE IA DPDT 14

SPST On/off 54 1ADPCott 15

SPOT1c/over/ 93DPDT 6 tags 75 PUSH BUTTON

,4DPOT c/off 133 Push -Make -DPOT Biased 145 Push -Break 18

ROCKER: SPST on/off 104/250V 213ROCKER: DPDT 10A/250V4049ROCKER: DPST ILLUMINATED

862°

ROTARY: (Adjustable Stopl 1 pole/2 to 12 way,2 pole/2 to 6 way; 3 pole/2 to 4 way: 4 pole/2 to3 way 46

TRANSISTORSAC125 35AC126/7 361AC128 30AC141/2 30AC176 137 30AC188 30ACY17A18 70ACY20 /1 75ACV22 8080140 120AD149 7980161/2 42AF115 60A6139 40AF178 75AF180 /6 70AF239 55BC107/13 10BC10819 128C108C 12BC109 10BC109E1 12BC109C 12BC117 /8 20BC119 38BC137 405C140 /3 300C147/8 9BC149 9BC153 /4 27BC157 /8 1000159 11

BC160 46BC1674 10BC168C 10BC169C 10BC170 15BC171 /2 11

BC177 /8 16BC179 2013C182/21 10BC813 /1 10BC184 108C1841 1080186 /7 260C212 10BC212L 10BC2 13 10BC2131 100C214 108C2141 10

0C30713 14BC328 96BC338 15BC441 34

BC461 345C477 40BC516/7 4000647/8 12BC549 14BC556 /7 16BC558/9 15BCY70 16BCY71 18BCY72 20130131/2 4860133 93BD135 4560136!7 4060138/9 4080140 40BD695A 125906968 1/5130517 195130460 160130Y61 160BF115 35BF167 290F173 VBF177 25136178 3013F17906180

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10060

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7090

40348 12040360 6040361/2 7040407 6040408 7040411 28640412 9040467 13040468 8540594 10540595 11040603 11040673 75

BFY52 2386539 40BSX20 20BSY65 36

BSY95A 25BU105 170BU205 1901311208 200E113 45E176 50E421 250MJ2955 70MJE340 54MJE370 100MJE371 100MJE520.'1 95MJE2955 70MJE3055 70MPF102 40MPF103 30MPF104 30MPF105 30MPF106 40MPSA05/6 25MPS412 30MPSA55 30MPSA56 30MPSUO6 56MRSU56 600C35 1250C36 1200C41 /2 750C44 750C45/70 400071/2 40OC78 500081 /2 500083/4 000C170 /1 50TIP29A 32TIP29C 39rim 48TIP30A 36TIP30C 37TIP314 38TIP31C 37116324 38TIP32C 42TIP33A 65TIP33C 78TIP34A 7471P34C 88TIP35A 110

TIP35C 128 ,

7I6364 130TIP36C 140TIP41A 50TIP41B 52TIP42A 56TIP42B 58T1P120 70T1P121 /2 73TIP141 106TIP142 1MTIP147 120TIP2955 601163055 60TIS43 3211544 46715888 5011690 3:1TIS91 32V61010 80VN1OK 55554686 78VN664F 80558886 94ITX107/8 11

ZTX109 12ZTX300 1327X301/2 16ZTX303 2527X304 17ZTX314 Z5ITX326 30ZTX341 30ITX500 142TX501.2 15

ZTX503 18710504 25ZTX531 25ZTX550 2525525 5826696 3025697 2325698 4025699 4825706 192591825930

3520

29961 55291132/2 24251304 %251305 602141306/7 65

121416716 120

12V 78112 30p 79L12 50p15V 78115 30p 79L15 60p

CA3085 %p LM317P 99p 78862513 75pLM300H 170p LM323K 500p 7081412 150pLM305H 1400 1-54337 1250 70H05 550,L M3091( 135p LM723 35P 781412 593pLM317K 360p 788650 50p 70HG5 550p

7303116K RAM Pack, Fully built & tested.

Plugs straight on to your ZX81.Onl £17.35y

We stock a wide selection of

DIL SOCKETS 791-10 71168 Computer ICs, Printers, Floppy DiscDrives, BBC Micro upgrade Kits,

Low WireProf. wrap

8 way 80 250PROTO DECEuroboerd 520

Micro peripherals, Booksetc. at very competitive prices.

14 pin 9p 36p16 pin 10p 42p18 pin 16p 52p20 pm 220 613022 gn 251 70124 pm 27p 70p28 pin 28p 60p40 pm 33p 99p

S Dec 460Bimboard I 500Veroblock 375

Adventures withElectronicsby Torn Duncan A

Complete Kit: 1151

DIODES I

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0A70 120479 15

6

ZENERS -7Range 2V7 to39V 400mW

lip eachRange 3V3 to33V. 1.3W

150 each

/SCRs ,

THYRIS-TORS54.'400V 405A/600V 088A/3005 608A/600V 95

DENCO COILS RFC 5 chokes'DP' VALVE TYPE 140pRange 1 to 5 BL., RFC7119rnt1

0A90 181'0A91 a

0A9504200 Si

NOISEDiode 1960

12A/100V 78128/400V 9512A/800V 189BT106 150

RD, TI Wht. 1229 160p6-7 6-5-19 110p 13; 14; 15; 16; 171.5 Green 1500 1200'1' type 1 to 5, BI, 18/1.6 1350Rd, Wht. VI 150p 18/465 152089A Valve Holder TOC 1 1240

42p MVV5FR 122p

149140A202 j i5916 51N4001/2 Sr#4003 51N4004/5 lN4006/7 7'N4148

BRIDGEI

RECTIFIERS1A/50V

41A/10051A/400V .1A/500V '''

01116 180C106D 36TTIC44 24

IC45I."T C47

1135

255062 32255064 382144444 130

RDT2 145p MW/LW SFR 1540:

N5401 ...24/50V 352A/200V 40' TRIACS

VEROBOARD0.1 Pitch clad plain21 x 31" 80p -

2f x 5' 91p -31 x 3r 910 -31 x 5' 105p 870

31 17" 389p 232p

COPPERCLAD BOARDSFibre glass6 x 6' 9°P6 x 12' 1506

S.R.B.P.

N5404 1_,N5406 ;IIN5408 '.S44 :S921

6A/100V 40'6A/400V 5016A/800V 851

2A/400V =2A/600V .,..,..

6A/100V ,t15A/000V .46A/6°" 125

1100AA//62000OVV nee_,215

25A/200V 240258/600V 395

38 1000 483A 200V 5434400V 568A 1005 80

8A 400V 698A 800V 115

12A 1005 71128 4005 82

x

41 x 17" 470p -Pkt of 100 pins 50p

9 x 8 %P We stock awide selection

,_,,65164 fVE418 .4.

124800V 135164 100V 103164500V 115

Spot face cutter 135pPin insertion tool 178p

Ferric Chloride1lb Anhydr. 196p

of ElectronicBooks andMe900ines.

DIALST2

25A 800V 22025A 1000V 4807280000 120 1


MONITORDirectory Update

The response to our Directory Of Elec-tronic Component and Hardware Sup-pliers has been tremendous, from bothreaders and the suppliers themselves.The reaction has been particularly strongfrom those suppliers who, for one reasonor another, were either not included inour listings - or those whose ad-dress/telephone number got scrambled.

Naturally, they will all be listed (cor-rectly) in our next Directory, here aresome more companies operating on thesupply side of our hobby . . .

A.P.T. Radar Systems Limited,Cybervox Language LaboratoryDivision,Unit B, Sprint Industrial Estate, ChertseyRoad, Byfleet, Surrey KT14 7LA. Tel.09323 41331.Specialists in the manufacture of taperecorders and related componentstogether with headsets and spares.Candis Electronics Ltd.Highdown Works, Highdown Avenue,Worthing, West Sussex BN 1 3 1 PU. Tel.0903 690750.Specialists in temperature sensing com-ponents of all kinds.Electronic Hobbies Ltd.,17 Roxwell Road, Chelmsford, EssexCM1 2LY.The correct telephone number is 024562149.Garland Bros. Ltd.,Chesham House, Deptford Broadway,London SE8 4QN. Tel. 01 692 4412."We are an established retail firm (20years) dealing in electronic components,audio equipment, in -car entertainment,and we also do a very large range of CBequipment. A repair service for audio andCB is also available".

Garland Bros. carry all the lines men-tioned in the charts, but do not operate amail order service.Roadrunner Electronic Products,1 16 Blackdown Rural Industries, HasteHill, Haslemere, Surrey GU27 3AY. Tel.0428 53850."Developed and manufactured inHazlemere, our most well-known pro-duct is the Roadrunner prototype wiringsystem. This British product is alreadyused extensively in industry and educa-tional establishments, and is also idealfor the 'home engineer'.

Our hardware products range frompacks of terminal pins to 19" subracks.We also handle computer and word-processing products, from typewriterribbons through to microcomputersystems.

With a combination of the right pro-duct, a competitive pricing structure andexcellent service, we make customersatisfaction our priority".

Roadrunner are moving to new, largerpremises in Haslemere, with the inten-tion of improving overall service to theprofessional and hobby markets. Ordersusing Access or Barclaycard arewelcomed, either by phone or letter.There is no minimum order level,although a 50p handling charge is madeon orders under £5. Carriage and pack-

ing charges are 5% of the total orderbefore VAT is added.TK Electronics,11 Boston Road, London W7 3SJ.The middle two numbers of TK's "easyto remember" telephone number wereinadvertently transposed, rendering it'not so easy'. The number should be, ofcourse, 5-6-7-8-9-10.The Vintage Wireless Company,64 Broad Street, Staple Hill, BristolBS16 5NL. Tel. 0272 565472."We are major stockists of obsoleteelectronic components, especiallyvalves, and operate on a mail orderbusiness as well as personal calls to ourpremises. We try and offer a personalservice, and also have a huge library ofservice data".

The range of services offered include:Sale of radio and television receivers,1914 to 1954.Sale of spare parts for the above.Sale of radio, television and industrialvalves.Sale of service data, technical informa-tion, sales data, historical and otheritems of interest in vintage radio and TV.Restoration and overhaul (but not basicrepairs of vintage equipment) of valvedomestic and automobile radio of alltypes.Sale of new and used books on the sub-ject, plus second hand magazines, oftendating back to the First World War!Hire of radios and related props fortheatrical purposes.Sale of restored radios, with guarantee.Sale of restored vintage car radios.

The full range of stock and vintageradio news can be found in The AntiqueWireless Newsheet, published by thecompany from the above address - con-tact them directly for subscription rates.

Credit card sales are offered via Ac-cess and Barclaycard, and credit cardorders are accepted by 'phone.

Flash Point Alarm

As if by magic, we have had replies to ourrequest for suppliers of the difficult bitsfor this project.

First, the ICL761 1 CMOS IC is readilyavailable from Rapid Electronics, HillFarm Industrial Estate, Boxted, Col-chester, Essex C04 5RD. The telephonenumber is 0206 36412.

The other tricky item was the ther-mocouple, without which the projecthad very little point; the exact ther-mocouple required is stocked in vastlengths by Candis Electronics Ltd..Highdown Works, Highdown Avenue,Worthing, West Sussex BN 1 3 1 PU. Tel.0903 690750. Candis are specialists inthe design and manufacture oftemperature sensing equipment, andthey carry a large stock of all kinds ofthermal devices.

Add-Ons For The ZXComputers

Thurnall Electronics have produced arange of accessories for Sinclair's ZX 80and 81 computers, with an adaptorsystem to fit the ZX Spectrum.

The range is based on a 16 -line I/Oport, and the modular system allows dif-ferent add-ons to be used simultane-ously via an inexpensive motherboard.

Thurnall recommend their system as. . . an ideal way of learning about in-

putting and outputting information . . . "from the computers. An analogue -to -digital converter and an RS232 interfaceare also promised. For details contactThurnall Electronics, 95 Liverpool Rd.,Cadishead, Manchester M30 5BG. Acatalogue is available - but send an SAEwith your enquiry.

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MONITORWe generally credit our designers -

where would we be without them - butdue to an oversight in this case, Dr.Blomfield's name was omitted from thearticle.

Full Protection, But No Racket

Radio buffs going mobile should take alook at a low -noise 24 to 12 voltswitched -mode voltage converter givesan output of 1 3.6V 0.2V) at 6A con-tinuous current, has a low noise rating of2 mV RMS below 1 MHz and 1 mV RMSabove 1 MHZ, and is fully protected andoperable up to 50°C.

The 6A version is priced at £39.95and is supplied with M4 bolts forbulkhead mounting if required. The unitis also available in a 1 OA version. For fur-ther information contact Davtrend Ltd.,89 Kimbolton Rd., Portsmouth, HantsP03 6DA.

And we'd better add that the unit issold in a proper case, and not open to theair as our picture shows it!

A Little Luxury

More advance builders, especially ofradio equipment, may find Centemp In-strument ' s hand-held digitalcapacitance meter useful, provided theycan spare £69. The little MT -301 issmall and robust and designed to travel.It comes complete with battery, alligatortest clips, spare fuse and instructions -all ready to go. A bold 1/2 -inch, 31/2 digit li-quid crystal reads out from Op1 to 200uacross eight separate ranges; the con-trols are all push buttons for easy one -hand operation.

This is a slightly unusual piece ofequipment, so anybody who feels theneed of a digital capacitance meter coulddo worse than to start enquiring here. In-cidentally, for the really rough rider,there's an optional "deluxe protectivecase" (fur -lined??) for an extra £6.00.Details from Centemp Instrument Co.,62 Curtis Rd., Hounslow, Middx. Tel.(01) 894 2723.

Hiding His Lights

Our apologies to Dr. D.L.H. Blomfield,who designed the Three -Aspect SignalLights Controller project which appearedin our September '82 issue.

Dr. Blomfield has certainly earned ourcollective congratulations for his excep-tional design, which has attracted highpraise from several model rail en-thusiasts.

Little Boxes

Things for putting other things in maynot provide the total answer to how torun an orderly workshop, but they cer-tainly do help, so SSI Fix Equipment havecome up with a new system of compo-nent storage modules known as Portafix6.

Each Portafix unit (sounds likesomething out of Asterix the Gaul,doesn't it?) has 12 bin -shaped drawers,each 2 x 4 x 3" deep. The overall size is14 x 14 x 4" , with a tray area on top, in-tegral carrying handle and (an unusualfeature) optional hooks, for carryingtools, at either end of the unit.

The whole thing seems to be design-ed for absolute minimum spillability and,for travelling, this principle can be takeneven further - any two units can behinged together face to face and secure-ly locked shut - no more drawers slidingout every time the car tilts! Each little binhas a transparent dust -cover whichopens upwards and the modulesthemselves can be stacked.

A very handy bit of storage equip-ment for any kind of craft which usessmall components, from cake -decorating to woodworking to . . . well,electronics. At £7.40 for a single unitand £14.80 for a double (hinged) unit,this could knock a few of your Christmaspresent problems on the head!

At the moment Portafix 6 is onlyavailable from SSI Fix Equipment Ltd., K-ingsclere Rd., Basingstoke, Hants RG212UJ, and prices don't include postageand packing, so you will have to enquireabout that: telephone 0256 26511.


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7 IC206D 44 400VThat. 40T L084 603mm red LED 67805 30Offer ends 31112182.

CMOS

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50 402214 402336 402424 402524 402611 402715 402820 402945 403040 4031

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20 403430 403645 403925 404042 404140 404245 404316 404433 404616 404775 404820 404940 405045 405114 4052

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140 4054 78 4081249 4055 80 4082280 4059 430 408540 4060 42 408640 4063 80 408938 4066 22 409340 4067 225 409440 4068 14 409550 4069 13 409745 4070 13 409838 4071 13 409921 4072 13 4010621 4073 13 4010942 4075 13 4016348 4076 45 4017348 4077 14 40175

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L000LS01LSO2LSO3LSO4LSO5LSO8LSO9LS10LS11LS12LS13LS14LS15

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L520LS21LS22LS26LS27LS30LS32LS37LS38LS40LS42LS47LS48LS51LS55LS731.074

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20 1.012317 1012517 LSI 2635 LS13248 LS13616 LS13824 LS13925 1.014524 L514738 LS14895 LS15140 LS15321 LS15421 LS15521 LS15622 LS15735 LS158

34 LS16024 LS16125 LS16235 LS16326 1016430 LS16530 LS16670 LS170

150 LS17375 LS17438 LS17538 LS19075 LS19133 LS19236 LS19326 LS19529 LS196

35 LS197 4535 LS221 5035 LS240 6035 LS241 6040 LS292 5555 LS243 5560 LS244 5575 LS245 7060 LS247 4845 LS251 2845 LS257 3235 LS258 3235 LS259 5535 LS266 2036 LS273 5832 LS279 3045 LS283 38

L5353 60LS365 28LS366 28LS367 28LS368 2915373LS374LS375LS377LS3 78LS390LS393LS399LS54110670

60604360574545

15678

135

741374147416

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555CMOS 80556CMOS 150709 25

14748 359400CJ 350Al -3-1270 720AY -3-8910 370AY -3-8912 625CA3046 60CA3080 65CA3089 215CA309040 375CA3130E 85CA31406 36CA3161E 100CA3189 290CA32406 110

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CL7106 700CL7611 95CL762I 180CL7622 180CL8038 295CL8211A 200

M7224 785CM7555 80LF351 45LF353 85LF356 90LM1O 360LM3014 25LM311LM318 120LM324LM3342 10f)LM335Z 125

LM339LM348LM358LM377

leLM381LM382LM384LM386LM387L M393LM709LA1711LM725LM733LM741LM747LM1458LM291 7LM3900

LM3909

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LM3911 120LM3914 175LM3915 195LM13600 105MC1496 68MC3340 135

MF10C9 350ML922 400ML924 195M1925 210ML926 140ML927 140ML928 140ML929 140MM5387A 465NE529 225NE531 150NE544 205eNE555 16A,16556 45NE565 110

NE566PNE567PNE570NE571RC4136RC4558SL480SL490SL76018106976477SP8629TBA1200T84800TBA810T84820

140100370370

5560

170250150380250

70759870

TBA950 220TDA1008 320TDA1022 490TDA1024 125TL061 4011062 60

T L064TL071T L072T L074PTL081T L082T L084IL170U42240ULN2003ULN2004XR2206ZN414ZN423ZN424ZN425EZN426EZN427EZN428EZN4592910346

9630509525459550

1208590

290100135135350330650480285200

TRANSISTORS

AC125 35AC126 25AC127 25O AC128 20AC176 25AC187 22AC188 22AD142 120AD149AC/161AD162AF124AF 126AF139AF 186AF 2398C107BC1078 8C108BC1088BC108C 8C109BC109C8C114BC1158C117BC119BC137BC139BC140BC14180142BCI43BC147BC148

BC517 408C547 7

BC548 10BC149 9 BC549 10BC157 8 BC558 10BC158 10 BCY70 18BC159 8 BCY71 18BC160 45 BCY72 18BC168C 10 80115 80BC169C 10 BD131 3580170 8 50132 35

80 BC171 10 130133 5040 BC172 8 BD135 5040 BC177 18 130136 3060 BC178 18 80137 3050 BC179 18 80138 3040 BC182 10 PA8 0139 3570 BC182L 8 P130140 3575 BC183 10 60204 11010 BC183L 10 80206 11012 BC184 10 80222 85

9 BC184L 7 8F180 3512 BC212 10 BF182 3512 BC212L 10 60184 25

9 8C213 10 BF 185 2512 BC213L 10 13F194 1222 8C214 10 BF195 1222 BC214L 8 BF196 1222 8C237 8 BF 197 1235 BC238 14 BF 198 1040 BC308 15 BF 199 1840 BC327 14 8F200 3030 8C328 14 03024413 2230 BC337 14 BF 245 3025 BC338 14 BF 256B 4525 BC477 30 BF 257 32

8 BC478 30 8F258 258 BC479 30 BF 259 35

BF337BF R40BF R8008 FR81BF X29BF 084BF X85BF X86BF 087BF X888F Y50BFY51EWA/528F Y53BF Y55BF 156BRY39BSX208574299519588U205131./206BU208MJ2955MJE340MJE520MJE521MUE3055MPF102MPF 104MPS405MPS406MPSA12MPSA 55MPSA56MPSUO5MPSUO6MPSU55

4023232025252528252523202332323240203525

160200170

995065957040402225303030555560

MPSU56 60TIP29A 30TIP298 55TIP29C 37TIP304 35TI17308 50TIP30C 37TIP31A 35TIP31C 37TIP32A 35TIP32C 37TIP334 50TI1733C 75TIP34A 60TIP34C 85T1/7354 105TIP35C 125TIP36A 125TIP36C 135TIP41A 45TIP42A 45TIP120 90TIP121 90TIP122 90TIP141 98TIP142 98119147 110TIP2955 60TIP3055 55TIS43 40TIS44 45TIS90 30TIS91 30VN1OKM 45VN46AF 75VN66AF 85V 9884F 95ZT X107 8

ZTX108 8 293055 50ZTX109 12 293442 120ZTX300 14 293702 6

ZTX301 16 2N3703 9ZTX302 15 2193704 6ZTX304 17 293705 9

ZTX341 30 2N3706 9ZTX500 15 293707 10ZTX501 15 293708 10ZTX502 15 293709 10ZTX503 18 2N3772 190ZTX504 25 P29377321029697 20 la 293819 1829698 40 293820 40297064 20 293823 6529708 20 293866 9029918 35 293903 102141132 22 2N3904 10291613 30 2N3905 62922184 45 293906 102922194 25 2N4037 45292221A 25 294058 102N2222A 20 294060 10

292368 25 2N4061 10292369 16 2N4062 10

292484 25 2N5457 36292646 45 295458 36292904 20 2N5459 30292904A 20 295485 36292905 22 295777 452929054 22 296077 30292906 25 40360 402192906A 25 40361 50292907 25 40362 502929074 25 40408 70292926 9293053 23293054 55

The Rapid Guarantee* Same day despatch * Competitive prices* Top quality components * In-depth stocks

MAIL ORDERS:Unit 2, Hill Farm Industrial Estate,Boxtect, Colchester, Essex C04 5RD.TELEPHONE ORDERS:Colchester (0206) 36412.

CAPACITORS

Polyester, radial leads. 250v. C280type: 0.01, 0.015, 0022, 0.033 -6p. 0.047, 0.068, 0.1 7p, 0.15,0.22 9p; 0.33, 0.47 - 13p:0.68

I u - 23p.Electrolytic, radial or axial leads:0.47/63 V, 1 /63V, 2.2/63V, 4.7/63V,10/25V 7p; 22/25V, 47/25V- 8p;100/25V- 9p; 220/25V 14P;470/25V - 22p; 1000/25V - 30p;2200/25V 50p.Tag end power supply electrolytics:2200/40V 110p; 4700/40V -160P2200/63V 140p; 4700/63V 230pPolyester, miniature Siemens PCB:In, 2n2, 3n3, 4n 7, 6n8, 10n, 15n, 79;22n, 33n, 47n, 68n, 8p; 100n, 9p;150n, 11p, 220n, 13p,330n, 20p:470n 26p;6800, 29p; 1u 33p: 2u2,500.Tantalum bead:0.1, 0.22, 0.33. 0.47, 1.0 @ 35V12p. 2.2, 4.7, 10 @ 25V - 20p;15/16V - 30p; 22/16V 279; 33/16V 45p; 47/6V 27p; 47/16V -70p; 68/6V - 40p; 100/10V 909.Cer. disc. 22p -0.01u 50V, 3p each.Mullett( miniature ceramic plate:I.8pF to 100pF 6p each.Polystyrene, 5%101; 10p -1000p, 6p:1500-4700, 8p:6800 0.012u, 10p.Trimmers. Mallard 808 sewer 2-10pF, 22p; 2'22pF, 30p; 5.5-65pF. 35p

RESISTORS

'4W 5% Carbon film E12 series 4.7ohm - 1M. . . . Ip each.IhW 5% Carbon film 612 series 4.7ohm to 4M7 . . . 2p each.'4W 1% metal flint E24 series 10ohm IM . . 6p each.

SOCKETS

8 pin14 pin16 pin18 pine20 pin.22 pin24 pin28 pin 25p40 pin 25pSoldercon pins 60P/100

Lowprof Ile6p8P9P12p13p16p189

Were.wrap25035p42p52p60p70p70p80p98p

SWITCHESSubrnin toggle;SPST 55p. SPDT 60p. DPDT 659.Miniature toggle;SPOT 80p. SPOT centre off 90P.DPDT 909 DPDT centre off 10017.Standard toggle.SPOT 35p. DPDT48pMiniature DPDT slide 122.Push to make 12p.Push to break 22p.Rotary type adjustable stop.1P12W, 2P6W, 3P4W all 55p each.DIL switches:4SPST 80p 6 SPOT 809. 8SPST10017.

VERO

VEROBLUCSize 0.1 Matrix.2.5 x 1

2.5 x 3.752.5 53.75 x 5VQ boardVeropins per 100Single sided 50Double sided 60Spot face cutter 105Pin insertion tool . 162Wiring pen and spool . 310Spare spool 75p Combs . 6

350

22758595

160

DIODES

131127 i20447 100490 80A9) 7

0A200 804202 81N914 401(44148 2

01N4001194002194006194007195401195404195406400mWzen

35

7

7

151617

6

CABLES

20 metre pack single core connect-ing cable ten different colours.65p

Speaker cable . . . 10p/rnStandard screened . . 16p/rnTwin screened . 24p/m2.5A 3 core mains . . 23p/m10 way rainbow ribbon 65p/m20 way rainbow ribbon 120p/m

POTENTIOMETERS

Rotary. Carbon track Log or Lin1K - 2M2. Single 32p. Stereo 85p.Single switched 80p. Slide 60mmtravel single Log or Lin 5K - 500K63p each.Preset submin. hor. 100 ohms -1 M7p each.Cermet precision multiturn, 0.75199" 100 ohms to 100K 88p each.

REGULATORS

78L05 30 79105781.12 30 7911278L15 30 79L157805 35 79057812 35 79127815 35 7915

656565404040

LM309K 130 LM723 35LM3I 7K 270 LM338K 475LM317T 120 78H05 5ALM323K 350 5V . 550

SOLDERING IRONSAntes CS 17W Soldering iron 4602.3 and 4.7mm bits to suit . 65CS 17W element . . 450Antes XS 25W . . . 4803.3 and 4.7mm bits to suit . 65Solder pump desoldering tool. 480Spare nozzle for above . . 7010 metres 22swg solder . 100

PCB MATERIALSAltar transfer sheets - please statetype (e.g. DIL pads etc.) . 45Delo etch resist pen . . . 100Fibre glass board 3.75"x8" 80Ferric chloride 250ml bottle. 100

1:7:233/54

ACCESS ANDBARCLAYCARD

WELCOME

TOOLS

Small trimming tool . . 22Small pocket screwdriver . 16Large pocket screwdriver . 136 piece precision screwdriver setin plastic case . . 170Low cost side cutters . 160High quality side cutters . 650Low cost pliers . . . . 160High quality pliers . . 650Wire strippers . . 120Expo reliant drill . . 695Expo Titan drill . . . . 1025Drill stand . . . . 1200Reduced shank drill bits forabove 0.8mm,

. 60

OPTO

3mrt-i red 7 5mm red 8I.3mrn green 12 5mr-n green 12P3mm yellovv12 P 5mm yellow/2Clips to suit - 3p each.Rectangular TIL32 40P red 12 TIL78 40green 17 TIL111 60yellow 17 ORPI2 85PTI L38 40 TIL100 90

' 2N5777 45 Dual colour 60Seven segment displays:Com cathode Com anodeDL704 0.3" 95 0(.7070.3" 95OFND500 F ND5070.5" 100 0.5" 100TI L3130.3"115 TIL3120.3"115111.3220.5"115 TIL3210.5"115LCD: 31 digit 580p. 4 digit 6209.

TRIACS 400V 8A 65400V 16A 95

400V 44 50 BR100 25

COMPONENT KITS

An ideal opportunity for the beginner or the experienced constructorto obtain a wide range of components at greatly reduced prices. '4W 5%Resistor kit. Contains 10 of each value from 4.7 ohms to IM (totalof 650 resistors) . . . . . . . . . . 480Ceramic Cap. kit. 5 of each value - 22p to 0.01u (135 caps) . . 370Polyester Cap. kit. 5 of each value from 0.01 to luF (65 caps) . 575Preset kit. Contains 5 of each value from 100 ohms to 1M (total65 presets 425Nut and Bolt kit (total 300 items); 180p25 6BA 'A" bolts 50 6BA washers 50 684 nuts25 6BA It" bolts 25413A 'A" bolts 50 6BA washers50 6BA nuts 25 6BA torts

TRANSFORMERS Please add carriage chargesto our normal post charges.

Miniature mains;606V, 909V, 12012V all @ 100mA 100p each.PCB mounting. Miniature:3VA 0-6, 0-6 @ 0.254; 0-9 0-9 @ 0.154; 0-12,0-12 @ 0.12A 200p each6VA 06, 0-6 @ 0.54; 0 9, 0.9 @ 0.3A; 0-12, 0.12 @ 0.25A 270p each.High quality. Split bobbin construction6VA 0-6, 0 6 @ 0,54; 0-9, 0-9 @ 0.44; 0-12, 0-12V @ 0.3A 2209 each.12VA 0-6, 06 @ 14; 0-9, 0-9 @ 0.84, 0-12, 0-12 @ 0.54; 0.15,0.15@ 0.4A 295p (plus 40p carriape).25VA 06, 06 @ 1.5A; 0-9, 0-9 @ 1.24; 0.12, 0.12 @ IA: 0 15, 0-15 @0.8A 330p each (plus 60p carriage)50VA 0-12, 0-12 @ 2A, 0-15, 0 15 @ 1.5A. 440p each (plus 75p carriage)

HARDWARE

PP3 battery clips . . 6Red or black crocodile clips . 6Black pointer control knob 15Pr Ultrasonic transducers 350fiV Electronic buzzer 6012V Electronic buzzer . 65OP82720 Piezo transducer . 7564mm 64 ohm speaker .

64r-rtm 8 ohm speaker .

20mm panel fuseholder

707025

BOXESAluminium

Plastic with 302x1" 70lid c screws 40301'4" 85302x1" 55 403x2" 1004%530112" 88 60402" 120704x2 160 604x3" 150

SCR01061) 30400V 84 70400V 12A 95

BRIDGERECTIFIERS

2A 200V 402A 400V 456A 100V 806A 400V 95

IA 50V 20 VM18 DIL 0.9414 400V 35 200V . 50

CONNECTORS

DIN Plug Skt Jack Plug Skt2 ptn 9p 9p 2.5mm 10p 10P3 pin 129 10p 3.5rnm 9p 9P5 pin 13p 11p Standardl6P 20pPhono 10p 12P Stereo 24p 25plmm 12p 13p 4mrn 18p 17pUHF (CB) Connectors:PL259 Plug 40p. Reducer 140.50239 square chassis skt 38p.00239S round chassis skt 40p.IEC 3 pin 250V/6A.Plug chassis mounting . . 389Socket free hanging 60pSocket with 2m lead . . 120p

MULTIMETERS

HT -120 4,000 opvA smart looking 11 range pocketsized multimeter with an impressivespec. Complete with battery, etc.650p each.HT -320 20,000 opv.Highly sensitive 19 range multi -meter including transistor tester.Overload protection. DC volts -1000. AC volts - 1000. DC current0.25A. 4 resistance ranges.Completewith batteries, leads, etc. 1395p

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:ORDERING INFO All components brand new and full specification.All prices exclude VAT. Please add to total order. Please add 50p carriage to all ordersunder £15 In value. Send cheque/P.O. or Access/Visa number with order. Our detailedcatalogue costs 45p (free with orders over EIC). Callers most welcome. Telephone orderswelcome with Access and Visa. Official orders accepted from Colleges Schools, etc.


Project

HE MicrologThe return of the Analog Computer.

K. Manison

WITHOUT DOUBT we are living in arapidly expanding digital world;everything is going digital. Clocks andwatches, once precise mechanicalinstruments with analogue dials, nowconsist of tiny electronic circuitsdisplaying the time in digits accurate toa tenth of a second. The acceptance ofdigital technology can be seen in therapid increase in the availability ofwomen's digital watches; it is nolonger a symbol of male technology!

Digits are also appearing in otherareas, long the exclusive domain ofanalogue indicators, but displaymethods are not the only field to fall todigital techniques. Our telephoneconversations are digitised andtransmitted as serial bit streams andwho, today, hasn't heard of digital hi-fi? And with the recent release of videodisc systems, digital video has finallyarrived.

One of the reasons for the digitalrevolution, of course, is cost. With therapid advances of digital integratedcircuits - and that superstar themicroprocessor - it has become muchcheaper to produce a silicon circuitwith an LED or LCD display, than tomake a complicated mechanicalindicator.

In many cases, the increasedaccuracy and resolution is definitelyrequired and digital systems may beused to excellent effect. In other cases,however, the older analogue systemshave many advantages, and that is truealso of the analogue computer.

The Analogue ComputerRemarkable though it may seem, theanalogue computer, which need nothave a single TTL or CMOS logic chip inthe whole of its circuit, manges toperform calculations that many digitalmachines would find difficult.Analogue computers have been aroundfor decades in one form or another. Infact, many of us have used a slide ruleWithout even being aware that it is ananalogue computer.

Whereas a digital computerperforms its calculations directly, usingnumbers, an analogue computer willuse some physical parameter torepresent the values it is to manipulate.The slide rule, for example, useslength; the length is considered torepresent the log of a number so thatadding two lengths together isanalogous to adding logarithms which,of course, is a method of performingmultiplication.

Until the cheap digital calculatorbecame available, the slide rule wasdexterously manipulated by

generations of engineers and scientists,and it has in no way hindered theadvance of technology! In fact,entering experimental results accurateto two decimal places into a calculatorand getting out a result with eightplaces of decimals can be meaningless.If the data is limited to two placeaccuracy so is the result, and we haveto round off the answer anyway. Theslide rule, being accurate to two places,can in many cases produce answersthat are just as valid as a calculator,and it is not much slower either!To further illustrate the differencebetween analogue and digitalcomputation, let us look at a commonproblem. When changing a note forcoins, the bank teller can count themoney in one of two ways. The mostobvious way is to empty a heap of1 Ops on to the table and count therequired number. For small sums this isadequate, accurate and, for theexperienced teller, remarkably fast.However, if a large sum has to bechanged, the digital computing methodbecomes too slow and also increasesthe chance of error. So, the teller willweigh the coins and, the weight of asingle 10p piece being known, thescale can be graduated in pounds andpence. This is an analogue method inwhich weight is the analogue of value.In this case, the analogue method willbe faster than physically counting eachcoin and, with an accurate scale, justas precise.

It is obvious that differentapplications are better suited to eitherdigital or to analogue computation. Forexample, analogue computers havelong been used for solving differentialequations of the type frequentlyencountered in control theory and

servo systems. While these equationscan be solved by digital means, it is atime consuming process and oftenexpensive as well. However, anelectronic analogue of the system canbe constructed on an analoguecomputer, the stimulus then fed in andthe output viewed in real time on anoscilloscope or chart recorder.Variables of the system can bechanged independantly and the processrun again and again.

It is the speed of computation, andthe graphical output, that give theanalogue computer the edge on thistype of problem. So now let's look intoan analogue computer and see what itconsists of and how it can be used. Forthose that are interested inexperimenting with these machine, theMicrolog is a simple and cheapanalogue computer that can be used totry out some of these concepts.

Analogue ComputingAn analogue computer performs thefunctions of summation (adding),multiplication, integration anddifferentiation. While a digital computercan perform all these functions, it canonly do them one at a time. So, eventhough it works very fast it has toperform a series of calculations.Particularly where integration isconcerned, many simple calculationshave to be made to solve one integral,and, if the step size is kept small toincrease accuracy or resolution, thenmore calculations are required and thetime taken is increased.

Say, for example, the solution to theproblem X = Y + (V + U)/2 is required. Adigital computer would tackle theproblem like this: first, V and U would


Projectbe added together and stored as avariable; second, that variable wouldbe divided by 2; last, it would be addedto Y to give the required answer. Aprogram, written in BASIC, to handlethe problem may look like this:

10 INPUT U20 INPUT V30 LET X = ( U + V I / 240 INPUT Y50 LET X = X + Y60 PRINT X70 END

For a simple problem like this thesesteps take very little time, but if a largecomplicated formula were beingcalculated you can see that thissequential type of process may take avery long time indeed.

The analogue computer, however,uses separate modules tosimultaneously perform each functionrequired in the calculation, and themanner in which the modules areinterconnected determines the formulabeing calculated. If two additions haveto be performed then two summers willbe used, one for each.

For the problem X = Y + (V +11)/2, anelectronic analogue computer wouldhave modules connected together asshown in Figure 1. The trianglesymbols are summers and produce thealgebraic sum of the input voltages.The circle symbol is a coefficientmultiplier, used to divide the sum ofV + U by 2 (multiplication by 0.5). Youcan see that as soon as the inputvoltages corresponding to Y,V and Uare presented to the modules, X will beinstantly available. Notice that theanalogue computer is effectivelyperforming all of its calculations inparallel, not one after the other. It isalso performing an 'on-line' calculationin that the output X will continuallyfollow the inputs. A digital machinewould have to prompt for updatedvalues, or interrogate I/O ports forthem. This is what gives the analoguecomputer a speed advantage, in manycases. To find out how an analoguecomputer works, let us examine eachof the building blocks; then we willdetermine how to put them together!

Computing UnitsAn analogue computer uses voltageand time to represent numeric values.For example, a voltage rising from 0volts to 3 volts over a period of aminute could be used to represent thefilling of a 300 gallon tank in the sametime. In this case, 1 volt represents100 gallons, and its variation with timeshows the changing level in the tank.So, a plot of voltage against time willshow the physical movement of thesystem we are simulating with theanalogue computer. The analoguecomputer, therefor, needs devices thatwill sum, integrate and multiplyelectronic voltages. If we think of thesedevices as circuit elements, then wecan connect them together as a circuitto produce the function we require.

U

OV0V

0

Figure 1. The analogue solution to theequation.

1M 1M

Figure 2(a). An analogue summing cir-cuit (above); 2(b) the graphic symbolused for a summer (below).

Figure 3. The circuit of an op -amp in-tegrator.

VIN

INITIALCONDITION

R1

I a I

R2

INITIALCONDITION

INPUT

Ibl c

Figure 4. Above (a), the integrator cir-cuit modified for initial condition input;(b) the usual graphic symbol; (c) therepresentation used on Microlog'spanel.

Figure 5. An op -amp differentiator.

SummersIf our computer is to use voltages torepresent physical values then we needan electronic device to add twovoltages together; it must produce avoltage which is the algebraic sum oftwo or more instantaneous voltages.

The simplest method is to use an op -amp; if we add several inputs throughresistors, we get an output proportionalto the sum of the input voltages. Atypical circuit is shown in Figure 2a.The summer circuit module is usuallyshown by the symbol of Figure 2b. Thegains, normally 1 and 10, are shownfor each input.

IntegratorsWe stated at the beginning thatanalogue computers are used toproduce solutions to differentialequations, and this means thatintegration and differentiation areinvolved. Integration is essentially thesum of all the instantaneous values of afunction. Normally it is performedbetween definite limits, say betweenthe times t = 0 and t = 100. Some initialcondition must also be specified if theintegration is to be valid. For example,when integrating a voltage signal V,the starting condition may be V = 2when t = 0. Therefore, the integratormust also have an "'initial condition"input.

We can use an op -amp to integrate avoltage; consider the circuit shown inFigure 3. The output is given as:

Vo = -f Vi dtRC

Of course, we can integrate multipleinputs in exactly the same waythat we

summed several inputs, and it shouldalso be clear that by changing the inputresistors the integrator gains,expressed as 1/CR, can beindependently set for each input.

Now to set the initial conditions: wemust be able to set the output (bysetting the charge on the capacitor) toa desired value. In effect, the circuitmust behave as a summer up to timet = 0, but operate as an integrator afterthat time. We achieve this by means oftwo switches, as shown in the circuitFigure 4a.

If switch SW2 is closed, you cansee that you have a summer with onlyone input, VI x R1 /R2. The capacitorwill also have this voltage across it andwill be charged to the desired initialcondition.

If switch SW2 is opened and SW1closed, we have an integrator withthree inputs. When both switches areopen, the circuit acts as a 'hold' circuit- the output will remain at whateverthe voltage was when SW2 wasopened. This is dependent, of course,on the capacitor remaining charged,but as the input impedance of the op -amp is very high, it can hold thevoltage for an appreciable time.

In a large analogue computer, theseswitches are replaced by relays, whichallows the machine to be switchedfrom Reset to Compute repeatedly, andthe response can be displayed on anoscilloscope. This mode of operation iscalled Rep -Op, short for RepetitiveOperation.

DifferentiatorsWe learn at school that integration isthe opposite procedure todifferentiation, so that the opposite


Project

RV1-6

10k

T1

COEFFICIENTMULTIPLIERS x6

R1 1M

R2 1M

R12

100k

R4 1M

R8 1M

R16

100k

R101M

RV7

20-0-20

4 7 u

C6

IC3

22u

C8

R4547014

ZD1

1 0 V

47u

C7

IC4 1""

ZD21 0 V

R464708

+15V

10v

V

lOy

15V

Figure 6. The complete Microlog circuit: (above)the power supply; (far left) the coefficientmultipliers; (near left) the meter circuitry; (belowleft) the four summing circuits; (below right) the

R44 47k four integrators. Not all the components aremounted on the PCB; connection points are mark -

50k ed to aid wiring, which needs careful attention -see NOTE, below, and Figures 8 and 9.

M1

NOTES:IC1,2 ARE 348IC3 IS 7815IC4 IS 7915M1 = 100uA CENTRE ZERO

R3 1M

R6 1M

R11 1M

NOTE:CIRCLED NUMBERS = PCB CONNECTOR POINTSLOWER CASE LETTERS= PATCH PANEL CONNECTOR POINTSNUMBER AND LETTERS = LEVER SWITCH TERMINALSLEVER SWITCH SHOWN IN "RUN"

R36 10k R37 10k

R22 1M

R23 1M

R30

1005

R24 1M

R25 1M

R32

100k

100k

R39 10k

R43 10k

configuration, in the op -amp circuit,will produce a differentiator. The circuitin Figure 5 produces the differential ofthe input voltage, and once again wecan have several inputs withindependent gains.

Coefficient MultipliersSo far we have shown our summers,integrators and differentiators withfixed gains of, eg., 1, 10, or 100. Wecould, of course, set them to any valuerequired - 2.375 for example - butwe lose flexibility if the gains are set tosuch 'strange' values, as they will onlybe useful for a calculation that needsthat particular number! However, if wehave a device that will divide a voltageby 1/.2375 (ie. multiply by thecoefficient, 0.2357) and then followthat by a summer with a gain of 10, wehave achieved our required gain of2.375. So we need a voltage, orpotential, divider - which is nothingelse but a potentiometer!

For analogue computers, thepotentiometers have to be precise andstable. Also, there must be somemeans of setting them to the requiredvalue. The way this is achieved is toconnect them across an accurate,known voltage and measure the outputwhile adjusting the pot until the desiredcoefficient is reached. In largemachines, this may be doneautomatically by small servo motorsconnected to the wiper mechanism. Forsmall machines, such as the onedescribed in this article, the pot has tobe set manually. In the example above,the potentiometer could be connectedacross 10 volts and adjusted until theoutput at the wiper measured exactly2.375 volts.

The HE MicrologMicrolog stands for Micro -AnalogueComputer (we can't have digitalmachines claiming sole rights to theterm 'Micro'!). It has been designed asa conceptual trainer to give you a feelfor analogue computing and, therefore,accuracy has been traded for low costand simplicity.

Microlog's patch panel shown inFigure 7 and from it you can see that ithas four integrators, four summers andsix pots (coefficient multipliers). TheInitialise -Integrate -Hold selection isperformed by the keyswitch labelledReset -Run -Hold; no rep -op mode isavailable as that would entail the use ofrelays, increasing the cost. Thecomplete circuit is built on one PCB andfits in a type 104 Verobox, with 2 mmplugs used for the patch connectors.The most expensive item in theMicrolog is the meter!

To keep everything simple, singlechip voltage regulators are used for the15 V power supplies and the referencesupplies are simple zener dioderegulators. Two 348 quad op -amps areused, one chip providing the fourintegrators and the other the foursummers. One of the summers has acapacitor on one input to provide adifferentiator function. The completecircuitry is shown in Figure 6.


Project0 0 1a 0 0 1d 12 0

a Fg41I

LIM 00

d ®

U ®

0

I I I

I I II IIII

KEYSWITCH

oe

0

. R20 0

< +O LEM1 0

R28

MEI 0

h 0

-10

10

/ I V ®

'..-e-Hd}®C1\ I\\ Iz ®

hh

30

OV

k 322 0

< I 0 LEI 0R30

101 ZD20

KIM 0

ILENI0

kk

cc ®

dd0

0

ON OFF

ImoL 0

Figure 8. The front panel wiring diagram, showing the mounting positions of the components and the wiring points leg, point 'f'goes to PCB point '1'; point "g" goes to the leverswitch terminal "la"). The switch terminal connections are shown in Figure 9.

The Patch PanelHaving designed the various computingelements that go to make up ananalogue computer, we now require amethod to interconnect them in orderto solve problems. This is usually doneby means of a patch panel. The inputsand outputs of each computing unit arebrought out to sockets and jumperwires may then be used to connect thedesired units to simulate a system orsolve an equation.

ConstructionThe first thing is to drill the front panelof the Verobox for the 2mm sockets,pots, switches and the meter. Then,using Letraset or similar rub -downlettering, mark out the patch panel andspray with a clear polyurethane lacquerso that the markings will not rub offafter a little use. The full-sized patchpanel is reproduced on page xx for useas a template in this operation.

Next, mount all the sockets andpots. When tightening the nuts on the2 mm sockets, take care not to overdoit or you may strip the thread. Usingthe wiring diagram, Figure 8, as aguide, connect up the pots to theirrespective sockets. Again, he verycareful when soldering to the 2 mmsockets, as the plastic body melts veryeasily!

The next step is to mount the inputresistors on the correct sockets for thesummers and integrators (mounting

HE

DEE

G

2

00ON

Micnolog HE

H

ELIE

METER RESET

RUN

E

HOLD

0 0 0Figure 7. The front panel of Microlog. 2nun SOCKETS G GREEN = POTENTIOMETERS

B BLUE = -10V Y YELLOW = INITIAL CONDITION INPUTSBI BLACK = OV W WHITE = OP AMP INPUTS AND OUTPUTSR RED = 410V M = METER INPUT (BLUE)

them here, instead of on the PCB,reduces the amount of wiring from thepatch panel to the PCB(. Use the circuitdiagram and the wiring diagram todetermine the correct place for eachresistor. Then mount the 10 volt Zenerdiodes, ensuring that you have putthem in the right way round, and the470R resistors.

The final front panel wiring is thatfrom the keyswitch to the sockets.Take special care that this wiring iscorrect, as it is easy to get confusedwith the connections on the keyswitch.Use the circuit diagram and Figure 9and double check it when you'vefinished. It is easier to change incorrectwires then, than at a later stage in the


Projectf is a 11 lm

«Jl

IC2

T

1f I a b q P ii

1] 1] 13

I 1

c°TICI

29[8212c r

0.1cc

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CC CC

2-61 25 FH 21 21 19 181 17

2m ee 2f ff \A, x

30 I

hh

RV 7

R44Oh as

L.)

+1-

kk

14

IC3

16

15

IC4

)0J0931m 3H

Figure 10. The PCB component overlay diagram; note the connection points.

9 I k

f-11-1h

HOLD .11-- RUN RESET

} T1 PRIMARY

BROWN(ACTIVE)BLUE(NEUTRAL)

Figure 9. The leverswitch (Keyswitch)wiring connections (left) and the on/offswitch connections (above). Note thatflipping from RUN to HOLD connects'h' to 'g' etc, and in RESET, 'b' is swit-ched to 'c' and 'e' to 'd'.

construction.Before the panel can be put back on

the Verobox, you will have to removethe central plastic strip that crosses thepanel aperture. Don't worry - itdoesn't weaken the box in any way.Some time before the testing stage,too, you will have to make up about 20patch leads with 2 mm plugs on eachend; it is best to make assortedlengths, say 3,6 and 9 inches long.

Now you can start to mount thecomponents on the PCB, using theParts List and component layout Figure10 to locate each part. First check the

tracks, to ensure there are no breaks orbridges, and then install the IC socketsand solder them in. Do not plug in theop -amps until the check-out procedure,later. Next, install the resistors on theboard and once they are soldered,mount the capacitors. Ensure that theorientation of the electrolyticcapacitors is correct; the layoutdiagram shows the way. Finally, installthe two voltage regulator ICs; these aremounted with the metal face againstthe PCB and held in position with asmall screw lockwasher and nut, andbe sure the regOlators are in the right

BRIDGE V+

OV

BRIDGE V-

places. One is a positive voltageregulator and the other negative and ifyou accidentally swap them around,they won't last a second when youswitch on! Bend the leads down intotheir respective holes and solder themin. Go over the board, then, checkingfor any solder bridges or dry joints,touching up where necessary.Once the board is complete you canstart wiring from the patch panel tothe PCB connection points, using thewiring diagrams, Figures 8 and 9. Thisis where great care must be taken, asit is all too easy to get wires crossed.Give yourself enough length on thewires to be able to route them rieatly,and to allow the panel or top. of thebox to be taken off without pulling thewires!

The wiring from the PCB to thekeyswitch can be done next, againtaking care that the correct connec-tions are made. The PCB is thenmounted to the panel, using the screwterminals of the panel meter, whichalso provides the electrical connec-tions to the meter.

The last part of the construction isthe power supply unit (Pal). This isextremely simple, consisting of thesmall transformer, a bridge rectifier


Projectand two capacitors. They can all bemounted on the transformer as shownin the internal photograph. The finalstage is the wiring from the PSU tothe PCB, and to the ON/OFF switch.After that, you are ready for testing.

TestingFirst make sure you have NOT in-

serted the ICs and that the ON/OFFswitch is OFF. Plug Microlog into themains, switch on and inhale strongly.No burning smell? So far so good!With a multimeter, check that you getplus and minus 15 volts at the correctpins of the IC sockets, and plus andminus 10 volts at the correct pins ofthe IC sockets, and plus and minus 10volts at the patch panel red and bluesockets, respectively. None of thesevoltages are critical, and the 10 voltsupplies may be a little out due to the'tolerance of the Zener diodes. If anyof these supplies are not presentcheck the AC voltage out of thetransformer. If this is present and youare getting good unregulated DC fromthe diodes, then check the ICregulators. Hope you didn't swapthem!

When all is well, patch from anyred socket into the meter socket andadjust the trimpot on the PCB for apositive full scale deflection. This setsthe meter to whatever voltage you getfrom the Zeners, and so eliminates theneed for an absolute 10 voltreference. For completeness, you canthen patch into a blue socket and seethat you get negative full scale deflec-tion.

Switch off, then, and plug in theop -amp (ICI) that is used for the sum-mer circuits. Patch up the circuitshown in Figure 1 1 , set RV1 fully an-ticlockwise and switch on. You shouldsee an increasing negative meterdeflection as you rotate the potclockwise, showing that the op -amp isinverting correctly. A mid -range set-ting on the pot should give a -5reading on the meter. Now patch intothe x10 input; the same thing shouldhappen, except that you can onlymove the pot about a tenth of itstravel before you get a full-scalereading. Test the other summers in thesame way.

Now for the integrators. Switchoff and plug in the second op -amp,IC2. Patch up the circuit shown inFigure 12, and make sure thekeyswitch is set to Reset.Switch on and check that operatingRV1 gives you a varying output on themeter; it should, in fact, behave justlike the summers. Re -turn the pot tozero and switch to Run. If RV2 is alsoat zero, nothing should happen but ifyou turn RV2 up a little, the voltageoutput will slowly move towardsnegative full scale. Turn RV2 to zeroand the ramp will stop. Now patch theinput of RV2 into the negativereference (blue socket) and repeat thetest; the voltage output should slowlyramp the other way. Switching thekeyswitch to Hold should stop theramp and hold the present value, whileswitching back to Run resumes the

Parts ListRESISTORS IC3 7815(All Y4 watt 5% carbon) + 1 5V regulatorR1-11, 20-27 1M IC4 7915R12-15, 28-39 100k - 1 5V regulatorR16-19, 40-43 10k BR1 .W01R44 47k bridge rectifierR45,46 470R

POTENTIOMETERS MISCELLANEOUSRV1 -6 10k SW1 DPDT

linear carbon 240V min. toggleRV7 50k SW2 lever switch

linear carbon trimpot (see Buylines)T1 20 -0 - 20

CAPACITORS 240V/3VA transformerCl -4 680n M1 meter

C352* polyester 50 -0 - 50uAC5,6 47u

25V axial electrolyticC7,8 22u

25V axial electrolytic*C352 series replaces C280

SEMICONDUCTORSIC 1 ,2 348

quad op -amp BUYLINES page 34

Case (Vero type 104 or similar); 6 xknobs; 2mm sockets (48 x white, 4x red, 5 x blue, 4 x black, 12 xgreen, 4 x yellow); 2 mm plugs (ap-prox. 301; PCB, wire, solder etc.

ramp. This test should be repeated forthe other integrators and be performedon each input. The speed of the rampwill be faster when you patch into thex10 inputs.

The last thing to check is the dif-ferentiator input on summer 3. Set upaccording to the patch diagram ofFigure 13. The output should be zerountil you move RV4. Any movementin the pot, ie. change in the inputvoltage, will cause a change in output,but as soon as you stop moving thepot, the output will return to zero. Apositive change in input will give anegative swing and a negative changewill produce a positive swing.

If all of the above tests work outas described, you now have a workingMicrolog. If they don't work, checkyour wiring very carefully, especiallythe wiring to the keyswitch. If that isOK, then check that the op -amps arefirmly inserted in their sockets. Thereis not much else that can be wrong!

Using MicrologAll being well, you are now the

proud owner of an HE Microlog, thesmallest analogue computer in thewest! So what do you do with it?Well, the best way to describe itscapabilities is to show some examplesof problem solving using it.

Earlier in this discussion wementioned using voltage as theanalogue of water level in a tank, solets use Microlog to solve that wellknown school problem: "How longwill it take to fill a bath if water isflowing in at X gallons per minute andflowing out at Y gallons per minute."Working this out at school, youassumed a constant inflow,(reasonable) and a constant outflow.However, with the wisdom ofadvancing years, you now know thatoutflow will actually depend on thehead (or level) of the water, so theproblem is not quite as simple as it


Project

Figure 11. Patch diagram for testing the summing amps.

Figure 13. Testing the differentiator.

Figure 12. The patch for testing the integrators.

Figure 16. Patching the bathtub.

first seemed. First, then, we shall lookat the filling problem with no outflowall all.

If we fill the bath from the tap theinflow will be a constant, 'K',determined by the setting of the tapand the water pressure. The quantitypoured in, 'di', during time interval 'dt'is:

di = K.dtNow the rise in level 'dh' for quantity'di' is:

dh = 1 /A.diwhere 'A' is the area of the bath.Rearranging to make 'di' the subjectwe get:

di = A.dhSubstituting this for 'di' andrearranging we get:

dh _ Kdt A

So now we have a differential equa-tion expressing the rise in level withtime. The value 'K' represents theamount by which the tap is turned onand the main water supply pressure.

Now about the emptying part; theamount of water that will flow out intime interval 'dt' we shall call 'do'.Therefore, 'do' will be equal to thehead 'h', multiplied by some constant'C', where 'C' takes into account thesize of the plug hole! Mathematicallythen:

do = C.h.dtIf the bath has a cross-sectionalarea of 'A' then the fall in head will beequal to:

dh = - 1 doA.

The sign is minus because the level isdropping. Rearranging we get:

do = - A.dhSubstituting we get:

K/A-h A.dh

or:= - C.h.dt

C/A .h

dhdt

-C. hA

Figure 14. Developing the bathtub cir-cuit.

Figure 15. The bathtub completed.

This, too, is a differential equationshowing the change of head withtime, but this time it is due to the bathemptying. Therefore, the change inlevel at any instant in time will be thesum of the filling and emptying. So,finally, we can write:

dh K -C. hdt A A

This is a differential equation of thetype that Microlog can solve withease; let's set up the circuit. First wewill need an integrator, so that if we

put 'dh/dt' in we will get ' - h' out(which is what we want. So, wehave to put voltage signals correspon-ding to the right hand side of ourequation into the integrator, and wewill then get out a voltage that will bethe analogue of the water level at anyinstant in time. The circuit, then, willlook like Figure 14. Notice that eachinput does in fact represent a term onthe right of our equation and that, asthe inputs are summed, the terms areadded, just as in the equation.

To complete the picture we haveto set the initial conditions of thesystem; in this case the initial condi-tion is the level of the bath waterbefore we start the filling and empty-ing process. We can set it to zero (anempty bath) or at any level up to full.The complete circuit is shown inFigure 15 and the Microlog patchdiagram is shown in Figure 16.

Now to run the program: first setMicrolog to Reset and adjust RV2 toset the water level to full. That will beminus full scale deflection of themeter. Ensure that RV1 and 3 areturned fully off, anticlockwise, andswitch to Run; the water level shouldremain constant. Now pull out theplug! You do that by turning up RV1;the value determines the size of theplug hole and thence the rate ofoutflow. Notice that the water level isdropping, as shown by the metermovement, and that the rate slowsdown as the bath empties. If we turnon the tap, RV3, you can fill the bath.Of course, the filling rate will have to


Projectbe greater than the emptying rate orthe level will slowly drop. It is in-teresting to start with an empty bathand start pouring water in. If the plugis open, the level will start to rise untilthe increased head causes the outflowto equal the inflow. At this point thelevel will remain constant. Turn downthe inflow rate a little and after awhile a new equilibrium level will befound. The time taken is the 'responsetime' of the system that we have justmodeled on our analogue computer!

So instead of doing lengthycalculations, or getting wet running anexperiment, Microlog has allowed youto set up an analogue of the systemunder test. You can try various set-tings for all the pots to see how theresult changes.

Let's look at another application.You may remember that integratingSINIX) gives -COS(X), and in-tegrating COSIX) gives -SINIX).

Again, this is a differential equa-tion of the type easily set up onMicrolog. Look at the circuit and patchdiagram in Figures 17 and 20. If youpatch this on Microlog, set the initialcondition of integrator 1 to 10 voltsand then switch to Run you will getout a sinewave or a 90 degree phaseshifted sine wave (COS). Using potsRV1 and 2, you can slow down thefrequency of oscillation (or by pat-ching into the x10 inputs of the in-tegrators you can speed it up). Thismakes quite a neat and simple verylow frequency sinewave oscillator.Due to the tiny leakage of thecapacitors and the small input currentsof the op -amps the amplitude willdecay eventually, but it will continueto oscillate for many minutes.

Loops and BumpsTwo areas in which analogue

computers are often used are those ofmodeling dynamic systems and servoloops. These two problems require thesolution of second order differentialequations of the type:

A d2x + Bdx +Cx =0c7t2- dt

Let's take the front suspension ofa car: what will happen if you hit alarge pothole in the road and yourshock absorbers are bad? Figure 19 isa simple representation of the type ofsystem we are going to model, andthe equation that describes theresponse of the system to a distur-bance (a pothole) is:MX + px + sx = 0where X = d2x and X = dx

dt2 dtMX is the inertial force due to the

mass of the car, DX is the viscousdamping force produced by the shockabsorber, and SX is the restoring forceof your front spring. X, of course, isthe displacement of the suspensionsystem, and we want to see howquickly this will be restored to theoriginal value.

To patch this on Microlog we firstrearrange the equation so the X is thesubject:

X= - DX -S XM M

Figure 17 (top left). The Sin X/Cos Xgenerator circuit.Figure 18 (top right). A model suspen-sion.Figure 19 (middle left). Suspension cir-cuitry.Figure 22 (middle right). Model of aclosed -loop servo system.

Figure 23 (right). Response curves of aclosed -loop servo.

SHOCK ABSORBER

DESIRED POSITION

CAR

SPRING

UNDERDAMPED

eV- CRITICALLY DAMPED

POTHOLE

OVER DAMPED

Integrating X gives X, and in-tegrating X gives X. These can thenbe summed according to the formulato give X. The circuit and patch areshown in Figures 19 and 21. Pot RV1is used to set'the D/X term and RV2determines S/X: Set them both toabout mid range. But if we drive alonga perfectly flat road the suspensionwill not move, so we have to simulatethe bump. This is done by setting aninitial condition into the integrators, toshow that the suspension has beendisplaced.

Turn Microlog to Reset and set RV4

to about mid value and RV3 to give- 50 on the meter - this is a mediumsized pothole! Now switch to Run andwatch the meter. It will return to zero(the original position) and then over-shoot, then reverse direction but over-shoot zero again, though not by somuch this time. Eventually, it will set-tle down to a smooth ride again. Tryplaying around with RV1 and RV2;reducing RV2 reduces the effec-tiveness of the shock absorber andyou will find the front end of your carbouncing up and down for the nextfew miles. Increase it, and it takes a


Project II

RE

00 0111111111

HE

DEE

RUN

1

000Figure 20. Sin X/Cos X patch.

0 00F R

©00Figure 21. Pothole patch.

long time to return to the level condi-tion again. If you increase RV1 youstiffen the spring. A high RV1 andRV2 setting simulates the rock hardsuspension of a sports car, while alow setting for both (especially P1)gives you the ride of a big AmericanCadillac!

A closed loop servo system, of thetype shown in Figure 22, also has asecond order differential equation todescribe its performance. In this case,instead of turning to the zero displace-ment position, the system must moveto the position corresponding to theinput signal Y.

Microlog can model this systemtoo, and in fact it is very similar to the

car suspension problem. To changethe patch to model the system shownin Figure 22, all you have to do is takethe output of RV3 from the initial con-dition input of the integrator and plugit into the free summing input; this potis now your position control. RV1 nowsets the gain of the feedback loop andRV2 the inertia of the system. SwitchMicrolog from Reset to Run and thenmove RV3 to a new position; themeter output will follow but over-shoot, and then come back. You candetermine the best response by play-ing with the gain and inertia of thesystem, and if you have anoscilloscope you can plot the responseand should be able to see the sort of

curves shown in Figure 23.These are just a few of the possi-

ble systems and problems that can besolved with an analogue computer.Microlog is not designed to produceaccurate numerical results; however, itcan give a good idea of how a systemwill function, and give you a feel foranalogue computing.

It can also be used to add signals,or the integrators can be set up togive you a very slow ramp. The dif-ferentiator input can be used tomeasure the slope of a ramp and itcan also be used to detect drift in acircuit, so Microlog can be quite auseful lab instrument as well!

Go on. Build one! HE

MODULES FOR SECURITY Et MEASUREMENTINTRUDER ALARM CONTROL UNIT

CA 1250This exciting new module offers all the possiblefeatures likely to be required when building anintruder alarm system. Whether used with only 1 or2 magnetic switches or in conjunction with severalultrasonic alarm modules or infra -red units. a reallyeffective system can be constructed at a fraction ofthe cost of comparable ready-made units. Suppliedwith a fully explanatory Data Sheet that makesinstallation straight forward. the module is fullytested and guaranteed.'available in kit form E16.95 VAT '

Built-in electronic siren drives 2 loud speakers Stabilised ouput voltage for external units Provides exit and entrance delays together 2 operating modes - full alarm/anti-tamper and

with fixed alarm time panic facility Battery back-up with trickle charging facility Screw connections for ease of installation Operates with magnetic switches. u/sonic or Separate relay contacts for switching external

I.R. units loads

Anti -tamper and panic facility Test loop facility

DIGITAL VOLTMETER MODULE DVM 314Fully built & tested

Positive Et negative voltage with an FSD of999mV which is easily extended

Requires only single supply 7-12V High overall accuracy - 0.1 % + 1 digit Large bright 0.43- LED displays Supplied with full applications data

With this fully built and calibrated module a wide range of accurate equipment such as multimeters.thermometers, battery indicators etc. can be constructed at a fraction of the cost of ready-made units. Fulldetails are supplied for extending the voltage range, measuring current, resistance and temperature.Fully guaranteed, the unit has been supplied to electricity authorities, Government departments. etc.

Temperature Measurement Kit DT.10 £2.25 + VATUsing the I.C. probe supplied, this kit provides a linear output oft0mV*C over the temperature rangefrom 10'C to + 100'C. The unit is ideal for use in conjunction with the DVM module providing anaccurate digital thermometer.

Power Supply PS.209 £4.95 + VATThis fully built mains power supply provides two stabilised isolated outputs of 9V. 250mA each. The unitis ideally suited for operating the DVM at Temperature Measurement module.

ULTRASONICALARMMODULEUS 4012Fully built8 tested

Adjustable rangefrom 5ft. to 25ft.

A reallyeffective fully built

module containing bothultrasonic transmitter and

receiver and circuitry for providingfalse alarm suppression. This module.

together with a suitable 1 2V power supplyand relay unit as shown, forms an effective

though inexpensive intruder alarm. Supplied withcomprehensive Data Sheet, it is easily mounted in a

wide range of enclosures. A ready -drilled case and necessaryhardware is available below.

Power Supply Et RelayUnits PS 4012 £4.25 + VAT

Provides a stabilised 12V output and relay with 3Acontacts. The unit is designed to operate one or twoof the above ultrasonic units. Fully built and tested.

Siren ModuleSL 157 £2.95 +VAT

Produces a loud and penetrating sliding tone operat-ing from 9-15V. Capable of driving 2 off 9 ohmspeakers to SPL of 1 10db at 2M.Contains an inhibit facility for use with shoplifting loops etc. or other break to activatecircuits

Add VAT & 50p post and packingto all orders.Shop hours 9.00 - 5.30 p.m.(Wed. 9.00 - 1.00 p.m.)Units on demonstration callerswelcome. S.A.E. with allenquiries. =..

Hardware KitHW 4012 £4.25 + VATA suitable ready -drilled case with the various mount-ing pillars, mains switch socket and nuts and bolts.Designed to house the ultrasonic alarm moduletogether with its power supply.Sue: 153mm x 120mm x 45mm.

* ACCESSORIES *3 -position Key Switch for use withCA 1250 supplied with 2 keys

Magnetic switch (with magnet)5" Horn speaker for use with CA1250and SL157

f 3 43

E 1 1 7

[4 95

RiSCOMP LiMiTEDDept: ETI/12,21 Duke Street,Princes Risborough, Bucks.Princes Risborough (084 44) 6326


COMING SOON TO . .

0

THE HE DIGITESTERA complete digital test system which will grow into a complete testing and breadboarding facility. The

series commences with the description of our Chip Probe, a simple logic tester that can also stand aloneas a handy test instrument.

SWITCHED MODE POWER SUPPLIESA complete explaination with a useful easy -to -build project included! A must for CBer's and other users

of mobile equipment.

CUMULATIVE INDEX, 1979 1982Not only the best, but the whole of Hobby Electronics indexed for you in one issue (we're hoping it will

cut down our mail!).

READER SURVEY, 1983Yes, folks, once again it's the time of the year when WE ask YOU the questions. Come on, tell us what

you think!

JFETS EXPLAINEDOften used in our projects, these devices are easily understood (which is why we use them).

Please reserve

o 0 0

forName

copies of the December issue of

Address

L J

-u-0 0 0 y

-ctroJanuary issue on sale at

your newsagentfrom 10th December .

Place your order now!

Although these articles are being prepared for the next issue, circumstances may after the final content.


Who but the people who made the micro possiblecould help you understand it?

The Texas InstrumentsElectronic Library.An in-depth series in understanding today's world of electronics.

The Understanding Electronics Series was speciallydeveloped and written to give you an in-depth knowledge of thisworld.

Each book is comprehensive, yet easy to understand. Asinformative for the electronics buff as for someone who's simplyinterested in what's going on today.

Together the library will give you the most complete rangeof titles available. Take advantage of our introductory offerand choose the book, or books you want from the titles belowYou'll find whole new worlds of advanced technology unfoldingbefore you.

Everything you've always wanted to know about:L Understanding Electronic Control of Energy Systems.1st edition. Ref LCB 6642. Covers motor, generator, power distribution,heating, air conditioning, internal combustion engine, solar and nuclearsystems. Softbound 272 pages. £3.95.

2. Understanding Electronic Security Systems.1st edition. Ref. LCB 7201. A complete guide covering the basics of hardwired, photosensitive, infrared, ultrasonic and microwave systems and theiruse in different applications. Softbound 128 pages. £3.95.

3. Understanding Solid State Electronics.3rd edition. Ref. LCC 3361. The principles of solid state theory. It explainselectrical movement, with intermediate tuition on the applications of solidstate devices. Softbound 282 pages. £3.95.

4. Understanding Digital Electronics. 1st edition. Ref. LCB 3311Describes digital electronics in easy -to -follow stages. It covers themain families of digital integrated circuits and data processing systems.Softbound 260 pages. £3.95.

5. Understanding Microprocessors. 1st edition. Ref. LCB 4023.An in-depth look at the magic of the solid state chip. What they are, whatthey db. Applications of 8 -bit and 16 -bit microprocessors; and designfrom idea to hardware. Softbound 288 pages. £3.95.

6. Understanding Computer Science. 1st edition. Ref .LCB 5471.This book tells you in everyday English how today's computer hasbeen developed, what goes on inside it, and how you tell it what to do.Softbound 278 pages. £3.95.

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8. Understanding Calculator Maths. 1st edition. Ref. LCB 3321Brings together the basic information - formulae, facts, and mathematicaltools -you need to "unlOck" the real power of the hand-held calculator.Softbound 230 pages. £3.95.

9. Understanding Optronics. 1st edition. Ref. LCB 5472.Optronics is the application of light and electronics to perform a widerange of useful- tasks. From car headlights to missile guidance systems.Softbound 270 pages. £3.95.

10. Understanding Automotive Electronics.1st edition. Ref. LCB 5771. Learn how electronics is being applied toautomobiles. How the basic mechanical, electrical and electronic functionsand the new microprocessors and microcomputers are being applied ininnovative ways for vehicle drive train control, motion control andinstrumentation. Softbound 288 pages. £3.95.

How to orderFill in the coupon below or if someone else has already used it, simply:1. List reference numbers and quantities required.2. Calculate total order value. Add £1.50 for postage and packing.3. Send the list, plus your cheque payable to Texas Instruments Ltd,PO Box 50, Market Harborough, Leicestershire.Allow 30 days for delivery.

TExAINSTRUMEsNTS

To: Texas Instruments Limited, PO Box 50, Market Harborough, LeicsPlease send me the following publications:

REFERENCE NO. QTY REFERENCE NO. QTY

I. 7.

2. 8.

3. 9.

4. 10.

5.

6.

Free title choice: Understanding

I enclose a cheque for £

Name

Company (if any)

Address

Registered office: Texas Instruments Ltd, Manton Lane, Bedford MK4I 7PA.

_11Registered nurnher: 574102 England. 1-11:

(9

I Project

Stereo NoiseGate

R.A. Penfold

Remove hiss and noise from your recordings!Mono or stereo, our noise gate

deals with both.

Stereo Noise GateNOISE is present in every electroniccircuit, and in audio circuits it results inthe all too familiar background "hiss".Although modern electronicscomponents have provided greatimprovements in noise performance inrecent years, noise in audio circuits canstill be very troublesome at times, andthere can sometimes be a build-up ofnoise which results in a poor signal-to-noise ratio when using certaincombinations of equipment. Re-recording material can also lead to abuild-up of noise.

Two useful ways of combattingaudio noise are to use either a noisegate or an expander. These two devicesare very similar, but there is a veryimportant distinction between them. Anoise gate is rather like an automaticswitch which normally allows the inputsignal to pass straight through, but cutsoff the output when noise only ispresent at the input. Noise is mostobtrusive during pauses in the mainsignal, and a noise gate can thereforegive a large subjective improvement inperformance.

An expander permits low levelsignals to pass normally but at mediumand high signal levels, it gives a

progressive boost to the processedsignal. Thus the noise level remains the

same but the maximum volume level isincreased; or, the noise level can bereduced with the maximum volumelevel remaining the same; or, a

combination of the two, as desired. Asimple volume expander was describedin the January 1982 issue of HobbyElectronics.

Whether a noise gate or an expanderis the best choice depends upon theparticular circumstances in which theequipment will be used and, to someextent, on personal preferences. Adisadvantage of an expander is that italters the dynamic levels of theprocessed signal, whereas a noise gatesimply cuts off the noise during breaksin the signal. A noise gate is thereforenormally preferable for use wherechanges in dynamic level areundesirable. However, a gate is likely tobe less satisfactory when the wantedsignal may, at times, be almost lost inthe noise, since it is then possible thatthe gate might cut off the signal. Anoise gate is of most use when there isa fairly strong noise level, but thewanted signal is usually significantlyabove this level.

The unit described here is a stereonoise gate, although by using only onechannel it can obviously be used inmono. Although expanders normallyprocess each stereo channel separately

it is preferable for a stereo gate circuitto switch the two channels in unison,as it can be rather disturbing if onechannel cuts out while the other is stillpresent! This circuit therefore switchesthe two channels on and offsimultaneously - see How It Works foran over -view of the system.

The CircuitThe full circuit diagram of the StereoNoise Gate is shown in Figure 1. It isbased on an LM1 3600N integratedcircuit, which is a dual operationaltransconductance amplifier. Anoperational transconductance amplifierhas features common with an ordinaryoperational amplifier, but there are alsoa number of important differences - atransconductance amplifier provides anoutput current (rather than an outputvoltage), governed by the differentialinput voltage, and it also has anadditional input which enables the gainof the amplifier to be controlled over awide range, from zero up to about 20dB. Note that a gain of less than one isequivalent to attenuation!

In order to make a transconductanceamplifier operate as a voltage amplifier,it is merely nec9f..:,, y to add a loadresistor at the output; R20 is the loadresistor for IC3a whit. R24 is the loadfor IC3b. The current flow into the


Project II

R6 R947k 4k7

5k6R8

D2 10k

i1300k

C2100n

R2 I+C15k6 100u

R141k2

7 SK2LEFT

OUTPUT0

NOTES:IC1 IS LF351IC2 IS CA140EIC3 IS LM1360001 IS BC109C01.04 ARE 1N4148

C910u

VV.R2515k

R213k9

Figure 1. Circuit diagram of the Stereo Noise Gate. Note that both channels are included.

R2212k

C104u7

R26390R

SK3RIGHT

1.1 INPUT

R29R23 R24 3k93906 10k

-0 +VSW1 (9V)

ON/OFF

C12100u

SK4RIGHT

OUTPUT

-vO(OV)

control input, rather than voltage,determines the gain of the amplifier.This is achieved by simply addingresistors (R15 and R25) in series witheach control input so that the currentflow is proportional to the appliedvoltage. Resistors R16 and R27 apply asmall bias current to the control inputs;this gives the _uit about -20 dB ofgain (ie, 20 dB attenuation) in the highattenuation mode, rather thancompletely cutting off the outputsignal, which usually gives moresatisfactory results. The circuit can bemade to operate as a true gate, ifpreferred, by simply omitting R16 andR27.

The LM13600N incorporates twoDarlington Pair output stages which areused as emitter follower buffer stages,to give the VCAs a low output

Figure 2. Pinconfiguration for theLM13600 dualtransconductanceop -amp.

DE LAY TIMERV2

N 0

A B C

RV1 THRESHOLD

Figure 3. Overlay diagram for the Noise Gate.

SK1LEFTINPUT

AMPBIAS DIODE

INPUT BIAS

16 15

INPUT INPUT- OUTPUT

14 3 12

.v

11

BUFFER BUFFERINPUT OUTPUT

10

AMP DIODEBIAS BIAS

INPUT

F G

SK2LEFT

OUTPUT

INPUT INPUT OUTPUT/ -

H I

SK 3RIGHTINPUT

-V BUFFER BUFFERINPUT OUTPUT

V (SVV11

-VrERv-)

SK4RIGHT


Projectimpedance. R21 and R29 are theiscrete load resistors for these stages.The LM13600N has 'linearizingdiodes', which enable a higher inputsignal level to be handled for a givendistortion level, and these diodes aregiven the appropriate bias by R17 andR28.

In order to operate as a voltagecontrolled amplifier, a trans -conductance amplifier must be usedopen loop lie, without any negativefeedback). R1, R2, and C1 form acentre tap on the supply rails and theinputs of the two transconductanceamplifiers IC3a, b, biased to thisvoltage by R18,19,23 and 26. R13and R22 are used to reduce the voltagegain through each section of the unit toabout unity (with a high controlvoltage), and also to boost the inputimpedance to a little over 12k.The mixer stage is a conventionaloperational amplifier, IC1, and gives avoltage gain of about 47. Thresholdcontrol RV1 is a volume control typeattenuator, and the output from this iscoupled to a high gain common emitteramplifier based on Q1; the combinedgain of Q1 and ICI is needed in order toboost weak input signals to a highenough level to drive the subsequentcircuitry.

The output of Q1 is coupled by C6 toa simple rectifier and smoothing circuit(D1, D2, C5 and R8) and RV2 controlsthe decay time of this circuit. Op -ampIC2 is used as a simple inverting triggercircuit, with positive feedback andhysteresis provided by R12;

'hysteresis' simply means that the inputvoltage at which the output triggers tothe high state is lower than that atwhich it triggers back to the low state.This prevents instability when the inputvoltaga is close to the switchingthreshold levels. D3 and R14 are usedat the output of the trigger to veryslightly slow the rise -time of the control

voltage, and to provide a slightly largerslowing of the fall -time. This prevents"clicks" from being introduced at theoutput as the gate changes state.

ConstructionAn aluminium and steel instrument casemeasuring about 152 x 114 x 44 mm isused to house this project - it is about

0 N

BATTERY +V(RED LEAD)

SW1

PCB PIN

SK4 SK3

JIGND) K(SIG) IIGND) H(SIG)

B C A

SK2 SK1

G(GND) F(SIG) D(GND) EISIG)

Figure 4. The internal wiring and connections inside the case of the Noise Gate.


Project the smallest case that could be used toaccommodate all the parts. The threecontrols are mounted on the front paneland four sockets are fitted on the rearpanel of the case.

Apart from the battery, all the othercomponents are mounted on the printedcircuit board, and this is detailed inFigure 3. As IC2 is a MOS device, itshould be fitted in an 8 pin DIL IC socketand the normal MOS handlingprecautions should be observed. UseVeropins where connections to off -board components will eventually bemade.

The completed board is mounted onthe base panel of the case using 6BAfixings, including 6.3 mm spacers tohold the connections on the undersideof the board clear of the metal case.The unit is then completed by addingthe point-to-point wiring, illustrated inFigure 4. Ordinary PVC coveredmultistrand connecting wire is usedhere; it is not necessary to use screenedleads.

In UseThe unit is intended for use with a highlevel signal and can take inputs of 2volts RMS or so without seriousdistortion occuring. The thresholdvoltage at which the gate switches tothe unity gain (zero attenuation) statecan be varied from about 1 mV RMS(with RV1 set fully clockwise) to about70 mV RMS. The best setting is likelyto be such that the noise signal alone isnot quite sufficient to trigger the circuitto the zero attenuation state, but it isworthwhile experimenting a little to find

the setting which gives the bestsubjective results.

The circuit will respond very rapidlyto an input signal (fast attack), but thedecay - the delay between thecessation of the main signal and thegate switching to the high attenuationstate - can be varied from less than a

tenth of a second to more than twoseconds. A fast decay time will oftengive best results, but it mightsometimes be found that the gate tendsto switch back and forth between thetwo states fairly rapidly; a slightlylonger decay time should eliminate thisproblem.

Parts ListRESISTORS(All 14 watt 5% carbon)R1,2 5k6R3,4 100kR5 4M7R6 47kR7,12 1M8R8,20,24 10kR9 4k7R10 470kR11 1M

12k1k2

R15,17,25,28 15kR16,27 220kR18,19,23,26 390RR21,29 3k9

R13,22R14

POTENTIOMETERSRV1 22k

log carbonRV2 1M

linear carbon

CAPACITORS (All axialelectrolytics unless noted)C1,12 100u 10VC2,3 100n

C280 polyester

C4,5,8 2u2 63VC6 1u 63VC7,10 4u7 63VC9,11 10u 25V

SEMICONDUCTORSIC 1 LF351

JFET op -ampIC2 3140E

MOSFET op -ampIC3 LM13600N

dual transconductance ampQ1 BC109C

silicon NPN transistorD1-4 1N4148

silicon signal diode

MISCELLANEOUSSK1-4 1/4" jack socket

standard metal chassis typeSW1 SPST

miniature toggle switchCase (see Buylines); PCB; 6BAnuts and bolts; Veropins; ICsockets; knobs (2); PP3 battery,clip, wire, solder etc.

BUYL INES page 34

THIS Noise Gate design is a stereo typewhich uses a separate VCA (voltagecontrolled amplifier) to process eachchannel. With a low control voltage,each VCA gives a substantial amount ofattenuation (about 20 dB - a 90%reduction in the signal voltage, in otherwords). A high control voltage givesunity gain (zero attenuation) througheach VCA and the input signal iseffectively allcwed to pass straightthrough.

Automatic switching - to zeroattenuation in the presence of a proper

LE FT 0INPUT

How It Worksinput signal but high attenuation withonly noise applied to the input - isachieved by first mixing the two inputsignals and then amplifying them. Theamplified signal is then applied to arectifier and smoothing circuit toproduce a DC output level proportionalto the strength of the combined inputsignals. this voltage is fed to a triggercircuit which has a high output voltageif the input voltage is above a certainthreshold level, and a low voltage if it isnot; this is the control voltage for theVCAs.

RIGHT 0INPUT

VCA

The circuit is adjusted so that withonly background noise present at theinput, the voltage fed to the triggercircuit is below the threshold voltageand the VCAs give a high attenuationlevel. With a high input signal, inaddition to noise, the input voltage tothe trigger circuit goes above thethreshold level and the VCAs 'open'producing zero attenuation. Thus therequired automatic attenuation of thenoise -only input signal is obtained.

0 LEFT OUTPUT

MIXER AMP

RECTIFIERTRIGGER

VCA 0 RIGHT OUTPUT

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Specially designed to let Grandad hear the telly clearly withoutannoying the rest of the household, it will also double -up as a

general-purpose bench amplifier.

ALTHOUGH we loved the old man andowed him a lot, Grandad was becominga pest with his complaints that hecouldn't hear the TV sound. For a whilewe did our best, though the volumewas painful, but something obviouslyhad to be done about it - if not forourselves, then certainly for the sake ofthe neighbours! Fortunately our TV setis a modern one, with two headphonesockets built in, so when we boughthim a pair of 'phones, we thought theproblem had been solved - but itwasn't long before he refused to wearthem because he didn't like the voices"inside his head" when they shouldhave been coming from the screen.Anyway they became too

80-

60-

40-

0 -

NOTE: OdB = 2 10-5Pa

SENSITIVEREGION

1."")

64 128 256 512 1024 2048 4096 8192

FREQUENCY (Hz)

Figure 1. The response curve for theaverage person's sense of hearing (afterFletcher and Muson).

uncomfortable for him, after an hour ortwo. Another solution had to be found.

Grandad wasn't really deaf; he didnot need a hearing aid, as he couldcarry on a normal conversation, but hedid find it difficult to followconversations on the telly. Strangely, itseemed to us, he preferred the soundfrom a small portable set to the onewith full range hi-fi reproduction.Indeed, several factors seemed to beinvolved, some of a general nature andsome peculiar to the elderly.

The diagram of Figure 1 shows theaverage frequency vs intensityresponse for an average person'shearing. Clearly, the energy required fora sound to be just audible varies greatly


Project

MIC IN

OV 0

C1100n

14V2

R1

33

R2

01

R3

15V

C34u7

ova At

1C23k3 10u

R41k

R5100k

2

PR1 c522k .100

ICI

7

14

7V4

C8100u 0-

7V8 Ie7100n

4u7

PINS 3,4,5, & 9,10,11,12,13 ARE ALL CONNECTED TO OV

15V2

NOTES.IC1 IS LM380Q1 IS 2N3819LED1 IS TIL211T1 IS 6V 10OrnA CT TRANSFORMERBR1 IS 1A 50V BRIDGE RECTIFIER

SWISPEAKER C9 ON/OFFOUT 1000u 0-0 L

LED1

0 E

Figure 2. The circuit; the input is high impedance adn wil accept any audio input of around10 to 50 mV.

Parts ListRESISTORS(All 1/4 watt 5% carbon)R1 330kR2,3 3k3R4,6 1kR5 100k

POTENTIOMETERSPR1 22k

miniature cermet preset

CAPACITORS(All radial electrolytic unless stated)C1,5,7 100n

disc ceramicC2,4 10u 16VC3,6 4u7 35VC8 100u 16VC9 1000u 25V

axial electrolytic

SEMICONDUCTORSIC 1 LM380

power amplifierQ1 2N3819

FET transistorBR1 50V1A

bridge rectifierLED1 TIL211

0.2" green LED

MISCELLANEOUSSW 1 SPST

mains toggle switchTi 6-0-6 1.2VACrystal microphone; centre -tappedtransformer; speaker (seeBuylinesl; Mains 'P' clip; mains leadand plug (2A fuse); case (seeBuylines); 1/4 " jack socket (plastic);LED bezel; PCB, wire, solder etc.

BUYLINES page 34

with frequency; very little soundenergy is needed if it is at the rightpitch, and the frequency range 2000Hz to 4000 Hz is where the averageear is most sensitive.

Anyone who has worked in longrange radio communication will knowthat restricting the audio bandwidth tobetween 500 Hz and 4000 Hz greatlyimproves the clarity of the transmission(especially in adverse atmosphericconditions), and this seems to indicatethat, for speech, most of the essentialinformation is contained in thatfrequency range.

Another factor, it seemed, was thatthe elderly find it difficult toconcentrate on more than one sound ata time. They are easily put off byunwanted 'noise' - this is as much todo with the way in which sound isinterpreted (psychoacoustics) as with

the sense of hearing. Hi-fi-qualitysound, with its extended frequencyrange, produces too much 'noise' atthe upper and lower limits of hearingwhich, for the elderly, masks theinformation in the mid -rangefrequencies. So, simply turning up theTV sound was not the solution becausethe unwanted frequencies are alsoboosted (this, also is why deaf aids arepersonally tailored to an individual'sfrequency response curve).

Grandad's SpecificationsSo, with these points in mind, we wereable to write a specification forGrandad's TV amplifier:

The output frequency must betailored to peak at about 2000 Hz,with little response below 500 Hz orabove 4000 Hz.

The output should be directional,so that it could be directed at Grandad,not at us!

The output level to be sufficient toallow it to be placed near the TVscreen, to give it realistic 'TV sound'.

The first step was to select a smallloudspeaker, which automaticallyrestricted the frequency response tothe specified limits and -also produced adegree of directivity. Unfortunately,the power available from a headphonesocket is not sufficient to drive aloudspeaker, so an amplifier had to bedesigned and constructed. A singleintegrated amplifier, the LM380,proved adequate for the job, especiallyas it needs very few externalcomponents.

The price of batteries being what itis (expensive!), a simple mains powersupply was built into the unit, togetherwith an on/off switch and a LEDpower -on indicator. Since most TV setsdo not have a headphone output, thecircuit was adapted for general use byincorporating a microphone input. Acrystal mic (use a short lead, becauseof its high impedance) is quiteadequate, or a more expensive electrettype can be used with a longer lead, ifnecessary. Dynamic microphonescontain a coil which will respond to thevarying magnetic field produced by thevideo scan, so they cannot be usedhere.


Project

SIG

GND-.

ACMAINS

TO SPEAKER

Figure 3. The PCB layout, viewed from the component side. Large areas of copper havebeen left to serve as a heatsink for the LM380 amplifier.

Grandad's CircuitThe microphone will give an output of afew tens of millivolts when placedfairly close to the loudspeaker with thevolume control set for normal listening,and this is fed via coupling capacitorC1 to a FET amplifier, Ql. Thisprovides the high impedance inputrequired for the microphone and avoltage gain of between five and six.

A 4u7 capacitor, C3, couples theoutput of the FET stage to the presetvolume control PR1, and C5 couplesthe signal to the inputs of ICI , theLM380 amplifier. This has an internallyfixed gain of 34 dB (50Vout/Vin), but itis reduced to 20Vout/Vin by using a'common mode' input, where part ofthe input voltage is coupled to theinverting input of the amplifier via the100k resistor, R5.

Capacitor C6, connected to thebypass pin (pin 1) of ICI de -couplesthe internal bias of the amp, preventingAC ripple on the output, while C7performs the same function on thesupply line.

The output is fed to the speaker viaC8; together, C8 and the speaker voicecoil impedance form a high pass filter,rolling off the response below 200 Hzwhen an 8R speaker is used. Thespeaker itself is the main factor inshaping the frequency response; bychoosing a small 4" diameter unit andmonting it in an unsealed box, most ofthe lower frequencies are attenuated,

while the mechanical properties of thecone ensure that frequencies aboveabout 4 kHz are also 'lost'.

Finally, the amp is powered from asimple DC supply derived from a6V/100mA centre -tapped transformerand a diode bridge; the ripple voltage isfiltered out by C9. LED 1 is included toprovide 'power -on' indication, with R6to limit the current through the LED.

ConstructionIn order to improve the stability of theamplifier (reducing the chance of itbecoming an oscillator), it is mountedon a PCB which has a very large area ofcopper. The unused pins of the IC aresoldered directly to these areas - donot use an IC socket in this project!This method also provides an effectiveheat sink.

The layout shown in Figure 3 isdesigned for a preset volume control tobe mounted on the PCB; should a full-sized pot be required as a front panelvolume control, leads must be takenfrom the PCB to the potentiometersolder tags. The choice of preset orvariable volume control is left to theconstructor - perhaps the solution,depends on how many "knob-twiddlers" there are in the house!

Grandad's TV Amp can be built intoany enclosure large enough to hold thecomponents, including the speaker.Our prototype was cased in a rather

classy custom-built box from NewradInstrument Cases Ltd (see Buylines forthe ordering details); this also has apre -drilled hole for a panel -mountedvolume control.

OperationThe problem with any microphone -amplifying system is the risk ofacoustic feedback, which will occurwhenever the mic is picking up soundfrom the loudspeaker. Steps must betaken to prevent this from happening!

First, the best position for the TVAmp is on the floor, or on a low table infront of the TV set, so that the sound iscoming from the same direction.Second, the mic should be placed asclose to the TV speaker as possible,but without actually touching it. Then,the preset or volume control must beadjusted so that, at normal listeninglevels, there is no trace of whistling or"howl round" from the TV Amp.

In most cases, this arrangement willbe quite satisfactory though for verydeaf people, it may be necessary toplace the Amp closer to the listener andto use a longer mic lead. If such is thecase, a crystal microphone should notbe used with a lead longer than aboutthree feet.

HEHobby Electronics, December 1982 27

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Now you can enter the exciting new world of computerswith this easy to understand system.FX-801P Casio's latest masterpiece. A high speed computerwith integral micro -cassette data control and hard copyprinter monitoring £349FX-700P NEW scientific OWERTY computer £79.95FX-702P The established favourite £79.95SHARP PC -1500 BUSINESS COMPUTER £169.95

SCIENTIFIC CALCULATORS

Dims: 19 x 76.5 x 149mmFX-7 8d, 231, (1311 £9.95FX-100 10d, 42f, SD, R/P, 11611

£14.95

Wallet sizeFX-550 10d, 48f, SD, R/P, 1160

£15.96FX-900 8d, 41f, SD, R/P, 111511, bSOLAR £17.95FX£950 10d, 49f, SD, R/P, 111511,H, b SOLAR f19.96

FX-8100 8 + 2d, 46f, SD, R /P, 1(511, H, b 1 year. Clock,calendar, 1/100 stopwatch, alarm, hourly chimes and 2countdown alarms. Wallet size £19.95

PROGRAMMABLE SCIENTIFICSWallet size, with wallet. Non volatile memory

FX-3600P 10 + 2d, 50f, SD, R/P, 11181), Integrals, Regres-sion. 2 program areas, 38 program steps, 7 memories £22.95FX-602P Plus FREE Program Pack worth £9.95 £69.9510 + 2d, 50f, SD, R/P, 113311. 10 program areas, up to 512steps, up to 88 memories. Alpha/numeric.

SINCLAIR SPECTRUM SOFTWAREProfessional quality software from MiCROL

USE AND LEARN Vol. 1 25 BASIC PROGRAMS oncassette tape plus SUPERB 100 PAGE BOOK £9.95USE AND LEARN Vol. 2 30 MACHINE CODE ROUTINES.On tape plus 50 PAGE BOOK £9.95THE DATABASE The best? 48K only £9.95THE SPREADSHEET The best? 48K only £9.95

BE AN AGENTSell our products to your friends

and family and earn yourself10% commission

r- EN INN SIN NM - In MI =I - =I =I IMO

TEMPUS, 38 Burleigh Street, CAMBRIDGE CB1 1DGPlease supply/send details of

IPrice includes VAT, P&P. Delivery normally by return, sub- iject to availability. Send cheques, PO, or phone your AC-

CESS/VISA number to:

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IHobby Electronics, December 1982 29

YOUR GUIDE 70 THE WORLDOF MICROPROCESSORS

MICRO PROFESSORA low cost tool for learning,teaching & prototyping.

Micro -Professor is a low-costZ80 based microcomputer whichprovides you with an interesting andinexpensive way to understand theworld of microprocessors.

Micro -Professor is a completehardware and software systemwhose extensive teaching manualgives you detailed schematics andexamples of programme code. Asuperb learning tool for students,hobbyists and microprocessorenthusiasts, as well as an excellentteaching aid for instructors ofelectrical engineering and computerscience courses.

The Micro -Professor is muchmore than a teaching device. Use itfor bread boarding and prototyping,designing your own customhardware and software applicationswith Z80, 8080 and 8085 compatiblecode.

The standard 2K bytes of RAM isexpandable to 4K, and the standard2K bytes of ROM can be increasedto 8K.

All this plus built-in speaker, acassette interface, and sockets toaccept optional CTC/PIO. Bus isextendable.

As well as being an excitinglearning tool, the Micro -Professoris a great low-cost board for OEM's.

VII.:NORM:

NOONN OON OOOOOO

1611111:::

IF SFrgm:

Flight Electronics Ltd.

Micro -Professor

7995EPB-MPF EPROMProgramming Board£84.95 + p&pFor all + 5V KP/21<8/4KBPROMS Read/Copy/List/

Verify Capability.

SSB-MPF SpeechSynthesizer Board£69.95 + p&pA vocabulary of up to 400words based on the TMS5200 chip.

PRT-MPF PrinterBoard £74.75 + p&pMemory dumpBASIC program LongZ80 disassembler

Micro -Professor is a trade mark of Multitech Industrial Corporation.Z80 is a trade mark of Zilog

Complete the coupon today! Please allow 28 days for delivery.

Please send me Price Oty p&pMicro -Professor E79.95 £2.95

SSB-MPF board £69.95 £2.95

EPB-MPF board £84.95 £2.95PRT MPF board £74.75 £2.95

Total

I enclose cheque/P.O. for £

,5af_ Mail order only Trade enquiries welcome Bulk order discounts Prices include VAT

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Feel like sounding off?Then write to the Editor stating your Point Of View!

New Devices for Old EffectsDear Sir,With regard to your Fuzz -Box project inthe February '82 HE, please could youinform me where I can obtain theBC650 transistors, as I have beenunable to find them listed in anycatalogue.Graham Walsh,Pudsey.

When the Noiseless Fuzz -box wasdesigned, the BC650 transisitor hadonly recently come on to theconstructors' market. Consequently itwas difficult to obtain (one source was,and still is, Magenta) and we had to doa lot of leg -work to seek out suitablesuppliers. Now, however, it has provedto be quite popular and should beavailable from the larger semiconductorstockists. Incidentally, it does no harmto ask about a component that doesn'tappear in a given advertiser's list. Oncethe enquiries start flooding in, mostcompanies will obtain stocks from thedistributors.

Echoes On The LineDear Sir,I tried to 'phone you for clarification ofthe HE Echo-Reverb (May '82, pages33-37) but apparently you are nolonger on the phone (why not pay thebill?). Two points: the circuit and layoutdiffer for the diodes, and the circuit andParts List differ on the value of R15.Are there any other discrepancies?

Do pay the phone bill - it's such along wait by Post Office NonCommunications system.H. W. Fletcher,Marlow Bottom,Bucks.

The HE Gremlins chose our Echo-Reverb unit for their piece de resistance- and they really did a job on it. Thefull list of errors are given in the reply tothe following letter. Our apologies to allconcerned; the Gremlins have beendealt with!

Our phone bill has been paid, but itwon't help you - we cannot takeenquiries and produce a magazineevery month, and if we didn't producethe magazine, you'd have nothing toenquire about, would you?

Designer on the DoleDear Sir,For an eight month old dole freak likemyself, the HE Echo-Reverb met a veryreal need.

Some months ago I had scraped upthe pennies and lashed out on two

TDA 1022 ICs with a view to designingmy own phaser/flanger/chorus/echo/reverb. Needless to say I found myselfhopelessly out of my depth (even withthe Mullard spec sheet to hand)! To cuta long story short, my courage hasbeen rewarded by the appearance ofyour design (heaven-sent!).

Thanks! I now hope to proceed with:switchable clock timing capacitors forphase/flange/chorus/echo and possiblya sine -wave modulator for the VCOinput of the 4046 clock. (I fear a saw -tooth oscillator would be prone tospikes and hence 'clicks' in the output.

Please keep up the cost pruning!Thanks again.D.P. Allen,Wembley,Middlesex.

The Echo-Reverb (HE May '82) hasbeen one of our more popular projects.For a modest outlay and with carefulsetting -up, the unit will producevarying degrees of reverberation andecho. However, as with some otherprojects of this standard, a few errorscrept into the printed article. So, to allreaders who've had a few problems,here's the list - exhausative, we hope!p. 34 Figure 1. RV2 wiper comes

from pin 9 of IC 1.D2 is showninverted (ie. cathodegoes to OV).

p. 36 Figure 2. The end tags ofRV2 are connectedto +15 and OVsupply rails.Transformer shouldbe 9-0-9 V.

p. 37 Parts List RV1 should be 47Klog.RV4 should be 22Klog.The transformershould be 9-0-9 V.R1 5 should be 27K.

A Better Building BlockDear Sir,I enjoyed the series of articles IntoElectronic Components. As a nowregular reader of your magazine,however, I must say the mostinteresting and informative articles todate are the "Building Blocks" - Iwould appreciate more of the same.Detailed information on ICs, etc. is ofgreat value, too.A. Easom (G40P1),Scarborough,N. Yorkshire.

We are pleased that you appreciate theBuilding Blocks series. A great deal ofwork goes into researching the

information and presenting it in a formthat is easy to understand. However,details of applications for ICs andgeneral constructional info can also befound in our How It Works sections,and Breadboard pages. And in thisissue we start a special Building Blocksseries on ICs used in mirocomputers,called Components for Computing.

A Better Class of MeterDear Sir,Having read copies of variouselectronic magazines, may I say thatyours is very enjoyable and you can besure that I will buy HE every month infuture.

Is it possible to construct avoltmeter of range 0-16 V DC with adigital LED seven segment display,calibrated to read to a tenth of a volt?

If so I would be grateful if you couldsupply me with any relevantinformation including circuit diagrams,etc.Paul Humphries,Newcastle upon Tyne,Co. Durham.

Thanks for the compliment, althoughwe'll answer your questions (usually)even if you're rude about us! It's notonly possible to build this voltmeter,but we have just done one in theAugust '82 issue, and with a betterspecification, at that.

A Little IngenuityDear Sir,In the Three -Aspect Signal Lightsproject (September '82) you suggestfitting micros witches to the points toobtain the required switching. Thosemodellers who have PECO points canuse the PECO "accessory switch".This clips to the point motor (if fitted). Isee no reason why this neat unitcannot be fitted to other makes ofpoints, with a little ingenuity. I thinkthis project has been one of your bestyet. It would be ideal for large clublayouts where there is more than oneoperator.Yours in electronics.M. Wilkins,Ipswich,Suffolk.

A double thanks to Mr. Wilkins; first forthe comments and second for theinformation on accessory switches. Weare always happy to pass on tips fromreaders who can provide extra infoabout any of our projects! Thanks too,to Dr. D.L.H. Bloomfield, who designedthat model project, but who was notproperly credited in the article. HE


ELECTRONIC IGNITIONMakes a good car better

TOTAL ENERGY DISCHARGE electronicignition gives all the well known advantages of the best capacitivedischarge systems.

PEAK PERFORMANCE higher output voltage under allconditions.

IMPROVED ECONOMY no loss of ignition performancebetween services.

FIRES FOULED SPARK PLUGS no other system can better thecapacitive discharge system's ability to fire fouled plugs.

ACCURATE TIMING prevents contact wear and arcingby reducing load to a few volts and a fraction of an amp.

SMOOTH PERFORMANCE - immune to contact bounce andsimilar effects which can cause loss of power and roughness.

PLUSSUPER POWER SPARK 3% times the energy of ordinary

capacitive systems - 3Y2 times the power of inductive systems.

OPTIMUM SPARK DURATION 3 times the duration of ordinarycapacitive systems - essential for use on modern cars with weak fuelmixtures.

BETTER STARTING full spark power even with lowbattery.

CORRECT SPARK POLARITY unlike most ordinary C.D. systemsthe correct output polarity is maintained to avoid increased stress on theH.T. system and operate all voltage triggered tachometers.

L.E.D. STATIC TIMING LIGHT for accurate setting of the engine'smost important adjustment.

LOW RADIO INTERFERENCE fully suppressed supply and absenceof inverter 'spikes' on the output reduces interference to a minimal level.

DESIGNED IN RELIABILITY an inherently more reliable circuitcombined with top quality components - plus the 'ultimate insurance'of a changeover switch to revert instantly back to standard ignition.

IN KIT FORM it provides a top performanceelectronic ignition system at less than half the price of competing ready -built systems. The kit includes everything needed, even a length of solderand a tiny tube of heatsink compound. Detailed easy -to -follow instructions,complete with circuit diagram, are provided - all you need is a smallsoldering iron and a few basic tools.

AS REVIEWED INELECTRONICS TODAY INTERNATIONAL June '81 Issueand EVERYDAY ELECTRONICS December '81 Issue

FITS ALL NEGATIVE EARTH VEHICLES,6 or 12 volt , with or without ballast

OPERATES ALL VOLTAGE IMPULSE TACHOMETERSSome older current impulse types (Smiths pre '74) require an adaptor -PRICE £2.95

STANDARD CAR KIT £15.90Assembled and Tested £26.70

TWIN OUTPUT KIT £24.55For MOTOR CYCLES and CARS with twin ignition systems

Assembled and Tested .f36.45

ELECTRONIZE DESIGNDept. E, Magnus Road, Wilnecote

Tamworth, B77 5BYPhone: (0827) 281000

PLUS£1.00U.K.P. & P.PricesIncludeVAT.

' VISA

DIMENSIONS: Length 12.5 cmWidth 8.9 cmHeight 4.3 cmLead length 100.0 cm

TECHNICAL DETAILSThe basic function of a spark ignition system is often lost among claimsfor longer 'burn times' and other marketing fantasies. It is only necessaryto consider that, even in a small engine, the burning fuel releases over5000 times the energy of the spark, to realise that the spark is only atrigger for the combustion. Once the fuel is ignited the spark is insignificantand has no effect on the rate of combustion. The essential function of thespark is to start that combustion as quickly as possible and that requiresa high power spark.

The traditional capacitive discharge system has this high power sparkbut, due to it's very short spark duration and consequential low sparkenergy, is incompatible with the weak air/fuel mixtures used in moderncars. Because of this most manufacturers have abandoned capacitivedischarge in favour of the cheaper inductive system with it's low powerbut very long duration spark which guarantees that sooner or later the fuelwill ignite. However, a spark lasting 2000pS at 2000 rev/min. spans 24degrees and 'later' could mean the actual fuel ignition point is retardedby this amount.

The solution is a very high power, medium duration, spark generated bythe TOTAL ENERGY DISCHARGE system. This gives ignition of theweakest mixtures with the minimum of timing delay and variation for asmooth efficient engine.

SUPER POWER DISCHARGE CIRCUIT A brand new techniqueprevents energy being reflected back to the storage capacitor, giving 3%times the spark energy and 3 times the spark duration of ordinary C.D.systems, generating a spark powerful enough to cause rapid ignition ofeven the weakest fuel mixtures without the ignition delay associated withlower power 'long burn' inductive systems.

HIGH EFFICIENCY INVERTER A high power, regulated inverterprovides a 370 volt energy source - powerful enough to store twice theenergy of other designs and regulated to provide sufficient output evenwith a battery down to 4 volts.

PRECISION SPARK TIMING CIRCUIT This circuit removes allunwanted signals caused by contact volt drop, contact shuffle, contactbounce, and external transients which, in many designs, can cause timingerrors or damaging un-timed sparks. Only at the correct and precisecontact opening is a spark produced. Contact wear is almost eliminatedby reducing the contact breaker current to a low level - jat sufficient tokeep the contacts clean.

TYPICAL SPECIFICATION

SPARK POWER (PEAK)

SPARK ENERGY(STORED ENERGY)

SPARK DURATION

OUTPUT VOLTAGE (LOAD 50pFEQUIVALENT TO CLEAN PLUGS)

OUTPUT VOLTAGE (LOAD 50pF + 500 KOEQUIVALENT TO DIRTY PLUGS)

VOLTAGE RISE TIME TO 20 KV(Load 50pF)

TOTAL ORDINARYENERGY CAPACITIVE

DISCHARGE DISCHARGE

140 W 90 W

36 mJ 10 mJ135 mJ 65 mJ

500 pS 160 pS

38 KV 26 KV

26 KV 17 KV

25 pS 30 NS

TOTAL ENERGY DISCHARGE should not be confused with low powerinductive systems or hybrid so called reactive systems.

32

Famous Names

Jean BaudotIan Sinclair

BAUDOT - the name might ring a fewbells if you are into computing: drop thelast two letters and you get baud, whichis a unit for the speed of transfer of infor-mation. The old-fashioned teleprinter,for example, operates at a rate of 110baud, but a modern cathode-ray terminalmay work at 2400 baud or higher. Hav-ing established the connection, let's lookat the story of J. M. E. Baudot.

Jean Baudot was born in 1845 atMagneaux in France, and you will searchin vain for details of his early life, unlessyou are prepared to look through a fairlylarge library. You won't find his namementioned, often; it's the usual problem- a brilliant engineer whose name hasentered our language hardly gets a men-tion, even in his own country.

He seems to have had the conven-tional schooling of the French middleclasses at the time, which was, inciden-tally, one of considerable social unrest,with minor revolutions breaking out allover Europe. His firm interest, from thetime that he left school, was the growingtechnology of the electric telegraph, andit was to this that he turned his attentionwhen the time came to earn his own liv-ing.

Dots and DashesIn these early days, the universal codefor telegraph use was Morse code,which relies on the use of two types ofelectric impulse, a long (dash) and ashort (dot) - the form of the code isshown in Figure 1. Now there is nothingwrong with this as a code, and it is used,to a limited extent, to this day, but it wasdevised in 1832, long before electricalcommunications began to evolve intothe systems that were beginning to becommonly used in the 1870s. Baudot, inparticular, thought that the use of Morsecode was very restricting. In 1874, hewas working on the development ofwhat we now call time -multiplextelegraphy, which allowed one telegraphline to carry several sets of messagesbetween different sets of transmittersand receivers, with no interference bet-ween the signals. The system that hewas working with was a completelymechanical one; each signal source wasconnected to a separate contact of agroup arranged in a circle, over which arevolving contact, like the brush of adynamo, revolved at high speed, con-necting each contact in turn to the singletelegraph line. The current return wasthrough the earth, which is why we usethe term "earth" to mean current returnpath to this day. At the receiving end, asimilar arrangement was used to con-nect the signals from the telegraph line tothe different receivers but obviously, thesytem could operate correctly only if themotors driving the rotating contactswere synchronised.

Another of the problems of using this

system with Morse code was that eachdash was liable to be broken up, by theaction of the rotating brush, into a seriesof dots, on different channels; unless thespeed of the brush was varied, so that itspent more time on a contact transmit-ting a dash than on one transmitting adot, it inevitably scrambled themessage. Many other people, at thetime, were trying to synchronise themovement of the rotating brushes to thevarying dots and dashes of Morse code,but Baudot came up with a completelydifferent answer.

DOT

(KEY TAPPED)

DASH

(KEY HELD DOWNFOR THREE TIMES

AS LONG AS THE DOT)

A=B= c=D=

Figure 1. International Morse Code. Thelength of the pulse determines themeaning - dot or dash.

MORSEKEY

47

TO OTHER MORSE KEYS

EARTHRETURN

TRANSMITLINE

Figure 2. Early multiplex telegraphy.

THE PULSES ARE OF THE SAMErLENGTH, BIPOLAR (+VE AND -VE)

1 0

MONOPOLAR PULSE

1 1i1 01 1

01

0 11

1* AND 0)

A 0 0 0B 0 0 C 0 0 ZERO OR -VE

0 0 0 0 MARK OR *VE

z 0 0 0 ,Figure 3. The modern 5 -bit code. Thebipolar version (top) is preferred becausethe difference between signal levels iseasier to detect. This signal laterbecame standardised as RS232.

A name to ringbells with.

Digital CodesHis approach was to use an entirely dif-ferent code, one which used what wewould now call digital signals - on andoff - as distinct from the Morse codesignals of 'long' and 'short'. The important point about Baudot's signals wasthat they were separated by equal timeintervals. For example, if we take thetwo Morse signals, R (. - .) and S( . ), the time between the first andlast dots of each letter is not the same,because the middle dash of the R takesabout three times as long as the middledot of the S. Baudot devised a new5 -digit code, using pulses and spaces ofequal length, so that the time needed totransmit a five -character message wasalways the same. This was thebreakthrough that multiplex systemsneeded because the speed of therotating contact (commutator) couldnow be synchronised to the pulse rate ofthe code.

Baudot patented his five -unit code in1874. Five digits gave a choice of 32characters, so that the early Baudotcodes allowed the transmission of theletters of the alphabet (upper case) plus afew punctuation marks and operatorsignals (eg, BELL), but no digits. A laterversion of the code used seven digits andit is this version which has evolved intothe ASCII seven -bit code that is usedalmost universally in computers.

The Baudot code was a major stepforward in telegraphy because, as wellas permitting more efficient multiplex-ing,it also permitted the faster develop-ment of the logical accompaniment tomultiplexing - mechanical methods ofsending and receiving telegraph signals.

The transmitter was primitive - if theoperator released the key too soon, thewrong character would be sent - but itwas a step forward from manualtransmission. It was soon superseded byother methods.

Baudot's equally ingenious receiverused a method that was to remain cur-rent right up to the time when fully elec-tronic printers were developed. It canstill be seen, with some modern im-provements, in some Telex terminals. Itall looks like a mechanical nightmare -and anyone who has tried to get an old-style teleprinter going will agree that it is.Baudot's work vastly improved the rateat which data could be transmitted, andthe principles which he established are inuse to this day, although the methodshave changed - for the better! Baudotcode was not entirely logical and it wasimproved by Don Murray in 1903, sothat the modern 5 -bit code and its 7 -bitsuccessor are often known as Murray -codes rather than Baudot codes. Theprinciples, nevertheless, are those ofBaudot, and a good reason for immor-talising his name in the term "baudrate".


mo-isinstror 14ANNOUNCING THE NEW MAIL ORDER DIVISION OF THEGRENSON GROUP. VAST STOCKS AND COMPUTER CONTROLLEDOPERATION HAVE ASSURED VERY COMPETITIVE PRICES.SEE FOR YOURSELF!

BENCH POWER SUPPLIESAs featured in Feb 82 'Practical Electronics'.

KIT BUILTUnit 113PU1 I £35 £59P x P £3.35 £3.35V.A.T. £5.75 £9.35

Triple output unit (1 ± 15V and +5V) available shortly.

The Grenson Group have over twenty years experience designing power supplies.Contact us now and we will try to solve your problem.

LARGE ELECTROLYTICS.Sprague/General Electric made - computer grade - ideal for power supplies - ONLY£2.50 EACH!

185,000 @ 15V,300,000 @ 7V, 120,000 @ 15V,100,000 @ 30V,71,000 @ 40V, 60,000 @ 40V, 9,000 @ 50V

SMALL ALUMINIUM ELECTROLYTICS.Axial Leads. Radial LeadsuF V Price uF V Price uF V Price1000 6.3 15p 470 16 15p 470 16 15p

22 10 05p 4.7 25 05p 1000 25 25p

100 10 05p 330 25 15p 220 40 25p22 16 05p 680 25 25p 470 40 25p

OLD TIMERS SECTION.0C44 70p 0C45 37p0C35 90p 0C25 75p

2S02400840083

200p25p40p

0C1390C41OAS

70p60p10p

0071 34p OC70OC16 200p 0C170(antique!)0C140 75p 2S3072S301 80p 00760A7 15p 0A10

uF V Price47 50 10p

4.7 63 05p100 63 15p27.0 63 20p

36p 0C42 70p44p 0C22 150p

85p 2STO1 80p40p 0073 40p15p 0A47 10p

MIXED BAGS.CAPACITORS - 30 ASSORTED VALUES ONLY f1.00!

TRANSISTORS - 20 SMALL SIGNAL PLASTIC - n.p.n. - 1 p.n.p. ONLY f1.50.

LISTS AVAILABLE ON REQUEST.

RESISTORS.We have, amongst others, the following resistors in stock: -Over 11 million 1 watt carbon film.Over-; million watt metal oxide.Over million wirewound.Further stock listed in our free catalogue.

Typical Prices.

watt carbon1 watt metal oxide6 watt wirewound

SERIES 74 I.C.'sComprehensive stocks, competitively priced.Simple gates from only 10p.See our free catalogue for details.

1-92p6p25p

I.C. SOCKETS14 way - 10p.46 way - could be broken to make smaller strips - 25p.16 way - gold pins - 20p.

TRANSISTORS.AC107 30p AC126BC149 7p BC159BC212L 9p BC213LBC337 13p BC558BF198 13p BF1992N706 15p 2N11312N3702 10p 2N37052N5172 15p 2N5179

30p12p9p

14p15p20p10p30p

10-99 100 +-

11p 1p4p 3p15p 12p

AC188 27p ACY17 66p ACY19 65pBC171 10p BC173 10p BC212BC237 12p BC308 13p BC327 18pBF115 29p BF194 13p BF197 13pBFR40 20p BFX29 25p BFY90 60p2N1132 20p 2N2222A 20p 2N2369A 15p2N3711 10p 2N3904 15p 2N4061 10p

VOLTAGE REGULATORS AND P.S.U. COMPONENTS+ 5V 1A TO220 50p 12V lA TO220+ 5V 1 5A TO3 1.50p 12V 1 5A TO3- 5V 1A TO220 .50p +15V 1A TO220- 5V 1.5 TO3 2.00p + 15V 0.5A TO3+ 6V 0.5A TO220 .50p -15V 1A TO220+12V 0.5A TO220 .50p - 18V 1A TO220+ 12V 0.5A TO3 .90p - 24V 1 A TO220+ 12V 1.5A TO3 1.50p

2N3055 .35p, 2N4347 (120V) 1.50p, 2N6258 1250W) 1.80p, 400 mW Zeners .05p723 .30p

* SPECIAL OFFER * SPECIAL OFFER * SPECIAL OFFER *For every order received in December 1982 of a value greater than ft 0.00, a free bag of assortedcomponents worth at least f2.00 will be sent with the order. Please allow 21 days for delivery.

.50p2.00p.50p.90p.50p.50p.80p

Dept. Cl High March, Daventry, Northants NN114HQ.Tel: 03272 5523 Telex: 311245 GRENEL G.

Please add 50p per order postage and packing plus 150/o VAT on total. No VAT onoverseas orders, postage at cost. Cheques and -

postal orders made payable to EmosLimited. Send large SAE for comprehensivecatalogue.

111111111111

HE MicrologOur prototype was built into a standardVerocase, code 65-2523E, howeverbecause of the amount of drilling andmarking involved, we had a chat withNewrad Instrument Cases, who have de-signed a suitable case for the Microlog.It is available from them (their addressis printed elsewhere in this column)for £7.90 including VAT, p&p, com-plete with screen printed front paneland all holes drilled and punched.The lever switch is a Post Office type1000.

Tape/Slide SynchronizerThere should be no problem obtainingthe parts for this project; just rememberthat the relay is a 12V, 2 -pole submini-ature (ie PCB mounting) type, andchoose the jack sockets to fit yoursound system.Phase FourIf your local supplier does not stock theTL064, it is always available fromTech-nomatic, who also stock the 2N5457FETs; a TL084 can be substituted forthe TL064, if you are willing to acceptincreased battery usage. Once again, thecustom case for our prototype wasmade by Newrad Instruments (see else-where in this column for their address).Intruder AlarmAll the components contained on thePCB should be easy to obtain. Theremainder will vary in availabilityaccording to the sort of system youenvisage. However as a guide, suitablesirens can be bought from Greenweld.

A source for most of the otherswitches, mats and foils etc is Maplin.Stereo Noise GateMost of the components are readilyavailable and you should be able to getthe thing working within a few hours.

The low voltage electrolytic is soldby Greenweld, who also stock a rangeof suitable cases. Other sources for acase are Lightning and West Hyde.

Big Ear

A complete list of parts for this projectis available from Bewbush Audio, 26Hastings Road, Pound Hill, Crawley,Sussex. The cost of the kit is £15.00,including VAT, post and packaging.TV AmpNewrad Instrument Caseshave produced a case for our proto-type, as shown in the photograph; thisis available for £5.00, plus posage. New-rad Instrument Cases are at Tiptoe Rd.,Wootton, New Milton, Hants BH255SJ.


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by7422 2407423 lip7425 lip7426 01p7427 lb7428 lip7430 1447432 lb7433 2407437 7247438 2247440 1114

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2214 75GUIC 2004LM3231 3A 5V 5004 79HGU1C 235pLM723 150.4 Ad, 374 79HGKC 703411.454 3004 11497 100p713540 225p 11,4306.01 2504

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. 554101=11L El 74 1304MC 126 1004MCS24 0 0 1904MOC302 0 1504

074 240P11111704T1

7/L12 MP711..13 704TIL 116 704

LEDs

- BOOKS (No VAT p&p £1)CMOS Cook Book £7.75CRT Controller H/Book £5.95

the Z80 £11.50Z80 Microcomp. handbook f 6.95Programming the 6502 £10.256502 Assy. Lang. £12.106502 Applications £10.206502 Software Design £9.056502 Games f 10.52

LM3302 7091613900 504

TRANSISTORSDIODES

1413909 OSP1413911 125p1413914 23%1.3915 2004LM3916 226p154131300 11%44515131. 300p44515101 50046.163712 ;noM53730 400441013104 190496C1446 2029MC1468 VPMC14961. 9304MC1496 70pMC3 3 40P 1209MC3403 854MF 1 0 2600MK503 9 8 63541.41920 MP14951160 620441652710 400173531 140

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vim11132 564111209 Red so111211 Gr lb11121270 144T11216160 lip

Large selection of databooks, inter -facingbooks, books on BBC, etc in stock. As for

Our list.-- - -02-111200 Red 104111272 Gr 12pis02. 0 ,ap

1.%.7.G7rr, 3045585031 570,T1L311 11034

TIL63;.2 lgrpT1L330 14047753/60 2004

All mating Connectors withCables in stock. Full range

of Acornsoft,PROGRAM POWER &

BUGBYTE SOFTWARE

BRIDGE

RECTIFIERS

14 505 194IA 1005 20p144005 254IA 6005 304

505 xis24100V 354244005 4643A250/0 .4,, 7.V W°5 asP

tr 505 1804W

6A 1 00V 100464 400V 130p

IDA 400V 2004250 4 0 0 V 380 P

LINEAR ICs46103 300pAY1.0212 100p451.1313 010p*91.1320 2160A Y1 5060 99p453-1350 350p473.8910 5504A Y3 8900 3904.AY3 691 2 625p*55 40070 Etco3021385 libCA3319 VPCA3046 700CA31648 220PC43059 neeCA3C805 NOPCA3110,6 712PCA3006 41PCP3009 XIV17530040 670409,30E 1044

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51531VT WOCA3103E 100417A31616 110p17A31524 460417431996 %Op17A32406 1104C432935 300p07002 4016pDAC140158 219341141366 111640A1368 meiicons 7004IC11721569 1101CM7217 7504IC187555 90pI.C7120 10041C7130 32154

1E3471E351 44,1.563 sae1.5356P 116416357 1,

DISPLAYS AVAILABLE phone or31019

140401707 Ree 140pF90357 1204F740503 104

55°5°1 904

MMP"416P36 2VP'ThP0

send for our BBC leafletmains switches andsafety interlocks

4000 SERIES

4000 ,4001 lo...p

4002 1244006 5044007 VIP4 91p4009 2444010 6/04011 11114012 liP4013 4044014 411p4015 OPo0164017 30440 18 4544019

25P4010 4%4021 ek,4022 4644023 1344024 3244025 1344026 4344027 20pnn 4%429 4544034 1544031 12544033 13p4,2,4 14044035 bp4.6 27544037 1104403g 29044040 4044041 404

404

DRIVERS9.6 2150,9270 300401356118 320401356154 3204

UV ERASERSU V 18 up to 6 Eproms £47.50

PCB

MOUNTINGRELAYS

,-...,,,,,, UV IT with timer £60.00..,...., I, XV r

140 to 14 Eproms £61.508 pre b UV upmon 104V pre 114 UV141 with timer £78.00

pn 1114

200e lip (Carr £2/eraser)22 pin VP24 pm 244

Sip All erasers are fitted with .

400e 304

6 or 125 DCCorISPOT 24240 CC 1534186,..9Inpr,12°°C.,

11.5' 'I" T ' I -I111/1)

240560,125 0, 5P5P

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,49r:21p313p

6MP 4648 pm 504

711 PIP 10p22 pin 1SP4 Pie 704

26 P1n 00974172

40 ten 1004

FOR FAST DELIVERYJUST PHONE01-452-1500/

450 6597Minimum order £5

SWITCHESTOGGLE SWITCHESSurneestureSPS1 lip %Map.ppo,40,4,,4,20,246w,144,

4615.519

RUGBY ATOMIC CLOCKThis Z80 micro controlled clock/calenderreceives coded time data from NPL Rugby. Theclock never needs to be reset. The facilitiesinclude 8 independent alarms and for eachalarm there is a choice of melody or alternativelythese can be used for electrical switching. Aseparate timer allows recording of up to 240 laptimes without interrupting the count. Expansionfacilities provided.Complete Kit E120 + £2.00 cart.Ready Built Unit £145 + E5.00 Carr.Reprint of ETI articles at E1.00 + s.a.e.

MICRO COMPUTEROFFICIAL DEALER

PLEASE PHONE FOR AVAILABILITYBBC Model B £399 (incl. VAT) + £8 carr.

Model A to Model B Upgrade Kit £50Fitting Charge £15

BBC FLOPPY DISC DRIVESSingle Drive 5,1" SSD £235

Double Drive 51" 800K £799 + £8 carr.Phone or send for our BBC leaflet.

ik..

'..../.-A-r.1.1.--D R AG 0 N32K/I/

32K Ram Hi -Lo Res Graphics REAL TIME CLOCK COLOUR SOUND PRINTER PORT

£173 + £4 p El- pWide Range of Software in stock.

AS DESCRIBED INJUNE/JULY/AUGUST

ISSUE

MICROTRAINERComplete Kit f64.00 + £1.00 p&p8V 1.8A PSU £7.00 + 70p p&p1802 Ref. £7.00IDEAL for HOBBYISTS - learn andexplore the workings of microprocessorsand unravel the mystical field of computers.INVALUABLE for training centres, schoolsand industries - gives effective insight intomicros to engineers, electricians etc notdirectly involved in the computer field.INEXPENSIVE - a truly low cost teachingaid - in fact a short step towardsdeveloping new ideas and systems.

MICRO TIMERThe programmable clock/timer is a 6502 baseddedicated micro computer with memory and 4 digit7 segment displays to form an extremely versatiletiming device with following features: 24 hour 7 day timer 4 completely independent switch outputs 6 digit 7 segment display output to indicate

real time turn-off times and reset times Individual outputs to day of week, switch and

status LEDs Data entry through a simple matrix pad

Further details on requestComplete Kit £56.00 + f1.00 p Et pPSU £7.00 1 70p p Et p

Construction details supplied

SIMPLY PHONE FOR A FASTAND EFFICIENT SERVICE.

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VISA Detailed Price List on request.Stock items are normally by return of post.


Project

Phase FourPaul Coster

A Four -stage audiophaser unit, basedon last month'sBreadboards design.

AN AUDIO PHASER is simply a circuitdesigned to produce a 'comb filter'(Figure 11. When the notches of the'comb' are swept up and down theaudio spectrum, the musical effectknown as 'phasing' occurrs. One of thefirst times this trick was used on arecording was in 1968; the song was"Pictures of Matchstick Men" by agroup called Status Quo. Another was"Itchycoo Park", by the Small Faces.

As a slightly more interesting (andrelevant) diversion, it is worthmentioning that 'phasing' is not thesame as a similar musical effect called'flanging'. Flanging depends on areasonably long time delay - as muchas, oh, a millisecond or so; mixing the_delayed signal with an undelayed signalalso results in a comb filter, but now thenotch frequencies are spaced at musicalintervals - thirds, fifths, flattenedninths and so on - and the effect soproduced has a more "musical" quality,so it is said. Flanging was discovered bythe American record producer, PhilSpector...but that's another story!

Shifting CircuitsThe HE Phase Four, however, is aphaser. It is based on the circuit ofFigure 2, a single stage phase shifterproducing 90° of phase shift from inputto output.

At zero frequency (DC), the input tothe non -inverting pin of the op -amp isblocked by the capacitor, Cl, so thecircuit acts as an inverter with a gain ofone; this, of course, is equivalent to aphase shift of 180°. At very highfrequencies, though, the capacitorbecomes a short circuit and so the op -amp becomes a non -inverting amplifier,still with a gain of one; the phase shiftnow is 0°.

But at some intermediate frequency,set by the time constant (RC) of the

high-pass filter network on the non -inverting input, the phase shift will beexactly 90°; the gain is still one!Essentially, the op -amp is buffering thephase -shift produced by the high-passnetwork of C1 and R3, maintaining aconstant gain of one.

If two of these units are cascaded -the input signal passing through one,then the other - the total phase shiftwill be 1 80° at the frequency set by theRC time constant, and if the phase -shifted signal is then added to an un-

FREQUENCY

Figure 1. A comb filter forms a series ofnotches in the frequency response curve.

OUT

ov

.R1 = R2

Figure 2. The basic phase shifting circuit. Figure 3. The frequency -phase responseof the circuit in Figure 2. The crossoverpoint is set by the values of R3 and C1.


Project

CALCULATORti3L grne

SW1aON/OFF

+9V (3---c

SIINPGNAL

OV 0

3

R147k

TRIANGLE 0INPUT

SW1bON/OFF

OV 0

9V 0

2

8

IC a

4

C1 C4

R247k

C2

T"n

47u

R382k

C3680n

R510k

IC2a

shifted signal, the result will be a notchin the response, at the specifiedfrequency.

In fact, there are easier ways toproduce a notch filter. The reason whythis circuit is used so often for phasingunits is because it is quite easy tochange the position of the notch. At itssimplest, this is done by varying R3,thus changing the time constant whichdetermines the corner frequency (thetwo are really equivalent). In a manuallyoperated phaser, this would be achievedby using a potentiometer in place of R3and varying it, by means of a foot pedalor something similar, to produce amanual sweep lie, movement of thenotch, up and down the response band).

It is just as easy to produce anautomatic sweep; Figure 4 also shows aFET transistor connected across R3; byvarying the voltage to the gate of the

R1

INR2

la;

Figure 4. By putting an FET in parallelwith R3, the effective resistance can bevaried over a wide range.

FET, its resistance can be changed froma few hundred ohms to around a fewhundred megohms. All we need now isa way of producing a varying voltage tocontrol the resistance of the FET, and asumming amplifier to combine thephase -shifted and unshifted outputs.

Phase FourAll these elements are brought togetherin the HE Phase Four circuit, shown inFigure 5. It uses four stages to producea total phase difference of 360°between input and output, producingtwo notchs in the response.

The input to the unit is buffered by aunity gain stage, ICI a; the IC used inthis position was chosen for its lownoise specification. The phase shiftersuse all sections of a quad op -amppackage, IC2 (elected for low powerconsumption).

The values of C3,6,7,8 are chosensomewhat arbitrarily, but they willaffect the total quality of the output.Capacitors C1,2,4 and 5 are todecouple the supply rails, eliminatinghigh frequency spikes from the output.

The phase shifted signal is fed to astandard virtual earth mixer. Theamount of shifted signal added to theoutput is set by the depth control, RV1,which determines depth of the notches.A switch is also included which allowsthe effect to be bypassed; PR1 is usedto adjust the output so that the gain is

11

Q1

NOTES:IC1 IS TL072IC2 IS TL064Q1-4 ARE 2N5457

54 R7 RIO82k 82k 82k

R682k

6

IC2b

R982k

0

C6 C7330n

13810k

t C5470-r

Q2

R1812k

R1947k

R2368k

3

2

8

IC3a

4

R24120k

R2047k

RV2220k

RATE

'VVV"R21Bk2

R221k

C9 CIO220u 220u+

NOTE:IC3 IS LF353

150n

R1110k

0 OV

IC2c

TRIANGLEOUTPUT

03

PR1470k

R1282k

C856n

0 R1410k

13

12

R17100k

R1382k

IC2d14

04

SW2BYPASS

N SIGNALOUTP1-,

0 OV

RV1100k

DEPTH

/7777

Figure 5. The Phase Four circuitconsists of an input buffer (IC1a), fourstages of phase shift (IC2), and an outputbuffer (IC1b). The triangle wavegenerator (left) drives the FET gates andconsists of a square wave generator(IC3a) and an integrator (lC3b).


Project

Parts ListRESISTORS(All 1/4 watt, 5% carbon)R1,2,19,20 47kR3,4,6,7,9,10,11,12 82kR5,8,11,14 10kR15 33kR16 22kR17 100kR18 12kR21 8k2R22 1kR23 68kR24 120k

POTENTIOMETERSPR1 470k

horiz. carbon presetRV1 100k

log carbonRV2 220k

log carbon

CAPACITORS(All metallised polycarbonate, unlessnoted)C1,2 10n

ceramic discC3 680nC4,5 47u

1 6V radio electroC6 330nC7 150nC8 56nC9,10 220u

16V radio electro

SEMICONDUCTORSIC1 TL072

dual BIFET op -ampIC2 TL064

quad BIFET op -ampIC3 LF353

dual J-FET op -ampQ1-4 2N5457

N -Channel FET

MISCELLANEOUSSW1 DPDT

min toggleSW2 SPST

footswitch2 x 1/4" jack sockets; 2 x PP3battery clips; 2 x 8 pin, 1 x 14 pinDIL sockets; 2 x knobs; case (seeBuylines); PCB; solder, wire etc.

BUYLINES page 34

the same in either case.The voltage sweep for the FETs is

produced by ICs 3a,b, and LF353. Thetwo op -amps are configured as atriangle -wave generator; in fact thesweep could be controlled by any slowlyvarying cyclic waveform, such as a sinewave or sawtooth, but the triangleshape works best in this application.

The circuit works in two stages: IC3aproduces a square wave output and thisis integrated by 3b to give the triangleshape. RV2 controls the frequency, iethe sweep rate, between the limits ofabout 0.1 and 10 Hz, with the values

OUTPUT

CHASSISEARTH

RV1DEPTH

4

4-9V

SW

9V

SW2

INPUT

EARTHON CASE

R16

Figure 6. The PCB component overlay.

d

02

2N5457AS VIEWEDFROM BELOW

POWER

117 OUT

chosen. The values of C9 and C10 arenot critical, but they must be connectedas shown, to form a simulated bi-polarcapacitor.

ConstructionAssembly of this project is not particularlydifficult; simply follow the componentoverlay (Figure 6), taking care that the ICsand electrolytic capacitors are correctlypositioned. One point to note is that RV2,a potentiometer with a logarithmiccharacteristic, must be connected theright way round; otherwise, the variation

in sweep speed will all come at one end ofthe rotation.

The ideal case for the Phase Four isthe custom built job supplied by NewradInstruments (see Buylines for details),though any case large enough to containthe PCB and batteries would do; itdepends on how heavy-footed you are!

The only adjustment required is to setPR1 so that the gain through the phaseris the same as in the 'bypassed'condition. Simply set the depth controlfor minimum and adjust PR1, switchingbetween effect and bypass, until thelevels sound equal. HE


HIGH QUALITY MODULES FOR STEREO

MONO AND OTHER AUDIO EQUIPMENT

AUDIO AMPLIFIERS5.10 watts 111141

111.20 5 watt Audio Amp Module 22-30e supply £157

ALMA 7.10 watt Audio Amp. Module 22-32v

1444Ph

POWER-' SUPPLIES

P812 24 Supply Slat: 2 a ALIO 2 x 01.20 2 x AL30

PROTIUM ELK SPM60 3.3. Stabilised supply Sat 1 yALIM PAM to 15 watts f4.64. SP44120145 45v

Slablisal supply Suit 2 x ALDO PA1011 to 25

watts 61.31 SPM12055 55v Stabilised apply Slit 2 x ALM PA200 5311.

SP141213165 86v Stabilised supply Suit: 2 a AL120 PA220 1 a AL250 1138.

SG30 150-15 Stabikied power supply for 2 x 6E100 MKII fiat

AUDIO AMPLIFIERS152535 watts (WS)

01.60 1525 watt Audio Amp Module 3150v

supply f5.15.

480 35 wan Audio Amp Module £8.07

MINIATURE FMTRANSMITTER MODULEFreq: 95-106 MHz Range la mile Size. 45mmx 20mm Add 9v. batt. Not licensed in UKIdeal for 007-M19-FBI-CIA-KGB-etc.Price.£5.50

MAGNETIC CARTRIDGEPRE -AMPLIFIEREnjoy the quality of a magnetic cartridge with your

ceramic equipment using the WAN which is a amity

pre -amp. enabling magnetic cartridges to be used where

facilities exist la ceramic cartridges ably With aDIN input socket to ha, easy to follow vaructions.

NPA30 Stereo Mag Cartridge, Pre -amp.

- input 15mv Output 100mv 13.27.

Transformers are not included with

power supplies. SPA1120 Range

also reapere reeve. and output capacitors

TRANSFORMERS2034 1.7 amp 35z sat SP144130 £4.90. 2035 2 amp

kw fiat 2036 7513nA 17v Sint PS12 MM. 2040 1.5amp 045z 55v Sat SPM120145 SPM12055v 1145.

21341 2 amp 0-55,65z Suit SPM120155

SPA4121365v PIM. 2839 1 amp OA Suit Stereo

30 £150 2043 150mA 150-15v Suit 80313 £1.60

ACCESSORIES139 Teak Cabinet Suit Stereo 30 320 a 235 x

81mm E7.00. 140 Teak Cabinet Sum STA15 425 a 2913 x

95mm £9.58 FP1M Front Panel for PA100

PA2130 £1.88. B4T1CC Beck Panel for PAM 6

PA200 GE10IMP Front Panel for one

GE1MMKII f1.75.TC60 'GI of Parts including Teak

Cabinet chassis, sockets to Mobs etc ho house STA15

Amplifier) f17.50. P5250 Consists - 1 capacitor ft 4

diodes for construcong unstobilised power supply for

AL250 to 125 watts ELK

SPMI20 a a fixed voltage

sublimer with an output voltage of

ether 4.5v, 55z or 65v Designed for use e

audio application, the stabiliser which provides anew

currents up to 2.54 operates tired from a mains

transformer motoring only the addition of two Electrolytic

capacitors to complete the power supply.

MONO PRE -AMPLIFIERSMM100 suitable for disco mixer. MM1OOG suitable for

guts preamp mixer.The MM100 and 1.8.4100G mono pre -amplifiers are

compatble with the ALM, ALSO A1120 aid AL250 power

amplifiers and their associated power supplies.

MM100 Supply voltage 4065v inputs. Tape Mag P.U.

Microphone Max output 560my £12.41 MM100G Supply

voltage 40-65z inputs: 2 Guitars, Microphones Max output

500rov

THEPROFESSIONAL

APPROACHOZ-PAK Audio Modules we famous for the variety, quality of design and ruggedness. For over 10 years 13I-PAK have

been suppliers to rrenufectrers of hob paddy audio equipment thicughout the world to date, well over 1E0,000

modules hue been sold -- this o why !harming amateur entlusiasts and professionals dikensat en using 13I-PAK

modules or their equipment.

They know that every item is designed and tested to do the job for which it is intended before it leaves the factory.

Whatever you ere building there is a let or module n the 81-PAK range to suit your every need.

AUDIO AMPLIFIERAudio Amplifier. 5011 R.M.S., with integral heat sink and

short circuit protection.

Introduced to tidbit the demand for a fully protected

power amp., capable fo driving high quality speaker

systems at up to SC% with distortion levels below 05%

Ideal for domesoc use. Discos, PA. systems, electronic

organs. etc. The generously rated components ensue

continuous operation at high

output levels. A1.120 50 watt

Audio Amp Module

50.70v supply

£1314.

STEREOPRE -AMPLIFIERS

PA12 Supply voltage 2232v Piga sensitivity 301.1rm Suit.

01101AL201A130 (155. PALM Supply voltage 3355v

inputs Tape Tuner Meg P.U. Suit. 0160)0180 f17.65.

PA2M Supply voltage 3573v inputs. Tape Tune. Mag

P.U. Suit. ALIMIAL129011.250 £1121

10 Channel,

Monographic

Equaliser.

Only 155mm a 65mm a 50mm including the 10x 101(45mm

Sider potentiometers and knobs which are mounted

on a hoard above the circuitry. In the range of 31Hz to

1610Iz you can cut and boost t12dB with the 10 sliders.

each with frequency marked on the Drawl board. The

GE100 uses include mixers, PA systems and discos. It

will moo irtiprove the sound reproduction of your earShng

audio equipment. Power supply for GEHM oil 5GM.Together with Transformer no 2041

6E103 MKII 10 Charnel mono -graphic gwy, g.LF_qualiser with sides 6 Knobs LLILUU. A

BI-PAK's COMPLETELY NEW CATALOGUECompletely re designed full al tee typecicomponert, rep require plus some

very interesting ones you will soon be using and of course the largest range of

semiconductors for the Arrtaleat and Professional you could hope to find

There are no wasted page. of useless intimation so often included in

Catalogues published nowadays lust solid facts , e price description aridindividual features of what we have available But remember Rr Pak s policY

has always been to sell quality components at competitive prices and THAT

WE STILL DO.

131-PAK S COMPLI If Ly NEW CATALOGUE is now available to you You will be

amazed how (rah you can save when you shop for Electronic Components with

a BI -Pak Catalogue Have one by you all the time -it pays to buy Al PAK

To receive your COpy send 75p plus 25p P&P

BI -KITSSTA5 5 watts per Manna Stereo Amphfier Kit consisting

of 2 x 0120 amplifiers 1 a NW preamplifier I x PS12

power supply 1 x 2036 transformer and necessary wiring

diagram £18.52. STAID 10 watts per channel Stereo

Amplifier Kit consong of 2 x A130 amplifiers 1 x PA12

preenpifier 1 a PS12 power supply 1 r 2036

transtomer and nes:assay wing dements Mil

STA15 15 watts per channel Stereo Amplifier Kit

consisting of 2 x ALDO amplifiers 1 a P11100 press-10Pa

1 x SPM90 power apply I a 2034 barnstormer 2 x

coupling capacitors for 8 ohms 470 mfd 513v and

necessary wiring &morns f36.76. STA25 25 watts per

channel Stereo Amplifier Kt consisting of 2 a ALDO

amplifiers 1 x PA103 pre -amplifier 1 r SP14120145 power

KSend your orders to Dept HE12131-PAKPO BOX 6 WARE HERTS

SHOP AT 3 BALDOCK ST WARE HEATS

TERMS, CASH WITH ORDER, SAME DAY DESPATCH, ACCESS

BARCLAYCARD ALSO ACCEPTED. TEL 1092013182 GIRO 388 7006

ADO 15% VAT AND 50% PER ORDER POSTAGE AND PACKING

AUDIO AMPLIFIER125 watts 110.151,

A power ampifiet providing an output of up to 125w

RMS. into a 4 ohm load. Four 115w transistors in the

output stage makes it extremely rugged while damage

horn incorrect or short circuit loads is prevented by a

four transistor protection Mad For use in many

applicabons such as disco wits, sound re -Placement

systems, background music players etc

AL250 125 watt Audio Amp f19.60.Module 50.80v

supply

The PA21113 is basically our popular PA100. modifications

being made to make it corripatble with the higher

output amplifiers i.e. NATO Er ALISO. The unit boasts sca

push button selectors giving a choice of 3 inputs 2

filters, for both high and low frequencies and a stereo a

mono button, as combining to dive a top quality stereo

preampifier and tone control

PUSHBUTTONSTEREO FMTUNERCited with Phase locked loop decoder

S453 Provides aslant programme selection at the touch

of a button ensuring accurate tuning of 4 preselected

stations, any of which may be altered as often as you

choose. simply by changing the settings of the preset

controls. Features include FEL inputstage. Varicap diode

tuning,

E19.00.

REGULATEDVARIABLE

STABILISED POWER SUPPLYVariable horn 230 volts and 02 Amps Kit includes. -1 - VPS30 Module, 1 -- 25 volt 2 amp transformer.

05Orr 7' Panel Meter. 1 - 02 amp 2" Panel Meter,1 -- 470 ohm vemewound potentiometer, 1 - 4K7 ohm

WirevroUnd potentiometer Wring Diagram

included VPS30 KIT up.SIREN ALARM MODULEAmerican Police type screamer powered horn any 12

volt supply into 4 or 8 ohm speaker Ideal for car burglar

alarm, freezer breakdown and ohm security

purposes. BP124 5 watt 12v max -Siren Alarm Module figs.

supply t 1-21)1(1 transformer 2 a coupling

capacitors tor B ohms 470 mfd 45. 1 a reservoir

capacoot 2200 mid 10Dv and necessary owing diagramf45.79. STA35 35 watts per channel Stereo Amplifier Kt consisting of 2 xALM amplifiers 1 x SP1412055 power supply 1 x PA200 preampilier

1 x

2835 transformer 2 x coupling capacitors 470 rld at 50z far 8 ohms t a

reservoir capacitor 2200 mfd 100v and necessary wiring diagram £45.76.

Use your credit card. Ring us On Ware 3182 NOW and

Bet your order even faster. Goods normally sent 2nd

Class Marl

Remember you must add UT at 15% to your Adel

Total Postage add 50p per Total cede


BI-PAK BARGAINS5121 SCREWDRIVER SET6 precision screwdrivers in hinged plasticcase. Sizes: - 0.8, 1.4. 2. 2.4.

2.9 and 3 8mm EL 75

5131 NUT DRIVER SET5 precision nut drivers in hinged plastic caseWith turning rod 21.75Sizes. - 3. 3 5 4. 4 5 and 5mm

5141 TOOL SET5 precision instruments in hinged plastic caseCrosspoint (Phillips) screwdrivers. -H 0 and H 1 Hex key wrenches -15 2 and 2 5mm £1.75

5151 WRENCH SET5 precision wrenches in hinged plastic caseSizes: - 4. 4.5. 5. 5 5 and 6mm. 21.75

BUY ALL FOUR SETS 5T21 -5T51 and get

HEX KEY SET FREEHEX KEY SET ON RING.

Sizes 1.5. 2. 2.5. 3.4. 5, 5 5 and 6mmMade of hardened steel

HX/t. £1.25

MINI VICEThis small cast iron quality made vice willclamp on to any bench or table having a max ..

thickness of I " The 212" laws open to max 01ot 1,78" Approx size 80 x 120 x 66mmBi-Pa k's Mini Vice at

a Mini Price only

£2.50ORDER NO SX82

BI-PAK SOLDER -DESOLDER KITKit comprises ORDER NO SX80

1 High Quality 40 watt General PurposeLightweight Soldering Iron 240v mains incl3/16" (4 Imm) bit1 Quality Desoldering pump High Suction withautomatic election Knurled. anti -corrosivecasing and teflon nozzle1.5 metres of De -soldering braid on plastic

dispenser-2 yds (1 83m) Resin Cored Solder on Card1 Heat Shunt tool tweezer Type.Total Retail Value over £12.00OUR SPECIAL KIT PRICE £8.90

r "IRRESISTABLERESISTOR BARGAINS"

PA No. Qty.' Descnptimi Price

5110 400 Mixed -MI Type Resistors El5111 400 Preformed 4,4 watt Carbon

Resistors ElS112 200 Tit watt Carbon Resistors LI5113 200 Try watt Carbon Resistors LI5114 ISO To watt Resistors 22 ohm

2m2 Mixed El5115 100 I and 2 watt Resistors 22

ohro2m2 Mixed LIPaks SX l2 15 contain a range of Carbon Film Resistorsof assorted values from 22 ohms to 2 2 meg Savepounds on these resistor paks and have a full range tocover your protects'Quantities approximate, count by weight

1705 pieces of Audio Plugs, Sockets and Corlnectors to include DIN 1W-240' Inline

36 Pin, Speakers, Phono, Jack Stereoand Mono etc Valued at well over E3normalOrderNo. SX25.

Our Price11.50per pak.Guaranteed to save you money.

SX26 3 Prs of 6 pin 240' DIN Plugs andChassis Sockets 50p

SX27A 60 Assorted Polystyrene BeadCapacitors Type 9500 Series PPD £ 1 20

SX28A 50 Assorted Silver Mica Caps.5.6pF-150pF £1 .00

SX29A 50 Assorted Silver Mica Caps.1130pF-4700pF £1.00

SX30A 50 High Voltage Disc Ceramics 750vmin up to 8KV Assorted useful values E1.00

SX31A 50 Wirewound 9 watt (avg) ResistorsAssorted values lohm-12K E1.09A

TheThird and% Fourth Hand...

.. you always needbut have never got 'until now

This helpful unit with Rod mountedhorizontally on Heavy Base. Crocodile clipsattached to rod ends Six ball 8. socket Jointsgive infinite variation and positions through360° also available attached to Rod a 21/2 diammagnifier giving 2.5 x magnification Helpinghand unit available with or without magnifierOur Price with magnifier as illustrated ORDERNO. T402 £5.50Without magnifier ORDER NO T400 £4.75

"CAPABLECAPACITOR PAKS"

PM No. Qty' Descriptiew

5116 250 Capacitors Mixed Types £1

200 Ceramic Capacitors MiniatureMixed LIMixed Ceramics 1pf 56of LIMixed Ceiamics6EMI 0.5rnt LIAssorted Polyester/PolystyreneCapacitors Li

S121 Mixed C280 type capacitorsmetal foil

5122 Electrolytics, all sorts5123 Quality Electrolytics

50,1000mi5024 20 tantalum Beads, mixed

L.:Quantities appioximate count by weight.

5117

SX18

5119S120

100100

100

60

100

50

Price

El

Ll

rBARGAINS

SX9I 20 . Large .2" RED LED LISX42 20 small 125 Red LED's ElSX43 10 Rectangular Green LED's 2 LI5146 JO Assorted Zenei Diodes

250mw-2 watt mixed voltages,all coded New LI

5147 4 Black InstrumentKnobs -winged with pointer Tv'Standard screw Fit size 2920mm

5149 20 Assorted Slider KnobsBlack/Chrome etc LI

911110 12 Neons and Filament Lamps, towvoltage and mains - various typesand colours - some panel mounting El.did

SOP

SX52

6 Black Heatsink will fit TO 3 and

10.220 Ready drilled. Hall price

value. El

SX53 I Power finned Heatsink This heatsink

gives the greatest possible

in the smallest space owing to its unique

staggered in design. pre drilled

10.3 Size 45mm squareiamea high 40p

SX54 10.66 size 35mm x 30mm x I 2mm 35p

5155 I Heat Efficiency Power Finned Heatsink

90mm a 80mm x 35mm High. Drilled to

take up to 4 x

TO 3 devices

E1.50 each

BI-PAK PCB ETCHANTAND DRILL KITComplete PCB Kit comprises1 Expo Mini Drill 10.000RPM 12v DC Ind 3

'collets 8 1 x lmm Twist bit1 Sheet PCB Transfers 210mm x 150mm1 Etch Resist Pen

1 1/2Ib pack FERRIC CHLORIDE crystals

3 sheets copper clad board2 sheets Fibreglass copper clad board.Full instructions for making your own PCB,boardsRetail Value over £15.00OUR BI -PAK SPECIAL KIT PRICE 29.75

L9.FIDER NO SX81

air

PROGRAMMABLE UNIJUNCTION TRANSISTOR"PUT" case 10106 plastic MEU22 Similar to2N6027 /6028 PNPN SiliconPrice: 1-9 10-49 50-99 100* Normal RetailEach: 20p 18p 15p 13p Price E0.35 each

SX33A 6 small (min (SDST/SPOT ToggleSwitches 240v 5a m p E1.00

SX35A 6 small (min) Rocker Switches240v 5amp £1.00

SX32A 12 Assorted Jack 8 Phono plugs.sockets and adaptors, 2.5m.3.5mm and standard sizes E1.00

SX71 50 BC108 "Fallouts" Manufac-turers out of spec on volts orgain You test. £1.00

SX72 A mixed bundle of Copper cladBoard Fibre glass and paper.Single and double sided. Afantastic bargain £I 00__A

TECASBOTYThe Electronic Components and Semiconductor Bargain of the Year A host of Electronic

components including potentiometers - rotary and slider, presets - horizontal and vertical.

Resistors of mixed values 22ohms to 2M2 -1,810 2 Wan. A comprehensive range of

Capacitors including electrolytic and polyester types plus disc ceramics etcetera.

Audio plugs and sockets of various types plus switches, fuses. healsines, wire nutsibolts,

gromets. cable clips and tyes, knobs and P.C.Board. Then add to that 100 Semiconductors

to include transistors. diodes. SCR's oplo's. allot which are current everyday usable devices

In ail a Fantastic Parcel. No rubbish all identifiable and valued in current catalogues at well

'vet E25.00. Our Fight Against Inflation Price -

- Down withwea DtheeprBeussdigeont JUST £6.50.

BI -PAKSend your orders to Dept HE12BEPAK P013006 WARE HERTS

SHOP AT 3 BALDOCK ST WARE HERTS

TERMS CASH WITH ORDER. SAME DAY DESPATCH. ACCESS

BARCLAYCARD ALSO ACCEPTED. TEL 1092013182 GIRD 3887006

ADD 15% VAT AND 75p PER ORDER POSTAGE AND PACKING

SX38 100 Silicon NPN Transistors -allperfect Coded mixed types withdata and eqvt sheet. No rejects.Real value. £3.00

SX39 100 Silicon PNP Transistors -all perfect. Coded mixed typeswith data and eqvt. sheet. Norejects. Fantastic value. E3.00

2113055 The best known Power Transistors in theWorld - 2N3055 NPN 115wOur BI-PAK Special Offer Price10 off 50 of 100 ofL3.50 £16.00 E30.00

80312 COMPLIMENTARY PNP POWERTRANSISTORS TO 2N3055

Equivalent M12955 - 00312 - T03SPECIAL PRICE £0.70 each

10 off ES.50

ConsumptionSizeRANGES

DC Voltage 0-200mV0.2-20-200-1000V Acc 0 8%AC Voltage 0-200-1000VAcc 1 2% DC Current 0.200uA0-2.20-200mA 0-10 A Acc 1 2%

Resistance 0-2.20-200K ohms0.2 Megohms Acc 1%BI -PAN VERY LOWEST POSS PRICE

£35.00 each

BRAND NEW LCDDISPLAY MULTITESTER.RE 188m

LCD 10 MEGOHM INPUT IMPEDANCE 3 1/2 digit 16 ranges plus hFE test facility forPNP and NPN transistors 'Auto zero. autopolarity Single-handed pushbuttonoperation Over range indication 12 5mm( Yr -inch) large LCD readout Diode check F ust circuit protection Test leads batteryand instructions included.Max indication 1999 or - 1999Polarity indication Negative only

Positive readings appearwithout + sign

Input impedance 10 Megohms

Zero adtust Automatic

Sampling time 250 millisecondsTemperature range - 5°C to 50°CPower Supply 1 x PP3 or equivalent 911

battery20mW155 x 88 x 31mm 1

r SINGLE SIDED FIBREGLASS IBOARD

Order No. Pieces Size Sq. PaliFBI 4 9 x 21ti" 100 £1.50

F82 3 11 x 3" 100 £1.50

E113 4 13 x 3" 156 £2.00

DOUBLE SIDED FIBREGLASSBOARD

F84 2 14 x 4" 110 £2.00

SILICON POWER TRANSISTORS- 1123

NPN like 2N3055 - but not full spec100 watts 50V min,10 for E1.50 - Very Good Value

Order No. SX90100s of uses- no duds

5 watt (RANNAudlo Amp INigh Quality audio amplifier Module Ideal for use inrecord players, tape recorders, stereo amps andcassette players, etc Full data and backup diagramswith each module

Specification Max Power Supply 301/ Power Output 5 wattsRMS Load Impedance B-16 ohms Frequencyresponse 50Hz to 25KHz-3db Sensitivity 70 myfor full output* Input Impedance 50k ohms. SizeB.5 x 64 x 30mm Iota) Harmonic

distortion less than .5%BI-PAK'S give away price

£2.25Yee could net Meld 111111

ler this price

MORE BARGAINS!

SX5I 60 metres PVC covered Hook-upwire single and stranded. Mixedcolours. £1

SX58 25 Assorted TEL Gates 7400Series 7401.7460 El

SX59 10 Assorted flip Flops and MSITIT El

5X60 20 Assorted SliderPotentiometers £1

SX62 40 Assorted Pre -Sets HoriVertetc LI

5179 10 Reed Switches - glass type3 Micro Switches - with lever LI

Ose row credit card Ring us on Plan. 3182 NOW ant

gel vow cede, even taste, Goods notmallv sent 2nd

Class Mail

Flemembir, you mull ado vAl al IS to you, °id,Intel Postage add 75p xi Total Dor


HE PROJECT KITS I.C.s TOOLS CASES

TRANSISTORS RESISTORS KITS

CAPACITORS HARDWARE MAGENTAMake us your No. 1 SUPPLIER OF KITS and COMPONENTS for H.E. Projects. Wesupply carefully selected sets of parts to enable you to contruct H.E. projects. Kitsinclude ALL the electronics and hardware needed. Printed circuit boards (fully etched,drilled and roller tinned) or Veroboard are, of course, included as specified in the originalarticle, we even include nuts, screws and I.C. sockets. PRICES INCLUDE CASES unlessotherwise stated. BATTERIES ARE NOT INCLUDED. COMPONENT SHEETINCLUDED. If you do not have the issue of H.E. which includes the project - you willneed to order the instruction reprint at an extra 45p each.

Reprints available separately 45p each + p. & p. 40p.

ODOMETER Nov. 82 E14.98DIANA V.C.O. Nov 82 £4.89FLASH POINT ALARM Oct 82 £19.98CB SQUELCH UNIT Oct 82 £9.19'JUNIOR' SLOT CAR CONTROLLERSept 82 £5.60 less case.ZX INTERFACE BOARD Sept 82 incedge con £11.33.AUDIO ANALYSER Aug 82 less case£63.97.SWR METER Aug 82 E8.95.T.V.I. FILTER July 82 E5.33AUTO WAH June 82 £18.98 inc case orE12.28 less case.AUTO GREENHOUSE SPRINKLERJune 82 £15.38 less pump and powersupply 112V 2A1.TELEPHONE TIMER June 82 £33.42 lesspower supply (suitable type below).POWER SUPPLY DESIGN 12V 500mAJune 82 £9.98ECHO REVERB UNIT May 82. Less case£33.98. Economy case WB3 £3.76 extraDIGITAL THERMOMETER May 82 ex-cluding case -r bezel £16.90AUDIO SIGNAL GENERATOR May 82f20.98.CABLE TRACKER May 82 £9.98DIGITAL CAPACITANCE METER Apr82 £21.37SIGNAL TRACER Apr 82 E3.86BIKE ALARM Apr 82 £11.74DIGITAL DICE Mar 82 £7.29BICYCLE SIREN Mar 82 f10.89NOISELESS FUZZBOX Feb 82 £10.45MASTHEAD AMPLIFIER Feb 82 E14.74DRUM SYNTHESIZER Dec 81. Full kit£21.37GUITAR HEADPHONE AMPLIFIERDec 81 £3.72IN CAR CASSETTE POWER SUPPLYDec 81 £4.77SCRATCH FILTER Nov 81 Mono £5.82Stereo E8.98LED VU METER Nov 81 less case E4.87SIMPLE STYLUS ORGAN Nov 81 lesscase £4.98METRONOME Nov 81 £12.71TELEPHONE BELL REPEATER Oct 81£13.67Med linking wire extra 14p metreCOMBINATION LOCK Oct 81 lesssolenoid E18.65BABY ALARM Oct 81 £8.70, Fig 8 linkingwire 7p metre

'DIANA' METAL LOCATOR Sept 81£34.50POWERPACK Snot 81 £10.25REACTION TESTER GAME Sept 81£12.81VARIABLE BENCH POWER SUPPLYAug 81 £26.98ULTRASOUND BURGLAR ALARMJuly 81 £1598ELECTRONIC DOOR BUZZER July 816.98ELECTRONIC METRONOME July 81£4.99CONTINUITY CHECKER June 81 £5.71ENVELOPE GENERATOR June 81£17.98AUDIO MIXER June 81 £5.33PUBLIC ADDRESS AMPLIFIER March81 £19.48. Extras horn speakers £6.83each, PA MIC £4.40FUZZBOX March 81 £10.98WINDSCREEN WIPER CONTROLLERMarch 81 £8.20STEAM LOCO WHISTLE March 81

£12.98PHOTOGRAPHIC TIMER March 81E3.50HEARTBEAT MONITOR Feb 81 £24.98TWO-TONE TRAIN HORN Feb 81 E5.60less casemedium wave radio Feb 81 £8.20BENCH AMP Jan 81 £10.80NICAD CHARGER Jan 81 £8.20CHUFFER Jan 81, less case £7.53BATTERY CHARGE MONITOR Dec 82£5.77MEMORY BANK - MINI SYNTH-ESISER Nov Er Dedc 80 £29.98TRANSISTOR TESTER Nov 81 £6.54 inctest leadsGUITAR PRE -AMP Nov 80 E6.65case (diecast) extra £2.29INTRUDER ALARM Oct 80 £20.98TOUCH SWITCH Sept BO £2.75 less case& contactsguitar phase, Sept 80 £16.28SOUND OPERATED FLASH TRIGGERJuly 80 no skt £5.33FOG HORN June 80 £6.64SPEED CONTROLLER FOR RIC April 80£17.55 (less case)DIGITAL FREQUENCY METER April 80E39.980101DICE Jan 80 E11.73GUITAR TUNER Nov 79 E12.82CAR ALARM Feb 79 £12.91

MORE PROJECT KITS - SIMILAR STYLE TO H.E.INSTRUCTIONS INCLUDED (SEPARATELY 45p EACH)

PLEASE QUOTE REF. NO. WHEN ORDERING

1

B1 PEST CONTROL 'Ultrasonic catscarer' £7.65B2 COMPONENT TESTER £8.88B4 GUITAR NOTE EXPANDER f17.98B5 CAMERA OR FLASH GUNTRIGGER Infra red system £12.51B6 SIMPLE INFRA RED REMOTECONTROL £1720B7 0-12V POWER SUPPLY E17.98B9 SOUND TO LIGHT - single channel£8.42810 THREE CHANNEL SOUND TOLIGHT £21.44

MORE KITS ANDCOMPONENTSIN OUR LISTS

FREE PRICE LISTPrice list included with

orders or send sae 19 x 41CONTAINS LOTS MORE

KITS, PCBs &COMPONENTS

B11 IN SITU TRANSISTOR TESTERE6.98

B12 WEIRD SOUND EFFECTSGENERATOR £5.9811113 AUDIBLE VISUAL METRONOME£5.98

B14 ELECTRONIC DICE E5.71

816 MINI EGG TIMER £4.34818 LED JEWELLERY - Cross brooch£2.77 Star brooch £9.91 Spiral brooch£7.98

1982 ELECTRONICSCATALOGUE

Illustrations, product descriptions, circuits all in-cluded. Up-to-date price list enclosed. All productsare stock lines for fast delivery.Sends 80p in stamps or add 80p to order.

MORE H.E. PLUS E.E. and E.T.I. PROJECT.KITS IN THE PRICE LIST

MAGENTA gives you FAST DELIVERY OF QUALITY COMPONENTS & KITS.All products are stock lines -and are new 6 full specification. We give personal service 6quality products to all our customers -HAVE YOU TRIED US?

MAGENTA ELECTRONICS LTDHS31, 135 HUNTER ST., BURTON -ON -TRENT, STAFFS.

bE14 2ST. 0283 65435. MON-FRI 9-5. MAIL ORDER ONLYADD 45p P&P TO ALL ORDERS PRICES INC VAT

ACCESS and BARCLAYCARD (VISA)ORDERS ACCEPTED BY PHONE ORPOST.SAE ALL ENQUIRIES.

Prices inc. VATOFFICIAL ORDERS WELCOMEOVERSEAS. Payment must be in sterling.IRISH REPUBLIC and BFPO. UK PRICES.EUROPE: UK PRICES plus 10%.ELSEWHERE- write for quote.

SOLDERING I TOOLSANTEX X5 SOLDERING IRON 25W

£5.48SOLDERING IRON STAND . £1.98SPARE BITS. Small standard, large,65p each. For X5+ X25SOLDER. Handy size 99p

£1.8469p29p

£6.4812p

£1.69

SOLDER CARTONDESOLDER BRAIDHEAT SINK TWEEZERSDESOLDER PUMPHOW TO SOLDER LEAFLETLOW COST CUTTERSLOW COST LONG NOSE PLIERS

£1.68WIRE STRIPPERS Et CUTTERS £2.69

HELPING HANDS JIG £6.30Heavy base. Six ball and socketjoints allow infinite variation of clipsthrough 360°. Has 20" diameter125 x I magnifier attached, used andrecommended by our staff.VERO SPOT FACE CUTTER ..E1.49PIN INSERTION TOOL £1.98VEROPINS (pk of 1001 0.1" 52pMULTIMETER TYPE 1 11.000 oov)

6.48MULTIMETER TYPE 2120,000 opvlwith transistor tester. Very good

£14.75CROCODILE CLIP TEST LEAD SET.10 leads with 20 clips 99p

RESISTOR COLOUR CODECALCULATOR 21pCONNECTING WIRE PACK TYPEED. 11 colours 49pILLUMINATED MAGNIFIERS

Small 2" dia. 15 x mag.) .... £1.14Large 3" dia. 14 x magi £2.40

CAST IRON VICE £2.98SCREWDRIVER SET £1.98POCKET TOOL SET £3.98DENTISTS INSPECTION MIRROR

£2.85JEWELLERS EYEGLASS £1.50PLASTIC TWEEZERS 69pPAIR OF PROBES WITH LEADS(cc)...77p

MULTIMETER TYPE 2 - 2A06 0 0+0oDpcv. volts.1c1

Includes transistorcurrent.

tester.yr,

YN360 TR, £14.75 useful resistance ranges.We've used it and we like it.

ISPCAKERS. Miniature. 8 ohm 87p MI N. BUZZERS. 6V 50p. 9V. £1 10.64-75 ohm 89p 12V. 657.CRYSTAL EARPIECE 65p MAGENTIC EARPIECE 15pMONO HEADPHONES £2 96 STEREO H Et,OPHONES £4 35TELEPHONE PICK-UP COIL .72p F.M. AERIAL 49p

VEROBOARD 0.1" COPPER STRIPS10 strips 24 holes £1.20 per 524 strips 37 holes24 strips W holes36 strips 37 holes36 strips W holesTerminal pins 0.1"

78p89p89p99p

52p/100 ,

PP3 CLIPS 10pPP9 CLIPS 11p

EUROBREADBOARD E6.20E3.98

BIMBOARD 1 BREADBOARD £838VEROBLOC BREADBOARD £4.20

S DEC BREADBOARD

PANEL METERS50uA; 100uA; 1rnA,1A. 25V 100uA-0-IOWA; 5A. AU£4.98 each. Statevalue

BOOKSSEMICONDUCTOR DATA BOOK Newnes

E5.90ELECTRONIC PROJECTS FOR HOMESECURITY E3.35ELECT. PROJECTS IN PHOTOGRAPHY

E3.35110 ELECT. ALARM PROJECTS £5.35MODEL RAILWAY PROJECTS E1.95BASIC ELECTRONICS. Theory & practice

£7.98BEGINNERS GUIDE TO BUILDING ELECT.PROJECTS £1.50

ADVENTURES WITHMICROELECTRONICS

Similar to 'Electronics' below.)Uses I.C.s. Includes dice, elec-tronic organ, doorbell, reactiontimer, radio, etc. Based on Bim-board 1 bread board.Adventures withMicroelectronics £2.55

Component pack £29.64 lessibattery.

ADVENTURES WITH ELECTRONICS

An easy to follow book suitable for all ages. Ideal for beginners.No soldering, uses an S -Dec breadboard. Gives clear instructionswith lots of pictures. 16 projects -including three radios, siren,metronome, organ, intercom, timer, etc. Helps you learn aboutelectronic components and how circuits work. Component packincludes an S -Dec breadboard and all the components for theprojects.Adventures with Electronics £2.40. Component pack £18.98less battery.

ADVENTURES WITH DIGITAL ELECTRONICS

New book by Tom Duncan in the popular 'Adventures' series. This book ofentertaining and instructive projects is designed for hobbyists, and students. It

provides a stepping stone to the microprocessor.The first part deals with the properties of some basic ICs used in digital

electronics.The second part gives details of how to build eight devices - shooting gallery, 2way traffic lights, electronic adder, computer space invaders game etc.For each project there is an explanation of 'how it works' and also suggestions for'things to try'.No soldering - all circuits built on 2 Bimboard 1 breadboards.Adventures with Digital Electronics book £3.25. Component pack £42.50 refEHDC. All the components needed including 2 breadboards and hexadecimalkeyboard. Available less breadboards E29.98 ref EHDF. Both less battery.

Hobby Electronics, December 1982

Into Radio

RADIO RULESIan Sinclair

Single side band transmitters and receivers.

Single SidebandIF you think back to amplitude modulationagain, you may remember that business ofsidebands. When a carrier is amplitudemodulated, the output signal contains thecarrier frequency and both sets ofsidebands (sum and difference), all requiringpower at the PA stage to transmit. All the in-formation of the audio signal is carried in onesideband, however (either one), and noneby the carrier, so that this well-worn double-sideband scheme is very wasteful oftransmitter power. The solution is to use on-ly one sideband, eliminating the other side -band and most of the carrier. This system iscalled single-sideband-suppressed-carrier,usually abbreviated to SSB, though thiscould also refer to systems that eliminateone sideband but retain most of the carrier.

Starting with transmitters this time,how do we achieve these two aims ofremoving one sideband and most of the car-rier? Once again, there are several methods,but the most popular one consists of using abalanced modulator to remove the carrier,and filtering to remove the unwanted side -band. A balanced modulator is a circuit towhich both carrier and audio signal can beapplied. If there is no audio signal, then thereis no output from the circuit, but adding anaudio signal spoils the balance of the circuitand the sidebands of the modulated carrierform the output. There is very little trace ofthe carrier frequency in the output.

A simple type of balanced modulator isillustrated in Figure 1. This is a bridge orring modulator and its action depends on theuse of the audio signal to bias a set of diodesinto conduction. Imagine that there is noaudio signal, so that the audio input to thediode bridge at A is at earth voltage as far assignals are concerned. The carrier signal isinjected at a point where the voltage lies ex-actly between the bridge outputs, so thatthe carrier signals to the transformerprimary ends are in phase. In this condition,there is no output.

Now imagine that an audio signal is ap-plied and that the audio voltage has reachedits positive peak. Diodes D1, D2 will con-duct when the carrier voltage is zero, put-ting a bias voltage onto the output line, at X.Now the carrier signal is no longer balancedbecause, when the carrier has its negativepeak at X and its positive peak at Y, thediodes D1, D4 will conduct carrier signal,and D2, D3 will not conduct. This will causesome out -of -phase carrier signal to reachthe transformer. The situation reverseswhen the audio signal at A goes to itsnegative peak. Now diodes D4,D3 conductwhen the carrier voltage is zero, but whenthe carrier wave is positive at Y, negative atX, then D1, D4 don't conduct but D1 , D2,D3 do, producing a signal to the transformeragain. These signals to the transformer areof sidebands only because no carrier canpass, by itself.

The circuit works well, but needscareful! setting up. An alternative is to use abalanced -modulator IC - the MotorolaMC1496G is an old favourite for this task.Even so, these methods can never totallyremove all traces of carrier, but suppressionof 30 to 50 db can be easily achieved.

The next part of single sidebandmodulation is the filtering system whichremoves one sideband. Unless you can testand adjust crystal filters, the filter units justhave to be bought - these can be quartzcrystal types or surface wave types. Thefilter characteristic can be arranged so that itcontributes to the suppression of the carrier,as well as removing the unwanted side -band.

IAUDIOINPUT

FROM OSCILLATOR)2-5V SIGNAL)

Figure 1. A bridge or Ring Modulator,which eliminates the carrier frequencyfrom the output, is the first and mostimportant stage in SSB transmission.

The combination of balanced modulatorand filter is the complete single-sidebandgenerator. The whole system can bedesigned around a low carrier frequency -455 kHz is a favourite - or at high frequen-cies such as 9 MHz - the choice is fixed bythe availability of commercially -built filters.You don't, of course, transmit at either ofthese frequencies. To reach the actualtransmitting frequency, you would normallythink of using multiplier stages, but this stepis taboo with SSB transmitter circuitsbecause multiplying up the carrier frequen-cy means multiplying up the bandwidth ofthe sidebands. The alternative is 'frequencymixing', using another mixer stage to obtaina signal which is the sum of the modulatedfrequency and another crystal -controlledfrequency.

Once the correct frequency has beenreached (and several mixings may be need-ed, particularly if the original modulationwas at 455 kHz and the final frequency isVHF), power amplification must use ClassA or Class B circuits rather than Class C, toavoid distortion. This will make the efficien-cy of the output stage lower, but the effec-tive power of the modulated signal, as com-

pared to a double-sideband signal with fullcarrier is so much greater that the loss is ac-ceptable. As a guide, if we assume that theoutput stage is 66.7% efficient (meaningthat 2/3 of the DC power fed to the outputstage causes useful output), then the max-imum allowed DC power of 150 W willcause an RF power of 100 W. This is alluseful power however, so that the way inwhich we measure SSB power is in terms ofwhat is called "peak envelope power",which is four times the actual output power(100 W in this example). This is an approxi-mation, but it implies that the SSB signal isequivalent in transmitted power to a con-ventional AM signal of four times its outputpower.

Problems, problemsProblems start when we want to receive aSSB signal. To start with, the demodulatormust be a balanced type, operating like themodulator in reverse, and it has to be fedwith a carrier signal of the correct frequencyand phase. This is most easily arranged iftransmitter and receiver share the sameoscillator in the form of a transceiver, as theoscillator section of the transmitter can thenprovide a signal of exactly the correct fre-quency and phase to the demodulator.However, all of this makes a single-sideband rig a very complicated piece ofgoods, particularly if it is to be used atseveral frequencies, because there is a con-vention that the lower sideband is used atfrequencies below 10 MHz while the uppersideband is used at frequencies above 10MHz. Not many readers are likely to get in-volved in SSB as a do-it-yourself project! It'sadvantages, however, make impressivereading, and even more impressive listen-ing. To start with, the bandwidth of the SSBsignal is the same as that of the audio signal,no more. This means that a lot more SSBrigs can use a band than conventional AMrigs. There is also a gain in range, because allof the output power of the SSB transmitteris concentrated on the one sideband whichthe receiver uses. In addition, SSB is muchless liable to atmospheric disturbance ef-fects, such as fading and blasting, than con-ventional AM or even FM. The advantagesof SSB can be increased by using speech -processing units which ensure that themodulation is always near the upper limitwhile you are speaking. SSB rigs of goodquality are never cheap, but they representjust about the optimum in modern radiocommunications and a dream for everyamateui licence holder to aspire to.

Due to space limitations in the Novemberissue, this portion of Radio Rules was heldover till December.

Next month we will back -track to ex-amine AM Receivers.


rr$tep.by-stepfully

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ere includedtogether

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Amateur ratliciwill becomemuch clearerafter 3rd Dec.

The radio market hasbecome more complex. Thingshave become more confused.

Wires get crossed as newequipment floods onto themarket.

At the end of the day,even the most avid enthusiastspends more time trying to findout about new equipment thanon the airwaves using it.

As for the novice?They stand little chance of

picking anything up at all.So we've decided to clear

things up.On December 3rd our new

magazine Ham Radio Todaybegins.

Not a magazine you needa degree in electronics todecipher.

Or one that still calls yourgear a wireless.

Rather a magazine thatsimply clarifies the vast range ofelectronic gadgetry available.

Lists new equipment,analyses its performance.

Thorough reviews, specialfeatures, news items andconstructional projects.

In a clear and concise waythat will give everyone a perfect5 + 9.

Ham Radio Today.Tomorrow . . . tune in and

find out, 73.

Published byArgus Specialist Publications Ltd.

Popular Computing

COMPONENTSFOR COMPUTINGThis is the first of a series of articles in which the components

of microcomputer systems will be discussed. We willinvestigate the many aspects of each type of component,

including general functions and areas of application, internalcircuit operation, external circuits and the range of products

on the market.WE WILL START by describing In-put/Output (I/O) port components. Thismay not seem entirely logical, but itfollows from our Micro -Trainer series ofearlier this year. Consequently, in thisissue alone, there will be specificreferences to the Micro -Trainer whenthe programming of I/O ports is con-sidered.

What Is An I/O Port?A port, whether input or output, is a

device that interfaces between the 'raw'hardware of a computer's central pro-cessing unit (CPU) and the externalmachinery of a control system. In itssimplest form , a port consists of a datalatch or register connected to the threebusses (address, data and control) of theCPU. The diagram of Figure 1 shows aneight bit output port and an eight bit in-put port connected to a simplemicroprocessor system. The ports havean eight bit capacity simply because themicroprocessor has an eight bit data bus,and can therefore transfer data eight bitsat a time!

The output port has eight inputs con-nected to the data bus and eightseparate outputs for connection to ex-ternal circuits, and a strobe. The outputsfollow the logic states of the inputs for aslong as the strobe input is high; howeverwhen the strobe is taken low, the data atthe outputs is frozen or 'latched' in-definitely. An IC of this sort is called an'Octal Transparent Latch", and a74LS373 is a typical example using TTLTechnology in the microprocessorsystem of Figure 1, the strobe is derivedfrom theWfisignal of the control bus andthe decoded address bus. Data will belatched into the port only when the MPUattempts to write to a specific address,as determined by the address -decodelogic. This configuration is called"Memory -Mapped I/O" because theport appears to the MPU as a single byteof memory, in this case a write -onlymemory location. Using simple 'store'instructions, the MPU is able to controlthe state of eight logical outputs, each ofwhich can be interfaced to anythingfrom a LED to a large industrial machine,

MPU

DATA BUS

ADDRESS BUS

ROM

OE CE

RD

RAM

RD CE WE

WR

ADDRESSDECODING

9 a

/7777

8 -BITOUTPUT

PORT

E 9

8 -BITINPUTPORT

STROBE

Figure 1. A simple microprocessor system with one output and one input port.

46

using no more than a few transistors andrelays.

The input port, as shown in Figure 1,is also an octal latch but this time the out-puts are wired to the data bus and the in-puts are taken from the external circuit.For an input port, the latch must have(like the 74LS373) a control which can'tri-state' the outputs to the data bus;this means that the outputs can go to ahigh impedance state, and thus have noeffect upon the data bus when it is beingused by other devices, such as RAM orROM. The output control signal is de-coded from the address bus and the R-13signal so as to 'map' the port to the de-sired memory location. The strobe to aninput latch is not synchronised with theMPU as with the output port; it has to beprovided by the external circuit to syn-chronise with incoming data. In certainapplications (A/D conversion being thebest example) the data presented to theMPU's input port may not be valid (true)at all times, which explains the reasonfor an external synchronising pulse.

However, the MPU is often required

0

1,0

YbO

la,

1,2

Yb2

1,3

Yb3

GND

VCC

0

Ya0

1b0

Vat

Ya2

11)2

Y,3

1b3

Figure 2. The logic diagram and pin outsof the 74LS244. The OE inputs latchthe outputs to the high impedence (off)state.


Popular Computing

EMI

VCC = PIN 20

GND = PIN 10

OE (I) -

DO (31

00 12)

D1 (41 02 (7)

D D

03 (8) 04 1131

D E

-Y-Y-Y4F1401 (5) Q2 (61 03 (91 Q4 (12) 05 (151 Q6 (16)

D7

vQ7 (191

18)

3

111111111

4 7 8 13

DO DI D2 D3 D4

11

OEC

00 Cil 02 Q3 Q4

VCC = PIN 20

GND = PIN 10 2 5 6 9 12

14 17 18

I I ID5 D6 07

05 Q6 07

15 16

Figure 3. The logic diagram (above) and pin -outs (right) of the 74LS373. Data is latched by taking the E input low; a high onthe OE input forces the outputs to the high impedance state.

only to sample the inputs periodically (if,for example, they connect to a set oflogically independent switches) and inthis case, latching of data is un-necessary; an "Octal Tri-State Buffer"(such as a 74LS244) will then be suffi-cient as an input port.

Memory mapped I/O is a systemwhich can be readily applied to anymicroprocessor, yet there is a commonalternative which is worth mentioning."I/O Mapping" is a system which is uni-que for each type of microprocessor(some simply do not have the facility, eg.the 6800 and the 6502) because it re-quires specific sets of hardware and in-structions. The 1802 has a three -bit ad-dress bus, separate from the normal ad-dress bus, which can be decoded to pro-vide 'enables' for up to seven I/Odevices; these addresses are generatedonly in response to special instructions(INP1 - INP7, OUT1 - OUT71.

Other processors leg. the Z80 andmany other Intel products) place I/O ad-dresses (0-255) on the usual addressbus and have a separate control line to in-dicate whether the instruction is to beexecuted on memory or on I/O.

I/O ports can easily be constructedfrom a few TTL chips, however themanufacturers of all microprocessortypes offer more 'clever' devices design-ed for flexibility in applications, in a

single low cost package, with eachdevice type intended for a particularmicroprocessor. Most of these containseveral ports within a chip, and can beprogrammed to behave either as input oroutput devices; many have other in-teresting facilities, as we shall see.

The 8255It is impossible, in these few pages, todescribe every I/O device on the marketso we shall concentrate on just one -the 8255. This device is intended to in-terface with the Intel 8080 and 8085family of microprocessors; however, itcan be used readily with the Z80 and, ofcourse, the 1802, as in the Micro -Trainer. It is one of the most versatilePPIs (Programmable Peripheral Inter-face) available and has recently becomevery inexpensive.

Referring to the block diagram ofFigure 4 and the pin diagram of Figure 5,you will see that the 8255 has threeeight -bit ports within a 40 pin package.Port A (PAO-PA7) and Port B (PBO-PB7)can be separately programmed as eitherinput or output, while Port C is logicallydivided into individually programmed up-per (PC4-PC7) and lower (PCO-PC3)portions.

The 8255 possesses all thenecessary signal inputs to interfacedirectly to the CPU. Signals DO -D7 con -

8080 CPUMODULE

INTERFACE

BI-DIRECTIONALDATA BUS

D7 -DO

RD

WR

AlAO

RESET

DATA BUSBUFFER

CS

READ/WRITECONTROL

LOGIC

INTERNAL LOGIC

GROUP ACONTROL

8 BIT INTERNALDATA BUS

GROUP BCONTROL

PERIPHERALINTERFACE

GROUP APORT A 181

GROUP APORT C

UPPER (41

GROUP BPORT C

LOWER (41

GROUP BPORT B (R)

Figure 4. The logic diagram of the 8255 PPI; the ports are splitinto two groups for control purposes.

I/O PA7-FAO

I/O PC7-PC4

I/O PC3 PCO

I/O PB7-PB0

nect directly onto the data bus, for bi-directional transfer of data between CPUand the ports and, likewise, the signalsTO and Tv7 connect directly to the cor-responding signal lines of the CPU. Thecontrol signal cs (Chip Select) is used toallow the CPU to use the 8255. For ex-ample, if cs is provided with a logic low,decoded from the address bus (theMicro -Trainer uses an address in therange 2000H to 2003H) the device willbe 'enabled'.

The signals AO and A 1 , the two leastsignificant bits (LSBs) of the addressbus, will select one of the four internalregisters, according to the address;three of these registers are, obviously,the ports A, B and C, while the fourth is acontrol register used for programmingthe device. These addresses (summaris-

PA3

PA2

PA1

PAO

RD

CS

GND

AlAO

PC7

PC6

PC5

PC4

PC0

PC1

PC2

PC3

PBO

PB1

PB2

PIN NAMES

PA4

PA5

PA6

PA7

WR

RESET

DO

D1

D2

D3

D4

D5

D6

D7

VCC

PB7

PB6

PB5

PB4

PB3

07 -DO DATA BUS (BI-DIRECTIONAL)

RESET RESET INPUT

CS CHIP SELECT

RD READ INPUT

WR WRITE INPUT

AO,A1 PORT ADDRESS

PA7-PAO PORT A (BIT)

PB7-PBO PORT B (BIT)

PC7-PCO PORT C (BIT)

VCC +5 VOLTS

GND 0 VOLTS

Figure 5. The pin -outs of the 8255 (top)and their meaning (bottom).


III Popular Computing

A B GROUP A GROUP B

D4 D3 01 DO PORT A PORT C(UPPER)

PORT B PORT C(LOWER)

0 0 0 0 OUTPUT OUTPUT 0 OUTPUT OUTPUT

0 0 0 1 OUTPUT OUTPUT 1 OUTPUT INPUT

0 0 1 0 OUTPUT OUTPUT 2 INPUT OUTPUT

0 0 1 1 OUTPUT OUTPUT 3 INPUT INPUT

0 1 0 0 OUTPUT INPUT 4 OUTPUT OUTPUT

0 1 0 1 OUTPUT INPUT 5 OUTPUT INPUT

0 1 1 0 OUTPUT INPUT 6 INPUT OUTPUT

0 1 1 1 OUTPUT INPUT 7 INPUT INPUT

1 0 0 0 INPUT OUTPUT 8 OUTPUT OUTPUT

1 0 0 1 INPUT OUTPUT 9 OUTPUT INPUT

1 0 1 0 INPUT OUTPUT 10 INPUT OUTPUT

1 0 1 1 INPUT OUTPUT 11 INPUT INPUT

1 1 0 0 INPUT INPUT 12 OUTPUT OUTPUT

1 1 0 1 INPUT INPUT 13 OUTPUT INPUT

1 1 1 0 INPUT INPUT 14 INPUT OUTPUT

1 1 1 1 INPUT INPUT 15 INPUT INPUT

Al AO RD WR CS INPUT OPERATION (READ)

0 0 0 1 0 PORT A= DATA BUS

0 1 0 1 0 PORT B= DATA BUS

1 0 0 1 0 PORT C= DATA BUS

OUTPUT OPERATION(WRITE)

0 0 1 0 0 DATA BUS = PORT A

0 1 1 0 0 DATA BUS = PORT B

1 0 1 ' 0 0 DATA BUS = PORT C

1 1 1 0 0 DATA BUS = CONTROL

DISABLE FUNCTION

X X X X 1 DATA BUS = 3 -STATE

1 1 0 1 0 ILLEGAL CONDITION

X X 1 1 0 DATA BUS = 3 -STATE

X = DON'T CARE

Table 1 (right). The ports can be set up in any of 16 differentways.Table 2 (above). Ports are addressed, as appropriate under pro-gram control. A WRite instruction to a port set up for Input willbe ignored.

ed in Table 3) are used in the Micro -Trainer to access the 8255.

In order to write data to a port, it issimply a matter of executing an 'STR' in-struction to the appropriate address, eg:

LDI $20LDI $01

LDI SOF

PHI R3PLO R3; R3 is pointer toPort BSTR (R3); data $ OF ap-pears on PBO-PB7

Data which has previously been writ-ten to an output port can also be readback from the same address - a featurewhich is not possible with the system ofFigure 1.

We have not, so far, discussed howthe ports are programmed - but thereare no prizes for guessing that the con-trol register is used for this. All the pro-gramming information is illustrated inFigures 7 and 8, but some explanation isalso required.

Al AO MICROTRAINERADDRESS

REGISTERENABLE

0 0 2000H PORT A

0 1 2001H PORT B

1 0 2002H PORT C

1 1 200311 CONTROL

Table 3. The Micro -Trainer I/O addresses.

AlAO

- cs

WR

RD

D6

D

D4

D2

+5V

6

7

28

29

30

31

32

33

2

IC4

14

15

16

17

13

12

11

10

4

3

2

40

39

38

37

18

19

20

22

23

24

25

2

3

4

5

6

7

16

15

14

IC7 1312

11

10

-o PCO-o PC1-o PC2-o PC3-O PC4--o PC5-o PC6

o PAO

o PA1

o PA2

o PA3

o PA4

o PA5

o PA6

o PA7

PBO

oPB1

oPB2

o PB3

o PB4

PB5

PB6

PB7

R5 R85k6 4k7

+5V

01

OV

R6 CASS

v,68OR.C3 I____01N/Our

R7470R

Figure 6. The I/O Port circuits of theMicro -Trainer; IC4 is an 8255.

CONTROL WORD

107106 D5112/411:1311:12101 DO

GROUP

PORT C (LOWER - PC3 -PCO)1 = INPUT0 = OUTPUT

PORT B1 - INPUT0 = OUTPUT

MODE SELECTION0- MODE 01 = MODE 1

GROUP A

PORT C (UPPER -PC7-PC4)- INPUT

0 = OUTPUT

PORT A1 - INPUT0 = OUTPUT

MODE SELECTION00= MODE 001 = MODE 1

= MODE 2

OP CODE

1 = MODE SET

Figure 7. The mode control word can beconstructed from this diagram.

CONTROL WORD

ID71D61D5104[D311)21D11001

NOT USEDSET TO 000

SET/RESET FLAG

0 = RESET BIT1 = SET BIT

BIT SELECT

D3 D2 D1 PORT BIT C

0 0 0 BIT 00 0 1 BIT 10 1 0 BIT 20 1 1 BIT 31 0 0 BIT 41 0 1 BIT 51 1 0 BIT 61 1 1 BIT 7

OP CODE

0 = BIT SET/RESET

Figure 8. Deriving the control word toset or reset bits of Port C.

The first step is to decide how theports are to be configured (output or in-put) then, using the two diagrams, workaout a control word on a bit by bit basis.You may be confused by the referencesto Modes 0, 1 and 2; just assume thesebits are set to zeroes. Our description ofthe 8255's operation are all in Mode 0;the other modes configure certain bits ofPort C as 'handshake' lines and as thisfacility is little used we will not discuss ithere!

As an example, suppose we requirePAO-PA7 as outputs, PCO-PC3 as out-puts and PBO-7, PC4-PC7 all as inputs.Figure 7 tells us that the required data is10001010 = 8AH so, simply by storing8AH in the control register, our ports areset up as required. The contents of thecontrol register may not be read back bythe CPU. It is also well worth noting thateach time a port is configured as an out-put, the contents are reset to zero.

During power -up, or reset of theMPU, it is normal to reset the 8255 also,using the hardware line RESET (pin 35).When this happens, all ports are con-figured as inputs in Mode 0, so that themachine's software must initialise thecontrol register, as required, after reset.Figure 8, shows how Port C an be con-veniently operated on bit by bit, whenprogrammed as an output. Here, by stor-ing the appopriate data in the controlregister, a single line of Port C may be setor reset. As an example, again, PC7 hasbeen interfaced to a transistor (Figure 6).

This forms the cassette interface forthe Micro -Trainer. It is controlled by aroutine in ROM which recognises aLOAD or SAVE instruction, configuresPort C (upper) as required, and then tog-gles bit 7 to transfer the data.

The other seven bits of Port C are allconfigured as outputs, buffered by aULN2003 (IC7 in Figure 6), which pro-vides open collector outputs suitable fordriving LEDs, relays etc. Each output cansink up to 500mA.

Next month's installment will investigatethe hidden depths of memory - RAMs,ROMs, and the multivariate degrees ofPROMs.

HE48 Hobby Electronics, December 1982

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This new design is based on theICL7126 (a lower power version ofthe ICL7106 chip) and a 31/2 digitliquid crystal display. This kit willform the basis of a digital multi -meter (only a few additional re-sistors and switches are required -details supplied),or a sensitive digital thermometer (-50 C to+150"C)reading to 0.1'C. The basic kit has a sensitivity of200mV for a full scale reading, automatic polarity in-dication and an ultra low power requirement -givinga 2 year typical battery life from a standard 9V PP3when used 8 hours a day, 7 days a week

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With Heathkit, not onlydo you enjoy big savings, you're sure of the finest quality.

Everything is provided, including detailed instructions. Eventhe solder you need is there. You'll end up with a superb piece ofequipment. Hand crafted. One you'll be extra proud of. Becauseyou built it yourself.

There are all sorts of kits to choose from. From a digital clockto a metal locator, a short wave listener's receiver, windspeed anddirection indicator, digital readout electronic scale and plenty more.

There's even the HS -89-2 All -In -One computer kit. With48K RAM, three serial ports, single density disc controller andgreen anti -glare screen. Now incredibly only £799 + VAT andcarriage. A genuine bargain.

Send off for your catalogue now.The sooner you do, the sooneryou'll see what you could get.

To: Heath Electronics (UK)Limited, Dept ( HE12), Bristol Road,Gloucester GL2 6E E.

I'd like to get building. Please sendme a copy of the Heathkit catalogue. Ienclose 28p in stamps. HE12

Name

Address

.g,"E'3-71. You buildon our e

EATH

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PROBABLY THETRANSISTORS

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PROFESSIONAL AMPLIFIER MODULESPRICE LIST -

ELECTRONIC MODULES Er ASSEMBLIES - APRIL 1981

CODE DESCRIPTION Less VAT INC WTVAT VAT (Kg)

f £ eCE 608 Power Amplifier Module 18.26 2.74 21.00 0.16CE 1004 Power Amplifier Module 21.30 3.20 24.50 0.20CE 1008 Power Amplifier Module 23.90 3.60 27.50 0.21CE 1704 Power Amplifier Module 30.43 4.57 35.00 0.22CE 1708 Power Amplifier Module 30.43 4.57 35.00 0.22CE 3004 Power Amplifier Module 42.60 6.40 49.00 0.40BD 1 Bridge Driver Module 7.13 1.07 8.20 0.06TR 80 Toroidal Transformer 80VA 18.00 2.70 20.70 2.00TR 150 Toroidal Transformer 150YA 20.07 3.01 23.08 2.35TR 250 Toroidal TRansformer 250VA 25.43 3.81 29.24 3.35TR 2500 Toroidal Tansformer (low noise) 33.20 4.98 38.18 2.80B 6 Bridge Rectifier 16 amp) 0.99 0.15 1.14 0.02B12 Bridge Rectifier 112 amp) 1.80 0.27 2.07 0.03C4700/40 Reservoir Capacitor and Clip 1.91 0.29 2.20 0.09C4700/63 REservoir Capacitor and Clip 2.40 0.36 2.76 0.11C4300/63 Reservoir Capacitor and Clip 2.60 0.39 2.99 0.11CPS 80 Power Supply 22.82 3.42 26.24 2.10CPS 80D Dual Power Supply 27.63 4.14 31.77 2.25CPS 150 Power Supply 25.86 3.88 29.74 2.50CPS 150D Dual Power Supply 31.65 4.75 36.40 2.60CPS 250 Power Supply 32.03 4.80 36.83 3.50CPS 250D Dual Power Supply 39.43 5.91 45.34 3.65TS 70 Thermal Switch 70°C 1.92 0.29 2.21 0.02HS 50 50mm Heatsink 1.60 0.24 1.84 0.15HS 100 100mm Heatsink 2.60 0.39 2.99 0.30HS 150 150mm Heatsink 3.65 0.55 4.20 0.45FM 1 Fan Mounted on 2 x HS 100 32.13 4.82 36.95 1.20FM 2 Fan Mounted on 2 x HS 150 36.10 5.42 41.52 1.50CPR 1X Pre -Amplifier Module 31.30 4.70 36.00 0.15MC 2 Moving Coil Pre -Pre -Amplifier Module 20.00 3.00 23.00 0.07REG 1 Regulated Power Supply 8.09 1.21 9.30 0.07TR 6 6VA Mains Transformer 2.87 0.43 3.30 0.21XO 2 2 Way Crossover Module 17.39 2.61 20.00 0.07X0 3 3 Way Crossover Module 26.09 3.91 30.00 0.07MU 1 Muting Circuit for XO 2 or XO 3 8.35 1.25 9.60 0.04CK 1010 Complete Pre -Amplifier Kit 78.26 11.74 90.00 2.50CK 1040 Complete 40 Watt Power Amplifier Kit 103.48 15.52 119.00 t7.30CK 1100 Complete 100 Watt Power Amplifier Kit 129.56 19.44 149.00 7.30MC 2K Add On Moving Coil Kit 21.74 3.26 25.00 0.12PSK 1 Pre -Amplifier Power Supply Kit 17.39 2.61 20.00 0.75

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A blast from the pastThis seems to be a year for revivals -musicals in the West End, old popsongs from the 50s and 60sreappearing in the Charts, and now . . .

Dear Clever Dick,I have "Experimenter" and "S -Dec"boards and I am wondering if you coulddevise projects for these for futureeditions of HE. I find it very difficult toget anything suitable.P. Siddi,Porthcawl,Mid-Glam.

. . . . "Short Circuits" have beenbrought back, in the shape of a newpage called "Breadboards". Althoughthese experimenter's circuits havebeen laid out and tested using Vero'sVerobloc system, they can easily beadapted to any other breadboardingsystem.

Dear CD,I have one short question; is there anyerrors in the shortwave Receiversveroboard diagram etc?T ChapmanFarehamHants

'Is there any errors' . . . it's enough tomake you ask : is good grammar a thingof the past? Another question, whichmight be pertinent; which short wavereceiver do you mean-we havepublished at least three?

However, passing over such minorconsiderations (it only took four timeslonger to sort things out), the receiverin question is probably that featured inSeptember '81 issue. There were threeerrors discovered at the time; missingtrack cuts at F 17 and G17, a missinglink (not the . . no it couldn't be)between F12 and G12 and nomarkings on Dl -the cathode shouldgo to F7.

Dear CD,I am eleven years old, and have beenalarmed to find a mistake on the"Intruder Con fuser". Capacitor (CI)has been connected (not across) but inthe same direction as the copper stripsand there is no break between the twoterminals. Also (according to theschemetic diagram) the integratedcircuit has been connected the wrongway round, there is also anotherproblem . . . . I have, nowhere to storemy Hobby Electronics magazine YoursFaithfully,R.EinsteinIpswichSuffolk

(hint, hint). Life isn't all problemsthough, because I think yourmagazine's great

Correct on both points-though theissue was raised in a previous HE (June'82, I think). As for the mag, I alsothink it's great too (especially thispage), but then I am a little biased!

Dear CD,I DO NOT WANT A BINDER!!!I would, however, like to pick youramazingly intelligent brain. Way back inJanuary '79, HE published a TouchSwitch project. I find it works fine if theOV level is connected to the mainsearth, but if I try to run it off batteries(as you recommended, all those yearsago) the operation becomes sporadicand unreliable.

So far as I can make out, the signalinput level drops dramatically undercertain conditions, depending on myposture (keep your remarks toyourself!).

Please could you suggest a circuitmod or, failing this, are there any ICs

use, preferably withseveral switches on one chip?

I am designing a piece of equipmentfor use by small children so that asingle touch -control switch isimportant, as, of course is the electricalsafety.Guy Inchbald,Burnage,Manchester.

The circuit is intended to be triggeredby the 50 Hz hum voltage which we allcarry around with us - effectively, thebody acts as an antenna. Touching thecontact transfers the voltage to theinput of IC 1 , which amplifies itenormously. This is rectified by a diodeand the resultant DC is used to switchanother op -amp from low to high, thusturning on a LED, relay or whatever.Note, too, that this circuit does notlatch up; it will turn off shortly after thefinger is removed.

The unreliable operation is probablybecause the 50 Hz signal is beingcoupled to all parts of the circuit,(remember that a battery is a shortcircuit for AC, even at 50 Hz), so thatthe input op -amp is seeing similar 50Hz voltages on both its inverting andnon -inverting inputs. The easiest wayto solve the problem is to physicallyisolate the touch plate from thecircuitry; metal shielding may even benecessary. Alternatively, you could tryincreasing the sensitivity by increasingthe gain of IC 1; reduce R2 by stagesuntil you find a value where theoperation becomes reliable. However,you may find that the circuit becomesunstable if R2 is taken too low.

Dear Richard,I have had the HE watch dog intruderAlarm (Oct 80) working on a test basisfor some months. But have found thatit is triggered by an external source/s.

A 3 foot instant start fluorescentfitting and a portable TV that I know of,have, when switched off, bought onLED2 showing a short.

I don't know what electricalappliances my neighbours have but ithas happened when / have only had afridge working. Its only occasionallythis happens, and after 2200 hrs, orthe early hours of the morning.

The PB1 doesn't cancel/ LED2 andRV1 has to be re -adjusted to cancel itthen adjusted back to its normalposition, which may take five minutesor more of adjusting. The circuit board(its not a printed circuit, they were notavailable) is mounted in a metal boxand the box is bonded to earth. Theonly alteration to the circuit is in thewindow, where the 22k resistor hasbeen changed to 56k. resister, to givea bigger window. But I find there is stillonly a small amount of movement ofRV1, when adjusting, to equal door andwindow switches LED 1 before LED2comes on.

The value of my switch resistorsare 470k. /have changed the ICs atdifferent times but trouble alwaysreappear's.

Have you had or heard of anyonehaving had this happen with the lntuderAlarm and how did you or theyovercome it? My knowledge at themoment of electronics is limited so I'mhoping you can throw some light on toit for me.N. KilbeyIlfordEssex

What can be deduced from this tale ofwoe? Gremlins in the alarm system .not likely . . . well, how about spikes inthe mains . . . ah, that sounds morelike it-mains borne interference.

What can be done about it? Well,first of all try putting the unit on aPCB-it's amazing the increasedstability you'll get. There are also someother steps you can take. One is towire a 100u capacitor across thesupply rails; and try a 100n in parallelto cut out HF spikes. Another filter canbe made by wiring a 10k resistor inseries with the line from point X,followed by 4u7 capacitor down toearth (try different positions around theboard). If you want to make RV1 moresensitive, change it to 1M and replaceR2 with the original 22k value . . andif all that fails, I hear Alsatians are alsopretty effective!

HE


Project

POPOwen Bishop

AMPSSimple measuring circuits based on operational amplifiers.

No. 1:MicroammeterTHIS circuit adapts any ordinaryvoltmeter to measure currents in themicroamp range. You can also use itwith a multimeter, switched to avoltage -measuring range. The lowestcurrent range on a typical multimeter is0 - 250 uA, but with this circuit therange can be as small as 0 - 1 uA. Ofcourse, if you have an FET multimeter,you will probably not need this circuit,as it is likely to be built in to your meteralready.

Measuring CurrentsAn ammeter is always connected inseries with the circuit which is to betested, and the current to be measuredflows from the test circuit, through themeter and back to the test circuit. Forthis reason, the ammeter must have aslow a resistance as possible, so thatthe flow of current in the test circuit isnot reduced by the resistance of themeter. A typical microammeter has acoil resistance of around 750R,though some microammeteis havecoils of considerably higher resistance.However in this circuit, when it is usedon its 1 OOuA range, the resistanceencountered by the current is only100R, resulting in much greateraccuracy. The improvement can beseen by taking a numerical example.

In Figure 1 a, the current flowingthrough the 2k7 resistor is 0.2/2700= 74uA. If we try to measure thisusing an ordinary microammeter (Figure1 b), with a coil resistance of 750R, thetotal resistance becomes 345OR andthe current is reduced to 58 uA. This isa 23% error!

Using the op -amp circuit (Figure 1c I,the total resistance is much lessaffected. It becomes 2800R, reducingthe current to 71 uA, and the error isnow only 4%.

Some reduction of current isinevitable, for we can not avoid usingpower to drive the measuringinstrument. The advantage of using theop -amp microammeter then, is that itneeds very little power and so has arelatively small effect on the currentyou are trying to measure.

The CircuitWe will assume that the circuit is beingused on its 100 uA range, when acurrent of 100 uA flows through R5,the potential difference between itstwo ends is [V = IR = 100 x 10-6 x

ov

«OV2

74uA

ov

.0V2

OV

b

71uA

2k7

2k7

900R 9k

1009

c)

Figure 1. Measuring current (a) using ameter alone (b) results in a large error.The op -amp circuit (c) increases theaccuracy of the measurement.

NOTE: ICI = 741

INPUTS

luA

10uA

100uA

ov

Figure 2. The Microammeter circuit.


Project

-VE INPUT at

100uA10uAluA A

1 2 3 4 5 6 7 8 9 10 11

0 0 0 0 0 0000 08 0

C

D

00

0F 0

G 0H

I 0

9V al-K 0L 0

I

M 0 0 0 0 0 0 0 0 0 0

M

K

1

H

D

C

12 13 14 15 16 17 18 19 20 21 22 23 4 25 26

0 0 0 0 0 0 0 010 0 0 0 0000000

4,0T

cr

00

0000 0 0 0 0 00 0 0

IP METER -VE

0 0 0 00 00 00 0 0 0 0 00 0 0 0 0 0 0 0 0 00 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 00 0 0 000 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

0 0 0 0 00 0 0 0 0 0 0 0 0 0 0 0 00 00 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 O 00 0 0 0 0 0 0 0 0 0. 0 0 0 0 0 000 0 0 0 00 0 0 0 00 0 0 0 0 0 00 00 0 0 0 0 0 0 0 0 0 0 0 0 0 00 0 0 0 0 0 0 0 00 00 0 0 0 0 0 0 0 0 0 0 0 0 O 0 0 0 0 0 0 00 00 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 00 00 0 0 00 0 0 50 0 0 0 0 0 0 0 0 0 00 0 0 00 0

0 0 0 00 0 0 0 0 0 0 0 0 0 0 0 0 00 0 0 0 0 00 0

0 0 O 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 01 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26

Figure 3. Veroboard component overlay and track -side view.

cp.

10138A

108A

18A

INPUTTERMINALSOCKETS

CIRCUITBOARD

Figure 4. Wiring up the off -board components.

OV

P +9V

-0 METER +VE

OFF

ON

DPDT OR DPSTSLIDE SWITCH

OUTPUTTO

100 = 0.01 V [or 10 mV.[ Thus, atfull scale deflection (FSD), the non -inverting input ( + vel of the op -amp isat 10 mV compared with the 0 V line.We can ignore the effects of R1/R2and R3/R4, since these are relativelysmall resistances compared with theinput impedance of the op -amp (theinput impedance of a 741 is typically2M, so these resistors merely increaseit to 2.0099M!1. If the non -invertinginput is at + 10 mV, the amplifieradjusts its output to try to bring theinverting input ( - vel to the samepotential. This is a special feature ofop -amps, and one that is made use ofin several other of the circuits we shallbe describing.

If the inverting input is to be at + 10mV, the junction of R6 and R7 must bebrought to + 10 mV. Since R6 and R7form a potential -divider network, theoutput voltage if the op -amp has to riseto + 1.01 V to achieve this, and this is

the voltage which is measured by thevoltmeter. When measuring a currentof 100 uA, the voltage reading is 1.01V; we can ignore the odd fraction of avolt and say that 1 V is equivalent to100 uA. The currents equivalent tolower voltages are easy to calculate -OV5 means 50 uA, OV73 means 73uA and so on, in proportion.

We work with a maximum potentialdifference of 10 mV on the other tworanges as well, so the reading obtainedon the voltmeter is always betweenzero and 1 V. If the test circuit isconnected to the 10 uA socket, thetotal resistance is 1 k. With 10 uAflowing through this, the potentialdifference across R3/R4/R5 is 10 mV,as before. Now, a reading of OV73means a current of 7.3 uA. The 1 uAsocket gives a total resistance of 10k,with a PD of 10 mV when 1 uA flows.A reading of 0.73 V means a current of0.73 uA.

Parts ListRESISTORS(All Y4 watt 1% carbon)R1 8k2R2,3 820RR4 82RR5 100RR6 1MR7 10kPOTENTIOMETERSRV1 10k

min. horiz. presetSEMICONDUCTORSIC1 741

op -ampMISCELLANEOUS2.5 mm stripboard, 66 x 33 mm; 9x 1 mm terminal pins; 2 x 4 mm redsockets, 2 x black; DPDT switch; 2x PP3 battery clips; optional case;wire; solder etc.BUYLINES page 34

ConstructionLike all the circuits in this series, thisone is built up on a single, small pieceof stripboard (Figure 3). Whether youmount it in a case or not is a matter ofpreference. The circuit is powered bytwo PP3 batteries, giving the ±9 Vsupply required, though it is possible tooperate on other balanced supplies,such as ±6 V or ±15 V.

Construction presents no problemsbut be sure to make the track cuts, andcheck the position of all components.Note that two pairs of resistors arewired in series (R1/R2 and R3/R4) toobtain the values 900R and 9kR, asnearly as possible.

Setting UpTo set up the circuit, connect thevoltmeter as shown in Figure 4. Thisshould, preferably, be a 1 V FSD panelmeter or a multimeter switched to the1 V DC range, but a 2 V or 3 V meterwill do almost as well.

It does not matter if it is a cheapmeter, with low coil resistance, sincethe op -amp is capable of supplying allthe current required. If you can afford ameter for the purpose, there is noreason why you should not wire it tothis circuit and mount it permanently ina case.

Now switch on the power; themeter will show a reading of somekind. Join the 1 uA input socket to thejunction of R6 and R7, using a test -lead; this connects the two inputs ofthe op -amp together. The reading onthe meter should be 0 V, but if not,adjust the offset null potentiometer(RV1)until the needle of the metercomes to rest at zero. The temporarylead may now be removed, and thecircuit is ready for use. This is a simplecircuit, with no provision for adjustingfull-scale deflection or range; it isassumed that the use of 1% toleranceresistors will have ensured all theaccuracy required. HE


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DISTORTIONT.H.D. I.M.D.Typ at 60Hz/1KHz 7/01. 4:1

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Typ

Sizemm

WTgms

PriceincVAT

.. it, 15 4-8 11015% <0.006% 2 18 76 u 68 x 40 240 [B 4011060 30 4.8 0.015% <0.006% 2 25 76 x 68 x 40 240 (9.55II V60611 31) 311 433 11.015% <0.006% 225 120 x 78 0 40 420 C18.69iiv124 611 4 0.01% <0.006% i 26 120 0 78 if 40 410 [20.75110123 6() 11 1201% <0.006% 2 35 120 x 78 a 40 410 [20.7511)+244 120 4 0.01% <0.006% 2 35 120 x 78 x 50 520 [25.471102/111 12)) 8 0.01% <0.006% 250 120 x 78 x 50 520 025.47I-IY:164 180 4 0.01% <0.006% 2 45 120 x 78 x 100 1030 E38.41110368 180 8 0.01% <0.006% 260 120 x 78 x 100 1030 (38.41

Protection Full load line. Slew Rate 15v/ps. Risetirne: Bps. S/N ratio: 100db.Frequenc response -3d8) 15H - 50KHz. Input sensitivity) 500mV rms.Input Impedance 100011 . Damping lector. 10011z >400.

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Module Functions CurrantRequired

Pros inc.VAT

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Most pre -amp modules can be driven by the PSU driving the main power ampA separate PSU 30 IS available purely for pre amp modules if required forE5.47 (inc. VAT). Pre -amp and mixing modules in 18 different variations.Reese send for details.Mounting BoardsFur ease of construction we recommend the B6 for modules HY6-H Y13 E1.05linc VAT) and the 666 for modules HY66-HY78 E1.29 (inc. VAT)

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For Use With Price on.VAT

PSU 210 1 or 2 HY 30 C11.93PSU 41 X 1 or 2 HY60, 1 x HY6060. 1 a HY 124 013.83PSU 42X I 0 H Y 128 [15.90PSU 43X 1 0 M05128 E16.70PSU 5IX 2 x HYI28, 1 x1-/244 E17.07

MOSFET MODULES

Module I Output Load DISTORTION Supply Size WT PriceNumb.. Power Impedance T.H.D. I.M.D. Voltage mm gms inc.

Wets /1 Typ at 60Hz/ Typ VATrms 1KHz 7101z 4:1

MOS 128 60 4-8 <0.005% <0.008% 3 45 120 x 78 , 40 420MOS 248 120 4-8 <0.005% <0.006% 0 55 120 x 78 a 80 850MOS 364 180 4 <0.005% <0.006% ± 55 120 x 78 0 100 1025

Protection. Able to cope with omplex loads without the need for very specialprotec ion circuitry (fuses will suffice).

Slew rate. 20v/ps. Rise time. 3ps. S/N ratio: 100dbFrequency response I-3481: 15Hz - 100KHz. Input sensitivity: 500mV rmsInput impedance. 100K 11 Damping factor. 100Hz >400.

'NEW to ILP' In Car EntertainmentsC15Mono Power Booster Amplifier to increase the output of your eor cassette player to a nominal 15 watts rms.

Very easy to use.

Robust construction.

ring car radio

£9.14 (inc. VAT)Mounts anywhere in car.

Automatic switch on.

Output power maximum 22w peek into 411Frequency response (-3481 15Hz to 30KHz, T.H.O. 0.1% at 10w 1K1 -1zS/N ratio (DIN AUDIO) 80dB, Load Impedance 311.Input Sensitivity and impedance Iselecteblel 700inV rms into 15K fl 3V rms into 811Size 95 x 48 a 50mm. Weight 256 gms.

C1515Stereo version of Cl5

Size 95 x 40 080. Weight 410 gms.

£17.19 linc. VAT)

ModelNumber

For Use With Price inc.VAT

8S0 52X 20 HY 124 E17.07PSU 53X 2 o MOS128 E17.86PSU 54% 1 x HY248 [17.86PSU 55% 1 x M05248 E19.52PSU 71X 2 0 HY244 E21.75

Plea. now. X in pert no. indicates primary voltage Please insert "0- in place ofX for 110V, "1" in place of X for 220V. and' 2- in plat of X for 240V.

ModelNumber

For Use With Price inc.VAT

PSU 720 2 x HY2413 [22.54PSU 730 1 it HY384 E22.54PSU 74X 1 x HY3613 C24.20PSU 750 2 x MOS248, 1 x MOS368 [24.20


WITH A LOT OFHELP FROM 1113C) ILELECTRONICS LTD

PROFESSIONAL HI -Fl THAT EVERY EN

CAN HANDLE

UnicaseIII

Over the years I LP has been aware of the need for a completepackaging system for it's products, it has now developed aunique system which meets all the requirements for ease ofassembly, adaptability, ruggedness, modern styling and aboveall price.

Each Unicase kit contains all the hardware required down tothe last nut and bolt to build a complete unit without theneed for any special tools.

Because of I LP's modular approach, "open plan" constructionis used and final assembly of the unit parts forms a compactaesthetic unit. By this method construction can be achieved inunder two hours with little experience of electronic wiringand mechanical assembly.

Hi Fi SeparatesUC1 PRE AMP UNIT: Incorporates the HY78 to provide a"no frills", low distortion, (<0.01%), stereo control unit,providing inputs for magnetic cartridge, tuner, and tape/monitor facilities. This unit provides the heart of the hi fisystem and can be used in conjunction with any of the UPUnicase series of power amps. For ultimate hum rejection theUC1 draws its power from the power amp unit.

POWER AMPS: The UP series feature a clean line front panelincorporating on/off switch and concealed indicator. They aredesigned to compliment the style of the UC1 pre -amp.Performance for each unit which includes the appropriatepower supply, is as specified on the facing page.

Power SlavesOur power slaves, which have numerous uses i.e.instrument, discotheque, sound reinforcement, feature inaddition to the hi fi series, front panel input jack, levelcontrol, and a carrying handle. Providing the smallest,lowest cost, slave on the market in this format.

UNICASES

HIFI SeparatesPrice inc.VAT

UC1 Preamp £29.95L,P1X 30 + 30W/4-8.0. Bipolar Stereo HiFi (54.95UP2X 60W/411 Bipolar Mono HiFi £54.95UP3X 60W/8n Bipolar Mono HiFi £54.95UP4X 120W/4/1. Bipolar Mono HiFi £74.95UP5X 120W/8n Bipolar Mono HiFi £74.95UP6X 6CAN/4-8n MOS Mono HiFi £64.95UP7X 120W/4 -8.n MOS Mono HiFi £84.95

Power SlavesUS1X 60W/411 Bipolar Power Slave £59.95US2X 120W/411 Bipolar Power Slave £79.95US3X 60W/4 -8n MOS Power Slave £69.96US4X 120W/4-81-1 MOS Power Slave £89.95

Please note X in part number denotes mains voltage. Please insert '0' in place ofX for 110V,'1' in place of X for 220V (Europe), and '2' in place of X for 240VIU.K.1 All units except UC1 incorporate our own toroidal transformers.

NTHUSIAS

TO ORDER USING OUR FREEPOST FACILITYFill in the coupon as shown, or write details on a separate sheet of paper,quoting the name and date of this journal. By sending your order to ouraddress as shown at the bottom of the page opposite, with FREEPOSTclearly shown on the envelope, you need not stamp it. We pay postage foryou. Cheques and money orders must be crossed and made payable to I.L.P.Electronics Ltd. if sending cash, it must be by registered post. To pay C.O.D.please add £1 to TOTAL value of order.

PAYMENT MAY BE MADE BY ACCESS OR BARCLAYCARD IFREQUIRED

IL 113ELECTRONICS LTD

Post to: ILP Electronics Ltd, Freepost 6,Graham Ben House. Roper Close.Canterbury. CT2 7EP. Kent. EnglandTelephone. 102271 54778.Technical: 102271 64723.Telex 965780.

Please send me the following

Total purchase price

I enclose ChequeD Pbstal Orders17 Int. Money Order

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Address

) Signature


IN Project

TAPE/SLIDEESYNCHRONIZER

Keep your audio in sync with your visuals!

THERE ARE several different types ofslide/tape synchroniser, but thefunction they all perform is to recordshort "bleeps" of tone, on a cassetteor tape recorder, and then use thesetones on playback to automaticallyoperate the slide -change mechanism ofthe projector. In its most basic form, aunit of this type is simply used with amonophonic cassette or tape -recorderas a programmable slide timer, or inconjunction with stereo tapeequipment the "bleeps" can berecorded on one channel while theother carries background music and (or)a commentary.

More sophisticated units enable thetone to be mixed with the music orcommentary during records. Then,during playback, circuits in the unitoperate the projector only when the"bleeps" of tone are detected andignore other signals on the tape, so thatspurious operations of the projector areavoided. This system has theadvantage of enabling the slide showto have a monophonic accompanimentusing a monophonic recorder, or astereo accompaniment using a stereorecorder, but is not very satisfactory inpractice since the "bleeps" are clearlyaudible to the audience, and aresomething of a distraction.

This problem can be overcome usingthe arrangement described above plusan additional stage which operatesduring playback to filter the "bleep"

signals from the output. The HESlide/Tape Synchroniser is of this type,but it is reasonably simple andinexpensive and does not require anytest equipment to enable it to be set upcorrectly for use. It would not be trueto say that there is no loss of qualityintroduced by adding in the "bleeps"to one channel and then filtering themout again, but the loss of quality is notlikely to be noticed, even if your slideshows are not quite as riveting as they

might be!The bursts of tone are at quite a high

frequency (about 5kHz) and whenthese are filtered out, any signals ataround this frequency in the music orcommentary are also removed. Thisobviously gives a certain loss of audioquality but, as only a very narrow bandof frequencies are seriously affectedand the fundamental frequencies inmusic are usually below 5kHz (so thatonly harmonics are attenuated by the

PLAYBACKINPUT

SW

Cl100u

Al220k

SW2TONE

-I- C2100n

RV147k

RV347k

4 R43k9

NOTES:IC1,2 ARE 741CD1,2 ARE 1N4148

2

PLAYBACK

RECORD

2 A

OFFSW1a

SK2RECORDOUTPUT

6IC2

C8R8 10u

100k

R7100k

+C5 C6100n T 47n

Figure 1. The Record section circuit.

C71u

R9100k

SK1RECORD

INPUT

819V


Project

How It WorksA MIXER and a tone generator areused to add bursts of high frequencytone to the input signal when a pushbutton switch is briefly operated; theoutput is fed to the input of onechannel of a tape recorder. Anothercircuit is used to process the signalwhen the tape is played back; thepurpose of this circuit is to separatethe bursts of tone and the mainsignal. The tone bursts are used toautomatically operate the projector atthe appropriate times, and this signalis filtered from the main signal using abandpass filter tuned tio thefrequency of the tone signal. Theoutput of the filter is fed to a drivercircuit which pulses a relay when thetone bursts are detected; a pair ofrelay contacts are used to operate theslide change mechanism of theprojector.

TONEGENERATOR

RECORD PLAYBACKOUTPUT INPUT

RECORDINPUT

NOTCHFILTER

BANDPASSFILTER

On playback the output from thetape recorder is also fed to a notchfilter which gives very highattenuation at the frequency of tonebursts, and thus eliminates them, butenables other frequencies to passunhindered. In practice, the notchfilter will actually remove some of thewanted signal, while the bandpassfilter permits some of the main signalto pass through to the relay driver.However, the loss of quality is notserious, and breakthrough to the relaydriver should not cause spuriousoperation of the unit.

The "bleeps" of tone are also fedto the bandpass filter and the RecordOutput so that the projector isoperated when the push button isoperated, so that the tone burst isadded to the sound track as theprojector is operated.

PLAYBACKOUTPUT

RELAYDRIVER RELAY

PROJECTORCHANGESWITCH

filtering) there is no drastic loss ofquality. There is also, inevitably, areduction in the signal-to-noise ratio,but this is marginal and is of nopractical consequence.

The unit is powered from anordinary 9 volt (PP6 size) battery, andit should be compatible with anynormal cassette or reel-to-reel tapedeck or recorder. It has unity voltagegain in both the recording and playbackmodes and should not introduce anyproblems of incompatibility between

the tape machine used and other itemsof equipment such as the amplifierused during playback.

The CircuitIf we consider the recording circuitfirst, (shown in Figure 1), ICI is usedas the tone generator. The oscillatorconfiguration is a form of the WienBridge which is capable of giving agood quality sinewave output. Theoperating frequency is determined by

R2, RV2, C3, C4 and R4; adjustingRV2 permits the operating frequency tobe varied from around 2kHZ to 10kHZ.In use, RV2 is adjusted to adjust theoutput frequency to give maximumattenuation from the notch filter in theplayback circuit; this is nominally at5kHZ.

R3, D1 and D2 form a negativefeedback network, RV3 can be set togive gentle oscillation with areasonably pure output. D1 and D2help to stabilise the feedback at thecorrect level and make the adjustmentof RV3 a little less critical.

IC2 is used as a standard operationalamplifier mixed circuit having unityvoltage gain. RV1 controls the volumeof the tone signal fed through to theoutput socket, so that it can be set at asuitable level relative to the mainsignal; however the tone signal is onlycoupled through to RV 1 when SW2 isoperated.

The circuit diagram of the playbacksection of the unit is shown in Figure 2.C 17 couples the input signal (from therecorder) to a notch filter, which isbasically a twin -T type using C18, 19,20, R1 7, 18, 19, and RV5. RV5enables the attenuation of the filter tobe peaked at a very high level (about80 dB or more).

A problem with a simple, twin -Tfilter is that it tends, also, tosignificantly attenuate signals atfrequencies well away from the centrefrequency, and in this application theaudio quality would be adverselyaffected. Typically, a twin -T filter givesabout 10 dB attenuation at half anddouble the operating frequency. In thiscircuit, the response of the filter isimproved by the negative feedbackloop around IC4. The circuit may look alittle confusing, due to the use of twonegative feedback loops, but the effectof this is to stabilise the gain of thecircuit at unity. This can only beachieved at frequencies where thelosses through the twin -T network arefairly low, however, and at theoperating frequency of the filter itslosses are far too high to besignificantly reduced by the negative

SK3PROJECTOR

CHANGESWITCH

+ C9- 100.

RLA1185R

01

C10

D3

D4

11

22n

105C12100n

6 B0 V+

R2215k

ar'SW16

FROM TONER14 GENERATOR

100k VIA S1N1aR20 NOTES:47k IC3,4 ARE LF351

1C16 Q1,2 ARE BC650D3,4,5 ARE 1N4148

C1510n

R16 C20 C21

3n3 22k 470P 470p

1-MAC-C131n

RV44k7 IC4

6

C224u7 SK5

PLAYBACKOUTPUT

2

C174u7

PLAYBACKAYBACK

2 HD)

41e-NYv R17 R19 R21

R12680k

INPUT 68k 68k 180k R241M

IC141n RV5

R1115k 4k7 100k

R1547k 618

180kC18470p "-

C19470p

0 OV.

Figure 2. The Playback section; the tone filter circuit is on the right (1C4)


Project

SK 1

SW1i 2)

1

CR

r T

C5

T 'E

( C4 )R4

I T

V FROM

SK 2PLAYBACK

BOARDRV2 SW2

Figure 3. PCB overlay for the Record section circuit.

PLAYBACK PCB

V TO PLAYBACK BOARD

V II

RV5

SW1(5,6) -0

SK4-

Sw11R).-.---

1

C17

e oRV4

J_

T T

SK4

SW1

T -CLL)--

C1

R 24 ,F.-

C11

IC2

KK SIN 18

C??

RI- LAY

Figure 4. The PCB and component overlay of the Playback section.

SK3

10 Al

SKY

feedback. Thus the response of thefilter is improved, with reduced lossesaway from the operating frequency butwith the deep attenuation notch beingretained.

C15 couples the tape input signal toan emitter follower buffer stage whichuses Q2, and this simply ensures thatthe next stage is fed from a suitablylow source impedance. The next stageof the circuit is actually a standardoperational amplifier bandpass filterusing IC3, tuned by RV4 to peak theresponse of the circuit at the correct

frequency.The output of IC3 is coupled to a

smoothing and rectifier circuit whichdrives Q1 which, in turn, drives therelay coil. When the bursts of tone arepresent on the input signal, theseproduce a strong positive bias at thebase of Ql, which is then switched on,activating the relay and the projector'sslide change mechanism via a set ofnormally open relay contacts.

SW1 is the mode swit ;11; thiscouples the output of the tonegenerator through to the playback

Parts ListRESISTORS(All Y4 W 5% Carbon)R1 220kR2 470RR3,20 47kR4 3k9R5,6,1 3 4k7R7,8,9,14,14 100kR10,11,22,23 15kR12 680kR16 22kR17,19 68kR18,21 180kR24 1M

POTENTIOMETERSRV1,3 47k

0.1W horizontal presetRV2 4k7

linear carbonRV4 4k7

0.1W horizontal presetRV5 47k

linear carbon

CAPACITORS(All C280 polyester unless noted)C1,5,9 100u 10V

axial electrolyticC2,10,12 100nC3,4,16 10nC6 47nC8 10u

25V axial electrolyticC11 22nC13,14 1n

polycarbonateC15 3n3

ceramicC17,22 4u7

63V axial electrolyticC18,19,20,21 470p

polystyrene

SEMICONDUCTORSIC1,2 741C

op -ampIC3,4 LF351

bifet op -ampQ1,2 BC650D1,2,3,4,5 IN4148

MISCELLANEOUSRLA1 12V 185n coil

2 pole changeover contactsSW1 3 way 4 pole rotarySW2 Push to make non -locking typeB1 PP6, 9 voltCase, about 203 x 127 x 51 mm;battery clip (PP3 type); PCBs; threecontrol knobs, wire, solder, etc.

BUYLINES page 34

circuit when the unit is in the recordmode (it also provides on/off switchingfor both circuits). Note that power isapplied to the playback circuit whenthe unit is in the recording mode, sothat the relay activates the projector tosynchronise the slide -change with thesound track.

ConstructionAn aluminium case measuring about203 x 127 x 51 mm will comfortablyaccommodate all the components,including the battery. The four controls


Project

HE SLIDER

PROJECTOR

PLAYBACK RECORDIN OUT IN OUT0 0


RECORDER

LINE IN LINE OUTL R

0 0

OUTTAPE '

IC IC

TAPE IN

AMPLIFIER/PRE AMP

I R L R L H

9 5 2 P/ /

SIGNAL SOURCE

ITAPE/TUNER/TURNTABLEI

Figure 5. Connecting the unit for Record deft) or Playback (right).

E SLIDE

PLAYBACKIN OUT

RECORDIN OUT0 0


LINE INL R

0 0

RECORDER

LINE OUTL R

0 0L R

TAPE OUT

AMPLIFIER,PREAMP

L R

TAPE IN

SIGNAL SOURCE

ITAPPTUNER,TURNTABLE/

are mounted on the front panel,although SW2 can be mounted in aseparate small (hand held) case andconnected to the main unit via a leadseveral feet long, if this will be moreconvenient in use. The lead would needto be terminated in a two way plug andSW2 would be replaced (on the frontpanel of the case) by a matching twoway socket. Note that this socketshould be a type which is insulatedfrom the case, such as a plastic jacktype or a two way DIN socket. SK1 toSK5 are mounted along the rear panel

of the case; these are all3.5 mm jackson the prototype, but can be changedto any other type of socket, if this willbe more convenient in use.

The other components are mountedon two printed circuit boards, one forthe recording circuit and the other forplayback. The component layouts andwiring are shown in Figures 3 and 4respectively; use Veropins at pointswhere off -board connections will bemade. The specified relay will fitdirectly onto the printed circuit board,but other types will work provided they

have a coil resistance of about 185ohms or more, will operate from about6 volts, and have at least one set ofnormally open contacts rated at about2 amps (AC) or more. However, if analternative relay is used it will benecessary to alter the PCB to suit, ormount the relay off -board. Incidentally,the specified relay has two sets ofchangeover contacts, with four of itspins unused.

Setting UpA quick initial check of the unit can bemade by switching the unit to therecording mode and operating SW2. Ifthe output of SK2 is monitored usingan amplifier and loudspeaker (or evenjust a crystal earphone), a tone shouldbe produced when SW2 is operated,provided that RV3 is set well into theanticlockwise position. RV1 shouldcontrol the volume of the tone, withRV2 giving pitch control.

The next stage is to set RV5 atabout half way and monitor the outputfrom SK5. By adjusting RV2, it shouldbe found that the tone is greatlyattenuated at some setting that gives afairly high pitch and, by repeatedlyadjusting RV2 and RV5, it should bepossible to eliminate the fundamentalfrequency of the tone. With the tonegenerator oscillating strongly there willbe quite strong harmonics (multiples ofthe fundamental frequency) at theoutput although, due to the highfrequency of the tone, probably onlytwo harmonics will be audible. SettingRV3 further in a clockwise directionwill produce more gentle oscillation butwill alter the pitch of the tone slightly,and RV2 will need to be readjusted. Alittle experimentation with the settingsof RV1 to RV3 should produce areasonably pure tone, with the filterattenuating this to an insignificantlevel.


ProjectBy adjusting RV4, it should be

possible to get the relay to operatewhenever SW2 is operated; at thisstage RV4 should be set in the middleof the range. If suitable test equipmentis available, this can be used to helppeak RV4 at the correct frequency. Inthe absence of test gear, the bestprocedure is to make a recording of thetone signal (taking the output fromSK2) at a recording level of about - 12dB to -18 dB and then play this backinto SK4; adjust RV4 to give reliableoperation of the relay.

It is just possible that the output ofthe recorder may be inadequate tooperate the unit reliably, and in thiscase it is better to boost the sensitivityof the circuit by using a higher value forC1 5 than to use a higher recordinglevel. Similarly if your recorder has anabnormally high output and the unitoperates with a wide range of settingsof RUG, it would be advisable to reducethe sensitivity of the circuit by makingCl 5 lower in value. Otherwise thebandpass filter might be overloadedand give spurious operations of theprojector.

Before using the unit it is a goodidea to check that RV2 and RV5 are setfor optimum attenuation of the tonesignal (RV3 should need no furtheradjustment, once set correctly). RV1 isset to give a recording level of about- 15 dB from the tone signal source,

having a substantially different signalsource. Once set, RV1 should not needany readjustment unless a differentsignal source, having a substantiallydifferent output level, is used.

The normal way of making a tapeusing a synchroniser is to connect theunit to the projector and load the slides.The commentary and (or) music are fedthrough the synchroniser (which shouldbe set to recording mode, of course)and into the tape recorder. SW2 isoperated at the points where slidechanges are required and this willoperate the projector via the relay, aswell as recording the tone bursts. Togive maximum reliability, SW2 should

be depressed as long as necessary, butwithout causing a double slide changeto occur, and a good quality tapeshould be used. This minimises the riskof tape 'drop -outs' causing a slidechange to be missed and the tapehaving to be re-recorded.

If the unit is used with stereoequipment, the convention is that it isused in the left hand channel. Input andoutput sockets for the right handchannel could be added to the unit, butin practice this channel can simply becoupled direct from the program sourceof the recorder during record, and fromthe recorder to the amplifier duringplayback. HE

BOXESHigh cloddy Black ABS plastic or diecast plain agrey

I W 0 ABS50 50 25

100 86 25 2007 96p113 63 31 2003 1880121 66 10 3361 115p152 82 50 2005 134P192 113 61 2006 236p

VERO RANGE plastic boxesI. W 072 47 15 11024

IN 50 35 11390IN 110 55 11391

stove

PLAIN STOVE ER50017 90p 5001 123p

5002P 117p 5032 154p50037 113p 5063 1Mp50317 182p 5004 ribp50)5P 216p 5005 21111p

50067 314p 5005 401pG RANEE broffissmnal InstrumentInstrumentCases

51p 134 90 41 21089 E11.481E83p

224 140 61 21090 E11.826151p 302 170 84 21091 014.8881

-yawmaw

VEROBOX CASES t'inilhl:.-n2Pc'het:114=1ABS, light grey top; dark greyhonor's .2 anodised panels

I D N TYPE PRICE205 140 40 21034 E4.52205 140 75 21035 E4.02205 140 110 21036 16.54180 120 39 21037 £4.11180 120 65 21038 14.40180 120 90 21039 E4.69155 85 39 21040 C3.31

155 85 60 21041 0.31155 85 80 21042 E4.30125 65 30 21047 02.35125 65 39 21048 £2.99125 65 50 21049 0 37

SWITCHES - WevechangeType CR - 1P/12 way, 2P/6W; 3P/4W; 47/3m80.MIN. TOGGLES - 57101, SPOT 57p; 57201 DPDT 87p, S7301 3PDTE1.54; 67401 4PDT 0.75; 7211 1P3W /1.40; Centre off 57103 SPDT71p; 57203 DPDT 960.Push button min 8531 make/8533 break Up; 8225 DPDT E1.34DUAL IN UNE ERG colour coded 03 x0 1 format. On/Off singlethrow 2P SDS2 54p; 4P SOS4 96p, 6P SDS6 E1.34. OP SDS8 61.1117.10P SDSO 0.10.LOW COST D -I -L 4P ON 004 (Op; 8P DNS08 E1

METERSLarge range of types in stock also probes,leads, CC0550,,e5, etc.

PANEL MOUNTING in 50, 100. 5000.A; 1, 5. 10, 50. 100500mA; 14 either model

MULTIMETERSINN

NEW10K1IN

A C OCIRES/dBn 2 3

ranges13048 88

37rorn01.211N

T Rene60 45nrn

ES.N

EN 3111101

213611,11AC/DC/R/dElfTransis

tor Testn 2 1

tinges145 96

45rnrn£1699"

MUM,.93 45ew

62.91

CIMMNW

ICON 314 di90119991

Push buttonit ranges

170 x 80

36mm02 WI

99sr

ELECTROWFJEFOR SERVICE YOU CAN TRUST

1 MORE IC SUPER SAVERS 1ALL PRI

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120138

CAPACITORSPOLYSTYRENE. SIEMENS 5% Tolerance 160V---(:41117-'.S. 7, 10, 12, 15, 18, 22, 27, 33, 39pF 12p; 47, 56, 68. 82. 100. 120, 150,180, 220, 270. 330 390, 470. 560, 680, 820pF; In. 102. 105, 108. 202,2e7, 3n3, 309, 4n7 13p, 506, 6n8. 8n2 10pCERAMIC Very small. 1.8. 2.2.2 7. etc up to 1 n Sp each 105. 202.303, 4n7, 6118 Sp; 100, 22n 6p. 33n. 470 7p; 100n Op.POLYESTER, SIEMENS LAYER -TYPE 7 5mm lead spacing 700VIn, 105. 202, 303. 69; 407. 6o8, 802. 10n. 12n, 15n, 180. 22n, 27n, 33n.39n, 47n 7p. 82n, 100n 9p; 120n. 150n 11p; 180n, 220n 12p; 270n, 330n15p: 390n, 470n 17p; 560n. 680n 24p; 70mm spacing 1,,F 28p, 15mmspacing 2µ2 36p; 22.5mm spacing leF 400V 47p; 3.3,,F 100V 89p; In-depth stocks.

ELECTROLYT1CS NON-potatr (for LS X-overs) 50V peek 20F 211p; 40F21p; 6, 13. 10, 164,F 32p; 25µF 37p; 40, 603pE1610; 100pF 59p.POLARISED, SIEMENS OR MULLARD IsoF/V) 1/63. 2.2/63, 4.7/63,6.8/40, 10 /25, 22 /10, 10p; 10/40, 22/25, 47/10 11p; 47/25 12p; 100/1013p; 10/63, 22/40, 100/16 14p; 22/63, 47/40, 100/25, 100/40 115p;220/10,220/16 15p;220/25 189; 220/40 20p; 470/10, 470/16, 470/25,100/10 19p: 470/40, 1000/16 27p; 1000/25 36p; 1000/40, 2200/1644p,1000/63 789: 2200/40,4700/16 73p.

PLUGGABLE SIEMENS single ended1/63, 2,2/53, 4.7/6310p; 10/63, 22/63 8p; 22/40, 47/1610p; 47/4012p;47:63 10p; 100/16, 100/25, 100/40 10p; 100/63 20p; 220/10 13p;220/16, 220/25 13p; 470/6.3 15p; 470/10 18p; 470/16 18p; 470/25 22p;470/40213p; 1000/1022p; 1000/1623p; 1000/25 40p.

LARGE CANS SIEMENS2200/63 E1,77, 4700/40 01.78; 4700/63 12,96; 4700/100 05.54;10000/1661.93; 10000/25 E2 .78 , 22000/16 E3.20; 22000/25 E4.73.

TANTALUM0.1/35, 0.22/35. 0.47/35. 1/35, 2.2/16 13p; 2.2/35, 2.2/16 13p;2.2/35, 4.7/16 16p; 10/6.3 18p:4.7/35. 10/16, 22/6.3, 10/2515p;22/16. 22/25, 33/10, 47/6,3. 100/3 30p

LOW LEAKAGE All single ended0.1/50.0.22/50, 0.47/50, 4.7/3511p; 1/50, 2.2/50.4 7/5011p; 10/16,22 /6 11p; 10/35, 22/10, 22/16, 22/35, 47/6, 47/10 12p; 47/16, 100/612p

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Project

POP -AMPSOwen Bishop

Simple measuring circuits based on operational amplifiers

No. 2: Voltagefollow -and -holdcircuit

ONCE in a while, and probably moreoften, it is necessary to measure avoltage which is changing rapidly -but trying to follow the needle of thevoltmeter by eye and read it at just theright instant is tension -generating, tosay the least! And, if your eye cannotfollow the needle, it is likely that theneedle cannot follow the rapidlychanging input voltage, either, sowhatever reading you have struggled toobtain will be doubly in error. Thiscircuit, however, gives your eye andthe needle a breathing -space in whichto catch up with the changing voltage.Pressing the button, it takes a sampleof the input voltage at any instant; thecircuit then holds the sampled voltagewhile the needle of the meter comes torest, and your eye has time to take thescale reading with all the accuracy youneed.

The CircuitThe output of the circuit (Figure 1)follows the input voltage as long as thebutton is held pressed. When thebutton is released, the output remainsconstant at whatever value it had atthe instant of release. When the buttonis pressed again, the outputimmediately becomes the same as theinput voltage. The operation of thecircuit is diagrammed in Figure 2.

The op -amp is connected as aninverting amplifier with unity gain andwith the button pressed, outputfollows input except that it is inverted.

NOTE: IC1 = 351

INPUT

Figure 1. The Follow and Holdcircuit.

10k

-12V

OV

I a

Figure 2(above). How it works; (a) with+ 2V on the input, a current of 200 uAflows into the op -amp output pin; (b)this causes voltage drops of 2V acrosseach resistor, so that the invertinginput is at OV, the output at - 2V andthe op -amp is stable; (c) in " hold" ,changes at the input cannot effect theop -amp output.

ANYVOLTAGE

ANYCURRENT

ANY OVCURRENT

INPUTSOCKET

OV -2V

ANYCURRENT

OV

RI R2

200uA 200uA

INVERTINGINPUT OFOP AMP

b

V

ANYCURRENT

OUTPUTTERMINALOF OP AMP


Project Now an op -amp is stable when there isno potential difference between its twoinput terminals. But since the non -inverting ( + vel input is wired to 0 V,the inverting input must also be at 0 Vif the circuit is to be stable. So given aninput of, say, + 2 V, a current of 200uA flows toward the inverting input,by way of the input resistor R1. Theamplifier input has extremely highresistance, so almost no current entersit, but, instead, flows on through R2and into pin 6 of the op -amp. Since R1has the same value as R2, and thesame current flows through each; thevoltage difference across each resistoris the same (Figure 2b). Therefore, witha drop of 2 V across each resistor, theoutput potential is -2 V, the potential

at the inverting output is 0 V and theop -amp is stable. In this state, one sideof capacitor Cl is at 0 V and the otheris at -2 V; there is 2 V across it.

When the button is released, thecircuit becomes as shown in Figure 2c.The input to the circuit may change,either increasing or decreasing involtage, and a varying current mayflow in either direction through Al, R2and into or out of the output terminal ofthe op -amp - but the output of the op -amp is entirely unaffected by this! Thepotential at its inverting input is held at0 V because of Cl and, since this isstill the same as the potential at itsnon -inverting terminal, the amplifier isstable; it maintains an output potentialof -2 V.

INPUT 41 2 3 4

-VE0 0 0

B 0C 0

O

E O

F 0

G O

H O+VE INPUT 4

0 0 09V 4

J

H

G

F

C

B

A

5 6 7 8 9 10 11 12 13 14 15(16 17 18

0 0 0

T0 0 0 0

0 0 0 0 0 0 0 0

CII

CC

0

OO

O

METER +VE

OV

0 0 0 0 0.

5000000.5 000000000000 oooeo000000o oo 000000000000 o0000000 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 00 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 00000000000000000 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0000000000000001 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

SW1

+9VMETER -VE

Figure 3. The Veroboard component overlay (top) and the track -side view (bottom),showing the positions where the strips are cut.

CIRCUITBOARD

INPUTTERMINALSOCKETS

OFF

ON

DPDT OR DPSTSLIDE SWITCH

SVV1PUSH-BUTTON

OUTPUTTO

METER

The capacitor retains its charge for along time, since there is no way inwhich a large current can flow fromone side of the capacitor to the other.The plates of Cl are effectivelyinsulated from each other by thedielectric, which has a resistance of20,000M or more, while leakage intothe amplifier is very small too, since theinput impedance is 1 012R - a millionmegohms! - and this high inputimpedance is the reason for choosing aJFET op -amp for the circuit. With suchhigh resistances, a charge of 2 V on Cltakes 47 seconds to drop just ahundredth of a volt. This should giveyou (and the meter) plenty of time tocope!

The circuit described has unity gain,so meter readings are equal to inputvoltages, though increasing the valueof R2, you can make the circuit amplifythe voltages as well as hold them. Theamplification is set by the ratio R2/R1;for example, if you replace R2 with1 00k, the op -amp amplifies ten times.

The reason for choosing the 531 inpreference to other JFET op -amps isthat it has a very high slew rate Irate ofchange of output voltage) of 1 3V/us,which compared with the rate ofOV5/us for the 741, makes it a gooddevice for sampling rapidly changingvoltages.

Operating the multimeter on the 10V range means that offset nulladjustments (see Pop Amps No. 1 inthis issue) are less important and anoffset potentiometer is not needed.

ConstructionThere are so few components thatconstruction of the circuit takes only afew minutes. The component layout isshown in Figure 3. Whether you decideto mount it in a case is a matter ofpreference. If you have a 10 V meter tospare, you can mount this on the case;it does not need to have a high coilresistance, so a cheap one will do.Otherwise, plug your multimeter intothe circuit, using the two socketsindicated. This circuit, like No. 1, canalso be used with the LEDMillivoltmeter featured in HE August1982.

Parts List

HE

RESISTORS(All 1/4 Watt 1% carbon)R1,2 10kCAPACITORSC1 470n

polycarbonateSEMICONDUCTORSIC1 7611

CMOS op -ampMISCELLANEOUS2.5 mm stripboard, 48 x 25 mm; 6x 1 mm terminal pins; 2 x 4 mm redsockets, 2 x black; push -to -makeswitch; DPDT switch; 2 x PP3battery connectors; optional case;wire, solder etc.BUYLINES page 34

Figure 4. Wiring the external components to the Veroboard.


ZX81 OWNERSSPECIALISED PRODUCTS

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TE10 INPUT/ OUTPUT PORT - Easy to use. Fits between ZX & RAMPACK /PRINTER lif required). No skill required to connect. Can be used forsuch things as:- motor control; sound/music generators, connection toprinters/floppy discs/light pens/other computers, temperature monitoring,square wave generating, control of rotating aerials, even train sets etc. Port has16 programmable 1/0 lines and may be used without any electronics knowledgeto connect other add-ons. Motherboard required ONLY when two or more add-ons are used at any one time.FULLY ASSEMBLED £17.95.KIT (WITHOUT CASE) £14.95.

TE12 4 CHANNEL RELAY BOX - To suit Port Contact rating:- 240vAC/1,5A - 24V DC or 110V AC/3A. Up to 4 units i.e. 16 relays can beoperated £14.95.

TE15 8 WAY TRANSISTOR DRIVER - £9.95TE17 8 WAY SWITCH UNIT (EDUCATIONAL) - £12.957E18 8 WAY INDICATOR UNIT (EDUCATIONAL) - £12.957E20 JOYSTICK & FREE GAME - 12 Joysticks may be connected viaMotherborsd.) £12.957E30 MOTHERBOARD - Allows multiples combinations of add-ons - upto 16 1/0 line$may be used - £15.957E126 POWER SUPPLY- 6/7.5/9V DC at 300 mA - Required for use withadd-ons T E12 / 15 Et 18 £4.9523 + 23 WAY ZX Edge Con £2.85. Contact cleaner £2.30.16 WAY SINGLE SIDED EDGE CON £1.95. EXTENDED PIO NOTES ft

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VOLTAGE I

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25p120p

TERMS OF BUSINESS - Professional quality electronic components brand new and fully guaranteed. Mailorder by return of post. Cash, Cheque, Postal Order or Bankers Draft with order payable to HEMMINGS ELEC-TRONICS LTD. Access or Barclaycard available using our 24 hour answerphone service. Monthly Credit Ac-counts available on request to government and educational authorities. Industrial customers wishing to open acredit account are required to furnish a bank reference and two trade references. Postage and packing add 45pto all orders under £10. All prices are exclusive of VAT. Please add 15% to total including p&p. No VAT on ex-port orders or books.

2N3822 120p1 2144922 95p2143823 96p 2144923 95p2143824 96p 2145190 75p2143866 901/ 2145191 75p2N3903 15P 2145192 75p2143904 15p 2145193 90p2143905 15p 2N5194 90p2143906 15p 2145195 90p2N4123 Sp 2145400 40p2N4125 25p 2145401 40p2144391 70p 2145415 85p2144392 70p 2N5416 90p2144400 20P 2N5457 35p2144401 251' 2N5458 36p2144402 25p 2145459 35p2N4403 25p 2N5460 35p2N441C 45p, 2N5551 40p2N4416 95p: 2SC495 60p2144856 80p 2SC1306 95p2144857 80p 2SC1678 105p2N4918 95p 2SC2028 75p2N4919 120p 2SC2078 105p2144920 130p VN1OKM 65p2144921 105p 40673 95p

LIQUID CRYSTALDISPLAY MODULESPCIMt77 Frequency Counter5 Digits, 0.35"FM, SW, MW, MHz, KHzAnnunciatorsSample and Hold CapabilityReset Capability25 Selectable IF OffsetsPrescaler AvailableIncandescent BacklightingSupply Voltage 5vOperating Current 4mA

£18.85PCIM176 Digital Meter Module3) Digits, 0.5"

, - and Decimal Point200mV Full Scale InputTrue Differential InputGuaranteed "0" ReadingSingle 9v OperationPower Consumption 20mWAccuracy 0.15%, -1- / - 1 CountTemperature Drift 80ppm /CLow Battery IndicatorIncandescent Backlighting

02.50Modules are supplied with DataSheet.

FIBRE OPTICPOLYMER CABLE

A 10m coil of 1mm core opticalfibre cable sheathed in blackpolyethylene for protection £4.95

ALFAC ETCHRESIST TRANSFERS

Make your own Printed CircuitBoards with our PCB transfers Draw your artwork on 0.1" grid

I Transfer to copper board1 using carbon paper

Burnish the Alf ac transfers tothe board using a spatula usingcarbon marks to assist in accuratealignment Using Alfac chemical eraser tocorrect mistakes Etch in Ferric ChlorideEC900 /1 0.1' Edge ConnectorEC902/1 0.156" Edge ConnectorEC940 0.016" LinesEC941 0.031" LinesEC942 0.039" LinesEC943 0.049" LinesEC944 0.061" LinesEC945 0.079" LinesEC946 0.100" LinesEC947 0.124" LinesEC950/1 0.031" 90° BendsEC950 /2 0.061" 90° BendsEC952/1 0.031" 300,45060°BendsEC952 /2 0,061" 30°,45°,60°BendsEC908 0.063" PadsEC910 0.094" PadsEC911 0.189" PadsEC960 /1 TO -5 Transistor PadsEC993/1 IC PadsEC997/1 IC Pads with tracks

between pads5 identical sheets in sealedpack 195pIndividual sheets 46pSpatula AR4 for burnishing 45pAlfac knife 180pSpare Blades (pack of 101 280pAlfac Eraser 40pAlfac Precision GridsPolyester film, matt finish0.14mm thickness, 20 lines/inA3 199pA4 100pDouble Sided Fibreglass Board1/16' thickness, 1oz Copper5" x 4' 25p5" x 8' 45p

ELECTRONIC HOBBIES FAIRNovember 18th to 21st

Visit us on stand 414 opposite the'Blue Bar' where we will beexhibiting a selection from our largerange. Do not miss the manybargains on offer.

LIGHT EMITTINGDIODES (LED)

3mm Red TIL209 10p3mm Green LD37C 15pPanel Clip 41'3mm Chrome Bezel 35p5mm Red MI1'40 L 10p5mm Green, Yellow 15pPanel Clip 4P5mm Chrome Bezel 42pStern Square Red 25p i

Green, Yellow 30pTricolour V51BP 70pRed Flashing COX21

31-1, at 5V 45p

INFRAREDTIL32 Emitter 54p ,TIL38 Emitter 511178 Phototransistor 54pTIL100 Photodiode 70p

EPSON MX80F/T TYPE IIIPRINTER

80 Characters per SecondFriction and Tractor FeedHigh Resolution 960 Dots/LineAuto UnderliningSubscripts and Superscripts

£335Securicor 613

VIC-20 COLOURCOMPUTER

SPECIAL OFFER VIC-20 Colour ComputerC2N Cassette UnitIntroduction to Basic (Part 11VIC Reference ManualDemonstration Tape10 Blank CassettesVIC Computing Magazine

£215 inc VAT

COMMODORE 64COMPUTER

64K RAM, 26K ROM25 Lines of 40 Characters16 Colours, 512 x 256 GraphicsOptions - VIC Peripherals

Alternative LanguagesSecond ProcessorKEYNET Network

f:299Securicor E6


Gadgets, Games Et Kits

HC6010 DMMPaul Coster

An accurate andreliable DMM withsome outstandingfeatures.

WHEN I unpacked the HC6010 from itsmustard coloured box, I could tell I wasin for a few surprises. Described by themanufacturers as accurate and reliable,it is a digital multimeter with all theusual AC/DC current and voltageranges and some extra ones not com-mon to meters in this price range - forexample, a basic DC accuracy of 0.5%.In use it was very robust - of thehighest electronic standards of con-struction - and well thought out. Infact, my only real criticism was of anaesthetic nature rather than due to anygreat failing of the meter.

The 6010 multimeter is made byHung Chang Products and distributedby Armon Products Ltd. The basicranges are AC/DC current and voltage(extending up to 1000 V and 10 A DC,and 750 V and 10 A DC) and tworesistance - low and high outputvoltages. The display is 31/2 digit LCDwith auto -zero, auto -polarity and '10 -

bat' indicators. Range and scale selec-tion is made via a series of push -buttonsalong the left-handside of the instru-ment. There are eight buttons in all, twofor selecting AC/DC (or hi/lo resistance)and voltage/current/resistance and sixfor setting up the correct full scaledeflection IFSD). For instance, tomeasure up to 20 mA AC you wouldpress the top button (conveniently cod-ed dark grey) for AC and the fifth buttonto read up to 19.99 mA. However,there's no need to worry if the value isover range, since the meter is protectedagainst overloads by sparkgap(voltage), inrush current limiter (cur-rent) and a 2A fuse (current). Also pro-tected are the battery eliminator inputand resistance ranges and as if thatisn't enough, the test lead sockets arerecessed - not to make plugging andunplugging the leads as difficult aspossible as I first thought, but to ensurethere is no bare metal to give you anynasty shocks - as part of an overallphilosophy of 'safety first'.

a A

20MI,

2000101

7001,)

201Aft

21tii

20011

Clearly A Better MeterThe voltage ranges are chosen bypressing the lowest of the (dark grey)buttons. Both AC and DC voltagescales have the same ranges (apartfrom maximum values of 750 V AC and1000 V DC) and so AC or DC can beswitched by a single button. Accuracyis quoted at ±0.5% (reading + 1 digit)DC and ± 1% (reading + 5 digits) AC,which despite being a strange way ofexpressing the tolerances, is prettygood for a meter of this price range.

Sinusoidal voltages are measuredwith an averaging response, but themeter is calibrated to read RMS (thoughthis is not as good as direct readingRMS) and resolution for both AC andDC is a very good 100 uV.

To measure current, you have toplug the red test lead into a differentsocket (slightly tedious with the safetymeasures mentioned earlier), and thetwo dark grey buttons operate in a

similar manner as when reading voltage- upper for AC/DC, lower remains'out'. In addition to this, if you want totake readings up to 10 A you must plugthe red lead into a third socket. Thiswas again a chore, but when you con-sider that most other meters need ashunt to measure such large currents,perhaps it's forgivable.

Accuracy on the current ranges isnot as high as on the voltage, but sincethe worst case (2 A and 10 A AC) is stillfairly good at ± 3% (reading + 5digits), I do not feel the 6010 is anypoorer than the competition (I was par-ticularly impressed by the clear mannerin which all the technical specificationswere presented). Resolution on both ACand DC current is adequate at 100 nA;but this meter, like others I have review-ed, would have benefitted from a lowerlimit of 10 nA, say - after all, isn'teveryone interested in the current con-sumption of their LCD calculator!

Resistance measurements are madeby pressing the lowest button and thenselecting either the 'hi' or 'lo' ohmsscale. These two scales are present, aswith other meters, to allow in -circuitreadings to be made. However, unlikesome other similar instruments, the looutput is low enough (280mV) tofacilitate testing around most semicon-ductors. Both outputs (hi and lo) havesix ranges from 200 ohms up to 20megohms, with resolution down to 100milli -ohms on the 200R. Accuracy isvery good on the four lower ranges(0.5% nominal) and creditable on the2M and 20M settings (better than 2%nominal). The high range (up to 20M) isquite rare for a unit of this type and Iwas pleased to see it included.

Specs And The RestThe HC6010 DMM comes completewith an instruction leaflet, which is veryclear but (sadly) not that well laid out -whatever happened to those neatpocket -sized manuals that used to ac-company most of the better meters!Even so, operation is easy to grasp andthe leaflet is only necessary as a sourceof reference information. What I docommend Hung Chang for, is the inclu-sion of a circuit diagram and parts list -it is always a good sign if a manufac-turer is proud enough of his design workto want to make it public. However, it'sa pity this pride doesn't extend to thefascia panel, on the front of the case,which has the lettering printed on it.Not only does this have a tendency topeel off, but it gives the meter a gim-micky appearance. A bit of time spenthere (and on improving the shape of thecase and buttons) would pay in the longrun - designers of the 'Mark II' takenote.

So, for those of you who are after arobust and accurate digital multimeter,that is easy to use and out -performsmost others at the price, I can recom-mend the 6010. However, if you'reafter something to show off to yourfriends, then keep looking . . . and onefinal surprise, a price tag of £34.44.For further information contact ArmonProducts Ltd, 53-63 Wembley HillRoad,

Wembley, Middlesex HA9 8BH. HE


CAMBRIDGE LEARNINGSELF= -INSTRUCTION COURSES

*NEW!*DIGITAL

COMPUTERDESIGN

£8.50Our latest, up-to-datecourse on the designof digital computers,both from their indiv-idual logic elementsand from integratedcircuits.

Digital Computer Design is the best way foryou to understand how simple computers are.You are first shown the way in which simplelogic circuits operate and then, through aseries of exercises, arrive at a design for aworking machine.

GSC SUPERKIT £19.90The original Cambridge Learning Superkit, apractical digital electronics kit for begin-ners, now re -written for the popular GSCEXP300 breadboard. The kit comes completewith an instruction manual, components, andbreadboard to teach you all the basics ofdigital electronics.

DIGITAL COMPUTER LOGIC& ELECTRONICS £6.00The theory course to support the practicalSuperkit, this 4 -volume set covers basiccomputer logic; logical circuit elements; thedesign of circuits to carry out logicalfunctions: flipflops and registers. No priormathematical knowledge other than arithmeticis assumed.GUARANTEE No risk to you. If you are not completelysatisfied, your money will be refunded upon return ofthe item in good condition within 28 days of receipt.CAMBRIDGE LEARNING LIMITED, UNIT 10 RIVERMILL SITE.FREEPOST, ST IVES, CAMBS, PE17 41312. ENGLAND.TELEPHONE: ST IVES (0480) 67446. VAT No 313026022

All prices include worldwide postage (airmail is extra -please ask for prepayment invoice ) . Giro A/c No 2789159.Please allow 28 days for delivery in UK.

SUPERKIT(S) @ £19.90DIGITAL COMPUTER DESIGN(S) @ £8.50DIGITAL COMPUTER LOGIC AND ELECTRONICS @ £6.00

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TRIO 20 MHZ DUAL TRACE SCOPES 2 YEAR GUARANTEE140mm Tube- DC to 201611Z, 5mV sensitivity: CH2 InverlCS1820 Delayed sweep:0 2 psec to 0.5 secSweep. Modes CHI. CH2. DUAL and ADD. silt "List Price £53900 inc. VAT.

Our Price £420.00 inc. VAT (UK c/p £4.001CS1566A NOB. AUTO. VIDEO. 0 5usec SweepModes CHI. CH2. ALT. CHOP and ADD.List Price E368.00 inc. VAT

Our Price £299.00 inc. VAT (UK c/p £4.00) optional

..--- '''"' 14Pi ii. -....... r.. -,-.:::::::: lei -......... .. 11 ...... :el' # .1.:

1 i..t.44,N 0 11al.A

; probes - see belo

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100 KHZ6 Band Trio RI Generatorvariable o/p lo 100mV

Special Price

a

TO 30 MHZint/ext. mod

AM int 400 HZ mod.

V C9&a) .95 IE 00*inc. (VAT 5^.

(UK c /p £21

116202A matching2011Z to 200 KHZ. inC. VATAudio Generator £78 (c/p £2)

LOW COST DIGITALMULTIMETERS3' digit LCD Hand Held DMM s:(SW - Slide switch. PB / Push ButtonRS Rotary((Models ' with carry case)UK c/p 65p all modelsKD25C 13 Range D2A DC 2 megohm ISWI £26.50'KE130C 26 Range IA. AC/OC 200 megohm (HO) £37.50'1(055C 28 Range 1011 AC/DC 200 megonmIRSI £41.50601 26 Range 2A AC/11C 20 megohm IPBI £36.50188m 16 Range I GA DC Ino ACI 2 megohmPlus HEEltransistorl Tester IRS) £43.50189m 30 Range 10.A AC/DC 20 megohmPlus HEE Tesler IASI £69.95

FREQUENCY COUNTERS(1111 models battery operated) 1UK C/P El IPFM 200/1 Pocket 8 digit LED200 MHZ 10mV ITHANOAR1 £67.50Max 50 50 MHZ 6 digitLED Pocket IGSCI £56.35Max 550 6 digitLED Pocket IGSCI °77581 IDA 8 digit LED? range 100 MHZBench ISABTRONICSI £77.008610A 8 digit LED 3 range 600 MHZBench ISABTRONICS1 E94.00Max 100 5HZ.I DOMHZ8 digit Bench LED IGSCI £97.7586108 9 digit LED 3 range 600 MHZBench ISABTRONICSI £113.8580008 9 digit 0E03 range 1000 MHZBench ISABTRONICS1 El 78.00TF040 8 digit LC040 MHZ ITHANDARI El 26.50TF200 8 digit LCD 2 range 200 MHZPHANDAR1 £166.75Mender prescalers for any counter up to 200 MHZ

TP600600 MHZ £43.13TP1000 with P/S 1 011Z £73.00OPTIONSTF series carry case £6.84 -AC adaptors ITF Series] £5.69 Nmie'z'n'It ei mIf series AC adaptors £569 - s,

All models probe kits £7.95

ANALOGUE MULTIMETERSGENERAL RANGELow cost reliable meters 10111 supplied withbans/leads] [UK C/P 55p1BANANA 15 range pocket 20K/Voltplus cont buzzer £20.64ET IO2 14 range 2K/Voll Pocket £5.95ST5 I I range pocket 4K/Vol( £6.50NH56R 22 range pocket 20K/Volt £10.95YN360TR ID range plus Ale test 20K/Noll £2.95KRT5001 16 range 10 amp DC rangedouble 50K/Volt £16.50ST303TR 21 range plus Ate Test 20K/Volt £16.95'AT 1020 18 range Deluxe 2KV and Hle Tester £17.50TMK500 23 range plus I2A DCplus cont. buzzer 30K/Volt £23.95168M 36 range large scale (0AAC/DC 50K /Volt £28.5036018 23 range large scale 10AAC/LIC Hle tell 50 meg ohm. I KVAC/OCIOOK/Voll £36.95

Choose from UK's largest range

GENERATORS -4.11.111111111.- RI IAIl with Int/Ext mod. variable output)R -C. Pulse. RI Function - is 0 . . 1E200 100KHZ-100MHZ 6 bandAudio 1UK c/p Ell .,'. iiests, (300MHZ harm' £49.95All models 220/2400 AC LSG17 100KHZ-150MHZ 1450MHZ-harm)AUDIO 4 hand Sine /so output LEADER £71.307E220 Max distortion I% 20HZ/200KHZ £59.95 FUNCTION tall sine/SO/Triangle/TTL etc I

LAG27 Max distortion 05.1% 5020A 1142100101Z ISABTRONICS1 £90.00(LEADER) IOHZ-IMHZ £86.25 TG100 I H2-100KHZ 'MANOR £90.85LAG120A 5 band 10HZ.IMHZ. T6102 0.2112.2MHZITHANOARI £166.75Sine/S00.05-0.8'° dist £146.00 PULSELAGI 25 As LAG120A but aan T6105 51115MHZ Various outputsdist (LEADER) Unit.,.,.' (THANOARI £97.75AG203 10142-1MHZ 5 band OA% Sine/SO 4001 Ultravariable 05H2 J5MHZ (GSC) £113.85(TRIO) £129.95

OSCILLOSCOPE PROBE KITS(UK C/P 50p per 1 to 3) ANC plug XI £7.95

X10 E9.45XIXIO £10.500100 £16.95

DIRECT READ HV PROBE(UK C/P 65p) 0/40 KV 20K /Volt £18.40

OSCILLOSCOPES(C/P Dual trace E4.00, SC110 £1.00:Single Trace £3.00)HM307 Single trace (0MHZ 5m11 0.5 microsec. Plus built in component tester6 x icm display IHAMEGI £158.70 tOptional case £18.40 e

t

e, ,rc -r

-Agilli,,i

rs IntlMittil /0:00

3030 Single trace I5MHZ 5mV: 0.5 micro a , , '' " . V:': SW.' (ei '..A4

sec. Plus built in component tester. 95mmtube. Trig. to 20MHZ ICROTECH1 £172.50 SCI 10A New model 10MHZ battery portable.HM203/3 Dual 20MHZ: Trig to 30MHZ 10mV13.1 sisec 2' trace.5mV:0.5 micro secs 81 10cm display All facilities ITHANDARI £171.00(HAMM £253.00 Options: Carry case £6.84HM203/4. As above but 2mV Algebraic AC adaptor £5.69add IHAMEG1 £276.00 Rinds £8.6313131 Dual trace I5MHZ trig. to 35MHZ SAFGAN - UK made dual trace5mV:05 micro sec. 130mm tube plus Salgan all models 5mV sens. 05 micro seccomponent tester £276.00 6.4 x 8cm display.HM204 New model with component tester DT4I0 Dual 10MHZ £205.85Dual 20MHZ delayed sweep: trig to 40MHZ. 01415 Dual 15MHZ £217.355mV 0.1 micro sec 8 x 10cm display IHAMEG1 £419.75 D1420 Dual 20MHZ £228.85

(Optional case E21.85) / _ALL

FFY"C7ES...1 _1- me-TT...W.7 w --a-...1.. a ---w-_-.-.., v_r_4111111111111 ..,(41.Limited

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404/406 EDGWARE ROAD. LONDON W2

Order by P.., 0th off oue5/ ACCESSVISA or Totephon your order. AlbtorVPto .0 cloy. for delivery

66Hobby Electronics, December 1982

THE HE BOOKSHELF is the easielectronics books. Order Coda

DIRECT TO

est way to build up your library ofy to have these top titles delivered

-- Beginners Guide

YOUR DOOR.

rolEffectiFecE rTott, ealtds t o

P

Counter Driver

Numeral DulPhtlfProjects

Radio CircuitsUsing IC's

IRIIC LM3900Protect'

52 PROJECTSUSING 1C741 £1.25More than 50 waysof using theubiquitous IC741.

50 IFET) FIELDEFFECTTRANSISTORPROJECTS £1.75Contains a widerange of projects, all

based onEffectTransistors.

COUNTER DRIVERAND NUMERALDISPLAY PROJECTS£1.75Features many variedprojects usingnumeral displays,counter and driverICs.

RADIO CIRCUITSUSING IC's £1.35All you need to knowabout using IC's forAM or FM reception.

IC LM3900PROJECTS £1.35Provides the groundwork for simple andmore advanced usesof IC LM3900.

PRACTICALCONSTRUCTION OFPRE -AMPS, TONECONTROLS, FILTERSAND ATTENUATORS£1.45Contains practicaldesigns for use withhome constructedequipment orcommercial modules.

Eloc tom,tiou,oholt1

BEGINNERS GUIDETOMICROPROCESSORSAND COMPUTING£1.75Basic introduction tobinary arithmetic,micro -processor

languagemarine

IC 555 PROJECTSf 1.95The 555 timer users'Bible'!

CHOOSING ANDUSING YOUR HI-FI£1.65Concise informationfor all hi-fienthusiasts.

ELECTRONIC GAMES£1.75Amusing electronicgames which caneasily andinexpensively beConstructed by theenthusiast.

ELECTRONICHOUSEHOLDPROJECTS £1.75Packed with circuitsfor projects that canbe used in or aroundthe home.

AMICROPROCESSORPRIMER E1.75A painless approachto understandingcomputers andcomputing.

belowTo receive your books you have only to fill in thup to 21 days for delivery. This offer applies only within the U.K. Prices may be subject to change without notice.

I am enclosing my Cheque/Postal Order/

Please allow---------------------------------------, urrey CR4 6AR.SEND TO: HE BOOKSHELF, 513 London Road, Thornton Heath S

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REMOTE CONTROLPROJECTS £1.95

control.

finformation

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ELECTRONIC MUSICPROJECTS £1.75Many practicalcircuits for lesscomplex items ofelectronic musicequipment.

ELECTRONIC TESTEQUIPMENTCONSTRUCTION£1.75How to build and usea wide range of testequipment for thehobbyist.

POWER SUPPLYPROJECTS E1.75Packed with circuitsfor building variouskinds of powersupply.

SINGLE ICPROJECTS E 1.50Easy to constructprojects basedaround a single IC.

PRACTICALCOMPUTEREXPERIMENTS£1.75Build and examine anumber of basiccomputer circuitelements.

Elct Ironic.

Pr Op, I4 4

Solar Coll,

ELECTRONICPROJECTS USINGSOLAR CELLS £1.95A range of practicalapplications usingsilicon solar cells.

VMOS PROJECTS£1.95Contains a number ofvaried and interestingprojects using VMOSpower FETs.

DIGITAL ICPROJECTS £1.95Simple and advancedprojects based ondigital ICs.

INTERNATIONALTRANSISTOREQUIVALENTSGUIDE £2.95Find possibleequivalents for apopular user -orientated selectionorientated selectionof moderntransistors.

HOW TO USE OP -AMPS £2.25All you need to knowabout Op -Amps, asource book ofcircuits and designcalculations.

AUDIO PROJECTS£1.95Clear information onhow to build pre -amps, mixers, poweramps, tone controlsetc.

and send it, together with your payment, to the address stated.

67

Sinclair ZX Specti16K or 48K RAM...full-size moving-key keyboard...colour and sound...high -resolutiongraphics...

From only

f125!First, there was the world-beating

Sinclair ZX80. The first personal computerfor under £100.

Then, the ZX81. With up to 16K RAMavailable, and the ZX Printer. Giving morepower and more flexibility. Together,they've sold over 500,000 so far, to makeSinclair world leaders in personalcomputing. And the ZX81 remains theideal low-cost introduction to computing.

Now there's the ZX Spectrum! Withup to 48K of RAM. A full-size moving -keykeyboard. Vivid colour and sound. High -resolution graphics. And a low price that'sunrivalled.

Professional power -personal computer price!

The ZX Spectrum incorporates allthe proven features of the ZX81. But itsnew 16K BASIC ROM dramaticallyincreases your computing power.

You have access to a range of 8colours for foreground, background andborder, together with a sound generatorand high -resolution graphics.

You have the facility to supportseparate data files.

You have a choice of storage capa-cities (governed by the amount of RAM).16K of RAM (which you can uprate laterto 48K of RAM) or a massive 48K of RAM.

Yet the price of the Spectrum 16Kis an amazing £125! Even the popular48K version costs only £175!

You may decide to begin with the16K version. If so, you can still return it laterfor an upgrade. The cost? Around £60.

BLUEEDIT

FN FN

SIN

ASN

READ

Ready to use today,easy to expand tomorrow

Your ZX Spectrum comes with a mainsadaptor and all the necessary leads toconnect to most cassette recordersand TVs (colour or black and white).

Employing Sinclair BASIC (now usedin over 500,000 computers worldwide)the ZX Spectrum comes complete withtwo manuals which together represent adetailed course in BASIC programming.Whether you're a beginner or a competentprogrammer, you'll find them both of im-mense help. Depending on your computerexperience, you'll quickly be movinginto the colourful world of ZX Spectrumprofessional -level computing.

There's no need to stop there. TheZX Printer -available now- is fullycompatible with the ZX Spectrum. Andlater this year there will be Microdrives formassive amounts of extra on-line storage,plus an RS232 /network interface board.

N.4LNs.

YELLOW

CLOSE # MOVE

VERIFY

SON

L PRINT

PAPER

MERGE

ABS

FLASH

WHIT

BRIGHT

Key features of theSinclair ZX Spectrum Full colour -8 colours each for

foreground, background and border,plus flashing and brightness -intensitycontrol.

Sound -BEEP command with variablepitch and duration.

Massive RAM -16K or 48K.

Full-size moving -key keyboard- allkeys at normal typewriter pitch, withrepeat facility on each key.

High -resolution -256 dotshorizontally x 192 vertically, eachindividually addressable for true high -resolution graphics.

ASCII character set -with upper- andlower-case characters.

Teletext -compatible- user softwarecan generate 40 characters per lineor other settings.

High speed LOAD & SAVE -16K in 100seconds via cassette, with VERIFY&MERGE for programs and separatedata files.

Sinclair 16K extended BASIC -incorporating unique 'one -touch'keyword entry, syntax check, andreport codes.

um

!X Spectrum software on:assettes -available now

The first 21 software cassettes areow available directly from Sinclair.roduced by ICL and Psion, subjectsiclude games, education, and business/ousehold management. Galacticwasion ...Flight Simulation... Chess...istory... Inventions ...VU-CALC...VU-3D.47 programs in all. There's something)r everyone, and they all make full usef the Spectrum's colour, sound and-aphics capabilities. You'll receive atailed catalogue with your Spectrum.

S232 /networkiterface board

This interface, available later this)ar, will enable you.to connect your(Spectrum to a whole host of ppinters,rminals and other computers.

The potential is enormous. And thetonishingly low price of only £20 is)ssible only because the operatingstems are already designed into the)M.

=ir-1=111r-nclair Research Ltd, Stanhope Road,imberley, Surrey GU15 3PS.

Camberley (0276) 685311.

The ZX Printer -available now

Designed exclusively for use with theSinclairZX range of computers, theprinter offers ZX Spectrum owners the fullASCII character set - including lower-casecharacters and high -resolution graphics.

A special feature is COPY whichprints out exactly what is on the whole TVscreen without the need for furtherinstructions. Printing speed is 50 charac-ters per second, with 32 charactersper line and 9 lines per vertical inch.

The ZX Printer connects to the rear ofyour ZX Spectrum. A roll of paper (65ftlong and 4in wide) is supplied, along withfull instructions. Further supplies of paperare available in packs of five rolls.

The ZX Microdrive-coming soon

The new Microdrives, designedespecially for the ZX Spectrum, are set tochange the face of personal computing.

Each Microdrive is capable of holdingup to 100K bytes using a single inter-changeable microfloppy.

The transfer rate is 16K bytes persecond, with average access time of 3.5seconds. And you'll be able to connect upto 8 ZX Microdrives to your ZX Spectrum.

All the BASIC commands required forthe Microdrives are included on theSpectrum.

A remarkable breakthrough at aremarkable price. The Microdrives areavailable later this year, for around £50.

How to order your ZX SpectrumBY PHONE -Access, Barclaycard or

Trustcard holders can call 01-200 0200 forpersonal attention 24 hours a day, everyday. BY FREEPOST -use the no -stampneeded coupon below. You can pay bycheque, postal order, Access,

Barclaycard or Trustcard.EITHER WAY -please allow up to 28

days for delivery. And there's a 14 -daymoney -back option, of course. We wantyou to be satisfied beyond doubt -and wehave no doubt that you will be.

Fro: Sinclair Research, FREEPOST, Camberley, Surrey, GUI5 3BR.

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Project

Low Cost AlarmSystemOw p

THE COST of a professionally installedintruder detection system can bemeasured in hundreds of pounds so, withhousebreaking on the increase, there is alot to be said for a simple DIY systemsuch as this. There are gains in theimmediate savings on the considerablelabour costs of installing the wiring,coupled with the fact that thecommercially made 'box of electronictricks' often seems to containsurprisingly little for the money. Theelectronic part of this system containssurprisingly little, too, but you will haveto pay more than about £13 for all thecomponents, including switches (but notincluding the case and battery). Perhapsthis system does a little less than someof the more advanced of thosecommercially available, but it is straightforward in its action and there is virtuallynothing to go wrong with it. Moreover itis not subject to false alarms caused bytransients in the detector circuits, as aremany of the simpler alarm systems. Ithas extremely low power consumption(only 0.75 mA) when quiescent, so it isideally suited to battery power. A set of'D' dry cells will last for many months ofoperation, 24 hours a day. A set of"AA" NiCad cells will last for 1 monthon one charging. Thus, the system isindependent of mains power failures orinterruptions.

The noise generated by the solidstate audiblO alarm is more than enoughto wake the household or to rouse theattentions of neighbours. The alarmdraws only 25mA, yet emits a piercingwarbling tone with a power of 95 dB at1 m. Since its current requirements arelow, it is feasible to wire two or moreAWDs in parallel and site them in variousparts of the house. But try using just oneto begin with, for it is more than likleythat you will find it does all that isneeded.

The system has two kinds ofdetection circuit, the peripheral loop andthe pressure mat system.

Peripheral LoopThis consists of normally closed switchesmounted on all doors and windows,forming a loop which surrounds the areato be protected. The switches are inseries so that, if any one switch isopened, the loop is broken and the alarmis sounded. It may be sufficient toprotect ground -floor entry -points only,but upstairs windows should beprotected too, if they are readilyaccessible from outside. Do not forgetthe less obvious points, such as coal -

An easy -to -build security systemthat can be expanded to provideprotection for any property.

shed doors, hatches and skylights.It is best to use a magnetic switch

specially made for the job. The switchconsists of two parts (Figure 1). The reedswitch itself is mounted on the frame ofthe door or window or may be concealedin a hole drilled in the frame. The otherpart contains a permanent magnet. Thisis mounted on or concealed in the door orwindow itself. When the door is shut, themagnet holds the reed switch closed.When the door is opened, even by only acentimetre or so, the switch opens and

the loop is broken.The use of a normally -closed loop of

this kind makes it difficult for an intruderto de -activate the system by cuttingwires. A cut at any point on the loopsounds the alarm immediately. However,it is worth remembering that intruders donot always open doors or windows in theconventional way, in order to gain entry,especially if the door or window issecurely locked or bolted. It may beeasier for the intruder to quickly cut awaythe glass of a french door or picture

FRAME

DOOR ORWINDOW

HOLE BOREDIN FRAME

FOR LEADS

MAGNET INSERTED REED SWITCHIN EDGE OF DOOR INSERTED IN FRAME MAGNET REED SWITCH

Figure 1 a, b. Two methods for fixing reed switches in a door or window frame.


Project II

window, and enter through the hole.Another ploy is to cut an entry hole in thepanel of a lightly -constructed door, or inthe thin panelling which is often to befound alongside front -door units. Glasspanes and thin panels may be protectedby fixing strips of thin metal foil acrossthem. Special window foil is sold for thispurpose, together with terminal blocksfor making connections to the end of thestrip. These strips can be included as partof the peripheral loop.

Where the devices mentioned aboveare not suitable, it is usually easy to rigup a normally -closed microswitch whichwill be opened by an attempted break-in.

Pressure MatsThese are specially made mats which areplaced beneath carpets or other floorcoverings. They act as normally openswitches, closing when stood on. If youhave large pets loose in the house atnight, or if any member of the family is ahabitual sleep -walker, take care whereyou place them! Otherwise, they may beplaced in strategic positions around thehouse, especially in areas such as theliving room, where expensive equipmentis likely to attract the intruder. The matsare wired in parallel, so that the circuit iscompleted when any one mat is stoodon. This section of the system may alsocontain other normally -open switches. Avaluable safety feature is to have a fewpush -buttons situated in the house wherethey can be used for sounding the alarmmanually. This provides a quick andeffective way of alerting the household incase of fire, for example. The wiring ofthis part of the system needs to be ascarefully concealed as possible, for thesystem can easily be de -activated bycutting the wires, but since much of thewiring is beneath the carpets, thispresents little difficulty. The wire used forthe pressure mat system and theperipheral loop can be light -duty PVCcovered wire (7/0.2 mm wire is cheapand perfectly satisfactory).

Circuit DetailsThe peripheral loop runs from the 12 Vline, around the premises and back to theloop input terminal. If the loop is broken,the pull -down resistor, R2, causes theinput voltage to IC 1 a to drop to OV. Theother input to IC1a is held high (at 12 V)by R1 . If any one mat is stood on, theinput voltage falls to 0 V (low). With twohigh inputs, the output of the NAND gateis low; this is the quiescent state. If theloop is broken, or if a mat is stood on, theoutput goes high.

A high output causes a current toflow through D1 and R3, charging Cl . Ifthe output remains high for long enough(about 0.5 seconds) the voltage risesabove 6 V, which is effectively a highinput to IC1 b. The output then changesfrom high to low. If the output of IC1 a ishigh for only a short time, as when atransient pusle appears on one of theinputs, Cl discharges through D2. Sincethere is no resistor in the return path, Cldischarges rather more rapidly than itcharges, quickly eliminating the effect ofthe transient voltage. It would take anincredibly severe series of transients tobreak through this filter.

+V 0

PERIPHERALLOOP

SW2

O

R118k

r - -0 SW3

9

PRESSUREMATS'

OV 0

2

R218k

NOTES.IC1 IS 401101,2 ARE ZTX300D1,2 ARE 1N4148

D1 5

1C1Y-4.-11111101-VVV-.-ER3

100k 6

02

t4u7

IC1b

R4100k

AUDIBLEWARNING

DEVICE

14

1112 ICld 01

R518k

9 ICU

810

C2 SW14700

1 RESET/DELAY1

02

Figure 2. Circuit diagram of the alarm system.

+12V

PERIPHERALI_OOP

(NC)

MATS(NO)

OV

.L

T

Figure 3. The component overlay.

AUDIBLEWARNINGDEVICE

Gates IC1c and d form a Set -Resetflip-flop. Its inputs are normally high andit is triggered to change state by a lowpulse on one of the inputs. The Set inputcomes from IC1 b. When this goes low,the flip-flop changes state, the output ofIC1c changes from low to high andcurrent flows to Q1 , which is connectedwith Q2 as a Darlington pair to givesufficient current gain to operate theAWD.

The Reset input to the flip-flopcomes from the junction of R4 and C2; itis held high by the pull-up action of R4,but when SW1 is pressed, the input fallsimmediately to low, thus resetting theflip-flop. While this input is low, a breakin the loop or pressure on a mat cancause the input of the IC1c to go highand sound the alarm, but only for as longas the condition lasts, because the flip-flop does not change state permanently.The input to IC1c rises very slowly from0 V as C2 charges through R4; it takeabout 30 seconds to reach 6 V ,providing the delay which allows thealarm to be set when the house is to beleft unoccupied. After that, the flip-flop isready to be triggered permanently by alow pulse from IC 1 b.

SW2 switches out the peripheralloop, by connecting the loop inputdirectly to the 1 2 V line. This switch isnot an essential part of the system, but itmay be useful to de -activate the loop if,for example, a member of the householdplans to return home late at night whenthe other members are in bed. Thisallows the mats to provide some kind ofprotection in the meantime. SW3disconnects the mat system, and this too

is useful but not essential. During theevening, when all doors and windows areshut and the family is engrossed in theTV, the mat system is probably best keptinactivated. The peripheral loop givesadequate protection against intruders,many of whom prefer to break in wheneveryone is settled in one room with thesound from the TV to mask the noise ofbreaking glass or splintering timber.

ConstructionThere should be no problems inassembling the board and getting it towork straight away. As alreadymentioned, this circuit is ideally poweredby a battery of 8 dry cells, or Ni-Cadcells. These may be contained in two4 -cell battery holders. Whether or not thecircuit needs a case is a matter ofopinion. It is preferable that the intrudershould not be able to locate the circuitand cut off the power supply, so there ismuch to be said for hiding it away in acupboard or drawer, eliminating theexpense of a case.

The dead space below a table(Figure 5) is a good place to hide thecircuit and batteries, though almost anyother odd space will do; accessibility isnot important, as you need renew thebatteries so infrequently, provided thatthe switches can be reached easily.Concealed wiring should lead to theReset/Delay button, hidden away in aconvenient location fairly close to thedoor by which you normally enter thehouse. The AWD should be in somerelatively inaccessible location,not besidethe circuit itself. The wiring to it shouldbe concealed as much as possible. The


Project

Parts ListRESISTORS(All 1/4 watt 5% carbon)R1, 2, 5 18kR3,4 100k

CAPACITORS(All electrolytic)C1 4u716VC2 470u 16V

SEMICONDUCTORSQ1,2 ZTX300

silicon NPN transistorIC1 4011

CMOS quad 2 -input NANDD1,2 1N4148

signal diode

MISCELLANEOUSSW1 Push -to -make

push-button switchSW2, 3, 4 SPST

standard toggle switchesSiren (AWD), 12 V with optionalmultitone; battery holder (2); doorand window switches; window foiland terminals; pressure mats; wire;solder etc.

BUYLINES page 34

BATTERIES AND PCB

Figure 4. Top, the circuit board andpower supply can be convenientlyhidden underneath a table top - butmake sure the switches are easilyaccessible (bottom) as well as beinghidden.

PANEL FORMSSHELF TO RESTBATTERIES ON

MATS LOOP ON/OFF

AWD could be mounted in the loft,where its sounds will readily be heardboth inside and outside the house.

MaintainanceA power -on lamp is not provided, sincethis would consume 25 times as muchcurrent as the quiescent circuit, so checkthe batteries regularly; remember that flatbatteries will run the quiescent circuitwell enough but may fail to provideenough power for the AWD. The checkshould include sounding the alarm; checkeach window and door switch every fewmonths, and also each pressure -mat.

How It WorksTHE TWO detecting systems, peripheralloop and pressure mats, provide inputsto the system which are normally high(1 2 V) but go low (0 V) when an intruderis detected. Since the wiring is manymetres long and surrounds a houseful ofelectrical and electronic appliances, itfrequently picks up transientelectromagnetic signals. The switchingon and off of equipment such as TV setsand refrigerators causes pulses to appearin the wires of detector systems, andthese are often strong enough to trigger aflip-flop. The delay circuit filters out allthese transients so that the alarm doesnot sound unless the detector circuitshows a low voltage for about half asecond. It is not likely that an intrudercould make an entry during so short atime, yet this is long enough for anytransient to subside.

The action of the intruder triggers aflip-flop which sets off the alarm. Thissounds continuously until the powersupply is disconnected or theReset/Delay button is pressed. Once thebutton is pressed, the flip-flop is inactivefor a period of about 30 seconds. If theperipheral loop is broken during thisperiod, the alarm sounds, but only for aslong as the loop is broken. This delay is

essential if you are leaving the houseempty, allowing the last person to remainin the house to press the Reset buttonand quickly leave by the front door. Thealarm sounds very briefly as the door isopened and closed, but is silent afterthat. A few moments later the systembecomes activated. On return to thehouse the alarm sounds but, if the firstperson in is prepared to act quickly and ifthe reset button is concealed not too faraway from the door (on the inside, ofcourse, it takes less than a second tosilence the alarm. The delay operatessimilarly on the pressure -mat system, sothere is no need to jump over thedoormat on the way out.

PERIPHERALLOOPS

DELAY

PRESSUREMATS

FLIP-FLOPAUDIBLEWARNINGDEVICE

HE


GreenbankGreenbank Electronics.

Dept E12H, 92 New Chester Road,New Ferry, Wirral, Merseyside L62 SAG

(Tel: 051-645 3391)

READ THIS IF YOU VALUE YOUR JOBI am writing to a worried man (or woman) I am writing to you. Are you scared of computers?

Well not scared of the computers themselves. but scared of what they can do Pretty welleverywhere at work, on TV. these micro -things are being seen more and more all the time andyou seem more and more to be getting left behind.

Do you have collegues wpo are always spouting on and on about computers? Do you under-stand a word of what they're saying? Be honest, do you? Do they understand a word of whatthey're saying really, or are they just speaking words they've read out of a magazine or heardon T V.?

What you need is a friend, an honest friend, who will try to help you. I will be your friend, I amyour friend My name is David Perkins. why not write to me or 'phone me? (my number is 051-645 3391).

I said I would be an honest friend so I'll begin now - I work for a firm which sells a computerin kit form, and I would like to sell you one. The name of the computer system is 'Interak 1'. I

know you are going to buy a computer kit of some sort very soon, because you just can't letthings go on as they are. 'Computing' is a club, and you're not a member yet. Worse still youmay have bought a computer and found you still haven't a clue what goes on inside. Miraclechips they may be but it will be a miracle if you can understand what they do by just looking atthem

What I want to sell you is not lust the pieces. I want to sell you 'the knowledge Then you'llknow as much as I do. and you won't need me anymore. All I ask from you is that when youknow wnat computing is really all about, that you treat others in the same way that you wouldlike to be treated. Don't sneer at them because they don't know the difference betweenPASCAL and BASIC, they don't know what an RS232C interface is, or how a DART works,remember we all had to start somewhere.

Computers are bound to make our lives easier and happier (and richer) if they are usedwisely, so it is vital that everyone be introduced to the 'Computer Club' as quickly as possibleOnce everyone knows about computers we will be free to continue to make an honest living -at the moment there are all sorts of people who are unscroupulously taking money frominnocent people by taking advantage of their ignorance, and I for one just don't want to be aPart of a business like that Just read through a few advertisements, and think to yourself howcan they all be the best?

When I said I am wanting to sell you 'the knowledge' please don't think I am offering acorrespondence course. In my view that's not a suitable way to learn - a course has toproceed in simple logical steps - how an 'AND gate' works, and what is a 'flip-flop' and so on- microcomputers have left all that simple stuff behind long ago and you'll never catch up thatway.

Learning computing is a bit like learning to swim but you've got no time to waste. What Ithink you need is to be plunged in at the deep end -- there's no time for splashing about in thePaddling pool learning a bit at a time. But if you're going in at the deep end you'll need a friendto save you from drowning - that's what I'm here for.

Of course it's not like swimming in one important respect you have to buy a computer firstbefore you can enter the water. Down at the shallow end this will cost you about E50 with afurther £50 for the necessary RAM (memory). - at the deep end. where you'll find me, the costIS at least double.

I bet you're saying 'some friend this - he's already wanting me to spend twice as much as Ithought' Well its true, I think you have got to, and here's why. The cheap systems are builtdown to a price - the 'chip count' (number of integrated circuits used) has to be kept rightdown, preferably to four or five There are two penalties to be paid. Firstly. no real expansioncan be accommodated - the system will go so far then no further, secondly some specialdesign 'tricks' have to be incorporated to make the chips do double duty and get the maximumperformance out of the minimum resources. Don't get me wrong - some of the tricks arebrilliant but the whole point in your buying a computer is so you can get an understandingyourself, not simply looking as a lump of silicon (integrated circuit) where all the skill is buried.Once the design is 'encapsulated' in a master integrated circuit there's no way you'll ever findout what's inside unless the designer chooses to tell you, and he's hardly likely to tell you - hemight want to use the same idea in the Mk II model next years

Some people go into this with their 'eyes open' -bull think computing has come to a prettypoor state of affairs if you have to be prepared to throw away a hundred pounds or so on asystem which cannot expand with you, but has to be replaced by the next model annually

I would also say beware of committing the diametrically opposite mistake - a gimmickcomputer This is one which is all things to all men. You name it, it's got it. This processor, thatprocessor as an option Level 1 expands to level 2 which has the optional what not interfacewhich can easily be adapted for this or that.

Do you think the purchase of a computer is going to solve your problems?, of course not.learning is hard work My computer (Interak 1) is ideal for your purposes I assume that youdon't really know much about computers, you've probably got an interest in electronics, andwith all the publicity that these micro chips are getting in magazines, TV, radio andnewspapers you know that you've got to know all about them Well I'll let you into a secret andgive you some valuable information There's too much going on for you to learn everythingand new information is being created every day at such a rate that the longer you leave it to getstarted, the harder it will be to catch up

Ask almost anyone what makes a good computer and they'll describe a monster. I'll showyou the way to obtain sufficient k nowledge to use computers for your pleasure, your work, andso that you can, if you want to. help others. It's all very well having a computer that haseverything. but if you have loo much hardware you'll be like the old woman who lived in theshoe - you won't know what to do

I have a friend who has bought an Interak 1 System. say he's a friend but at the moment hethinks he's lust a customer) and he's received a parcel, he's opened it and checked that he's gotwhat we think we have sent him and I imagine he's ploughing his way through the manuals(yes one of the problems of being presented with a lot of information is having to read it all -carefully). He's got a lot of work ahead of him. Although he doesn't understand what it's allabout, he'll learn from reading the manuals how to assemble the computer from its componentparts, and then how to make it work

I've put a lot of time and effort into this friendship, writing the words. and drawing what Ithink are helpful diagrams. I'm sure my friend will write to me with his problems and I'm alsosure he will be delighted with his computer and any helpful remarks I may make

I admit some of my answers to his problems may take the form of 'application notes', in factmost of them will, but that's just the way that I cope with helping lots of friends (when I get aletter with a problem or misunderstanding of something I've put in the manual, I write myanswer in the form of an application note, then if I'm presented with the same problem again Ican quickly give a well thought out answer in an application note with maybe just a coveringletter.)

You've got a problem at the moment. you've either got a computer and not been able to learnall you need to know, or you haven't got one yet. Don't lust go out and buy the first computeryou see. or the biggest or the cheapest, buy the one that will help you to solve your problemsRemember that I'm here to help you. I've got a leaflet/data sheet set, that will probably tell youeverything you need to know about my Interak 1 System. Write to me at GreenbankElectronics, using the above address and ask me to send you my Interak 1 leaflet. Now I warnyou, there's quite a lot that I'll send you (about 38 sides of A4 -size paper). It's type -written, withsome hand drawn illustrations of the various kits. Of course it costs quite a bit to send throughthe post so an A4 SAE would be appreciated but as you are my f hand, if you don't enclose one Iwon't mind. By the way I'll probably enclose leaflets on some of the other things that mycompany sells but as I say to people I speak to, 'If I give you a leaflet you don't want pleasedon't be offended'

I'm being honest with you. I'm trying to make you into a Inter. 1 user, because the morepeople who have this system. the more people I'll be able to exchange my programs with, andthat's important.

You might not think that you are capable of building up a sophisticated computer systemfrom component parts, but you need have no worries on that score You do of course have towork carefully and patiently, but that's all you have to do I haven't met anyone yet who wasincapable of doing the lob. Some people need a bit of help. some people need more help thanothers, but the way I look at it is that if you can't follow the instructions I have provided then it'smy fault not yours. The same applies to testing the completed computer. If you make a boardand you can't gel it to work. I am here to help you - just pop the board into the post to me, andI'll plug it into my own system and will soon get it going for you.

Even if you don't buy the Interak 1 System then I do urge you to buy some sort of computeras soon as you can If you have any children this is even more important Children needcomputers almost as much as they need food and drink. There never was a more nutritiousfood for a young mind than a digital computer Without a preconceived feeling that computersare somehow mystical, children are in a far better position to learn than we mere adults.

So far I have only let you think that the Interak 1 System will cost you money, but there areplenty of ways it will bring money in. Obviously if you have your own business you will knowhow much time and money a computer will save And if you have brought yourself up to astandard where you can write your own programs and fix the system yourself (not that it will gowrong. you built it - remember) there won't be any hidden overheads to , paid. Other waysyou can make money are writing programs that you can sell, or even An a book. Don'tthink that you have lo be particularly clever to do this. There may be thousands of people lessfortunate than you who will be dying to hear of another's experiences. The last thing they willwant will be some high faluting tome written by some lah-di-dah computer boffin.

I look forward to hearing from you so I can tell you about my Interak 1 Computer. Write soon,David

Post & Packing, 50p forKS kits, 75p for UK kits,£1.00 for cabinets. SendS.A.E. for catalogue ofour extensive range ofkits & cabinets. Trade,

41111

iraillarksI il rD r),..

07, Hughenden Road,Hastings, Sussex,

TN34 3TGTelephone: Hastings I

Educational & Export LTDenquiries welcome.

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KS 100100 `,..Mini VHF Super -regenerative I

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00/3001.04 7,54 191,1 74 089 175 5.77


Project

LoftyA handy loft -lightalarm to buildRETURNING from a weekend away, notso long ago when the weather was stillwarm, we happened to meet ourneighbours from across the street. Theevening was balmy, though the lightwas fading fast as we exchangedpleasantries about the weather andBotham's batting while we unloaded thecar; then our neighbour dropped hisbombshell. " By the way" , he saidinnocently, "did you know you left alight on in your loft? We can see it fromour upstairs window" . In fact, we couldsee it from across the street, shiningbrightly through narrow chinks betweensome of the tiles.

That rapidly put an end to theconversation as, feeling foolish, I hurriedinto the house thinking, as I climbed theladder, of the electricity bill we wereabout to receive (without thanks, ohlord); those lights (two 150 watt bulbs)had been burning continuously for atleast three weeks!

From that incident, Lofty was born -a simple device that could be connectedacross the light switch and which wouldsound an alarm after a preset period,unless the light had been turned off. Asfinally constructed, Lofty actually hastwo alarms; a winking LED for visualwarning and a two-tone beeper which,although not particularly loud, generatesa penetrating tone that will be audiblethroughout a quiet house.

Another aim, when we designedLofty, was to keep the size of the unitas small as possible, and to keep thecost low.

For these reasons, we used a noveltransformerless power supply. As aresult of this design, though, all parts ofthe circuit are at mains potential withrespect to earth and are thereforepossibly lethal to touch. No metallicparts must be exposed when the unit isoperational, and particular attentionmust be taken in the construction toensure that the unit is effectivelyinsulated.

As an added precaution, it should bemounted in an inaccessable position,well out of the way of prying fingers!The method is perfectly safe providedthese precautions are taken.

The CircuitThe transformerless power supply isbased on Cl; this has an impedance of6k7 ohms at 50 Hz mains frequency.Therefore, the current through it at 240VAC is 36 mA. Although it is acting as a'dropping resistor' and is passing a fairlyhigh current, C1 does not dissipate anypower; that is, it does not get hot.

CAUTIONThe 'Lofty' uses a transformerlesspower supply and, as a result, allparts of the circuit are at mainspotential and are possibly lethal totouch. No metallic parts must beaccessible when the unit iso erational.

The AC current through C1 is thenrectified by the diode bridge, BR1, andcharges C2 to a maximum of 1 5V,determined by ZDI; this is the powerrail for most of the circuit. Resistor R1drops the supply voltage further beforeit is fed to the internal shunt regulator inIC 1 , and C3 provides some additionalfiltering.

IC 1 is a ZN1034 precision timer ICmade by Ferranti. It contains anoscillator, a 1 2 -bit counter and aregulator circuit. When power is appliedto the chip, the counter is reset; 4095oscillator cycles later, the output at pin2 goes high.

The time period is determined by theoscillator frequency; the higher thefrequency, the longer the time period.The frequency is set by just twocomponents - R2 and C4. The valuesused here give a period of around 45minutes, but this can easily be altered,as described later.

While IC1 is still counting, the twosections of IC2, a dual 555 timer, areprevented from operating by the lowoutput from pin 2 of IC1 on their resetinputs, pins 4 and 10. Then, when ICItimes out, its pin 2 goes high andenables both sections of IC2. It is nowpossible for LED1 to light, since itsanode is no longer at OV.

IC2b will oscillate at a frequency of afew kilohertz, but the tone will bemodulated from the output from ICI a,which is generating a asymmetricalwaveform at 1 or 2 Hz. As well asmodulating the output from IC2b, thiswaveform also causes LED1 to flash onand off. The output from IC2b is fed tothe piezo-electric sounder, X1, whichgenerates the audio tone.

ConstructionStart by assembling the timer and tonegenerator components on the PCB;points to watch here are that the ICs

and the tantalum capacitor (C4) arecorrectly oriented. At this stage, thetime period can be changed by alteringthe values of R2 and C4. The delay, inseconds, is equal to 0.7 x 4095 x R2 xC4, with R in megohms and C inmicrofarads; R2 should not be reducedbelow 10k and C4 must be between10n and 100u.

Before proceeding with the powersupply section (BR1, ZD1 and C2), testthe timer and audio beeper byconnecting a temporary 1 2-1 5 voltsupply to the unit. Naturally, you willhave to wait 45 minutes (or whateverperiod you have set) to find out if all iswell! If the unit does fail to work forsome reason, first carry out the usualchecks for solder bridges, dry joints andso on. The operation of IC2 can bechecked by first removing IC1, thenapplying about 3V to the IC1 pin 2connection. This will enable bothsections of IC2 and it shouldimmediately burst into life unless thereis a fault present. Testing IC1 will bemore difficult, although there is verylittle that can go wrong here. If you doneed to check the IC, it would be best tochange R2 and C4 to give a short timedelay - 39k and 1 On give a one seconddelay - otherwise fault-finding couldtake a very long time!

When the timer and audio generatorare working, the power supply can bewired up. Before proceeding with this,however, check that the LED is brightenough to be seen. If not, reduce thevalue of R3, but not below 100R.

Power SuppliedThe vital component in thetransformerless power supply is Cl; thismust be rated for 240V/50Hz operationie, at least 250 VAC, 600 VDCworking. When it has been soldered inplace, make sure Cl cannot vibrate bytying it down with two cable ties passed


Project a

FS1250mA

ACTIVE 0C1

470n250V AC

240V AC

NEUTRAL 0 ZD115V

R147011

R21M

C3100n

C2100u

12

14

13

+C4

NOTES:IC1 IS ZN1034IC2 IS 556D1,2 ARE 1N4148 OR SIMILAR

D11-

113

180RR3 180R

R8100k

R5 LED1470k

R71M

13

14

ZD1 IS 15V 1W3 ZENERBR1 IS 1A 800V (W08)LED1 IS LARGE RED LED (PLASTIC)FOR PANEL MOUNTING

714

X1 IS P62720 PIEZO BUZZERR4 R6 R9

IC12

0-441M 4M7

2 IC2a100k

8 IC2b

D26 12

10

C5 C6T 220n T 4,17

Figure 1. The complete Lofty circuit - note that the mains earth lead is not connected.

C2

C1

LED1

CATHODE

ACTIVE(BROWN)

NEUTRAL(BLUE) j

240V AC

CABLE TIE

Figure 2. The PCB component overlay. Capacitor C1 takes up most of the boardspace!

through the holes in the PCB. Next,mount the diode bridge, C2 and theZener diode, then the fuse, FS1. This isincluded to protect against the possiblefailure of Cl; if it ever needs to bereplaced, remember to totallydisconnect the 'Lofty' before doing so!

InsulationThe last stage is to mount the piezotransducer and connect it to theappropriate points on the PCB. Use astout piece of plastic film between X1and the underside of the case to insulatethe diaphragm of the transducerbecause, as explained earlier, this couldbe 'live' and thus potentially lethal totouch. Finally, mount the PCB in thecase using M3 screws. It is now readyto be wired into the loft light circuit.

Wired UpThe unit should be placed near the loftopening, where it can easily be seen andthe sound of the alarm will not bemuffled. A length of ordinary two -corelighting flex is connected from theLofty's mains input to the loft light, sothat the unit is turned on with the lights.Forty five minutes later, the alarm willsound. If you are still working in the loft,reset the unit by briefly turning off thelights, initiating another timing period.

Parts ListRESISTORS

(All 1/4 watt 5% carbon)

R1 470RR2,4,7 1 MOR3 180RR6 4M7R8,9 100k

CAPACITORS

(All polycarbonate unless noted)

C1 470n250 VAC/600 VDC minimum

C2 1000u25 V electrolytic

C3 100nC4 1u

35V tantalumC5 220nC6 4n7

SEMICONDUCTORS

IC1 ZN1034precision timer

IC2 556BR1 W08

800V, 1 A bridge rectifierZD1 BZX61C15

1 5V, 1.3W Zener diodeD2,3 1N4148LED1 panel mounting LED

with plastic (not metal) bezel

MISCELLANEOUS

FS1 250mA20 mm fuse

X1 PB2720piezo-electric buzzer

Chassis -type fuse holder; small cablegland; plastic LED bezel; Veroboxenclosure (see Buylines); PCB; ICsockets; stout plastic film, 1" x 1" ;M3 bolts; cable ties; wire, solder etc.

BUYLINES page 34

HE


CIET liKiNT FIRST MEI

aeWw...4

r-

BACKNUMBERSFebruary 1980 September 1980Passion Meter, Win Indicator,Short Circuit Special, Kit ReviewSpecial, Into ElectronicsConstruction Part 1.

May 1980MiniClocks, 5080 Preamp, ModelRailway Track Cleaner, 5080Loudspeakers, LoudspeakerCrossover Design, RadioControlled Model Survey.

June 1980Microbe Radio Control System,Egg Timer, Two Watt Amplifier,Fog Horn, Short Circuits, LEDsand LED Displays.

July 1980Sound -Operated Flash Trigger,18 + 18 Car Stereo Booster,Hazard Flasher, Electronics inPhotography, ElectronicEspionage, Piezo Electricity.

August 1980EquiTone Car Equaliser, Pass -The -Loop Game, Gaztec GasDetector, OP -Amp Checker, In -Car Entertainment Survey,Introducing Microprocessors.

MicroMixer, Reaction Tester,Guitar Phaser, DevelopnientTimer, Teletext Explained, IntoDigital Electronics Part 1.

October 1980Kitchen Timer, Tug 'o' WarGame, Light Dimmer, FreezerAlarm, Intruder Alarm,Temperature -ControlledSoldering Iron.

January 1981Car Rev -Counter, BenchAmplifier, Sound -Into -LightConverter, Chuffer, ElectronicGames reviewed.

February 1981Heartbeat Monitor, High -Impedance Voltmeter, MediumWave Radio, Two -Tone TrainHorn, Audio Signal Generator.

March 1981Public Address Amplifier,Windscreen Wiper Controller,Bicycle Speedometer,Photographic Timer,Microcassettes.

April 1981Pre -Amplifier Part 1, SuperSiren, Guitar Tremolo, RussianRoulette Game, DoorbellMonitor, Anatomy of a SpaceShuttle.

May 1981Electronic Organ, Voice -Operated Switch, Infra -RedController, Pre -Amplifier Part 2,Audio Millivoltmeter.

June 1981Power Amplifier Part 1,Continuity Checker, EnvelopeGenerator, Early Radio, Gadgets,Games and Kits Supplement.

July 1981Burglar Alarm, Doorbuzzer,Treble Booster, Electronic Aidsfor the Disabled, PowerAmplifier Part 2.

August 1981Electronic Ignition,Thermometer, Electronic Organ(final part), RPM Meter, BenchPower Supply, Radio ControlSurvey, Into ElectronicComponents Part 1.

All of the 1980 issues, except January and April, are still available togetherwith the remaining issues from 1981.

Alarm

All backnumbers cost £1.25 each. For those of you who only want copies of articles, wedo offer a photocopying service. Each copy costs E1.25 and information as to its title andpublication date should be given. Ordering backnumbers and photocopies could hardly be

easier, just fill in the coupon, cut it out and send it to:

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Please remember to mark your envelope with the service youBACKNUMBERS or PHOTOCOPIES,otherwise our mailroom won't like you.

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I enclose £Cheques and Postal Orders should be made payable to ASP Ltd.


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Price £49.95 includes VAT, postage & packing.Optional accessories.

Deluxe protective case £6.90 including VAT pErp10AC current shunt £6.90 including VAT pEtp

F0012

err OA

* 12.5mrn DISPLAY* 10M0 INPUT IMPEDANCE* AUTOMATIC ZERO ADJUSTMENT* AUTOMATIC POLARITY SWITCHING* OVER RANGE INDICATION

44 * FUSE CIRCUIT PROTECTION* BATTERY LOW INDICATION

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26towl

* DIODE CONTINUITY CHECK* ACCESSORIES INCLUDED

790 wor,31

TEST LEADS, BATTERIES ErINSTRUCTION MANUAL

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Revolution in circuitboard maker kits fromleading manufacturer

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and price details, post to: ParaWrrliaSend for full illustrated brochure

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ELECTRONICSCoronet House,Upper Well StreetCoventry CV1 4AFTel: (0203) 58541

B.N.O.S.ELECTRONICS /

Don't miss the Christmas rush. Don't waste yourmoney on throw away Dry cell batteries. BuyEverReady RECHARGABLE Nicad Batteries,run your toys, radios, cassettes or even kitchenequipment. Each charge lasts as long as a dry cell,but you can re -charge them up a 1,000 times ormore, so think of the money you can save at 1p acharge.

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(Available in four standard sizes)

Dry CellNI -CAD Equivalent Capacity 1-9 10-24 24-100

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Also ACCESS & VISA cards welcome

MIGHTY NINETY PACKSSUPER VALUE PACKS ALL AT 90p each

BUY SIX PACKS AND GET A SEVENTH FREEPlease add 20p

Please allowMN2. 200 1 Er I -watt Resistors.

MN3. 100 1 Et 2 -watt Resistors.

MN4. 50 Wirewound Resistors.MN5. 100 metal oxide Resistors. 1%, 2% and5%.MN6. 12 asstd potentiometers.MN7. 25 asstd skeleton preset Resistors.MNE. 50 asstd Electrolytic Capacitors.MN9. 100 asstd Ceramic Capacitors Pite. disc.tub and monolythic etc.MN10. 100 mixed capacitors. Polyester,Polystyrene, Metallised, Radial and Axial types.MN11. 20 asstd Silver Mica Capacitors.MN12. 8 Tantalum Bead Capacitors (usefulvalues).

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ELECTRONIC COMPONENTSTHE CHOICE IS YOURS - CALL AT OUR NEWSHOWROOM OR USE OUR VERY FAST MAIL ORDERSERVICE.EITHER WAY WE'LL KEEP YOU HAPPYFurthermore we promise if any part ordered by mail failsto please just return within 7 days for a full refund.For a vast selection of electronic components &equipment of all kinds. Here is just a selection of ourstocks. Many more items listed in our catalogueavailable now 70p post paid.

. DIL SIRS

!SPARE TIP ST456p soldering iron56p stand with55p large sponge55p E1-70

DENCO COILSIFT13 £1.151F114 e1-201E718 £1 -45

3T Pt 5T Blue orRed E1-34

SPARE

ELEMENT1-702-101-80

8 P. 10p14 Pin 11p

16 P'n13p

18 Pin 17p20 Pin22 Pin 24p24

20p

Pin 27p

DIODES1144005 Elp

1N5408 29p1 nia 148 5p100 for E2-500447 10p0A91 OP

Spare tip sizes available lmm, 2.3mm, 3mm or14.7rnmllmrn not for X251

1-80 28 Pin 35p40 Pm 40p

400rnW Zener13W Zener 190

RESISTORS1W 5% C.F. 18 to 10M 2p each 100 for E1.00IW 5% C.F lOR to 1M 2p each1W 5% C.F. lOR to 820K 5p eachDA, 1% M.F IOR to 680K 5p each 100 for DEM100 off prices one value only - no mixing

POTENTIOMETERSPreset .1W Horiz OP

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audio power transistors

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- special prices

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available to bulk

T1P147 1-25TIP2955 0-60TIP3055 0-57TIS43 0-37TIS90 0-262141309 0-002N3053 0-222N3054 0482N3055 0-482143904 0.142143773 2.2540673 69240871 1-0540872 1-05

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INTEGRATED74LSTTILSOO 0-12LSO4 0-1510013 0-15L510 0-15LS13 0-29LS20 0-l5LS30 018LS74 0-24LS107 0-40LS154 086LS244 0-80LS386 0-28

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LINEAR-14

1 F351N 049LF353N 0-94LF355N 0-861F356N 0-89LM301AN 0-28LM308 0-94LM311 0-701M324N 0-50LM348N 046LM380N 0-75LM381N 1-46LM382 1-25LM384 1-40

LM386 0-90LM387 1-18LM3909 0-70LM3914N 280LM3915N 2-16LM3916N 2-15MC1458 0-47NE555 0.20NE556 040140565 1-20NE566 1-56NE567 1-50TBA120 0-90

TBA440 2.62TBA520 1-92T84530 1-78TBA800 045TBA900 2-20TDA2640 2-16555 0-20709 0-50741 lOpmnl 0-111747 0-70748 0-36

V. REGULATORS (FIXED)-i- Ve 100mA 78L05 - 78112 -- 78L15 3113

- Ve 10OrnA 79L05 - 79L12 - 79115 59p

+ Ve 1 Amp 7805 - 7812 - 7015 80p

- Ve 1 Amp 7905 - 7912 --667915 p

V. REGULATORS (VARIABLE)LM317K 1.5 Amp 03-35LM338K 5 Amp 0470LM396K 10 Amp E11.00L23 14 OILL123 1099 000-457-80

PRINTED CIRCUIT BOARDS - High qua ity fibre glass laminate1.6mm Single sided board 1.6mm Double sided board6 x 6 685 6 x 6 0-906 x 12 1-65 6 x 12 1-70

12 x 12 3-05 12 x 12 3-16

TRIACS b SCR's11C22613400V 8A triac 65p

FOTO COATED RESIST BOARD - High quality fibre glasslaminate precoated with positive foto resist. For small batch production of PCB's

Cl064001 4A SCR 48p

lmrn single sided 12' x 18" 013-801.6mm Single sided 1 6mm Double sided100 x 160mm Euro 1.53 100 x 160mm Euro '-..'"203 x 114mm 1-83 203 x 114mm 2-10.4203 x 228mm 3-60 203 x 228mm 4- '.467 x 305mm 9-10

Fotodeveloper concentrate £242 Ferric Chloride rock 67.Chemical Dishes 12" x 10' f1-50 Plastic Tongs ... =Acetate Sheet f0-20 Dalo Pen se'reeTransfer Pack 5 asstd. sheets C2-00

LED's EACH3mmRed llp3mm Green 17p3mm Yellow 18p3mm Clip 4p5mm Red 13p5mm Green 20p5mm Yellow 20p5mm Clips 4p

PANEL METERSUntil now panel meters have

The following Dc

MIC INSERTSXtal 45pCondenser 60p

proved an expensive Pal of year ' 1

tames:-50uA - 100uA - 500t)A - I rnA Dynamic 75p

Nowproject vailable this new quickfit type.32mm Square Meter

- -500mA - 14 - 54 - 25V - 50VONLY E1-96 each

MINISPEAKERS2i" 64 ohm 70p

8 75p

BARGAIN PACKS 12 Asstd Presets12 Asstd Panel Mtd Pots E1-10 30 Asstd Silver Mica Caps20 Asstd Electrolytic Caps (0-88 5 Asstd Relays7 Asstd Blob Boards E1-10 30 Asstd C296 Polyester Caps

150pF Trimmer Cap MO 250 Asstd Preformed resistors30 Asstd MM Ceramic Caps (0-70 8 Asstd Switches Micro, slide9 Asstd 4000 Series CMOS (1-10 lever, key. push, toggle

10 Asstd 5 redi 5 black croc Excellent valueclips f0-50 I Electrolyte Can 15000uF 25V

20 Plastic type BC109 trans. £0-78 Micro SPOT 10p each 6 for 60pPush Buttons SPDT 15p each 10 for 01-00

3

E0-60ED -90f1 -10E0-800475

f0-90E670

ohm

103 forE7

£9E10£3E7

£9£10f2-50

'EARPHONES

LIGHTNING ELECTRONIC 174 `Solhe7r4P:n esMag. 2.5rnin Plug 16p 60p

COMPONENTSPostage Er Packing 50p per order !free over 0101 Please add VAT at 15%.Telephone orders welcome by Access or Barclaycard

Showroom & Mail Order Distribution Centre at: -18 Victoria Road, TAMWORTH, Staffs B79 7HR Tel 0827-65767.

A.

NEW GOODIES JUSTARRIVED!

C12 K88A Darlington Power 103 PNP 60V12A 117W Hfe 750 @ 6A 75p

C13 Nixie - Siemes ZM1336K, 14mm digitheight, overall 25mm. Wire ended 60p

C14 BY212 -750 power switching rect, 800V4A. 4 for E1.50

C15 GRO5R 50V 5A switching rect. 4 for 50pC1621PT5 50V 20A rect. 75pC17 KBLO4 4A 400V bridge 50pC18 BSI 1A 100V bridge. 5 for f1

Previous Months New ItemsNI 8085A CPU E3.50N2 MC14175 50pN3 LM380 55pN4 1000uF 16V Ax 15pN5 6850100pN6 MM5290 50pN7 MM2114 60pCl 7912CK 1T03 Case/ 75pC2 3.579545MHz Xtal HC6U case 50pC4 25 way screened cable 7/0.2 50p/metreC5 Reed switches, 20mm body SP make

2041C6 12V reed relay, SP break 40pC7 Ni-cads, C size 2AH E2, 10/016C8 68400 CPU 01.50C9 UDN6116A display driver 50pCIO Speedbloc ribbon cable: 10 way 30pirn;

20 way 60p/m; 40 way E1.20/m

BRAND NEW VEROBLOCKIT!!!

Just published by Babani, Mr R. A. Penfoldsnew book, "30 SOLDERLESS BREADBOARDPROJECT" - this book features 30 differentprojects for assembly on a Verobloc, and the kitcontains all parts necessary to make:Audio AmplifiersLight & Dark Activated Switches & AlarmsTimersMetronomeOscillators & Tone GeneratorsWarbling Door BuzzerTwo-tone Train HornTouch SwitchReaction GameSound Activated SwitchRadio ReceiversFuzz Unit+ lots more!The introduction shows all the different com-ponents and explains how to use the bread-board. The Verobloc layout is shown for everyproject together with the circuit diagram and anexplanation of how it works. Ideal for beginnersin electronics, but also suitable for more advanc-ed students.The complete kit is contained in an attractiveplastic case, which can be divided up into 15compartments in which your components maybe stored.Complete Kit, including book, Verobloc & allparts E24.95Book only E2.25Kit without Veroblock 820.45

1982/3 CATALOGUEBigger! Better!! Buy one!!!

Only 75p inc. post - Look what you get!! Vouchers worth 60p 1st class reply paid envelope Wholesale list for bulk buyers Bargain List with hundreds of surplus lines Huge range of components Low, low prices

Sent free to schools, colleges etc.

REGULATED PSU PANELExclusive Greenweld design, fully variable0-28V & 20mA-2A. Board contains allcomponents except pots and transformer. OnlyE7.75. Suitable transformer and pots E6. SendSAE for fuller details.

SOLENOIDS AND RELAYSW821 Solenoid rated 48V at 25% duty cycle,but work well on 24V 1700gm pull, 10mmtravel/ push or pull 27 x 18 x 15mm 55pW922 Mains 240V ac solenoid. 10% duty cycle,push or pull, 16mm travel. 50 x 20 x 16mm. On-ly f1.50W895 9V DC relay 500 8 SPCO 28 x 24 x 19 50pW733 11 pin plug in relay. 240V ac 3PCO 5Acontacts 12.50. Base 36pW838 700R 24V 4PCO 'continental' relay35 x 30 x 18. Only 84p. 10/E7.W847 37R 5 10V relay. SP 3A contact, PCBmntg 11 x 33 x 20 96p. 10/E7.50W893 Omron LY4 mains relay, 4PCO 5A con-tacts E2.50191896 24V ac coil, but works well on 6V DC. 210A c/o contacts. Ex -equip. only 60p

30 SolderlessBreadboardProject - Book 1RecommendedB BICC VERO

1 4.

*+

4.

*1.

'4 +

4'+ + p

* 4. IP. .1

"+

",

5mrt; RED LED SCOOPAnother company gone bust - to your advantage!!! We've bought all their 5mm red LED's -

GI type MV5754, and offer them as follows:25 01.95; 100 06.00; 250 013.50; 1 k E39.50; 5k

f185.Add 30% for 2 -part clip if required.

1,000 RESISTORS12.50

We've just purchased another 5 million preformed resistors, and can make a similar offer to thatmade two years ago, at the same price!!!K523 - 1,000 mixed and 1W 5% carbon filmresistors, preformed for PCB mntg. Enourmousrange of preferred values. 1,000 for E2.50;5,000 E10; 20k £36.

FILAMENT DISPLAYS2653 7 seg display 12.5mm high. Ideal for TTLoperation, taking 5V 8rnA per seg. Std 14 DILpackage. Only El each, 4 for E3.00. Datasupplied.

ELECTRO-DIAL

NOWDOWN

INPRICE!!

Electrical combination lock for maximum securi-ty, absolutely pick -proof!! One million combina-tions!! Dial is turned to the right to one number,left to a second number, then right again to athird number. Only when this has been com-pleted in the correct sequence will the electricalcontacts close. These can be used to operate arelay or solenoid etc. Overall die 65mm x 60mmdeep. Finished in bright chrome. With combina-tion the price is reduced to E3.95.

LIE DETECTORNot a toy, this precision instrument was original-ly part of an 'Open University' course, used tomeasure a change in emotional balance, or as alie detector. Full details of how to use it aregiven, and a circuit diagram. Supplied completewith probes, leads and conductive jelly. Needs 241V batts. Overall size 155 x 100 x 100mm. On-ly £7.95 - worth that for the case and meteralone!

COMPONENT PACKSK503 150 wirewound resistors from 1W to12W, with a good range of values f1.75K505 20 assorted potentiometers, all types in-cluding single ganged, rotary and slider (1.70K511 200 small value poly. mica, ceramic capsfrom a few pF to .02uF. Excellent variety (1.20K514 100 silver mica caps from 5pF to a fewthousand pF. Tolerances from 1% to 10% 02K520 Switch Pack. 20 different rocker, slide,rotary, toggle, push, micro, etc. Only 12

COMPUTER BATTLESHIPSProbably one of the most popular electronicgames on the market. Unfortunately the designmakes it impractical to test the PCB as a work-ing model, although it may well functionperfectly. Instead we have tested the soundchip, and sell the board for its component valueonly (PCB may be chipped or cracked).SN76477 sound IC; TMS1000 coprocessor;ban clips, R's, C's etc. Size 160 x 140mm. Only0.50. Instruction book and circuit 30p extra.

ALL PRICES INCLUDE VAT - JUST ADD 50p P&P

GREENWELD443F Millbrook Road, Southampton SO1 OHX

79

Project

Big Ear

A high gain, directional microphone, ideal for nature studies.THIS is one project where themechanical work is greater than theelectronic! The Big Ear consists of anomnidirectional microphone insertmounted in a length of common,garden variety 21/2" PVC pipe, and asimple two -stage amplifier circuit. Itwas originally designed for recordingor listening to the sounds of wildlife;however, the prototype has alsoproved useful as a stethoscope, andfor listening in to distant conversations(be warned - the listener may notalways like what he.hears!)

The length of pipe serves twopurposes; first, it acts as a resonantcavity with many resonant frequenciesextending from a few hundred Hertzright up to the top of the audio band.Any pipe or tube has a fundamentalresonant frequency which is afunction of its length, and it is alsoresonant at overtones (harmonics) ofthe fundamental frequency. In general,the fundamental frequency, f, of apipe which is closed at one end isapproximately equal to c/4I, where Iis the length of the pipe and c is thevelocity of sound (330 metres persecond, for most purposes). Thus thefundamental frequency of a pipe0.25m long will be at 330 Hz; theovertones produced by a closed pipeoccur only at odd harmonics, thereforeresonant peaks will also occur at 990Hz (3f), 1650 Hz (5f), 2310 Hz (7f)and so on. The effect of theseresonances is to accentuate any soundat those frequencies, increasing thegain of the system at specific points inthe audio spectrum. The length of the

Figure 1. The directional response ofthe Big Ear.

pipe specified for this project has beenarrived at after considerableexperiment, and provides good resultswith minimum undesirable side -effects.

Second, the pipe provides a usefulmeasure of directivity, due todiffraction effects. Diffraction issimply the change in direction ofsound when it passes around anobstacle. The degree of bendingdepends on the ratio of thewavelength of the sound to the size ofthe obstacle and is greatest when thesize of the object approaches thewavelength of the sound. In general,long wavelengths (bass frequencies)bend more easily because feweveryday obstacles are more thanabout one metre long (the wavelengthof a 100 Hz note, for example, isabout 3.3m). The higher frequencies

RI470R

C1100n

3

R2< R3100k < 100k

R6100k

2

8

1Cla

4

C2100n

R4100k

RV110k

C5 l+ C3100u 100u

8582R

R7100k

SK2

---0+9VSW I

NOTE:1C1 = TL082

4- C4100u

SK1

Figure 2. The internal circuitry of the Big Ear.

0 0 V


Project

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

o o 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0I 0

L ° MOUNTINGM

N

0 HOLE0 0

R5

R

MOUNTINGHOLE

O 0

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

SWI

PP3

Figure 3. The project is simple enough to build on Veroboard. The diagram showsthe component layout and the track cuts viewed from the top.

bend less easily and therefore aremore directional, since they arereflected by common -sized obstaclesrather than bending around them.

In the Big Ear, the pipe tends to'hear' only those mid -range and highfrequency sounds coming fromdirectly in front, whereas sounds fromthe sides or rear will be rejectedbecause they cannot bend around theedges of the opening. At lowfrequencies, however, the tube has noeffect and so the response of thesystem reverts to that of themicrophone insert, ie omnidirectional.To prevent these frequencies frombeing transmitted through to theoutput, the response of the amplifier isrolled off at the bass end. Overall, thiscombination of techniques gives aback-to-front ratio of 2:1 (see Figure1).

The Big Ear is designed to be hand-held, and for this purpose, a standard21/2" pipe clip serves quite well as ahandle in normal use; it will also do asa tripod mount, should that berequired.

The amplifier section has twooutputs: a headphone socket formonitoring purposes and a 1/4 jack

socket for connection to the line inputof a tape recorder.

The Circuit.The circuit (Figure 2) consists of twoop -amps contained in a single TL082IC package. The circuit can be split in-to two sections: a voltage amplifierand an output buffer.

Starting at the input (where else?),notice that the microphone has threeconnections to it. This is because it isan electret insert which contains a FETpreamplifier to provide a low im-pedance drive from the high im-pedance microphone source. Thus, itmust be connected to the supply railvia R1.

The input from the mic is fed tothe non -inverting ( - ve) input of IC1a.The value of the coupling capacitor,C1, is chosen to filter out the verylow frequencies generated by handlingthe unit. Otherwise, these wouldcreate low rumbling sounds whichwould seriously interfere with the per-formance, especially at high gain set-tings! The voltage gain of this stage,set by the ratio of the values of R4and R5, is x1000.

The Big Ear was intended to be

Parts ListRESISTORS(All 1/4 watt 5% carbon)R1 470RR2,3,4,6,7 100KR5 82R

POTENTIOMETERSRV1 10K

log carbon

CAPACITORSC1,2 100n

C352* polyesterC3,4,5 100u

1 6V electrolytic*Replaces C280 Series

SEMICONDUCTORSIC1 TL082

dual op -amp

MISCELLANEOUSSK1 3/4" stereo socketSK2 1/4" mono socketSmall ABS case, approx. 80 x 60x 40 mm; omnidirectional electretmicrophone insert; 0.1"Veroboard, 50 x 38 mm (20 holesx 15 strips); slide switch; PP3 bat-tery clip; PVC pipe, 254 x 63 mm(10" x 21/2"); wire, solder etc.BUYLINES page 34

portable, and therefore a dual supplysystem, positive and negative rails,was not suitable because of the extrabattery requirements. Instead, a half -supply voltage reference is created bythe resistive divider network R3 andR6. The junction of the two resistorsis bypassed to OV by C3 to removeany noise from the signal.

The full gain of the first stage isnot always required (the results couldbe ear-splitting), so the output fromIC1a is coupled to the buffer stage,IC1b, via a volume control, RV1;coupling capacitor C2 is chosen toroll -off the bass response. IC1b is set-up as a unity gain amplifier; its outputis at a low impedance and is sufficientto drive an ordinary set of headphonesor the input circuit of a tape recorder,via socket SK 1 . Blocking capacitor C4is included to prevent the DC level atthe output of IC1 b from reaching theload.

ConstructionAs the circuit is so simple, it wasdecided to build it on Veroboard; theusual precautions concerning layout,track cuts and solder bridges apply!Pay particular attention to the correctorientation of the electrolyticcapacitors and the IC.

When the board is assembled, at-tach flying leads about 9" long toeach of the off -board connectionpoints. Next comes the mechanicalassembly.

Mark out and drill the mountingholes as shown in Figure 4. These areeasily made - but the slot for theslide -switch will cause greater pro-blems! Carefully drill 1/4" holes at each


Project

66

DISC

40

10 mmdia

BASE

34

12

I ID

22-165

58

LID BASE

25

11

ao

157 ,

10mmdia

10mmdia

BASE

0

LID

Figure 4. The mechanical details.

75

50

15mm THICKWOOD DISC

63

0

0

3

end of the slot, then file it to shape. Asmall flat file will be useful forfinishing the task. Although the boxcut-out for the microphone is shownas a square, this can be drilled out to3/8" clearance, the size of themicrophone insert.

Lastly, the wooden disc whichholds the mic insert, and to which thelength of 21/2" pipe attaches, must becut out; the dimensions are shown inFigure 4. Preferably, the disc shouldbe cut from a solid piece of wood; thepipe is held by screws into the sidesof the disc, and chipboard has a ten-dancy to fall apart if used in thisfashion.

After the parts have been made,the Big Ear can be assembled. Mountthe sockets, poteniometer andVeroboard; the mic insert should be atight fit in the 3/8" hole through thecentre of the wooden disc; glue it ifyou must, but the arrangement thenbecomes somewhat permanent! Thedisc itself is attached to the box bytwo small self -tapping screws, and thepipe can then be screwed onto thedisc with three or four self -tappers.Finally, the flying leads should be con-nected as shown in Figure 3; the bat-tery should be fixed to the base of thebox with a piece of double -sided tapeor Blu Tack, to prevent it rattlingaround inside.

At this point, the Big Ear is readyto use. Switch on and try it. There willbe silence for a couple of seconds,then it should burst into life.

Why Not Experiment?Although the final form of the Big Earwas arrived at after a considerableperiod of trial -and -error experiment,there are several other methods whichcould be used to improve the direc-tional response.

The most effective would be toreplace the omnidirectional mic insertwith a directional type; however,these do not seem to be readilyavailable and can probably only be hadby dismantling a cheap directionalelectret mic of the type usually soldwith cassette recorders.

The next most important factordetermining the directivity is the aper-ture of the pipe; decreasing thediameter will increase the directionalresponse to high frequencies, at theexpense of less directivity at lowerfrequencies. Another trick is to formmany small resonant cavities, ratherthan one large one, by filling the pipewith ordinary plastic drinking straws;the overall response can be 'tuned' bycutting the straws to different lengths.The directional response can also beimproved by isolating the mic insertfrom the case and pipe, as some ofthe sound from the sides and rear willotherwise be conducted through thesolid material to the microphone.

Finally, there are alternatives tothe resonant tube system; one methodworth trying is to use a parabolic ordish reflector; a simple plastic bowlwould be adequate!

HE82 Hobby Electronics, December 1982

witmaunviDoff

L The firm for Speakers

Bigger and Better for 1982the colourful Wilmslow Audio brochure-the definitive loudspeaker catalogue!

Everything for the speaker constructor - kits, drive units,components for HiFi and PA.50 DIY HiFi speaker designs including the exciting newdB Total Concept speaker kits, the Kef Constructor range,Wharfedale Speakercraft, etc.Flatpack cabinet kits for Kef, Wharfedale and many others.

* Lowest prices - Largest stocks ** Expert staff - Sound advice *

* Choose your DIY HiFi Speakers in the comfort of our *two listening lounges

(Customer operated demonstration facilities)* Ample parking *

Send £1.50 for catalogue(cheque, M.O. or stamps - or phone with your credit card number,)

* Access - Visa - American Express accepted *also HiFi Markets Budget Card.

WILMSLOWCUM

L The firm for Speakers

35/39 Church Street, Wilmslow, Cheshire SK9 1AS

2L60625 529599

Lightning service on telephoned credit card orders!

TECHNICAL TRAININGIN ELECTRONICS,TELEVISION AND AUDIOIN YOUR OWN HOME - AT YOUR PACEICS can provide the technical knowledge that is so dssentialto your success, knowledge that will enable you to take advant-age of the many opportunities open to the trained man. Youstudy in your own home, in your own time and at your ownpace and if you are studying for an examination ICS guaranteecoaching until you are successful

City & Guilds CertificatesRadio AmateursBasic Electronic Engineering (Joint C&G/ICS)

Certificate CoursesTV and Audio ServicingRadio & Amplfier ConstructionElectronic Engineering* and MaintenanceComputer Engineering* and ProgrammingMicroprocessor Engineering*TV, Radio and Audio EngineeringElectrical Engineering,* Installationand Contracting *Qualify for IET Associate Membership

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POST OR PHONE TODAY FOR FREE BOOKLETPlease send me your FREE School of Electronics Prospectus.

Subject of Interest

Name

Address

I ICSDept B262ICS School of Electronics160 Stewarts Road,London SW8 4UJ ...... Hours)

.-1111-11. IIII Ell IIII MI NM

Post to

O

CP01-622 9911 I

A HANDBOOK OFDIANETIC PROCEDURE

L. RON HUBBARD

5 MILLIONBESTSELLER

How to keep yourself-respect...

Dianetics:. the bright new science of the mindyou can use. Understand how to think clearly andlearn the techniques to really help people.Dianetics gives you the confidence of realsolutions, not just interesting information.

CS In Dianetics awareness is. increased - withoutthe use of drugs, hypnosis or any, physicalmethod- to the point at which the person canbecome aware of the source of his problems.gg

Encyclopaedia of Alternative Medicine and Self -Help

£2.95 from leading bookshops or for furtherinformation from Dianetics, St. Mary's College,Rottingdean, Brighton BN2 7FS FREEPOST36

DESOLDERING TOOL Make life easy with this superb anodised high suction desoldering tool.Essential for desoldering multi hyphen lead e.g. transistors IC's. Especially handy for theexperimenter and service engineer. Eliminating damage to PCB's and components. E4.46VAT Spare teflon nose 85p + VAT.JAPANESE TRANSISTORS Equivalents available for most types. Please call, phone

write.LOW COST VERSATILE MULTIMETER.THE MIGHTY MINI MULTI -TESTER. Ideal for beginner and service engineer(fits into shirt pocket) DC and AC voltage ranges: 10V, 50V, 250V, 1000V. DCcurrent range 100mA. Resistance: two ranges 0-1M OHMS (60 OHMS CENTRESCALE). DECIBELS - 10 to 22 DB mirror arc scale. Overload protection.complete with battery leads and instructions. E6.66 + VAT.ORDER FORM (ORDERS ON PLAIN PAPER ACCEPTED)NameAddress

. Desoldering tools at E4.46 =E

Or

Postage, packing and insurance at 60p per one device, 25p for each additional device.Sub total

Add 15% VATI enclose cheque no/P.O. noAlternatively please credit my VISA/ACCESS/AMERICAN EXPRESS No.SignatureThis offer applies to UK only. Please allow 7-10 days delivery. Overseas customers please do not addVAT but allow to cover postage. TRADE ENQUIRIES WELCOME.

CRICKLEWOOD ELECTRONICS LTD.40 Cricklewood Broadway, London NW2 3ET. Tel: 01-452 0161

Electronic kits for the thrifty!Build 50 Interesting Projects 011 a PC Chassis with surplus components from your 'Spares Box.

EXPERIMENTERS'S PRINTED CIRCUIT KITContents: 4 assorted boards to suit the enclosed designs. Etching Powder, Resist Paint, Solvent,Degreaser and Etching Instructions: also 50 Circuit diagrams, Chassis Plans and Layouts for simpleCrystal Sets, Transistor Radios, Transmitters, Amplifiers, Intercoms, Radio Control, Metal Detector,Photoelectric and Ultrasonic Alarms, 'Perpetual Motion', Light Beam Telephone Instruments,Testers, Gadgets, etc. You can build at negligible cost with 'Surplus' or reclaimed parts and tran-sistors you already have. Price: £2.50. Postage and Packing 50p

PHOTOELECTRIC KITA kit of basic parts to build a simple Infra -Red Sensitive Photoelectric Switch. Contents: Phototran-sistor, Transistors, Diode, Resistors, Connector, Latching Relay, Chassis Board, Case, Screws andInstructions.

Price: £4.50. Postage and Packing 50p

OPTICAL KITA kit of parts to build an IR folden-beam Projector and Receiver to suit the above kit. Contents: 2Lenses, 2 Mirrors. 2-45. blocks, Infra -Red Filter, Larnpholder, Building Plans.

Price: £3.70. Postage and Packing 30pBoth kits together make an excellent Invisible -Beam Burglar Alarm.

EXPERIMENTAL ELECTRONICS335 Battersea Park Road, London SW11 4SL

Tel: 01-720 2683Send SAE for full details of all kits and circuits


Send for my CATALOGUE ONLY 75p(plus 25p post/packing)

My VAT and post/packing inclusive prices are thelowest. All below normal trade price - some at only

one tenth of manufacturers quantity trade.

See my prices on the following:

CAPACITORS . . . ELECTROLYTIC; CAN, WIRE END, TANTALUM, MULTIPLE,

COMPUTER GRADE, NON POLAR, PAPER BLOCK, CAN, POLY, MICA, CERAMIC.

LOW AND HIGH VOLTAGE, RESISTORS. 118th WATT TO 100 WATT; 0.1% TO

10% CARBON, METAL AND WIRE WOUND + NETWORKS. FANS, BATTERIES,

SOLENOIDS, TAPE SPOOLS, VARIABLE CAPACITORS AND RESISTORS,

TRIMMERS, PRESETS, POTS . . . SINGLE, DUAL SWITCHED, CARBON,

CERMET AND WIREWOUND, SINGLE OR MULTITURN, ROTORY AND SLIDE.

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TAPE, BOARDS and others.

Prices you would not believe before inflation!

BRIAN J. REEDTRADE COMPONENTS

ESTABLISHED 25 YEARS161 St. Johns Hill, Battersea, London SW11 1TQ

Open 11 am till 7 pm Tues. to Sat. Telephone: 01-223 5016

TYPE 161B

DUAL POWER SUPPLY KITINCORPORATES A POSITIVE & A NEGATIVE REGULATED SUPPLY

BOTH ARE ISOLATED Et ADJUSTABLE 1.3V TO 16V D.C.Interconnect to give 2.6V to 32V or-1.3V/0/ +1.3V to -16V/0/ +16V

Output current 1A at 16V to 0.35A at 1.3VRipple is less than 1 mV

£25.99inc.P & P and VAT

Built & Tested£37.95 inc. P&P and VAT

Comprehensive designdetails with calculationsare included so that the kit is an excercise in power supply design. Thekit, which uses quality components, is complete with instructions. Casepunched and stove enamelled in attractive blue and grey with a printedfront panel to give a professional finish.Excellent for the beginner, the experienced amateur and as a tutorial forschools and colleges.

SEND CHEQUE OR P.O. ALLOW 21 DAYS FOR DELIVERY

BRANIME MARKETING LTD DEPT. EBALTHANE IND. EST., BALLASALLA, ISLE OF MAN

84

LB ELECTRONICSBrand New 4k" square mains fans, 115 volts AC£4.50 p/p 75p.Brand new 31" square mains fans, 220 volts AC£9.50 p/p 75p.DC Power leads complete with power plug 3.5mmto fit your calculators, micros etc £1 for 10 p/p25p.

REJECT RED FLASHING LED (some flash,some don't, some stay on permanently). Pack of25 £1, 10 packs for £9 p/p free.PCB Amplifier containing LM380 (or equivalent) 9volt rail 1 watt output, brand new £1 each p/p35p.

PCB TA 61" x 9" Approx Alpha mumeric touchkeyboard, ASCII, with Data £7.95 p/p 65p.

EPROMS 1702A £5.00p. 2708 £2.50p. 2516(450 NS), 5 Volts used once, erased andguaranteed by us £1.95p. 10 for £17.00p. 2732£5.00, 2532 £6.00p.

RAM 2114L £1.25p (450NS), 4116 (200NS)£1.00p, 2114 (200NS) £1.35p p/p 35p.

CPU 8080 £2.50p, 6502 £4.50p, Z80A (4 MHZ)£4.50p, Z8671 (Basic/Debug) £21.00p.

LB ELECTRONICS11 Hercies RoadHillingdonMiddlesexTel. 0895 55399

.AMIAK AND

11"1111

Containsall you needto solder/de-solderany electronics project:LITESOLD LC18H 240v high performance iron, made to professionalstandards in our own works, fitted with 3.2mm bit. 2 alternative bits, 1.6and 2.4mm. Reel of 3 metres 18 swg flux -cored solder. Stainless steeltweezer. 3 soldering aids. Reel of 1.5 metres de -soldering braid. Packedin clear PVC presentation/storage wallet. Superb present - ideal forbeginner or expert.SPECIAL PRICE - £13.95 inc. VAT & P. P.(normal resale value £17.49 inc.) IRON only- £5.66 inc. (normally £6.92).Spares, accessories and after -sales service available from us.16 -page colour catalogue - 60p. Send cheque/P.O. to LITESOLD orring for Access/ 1111111400Basales.rclaycard

LIGHT SOLDERING DEVELLOOPMENTS LTD.

Spencer Place, 97/99 Gloucester Road, Croydon CR0 2DN, Surrey. Tel: 01-689 0574.


:RHE PCB SE RV C E apd8fe Bnieard,

PRINTED CIRCUIT BOARDS (PCBs) for HE projects have often represented anFID

obstacle for our readers. Some of you, no doubt, make your ownbut our PCB Service saves you the trouble.NOW you can buy your PCBs direct from HE. All (non -copyright) PCBs will be availableautomatically from the HE PCB Service. Each board is produced from the same master asthat used for the published design and so each will be a true copy, finished to a high stan-dard.Apart from the PCBs for this month's projects, we are making available some of thepopular designs from earlier issues. See below for details. Please note that only boards forprojects listed below are available: if it isn't listed we can't supply it.

October 80 August 81 Telephone TimerNobell Doorbell £2.64 RPM Meter £1.77 (Set of Two) £7.39Intruder AlarmTug 0' War

£2.51£2.65

Thermometer

September 81

£1.67 July 82Tanover £2.31

November 80 Power Pack £1.69 TVI Filter £2.17Memory Bank Synth: Reaction Tester Game £1.71 Computer PSU £8.72

Mainboard PCB £3.31 'Diana' Metal Detector £3.31 Solar Radio £2.15Keyboard PCB

Party Grenade (set of three)Double Dice

£3.60£3.47£2.95

October 81Combination Lock £2.65

August 82Digital M ill ivoltmeter

December 80Stereo Power Meter £2.83

November 81Sound Torch (Set of Two) £5.31

(Set of Two)Audio Analyser

£4.82

January 81Car Rev Counter

February 81

£2.99December 81Pedalboard OrganJanuary 82Intelligent NiCad Charger

£5.97

£3.04

(Set of Two)September 82Signal lights

£12.30

Heartbeat Monitor £2.53 February 82 Main Module £2.34Audio Signal Generator £2.47 Relay Driver £2.20 Junction Module £2.27March 81 Mast -Head Amp £1.31 ZX PCB £3.75Steam Loco Whistle £2.65 March 82 Slot Car Controller £1.99

April 81Super SirenRussian Roulette Game

£1.97£1.60

Digital DiceApril 82Digital Capacitance MeterDual Engine Driver

£1.95

£4.73£3.37

October 82Flash Point AlarmNegative Voltage Generator

£2.31£1.57

May 81 Bike Alarm £2.64 Squelch Unit £2.77Voice Operated SwitchOrgan 1

£1.67£4.64 May 82

Digital ThermometerNovember 82Pedometer/Odometer £2.31

June 81 (Set of Two) £5.31 December 82Envelope Generator £1.87 Echo-Reverb £5.81 Phase Four £3.18Organ 2 £2.53 Cable Tracker £2.21 Microlog £4.28July 81 June 82 Tape/SI ide £5.48Organ 3 £6.00 Power Supply Design £2.64 (two boards)Organ 4 £6.00 Auto-Wah £3.58 TV Amp £5.99Ultrasound Burglar Alarm £2.53 Auto Greenhouse Sprinkler £3.88 Lofty £2.87

PLACE an order for your PCBs using the form below (or a piece of plain paper if you prefer not tocut the magazine), then simply wait for your PCBs to drop through your letterbox, protected bya Jiffy bag.

HE PCB Service, Argus Specialist Publications Ltd, 145 Charing Cross Road, London WC2H OEEI enclose a cheque/Postal Order made payable to ASP Ltd,for the amount shown below Price. Boards Required PriceOR

I wish to pay by Barclaycard. Please charge my account number

VISAOR

I wish to pay by Access. Please charge to my account number

SIGNATURE

NAME(BLOCK CAPITALS)

ADDRESS(BLOCK CAPITALS)

Please allow 21 days for delivery

Add 45p p&p

Total Enclosed £

0.45

I


ro0

RECORD

r7-seL\ ic:/.

PLAYBACK

Li\

0

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Left: Both PCB patterns for the Tape/Slide Synchroniser; top, the Recordingboard; bottom, the Playback board.


PCBs

Right: The HE Phase Four PCB

The Stereo Noise GatePCB pattern (right).Note that there areonly two mountingholes.

Left: The PCB foil patternfor the Low Cost Alarm.The three large holes arefor mounting bolts.

HE Microlog PCB

To+ ilisiLATti

1WT:14'11:

HE MICROLOG


Serums8 Tufnell Gdns.,

Mackworth,Derby DE3 4DY

MAKE YOUR OWN CIRCUIT BOARDSSPEC

VUI- .4.

CIRCUIT MAKER P Etr-Ftl?

Offer for limited period only p.

Reproduces direct from magazine circuits, etc. Complete kit including film, exposing lamp,

D/S fibreglass boards, printing/assemblyframe, etc.

No darkroom or photographic experienceneeded

Full after sales service and consultancySend loose stamp for free brochure

with the

r

XMAS ELECTRONICS SALE(Deduct 15% discount on orders of C15 and over)

MODERN DYNAMIC MOVING COIL MICROPHONES 200 ohms impedance. With switch. Fitted with lead and DIN plug. Used but in nice condition. Only E2 each p.p 50p. MICROPHONEHEADPHONE EXTENSION LEADS Curly 4 core unscreened leads. High quality. Over 1 metre inlength. 35p each p.p 15p. 4 for (1.25 post free. AIRLITE HEADSETS with Boom Mike. Cost overE40 per pair. Our price C4.50 per pair p p. El 2 pairs for E9 post free. Less boom mike (4 per pairp.p. EL 2 pairs E9 post free. AMPLIVOX HEADSETS WITH BOOM MIKE (4.50 per pair postageEl. 2 pairs for (9 post free. Less boom mike E4 per pair, p.p. Cl. 2 pairs for E8 post free. Impedanceof above headphones 600 ohms. All headphones fitted with exMinistry plug. Standard new jackplugs available at 25p each. 2 for 40p. Headphone extension sockets only 25p each. 2 for 40p. GE-NUINE AFV TANK HEADSETS and MIKE E3.50, p.p. E1. 2 pairs for E7 post free. HAVE YOUSEEN THE GREEN CAT? 1000s of new components, radio, electronic, audio at unbelievably lowprices. Send 50p and receive catalogue and FREE RECORD SPEED INDICATOR. Try a JUMBOPACK. Contains transistors, resistors, caps, pots, switches, radio and electronic items. Over E50worth for Ell, carriage E2.50. MINI JUMBO PACK 1E20 worth) (5, p.p. 1.50. BRIDGE REC.TIFIFRS (Phillips) 400 PIV at 4 ampls. Well made. Should be over E2 each. Our price 90p, p.p. 20p.SEMICONDUCTOR SALE ITT BC183 transistors. 10 for 30p or 4p each. IT!" IN4002 diodes 3peach. 10 for 25p. OPTRON TYPE OP160 INFRA RED DIODES High output power. Matched tothe OP500 and OP500SL series photo transistors. Our price 40p. 3 for Et.RIDICULOUS RESISTOR SALE. 1 watt carbon film resistors. 5% tolerance. High quality resistorsmade under exacting conditions by automatic machines. Ell range IRO to 10M0. In lots of 1000 125per value). Only E8 per 1000. Lots of 5000 for E35.GENUINE EX GOVT COLLAPSIBLE AERIALS. A fully adjustable highly efficient whip venal in 5sections. Length open 1,- metres. Closed 300mrn. Copper plated sections. As used on Ex. GovtManpacks. Brand new in makers boxes. £2.50 each, P.O 75p. 2 for E5 post free.

Please add 15% VAT to all orders including post pecking and carriage.

MYERS ELECTRONICS(HE), 12/14 Harper Street, Leeds LS2 TEA. Leeds 452045

New retail premises at above address (opposite Corals). Callers welcome 9 to 5 Mon. to Sat. (Lunch2.15 to 3.15pm) Sunday open 10 to 3pm.

CNC 10 PCB HOLDERIdeal for small scale production, testing, research, service engineers, education andthe home constructor.

. The CNC 10 has a board capacity of 8" x 8" and longer boards (maximum 8" wide)may be accommodated since they can project beyond the ends of the rails,Adjustment of the board rails is extremely simple and they are locked in the desiredposition by one central locking clamp. A further clamp enables the PCB, when inposition, to be rotated through 360 degreesand locked in the required position.An optional foam pad is available whichenables a number of components to beinserted prior to soldering. Pad size 8" x

CNC 10: £16.10 INC. VATFOAM PAD Et CLIP:£5.64 INC. VATPlease add £1.50 to cover postage.Available direct from the manufacturer:

4,t

CARLTON NICHOL Et CO. LTD.,GOLDKEY INDUSTRIAL ESTATE,

KELVEDON, COLCHESTER, ESSEX

ELECTRONICS EMPORIUMEasily reached from Leeds, Manchester, Yorks

and LancsOpen 8.30 to 5.30; Saturday 9 to 1

Vast range of bargains in stock includes Diodes,Heat Sinks, Thyristors, Bridge Rectifiers,Resistors, Capacitors, Terminals, Connectors,Relays, Switches, Wire and Cable, PCBs,Transformers, Measuring Instruments, Nibblerand other Hand Tools. Also ex-M.O.D. Surplus

Test and other Equipment.Some items by mail order - lists available.

A.C. TOWNLEY LIMITEDHarehill, Todmorden, Lancs OL14 5JY

MASTER ELECTRONICS NOW!The PRACTICAL way!

This new sty le course will enableanyone to have a real understandingof electronics by a modern, practicaland visual method. No previousknowledge is required, no maths, andan absolute minimum of theory.

You learn the practical way in easysteps mastering all the essentials ofyour hobby or to start or further acareer in electronics or as a self-employed servicing engineer.

All the training can be carried out inthe comfort of your own home and atyour own pace. A tutor is available towhom you can write personally at anytime, for advice or help during yourwork. A Certificate is given at the endof every course.

NewJob? NewCareer?NewHobby?Getenr into Electronics Now!

You will do the following:Build a modern oscilloscopeRecognise and handle current electronic

components Read,draw and understand circuit diagramsCarry out 40 experiments on basic

electronic circuits used in modernequipment

Build and use digital electronic circuitsand current solid state 'chips'

Learn how to test and service every typeof electronic device used in industry andcommerce today. Servicing of radio, T.V.,Hi-Fi and microprocessor/computer

II Please send your brochure without any obligation toNAME

COLOUR BROCHURE

I

I

ADDRESS

BLOCK CAPS PLEASE

BilisliNationalliadio8cElectronics School Reading, Berks. RG 1 7BRL.

I am interested in:

f I COURSE IN ELECTRONICSas described aboveRA DI 0 AMATE UR LICENCEMICROPROCESSORS

LOGIC COURSE

HE

OTHER SUBJECTS

map

12 821 I

I

I

I

I


'w

[ftwit,visA

ADVERTISEMENTRATES Semi -Display (min 2 cms)1-3 insertions £7.50 per cm4-11 insertions £7.00 per cm12 + insertions £6.50 per cmLineage 26p per word (min 15 words)Box Nos. £2.50Closing date 2nd Friday of the monthpreceding publication date.All advertisements in this section must he prepaidAdvertisements are accepted subject to the terms andconditions printed on the advertisement rate card !availableon request)

HOBBY ELECTRONICS CLASSIFIEDADVERTISING, 145, CHARING CROSS RD,LONDON WC2H OEE.

AERIAL AMPLIFIERS Improve weaktelevision reception. Price £6.70. S.A.E. forleaflets. Electronic Mailorder, Ramsbottom,Lancashire BLO 9AGH.

ELECTRONICS component shop in MAID-STONE, KENTI Thyronics Control Systems,8 Sandling Road, Maidstone, Kent.Maidstone 675354.

1Our Big Bargain Box contains over a thousandcomponents - resistors, capacitors, pots, switches,diodes, transistors, panels, bits and pieces, odds andends. All useful stuff - would cost many times theprice we are asking if bought separately. Approx.

weight 41bs.

ONLY £5.00 inc post - you're bound tocome back for another!!!

BIG BARGAIN BOX

ESP 147F FOUNDRY LANE, SOUTHAMPTON, 5013LSLots of surplus bargains on our latest list - send an

SAE for your copy now.

7LBS ASSORTED Components £5. 10Ibs£6.50. 300, small components, transistors,diodes £2.20. Forty assorted 74 series ICs onPanel(s) £2.20. P.C.B.'s s/sided copper 11"x 8" 90p. 16" x 11" £1.70. Fibre glass 11"x 8" £1.50. 16" x 8" £2.90. Post paid. List25p refundable. J.W.B. Radio, 2, BarnfieldCrescent, Sale, Cheshire M33 1 NL.

DIGITAL WATCH REPLACEMENT parts.Batteries, displays, backlights etc. Alsoreports, publications, charts. S.A.E. for fulllist. Profords, Copnersdrive, Holmergreen,Bucks HP156SGE.

REMOTE telephone bell kit, switches onyour siren, buzzer bell, lamp etc when thephone rings. Battery operated micropowercircuit draws negligible current from phoneline. Complete kit including case and PCBonly £9.95. Dept HE5, Unitech (Midlands),Freepost, Sutton Coldfield, West MidlandsB74 2BR. (Not British Telecom Approved).

WANTED Automatic reset timer preferably9v supply, timer to run for 30 secs and thenre -set itself. Cash by return post. Tel. 550-8902

20 SIMPLE Electronic projects for your ZX81by Stephen Adams, £6.95 including p&p.Come and browse or send SAE for list.Watford Technical Books, 105 St AlbansRoad, Watford, Herts. Tel. 0923 23324.

SPECTRUM VENTURE. Exciting new gamefor the Spectrum. (7 games in 1). In colour,with sound & fantastic screen effects. 16K Et48K version supplied on one cassette for £6.Bobker, 29 Chadderton Drive, Unsworth,Bury, Lancs.

TRANSISTORS GP PNP silicon typeMPS6518 5p each. SAE to SM Enterprises,28 Preston Gardens, Enfield, London.

KIA RETURN AN.AD No 3: . . .Free - 3Ferranti ZTX107 Transistors!! . . . Post +SAE. 8. Cunliffe Road, Ilkley.

BUY BULK - SAVE MONEYAll goods new full spec devices, sent by return.

Post ft any qty. No VAT. SAE List1N4148 £10/k. 154003 £16/k. 1N4007 122/k. BC107 E6/100.BC108 E6/100. 7805 f27/100. 7905 E27/100. 74L593 68/100.74LS112 62/100. 74LS132 C2/100.TBA120C 15/100. 211460/100 8085A E27/10. 14DIL skt 6/100. 1601Lskt E8/100.5rnrn Red LED 122/k, E5/100. BC182L E41100. 253904 6/100.

555 03/100. LM380 E40/100

PC ELECTRONICS2 Thornhill, Romsey Road, Whiteparish, Salisbury. Wilts

SP5 2SDMAIL ORDER ONLY

SOLAR CELLS 3" dia. 900mA at 0.45V£7.59. Price lists 75p. Edencombe Ltd., 34Nathans Road, Wembley, Middx. HAO 3RX

PSUs 5V 1A £10.99. 5V 3A £11.99. 5V 5A£25.99. Adj 1.2-30V 100mA £14.99. 1.5A£24.99. 5A £32.99. Edwards Etectrics, Unit3, Mill Lane, Bridgwater, Somerset.

WANTED Electronic components, boards,connectors, test equipment, good pricespaid. "Q" Services, 29 Lawford Crescent,Yateley 871048 Camberley Surrey.

ELECTONIC kits for sale: Electronic Organ£7, Dice £8.10. SAE for details. Bee Micro,33 Bevendean Crescent, Brighton, E.Sussex.

H.E. ORGAN KITS £99.50 inc. p&p. 61 notekeyboards £32.00. 13 note pedal boards£25.00 inc. p&p. A.T. Hawkins, 23, BlenheimRoad, St. Albans, Herts. AL1 4NS.

500W Dual Channel Flasher Unit in amains plug.

Use for parties, Xmas lights, discos, lowbudget pop groups.

Variable speeds, fused, no interference£7.95 cheques/POs to

AIVIK11 Queensway, Sunbury -on -Thames,

Middlesex TW16 6HAMAIL ORDER ONLY

SMALL reed switches 10p. Magnets 16p.Small DC solenoids 35p. Postage 25p.Grimsby Electronic Components, LambertRoad, Grimsby, S. Humberside. Hundredsbargains at shop. SAE list.

SPECIAL OFFERSAll Capacitors & Diodes are packed in 10s.

Price per pack of 10

220uF 25V220uF 40V220uF 70V470uF 10V

901.201 401.00

DIODES 2200pF 50V .20 470uF 16V .86

153470 E022 3000pF 50V .20 ELECTROLYTIC154001 .25 4700pF 50V .25 CAPACITORS154148 .15 10n 50V .15 RADIAL154383 .30 47n 25V .35 4.7uF 50V PC 6.25155401 1.00 100n 50V .50 4.7uF 100V PC 40

V.REOULATORS ELECTROLYTIC 10uF 25V PC .35

78L05 03.25 ea CAPACITORS 10uF 250V PC .90

7924 .25 ea AXIAL 22uF 100V PC .90

LM723 DIL 30 ea 2.2uF 63V £0.35 33uF 25V PC .30

12V 1W Zeners .06 ea 4.7uF 35V .29 33uF 160V PC .70

POLYSTYRENE 10uF 25V .40 100uF 40V PC .40

CAPACITORS 33uF 100V .60 220uF 10V PC .46

1000pF 160V 6.40 47uF 10V IP) .45 330uF 6.3V .40

CERAMIC DISC 47uF 16V IP/ .45 330uF 10V .60

CAPACITORS 100uF 10V IPI 50 330uF 25V .40

4.7pF 50V 6.25 100uF 16V .60 470uF 10V PC .66

10pF 50V .25 160uF 25V .65 470uF 16V PC .99

120pF 50V .26 220uF 10V .50 2200uF 6.3V 1.00

1000pF 50V .20 220uF 16V .75 PC Short Leads for PCB

All devices brand new & guaranteed. Orders despatched by return of post. Cash/Cheque/PostalOrders with order. Plea. add 60p p&p. MAIL ORDER ONLY PLEASE

A. M. ELECTRONICSTRADE/RETAIL SUPPLY OF ELECTRONIC COMPONENTS & EQUIPMENT

5 Wilson Street, Leicester LE2 OBB


ADVERTISERS INDEXAitken Bros 61 ICS 83Alcon Inst Ltd 77 ILP 54, 55Ambit 2 LB Elec 84A. M. Elec 90 Lightning Elec 79

Amtron UK Ltd 73 Litesold 84Armon Elec 49 Magenta 42Audio Elec 66 Marco Trading 77BK Elec 91 Mercia Elec Ltd 78

Bib 4 Myers Elec 88

Bi-Pak 40, 41 New Era Publications 83

BNOS Elec 78 Photo Etc Systems 88BNRS 88 Pimac 64Bradley Marshall 50 Rapid 8

Bramine Mktg 84 Relay A Quip 77

Cambridge Learning 66 Brian J Reed 84Carlton Nichol 88 Riscomp Ltd 17

Centemp 78 Roadrunner 61

Chordgate 78 Silica Shop 92

Cricklewood Elec 24, 83 Sinclair Research 68, 69Electronize Design 32 Sparkrite 44Electrovalue 60 Technomatic 36Experimental 83 Tempus 28, 29Flight Elec 30 Texas lnst 19

Greenbank 73 TK Elec 49Greenweld 79 Thumall (Elect Eng 64Grenson Elec 34 Townley AC 88Heath 50 Watford Elec 5

Hemmings 64 Wilmslow Audio 83

THERMOCOUPLES for flash point alarmproject available ex -stock £1.00 each incp&p. From Candis Electronics, HighdownWorks, Highdown Avenue, Worthing,Sussex BN13 1PU. Tel. 0903 690750.

r

BURGLAR ALARM EQUIPMENT. Pleasevisit our 2,000 sq. ft. showrooms or writeor phone for your free catalogue. C.W.A.S.Ltd. 100 Rooley Avenue, Bradford BD61 DB. Telephone 0274-308920.

CENTURIONALARMS

We manufacture, you save EEE'sSend s.a.e. or phone for our Free list ofprofessional U.I.Y. Burglar Alarm Equip-ment and accessories.Discount up to 20% off list prices,e.g. Control Equipment from £15.98,Decoy Bell Boxes from £5.95 inc.

TRADE ENQUIRIES WELCOME

0484-21000or 0484 35527 (24 hr. ans.lCENTURION ALARMS (HE)

1265 Wakefield Road, Huddersheia98E, W. Yorkshire'Access Et Visa

Orders Welcomed

HAVEN Hardware. Spectrum fruit machine£4.95. UK101/Superboard products stillavailable. ZX kits: repeat key £3.95. Inversevideo £3.45. SAE for builtprices/beeper/keyboard/software details. 4Asby Road, Asby, Workington, Cumbria.

PRINTED CIRCUITS. Make your own sim-ply, cheaply and quickly! Golden Fotolac'light-sensitive lacquer -_now greatly im-proved and very much faster. Aerosolcans with full instructions, £2.25. De-veloper 35p. Ferric Chloride 55o. Cleatacetate sheet for master 14p. Copper -cladfibreglass board, approx. 1mm thick£1.75 sq. ft. Post/packing 75p. WhiteHouse Electronics, Castle Drive, PraaSands, Penzance, Cornwall.

STEREOPOWER 120 WATT AMPLIFERS!!(60 + 60W protected). Case + controls.D.I.N. sockets. Fibreglass. Boxed + Data.£10.85. A. Law, 8 Cunliffe Road (OverIncatile), Ilkley LS29 9DZ.

HOBBY ELECTRONICSCLASSIFIED ADVERTISEMENT - ORDER FORM

If you have something to sell now's your chance! Don't turn the page - turn to us!Rates of charge: 26p per word per issue (minimum of 15 words). Box Nos. £2.50and post to HOBBY ELECTRONICS, CLASSIFIED DEPT., 145 CHARING CROSS ROAD, LONDON WC2

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mi


MULLARD SPEAKER KITSA PURPOSELY DESIGNED 40 WATT R.M.S.8 OHM SPEAKER SYSTEM RECENTLYDEVELOPED BY MULLARD'S SPECIALISTTEAM IN BELGIUM. Kit comprises a Mallard 8"Woofer with foam surround and aluminiumvoice coil.' Mu[lard 3" high power dometweeter. B.K.E. built and tested crossover,based on Mullard circuit combining low losscomponents, glass fibre board and recessedloudspeaker terminals. Recommended cabinetsize 240 x 216 x 445 mm.A superb sound at a relatively low cost.Complete With instructions. Price £14.90 +E1.60 afro per kit.

New 5" 30 watt mini version of above now avail-able.Recommended cabinet size 180 x 155 x 295mm

Price E13.90+E1.00 p&p per kit.

STEREO CASSETTE TAPE DECK MODULE.Comprising of a top panel and tape mechan-ism coupled to a record/play back printedboard assembly. Supplied as one completeunit for horizontal installation into cabinet orconsole of own choice. These units are brandnew, ready built and tested.Features: Three digit tape counter. Auto -stop. Six piano type keys, record, rewind,fast forward, play, stop and eject. Automatidrecord level control. Main inputs plussecondary inputs for stereo microphones.Input Sensitivity: 100mV to 2V Input Im-pedance: 68K. Output level: 400mV to bothleft and right hand channels. Output Im-pedance: 10K. Signal to noise ratio: 45dB.Wow and flutter: 0.1°c. Power Supply re-quirements: 18V DC at 300mA. Connections:The left and right hand stereo inputs andoutputs are via individual screened leads, allterminated with phono plugs (phono socketsprovided). Dimensions: Top panel 51/2in x111/4in. Clearance required under top panel21/4in. Supplied complete with circuit dia-gram and connecting diagram. Attractiveblack and silver finish.Price £26.70 + £2.50 postage and packing.Supplementary parts for 18V D.C. power supply(transformer, bridge rectifier and smoothingcapacitor) £3.50.

NEW RANGE QUALITY POWER LOUD-SPEAKERS (15", 12" and 8"). Theseloudspeakers are ideal for both hi-fi anddisco applications. Both the 12' and 15'units have heavy duty die-cast chassisand aluminium centre domes. All threeunits have white speaker cones and arefitted with attractive cast aluminium(ground finish) fixing escutcheons.Specification and Price: -.

15" 100 watt R.M.S. Impedance Rohm59 oz. magnet, 2" -aluminium voice coil.Resonant Frequency 20Hz. FrequencyResponse to 2.5KHz. Sensitivity 97dB.Price £32" each £3.00 Packing and Car-nage each.

12" 100 watt R.M.S. Impedance 8 ohm, 50 oz magnet. 2 aluminium voice coil.Resonant Frequency 25Hz. Frequency Response to 4KHz. Sensitivity 95dB. Price£23.70 each. £3.00 Packing and Carriage each.

8" 50 watt R.M.S. Impedance 8 ohms, 20 oz. 1 V2" aluminium voice coil, ResonantFrequency 40Hz, Frequency Response to 6KHz, Sensitivity 92dB. Also available withblack cone fitted with black metal protective grill. Price: White cone £8.90 each. Blackconelgrill £9.50 each. P & P £1.25 each.

PIEZO ELECTRIC TWEETERS -- MOTOROLAJoin the Piezo revolution. The low dynamic mass (no voice coil) of aPiezo tweeter produces an improved transient response with a lowerdistortion level than ordinary dynamic tweeters. As a crossover is notrequired these units can be added to existing speaker systems of upto 100 watts (more if 2 put in series). FREE EXPLANATORY LEAFLETSSUPPLIED WITH EACH TWEETER.

TYPE TYPE 'B''A'

TYPE 'C

TYPE 'E'

TYPE 'D'

TYPE 'F"

TYPE 'A' IKSN2036A) 3" round with protectivewire mesh, ideal for bookshelf 'and mediumsized Hi-fi speakers. Price £3.45 each.

TYPE (KSN1005A) 3'h" super horn. Forgeneral purpose speakers, disco and P.A.systems etc. Price E4.35 each.

TYPE 'C' IKSN6016A) 2" 5" wide dispersionhorn. For quality Hi-fi systems and qualitydiscos etc. Price £5.45 each.

TYPE 'D' IKSN1025A) 2" , 6" wide dispersionhorn. Upper frequency response retainedextending down to mid range 12KHz). Suitablefor high quality Hi-fi systems and qualitydiscos. Price £6.90 each.

TYPE 'E' (KSN1038A) 3% " horn tweeter withattractive silver finish trim. Suitable for Hi-fimonitor systems etc. Price E4.35 each.

TYPE 'F' IKSN1057A) Cased version of type'E'. Free standing satellite tweeter. Perfectadd on tweeter for conventional loudspeakersystems. Price £10.75 each.U.K. post free (or SAE ,for Piezo leaflets).

1000 MONO DISCO MIXERA superb fully built and tested mixer/pre-amp with integral power supply. 4Inputs 2 turntables (ceramic cartridge). Aux. for tape deck etc., plus Mic. withoverride switch, all with individual level controls. Two sets of active tone controls(bass and treble) for Mic. and main inputs. Master volume control. Monitor outputwith select switch and volune control.Outputs Main 750 mV Monitor 500 mW into 8 ohms. Supply 220/240V AC50 /60HzSize 224" x 44" x 24" price f39.99 + E2.50 P&P

1K.WATT SLIDE DIMMER Controls loads up to 1KW Compact size

134%"x "x2%

Easy snap in fixing thrOughpanel/cabinet cut out

Insulated plastic case tFrullcwave control using tamp

Conforms to BS800 Suitable for both resistance

and inductive loadsInnumerable applications inindustry, the home, and discos/theatres etc.

Price: £11.70 each + 50p P&P(Any quantity)

BSR P256 TURNTABLEP256 turntable chassis S shaped tone arm Bert driven Aluminium platter Precision calibrated counter balance Anti -skate (bias device), Damped cueing lever 240 volt AC operation (Hzl Cut-outtemplate supplied Completely manual arm.This deck has a completely manual arm and isdesigned primarily for disco and studio usewhere all the advantages of a manual arm are

required.Price, £28.50 £2.50 P&P

dVI) POWER AMPLIFIER MODULES

BK ELECTRONICS'Prompt Deliveries

VAT inclusive

prices

Audio Equipment

Test Equipment

by

Thandar

and

Leader

KEYBOARDS11111.11181111111111111111111111116111111011Wel * f it,

MEMBRANE KEYBOARDS rmanufactured from a tough poly- -

carbonate film mounted on 1 mm

glass fibre printed circuit boardassembly incorporating silver platedcontacts.16 way numeric keyboardStandard keyboard providing 0-9and A -F functions.Size: 100mm x 100mm x 2mm Price: E5.99+ 35p papAlpha Numeric Keyboard Fullsize 55 key non encoded keyboardwith the commonly requiredfunctions in a Owerty array. Matrixoutput via a 16 pin OIL socket.

Size: 350mm x 100mm x 2mm Price: £13.99+50p p&p

100 WATT R.M.S. AND 300 WATT R.M.S.MODULESPower Amplifier Modules with integral toroidaltransformer power supply, and heat sink. Suppliedas one complete built and tested unit. Can be fittedin minutes. An LED Vu meter is available as anoptional extra.SPECIFICATION:Max Output Power: 110 watts R.M.S. (OMP 100)

310 watts R.M.S. IOMP 300)Loads: Open and short circuit proof. 4-16 ohms.Frequency Response: 20Hz - 25KHz ±3dB.Sensitivity for Mae. Output:500reV at 10K (OMP 100) 1V at 10K IOMP 3001T.H.D.: Less than 0.1%Supply: 240V 50HzSizes: OMP 100 360 x 115 x 72mm

OMP 300 460 x 153 -it 66mmPrices: OMP 100 E31.50 each + £2.00 P&P

OMP 300 E89.00 each + E3.00 P&PVu Meter E6.50 each + 50p P&P

Matching 3 -way loudspeakersand crossoverBuild a quality 60watt RMS system 8ohms

Build a quality 60 watt R.M.S. system.

* 10" Woofer 35Hz-4.5KHz* 3" Tweeter 2.5KHz-19KHz* 5" Mid Range 600Hz-8KHz* 3 -way crossover 6dB/oct 1.3 and 6KHz

Recommended Cab -size 26" x 13" x 13"Fitted with attractive cast aluminium fixing escutcheons arid mesh protective grills which areremovable enabling a unique choice of cabinetstyling. Can be mounted directly on to bafflewith or without conventional speaker fabrics.All three units have aluminium centre domesand rolled foam surround. Crossover com-bines spring -loaded loudspeaker terminals andrecessed mounting panelPrice E22.00 per kit + £2.50 postage and pack-ing. Available separately, prices on request

12" 80 watt R.M.S. loudspeaker.A superb general purpose twin cone loud-speaker. 50 oz. magnet. 2 aluminiumvoice coil. Rolled surround. Resonant fre-quency 25Hz. Frequency response to13KHz. Sensitivity 95dB. Impedance 8ohm.Attractive blue cone with aluminiumcentre dome.Price £17.99 each + £3.00 P&P.

B.K. ELECTRONICS37 Whitehouse Meadows, Eastwood, Leigh -on -Sea, Essex SS9 5TY

* SAE for current lists. * Official orders welcome. * All prices include VAT. * Mail order only. * All items packed (whereapplicable) in special energy absorbing PU foam. Callers welcome by prior appointment, please phone 0702-527572.

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7:1ATARI PRICES REDUCED!We at Silica Shop are pleased to announce somefantastic reductions in the prices of the Atari 400/800personal computers. We believe that the Atari at itsnew price will become the U.K.'s most popular per-sonal computer and have therefore set up the SilicaAtari Users Club. This club already has a library ofover 500 programs and with your purchase of a 400or 800 computer we will give you the first 100 free ofcharge. There are also over 350 professionally writ-ten games and utility programs, some are listedbelow. Complete the reply coupon and we'll sendyou full details. Alternatively give us a ring on 01-3011111 or 01-309 1111.

ivT1136IK 400 £199

wARI3R2I1(400 £248ATARI 800 £449

Lwith 16K A

r 400/800 SOFTWARE & PERIPHERALSDon't buy a T.V. game! Buy an Atari 400 personal computer and a game cartridge and that's all you'll need. Later on you can buy the BasicProgramming cartridge (C35) and try your hand at programming using the easy to learn BASIC language. Or if you are interested in businessapplications, you can buy the Atari 800 + Disk Drive + Printer together with a selection of business packages.Silica Shop have put together a full catalogue and price list giving details of all the peripherals as well as the extensive range of softwarethat is nowavailable for the Atari 400 800. The Atari is now one of the best supported personal computers. Send NOW for Silica Shop's catalogue and pricelistas well as details on our users club.THE FOLLOWING IS JUST A SMALL SELECTION FROM THE RANGE OF ITEMS AVAILABLE:ACCESSORIESCablesCassettesDiskettesJoysticksLe Stick JoystickMisc SuppliesPaddles

AUTOMATED InvoicingSIMULATION§ LibrarianCrush Crumble Cmp Mort & Loan AnalDatestones of Ryn Nominal Ledger

ADVENTURE INT Dragons Eye PayrollScott Adams Ads Invasion Orion Personal Full MgmtNo 1 Adventurelnd Rescue at Rigel Purchase LedgerNo 2 Pirate Adv Ricochet Sales LedgerNo 3 Mission Imp Star Warrior Statistics 1No 4 Voodoo Cast Temple of Apshai Stock ControlNo 5 The Count Upper Reaches Aps Telelink 1

No 6 Strange Ody VisicalbNo 7 Mystery Fun BOOKS Weekly PlannerNo 8 Pyramid of D Basic Ref Manual Word ProcessorNo 9 Ghost Town Compute Atari DOSNo 10 Say Island I Compute Bk Atari CR YSTALWARENo 11 Say Island 2 Compute Magazine Beneath The Py ramNo 12 Golden Voy De Re Atari Fantasyland 2041Angle Worms DOS Utilities List Galactic QuestDeflections DOS? Manual House Of UsherGalactic Empire Misc Atari Books Sands Of MarsGalactic Trader Op System Listing Waterloo

LLunar Lander Wiley Manual World War III

Mountain Shoot 131,J$LH§§,§Rearguard Calculator

PYNACOMPAlpha Fighter Metric & Prob Solvg StatesSc & Capitals Centurion

Castle Sleazy AdventureMission Asteroid

PROGRAMMINGMathsTac-Toe

Star Fine Database Managemt Chompelo TMhouressIthaotlIdeck

AIDS Isom AierkMusicMuu Tmvpm.,No.,r. Touch Typing Checker King

SolitaireAssembler Editor

Sunday Golf Decisidn Maker CrystalsChinese Puzzle Space ChanDsemblnr (APX)

Graph It Forest Fire Musical Compute/ EMI SOFTWARE Codecrackerstace,..TPreakh...

Ulysses/Golden Ft Microsoft BasicIntruder Alert Wizard & Princess. Pascal IAPX)My First Alphabet

Darts Dog

Heritage Comedy Diskette Tact TrekMonarch Number BlastMoonprobe Polycalc

Cribbege/Dorninces Dice Poker TerDog Daze Wizards Gold

Terry Pilot (Consumer)PERIPHERALS Pilot (Educator)

Moving Maze Presidents Of U.S. European Scene Jig Domination Wizards Revenge Centronics Printers Programming KitNonnnoes Jigsaw Quiz Master Hickory Dickory Downhill Disk DriveRings of The Emp Starware Humpty Dumpty Eastern Front ENTERTAINMENT Epsom Printers SANTA CRUZSpace Tilt Stereo 3D Graphics Jumbo Jet Lander Galahad & Holy Grl from ATARI Program Recorder Basics of AnimationSpaceThree R Math Sys Snooker & Billiards Graphics/Sound Asteroids RS232 Interface Bobs BusinessStudTrapPoker Video Math Flash Submarine Commdr Ja4-0 Basketball Thermal Printer Display ListsTriple Blockade Wordmaker Super Cubes & Tilt Jukebox Blackjack 16K Memory RAM Graphics Machine

Tournament Pool Lookehead Centipede 32K Memory RAM Kids 1 & 2EDUCATION EDUCATION Memory Match Chess Horizontal Scrollingfrom__LAID.S from ATARI Entertainment Kit P F_EA,VaNALIeLT Master Memory Map

Cony French fromENTERTAINMENT Midas Touch

Minotaur Missile Command fromAlgicalc Mini Word ProcessorAtlas of Canada Cony German Alien Egg Outlaw/Howitzer Pm Man Adv Music System Page FlippingCubbyholes Conn Italian Preschool Games Space Invaders Banner Generator Player Missile Gr

F rogmaster

Anthill

AAvTlan:chePro Bowling Star RaidersElementary Biology Cony Spanish Blackjack Tutor Player Piano

Energy Czar Pushover Super Breakout Going To The Dogs SoundsHickory Dickory European C & Caps Babel Rabbotz Video Easel Keyboard Organ Vertical ScrollingInst Corriptg Dem Hangman Blackjack Casino Reverse II Morse Code

Personal TtoFitnessurLemonade Invit To Prop 1/2/3 Block Buster Salmon Run ON LINE SYSTEMSPeg SILICA CLUBLetterman Kingdom Block 'Em 747 Landing Simul Crossfire Player Piano Over 500 ProgramsMeuware Music Composer Bumper Pool Seven Card Stud Frogger Sketchpad tmkorftjaisg .....4

FOR FREE BROCHURES -TEL: 01-301 1111PIP

or tree pose, and fewer. ron Our range or ereclrone producIS plea, terephOne 01 301 1111id order sv lelepeOrte tost yOur name ask., male card number and order redurremenlaane red, tee real lo us Post and ea., ts FREE OE CHARGE WI TeebUN.UN E... 24 hewdelwery avelapie al an addeOnar charge

SHOP OE SIONSTRACON ACE IDES - We prOvv, lull lacebes ai ow shop rn SidSup To1Onday 10Saturday garnIo 30, ClOeng Thursday I, Fre, eo,

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EXCHANGE SECOND CHINES- *ea./ea...change sc.rne id trap., Ma.maa. or T V gm, Bosons. [OnIputerS

COMPETITIVE PRICES - dices otters ane Se, vse are very COeS.Pve eitare never anovencayunderabld and vaa al, any b., prkl .0Ia0 by Our <CMpeb.C.'S

HELPFU, ADviCE ,'wankOn me 51.11...ty 01 waroOus cornpuleIS army SOLES SERVICE - available on all computers our or puarant,

VAT - air perces qua, above tnelarte VAT at +Sae

SILICA SHOP LIMITEDDept HEii 082, 1-4 The Mews, Hatherley Road, SIdcup,Kent DA14 40X Telephone 01-301 1111 or 01-209 1111

'III Ill

r FREE LITERATUREI am interested in purchasing an Alan 400/800 computer and wouldlike to receive copies of your brochure and test reports as well asyour price list covering all of the available Hardware and Software.

Memo

Address

PostcodeHE 12 82

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