ROBOTICS REVIEW INDUSTRY NOTEBOOK BAZAAR

PiDIP4PLF

'K' SERIESSOLDERING TOOLSFOR ALLAPPLICATIONS

K1000 micro solderingK2000 general electronicsolderingK3000 heavy duty soldering

Small selection ofAD -IRON® LONG LIFESOLDERING TIPSsuitable for all Adcolasoldering irons.

842LL

ADCOLA,61, rsef Mee

ELECTRONIC PRODUCTION EQUIPMENT

ndustrial SolderingEquipment -for the

discerning

101 ELECTRONICCONTROLLEDSOLDERINGSTATION

for precision solderingwith accuracy suitablefor use on MOS, FET etc240V input - 24V on tool.Temperature range120-420°CMany extra features

labs838LL 85OLL B14LL B35LL Baal L B36L L B37L L B46L L 8401L

ADCOLAACCESSORIES

include:SIDE CUTTERS

SNIPE NOSE PLIERS

PLUS Desoldering Braid Desoldering Guns Tip cleaners Soldering aids Lamps, Lenses etc

For a no obligation demonstration, please contact:ADCOLA PRODUCTS LIMITED Gauden Road London SW4 6LHTelephone Sales (01) 622 0291 Telex 21851 Adcola G

ROBOTICSMICROSELECTRONICSINTERFACING

ISSN 0032-6372

VOLUME 21 1\1912

CONSTRUCTIONAL PROJECTSEXPERIMENTING WITH ROBOTS by Mark StuartHigh performance stepping motor driverDISCO LIGHTS CONTROLLER by John M. H. BeckerPart Two: The "Chaser" circuit, and interwiring detailsMODEL RAILWAY TRACK CONTROL by J. MilnePart Two: Final construction and testingMICRO -SCOPE by John M. H. BeckerPart One: Make an "oscilloscope" out of a micro

GENERAL FEATURES

DECEMBER 1985

10

24

32

42

INTRODUCTION TO MICROPROCESSOR SYSTEMSby Michael Tooley BA and David Whitfield MA MSc CEng MIEE 16

Part Three: Getting started-Initialisation and configuring peripheralsROBOTICS REVIEW by Nigel ClarkA regular look at robotics and cyberneticsSPACEWATCH by Dr. Patrick Moore OBEHALLEY'S COMET by Dr. Patrick Moore OBEIf you miss this you'll have to wait 'till 2061BBC MICRO FORUM by D. Whitfield MA MSc CEngImproved light pen and software21 YEARS OF ELECTRONICS by Mike KenwardPart Two: The past seven years plus forthcoming trends

NEWS & COMMENT

20

2228

36

38

EDITORIAL 7 INDUSTRY NOTEBOOK 15 P.C.B. SERVICE 48NEWS & MARKET BAZAAR 23 SUBSCRIPTION SERVICE 48

PLACE 8 LEADING EDGE 46 INDEX FOR VOL. 21 51

FRONT COVERArtist's impression ofGiotto about to encoun-ter Halley's comet. Illus-tration by Paul Doherty.

OUR JANUARY ISSUE WILL BE ON SALE FRIDAY, DECEMBER 6th, 1985 (see page 47)

c IPC Magazines Limited 1985. Copyright in all drawings, photographs and articles published in PRACTICAL ELECTRONICS isfully protected, and reproduction or imitations in whole or part are expressly forbidden. All reasonable precautions are taken byPRACTICAL ELECTRONICS to ensure that the advice and data given to readers are reliable. We cannot, however, guarantee it,and we cannot accept legal responsibility for it. Prices quoted are those current as we go to press. .

Practical Electronics December 1985

WATFORD ELECTRONICS250, HIGH STREET, WATFORD WD1 2AN, HERTS.

MAIL ORDER & RETAIL SHOPTel. (0923) 37774. Telex: 8956095 WATFORD

ORDERS NORMALLY DESPATCHED BY RETURN OF POST

All Devices Brand NEW & Fully guaranteed. SEND Cheques, P.O.s & Bank Draft or ACCESS/PiasterCharge & VISA card number with order. Government & Educational Establishments' OFFICIAL ordersaccepted. P & P add £1 to all Cash orders. Overseas orders, postage charged at cost AIR/SURFACE.PRICES SUBJECT TO CHANGE VWTHOUT NOTICE AND AVAI/ 1191 E ON REQUEST.

VATExport orders NO VAT. UK customers please add 15% VAT to the total cost incl. p&p. We stockthousands more items, it pays to visit us. Newest Underground/British Rail station: Watford HighStreet. FREE car parking for customers. Open: Monday to Saturday, 9.00 am to 8.00 pm.

TRANSISTORSAC126/7 30AC127/8 35AC141/2 35AC176 25AC187/8 25AC188 25AD142 120AM.: 75AD /2 42AF118 95AF124/6 60AF139 404F239 55BC107/8 12BC107B 14

8C237/88C307B8C3088BC327/8BC337/8BC441EIC461

13C47713BC516/7BC547/8BC549CBC556r7BC558/9BCY41/42BCY70BCY71BCY72BCY78BD131/2BD13380135BD136/7

D138/90140D158D2450534D695406964F115F154/8F167F173F177F178F179F184F194/5Fl9EV9F200F224F244AF448F2245F2566F257/8F259F394F451F494/5F594/5FR39/40

10151212123434!.'30121215153018201830555045353540686570

1501504530353535354035121835402829384532304040403025

S21411791 1:BER98 10513FX29/84 28BFX84 35BFX85/86 358FX87/88 28BFY50151 305FY52 30BFY5.3 35BFV55 35BFY56 35BFY64 40BFY90 80BRY39 50BSX20 28BSX29 328SY26 35BSY95 35BU105 180BU205 160BU206 2008U208 170MJ520 50AAJ521 90MJ2955 90MJE340 54MJE371 100MJE2955 99MJE3055 70MPF102 40MPF103/4 30MPF105 30MPS405 23MPS406 25MPS40 30MPSA12 29MPS455 30MPSA56 30MPS470 40MPSU02 58MPSUO5 50MPSUI36 55MPSU52 65MPSU55 60MPSU56 550C23 1700C28/36 2200C41/42 750070 400072 500075/76 550076 500081/82 500083/84 70

TIP294 32TITIP304 35TIP313C 37TIP314 38TIP31C 45T1P324 43TIP32C 4511P334 70TIP33C 75TIP34A 85T1P34C 105T1P354 120T1P35C 130TIP364 130T1P36C 140TIP414 5011P41B 52TIP42A 55T1P420 5811P120 70T1P121 73DP141 120TIP142 120TIP147 12011P2955 7011P3055 7011543 50T1S44 45TIS884 50T1S90 307159193 32VK1010 99VN1OKM 65VN46AF 90VN664F 110VN88AF 220VN89AF 120ZTX107/8 12ZTX109 12ZTX212 28ZTX300 13ZTX301/2 16

ZTX304 17ZTX320/26 30ZTX500/1 14I1X502/3 18ZTX504 25ZTX531 25ZTX550 252N696 302N697 232N698 402N699 48

4 2522077008

252N914/5 32214918 402N930 202N1131/2 402N1303/4/52N1307 702N1613 302N167113 1502N2160 3252N22194/204/21A/22A 252N23694 182N2646 452N2846 802N29044/05N064/074 252N2926G 102N3053 252N3054 552N3055 502N3442 1402N3615 1992N3663 202N3702/3 102N3704/5 102N3706/7 102N3708/9 102N3710 102N377I 179203772 1952N3773 210203879 52N3820 602N3822/3 602N3866 902N390314 152N3906/5 152N4037 602N4058 152N4061/2 152N4264 30204286 252144289 252N4400 252N4427 80204859 78205135 302N5138 252N5172 252N5180 45205191 752N5194 802N5305 24

2NN5457 3025458/9 302N5485 382N5777 452N6027 322N6109 602N6290 70254636 250254671 250254715 762SC495/6 852SC1061 2502SC1096 852SC1162 452SC1172/3 12525C1306 10025C1307 1502SC1449 952SC1679 19025C1678 14025C1923 6525C1945 2252SC1953 9025C1957 9025C1969 1652SC2028 852SC2029 2002SC2078 17025C2091 852$C2166 1652SC2314 852SC2335 2002SC2465 1252SC2547 402SC2612 2002SD234 752SK45 9025K288 22525J83 22525J85 2253N128 11530140 11540251 15040311 6040313 13040361/62 7040408 7640412 9040467 13040468 8540594 10540595 11040603 11040673 7040871/2 90

POLYESTER RADIAL LEAD CAPACITORS: 250V; 10n, 20n, 15n, 22n, 27n 6p; 33n, 47n, 68n, 100n Sp; 150n,220n 109; 330n, 470n 159; 680n 199; I.. 23p; 1;15 40p; 292 489.

BC1086 148C108C 14BC109 12

ELECTROLYTIC CAPACITORS (Values in lin. 500V: 10pF 52p; 47 78p; 63V: 0-47, 1.0, 16, 2.2, 3.3, 8p; 479p; 10 109; 15, 22 12p; 33 15p; 47 12p; 68 169; 100 19p; 220 26p; 1000 70p; 2200 909; 50V: 68 20p; 10017p; 220 249; 40V: 6815p; 22 91/13312P; 330, 470 32p; 1000 489; 220090p; 25V: 47, 10, 22, 47 8p; 10011p; 150 12p; 22015p; 33022p; 4702511; 680, 100034p; 150042p; 220050p; 330076p; 470092p; 16V: 2-5,4089; 47, 68, 10090; 1251211; 220139; 330109; 4702011; 680349 1000 27p; 150031p; 2200369; 470079p.

8C1096 14BC109C 14BC114/5 215BC117/8 25BC119 35

TAG -END TYPE: 64V: 4700 246p; 3300 145p; 2200 120p;50V. 3300 155p; 2200 95p; 40V: 4700 160p; 2200 70p; 330085p; 4000, 4700 75p; 10,000 250p; 15,000 2709; 15V: 2200200p; 25V: 4700 989; 10.000 3200; 15,000 345IL

POTENTIOMETERS: Carbon Track,0.25W Log & Linear Values.

500W, 1K & 2K (UN ONLY) Single 35p5K0 2- MC/ single gang 358

BC140 298C142/3 288C147/8 12BC147B 15801480 10

TANTALUM BEAD CAPACITORS:351f: 61m, 622, 03315p 0-47, 0.68,1-0,1.516p 2.2, 3-318p 4.7,

5101-2M0 single gang 0/P switch 95p51(0-2M0 dual gang stereo 55P

BC149 12Kinc 15BC153/4 30

6.8 22p 10 28p 16V: 2-2, 3-3, 165 47, 6.8, 10 15p 15 38p 2236p 33, 47 50p 100 95p 220 100p 10V) 15, 22 26p 33, 47505 100 75p.

sum, 9075975351Er555025W log and linear values 60mm track5K0 -500K0 Single gang $09

BC157/8 14BC159 11BC1674 14BC168C 12

SILVER MICA (pf) SIEMENS mulitlayer miniature 8C169C 122, 23, 47, 68, 82, 10, 12, 18,22, 27, 33, 39, 47, 50, 56, 68, 75,82,85,100, 120, 150,180 15p.220, 250, 270, 330, 360, 390,

capacitors.250V: 1nF, 1n5, 2n2, 3n3, 4n7,6n8, 8n2, 10n, 15n, 22n 7p; 18n,27n, 33n, 47n Sp; 39n, 56n, 68n

PRESET POTENTIOMETERS ..51W 500-2-2M Mini Vert & Hord. 0'

25W 2200-4M1 Vert & Hem 129L.,,..... .s.,s- s,, ss_040,01 MI.,..m Preset 00 to ..." ..0

BC171/2 12BC173 16BC177/8 16BC179031 20

470, 600, 800 & 820pF 21p.1000, 1200, 1800 30p each3300, 4700 60p each

9p, 100nF 11p.100V: 100n, 120n, 10p; 150n 11p;220n 13p; 330n 18p; 470n 23p;680,s 309; IMF 349; 2M2 509.

RESISTORS Hi -stab, Miniature, 5%cm...RANGE Val. 1-99 100+

0.25W 202 - 4.M7 E24 3p 1p

BC181 30BC182/3 10BC84 1

BC182L 100BCI 83L 10

CERAMIC Capacitors: 50VRange 1pF to 6800pF 4p; lOnF,15n, 33n, 47nF 5p; 100nF/20V 7p220nF/6V 8p.

POLYSTYRENE Caps:10pF to 'ME1n5 to 12nF ......8°'",'

05W 202 - 4M7 E12 3p 1P1W 202 - 10M E12 6p 4p5W 0.220- 1M 20p 10p1% Metal Film 510-1ME24 8p 61,

BC184L 10BC18&7 2813C212/3 12BC212L 10

RESISTORS &I -L. Package: 7 Commoned, 1000, 4700, 6800, 1K, 21(2, 4K7, 10K, 47K, 100K 18p.8 Commoner!: (9 pins) 1500, 1800, 2700, 3300. 3300, 1K, 2K2, 4K7, 6K8, 10K, 22K, 47K, 100K 20p.

BC213L 12BC214 108C2141 12

LINEAR IC's SP0256AL 425558629 350TA7120 120y47130 125747204 150TA7205 goTA7222 150TA7310 120TAA900 395TAA700 275TAD100 159794170S 70TBA540 2757845500 330TBA641 noTELA800 80TBA810S 9675A820 80TBA9200 200784990 350TC4270 350yrawina- 220TC4940 175TCA950 00TC4965 150TDA1008 310401DA1010 2201D41022 4007041024 110T0A1034 350TDA1054 00TDA1490 35071)42002 32571)42003 190- -1042004 230TDA20136 320T0A2020 32011)42030 190TDI30791 420TL06105 40T1362CP 50TL064CN 95TL071CP 40TL072CP 60TL074CN 110TL081CP 30TL082CP 507108305 nTL084CP 100TLOSICP soTL170 50TL497A 18511507 110TL509 110U42240 120u470550 225uA4170 180U44180 180ULN2003 75ULN2004 75U1N2283 150U1N2803 190

UPC575 275UPC1025H 375UPC1156H 295UPC1181UPC1182 425UPC1366 196XR2206 365x52207 400XR2211 575XR2216 675XR2266 3602N40ec 180ZN414 80ZN423E 130ZN424E 130ZN425E-8 350ZN426E-8 3002N427E-8 600ZN428E 450ZN429E-8 2402N450 245201034E 200ZN1040E 565ZNA234E 925

JUST PHONEYOUR ORDER,

WE DOTHE REST

El I =

COM .IC's

2102L 1602114 2502147-3 E32516 3002532.4 30025L32

4502564 "27108 4502716-5V 3002732 3502732A 58527256-2 10552764-250 28527C64 80026501 75271281250n 400256K DRAM3242 6754027 984116-200n 1004164-150 2254416-2 2994532-3 2504816-100ns 1254864-15 2256116-150 2006116L-120ns 2206117-100n 5756167-6 755..,,, ,.-- 54063403 E146464L-15 75065CO2 8506502 CPU 32565024 5456503 6506520 17565224 5456522 VIA 340.....,..:.,-,T £11--"'"'6532 RIOT 6506545 CRTC 0996551 -CIA 5256800 2206802 2756803 8506805 6706809E 6506810 150

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8250 9508251 3258253 3800255 3508258A £158257A 4008259 4008271 £458272 £158279 7508282 4508283 4508284 5508288 £118748 £3381264 998T27 1508T31 3508T95N 908197N 909360AP 5509602 220AM261531C 126AM26LS32A 125AM26LS33 150AM7910 £19Ay -31015 300AY -5-1013 300Ay -5_1350 3103Ay 5,,,,,,, 750. . . - -CD4724 150

COM8017 275DM8131 275DP8303 450OP13304BN 350DS3647 600D53031/4 3501)88820 110DS8830 140D58831 125058832 150D58815120 300E9364 800E9365 £28FD1691 £15FD1771 £15F01791 £22FD1793 £23FD1795 £28F01797 £28H026501 75H04315 250I-106301 225HM6845 755IM6402 350INS8060N 1250M58174 825MC1488 100MC1489 100MC14411 675MC14412 725MC3242 590MC3446 250MC3447P 315MC3486 175MC3487 175MK3886-2M £7MM52800 695MM5303 535MM5307 1275MM5387A 865MM58174 875R0-3-25131 700RO-3-2513U 65054.45050 875SPP96364E 800850256412 475TCM3101J £13TM52716-3 725TMS4047 100TMS4164-15 255TMS4416-2 355TMS4500A £121M54532-3 350TMS6011 500TMS9914 895TMS9927 £14TMS.9928 £10TMS9929 £10ULN2003 75

UP07002 440UPD7007 726WD1691 £14WD1770 £14WD2143850Z80CPU 2-5 2952804CPU4M 199Z8OACTC 3102808 £8ZBODART 650ZBOADART 800Z8OADMA 900280DMA 795280P10 250Z804P10 315Z80510-1 5502804510 900Z804510-2 £9

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8 pin 185160375£10

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74147 13074148 10574150 13074151 6074153 7074154 13574155

80757415674157 7574159 17574160 9074161 9074162 9074163 9074164 11074165 9074166 13074167 20074170 16074172 39074173 10074174 10074175 8074176 8074177 8074178 12074179 9074180 8574181 23074182 8574184 16074185 16074186 7074188 7574190 11774191 14074192 19174193 11074194 9074195 6374196 12074197 85

- -74LSLSOO 22L501 22L502 22L503 22LSO4 221_505 221508 251S09 22LSIO 221511 221S12 221513 301.514 50LS15 22LS19 45LS20 22LS21 221S22 22LS24 50L526 22

CMOS4000 204001 204002 204006 704007 204008 604009 404010 404011 204012 204013 30

2Practical Electronics December 1985

SPEAKERS80, 06W, 2"; 2.25", 2-5",

80p0.3W, 2-5" 400; 640 or800 80p

DIODESAM1944129AAY30BA100BY100BY126BY127CR0330A9 1

0A47 1

0A700A79 1

0A81 1

04135 1

0A900A910A950A2000A2021N9141N9161N4001/21N40031N4004/51N4006/71N41481N5401 1

1N5404 11N54136 1

1N5408 1

15441S9216A/100V64/400V6A/800V

810

810151210

198

405065

BRIDGERECTIFIERS(plastic case)

14/100V14/400V14/600V24/50V24/200V24/400V24/600V64/100V64/400V64/600V10A/200V104/600V25A/200V25N600VBYI64

202530264042508395

125215298240395

56

ZENERSRange: 2W to39V 400mW

Bp eachRange: 3V3 to33V. 1.3W

15p each

VARICAPSBB105B 40BB106 40

SCR'sThyristors0.84-100V 3254/300V 3854/400V 4054/600V 48

608A1600V 9512A/100V 78124/400V 95124/800V 188BT106 150BT116 180C106D 38TIC44 24TIC45 2911C47 352N5064 382N4444 130

TRIACS34/100V 4834/400V 563A/800V 8584/100V 8084/400V 698N800V 115124/100V 78124/400V 82124/800V 135164/100V 103164/400V 105164/800V 22025A/400V 185254/800V 295254/1000V

480304/4.00V 525128000 125

OPTO ELECTRONICSLED

0-125"TIL209 Red 10pTIL211 Green 14pTIL212 Yellow 14pTIL213 Amber 14p0-2"TIL220 Red 12pTIL222 Green 14pTIL226 Yellow 14pFlashing Red 55pBi colour R/G 100pBi colour GN 100pIn colour R/GN B5pHI -Bright Red 95pHI -Bright Green 100pHI -Bright Yellow 95pRectangl. R,G & Y 35pRectang. StackableRed Green Yellow 18pTriangular R & G 18pInfra RedLD271 (emit) 46pTIL32 (emit) 52pSFH2O5 (detector) 100pTIL78 (detector) 55pTIL38 (emit) 509TIL100 (detector) 90p7 Segment DisplayDL704 3" C.An 120pDL707 .3" c.Cth 120pFND357 or 500 100pTIL321 5" C.An 140pTIL322 .5" C.Cth 140p.3" Green C.An 140p.3+1" Red or Green 150pBargraph 10 Seg. 250pBargraph NSM3914 400p

pIL74ILCT6

13580p

ILD74 130p1L074 220pTIL111 70pTIL112 70pTIL113 70pTIL114 70pTIL116 70pBPX25 150pBPX65 320pBPW21 280pTIL81 82pOCP71 120pORP12 78p2N5777 50p4N33 135pPin Diode 720pSmith Rec.700p

ALUM.BOXES4021/2+2 1004023/4021/21034x4021/2" 12050402 1055x23/4011/2 905023/4x21/2130504011/2' 995.4021/2 12060402 120604+3 15070503 18080603' 21010041/403 240100703' 275120503" 260120803' 295

VOLTAGE REGULATORS1A T0220 Plastic Casing

+ve -ye5V 7805 45p 7905

12V 7812 45p 790815V 7815 45p 791218V 7818 46p 791524V 7824 45p 7918

50955p65p55p50p

100mA 1092 Plastic Casing5V 78L05 30p 79L05 50p6V 78L62 30p8V 78182 30p

12V 78L12 30p 79112 5- 0p15V 78115 30p 79L15 50p

ICL7660 248 LM317K 25078H05 5V/5A 550 LM317 9978H12 12V/5A 640 LM323K 50078HG+5 to LM3377 175+24V 5A 695 LM723 3079HG -2.25V to TBA625B 75

24V 54 785 RC4194 375LM309K 120 RC4195 16011497 185 78440 225

DIL SOCKETS Turpni:dLow Wue Low

profile wrap profile8 pin Bp 25p 22p

14 pin 10p 35p 25p16 pin 10p 42p 32p18 pin 16p 52p 38p20 pin 20p 60p 42p22 pin 22p 65p 48p24 pin 25p 713p 52p28 pin 28p 80p 60p40 pin 30p 99p 80p

ZIF SOCKET(TEXTOOL)24 way28 way40 way

550p650p800p

SPECTRUM32K UPGRADE

Upgrade your 16K Spectrum to full48K with our RAM Upgrade Kit. Verysimple to fit. Fitting instructionssupplied. ONLY £18

FERRIC CHLORIDECrystals 1 lb150p + 50p p&pDALO ETCH RESISTPen plus spare tip 100p

0.5" LCDDISPLAYS31/2 digit 4956 digit 625

COPPER CLAD BOARDSFibre single doubleGlass sided sided6'06" 100p 125p6" x 12" 175p 225p

OPTOSWITCHReflectiveTIL139 225Slotted similarto RS 188

SWITCHESSLIDE 250V TOGGLE 2A 250V1A DPDT 14 SPST 3514 DPDT GOFF 15 DPDT 481/2A DP on/on/on 40 4 pole on off 54

PUSH BUTTONSpring loadedLatching orMomentary 6ADPDT clover 200

SUB -MINTOGGLE 2 ampSP changeover 64SPOT on off 58SPDT c/off 85SPDT Biased 105DPDT 6 tags 80

MINIATURE DPDT C/OFF 88Non Locking DPDT on/on/on 185Push to make 15p DPDT Biased 145Push break 25p 4 -pole 2 way 220ROTARY: (Adjustable Stop Type)1 pole/2 to 12 way, 2p/2 to 6 way, 3 pole/2 to 4 way, 4 pole/2 to 3 way 48p

ROTARY: Mains 250V AC, 4 Amp 68p

DIL PLUGS (Headers)Pins Solder IDC14 40p 95p16 45p 100p24 85p 135p28 150p 195p40 200p 225p

RIBBON CABLE(price per foot)

Ways Grey Colour10 15p 25p16 2 30p20 25p 40p26 40p 65p34 50p 80p40 60p 90p64 90p 125p

2764 - 250ns27128 - 250ns6116LP - 150ns6264LP - 150ns

IDC CONNECTORS (Speed block type)

PCB Male Femalewith latch Header

2 rows Strt. Angle SocketPins Pins

10 way 65p 66p 65p1620 way

way90p75p 790p

95pp80p

26 way 105p 110p 115p34 way 115p 130p 135p40 way 140p 145p 150p50 way 165p 170p 175p60 way 195p 210p 225p

FemaleCard -EdgeConnector

1113p185p185p2313p320p335p350p495p

SPECIAL OFFER1+220350200480

10+205345195475

DIP SWITCHES: (SPST) 4 way 65p;6 way 80p; 6 way 87p; 10 way 100p;(SPOT) 4 way 190p.

DIACST2 25

SOLDERCONPINS

100 45p500 200p

VERO TOOLSSpot facecutters 150pPin insertiontool 185p

VERO BOARDS 0.1"2112 x 1 30p21/2 x 31/4 95p212 x 5 110p

.33/4 x 33/4 110p33/4 x 5 125p33/4 x 17 420p43/4 x 17 590pVD Board 195pVERO WIRINGPEN + Spool 380pSpare Spool 75pCombs 8pPen + Spool 4Combs 599p

DIP BoardVero Strip

395p

PROTO DEC.Veroblock 480pS -Dec 350pEurobreadboard 590pBimboard 575pSuperstrip052 1350pVERO PINS per 100Single Ended 55pDouble Ended 60pWire Wrape S/E1156pWire Wrape D/E255p

AMPHENOL CONNECTORSIDC Solder

24 way IEEE plug 465p 460p24 way IEEE socket 485p 480p36 way Centronics plug 395p 390p36 way Centronics socket 480p 450p

'D' CONNECTORS:Pins 9 15 25 37

way way way way

MALESolder 55p 80p 120p 150pAngle 110p 175p 225p 3009Strait 1009 100p 160p 250pFEMALESolder 90p 125p 180p 275pAngle 150p 200p 260p 390pStrait 100p 125p 195p 355pCOVERS 75p 70p 70p 85pIDC 25 way Plg. 385p, Skt. 450p

ASTEC UHF MODULATORS6MHz Standard8MHz Wideband

375p450p

ANTEX Soldering IronsC15W 600p C517WG18W 620p XS25W

620p650p

SILSockets0.1"

20 way65p32 way95p

EDGE CONNECTORS

20 6 way2012 way2015 way2018 way2x22 way2023 way2025 way2028 way2030 way2036 way2040 way2043 way2075 way

- 7ep- 160p- 165p175p 160p200p150p

170p

250p 245p180p-2809-300p -320p -4009-0009-

TRANSFORMERS3-0-3V; 6-0-6V; 9-0-9V; 12-0-12V; I5 -0-15V Gri00MA 130pPCB mounting; miniature; Split bobbin.3VA: 2x6V /0.25A; 2x9V /0-15A; 2x12V /0.12A;2x15V /13.2A 235pOVA: 2x6V /0-5A; 2x9V 413A; 2x12V 0.25A;2x15V /112A 209pSranderd split Bobbin type.6VA: 2x 6V /0.5A; 2 x 9V /0-4A; 2 x 12V /0-34;2x15V /1125A 250p12VA: 2x4V5 /1A3; 2x9V /0A6; 2x12V /0A5; 2x15V2x20V /0A3 3E91359 API24VA: 2x6V /1A5; 2x9V /1A2; 2x12V /14;2 x 20V /13.45 ,,,,,,,,,,,,, 3/60130p p&p)50VA: 2x6V /4A; 2x9V /2A5; 2x12V /2A; 2x15V /1A5;2020V /142; 2 x25V /14; 2),3pV /648 ,, 520p (65p p&p)501/A muldrail: +5V/5A+12V,+25V,-5V,-12V 14 520p

IMP P&P/100VA: 2x12V /4A; 2x15V/34; 2x20V /2A5; 2x25V /24;2x3OV /1A5; 2 x5OV IA 955p (75p p&P)IPS Ay charge to be added over 4 above our normal postal charge)

AMMER LFJU/SKIC FEMALE RECEPTACLE Jumper Leads 36"

201. 26Piaend 160p Zap 2file

2 ends ?Xs 310p asp

Mein300p525p

COMPUTER CORNER EPSON LX80 Printer NLQ £225

EPSON RX80 F/T Printer £215

EPSON FX80 Printer £315

EPSON FX100 Printer £429

KAGA/TAXAN ICP810 Printer £235

KAGA/TAXAN KP910 Printer £339

BROTHER HR15 Daisywheel Printer £318

Centronics PRINTER CABLE for all the aboveprinters to interface with the BBC Micro £7

KAGA KX1201G Hi-RES, Green Monitor. £90

ZENITH 12" Hi-RES, Green Monitor 40/80column select switch, value for money. £66

MICROVITEC 14" colour monitor. RGB input. Leadincl. £185

MICROVITEC 1451 Hi-res 14" Monitor incl.Lead £229

KAGA II 12" HIRES, RGB ColourMonitor £255

KAGA III 12" ULTRA Hi-RES, RGB ColourMonitor £310

TEX EPROM ERASER. Erases up to 32 ICs in15-30 min. £30

Spare 'UV lamp bulbs £8

81M or 91/7" Fan fold paper (1000 sheets) £7 (150p)

MANY MORE PRINTERS, MONITORS, INTERFACES,AVAILABLE. CALL IN AT OUR SHOP FOR DEMON-STRATION OR WRITE IN FOR OUR DESCRIPTIVE

LEAFLET.

(P&P on some of the above items is extra)Call in .at our shop for demonstration of any of theabove items. Be satisfied before you buy.

BT TELEPHONECONNECTOR

LJU 1/44 Mini Line MasterUU 1/6A Mini Line ExtensionUU 2/4A Line MasterUU 2/6A Line ExtensionUU 3/44 Flush MasterUU 3164 Flush ExtensionUU 10/34 Dual Splitter4 WAY BT plug

430p295p370p250p370p240p550p

65p

DISC ALBUMSAttractively finished in beigeleather -vinyl, these convenientlystore up to 20 discs. Each disccan easily be seen through theclear view pockets.

ONLY £4.2551/4" Disc Drive

HEAD CLEANING KIT£8

BBC MICROWORD PROCESSING

PACKAGE

A complete word process-ing package (which can beheavily modified to your re-quirements, maintaininglarge discount). We supplyeverything you need to geta BBC Micro running as aword -processor. Please callin for a demonstration.

Example Package:BBC Micro, with DFS Inter-face, Wordwise, Twin 400KEPSON Disc Drives, 12"High-res green monitor,Brother HR15 Daisywheelprinter, Beebcalc & Data-base software on Disc, 103M Discs, 500 sheets of pa-per, 4 way mains trailingsocket, manuals and allcables.Only: £999

CRYSTALS32.768KHz 100100KHz 400200KHz 370455KHz 370IMHz 2701.008M 2751.28MHz 4501.5MHz 4201 6MHz 5951.8MHz 5451.8432M 20020MHz 2252.4576M 20025MHz 2252.56250M 2203.2768M 1503-57954M 953-6864M 30040MHz 1404 032MHz 2904194304M 1504433619M 1004.608MHz 2004-80MHz 20050MHz 1505.185MHz 3005.24288M 39060MHz 1406.144MHz 1406.5536MHz 2007.0MHz 1507.168MHz 1757.68MHz 20080MHz 140808333M 3958.867237M 175600MHz 2009375MHz 35010.0MHz 17010-5MHz 25010.7MHz 15010.24MHz 20012-0MHz 17512-528MHz 30014.31818M 15514-7456M 17514-765MHz 25015.0MHz 20016-0MHz 20018-0MHz 1501B -432M 15019.968MHz 15020-0MHz 15024.0MHz 15024-930MHz 32529.695MHz 15025670MHz 32527,125MHz 29527.145M 19027.648MHz 3003866667M 24048.0MHz 17555.5MHz 400100MHz 270116.0MHz 300145,8MHz 225

BBC MICROCOMPUTERSPECIAL OFFER THIS MONTH ONLY £299We stock the full range of BBC Micro peripherals, Hard-ware & Software like, Disc Drives (Top quality Cumana &Mitsubishi), Diskettes, Printers, Printer Paper, InterfaceCable, Dust Covers, Cassette Recorder & Cassettes, Mon-itors, Connectors (Ready made Cables, Plugs & Sockets),Plotter (Graphic Tablet) EPROM Programmer, LightpenKit, Joysticks, Sideways ROM Board, EPROM Eraser,Machinecode ROM, The highly sophisticated Watford's16K BEEB DFS, WORDWISE, BEEBCALC, Software (Edu-cational Application & Games), BOOKS, etc. etc. Pleasesend SAE for our descriptive leaflet.

51/4" DISC DRIVES CASEDWITH POWER SUPPLY & CABLE

CS100 - TEC Single sided 40 track 100K 51/4"Single Disc Drive £105

CS200 - Epson Double sided 40 track 200K51/4" Single Disc Drive £107

CS400S - MITSUBISHI Double sided 80track 400K 51/4" Single Disc Drive £130

CD400 - EPSON Double sided 40 track 400K51/4" TWIN Disc Drives £175

CD800S - MITSUBISHI Double sided 80track 800K 51/4" TVVIN Disc Drives £235

DFS Manual (comprehensive) £7 (NO VAT)

TWIN Disc Drive CASE with Power Supply tohouse your own Drives £38

N.B. All single drives with power supply with besupplied in a twin Case for later inclusion of asecond Drive.

(Carriage on disc drives £7 Securicor)

WATFORD ELECTRONICSTel. (0923) 40588 Telex. 8956095

Practical Electronics December 1985

SIREN KIT

Producesaloud swept

frequencytone

from a9-15V supply . Enable

input tOE

easy connectionto alarm circuts.

includesSin horn spe

eaker & box)aker 0.90

Mini siren£4a sp

E4.30

BELL °ledi h deteten

colbult

anda950 130

Itaes10.0°

11t£DAA1PS055131.162. ,(1,6t,s

ivr int011fs

Rjonl'ect° ccstattet69'FSO

vgito

PASSIVE IR DETECTORDetects intrudersbody heat at up to10m. 12Vdc supply.Output N/c contacts

950 135145.00

e ICON00N 0 L44' vtge1osotal'2.%1 terPc

33OP?°50Nea950

ALARNICONTROL

UNIT

4 Inputcucons.

2 instantdelayed

Achustableentry

exist and alarrntimes

Bat & testedPull instructions

supphed

Size 180)(133orran

12. dc supply

9500 1x60£26.00

BOXEPlastic, diecsastaluminium

AMDigital

frollif4mrERSE6SOfrom 06 -SS

FREE 28 pagecatalogue. Send 9x6 SAE

NOW!Telephone orders -

Access & BarclaycardRING 01-567 8910 (24hrs)

TOOLS2e cutters£.10Side Cat. for full

range.

DIGITALLOCK la?'operates from

S to 18Vdcsupply and gives 5040coin supply10 way keyboardsupplied. 750mA

output. Ideal fordisabling car ignition or for doorlock whenused with 701lock mechanism £11.50150

701 150174.95

Operatingfrom 9-15Vdc.

both unitshave 8 switches

and will operateonly

if thesehave been set 70

the samecode

Receiverprovides

latchedor momentary

output Idealfor car locks. garage

door openers.burglar

alarm switchesetc

XKII9 £21.75

WINDOW TApr50ro

Terminators

361P4Pr

BATTERIESN1CADS eg AA 90p

& chargers

0O

-.4A,0s90/7145;0

from o4417)s

for doors TSMa s wind°

Plush Poet Reedc.Surfa 14047 oc.Surface

950 142

ELECTRONICS13 BOSTON RD

LONDON W7 3SJTel. Orders: 01-567 8910Enquiries: 01-579 9794

Shop Hours: Mon -Fri. 9am-5pmSat. 10am-4pm.

ORDERING INFORMATION:ALL PRICES EXCLUDE VAT

FREE P&P on orders over £20 (UK only), otherwise add75p + VAT. Overseas P&P: Europe £2.75. Elsewhere

£6.50. Send cheque/PO/Barclaycard/Access No.with order. Giro No. 529314002.

LOCAL AUTHORITY AND EXPORT ORDERSWELCOME

GOODS BY RETURN SUBJECT TO AVAILABILITY

IIHEEMS434000 46,,a400240364007408400940104011401240134014401540164017401840194020402140'2240234024402540264027402840294030403140324033403440354036403740384039404040414042404340444045404640474048404940504051405240534054405540564060406340664067406840694071407240734075407640774078408140824085408640894093409540984099

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PL63PL84PL95

5611 PL500659 PL504469 PL508.5.6F. PL519

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PY5004 1004 7924729 78105

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35p 7810(6 5709Telex: 9321935 Summit

ESR13a Station RoadCullercoats - North ShieldsTyne & Wear - NE30 4P0

Telephone 091 2514363

TRANSISTORS - RESISTORS - CAPACITORS -DIODES - LED'S - SCR'S - ICS - VOLTAGEREGULATORS - DISPLAYS - AUDIO & EDGECONNECTORS - VERO/PCB'S - INSTRUMENTCASES & BOXES - POWER AMPLIFIERS &MODULES - MICROPHONES & STANDS.

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4 Practical Electronics December 1985

CROFTON PM101

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This 9 inch metal cased, mono-chrome monitor offers you thechance to obtain a high qualityproduct at a budget price!

SPECIAL OFFERSMONITOR KITS Brand new profes-sional 12 inch. P31 anti -glare paneltube with T.T.L. 12v pcb. Easy to con-vert to composite. ONLY £30. ZX81 Fullsized keyboard in metal case £13.80.COMPUTER DESKS £20.

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Though not new, these cameras have been completely refurbished to ahigh standard in our own workshops and come complete with astandard lens, ready to work. Short mains lead version requiring caserespray available from £66.70. Weatherproof housings, motorised pan& tilts etc. available at extra cost.

THE CROFTON SPECIAL CCTV OFFERThe Crofton special CCTV package and the door entry system describedby P.E. in the September 1985 issue are available at the following pricesSPECIAL CCTV PACKAGE £193.00DOOR ENTRY SYSTEM £103.45NOTE: We can also offer a multiscan system enabling the outputs from 4 cameras tobe displayed simultaneously or individully on a single screen.

Be sure to request our free catalogue describing our range of T.V.cameras, fixed and zoom lenses, sequential switchers, special andgeneral monitors (colour and b/w including the PHILIPS 7502, PHILIPS7522 and PHILIPS 2007 plus the full IKEGAMI range), video digitisers,

light pens, eprom erasers etc.

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35 GROSVENOR ROAD, TWICKENHAM, MIDDLESEX TW1 4AD

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MULTIMETERRELIABLE STABLE ACCURATERUGGED & EASY TO HANDLE 31/2 DIGIT DISPLAY 13 RANGE FULL AUTOPOLARITY OVERANGEINDICATION OVERLOADPROTECTION ON ALL RANGES TEST LEADS, BATTERY, SPAREFUSE, INST MANUAL DC -1000V DCmA-200 ACV -500V 1 O -2M0

NI -CAD RECHARGEABLE CELLS -M -HP7 pack of 4 £1.50 or 4 packs for£5.00. Ex -equipment, tested & guaran-teed 500mA Hr. Bargain! NI -CADCHARGER & 4 AA cells + holder £5.00

UNIVERSAL NI -CAD CHARGERWith battery test fa-cility and LED indi-cators. For PP3,AA,C & D cells. £5.99

BUTTON BATTERIES1.5V for watches. calculators, cameras, lighters,etc. 4 types any mix £1.50. AG13 11.58 x 5.4mm,AGIO 11.58 x3mm, AG12 11.58 x4.2mm, AG37.87x 3.6mm or any 8 for £2.50.

SEALED LEAD ACID RECHARGEABLE BATTERY 6V2 6AHr 132x 60x 32mm. Brand new stock 8 fullyguaranteed £9.95 (sold elsewhere for £17).

SOLAR CELL PANELS 3.75 x 2.5ins. With multi -cellular lens 8 rear terminals. Gives 100mA fir0.42V in weak sunshine. £3.95 each.

DNIOFF OPTO-ISOLATOR 20 Milk -second re-sponse. 6V 60mA lamp 8 cadmium photo -resistorhoused in small metal can for PCB mounting. Willdrive medium current relay. F1.20 each or 5 for £5.

SLOTTED OPTO-SWITCH RS306-061 Infra -redsource 8 sensor housed in slotted moulding. The3.8mm slot permits beam to be broken e.g. switch-ing, counting, tape detection. Readily interfacedwith TTL circuits. £1.90 each or 5 for TB.

LARGE CADMIUM PHOTO RESISTORS Flat type0 8in dia 250V IA. Dark R +1 M0. Illuminted 150Ohm. £1.50 each or 5 for £6.25.

ULTRASONIC TRANSDUCERS 4010t2 Matchedpairs TransmitterReceiver. Per pair £4.20.

DIGITAL LCD MULTIMETER£29.95 Nee

BUIIER AND FLASHING LED ALARM 12V housedin neat box with reset button. Used in car for belt -upor trafficator reminder etc., or anywhere a resetta-ble alarm is required. High resistance trigger possi-ble. f1.90 each or 5 for £6.

MICRO SWITCHES Selection of Micro Switches. 7different types, with levers, buttons or rollers. 7 for£4. Further supplies of individual types, pleaseselect 8 describe 21 each or 5 for £3.

STEREO AMPLIFIER MODULE PCB with completecircuits for 1 Watt per channel or 1 1,2 Watt withsmall heat sink - requires 9V to 15V supply. Idealas Walkman amplifier or phono etc. £2.50 each or2 for £4.

MINI -DRILL KIT & SPEED CONTROLLERHigh Torque motor, 12V to 18V, 40W reversible1000 rpm 5 pole rotor, carbon brushes 50 x 28mmdia Chuck 8 set of Collets. 3 HSS Bits 1mm,0.8mm 8 0.6mm. Speed controller kit 8 trans-former + 3m of flex. Instructions £11.95.

OR ITEMS MAY be purchased separately. SpeedControl £4.50; Transformer £2.90; Motor 111.90;Chuck 8 3 precision collets £2; HSS Drill bits withshanks 1mm - 5 bits f1.50; 0.8 or 0.6mm - 5 bits0.50 (bits not recomm. for glass fibre).

TUNGSTEN CARBIDE BITS1mm. Ideal for glass fibre PCBs. £1.20 each or 5for £5, or 10 in holder 03.75.

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clad, circuitetchant, 2ens,

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Goods sent by return post - please add 80p p&p to total orderSho o -n dail 10-5.30 or send s.a.e. for stock list.

CROYDON DISCOUNT ELECTRONICS40 Lower Addiscombe Road. Croydon CR0 6AA. Tel 01-688 2950

Practical Electronics December 1985 5

Tandy

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You select the function and it selects the proper range! "Beep"continuity, range -hold to override autoranging, "diode check"function and zero -adjust. Folds up for portability. Measures to1000 volts DC, 500 volts AC. AC/DC current to 10 amps.Resistance to 2 megohms. 107/8 x 55/s x 1 /2". Requires 2 "AA"batteries. 22-193 £69.95

Micronta°Multimeters -Your Best Value

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Just select the function and it does therest! "Diode check" function for testingsemiconductiors. Measures to 1000 voltsDC in 5 ranges, 500 volts AC in 4 ranges.Accurate from 45Hz to 10kHz. DC currentto 200mA. Resistance to 2 megohms in 5ranges. 47/8 x 213/16 x 11/4". With sparefuse. Requires 2 "AA" batteries.22-188 E34.95

25 -Range Multimeter5 Detented Hinge With Hold

Positions At 90, 120, 150 and180

25 ranges, 20,000 ohms per volt with fuse and surge -absorber protection. 4" three -colour mirrored meter withautomatic shunt protection (when shut). Measures to 1200volts DC in 7 ranges, 1200 volts AC in 5 ranges. DC to 300mAin 4 ranges. Resistance to 2 megohms (24 ohms centrescale). dB: -20 to +63, 5 ranges. Accuracy: ±3% DC,±4% DC, ±4% AC. Open: 71/4 x 45/16 x 11/4". Requires"AA" battery. 22-211 £22.95

Transistor Checkero And Logic Probe

El Easy -To -Use Dynamic Transistor Checker. Makes Go/No -Go tests on small -signal and power types and allows youto match similar transistors. Lamp indicates relative currentgain, "opens" and "shorts". Output jacks let you connect toan external meter or scope. 23/4 x 43/8 x 13/18". Requires"AA" battery. 22-025 £9.95E Digital Logic Probe With Tone. Colour -coded LEDsindicate high, low or pulsed logic states (up to 10MHz).Switches for normal or pulse modes. CMOS or TTL/LStesting. Input impedance 100K ohms. Minimum detectablepulse width: 5Ons. Has 36" leads with clips to obtain powerfrom tested circuit. 22-302 £14.95

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6 Practical Electronics December 1985

EVOLUME 21 1W12 DECEMBER 1985

TRANSPUTERIN APRIL '84 we published a featureon the Transputer; that feature

was used by INMOS to aid theirinformation to the industry andthey reprinted it from PE-a nicecompliment to Ray Coles whowrote it and we feel to PE.

At the time the Transputer wasexpected to be around by the endof the year. In fact INMOS have justrecently announced availability ofevaluation boards-perhaps notfor the hobbyist at around £2,000to £3,000. The component is sig-nificant because as most indepen-dent industry watchers acknow-ledge; it is the shape of things tocome. INMOS are keeping thenames of buyers and interestedindustry to themselves but it couldlead the way to fifth generationcomputers, and we are told that itis being used in a number of experi-mental systems. When asked ifAmstrad and Sinclair are showinginterest, INMOS declined to com-ment. However, it is known that tobe profitable INMOS must turnover large quantities. Other areasof particular appeal are concurrentworkstations-where you canboth simulate and create designsat the same time-and robotics.

At the present time a few thou-sand chips have been made with"a good yield". INMOS claim acapacity of a million a month. Ifthey ever make that many I guesswe will all have fifth generationwatches! The transputer could bevery good for INMOS, it could do apower of good for the UK's stand-

ing in high technology, and it couldmake incredible computing powerreadily available. Time will tell andmuch depends on swinging manu-facturers away from "traditional"microprocessors.

HOBBYISTHow will it all affect the hobby-

ist? I doubt if we will ever publish adesign using a transputer but wehope before long to be looking atdevices which use them and weexpect to be able to go on assistingreaders' understanding of such de-vices so that interfacing, etc. canbe undertaken. As Ray Coles saidin '84 "the age of the truly intelli-gent supercomputer cannot be faraway!"

FREE CHARTWe are pleased to carry the free

Data Chart in this issue. This is theresult of a special arrangementbetween PE and Electrovalue withassistance from Siemens. Thechart will introduce many readersto a new range of i.c.s, and wehope a number of new designs willresult. Due to various packagesbeing available for most chips pindata has been omitted but this isavailable from Electrovalue as areall the featured devices.

BACK NUMBERS and BINDERS . .

AIMMV,41306,

nws,wq wcr..."vT 6n41, trAc

4

Copies of most of our recentissues are available from: PostSales Department (PracticalElectronics), IPC Magazines Ltd.,Lavington House, 25 LavingtonStreet, London SE1 OPF, at £1each including Inland/Overseasp&p. When ordering please statetitle, month and/or issuerequired.

Binders for PE are availablefrom the same address as backnumbers at £5.50 each to UK oroverseas addresses, includingpostage, packing and VAT.

Editor Mike Kenward

Secretary Pauline Mitchell

Editorial Tel: Poole (0202) 671191

Advertisement ManagerDavid Tilleard 01-261 6676

SecretaryChristine Pocknell 01-261 6676

Ad. Make-up/CopyBrian Lamb 01-261 6601

Classified Ads.Mandy Morton 01-261 5846

Queries and letters concerningadvertisements to:Practical Electronics Advertisements,King's Reach Tower,Stamford Street, London SE1 9LSTelex: 915748 MAGDIV-G

Letters and QueriesWe are unable to offer any advice on theuse or purchase of commercial equipmentor the incorporation or modification ofdesigns published in PE. All letters requir-ing a reply should be accompanied by astamped addressed envelope, or ad-dressed envelope and international replycoupons, and each letter should relate toone published project only. We areunable to answer letters relating toarticles more than five years old.

Components are usually available fromadvertisers; where we anticipate difficul-ties a source will be suggested.

Old ProjectsWe advise readers to check that all partsare still available before commencing anyproject in a back -dated issue, as we cannotguarantee the indefinite availability of com-ponents used. We are unable to answerletters relating to articles more thanfive years old.

Technical and editorial queries and letters to:Practical Electronics Editorial,Westover House,West Quay Road, Poole,Dorset BH15 1JG

SUBSCRIPTIONSCopies of Practical Electronics areavailable by post, inland for £13,overseas for £15 per 12 issues, from:Practical Electronics, SubscriptionsDepartment, IPC Magazines Ltd.,Room 2816, King's Reach Tower,Stamford Street, London SE1 9LS.Cheques, postal orders and interna-tional money orders should be madepayable to IPC Magazines Limited.Payment for subscriptions can also bemade using a credit card. .

Phone:Editorial Poole (0202) 671191

We regret that lengthy technical enquiriescannot be answered over the telephone.

Practical Electronics December 1985 7

Items mentioned are availablethrough normal retail outlets,unless otherwise specified.Prices correct at time of goingto press.

°Halley Comet cash -in PRESTO. FOR

AMSTRADSOnly once in every 76 years does the cosmos provide us with such avisual treat as Halley's Comet. It is mankind's nature to exploitnature and this cosmic phenomenon will be no exception. Itscommercial potential is being pushed to an all time high, the HalleyComet bandwagon is estimated to be worth around $500 million.

A recent New Scientist article highlightedthe ingenious money making efforts ofmany groups, General Comet Industries,for instance, has trademarked the words"Halley", "comet" and "official" and islicensing others to use its logo. Besidesthe usual T-shirts, badges and bags thecompany have launched a "Pin -the -tail onthe comet" game. According to OwenRyan the founder, his company is likely toreap around $10 million worth of themarket.

Andrew Fraknoi, executive director ofthe Astronomical Society of the Pacific isno exception. He is leading a party ofaround 80 enthusiasts to a prime viewinglocation in the outback of Australia. Thegroup will be housed in a make -shift tentcity.

Because the comet will be higher in thesky in the southern hemisphere viewingconditions there will be most favourable.The comet will be so far away on its returnthat it will be a great deal dimmer than ithas been on recent visits. The far side ofthe sun will witness its peak activity.

Many trips to the southern hemisphere

are planned, not all of them for dry landobservation. A Royal Viking Line cruisefrom Auckland to Sydney will have CarlSagan on board to address starry-eyedpassengers who could pay up to $10,000for the privilege. Other global viewpointswill be Argentina, Chile, The PeruvianAndes and South Africa.

Share certificates in Halley's Comet areavailable from Owen Ryan's company at$9.95 for 100 shares. The reverse of thecertificate promises a cometary return onApril 29th, 2061. It would seem that MrRyan is not a complete capitalist, for whenhe received an order for 5,000 bottles forhis "comet -pills" from a film companywishing to promote the film Lifeforce, hewould not supply the goods. "The filmwas negative and contained unpleasantgraphic effects," he said. The plot depic-ted a hostile comet upon which astronautshad managed to land only to be over-whelmed by blood -sucking space vam-pires-well it takes all sorts.

Halley's Comet is the subject of a featurearticle, by Dr Patrick Moore OBE, in thisissue (see page 28).

WITCH KNIRATS __EROBOT BOOKSwissinco UK Ltd. is now offering a totalmembrane switch and keyboard service tosmall users.

Because of the unique membrane switchtechnology used and the size of the range, itis possible to implement a variety of solu-tions, ranging from a full custom -designservice for large users down to a low-cost,easy -to -use prototyping kit for one-off orsmall -quantity applications.

Products can also be supplied to specialrequirements, including environmental pro-tection to different standards and the incor-poration of visual, tactile and audible feed-back. Details from, Swissinco UK Ltd., Unit2, 225 Hook Rise South, Surbiton; SurreyKT9 7LD. (01-397 7041).

14.1111

Robotics is one of the most rapidly expand-ing areas within the electronics and engi-neering world. Recently published The RobotBook by Richard Pawson takes a well illus-trated look at the world of robotics and wouldbe an ideal Christmas gift.

The introductory pages skip through theancestry of this fascinating subject, and showhow the automatoms (sophisticated clock-work "toys") of the eighteenth century pavedthe way for present day experimentors.

Subsequent sections deal with all aspectsof the science on a fundamental level, fromscience fiction, films and toys, to interfacingand artificial intelligence. A substantialquantity of pages are dedicated to practicalprojects using Lego and Fischertechnik con-structional components.

This book cannot be regarded as an in-depth reference. It provides, however, acomprehensive insight into the world ofrobotics. For those requiring information atthis level it will provide a fine source offactual and pictorial information. The RobotBook by Richard Pawson is published byFrances Lincoln Ltd. Measuring 210 x280mm and with 192 pages, it is priced at£7.95 paperback (ISBN 0 7112 0414 4); and£12.95 hardback (0 7112 0414 4).

This special offer from Cirkit should interestAmstrad users who wish to access Prestel.The package comprises modem, interfaceand software, compatible with the CPC 464,CPC 664 and CPC 6128. The set-up whichretails at a fraction under £30 is fullyapproved by British Telecom.

The modem is British designed and isacoustic, it will fit all standard and Heraldtype telephones. 1200/75 baud operationallows access to Prestel, Micronet, BT Goldetc.; furthermore 1200 baud half -duplex al-lows program and data transfer betweenusers over the telephone system. An earpieceallows the progress of a call to be monitored,battery operation gives portability and easeof use.

The interface is housed in a plastic enclo-sure that plugs into the disc drive poil, athrough bus connection allows the disc driveto be plugged into the back of the interface.

Full support is provided for the modem, withadditional features enabling the driving offurther modems, printers, plotters etc. Baudrates supported are 75/1200, 300/300 and1200/1200.

The software supplies full feature supportfor the modem, it is supplied on cassette butis fully disc compatible. Information is dis-played in real time, allowing page exit assoon as header details have been seen. FullPrestel support is featured, including up to 16on -screen colours and dynamic frames. Thesoftware has many other features includingaccess to BT Gold (and similar), it is suppliedwith "extensive documentation".

Limited Prestel access can be gained freeof charge using the identification code44444444444 (password 4444).

The menu driven package is priced at£29.99 (inc. VAT and p & p). Access/Barclay-card accepted, cheques payable to CirkitHoldings PLC. Allow 28 days for delivery.From Cirkit Holdings PLC., Park Lane,Broxbourne, Herts. EN 10 7NQ. (0992444111).

8 Practical Electronics December 1985

MARCH= putenDrawing onexperienceNow if you're wondering what to buy for theprofessor in your life this Christmas, andyou have £99.95 to spare, how about thisamazing calculator from Casio.

The FX7000G draws graphs, charts sta-tistics and plots data on a screen as well asbeing a powerful programmable scientificcalculator.

Data can be entered as a series of Carte-sian points, from which the user can quicklyjudge the shape on the display, whether it bea straight line, a single exponential ordouble exponential curve. For linear rela-tionships, the machine can calculate theparameters of, and then actually draw, theregression line through the plotted data.

For visual presentation of statistics barcharts can be displayed, representing popu-lations of data cells, and draw lines toconnect peaks together. Approximations toGaussian or Poisson distributions can bequickly recognised. This is in addition to itsroutine standard deviation analysis.

In the realm of purer mathematics,FX7000G is equipped with 82 prepro-grammed scientific functions, and can di-rectly draw graphs of 20 of them, includingtrigonometric, hyperbolic and logarithmicfunctions and their inverses. Graphical rep-resentation of more complex equations isobtained through programming-to a maxi-mum of 422 program steps, allowing use ofa minimum of 26 memories, and up to 10program areas.

One graph can be overlaid on another,traced by a cursor and points of intersectionassessed with great precision.

The FX70000G measures 35 x 52mm. Itaccommodates 63 x 95 dot graphics, or 8lines of 16 alphanumeric characters forinput, output, status display or programlistings. Details from Casio Electronics Co.Ltd., Unit Six, 1000 North Circular Road,London NW2 7JD. (01-450 9131).

RADIO FORTHE DEAF?A recent report in Electrical and RadioTrading (Aug. 8 '85) casts a 'gloomy'shadow over the future of the radio world,it shows that listening figures are down.The report is mainly concerned with thedilemma faced by 'brown -goods' businesspeople, and in particular with what can bedone to revitalise their industry. Apparent-ly the market is saturated, and listeningfigures have declined in the last three yearsto a level where the percentage of the adultpopulation who listen to the radio hasfallen from 62 to 54 per cent.

. The re -vitalisation of this market couldconceivably come from any quarter, butone rather bizarre suggestion has been putforward by Mintel Market Intelligence, thepeople who provided the facts and figuresused in the report. They suggest that thesort of development required might trans-mit words, via digital technology, thatwould appear on a visual display simul-taneously with the sound output, thus"creating a fashionable new product".

Mintel point out that the average house-hold has access to at least two radios.

FARADAY DA(British Telecom is presenting the 1985-86series of Faraday Lectures on behalf of theInstitution of Electrical Engineers. Entitled"Beyond the Telephone: the IntelligentNetwork", the lecture began its tour of 16towns and cities in October this year and willend in March 1986, playing to an estimatedaudience of more than 70,000 people.

The lecture explains to the layman howmicrochip technology is changing telecom-munications, and how engineers are bring-ing its benefits direct to the user.

Many of those attending will be studentsfrom schools and colleges, and British Tele-com's lecture aims to give them a greaterunderstanding of how modern telecommuni-cations operate.

Mr Bill Jones, British Telecom's ChiefExecutive of Technology and the seniorFaraday lecturer, said: "As we move into theinformation age it is becoming increasinglyimportant that people understand the tech-nology that is changing our lives. Youngpeople, who may be about to choose acareer, will be a particularly important part ofthe audience."

There are usually three performances ateach venue. Morning and afternoon perfor-mances are attended by local schools; theevening performance plays to the generalpublic, members of the lEE and their fam-ilies. For venues, dates and (free) ticketinformation contact: The Faraday Officer,The Institution of Electrical Engineers, Sta-tion House, Nightingale Road, Hitchin,Herts. SG5 1RJ. (0462 53331). POINTSARISING . . .

NOV '85Disco lights controllerThe captions for the photographs on page47 (3 and 4) should be transposed.

Please check dates before setting out, as we cannot guaranteethe accuracy of the information presented below. Note: someexhibitions may be trade only. If you are organising any electrical/electronics, radio or scientific event, big or small, we shall be glad toinclude it here. Address details to Brian Butler.

Compec Nov. 12-15. Olympia. AElectron & BBC User Nov. 14-17. New Horticultural Hall,London. BWhat Telephone & Communications Show Nov. 17-19. Novotel,Hammersmith. CComputers In The City Nov. 19-21. Barbican Centre. DAcorn User Christmas Show Nov. 22/23. Central Hall, West-minster. E

Scottish Home Computer/Electronics Show Nov. 22-24. AnderstonCentre, Glasgow. F6809 Show Nov. 23/24. Royal Horticultural Halls, London. EInternational Test And Measurement Nov. 27-29. Olympia. GWhich Computer Show Jan. 14-17. NEC, Birmingham. HHi -Tech And Computers In Education Jan. 22-25, BarbicanCentre. I

ABCDEFGH

Reed Exhibitions V 01-643 8040Database v 061-429 8157Judith Patten PR V 01-940 6211Online V 01-868 4466Edition Scheme V 01-346 6566/7Trade Exhibitions Scotland V 041-248 2895Network V 0280 815226Cahners 01-891 5051BEEA & Computer Marketplace'' 01-930 1612

Practical Electronics December 1985 9

fVein"Sirk

ROBOTSA40,6) pdit4

High Performance Stepping Motor DriverTHE current interest in robotics, and the interfacing of comput-

ers to a wide variety of mechanisms, has led to the extensiveuse of stepping motors. The principles of stepping motoroperation have been described in many recent articles, notablyEveryday Electronics August 85 issue. An accompanying article inthe same issue described a simple interface for driving suchmotors from a computer user port. This interface used the verypopular SAA 10271C which provides a simple low cost circuit witha minimum of components. Because of its simplicity theSA A1027 i.c. is incapable of extracting anywhere near the fullperformance from a motor. The maximum stepping rate and thehigh speed torque are limited and there is no facility for half stepoperation.

To obtain the highest performance from stepping motors it hasbeen necessary to use complex control circuits built from discretecomponents and logic i.c.s. Now, however, a new i.c. is availabledeveloped exclusively for driving unipolar 4 phase steppingmotors. It provides all the switching functions for forward andreverse stepping in half and full step mode. Four inputs arerequired by the i.c. and these are all TTL compatible. The i.c. is notdesigned to drive stepping motor coils directly. Instead fouroutputs are provided which are capable of sinking up to 50mA.These are used to drive external power transistors.

THE TEA1012The i.c. is known as the TEA 1012. A functional diagram is

shown in Fig. 1. Four inputs are required to control the i.c. Thesecan be derived from any four bits of a computer user port (hencetwo drives could be handled by a standard 8 bit port).

Their functions are as follows.

PIN 14 F/T-I - Selects full or half step operationPIN 13 CW/CCW - Selects direction of rotationPIN 12 STOP - Holds the motor in its present position

disregarding further clock pulsesPIN 15 CL - Clock. The motor moves one step or half

step on each low to high transition of thispin

The operation of these four inputs from a computer is quitelogical. When the direction and step mode are set up and the stopcondition disabled the motor steps each time a pulse is sent to theclock pin. As with all stepping motors there are limits to themaximum pulse rate and motor acceleration. These limits must betaken into account in the computer program.

STEPPING MOTOR DRIVE CHARACTERISTICSWhen stepping motors are driven from a constant voltage

source the torque decreases at higher step rates because thewinding current has insufficient time to rise to its full value.

One way of overcoming this is to feed the motor with a highervoltage. This is fine at high stepping rates. At low stepping rates,however, the coil current has plenty of time to rise and the motorwill overheat. A means of control is needed that produces a fastrising of motor current limited to the motor's maximum rating.

The TEA 1012 offers two alternative methods of such control.These are: BI -Level Voltage Drive, and Constant Current ChopperDrive.

BI -LEVEL VOLTAGE DRIVEIn bi-level voltage drive the motor is driven from two supplies.

At the start of each step a high voltage supply is switched on tothe motor for a predetermined time. This time is set to be just longenough for the current to rise rapidly to the maximum rated valuefor the motor. After this the high voltage is disconnected and thesecond lower voltage supply takes over. The lower voltage isequal to or less than the motor rated voltage so that the motorcurrent is held safely at or below its maximum rated value.

In this mode of operation the TEA 1012 uses a resistor andcapacitor connected to pin 1 (TBL) to determine the pulse width ofa monostable which sets the time for which the high voltage is ap-plied. The output from the monostable appears on pin 2 (QBL). Itis used to drive external devices which switch the high voltagesupply.

This method is simple to understand and has advantages wherea motor is stationary for a large part of the time. In suchapplications where only a low holding torque is required the lowervoltage can be well below the rated motor voltage so that themotor can run very cool and power consumption is minimised.

Its only disadvantage is that two supply voltages are required. Itis possible to use just a single high voltage supply and obtain thelower voltage by means of resistors, but this method is inefficient.

Fig. 1. TEA1012 block diagram

TEA1012TBL BI-. E , E',

2SWITCH

L

CL'' CLOCK OUTPUTSTAGE

n07

F/171" STEP MODE IL 0,0' C

OUTPUTSTAGE

1002

c7§,,tcw 13 ROTATION A OUTPUTSTAGE

2STOP1 DISABLE

SWITCH ....OUT PUTSTAGE

FL

S1 COMPARATOR MSTABLE

MONO 1---.COMPARATORSTABLE

STABILISER

16 I.6 le10,E700A

TOFF TOFF Voc SEE1 2

CONSTANT CURRENT CHOPPER DRIVEIn this method the motor is driven from a single high voltage

supply which is switched to the windings according to the stepsequence.

10 Practical Electronics December 1985

+35V -45V

TI

.C12200p 100 0

OUT +5V

C

/COM (LI,L2)1,010,011

COM (L3,L4)

LI L2 ...if -SEE TEXT L3 L4 LI -14 t MOTORDI 03Q WINDINGS

D2 04

DI -DE IN 003

R6k

1k

16

R7

TR3710122

D7 D8

R816 ,9

33n

TR4T I P122

R91012

R210k

R310k

mim C5T,00n

MmIC7T2n2T2 n2

IC2TEA1012

0101k

CLK

F/1710PB1

M/ccwOPB2

STOP0P83

C13

InRI210k

Cl2

TInR13

101CII R14

10kCIO

T1nR11

00V

Fig. 2. Circuit diagram

The current in each motor winding is sensed, and when therequired maximum current is reached the transistor driving thewinding is switched off and on at a high frequency The markspace ratio of the switching is set so that the average motorcurrent stays at the required maximum level.

Power dissipation in the driving transistor stays low because itis either fully on or fully off, and so the circuit is very efficient.

This method provides full power to the motor at all times and sois suitable for all applications. As with BI -LEVEL VOLTAGE DRIVEthe motor current rises rapidly because of the high appliedvoltage, and equally good high speed performance results.

PRACTICAL CIRCUITA circuit using the TEA 1012 in the constant current chopper

mode is shown in Fig. 2. This circuit uses a 35 to 45 volt supply.Its effect on stepping motors rated between 5 and 12 volts isquite spectacular. Maximum stepping rates exceeding 3000steps per second are possible with excellent high speed torque.

The circuit has been evaluated using a BBC computer user portto provide the drive signals, but any computer port will do andprogramming is quite straightforward.

The four input lines are fitted with pull down resistors R1 1-14and small decoupling capacitors C10-13 to prevent spurious pickup of the motor switching pulses from affecting operation.

Four outputs from the i.c. on pins 7, 9, 10 and 11 are used todrive power switching transistors which handle the full motorwinding voltage and current. These outputs are 'open collector'types and so pull up resistors R1, 6, 7 and 10 are needed toprovide the transistors with base current.

The coils of four phase unipolar stepping motors are wound inpairs and only one winding of a pair is energised at a time. Thismeans that only one current sensing resistor is required for thetwo transistors feeding each pair of windings. R4 is connected inthe emitters of TR1 and TR2 and senses the current for motorwindings L1 and L2. Similarly R9 senses the current for L3 and L4.

The voltage across the sensing resistors passes to the i.c. viasimple low pass filters consisting of R5 and C6 for L1 and L2, andR8 and C9 for L3 and L4.

These filters are there to remove switching transients from thefeedback signal.

The i.c. compares the feedback signal with an internal 0.4 voltreference. As each winding is switched on the current risessteadily from zero at a rate determined by the inductance andresistance of the motor coil. As the current rises so the voltageacross the sensing resistor rises. When this voltage reaches 0.4volts a monostable circuit in the i.c. is triggered which turns off thesupply to the winding by removing the base drive from theassociated power switching transistor.

The current in the winding does not fall to zero instantlybecause of the inductance of the winding. Instead it continues toflow, finding an alternative path via D2 (for L1) and D1O-D11, anddecays steadily. This decaying current also induces a current inthe other winding of its pair (which is wound in the oppositedirection on the same core). The induced current flows via D6 (forL2) and is in such a direction that it aids the current in the otherwinding, thereby adding to the efficiency of the circuit. After atime, set by the period of the monostable components, thewinding is again switched on. The current rises again until thefeedback voltage reaches 0-4V, the monostable is then triggeredand the cycle repeats.

Fig. 3 shows the saw tooth waveform of the current in thewinding which results from the switching action. The frequency ofthe switching action is set by the current rise time and themonostable off time. The upper level of the current is that which

1pCURRENT

IFT702A1

1p t PEAK CURRENTTopp MONOSTABLE TIMEI/ FR t TOTAL CYCLE TIME r. ( Topp + CURRENT RISE TIME)

FR t CHOPPER FREQUENCY

TIME

Fig. 3. Current waveform: Constant current choppermode

Practical Electronics December 1985

produces a 400mV drop across the sensing resistor. A 1 ohmsensing resistor give 400mA and so on. The monostable off timeis set by R2 and C7 for L1 and L2, and R3 and C8 for L3 and L4.The time is equal to 0.8 R.C., or 18 microseconds with the valuesgiven. The current rise time depends upon the motor inductanceand resistance, and the supply voltage.

Ideally the switching frequency should be set just above theaudible range ie 16-20kHz.

Note that this current regulation system is completely indepen-dent from the stepping action of the circuit. At sufficiently highstepping rates the current never rises high enough to trigger themonostable and so chopper action does not take place at all.

When the motor is stationary the chopper action operatescontinuously. The power supply is quite straightforward. A bridgerectifier and smoothing capacitor provide the main supply to themotor. D9 drops the voltage so that it is within the input rating ofIC1, a standard 5 volt regulator i.c. which feeds IC2.

Zener diode 010-011 limits the voltage to which the back EMFrises as each winding is switched off by the chopper control. Itsvalue is selected to be just above the maximum operating supplyvoltage-in this case 45 volts. It is made up from two low voltagedevices connected in series so that more readily available partscan be used.

Darlington power switching transistors have been used to keepthe base current requirements down. As the collectors can swingup to twice the supply voltage 100 volt types are specified.

STEP SEQUENCEFig. 4 shows the state of the four switching transistors for each

step in full and half step mode.In full step mode two windings are energised at a time and the

sequence repeats every four steps.In half step mode the windings are energised individually as well

as two at a time to produce an eight step sequence. There are twomain advantages in using the half step mode. The motorresolution is doubled and resonance effects are greatly reduced.

Double resolution means that a motor which has 48 steps perrevolution in full step mode will give 96 steps per revolution in halfstep mode.

Resonance is a problem affecting stepping motors which aredriving loads that have low friction and high inertia. At certainspeeds the inertia of the load causes the motor to overshoot aftereach step to such an extent that steps are lost and the motor'dithers' out of control.

In practice resonance can be overcome by adding frictionalresistance to the load and avoiding operation at the criticalspeeds. By operating the motor in half step mode these measuresare usually unnecessary.

L1 L2 L3 L4

1 ON OFF OFF ON

2 ON OFF ON OFF

3 OFF ON ON OFF

4 OFF ON OFF ON

1 ON OFF OFF ON

1 ON OFF OFF ON

2 ON OFF OFF OFF

3 ON OFF ON OFF

4 OFF OFF ON OFF

5 OFF ON ON OFF

6 OFF ON OFF ON

7 OFF ON OFF ON

8 OFF OFF OFF ON

1 ON OFF OFF ON

FULL STEP

AV

CW CCW

HALF STEP

AV

CW CCW

Fig. 4. Switching sequences for full -step andhalf-step modes

One minor disadvantage of half step operation is that onalternate steps when only one winding is energised the torque ishalved.

CONSTRUCTIONThe circuit is built on a single printed circuit board which has

been carefully designed to prevent interaction between the highmotor voltages and currents, and the sensitive signal circuitsaround IC2. The four transistors are lined up so that a singleheatsink may be fitted if high output currents are required. As thetransistors are operated as switches the dissipation is small andheatsinks were not considered necessary in the prototype.

Fig. 5 shows the board foil pattern and the component layout.To simplify motor connections a 6 way terminal block is used forthe output.

Input connections are shown labelled for a BBC micro user port,however, the circuit is suitable for use with any computer with atleast 4 output port lines. A transformer rated at 18VA and 30volts provides sufficient power for motors operating at up to400mA per winding.

COMPONENT VARIATIONSDifferent stepping motors require different operating currents

and have different values of winding resistance and inductance.The motor current is set by the values of R4 and R9 whichdetermine the peak current at which the monostable circuits aretriggered. The chopper frequency depends on the monostabletime, the motor inductance and resistance, and the motor supplyvoltage.

COMPONENTS . . .

RESISTORSR1,R5-R8,R10 1k (6 off)R2,R3,R11-R14 10k (6 off)R4,R9 142all Watt 5% carbon film

CAPACITORSC1C2C3C4C5C6,C9C7,C8C10-C 13

SEMICONDUCTORSIC1IC2REC1D9D10,D11

D1-08TR1-TR4

2200p 63V axial electrolytic100p 25V axial electrolytic220n C280 polyester100p 25V radial electrolytic100n C280 polyester33n C280 polyester (2 off)2n2 polystyrene (2 off)1n ceramic (4 off)

7805 regulatorTEA 1012WO4 bridge rectifier13V 1.3 watt Zener diode30V and 15V 1.3 watt Zenerdiodes1N4003 diodes (8 off)TIP122 transistors (4 off)

MISCELLANEOUSP.c.b. mounting terminal blocks 3 way (2 off); 16 pin i.c.socket; tinned copper wire 22 swg approx; metre,Veropins; printed circuit board; transformer -30V 18VAmains transformer; etc.

Constructors' NoteA full kit of parts is available from Magenta Electron-ics Ltd., 135 Hunter St., Burton -on -Trent,Staffs., DE14 2ST. T 0283 65435. Price £20.98excluding transformer. Transformer £5.98 extra, casefOr p.c.b. £2.95, BBC lead and plug £1.98,1035 stepper-motor £14.50. All prices include VAT. P&P 60p extra perorder. A cassette of the software is also available for £2inclusive of VAT, etc.

I2 Practical Electronics December 1985

30V A.C.( OR 35V

TO 456 D.C.)

L 1

L2

COM (L3,L 4

L3

L4

C13 CLK(Pb0)

R1. -R14

.c)c"

,c),C12

C10

- STOP (Pb3)

CW/CCW(Pb2)

F/171 (Pb

OV

Fig. 5. Component layout of the Stepping Motor Driver

The values specified should work with most small motors, theideal values for a particular set up can be found by experiment. It isworth noting that a stepping motor running at full power will runvery hot. This is quite normal, the manufacturer's specificationsallow a maximum operating temperature of 120*C.

PROGRAMMINGThe functions of the four input lines have already been

explained. It is a fairly simple matter to set up the necessary codefor direction, and step mode, and to inhibit the 'stop' line.

The motor will step on each negative to positive (low to high)transition of the 'clock' line.

A simple BASIC program can be used for low stepping rates,but for the highest speeds a clock rate of 3,000 steps per secondmeans machine code will need to be used. The motor and load in-ertia will limit the maximum speed at which the motor can beclocked from a stationary start. To run above this speed themotor must be accelerated by gradually increasing the clock rate.

6 TAG TYPE1031 & 35

2

SPINDLEOCCI7;1

000 0

D 0

3

COM3/4

4

6 WIRE TYPEHR23

SPINDLE END REAR

YELLOW -3 YELLOW -1RED -3/4 COM RED -1/2 COM

GREY -4 GREY -2

PE70341

Fig. 6. Standard stepper -motor connections

FISCHER TECHNIKIn Part Two of ExperimentingWith Robots (Oct. 85) we gave theaddress of Fischer Technik for thebenefit of those wishing to obtaincomponents of this constructionmedium. We have since been in-formed that all small orders fromthe general public should be ad-dressed to: Economatics (Educa-tion) Ltd., Epic House, OrgreaveRoad, Hansworth, Sheffield S139LQ. ^ 0704 690801.

Similarly it must be decelerated in a controlled manner. Themaximum acceleration and deceleration can be determined byexperiment for the particular motor and load. One way to producethe ideal acceleration and deceleration from a computer programis to use a look up table to store a range of ever decreasng valueswhich are used in succession by a timing loop. There are moreelaborate (and compact) ways than this, but the programmingskills needed are greater.

Practical Electronics December 198513

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14 Practical Electronics December 1985

911E

NOTEBOOK

Graduate DemandLast month I noted the shifting pattern of

employment in the electronics industry inScotland. Since then I have seen the figuresfor the whole of the UK published by theEngineering Industry Training Board. In

round figures there were 21,000 scientistsand technologists in the electronics indus-try in 1978. By 1984 the figure had grownto 34,500 although the total labour forcehad increased only moderately.

Today no less than 10 percent of allpeople in the electronics industry are ofdegree or equivalent status and this com-pares with only four percent for the engi-neering industry as a whole.

Looking at individual sectors of the in-dustry the most startling increases havebeen in data processing and radio andelectrical capital goods where the numbersof scientists and technologists have virtual-ly doubled. Lowest increases were in officemachinery and consumer electronics.

But while the ratio of skilled to unskilledemployed has changed dramatically thegeographical distribution of the industryhas shown little change. The south-east isstill dominant with 48.1 percent of employ-ment, marginally up since 1978 whilemany of the less -favoured areas sufferedsmall percentage losses. Scotland in-creased its share of the total from 9.3percent to 11 percent and Wales came upfrom 3.3 percent to 4.5 percent. So even ifyou add Wales and Scotland together theyare still dwarfed by the massive concentra-tion in the south-east.

The message is plain. The greatestchoice for a career in electronics is found inthe south-east and the best chance ofemployment anywhere is to become wellqualified though not necessarily in a narrowspecialisation in the first instance. This willpossibly come later.

The chronic shortage of well -trainedpeople persists. Professor Richard Bishop,vice-chancellor and principal of BrunelUniversity, reported recently that in designtechnology each graduate this year has hadon average five offers of employment.Over the whole range of disciplines 95percent of Brunel graduates are employedwithin six months of graduation.

Professor Bishop, a professional engi-neer, attributes much of the success ofBrunel to the practice of every studentspending three six-month periods workingin industry during the four-year degreecourse. The newly graduated is thus any-thing but raw when entering full-time em-ployment. From the employer's point ofview the new recruit may still have much tolearn but at least he has first-hand industrialexperience and doesn't need six months toacclimatise in a new environment.

EducationPE Editor Mike Kenward is to be praised

for expressing a view and inviting corre-spondence on electronics instruction(more generally lack of it) in schools. May Iadd my pennyworth by quoting Sir Ken-neth Corfield, recent Chairman of STC.

In an interview published in the IEE

journal Electronics and Power Sir Kennethtold of his own experience on leavingschool. 'I remember very well the awfullook on my headmaster's face when I toldhim I was going to become an engineer.And what he actually said to me was: "I amsurprised Kenneth; we had you down atleast to become a bank manager'"

Well, that was the attitude 50 years agoand it doesn't seem to have changed muchalthough some teachers would no doubtprefer the goal of trendy sociology to thatof respectable bank manager, but even thatin preference to science and engineering!

However, my somewhat jaundiced viewof the teaching trade, brought about byover -exposure via TV to months of indus-trial action, has now been modified by thecorrespondence in PE. I am reassured thatall is not yet lost and there is a silentmajority of teachers who deserve to beregarded as professionals, the more so fordecently doing their best in often difficultcircumstances and encouraging their stu-dents by example to do the same. (Here,here. Ed.)

Industry YearThe Royal Society of Arts has desig-

nated 1986 as Industry Year. Apropos ofthe previous paragraphs I note that one ofthe RSA objectives is the establishment oflinks between schools and industry topromote mutual understanding, having re-cognised that we are an industrial countrywith an anti -industrial culture.

I hope that the special Industry Weeks tobe organised in schools and colleges willpoint out to teachers and pupils that thereis no such thing as free education. It is paidfor from money generated in industry andother profitable enterprises-a brutal facttoo often overlooked.

PartnershipA New Partnership: A New Britain. Such is

the brave title of the joint TUC -Labour Partydocument published last August. Packedwith bright ideas I believe it has a majorflaw. The strategy outlined is based on theromantic concept of the brotherhood ofman, of universal love, an ideal never yetachieved anywhere, least of all in thepolitics of the British left.

Although politics clearly has some influ-ence on industry I often wonder whetherthat influence is not often overrated. I amreminded of Mr Ronald Ferguson who diedthis year at the age of 91 and spent 60years in electronics. A school-leaver at 14he taught himself telegraphy and went tosea in 1909 at the age 16 as the MarconiCompany's youngest wireless operatorand retired as managing director of Mar-coni Marine in 1961.

His active life spanned every develop-ment in electronics from the earliest sparktransmitter to satellite communications.And this majestic progress from electronicinfancy to our present maturity was virtual-ly unimpeded by the policies of variousgovernments. It mattered not who was inpower or when because all the principaladvances came about through scientificprogress, private enterprise and an ex-panding and eager market.

Nonetheless we have to bear politics inmind and the TUC -Labour document de-serves a fair scrutiny if only for the remark-able omission of any reference to renat-ionalisation or even socialism.

InvestmentGood news for Scotland is the £82

million investment by Digital EquipmentCorporation in a new microchip plant atEdinburgh. Most of its output will go to thenearby DEC plant at Ayr for assembly intoICs. DEC's present workforce in the UK isabout 4,300 expanding in the next 12months to over 5,500. DEC's UK operationis second in size only to that in the UnitedStates.

An interesting development is the ex-pansion at Telford of Tatung Co where anew factory (a refurbished aluminium fac-tory) has been officially opened by MrNorman Lamont, formerly Minister for In-dustry. Tatung is Taiwan -based but has alabour force in the UK of some 700 peopleproducing colour TV and sub -assembliesunder contract. It was Tatung who boughtthe Decca TV business from Racal afterRacal's acquisition of the Decca group ofcompanies.

It is a tantalising question why Far Eas-tern companies manage to be successful inconsumer electronics production in the UKwhereas wholly UK companies consistent-ly fail. This despite the fact that the work-force and the economic environment arethe same. The answer has to be motivationand better management.

Among the largest investment pro-grammes this year has been that in cellularradio which has easily surpassed its initialtargets in user take-up. The only pity is thatso much of the equipment has been import-ed. Happily the situation is now changingwith Technophone Ltd receiving full ap-proval of the Excell pocket phone for use inthe Vodafone network. Transportable Vo-dafones are also being manufactured underlicence from the Finnish Mobira Companyat Racal's Seaton factory and base stationequipment at Carlton, Notts.

Cellular radio has certainly been thegrowth success story of 1985 and prom-ises to provide steady growth for manyyears ahead.

15Practical Electronics December 1985

du etionMICRO SYSTEMS

MICHAEL TOOLEY BA DAVID WHITFIELD MA MSc CEng MIEE PART 3

APOINT which usually occurs to most people sooner or later intheir introduction to micros is: "How does a micro system

actually start operating?". It is all very well to look at how the CPUis able to fetch and execute its instructions from memory, and thedifferent ways in which it can manipulate data when up andrunning. However-and remembering the frequently -repeatedpoint that there is no inherent difference between code anddata-the question arises as to how the CPU knows where to startrunning this program when it is switched on. To put it another way,what prevents the CPU just starting to execute bytes in memory(from a random start address) as if they were instructions?

GETTING STARTED

The preoccupation with running systems just mentioned canobscure this type of consideration. It can also result in the situationwhereby so much time is spent in looking at the way in which thesystem functions when it is running, that the problem of how to getit started up properly can easily be skipped over quickly, or evenignored altogether.

If this is the case, it can lead to significant problems when youcome to actually design and develop a system. Indeed, it veryquickly becomes apparent that one of the first milestones indeveloping a working system is to be able to get the system to startrunning through the main part of the program that has been writtento control it. Only then do you need to start worrying about whetherthe program is actually designed correctly.

In some ways, the problem just described is somewhat analogousto worrying about the performance of a new racing car engine beforeyou even know whether it is going to start for the race. Once started.it may function beautifully, but as every motorist will testify,starting can be a very big "if"!

SWITCH ON

The exact details of what happens at switch -on vary from onemicro to another. The general principles, however, are very muchthe same and apply to almost all micros. With most, the start-up se-quence can also be initiated even when the system has been runningfor some time by activating the "reset" input on the micro.

This is typically anactive low input, andthe micro restarts asthe signal changesfrom low to high.This type of reset isoften provided to al-low recovery of thesystem from a "lock-up", or error, and is afacility which isusually very well ex-ercised during debug-ging! A simple man-ual reset circuit for a 6800 system is shown in Fig. 3.1.

Fig. 3.1. 6800 manual reset circuit

IN PRACTICE

In practical systems, the power -on state is usually arranged tocause a reset to the system automatically to guarantee that the microbehaves in a predictable fashion. This usually means that afterpower is switched on, the reset input is held low for long enough toguarantee that the power supply has reached the required minimumoperating voltage (typically +475V), and for long enough thereafterto allow the micro to complete the reset sequence. Fig. 3.2 shows a

typical such reset circuit for a 6800 -based system, whose timingrelationships for the reset pulse and power supply start-up areshown in Fig. 3.3.

If required, the circuits of Fig. 3.1 and Fig. 3.2 can be combinedby following the inverter in Fig. 3.2 with a 2 -input AND gate, withits inputs fed from the two different reset signal circuits. The resetsignal generated by this circuit can also be used to reset any othercircuitry in the system.

As mentioned, there is usually a minimum time for which thereset input must be active to allow the internal operations involvedto be completed. For example, the Z80 requires a minimum of 3 fullclock cycles for the reset.to operate correctly.The 6800. on the otherhand, requires 8 cycles to elapse. The combined actions which areperformed during the reset period or immediately afterwards areusually very similar for most micros. Only the order and the detailstend to vary between different types. The reset pulse then, has aspecified minimum duration, and after the pulse ends the nextaction is usually a delay for a small number of clock cycles beforethe processor starts/resumes processing.

Rather than continue the discussion in abstract, we will insteadput these general concepts into more practical terms by looking alittle more closely at the behaviour of the 6800 during and followinga reset.

6800 RESET

While the reset inputleast 8 clock cycles havethe following states:

VMABAData BusR/Address Bus

on the 6800 is low, and assuming that atpassed, the CPU's output signals will be in

LowLowHigh ImpedanceReadFFFE

A timing diagram for the complete switch -on sequence is shownin Fig. 3.4. This shows the way that the conditions above areestablished.

Following the detection of a rising edge on the reset input, the re-set sequence is executed by the CPU. During the reset sequence, theinterrupt bit in the CCR is set to prevent any user interrupts (IRQs)from occurring too soon, and thereby throwing the CPU out ofsequence before it has been set up to handle them. The contents ofthe last two memory locations (FFFE and FFFF) are then loadedinto the program counter (PC).

The CPU then starts executing instructions. starting at theaddress just loaded into the PC (which points to the address of thenext instruction to be executed). Thus, for example, to cause theCPU to start running its program from an address of (say) C000after start up, the following would need to be set up in permanentmemory:

FFFE: CO (start address high byte)FFFF: 00 (start address low byte)On a practical note, it should be noted that it is the memory

addresses which respond when values of FFFE and FFFF are putout on the address bus which matter here. This can be a useful factto bear in mind when designing the address decoding for thesystem's memory. This is essentially of academic interest, since aprogram normally only ever refers to a particular location by meansof a single address. However, it does mean that it is possible toarrange that locations other than FFFE and FFFF are accessedwhen the reset sequence is executed.

It is quite usual for the reset vector (that is, the address which theCPU always accesses after a reset) to be located within the program

16 Practical Electronics December 1985

RESET INPUTS

MASKABLE INTERRUPTS

NON- MASKABLE INTERRUPTS

01

HALT INPUTS

1=3

Vcc

3k3 3k3 L1

4

6

FLIP-FLOP

1/2 OF 7474

CLN

OUTPUT

D INPUT

vs5

HALT

01

IRO

AMA

NMI

T. BA

Vcc

L AOA 1

- A2tz

A3A4

14A5

2- A616

A711

AAAISBO

IL All

6800

RESET

T5C

NC

02DBE

NC

R/WDO

DI

DI

D4

D5

D6

D7

AI5Al4A13Alt555

3k 3

34

33

22

31

30

25

25

24

23

22

O

4 I

1/6 OF 7405

RST

OUT

Vcc

TRIG

THRES

DSCRG

555

GND C

470n 100n 100n

Fig. 3.2. Practical power -on reset circuit, ensuring that the micro starts up in a known state

ROM, right at the highest addresses. If we look back at the systemdescribed in Part One, the ROM represents addresses C000 toC3FF. However, if FFFF is put out on the address bus, this will ac-tually access the ROM location at C3FF, due to only a partialdecode being performed on the address bus for addressing theROM. This is a very useful way of avoiding the need for special ad-ditional ROMs just to hold the reset (and other) vectors.

So, we have seen that in order to get a 6800 CPU to start up cor-rectly, it is necessary to arrange for the reset line to be held low untilat least 8 cycles after the supply rail reaches +475V. Thereafter, theline may be released to return to its normal high state at anyconvenient time. This will then cause the program whose startaddress is contained in FFFE and FFFF to be executed. This issummarised in the flowchart shown in Fig. 3.5.

What happens then is totally up to the programmer, so we nowmove on to look at the sort of actions which need to be taken to con-trol a typical micro system after it starts up if it is to continuerunning as required. This section of the control program is usuallyreferred to as initialisation.

INITIAUSATIONOnce again, the exact details of the initialisation routine will

depend on the CPU and the configuration of the micro systemitself. There are, however, a number of basic steps which arecommon to all systems.

The state of the CPU following the reset is that interrupts have

V

+5 251..

POWER SUPPLY

5 5

25$5mS 400m5

Fig. 3.3. Timing for power -on reset

been masked out. The basic steps which need to be followed arethen:I) set up the stack2) configure any peripheral devices3) enable interrupts

Of these operations, enabling of interrupts is certainly best leftuntil the first two operations have been completed. If this is notdone, the CPU may well be caught "on the hop" as it were, since aninterrupt could occur (automatically performing a series of stackpushes) before the stack has been initialised. It is as well, therefore,to work through each of these stages in the order given above.

It may be occurring to some readers at this point that these issuesare almost incidental to the workings of a micro system. However,

12 1 1 5 I I7

I I9

I 2 I "I I "2 I "3 I n+4 I "5

POWER ONSWITCH

5525

POWER "IjOrSUPPLY

RESET

R/W

VMA

DATA BUS

FFFE

200nS MIN

-.4 SON'S MAX=====CFFFE FFFE FFFE FFFF NEW PC

5

( HIGH IMPEDANCE)

ASRESET ROUTINE

ADDRESS BITS 0-7

RESET ROUTINE INSTRUCTION OFADDRESS BITS B-15 RESET ROUTINE

Fig. 3.4. Timing diagram showing the sequence of events after the micro is first switched on

Practical Electronics December 198517

experience shows that the majority of time spent in debugging amicro system can often be traced back to problems skipped over atinitialisation. Thus, a properly set up stack is all but invisible in aworking system and can be taken for granted, but a stack ofinadequate length or with improperly matched push and popoperations can cause some very strange problems. Worse still, thistype of error may only occur very occasionally, and to say that thistype of bug can be hard to track down is something which does notneed repeating to anyone who has tried.

The other point in discussing these topics in some detail is thatthey give a much better practical insight into how a micro systemactually works. At the end of the day, writing the inner loops of theapplication code (e.g. the admittedly often complex routines toperform exotic mathematical functions or signal processing of data)is a relatively straightforward matter of using the availableinstructions in the most effective manner to achieve the requiredresults.

The instructions themselves are well explained in the data booksfor the individual micros, and it is just(!) a question of selecting theappropriate ones for the particular task. At the worst, the answersproduced are wrong, but there is usually something to indicate thenature of the problem, thus providing a starting point for trackingdown the "bug".

However, getting the system to the point where the data isavailable to be manipulated, and being able to communicate withthe outside world, usually involves more than two-thirds of theoverall work required to complete the system.

The difficulty which causes the greatest delay at this point is thatthe usual response from the system prior to completing this stage isa stubborn silence. A major objective of this discussion, therefore, isto try to avoid or minimise the problems by covering the necessaryground rules for getting a system up and, if not exactly "running",not hanging up immediately after switch -on due to potentiallyavoidable reasons.

SETTING UP THE STACK

The stack needs to be set up in an area of RAM which is largeenough to allow for the expected usage. Locating the stack is astraightforward matter of loading the stack pointer (SP) with theaddress in memory (RAM) where top of the stack is located. This isdone by means of a special instruction, LDS, which loads two bytesfrom the specified memory locations (or which immediately followthe opcode) into the SP register. Thus, to load the value of 007F (i.e.the top of the RAM in our example system) into the SP, one waywould be to load it as an immediate value with the followinginstruction:

LDS #007F

This would actually be coded as:

8E 00 7F

However, any of the other addressing modes available with LDScould be used to suit the particular application.

It should be noted that most micros do not include facilities forspecifying a limit for the length of the stack, or detecting when stackspace is exhausted. It is necessary, therefore, to make sure thatsufficient memory is reserved for use by the stack. The spacereserved (i.e. the unused area of RAM below the top of the stack)should take account of the number and type of stack operations thatcan be current at any time. System operations which make use ofthe stack are:1) subroutine calls (BSR or JSR): 2 bytes each2) interrupts (caused by external IRQ events): 7 bytes each3) wait for an interrupt (WAI, same as an interrupt but saves time):

7 bytes each4) push accumulator data onto stack (PSHA or PSHB): 1 byte each

Within a program, the use of the stack should be kept undercareful control by the programmer. For example, the programmershould know how deep the subroutines will be nested, and allowsufficient stack space. Similarly, if the stack is to be used fortemporary data storage, this must be taken into account whenallocating space.

The only area of uncertainty here may be in the use of the stack byinterrupts. This will be covered more fully later in the series, but

essentially, the amount of space reserved for this purpose needs totake into account the maximum number of interrupts which can bepending at any given time, and 7 bytes must then be allowed foreach. Overall, the golden rules to remember in using the stack are:1) initialise the stack pointer before using the stack or enabling

interrupts2) allocate sufficient stack space to take account of the maximum

expected usage (plus some extra space)3) make sure that all stack pushes have corresponding stack pops

(otherwise the stack will just continue to grow, and grow, . . .)4) use RTS to return from a subroutine; never just jump out directly

(subsequent nested subroutines will otherwise return to thewrong place, and the stack will grow)

5) use RTI to return from interrupt service routines (to prevent thestack just growing, as for RTS)One point worthy of repetition is to remember that the 6800's

stack pointer must be set up during initialisation to point to the topof the stack area, i.e. the highest address. Other CPUs have stackswhich may work differently, and the details should be checkedcarefully before use.

Many of the points listed above are arguably simply examples of"good programming practice". They are nevertheless worth reiter-ating, if only to indicate why they must be observed. If the rules forstack usage are followed, the stack can usually be forgotten once setup, since it will automatically be maintained by the CPU, with theaddress in SP always pointing to the next free location on the stack.

CONFIGURING PERIPHERALS

In most micro systems, the setting up of peripheral hardware isusually a great deal more complicated than the setting up requiredfor the CPU itself. As time has passed, peripheral control devices(such as floppy disc controllers and CRT controllers) have becomeever more sophisticated.

The benefit of these powerful controllers is that they relieve theCPU of much of the detailed operations required to control theperipheral equipment. One consequence of this trend, however, isthat peripheral controllers are rapidly becoming as complex and"intelligent" as the CPUs themselves.

Indeed, anyone who has struggled over the finer points of some ofthese controllers will probably lend their support to the theory thatthe controllers have already overtaken many CPUs in terms ofcomplexity.

A good example of this trend is in the field of controlling floppydisc drives. With simple peripheral controllers, each CPU instruc-tion which affects the controller has an effect on its own. In a floppydisc controller (FDC), the CPU must perform a sequence ofoperations (usually a mixture of read and write operations). It isthese operations combined which represent what the FDC is beingasked to do.

Once a sequence has beeninitiated, the FDC carries outwhatever operation has beenspecified and, when complete,returns a result to the CPU.

One consequence of thismethod of interfacing with aperipheral controller is thatthe initialisation require-ments are correspondinglymore complex. While thesimpler peripheral devices arerelatively straightforward toinitialise, it is a rather moreinvolved matter for these "in-telligent" peripheral devices.The 8271 is an FDC whichwas developed for use with the8080 CPU, but which hassince been much used withother CPUs, for example, in the 6502 -based BBC Micro. It uses acontrol sequence, shown in Fig. 3.6, of the type described above. Togive an idea of the practical initialisation requirements for suchcontrollers, the flowchart in Fig. 3.7 illustrates the steps required toinitialise the 8271 before it is ready for use.

In contrast to the complexity of an FDC, the simplest of all

MEM PE127M I

SET IN

LOAD PROGRAM COUNTERWITH CONTENTS OF MEMORY

LOCATIONS FFFE PC H

FFFF PCL

JUMP TO NTERRUPT

SERVICE ROUTINE ASDETERMINED BY PC

Fig. 3.5. Start-up routine

18 Practical Electronics December 1985

START

COMMANDPHASE

EXECUTIONPHASt

RESULTPHASE

END )

CPU writes command andparameters into 8271registers

The 8271 is now on its ownto carry out the command

The 8271 signals the CPUthat execution has comple-ted. CPU reads one or moreregisters to determine result

Fig. 3.6. Sequence of operations for an 8271 floppy disccontroller. The CPU initiates action by sending asequence of commands to the 8271; the 8271 thencarries out the action independently, and returns theresult to the CPU

I RESET INTERFACEAND FDC

SPECIFY DRIVECHARACTERISTICS

SPECIFY BADTRACKS. DRO,DRI

NON -DMA ORSINGLE ACT

SEEK TO TRACK0 ON DRIVE 0

WAIT FORINTERRUPT

INTERRUPT

SEEK TO TRACK0 ON DRIVE 1

WAIT FORINTERRUPT

INTERRUPT

READRESULT

SET NON -DMA 8/ORSINGLE ACTUATOR

READRESULT

2nd DRIVE

Fig. 3.7. Initialisation includes a reset to the interfacehardware between FDC and CPU, and indication ofwhether or not this is a Direct Memory Access (DMA).The DMA facility allows the CPU to continue with othertasks while the FDC is finding the required data

ADDRESSBUS

ADDRESS

DECODER

GI 2

VMA

DATA

BUS

CLK

LATCH

CLR

RESET 0

OUTPUTS

Fig. 3.8. Simple output port schematic

peripheral interfaces is probably an output port. A block schematicfor such an interface is shown in Fig. 3.8. The output from theinterface is set to the current value of the data bus whenever theCPU writes to the address it is set up to represent (as governed bythe address decoder). This requires no initialisation at all before itcan be used as an output port; the only consideration is to decidewhether the output value at reset needs to be set to a particularvalue. If not, and as long as the port has been arranged to be resetautomatically by the "system reset" to the CPU, there is noinitialisation sequence required at all.

The basic point which comes out of all of this discussion is that,although the system reset will usually cause peripheral controllers topower up in a known state, they may well require further setting upbefore they are ready to be used in a particular application.

The more powerful and flexible the controller, the more likely it isthat this will be so. The rules to follow for designing the peripheralinitialisation sequence, therefore, are as follows:1) Check that the system is designed so that the "system reset"

signal also resets the peripheral hardware.2) Check the states which inputs, outputs and any internal registers

start up in after a reset.3) Decide what initial Conditions the system or external hardware

requires.4) Design the initialisation routine to make sure that any required

conditions are set up.5) If there is any doubt about any condition which will affect the

operation of the system, set it specifically during initialisation.We shall be starting to look at peripheral hardware in micro

systems a little later. For the moment, however, let us finish lookingat the problem of starting the system up and getting it runningproperly.

ENABLING INTERRUPTS

The 6800 is typical of most micros by starting up with userinterrupts disabled. This allows the CPU to set up any peripheralhardware which will give rise to these interrupts, as well as the stack,before having to worry about handling an IRQ. If the system is notusing interrupts, however, they can be left masked out. Otherwise itis a question of simply clearing the interrupt mask once the CPU isready to respond.

The interrupt mask in the 6800 is one of the bits in the conditioncode register (CCR). Special instructions are provided to allow theinterrupt mask (the "I" bit, or bit 4 in the CCR) to be manipulated.The instructions SEI and CLI (op codes OF and OE, respectively),set the "I" bit to 1 and 0 to disable and enable IRQ interrupts, re-spectively. The action of enabling interrupts is thus simply a matterof issuing a CLI instruction when ready to respond. We will start tocover the subject of interrupts in much greater detail next month.

NEXT MONTH: A review of the start-up process, andthen we move on to look at peripheral devices in moredetail, and the workings of interrupts.

Practical Electronics December 1985 19

Robotics Review MI

BRITISH robats lead the world. However,our previous pre-eminence in the

micro -mouse field is being stronglychallenged by the Japanese.

Those have been the results of muchtravelling throughout the world during thelate summer by enthusiasts from thiscountry. Dr John Marr, winner of theBritish heat of robat, travelled to SanFrancisco for IPRC '85 to find no chal-lengers from the States despite a greatdeal of interest and some rumoured at-tempts to build a robot ping pong machine.While in Belgium, for the European finals,Britain provided all five entries.

In Japan, however, the home countrytook the top six places in what was billedas the World Micro -mouse Final with thetop British competitor coming seventhwith a time almost double that of thewinner.

The originator of the contest, JohnBillingsley of Portsmouth Polytechnic, wasthere to witness the Japanese triumph butwas not completely happy with the way itwas achieved. Although they had beenwithin the letter of the rules he did not thinkthey had been within the spirit.

All the entries came from one club andused the same basic hardware which theindividual entrants then adapted, withouthaving to think out the complete mousefrom scratch.

Billingsley was full of praise however forthe way the Japanese had organised theevent and the resources which had beenmade available by the Government to payfor the travel and accommodation of thecompetitors from Britain, Korea and theU.S.

Charlie, complete with bowlerhat and large flapping ears, wasa far more sophisticatedattempt ...

The one major development from all theactivity was a much improved robatmachine from John Knight and DavidLowery of Fareham, Hampshire. They havesubstantially rebuilt Kung Fu which camesecond in the British heats and with Charliehave a device which was able to hit theping pong ball every time in the main testwith considerable force. It was not assuccessful when the direction from whichthe ball came was deliberately altered butBillingsley said it was a great advance anddid not think it would be long before arecognisable game could be played.

The vision system was much the sameas for Kung Fu with three spinning cylindri-cal lenses which focussed the light fromthe ball onto a photo cell. The spinninglenses created pulses and the ball's posi-tion was judged by the time it took thepulses to reach the cell.

The ball was tracked by the bat on an XYplotter arrangement driven by servos. Thehitting mechanism was activated by theball crossing a light beam but it was tooenthusiastic and the ball travelled muchtoo far.

An Electron computer controlled thewhole apparatus.

Charlie, complete with bowler hat andlarge flapping ears, was a far more sophis-ticated attempt at solving the problemsthan Kung Fu. That needed a Dragon andAtom and the bat was attached to someplastic drainpiping and powered bysprings which were rewound betweenstrokes. When released the bat was haltedin the required position by magneticclutches.

John Knight took Charlie to Strasbourgin October. It was part of an exhibition toshow the European Parliament what washappening in new technology in Europebefore they debated the subject. After thatthey and their competitors have until nextsummer to work on their machines beforethe next round of the contest, which is stillseeking a venue.

A new company to the robot world isHCCS Associates of Gateshead. It is inthe final stages of developing an armwhich will be in the mid -range of prices atabout £700. No firm figure can be given asthe final design and manufacturing systemfor the gripper has not yet been decidedbut Jim Golightly said it would not be morethan £1,000.

The design is the usual articulated armwith five axes plus gripper and will be ableto lift 2kgs. It will be driven by servos withpotentiometers providing feedback,though it will be possible to add opticalencoders.

It has an on -board processor and can beconnected to micros via RS232 and Cen-tronics ports. Software will be available forthe BBC B.

No launch date has been fixed but Go -lightly is hoping that it will be before theend of the year.

. MAX I-now to be called theE-RIC...

Flight Electronics has changed itsmind about its Ogre lookalike, the MAX 1.It is now to be called the ERIC, EducationalRobot Incorporating Cybernetics. As re-vealed in the October issue it is a three axisarm driven by servos through worm gearsand costs about £400. To that must beadded £130 for the control board andpower supply. The board allows connec-tion to any of Flight's Three Microprofes-sor micros and has I.e.d. indicators toshow the status of the motors and opticalencoders and five spare inputs to allowcustomised sensors to be interfaced.

To complete the package there areexperimental packs for each of the micros,including a manual and control ROM givinga number of routines.

Cybernetic Applications has added awork cell to its range. It consists of aconveyor and indexing table and unusuallythe conveyor is driven by stepper motorsunder the control of the computer. Furtherpieces will be added later.

The Mentor, from the same company,has been improved so that it can lift lkginstead of its original 300 grams and canbe given routines by lead -by -the -nose.Unlike Neptune, which uses touch sen-sors, the Mentor system works by simply

disabling the motors and then moving thearm to the required positions. The Serpentsystem is operated by a button whichwhen pressed allows the arm to bemoved.

A full price list has been worked out forthe Naiad with a complete built system,including a simulator and BBC B interfacefor £975 +VAT. The arm on its own in kitform costs £595 + VAT.

In addition IBM PC interfaces are nowavailable for all Cybernetic machines.

. . . electronic pets calledPetsters

It appears that Nolan Bushnell, founderof the now ailing Androbot company inthe U.S., has finally persuaded Americansthat robots do not have to do anythingparticularly useful other than "enhance thepersonality of the owner". After leavingAndrobot he re-entered the personal robotmarket with electronic pets calledPetsters.

With Catsters, Dogsters and moresimply Petster Jnrs they are activated byhand claps and perform various routinessuch as coming when called and makingnoises in response to voice detection.

They have proved very successful. Canit be long before we see them in the shopsin Britain?

John Knight and Charlie in Stras-bourg. Is the name due to the hat orears?

Mentor, Serpent I, indexing tableand conveyor belt

20 Practical Electronics December 1985

P.E. PROJECT KITSFull kits include pcb's, hardware, cases (unlessstated otherwise), IC sockets, wire, nuts & bolts.

Article reprints extra 70p each.HIGH PERFORMANCE STEPPING MOTORDRIVER Dec 85 00.98EXTRAS: Transformer MM. Case 12.95, BBClead Motor-1DSER

PORT35CO

NovNDER

f 10.91MODEL RAILW4Y TRACK CONTROL Nov 85

E41.04SQUINT ROBOT EYES Nov 85 EBBSTOUCH CONTRC4. PSU Oct 85 E28.38MODULATED SYNDRUM Oct 85 E26.58GENERAL PURPOSE ROBOT INTERFACE, fully=mod board Sept/Oct 85 E74.99

TO CENTRONKS CONVERTER Sept 85£44.95

CAR BOOT ALARM Sept 85 E11.72

GENERAL PURPOSE.ROBOT INTERFACE

As featured in Sept/Oct/Nov issues 'EXPERI-MENTING WITH ROBOTS' Feature.Full kit includes Double Sided PCB, TerminalPins. IC Sockets. OIL Switches. and ALL ICs,Transistors, Capacitors etc. To build a FULLYPOPULATED Board. Provides 4 servo channelsand one Gripper Channel.Full kit (requires 5V, .9. and --9V supplies) lesscase. E74.99.

COMPUTER ENVELOPE SHAPER Aug 85 E22.19VOLTMETER MEIN3RY ADAPTOR July 85 E10.96STYLUS KEYBOARD FOR COM 64 Jun 85 F.9.55SYNTHEKKER INTERFACE FOR COM 64 Jun 85

E15.89AMSTRAD SYNTHESISER INTERFACE May 85

E26311CYUNDER THERMOSTAT May 85 821.77BBC POWER CONTROL INTERFACE Apr 85

E20.99GUITAR ACTIVE TONE CONTROL less case

E11.97E18.67E34.62

E8.24E13.25

Sept 83PROGRAM CONDITIONER June 83AUTO TEST SET May 83ASPER DELAY Apr 83 less relayBATTERY TESTER Apr 83

LOGIC TUTORA specifically de=reltbs:1 for the practical sideof the 8 pan sense introduction toPortal Electronics' Practical Electroreas Oct 83 -May 84. Fult tut ncludeS Screen ponied pcb. powersupply. connector strips arid turned pin sockets (lesscase(

£34.98REPRINTS EXTRA 70g EACH

HIGH PERFORMANCESTEPPING MOTOR DRIVER

As featured in this icsiksKit including PCB, I.C. & All Parts £20.98

Transformer 30V 18VA £5.98 extraCase (houses PCB on N) 12.95 extra

Lead & Connector for BBC Computer £1.98Motor - ID35 £14.50

TEA1012 also available separately £6.88. Data £1.00

TOOLSAntex X5 srartrtring iron 25W 240V £7.25, 12V £7.45, 24V£7.65, 110/115V £7.35.Antex Model C soldering iron 240VHeat sink tweezersSolder handy size 5Solder cartonSolder reef size 10Low cost pliersLow cost cuttersBent nose pliersMini dnll 12V (MD1)Multimeter Type 1 1000opvMultimeter Type 2 20,000opvMuttimeter Type 3 30,000opy (taut baud)Multimeter Type 4 10M digitalDesolder pumpSignal injectorCircuit testerHelping Hands jig & magnifierMiniature vice (plastic)

£6.9845p

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78p£798E1.85

BOOKSA Practical Introduction to Microprocessors. Pentad £2.10Basic Electronics. Holder & Stoughton £8.98Beginners Guide to Building Electronic Protects.Penfold £2.25BBC Micro. Usbome First Guide to 2.26DIY Robotics & Sensors Billingsley. BBC E7.95

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1 I

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We offer a range of the superb Fischertechnik sets. Thesecover robotics, electronics. electromechanics. motors andgears, and basic construction.Robotics kit build 11 different working models including arobot arm, graphics board, sorting system etc Note that notall the models can be built at the same time. Simple toassemble. Easily combined with all other Fischertechnikkits. Top quality. Includes 2 motors, an electromagnet,lambs, potentiometers, switches etc.ROBOTICS Kit (554) PE E64.99Construction/base kit (1.41) £37.50Motors and Gears (ut2) £42.70Use ut2 to motorise tiltElectromechani (u13) £73.20Electronics (ut4) £93.90

BBC - ROBOTICSINTERFACE

A READY TO USE INTERFACE for the BBC computer andthe Fischertechnk Computing and Robotics Kit (554).Allows the BBC computer to operate all 11 of the standardmodels which can be built from the Fischertechnik Roboticskrt.

The interface features forward - reverse and onioff controlof four DC motors; orvoff control output for driving anelectromagnet or similar device; and eight s1IRJ1 inputs forreading mecroswitches or other binary inputs.Two independent analogue input channels are provided forposition sensing.Supplied complete with connectors and leads the interfacerequires a power source of 9-12 volts at 1A.Detailed programming information is supplied with the inter-face. A software disc with a comprehensive set of programsis also included.FISCHERTECHNIK ROBOTICS - BBC COMPUTERINTERFACE (BUILT) (PE) £69.95

CATALOGUEBrief details Of each kit, book contents. and illustrations anddescriptions of our range of tools and components are allincluded.Robotics and Computing section included.Our advert shows just a selection of our products.Up to date price list enclosed. Official orders welcome.Catalogue & Price Ust - Send £1 in stamps etc or add £1to your order.Price list only 9x4 SAE.Catalogue hoe to schools/colleges requested on officialletterhead.

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Practical Electronics December 1985 2I

NEW STUDIESThe Leonid meteor shower is at its maxi-

mum on the night of November 17. Occa-sionally the Leonids can be magnificent, asthey last were in 1966; usually the shower isvery sparse-but one never knows, and it isworth keeping a watch just in case we aretreated to another major display.

New studies have been made of what istermed "galactic cirrus", material detectedby the highly successful IRAS (Infra -RedAstronomical Satellite). Dutch investiga-tors, headed by F. Boulanger of Groningen,have produced evidence that the cirrus ismade up of graphite or silicate grainsembedded inside clouds of hydrogen. The

temperature is too high to be explained byheating from local interstellar radiation,and it may be that the grains are verytiny-no more than a dozen Angstroms indiameter-and are briefly heated to hightemperatures each time a grain absorbs aphoton of light.

IMPOSSIBLE GALAXIESIn the constellation of Pisces there are

two galaxies, NGC 7603 and NGC 7603B,which have come under recent scrutiny andwhich seem to present problems which areexceptionally puzzling.

The larger of the two is NGC 7603. It islinked to its companion by a luminous"bridge" made up of stars, dust and gas, andsince 7603B lies at the end of the bridgethere seems no obvious doubt that the twogalaxies are genuine companions.

Yet-and this is a real puzzle!-the spec-tral red shifts are different. They indicatethat the large system is moving away atabout 5,000 mile per second, and the smallsystem at about twice this speed. Accordingto present theory, this would push NGC7603B far into the background.

For many years there have been argu-ments about the significance of the redshifts in the spectra of external systems. Ifthey are pure Doppler effects, they give areliable key to the distances of the objectconcerned. Quasars, for example, have verylarge red shifts, and on the conventionalinterpretation they are the most remote

systems known; some of them must be wellover 10,000 million light-years away.

On the other hand, a few eminent astron-omers have serious doubts. In America, H.C. Arp has listed many cases of apparentlyaligned galaxies and quasars which havedifferent red shifts, and Sir Fred Hoyle, inparticular, is firmly of the opinion that thequasar red shifts are misleading, so that thequasars themselves are relatively local toour Galaxy.

If NGC 7603 and 7603B really are com-panion systems, with different red shifts,the effect upon cosmological theory will beprofound indeed. So what does the evidenceshow us?

Dr. Nigel Sharp, of the Kitt Peak Obser-vatory in Arizona, has made a new exami-nation of the pair, and believes that theluminous "bridge" does not end exactly atthe smaller galaxy, but extends past it. If so,then the main argument in favour of realassociation is removed, and NGC 7603Bcould really be in the background, so thatwe would be dealing with a line of sighteffect.

Yet there are some other considerationsto be taken into account. The total lumino-sity of NGC 7603B seems to match that of adwarf elliptical companion galaxy, and thespread of velocities of its individual starsseems to be only about 100 miles persecond, which is much lower than onewould expect at the indicated cosmologicaldistance.

The Sky This MonthThe planets are, in general, not particularly well placed thismonth. Mercury is theoretically an evening object, but it isso far south of the celestial equator that it is not likely to beseen from Britain. Venus is visible in the eastern sky for abrief period before sunrise, but it rises later and later eachmorning, and after the middle of next month it will be lost inthe dawn brightness.

Jupiter continues to be a splendid object in the south-westafter dark: telescopically it has been of great interest lately,because there has been great activity in the planet's southequatorial belt, which has been the darkest and broadestbelt on the disc-though normally it is less pronounced thanthe north equatorial belt. Saturn is in conjunction with theSun on 23 November, and is therefore out of view.

Mars is coming back into the morning sky as it movesthrough Virgo. It is still a long way away, and its magnitudeis only 1.9, so that it is little brighter than the Pole Star, but itwill increase steadily until it next comes to opposition inJuly next year. Its present apparent diameter is a mere fourseconds of arc, so that no telescope will show much upon it.

The Moon is new on 12 November, and full on the 27.There will be a total solar eclipse on the 12 November, butnot even the partial phase will be visible from Britain; thetrack of totality begins in the South Pacific Ocean and endsin Antarctica, but the length of totality is less than twominutes.

Of course, the most -studied member of the Solar Systemat the moment is Halley's Comet (see special feature onpage 28), which is on view throughout the month and stillmoving in the Tauraus area, well north of the celestialequator. By now it is within binocular range, and themagnitude may increase from about 8 at the start ofNovember to above 7 at the end, though exact forecasts arealways difficult to make; comets-even Halley's-are noto-riously unreliable, and we cannot even tell whether therewill be much in the way of a tail or tails.

On 12 November the comet will pass between the stars 65and 67 Tauri, magnitudes 4.4 and 5.4 respectively, and onthe night of 16 November the position will be two degreessouth of the Pleiades star-cluster-a good opportunity forcelestial photographers. On 27 November the comet makesits first approach to Earth, at just under 60,000,000, milesby which time it will have moved into Aries and will be justsouth of the famous telescopic double star Mesartim orGamma Arietis.

At the time when I write these words (September 7) all thefive comet probes - two Russian, two Japanese and oneEuropean-are on course, and performing well. All willmake their rendezvous with the comet during the secondweek of March next year.

Comet Giacobini-Zinner, which has a period of 61 yearsand which has been well seen during the late autumn, hasnow faded to below the tenth magnitude, and has moved sofar south in the sky that British observers have lost it.

VOYAGERThe concentration upon Halley's Comet must not make us

forget the other important probe of the moment: Voyager 2,which is on its way to an encounter with Uranus at the endof January. There have been problems with Voyager, butthere is every reason to hope that the Uranus mission will besuccessful-and no doubt Uranus, like the other giantplanets, will provide plenty of surprises!

With the onset of winter, Orion and its retinue are comingback into view; Orion itself rises in the east during lateevenings, and is always unmistakable with its two brilliantleaders, the red supergiant Betelgeux and the glitteringwhite Rigel. The Square of Pegasus remains prominent inthe western part of the sky, while much of the southernaspect is occupied by the large, dim constellation of Cetus,the Whale.

22 Practical Electronics December 1985

Dr. Sharp himself has come down on theconventional interpretation -that is to say,the red shift really is a Doppler effect, andNGC 7603B is a system in the far back-ground. But it does look more like a dwarfelliptical. and certainly the "bridge" seemssignificant even if it does not end abruptlyat the smaller system.

If the association between the two is real,we may have to re -think many of ourcurrent theories about the red shifts as keysto the distances of galaxies -and quasars. Itmay be unlikely, but it is certainly not

impossible, and astronomers will eagerlyawait the results of future investigations.

ERNST OPIKAstronomers the world over will be sad-

dened at the death of Ernst Opik, at the ageof 92; he died in September at his home inNorthern Ireland. Opik had an eventfulcareer. He was Estonian by birth, but wasstrongly anti-Communist, and eventuallymade his escape to arrive in Britain penni-less. Luckily he was invited to ArmaghObservatory by. the Director. Dr. Eric

Lindsay, and remained there for the rest ofhis life. Opik was very much of an "all-rounder", who made major contributions toboth stellar and Solar System astronomy; hewas also a prolific writer.

It is fair to say that some of his opinionswere unconventional -for example he be-lieved that there was a link between sunspotactivity and political revolutions, and I donot think he ever believed that the Russianshad sent men into space! But certainly hewas a major figure, and he will be greatlymissed.

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Crofton Computer Monitor, 9" P31,green, high resolution screen. Compositevideo, metal case, lead for BBC. £65 ono.Danny Fellows, 26 Westbourne Avenue,Emsworth, Hants P010 7QU. Tel: 024 345548.

Dual -trace Tektronix oscilloscope10MHz good condition £85. Splitting col-lection of plug -ins from £15. T. Haley. tel:01-868 4221.

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16K RAM expansion board. MB8118120nS rams used. Complete with Sche-matic to aid interface. £12. Mr. P. Hale, 31South Road, Stourbridge, W. MidlandsDY8 3YA. Tel: 0384 379120.

RULES Maximum of 16 words plus address and/or phone no.Private advertisers only (trade or business ads. can be placed in ourclassified columns). Items related to electronics only. No computersoftware. PE cannot accept responsibility for the accuracy of ads. orfor any transaction arising between readers as a result of a free ad.We reserve the right to refuse advertisements. Each ad. must beaccompanied by a cut-out valid "date corner". Ads. will notappear (or be returned) if these rules are broken.

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Practical Electronics December 1985 23

part of this project last month, the theory of the mainunit of the controller was explained. This month, the project is

completed by showing how a "chaser" circuit can be added. Thecomponents for the "Auxiliary Units" are those for the chaser, andalso for the ALC and computer interface (see last month).

CHASER CIRCUITMany DJ's like to have their lights flashing even when music is

not being played, and so some sort of sequential control is also de-sirable, though not necessary to the operation of the rest of the cir-cuit. The method of sequential, or chasing control used here is tofeed a variable audio frequency from a VCO to the filter circuit, andto vary the way in which the frequency is automatically changed.

Refer to Fig. 2.1: the VCO is formed around IC7b, IC8a and IC8b.Its output waveform at C19 is triangular and has an amplitude ofabout 4V p -p. The frequency is set by C18 in conjunction with thecurrent at IC8 pin 1. This is derived from the voltage seen acrossR36 and VR7, the latter presetting the optimum range.

The circuit around IC7a produces the varying voltage, and fouroutput waveforms are available. The circuit is basically a squarewave oscillator with its rate set by C17 and the feedbackresistance of VR6 and R34, and variable between 200ms and 1.5minutes, depending on the mode selected. The rate of charge ordischarge of C17 controls the rate at which the comparator trippoint set by the voltage on IC7 pin 5 is passed, at which point thecomparator output changes state.

The waveform seen at Cl) is normally an approximation of atriangle wave that is slightly distorted due to the chargingcharacteristics of C17. By switching D12 in parallel with VR6, C17now charges slowly via VR6, and discharges rapidly via D12,producing a rising ramp. With D13 in parallel instead, a falling rampresults. Although all three waveforms at C17 are non-linear, they

can be used to control the VCO by tapping them via the highimpedance buffer IC8c. Fourthly, the squarewave output can itselfbe tapped directly. The modulation mode by which the VCO has itsfrequency varied is selected by S4. (Photos 2.1, 2.2, 2.3, 2.4.)

As the frequency shifts across the filter spectrum, so thedifferent filter bands will. be operated and the relevant lights willcome on and off. Different chaser patterns can thus be generatedby selecting the desired controlling waveform. Additional varia-tions to the pattern can also be achieved by altering the levels atwhich VR1 to VR3 are set. In the chaser mode the filter control potVR4 is out of circuit and has no effect, the control node of IC2 be-ing held at a midway level via S3b. S3a is ganged with S3b and inswitching to chase mode, the input music socket'is removed fromcircuit.

ASSEMBLYThe full unit just nicely fits into the box size shown -230 x 133 x

63.5mm. The drilling should be carried out after adequate pre-planning, which should also take into account that any mainsconnections must not come into contact with other parts.Particularly ensure that if using bayonet lampholders, their termi-nals cannot contact the triac flanges when the lamps or plugs areinserted. It is preferable from a safety point of view that the mainsneons should be omitted until the rest of .the circuit has beencompleted and tested. This ensures that at this stage all mainsconnections are confined to the rear of the box. Where feasible,cover any exposed mains contacts with adequate insulating tape.FUII interwiring details are shown in Fig. 2.3.

Except when adjusting the presets VR5 (main board) and VR7,or checking voltages, the unit should never be worked on unlessunplugged from the mains. If you are in doubt or inexperienced,seek authoritative advice.

+V

R30467

R33

100k

R314k7

MIMC1615n

R34

VR6 46711,1

lC7o7L072

R35

47k

, I I-1, 1.4113600 R32

T22p 10k 5

013°1,24,48

COmmi.

R39

NAAI100k

R36 R37 R38 .... C 1 8 ,-.."47k 100k 100k 1,-, 101'

2504

107 PIN 4 = OVPIN 8 = +129

1C8 PIN 6 = OVPIN 11 = +12V

Fig. 2.1. Circuit diagram for the "chaser" sequential control option IK413241

24 Practical Electronics December 1985

Below, chaser VCO modulation by LFO. Upper trace VCO,lower trace LFO. The VCO frequency is shown lower thanactual amplitude for illustrative clarity

Photo 2.1: S4 position 1 Photo 2.2: S4 position 2

r

Photo 2.3: S4 position 3 Photo 2.4: S4 position 4

CHECKING OUTSetting up simply consists of adjusting the two presets VR5 and

VR7 and can easily be done while watching the output lamps. Firstthough, it is best that correct operation of the various circuit stagesis checked methodically.

Before inserting any of IC1 to IC8 in their sockets, plug into themains and check that a d.c. voltage of about 18V is present at theinput of IC9, and 12V at its output. If either voltage is significantlydifferent, recheck your assembly. Next insert IC I and IC2 togetherwith IC6 if it is being used. Operation of the filter can be checkedwith the meter on a 12V d.c. setting. Whilst playing a musicrecording into the unit, monitor the signal side of VR1 to VR3, anda small variation in the meter reading should be seen. Now adjustVR5 around its midway point until, with VR1 to VR3 fully up, fullscale deflection of the meter occurs roughly in time with the musicwhen looking at pins 1, 7 and 8 of IC1. If using the chaserextension, check also that a varying voltage is seen at the pole ofS4a.

The frequency output of IC8 will be too fast to be seen by themeter, but can be monitored indirectly by referring again to thesignal ends of VR1 to VR3, with S2 and S3 in the correct position.

When satisfied, IC3 to IC5 can be inserted, and low power lampsconnected to the output sockets. Set switches S2 and S3 back tomusic input mode, but remove music from the input. VR5 can nowbe more accurately set. First adjust it until all three lights are on,then turn it back again slightly until the lights are just off. When ap-plying music, as VR1 to VR3 are brought up, so the lights shouldflash as required, and turning VR6 will vary the emphasis of thefrequency range.

If the response of the lights is a bit too edgy with regard to thelow settings of the control pots VR1 to VR3, slightly back off VR5,so setting the comparator threshold point a bit further away. VR7of the chaser circuit should be adjusted from the best observedresponse of the sequences when VR1 to VR3 are at about onequarter rotation.

COMPUTER CONTROLControl of the three lamps by the computer requires probably

one of the simplest control programs that will ever be needed. Alow output bit from the computer turns a light on and a high bitturns it off. This control can be carried out quite readily from thenormal IEEE output, or from the User Port socket possessed bymany computers. Below the code required for the Commodore Petseries is given, for other machines your manual should give the

35

VR7

I27

I29 30 31

LEIN

LEIILEIE

R 36

R38

939

..r R37 1.0

ZOEC19 +

I

KEEN

KEN

ED

R35 D t

.3 0KEEN

CI6

ve

R31

3233

- 34

LPEI7330 1

35

Fig. 2.2. Component layout and p.c.b. design. The off -board numbered lines refer to numbered lines on the mainboard, and on the interwiring diagram

COMPONENTS ...AUXILIARY UNITSResistors

R1

R2, R3R26R27 -R29, R35, R36R30, R31, R34R32, R40R33, R37 -R39, R41, R43R42All W ± 5% carbon film

CapacitorsC1-3, C19C4C5C6, C17C16C18

PotentiometersVR6VR7

SemiconductorsD506-D13IC6IC7IC8

SwitchesS2, S3S4

560k30k (2 off)1k47k (5 off)4k7 (3 off)10k (2 off)100k (6 off)300k

1 p 63V electrolytic (4 off)4p7 63V electrolytic56p polystyrene22p 16V electrolytic (2 off)15n polyester1n polystyrene

1M mono rotary250k skeleton

7V5 400mW zener1N4148 (8 off)571TL072LM13600

min. d.p.d.t. (2 off)3 -pole, 4 -way

Miscellaneousp.c.b. clips (4 off); knobs (2 off); mains neon (4 off);PCB245B; 8 -pin i.c. socket; 16 -pin i.c. socket (2 off).

Practical Electronics December 1985 25

20( LP1 -LP/. OMITTEDON SHORT VERSION)

LP1

22

L P2

24

IC;:)L P3

VR1

HIGH

!Fee.13e]

4 10

MID

It 14

3 12

VR3 ;';].,

LOW

18

S2

0 00..j4 J 1)..-11.- 39

8-41-41

(52,53 OMITTEDWITH SHORT

37 VERSION AND WIPEROF VR4 TAKEN

LIS3 DIRECT 10 PCBPIN 11)

SKI( L P5)

5Y2 SK3LPE (LP2)

LINK PCB PINS15 TO 2919 TO 38

25

FILTER MOD RATE(VR6 AND 54OMITTED ON

\..SHORT VERSION)

30

32

33

4

35

S4MOD WAVEFORM

11

SK4

27

40

INPUT /

I11)1111(1

F52

FS1

2

(DAD) 7

(DIG GNO) 28

USED INPLACE OF PIN39 IF SHORT

44, VERSION IS5, BEING BUILT

Si

30 0

SKS

COMPUTER INPUT

E

9 (DA1) WIRING OF SK5 IS EXAMPLEONLY. ACTUAL WIRING WILL

13 (DA2) DEPEND UPON SOCKET CHOSENTO SUIT COMPUTER.

Fig. 2.3. Complete interwiring diagram for the Disco Lights Controller. The numbered lead -out wires relate to numberedlines on the main p.c.b., published in Part One, and to the optional "chaser" board. If the simplest version of this projectis being built, manyp.c.b. In the full version, line 40 is omitted, and the input taken from line 39

simple equivalent codes. (C64 equivalents are 56579 and 56577respectively.)

First open the port as an output for the first three data bit linesby:

POKE 59459,7 (7 = binary 00000111)

POKE 59459,255 would do equally well, this opening all eightbits as outputs, (255 = binary 11111111). Once having POKEDthis number there is no need to change it during the rest of the pro-gram. To turn on the particular lights required all you do then isPOKE 59471 (the output port), with one of the following numbers.

Lamp 1Lamp 2Lamp 3Lamp 1 and 2

= 254 (binary 11111110)= 253 (binary 11111101)= 251 (binary 11111011)= 252 (binary 11111100)

Lamp 1 and 3 = 250 (binary 11111010)Lamp 2 and 3 = 249 (binary 11111001)Lamps 1, 2 and 3= 248 (binary 11111000)No lamps = 255 (binary 11111111)

In each case where a "0" occurs the lamp associated with thatbit will be turned on. Examination of a decimal to binary chart willshow that other numbers, such as 0 to 7, will also produce asimilar response with the 3 lamps.

Holding loops can be inserted in between each program step sothat the length of time between lamps changing can be varied.Such a loop can be written as:

FOR Z = 1 TO T : NEXT Z

where T is the delay factor. On my Commodore 3032 with T at4000 a delay of approximately 5 seconds occurs. This may varybetween machines depending on their internal clocking rate, andany auxiliary editing aids.

A random lighting sequence can also be -run from a sub -routinesuch as:

10 T = 10020 R = INT(RND(1) x 256)30 POKE 59471,R40 FOR Z = 1 TO T50 NEXT Z60 POKE 59471,25570 GOTO 20

In this fashion random or specified sequences with delays fromfractions of a second up to several days can be programcontrolled.

Constructors' NoteSend a large SAE for full details and prices for this project to:

Becker Phonosonics, Dept. DLC, 8 Finucane Drive, Orpington,Kent BR5 4ED.

26 Practical Electronics December 1985

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Practical Electronics December 1985 27

Dr Patrick Moore OBE

extending away from the Coma is the tail-or, rather, tails; a largecomet may have both a gas tail (the 'ion' tail) and 'dusty' tail. Manysmaller comets, however, never produce tails, and look like nothingmore than tiny patches of luminous haze in the sky. Basically, acomet depends upon reflected sunlight, though when close to the Sunits gases may fluoresce and emit a certain amount of light on theirown account.

HEAD IN THE CLOUDSAs yet we do not know a great deal about the nucleus of a comet. As

the distance from the Sun grows less, as the comet draws in toward itsperihelion or closest approach, the ices in the nucleus start to 'boiloff, and the resulting coma hides the nucleus completely. Generallywe are not even sure just where the nucleus is. This is where we hopethat Halley's Comet will help us in March next year.

Comets are believed to come from the 'Oort Cloud', a wholecollection of comets orbiting the Sun at a distance of at least a light-year (nearly 6 million million miles). They are, naturally, quiteinvisible from Earth; if a member of the cloud is perturbed for any rea-son, it may swing inward toward the Sun. Its journey will take a verylong time indeed, because not until it is reasonably close -in will itstart to move quickly, but eventually it will enter the observable partof the Solar System. One of several things may then happen.

On July the second this year 1 flew to French Guiana. I wentat the invitation of British Aerospace, and for a very special re'the launching of the Giotto probe to what is probably our most famouscelestial visitor, Halley's Comet.

I am quite sure that a great many people know what a comet is; and.by now there can be few who have not heard about the return ofHalley's Comet; but it may be as well to clear up a few points at theoutset. I still have letters from writers who say, in effect, "Last night I ' saw something crossing the sky; can it be a comet?" Of course theanswer is 'no, because a comet is millions of miles away, and has tobe watched for hours before any noticeable movement can be seenagainst the starry' background. Secondly, any object which movesperceptibly must be in our air, or close to it. It will be either an artacial satellite or a meteor-unless, of course, it is something more'mundane, such as a high -altitude weather balloon or a distant,.aircraft.

DIRECT HIT IN 1908The other point to be made at once is that comets are very

insubstantial, and even a direct hit on Earth could do no more than.local damage. (There is good evidence that a part of a comet did landin Siberia, in 1908, and although it blew pine trees flat over a wide 1 ,

area there were no human casualties.) And though the gases in acomet's tail would be dangerous if dense, they are in fact sorarefied-millions of times less dense than the air you and I arebreathing-that they are totally harmless. In 1910, at the last return of Halley's Comet, the Earth went right through the tail, and nothingcould be noticed. This time the comet will not come within 30 millionmiles of us.

A comet has been described as "the nearest approach to nothingthat can still be anything". The only part which is reasonably massiveis the nucleus, no more than a few miles in diameter, and presumablymade up of ices, mainly water ice, together with rocky fragments.Surrounding this is the head or coma, which may be extremely large(the coma of the Great Comet of 1843 was larger than the Sun), and,

ectronics December 1985

If the comet is not affected by the pull of a planet, it will simplyswing past the Sun and return to the Oort Cloud, not to come backfor many centuries. If it is perturbed by a massive planet (usuallyJupiter, which is more massive than all the other planets com-bined), the comet will either be thrown into an open orbit, andexpelled from the Solar System altogether, or else put into a smallorbit with a short period, in which case it will pass throughperihelion every few years.

PERIODICAL COMETSApart from Halley's, all these so-called periodical comets are

faint; very few of them become visible with the naked eye, and fewdevelop tails. We know when and where to expect them; Encke'sComet has the shortest period of all (3.3 years), and there are manyothers with periods of from 5 years to a few tens of years.

The brilliant comets seen throughout history-for example in1811, 1843, 1858, 1861, 1882 and 1910-are regarded as non -

30

20

11-1 10CC

O 0

zo -10z -20O -30

-40

- 50

CLUE TO ORIGINComets are important because they are very ancient. They date

back to the very early days of the Solar System; we know that theEarth is over 4,500 million years old, and if we could find out moreabout the make-up of comets we would be adding to our knowledgeof the past history of the entire planetary system. We are learning allthe time.

On the other hand, every time a comet passes through perihelionit loses a certain amount of its material by evaporation; inparticular, the tails are formed from material in the nucleus andcoma. No comet can tolerate this loss indefinitely, so that the short -period comets have limited lives. Several last -century comets whichwere regular visitors have now disappeared; for example, Biela'sComet, which had a period of 6i years, but broke in two at thereturn of 1845 and has not been seen since 1852, though a brilliantmeteor shower was seen in 1872 radiating from the position wherethe comet ought to have been.

PEGASUS

_ -- PLEIADES---_

Nov 1 Nov 21 -1985 *Aldebaran

ORION u Dec 11s -

Dec 31`.

Feb 9

CAPRICORNUS

*Fomalhaut

Limiting Horizon -Southern England

AQUILA OPHIUCHUSAltair

Fig. 1. Path of Comet Halley 1985-86

SAGITTARIUS

Antares

Mar 31\

VIRGO

Spica

SCORPIUS

Apr 10

LEO

Regulus

May 3041986

/-1/HYDRA,/

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CENTAURUS

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RIGHT ASCENSION -HOURS

periodical. This is not completely true, becausee they will returneventually (unless they have been thrown into open orbits), but theyare visible only at one return in many lifetimes, and there is no wayin which we can predict them.

BYGONE SIGHTINGSThe exception is Halley's Comet. It has a mean period of 76 years,

and it has been seen regularly since well before the time of Christ.Records of it-mainly Chinese-go back to the year BC 1059, andevery return since that of BC 240 has been observed.

It "shone down" in 12 BC-much too early to be associated withthe Star of Bethlehem. It was visible in 1066, just before William ofNormandy launched his invasion of England; in the famous BayeuxTapestry it is shown, with King Harold toppling from his throneand the Saxon courtiers looking on aghast. In 837 it was magnifi-cent, with a nucleus and coma as bright as the planet Venus, and atail stretching for more than 90 degrees across the sky.

In 1301 it was seen by the Florentine artist Giotto di Bondone,who represented it in his picture "The Adoration of the Magi". In1456 there is a story that it was excommunicated by the Pope,Calixtus III, as an agent of the Devil; this is certainly not true, butthe Pope does seem to have had some unkind things to say about it.

In 1682 it was seen by Edmond Halley, friend of Isaac Newtonand the future Astronomer Royal, who worked out its path andrealized that it was identical with comets previously seen in 1607and 1531; he predicted its return for 1758-and on Chriitmas Nightof that year it was duly picked up by the Saxon amateur Palitzsch,passing perihelion in 1759. It returned in 1835 and again in 1910,after which it was lost once more until it was recovered in 1982. Thedate of the next perihelion passage is 9 February 1986.

Until Halley's time, the movements of comets were not known; itwas generally believed that they travelled in straight lines, by-passing the Sun only once. Therefore, it is only just that the cometshould have been named in Halley's honour.

16 14 12 10

There is, in fact, a close association between comets and meteors.As a comet moves along, it leaves a 'dusty' trail behind it; when theEarth passes through such a trail, the particles enter our atmosphereand burn away by friction, producing the familiar shooting -starappearances. Many of the annual meteor showers have knownparent comets, and Halley's Comet is associated with two showers,the Eta Aquarids of May and the Orionids of October. (Note, by theway, that there is no association between comets and meteorites.Meteorites are more closely related to the minor planets ofasteroids; there may be no essential difference between a largemeteorite and a small astroid.)

HARMFUL GASESIn 1910 Halley's Comet was a brilliant object, because at the time

of perihelion it and the Earth were on the same side of the Sun. Itattracted a great deal of attention, and even some alarm; peoplejumped to the conclusion that the gases in the tail would be harmful,and one enterprising American even made a large sum of money byselling anti -comet pills, though nobody seems to be sure just whatthey were meant to do! This time, alas, the situation is lessfavourable, and at the time of perihelion, in early February, thecomet will be almost directly behind the Sun, so that it will beunobservable. Our only hope of recording it then will be from one ofthe space -craft now in orbit round the planet Venus.

It is unfortunately true to say that people in general may bedisappointed at the appearance of the comet, but at least it will bevisible, and of course we know exactly how it will move. DuringNovember it will pass through the constellation of Taurus, and asthe magnitude will rise to 6 it will be an easy binocular object(Fig. I ). On the night of 16 November its position will be just southof the Pleiades star -cluster; by the 27th the distance from Earth willhave been reduced to just under 60,000,000 miles, and the cometwill be just south of the well-known telescopic double star GammaArietis.

Practical Electronics December 1985 29

RelativeGIOTTO trajectory

Tuwinds

O

lar wind mg(400 km/sec).1

Dust tail

SuriHr".e

Shock front

03 Hydrogen corona

Ion tail

On board experiments will include dust, plasma andnucleus make-up analysis. Good quality photographsare expected

NAKED EYE OBJECTDuring December the comet should become a naked -eye object as

it passes from Pisces into Aquarius; whether by that time it willhave developed a definite tail remains to be seen. In early January itwill 'set' soon after the Sun, and by the middle of the month it willdisappear from view.

It will re -appear in late February, and the best chances of seeing itto advantage will be in March and April-I./you live in the southernhemisphere! When at its best, in early April, the comet will be inCentaurus, which means that it will not rise at all in Britishlatitudes, though from countries such as Australia and South Africait will be almost overhead before dawn, and should be quiteprominent, with a nucleus of at least the third magnitude and a tailwhich should extend for up to 30 degrees.

By the end of April it will have reached Hydra, and will again bevisible from Britain, though it will fade quickly. Modest telescopeswill be able to track it until August, but by the end of 1986 the mainpart of the return will be well and truly over.

On 24 April there will be a total eclipse of the Moon. This will be agreat opportunity for spectacular photography-a chance which isunlikely to recur for many hundreds of years. Halley is bound to bethe best -photographed comet of all time.

TAIL FIRSTIt is never safe to forecast the development of a comet's tail or

tails; in the case of Halley, records indicate that the maindevelopment takes place after perihelion. The ion tails are straight,the dust -tails curved; they always point more or less away from theSun (due mainly to the effects of 'solar wind', a stream of atomicparticles being sent out from the Sun constantly in all directions), sothat when it has passed perihelion, and is moving outward, a cometactually travels tail -first.

Earth -based astronomers will be very busy throughout theapparition. There is full international co-operation, and the cometwill be monitored as continuously as possible, so as to checkphenomena such as short-term changes in the tails. Since 1910 newtechniques have been developed, and spectroscopic investigationsshould tell us a great deal more about the comet's make-up. But themost exciting possibilities involve spacecraft.

Remember, Halley's is the only major comet which we canpredict, and this is why it is of such importance. Smaller comets canbe contacted by probes (as the periodical Giacobini-Zinner, inSeptember last), but Halley is unique, and plans to by-pass it werelaid many years ago. The Americans had a very ambitiousprogramme, but abandoned it on the grounds of expense-adecision which they will no doubt regret for the next 70 years atleast. So we are left with five probes: two Russian, two Japanese andone European.

HEART TO HEARTBecause we do not know the size or the precise nature of the

nucleus, or even just where it is, the only real hope of finding out isto send a spacecraft right into the comet's heart. This is the role ofthe European probe, named Giotto in honour of the Florentinepainter. It is modest in size, but it is crammed with instruments ofall kinds, and we hope that on the night of March 13-14 next year itwill penetrate the coma and send back close -range pictures of thenucleus itself. The results will come through to the Parkes 210 -footradio telescope in New South Wales, and will be transmittedstraight to Darmstadt in Germany, where the pictures will beelectronically assembled. I will be at Darmstadt, hoping to show theresults on BBC television immediately. If all goes well, it will be anexciting night.

Previously, the two Russian and two Japanese probes will havepassed by the comet at a more respectful distance, and will havecarried out surveys of all kinds-including radar determinations ofthe position of the nucleus inside the coma, which should enableGiotto's trajectory to be corrected at the last moment. The Russianspacecraft, Vega 1 and Vega 2 (nothing to do with the star Vega)travelled to the comet by way of Venus, and as they passed by theydropped balloons and landing probes into the atmosphere of thatdecidedly peculiar and hostile world. The Japanese probes aremuch smaller, but they too have an important part to play, and sofar all seems to be going well with them.

GIOTTO-MAIN HOPEYet it is fair to say that our main hopes rest with Giotto. Because

Halley's Comet moves round the Sun in a retrograde direction (thatis to say, in a sense opposite to that of the Earth) Giotto will meet italmost head-on, at a very high relative velocity, and this means thatthe mission is fraught with danger. We do not really know muchabout the conditions in space close to a comet, but there must bemany solid pieces of material around-both rock and ice-and acollision between Giotto and a sizeable lump of solid matter can

The launch pad at Kourou, French Guiana, where thesuccessful launch took place in July this year. AnAriane rocket, a direct competitor with the spaceshuttle for satellite launches, was used

30 Practical Electronics December 1985

have only one result. Frankly, the chances that Giotto will passthrough the coma and emerge unscathed are very slim indeed. Whatwe hope is that the probe will survive for long enough to send backthe data we so badly need.

What exactly will it show? We can at least speculate. As the cometis heated by the Sun, its nucleus will be in a state of constantagitation; there will be cracks, outbursts and small explosions as theices evaporate, and the entire scene is likely to be one of chaos.There is no reason to doubt that the picture quality will be good-ifGiotto survives for a sufficient length of time, but the whole climaxof the mission will be over in a very short time, and there can be nosecond chance.

Even when the main excitement is over, there will still be much todo, as the comet makes its closest approach to Earth during itsoutward journey and is intensively studied from all major observa-tories. Amateurs also can play a useful role in helping to maintain acontinuous watch. We can never tell just how the comet is going tobehave.

Giotto under laboratory conditions at the British Aero-space facility at Bristol. The probe is almost 3 metreshigh and is 1.84 metres in diameter

GLOBAL SCRUTINYThe International Halley Watch (IHW) was formed by Louise

Friedman, then of the Jet Propulsion Laboratory in California, in1979. The idea was to set up an organizing body which wouldco-ordinate worldwide ground -based observations of the cometthroughout the apparition, and at the present time the 1HW is in fullswing; the organization has proved to be very effective indeed.

The main investigations concern astrometry, infra -red spectros-copy and radiometry, large-scale phenomena, near -nucleus studies,photometry and polarimetry, radio science and spectroscopy.

The amateur network, co-ordinated by S. J. Edberg, involvesvisual observations, photometry, spectroscopy and photoelectricphotometry, plus data on the two associated meteor streams, theEta Aquarids and the Orionids. There is a regular IHW Newsletter,prepared by the Jet Propulsion Laboratory together with NASA,and at the end of the apparition all the results will be summarised inthe official Halle), Archive.

How long will we be able to follow Halley after perihelion?Certainly for some years; the Hubble Space Telescope, a 94 -inchreflector due to be launched in the near future, should be able totrack it until it passes out into the remoter parts of the Solar System.We intend to learn all we can, and no effort is being spared. But for

When Giotto finally encounters the comet, aroundmidnight of March 13/14th 1986, it will have travelledsome 435 million miles and will be around 93 millionmiles from Earth

most of us, this coming period is our sole chance of seeing Halley'sComet. It will not be bright again until the year 2061; so let us makethe most of our current opportunities. It is comforting, too, toremember that Giotto, though a full-scale European project, had aBritish firm-British Aerospace-as its main contractor, and thatthe probe was built in Bristol. This is fitting, particularly as whenEdmond Halley forecast that the comet would return in 1758, hemodestly added that if he were proved right, then 'posterity will notrefuse to acknowledge that this was first discovered by anEnglishman'.

ACKNOWLEDGEMENTThanks to British Aerospace for kindly supplying photographs

used in this article.

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Practical Electronics December 1985 31

PART TWOAST MONTH, we described the circuit operation of the Model

Railway Track Control project in full detail. The p.c.b. layoutand construction of the main control unit was also covered andthis month, the final part, deals with receiver boards, constructionand testing.

CONSTRUCTION AND TESTING (TYPE A RECEIVER)The circuit board and the component layout for the Type A

receiver are shown in Fig. 12. When the components areassembled on the board, but before inserting IC1 into its socket,some checks can be carried out. Connect a d.c. power supply tothe board line terminals. Switch on, and gradually increase thevoltage up to 28V. When the supply current has stabilised, itshould settle at about 2mA. Check the voltage at C1 is 15V, andTR I collector at OV. Using a 104 or similar value resistor,discharge capacitor C4, when the supply current should fall to1.5mA for about 1s, and then increase to around 25mA, while C4is recharging. The recharging time will be about 1s for each1000p.

The receiver i.c.s are of MOS construction, so the usualhandling precautions should be taken. After switching off, and thecapacitors have discharged, the chosen IC1 can be plugged in.Switch on the power supply, and the current, when stable, shouldbe about 6mA.

If an oscilloscope is available, the decoding oscillator can beseen to be running, producing a 3V peak to peak sawtooth atpin 2.

SETTING UP (TYPE A RECEIVER)Connect the receiver (Type A) line termi-

nals to the control unit output. On thecontrol unit, select the appropriate posi-tions on the rate and word switching forthe board. From the fourth column in Table2, select which output pin on IC 1 will beenergised when the word is recognised,and connect it to a voltmeter to read 15V.Transmit the code word while adjustingVR1 over its full travel. Note the twopositions of VR 1 where a steady highreading is just obtained, and then adjust itmidway between them.

CONSTRUCTION AND TESTING(TYPE B RECEIVER)

The circuit board and component layoutfor the Type B receiver is shown in Fig. 13,and for the extension board in Fig. 14.Three links are required, one of whichconnects either D or 5 to IC2 input,and must select D when an extensionboard is used. Where 15 is not required,TR5 and R16 can be omitted, and R15replaced with a link.

The board should be assembled asnormal, taking care to ensure there are nodry joints or solder splashes.

When the components are fitted to the board, the initial testingprocedure is the same as that for the A type receiver, and similarreadings should be obtained.

SETTING UP (TYPE B RECEIVER)Connect the receiver (Type B) to the control unit output

terminals, and select the appropriate rate and word switchpositions. Connect a voltmeter to read 15V between V- and IC 1,C -bit output, both easily accessible at the edge connections forthe extension board. Rotate VR1 fully anticlockwise, and on thecontrol unit hold switch S5 in position A. Rotate VR1 slowlyclockwise until the meter reading becomes erratic, and note itsposition. Rotate VR1 fully clockwise, hold S5 in position B, androtate slowly anticlockwise. Again a position should be foundwhere the voltage reading is unsteady. Position VR1 midwaybetween the two points, and check that the voltage is high afteran A signal, and low after a B signal.

Change the voltmeter connection to check D, again at the edgeconnection. From Table 3, select the switch positions that willcause ICI, D output to be high. This will cause 5 to become low,but the actual voltage reading will depend on both the gain of thetransistor used for the inversion, and on the impedance of themeter used. To reduce the time taken for a change of state, TR5should not be driven into saturation, and a collector voltage of0.2V to 2.0V should confirm this. This voltage must not exceed4.0V, and the value of R16 can be altered to correct it.

TYPE A AND B RECEIVER, FINAL TESTINGBefore the boards are screwed down under some inaccessible

corner of the layout, it is advisable to see that they really work. Forthis, all the receivers that operate at a particular data rate shouldbe checked at the same time. Connect the boards to the controlunit and to the appropriate number of spare motors, if you havethem. As an alternative, the test circuit, shown in Fig. 15, can beused. I found this useful during the development of the system, asit is easier to spot the flash of an I.e.d. in the wrong place, ratherthan trying to trace where the noise came from.

Whichever method is used, the checking procedure is thesame. With VR1 on the control unit set so that the I.e.d. is justout, try each of the code words in turn, checking that the correctoperation occurs. The control unit I.e.d. should be illuminatedafter each operation, showing that the storage capacitor isrecharging, and the next operation should not be attempted untilthis is complete. Also check that code words at higher and lowerdata rates do not cause an operation.

04- A A C Ti V-

C5R15 "N 414 R53 Iv.

/328126 Mil 8611.6

CSC "

R 7

4545 C25 02631i R 63 HD 1

IT c.Q.9i. . C5R131413/348..-,f 855 I-.

12A /32 A -40--®j':IR16

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860 jcs, ,28 R48 , 0'26,4,n,bb -.1 R64 kb Ai R44 g.

li- 'SR12(i14 A/344Si R56 H .1 R51 (.4b

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_1 (,:i)--. 114 / 314

-.4 849 kip

7'..-

(P51739011

Fig. 12. Type A receiver board constructional details

32 Practical Electronics December 1985

1111111111111111111111111 HOME PROJECT

EXTENSIONBOARDCO NN

LINECONNECTIONS

0 LINK

LINK

g/

Int R23 ).CII

0=0 Cl 9

811

0.1 R 2 4 IA* wet R 2 2 }a, 4 R17 1.a,

al C12 I . 4 C5 111

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MOTOR COIL CONNECTIONS

C10

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3

1qD61 I R9

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6-1 R18 R19 IArr{R 20 }

CT 111 C13 1 C9

0=20 0=0 0=0C14 C15 C Cl

R33 cl(_1, 01(1 1135 oge: R36 c1(. 10

(7

2

5 R26 R27 R28

CSR2 g C5A3 g CSR4g CSRS

111

to

C6

4838

02 b

T R 4

MOTORCOI LCONN

Fig. 13. Type B receiver board constructional details

CONNECTING UPThe receiver boards can be fitted under the layout unprotected,

except for a thin coating of suitable lacquer, providing there is nodanger of them becoming wet, or of physical damage. The wiringfrom the control unit to the receivers will depend on layout, but abasic supplying a series of connector blocks, with spurs toeach receiver, is probably the most flexible. When connectingmotors similar to the Peco and "H and M", the common coilconnection should be made to terminals on the same side of themotor. This ensures that the small inducedwinding is negative at the thyristor anode,important when 30V devices are used.

When all the connections are made,switch on the control unit and allow all thestorage capacitors to charge. When condi-tions have stabilised, the control unit linevoltage I.e.d. should be at normal bright-ness, and by adjustment of VR1, the linecurrent I.e.d. should be just off. If this isnot so, there is a fault on the wiring, orconnections, which must be corrected. Ifthe indications are satisfactory, check theoperation of every point, in bothdirections.

If a second operation is attempted onthe same receiver during the rechargingcycle, it is possible for a thyristor to latch,so preventing the cycle completing. Thecure for this is to switch off the controlunit, count to twenty slowly, and switchon again, when all should be well.

MOTOR RATINGSMeasurement of a motor minimum oper-

ating current can be difficult with theequipment found in the average workshop,and it is also too easy to accidentally burnout a coil. An alternative method is toestablish the required value of the storagecapacitor empirically.

This may be achieved using a d.c. powersupply, capacitor and a 1k resistor.

pulse in the unusedwhich is particularly

Connect a variable d.c. power supply to the capacitor with a 1kresistor. Connect the point motor and switch, and find the lowestcapacitor charge voltage which will operate the motor, in bothdirections, when the switch is closed. A capacitor of suitablevalue should operate the motor at a voltage of 15V to 20V.

To calculate a realistic value for the maximum motor current,the coil resistance has to be measured with a reasonable degreeof accuracy, but the figure for coil inductance can be less precise.

The average test meter is not noted for accuracy whenmeasuring low values of resistance, but the d.c. voltage indicationcan be good, particularly when comparing voltages on the same

MOTOR

COMMONCONNECTIONS

-{ Re*-4=3.-

{=1:01005

4=34103

C

I -D6

R3eicio);Tb

R 9 1.0

141),

IICbIR2T 1111.°R13

.4 RIO

ct

s-C=3-TR1

or.-f R 2 }-C2

DI

LINE CONNECTIONS

R3

R12

RII

r

T

LIM

C SR4

11;671

(PE17374.

Fig. 14. Type Bextension boardconstructionaldetails

28/413

2A /4 A

MOTOR COILCONNECTIONS

Practical Electronics December 1985 33

OTHERCIRCUITS

RS - R8680

DI -D4

if RI - 84 NOT LESS THANCOIL RESISTANCE +1115

(PEI741G]

(PE1140G I

0:71 RI 1,4h

-Cl co) I

01 R5

117-4 R2 J-

CI 02

81-{ ---*CSR

116 1

ANODESR3 1--8,

C)D3

R '

PEI1410

R B 1-0

Fig. 15. Circuit diagram and p.c.b. layout of the testcircuit together with schematic diagram of theconnection details of the test set-up

Photograph illustrating the Type B receiver andextension board connected to the test boards

+vE

range setting. Connect a resistor of similar value to that of the coil,and 5% or better tolerance, in series with the coil. Connect to ad c. power supply, at about 2V, or full scale on the nearestvoltmeter range. Take readings of the supply voltage, V, and thevoltage drop through the coil Vc, then:

RCoil resistance

Rc - Vx

V Q

In a similar way, the coil inductance can be found, but this timeusing an a.c. supply of around 2V. The measurements must betaken with the motor armature in the ready to operate position.

Coil inductance:

V x R + V2 - V1)H.Vr x 100n x 2. Vr.V

The theoretical circuit for the motor and storage capacitor relieson a perfect switch for correct operation. For the circuit to operateas designed, it should be over damped, and not tend to oscillate,that is:-

c C

At any time t secs, after the switch is closed, the instantaneouscurrent

where

V . (e -la - fIf -e-1a + Olt) A.

V C

a = , and 132L, (2L7,) L,C

The maximum current will occur at a time:-

1 , (a - s)t = - loge6)

secs.213 (a +

The thyristor is an imperfect switch, and so modifies the currentin the circuit. An approximation to the forward characteristic ofmost thyristors can be made by assuming a voltage drop of 0.9V,and by increasing the motor coil resistance by 0.4Q. The capacitorcharging voltage is also reduced by the receiver diode D2, whichshould be taken as 1 volt. This reduces the effective chargingvoltage, in the above equation, to 26.1V, with a line voltage of28V.

The result given by the above calculations will give a guide tothe choice of a suitable thyristor, and should not exceed 50% ofthe surge rating of the device.

1 4 Practical Electronics December 1985

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Practical Electronics December 1985 15

3,3e /*to ronapkDavid Whitfield MA MSc CEng MIEE

His month we continue to look at appli-I cations for the lightpen whose construc-

tion was described last month. As users ofthe lightpen with the simple test programwill have noticed, the results are far fromideal. To begin, therefore, I shall be offeringan improved program which makes rathermore use of the capabilities of both thelightpen and the BBC Micro.

DRAWING ON THE SCREEN

The most natural medium for drawing issurely with coloured pens on a sheet ofwhite paper. The graphics capabilities of theBBC Micro theoretically make this type ofdrawing quite a feasible proposition. Theusual problem encountered by users, how-ever, is the difficulty of programming thecomputer to perform as required. What isreally required is the natural hand -to -eyecoordination which is present in conven-tional freehand drawing, rather than wrest-ling with streams of PLOT commands.

The use of a lightpen on the screen isprobably the most natural currently feasiblemethod of interacting with a computer,since it involves so little change to thehuman operator's normal method of work-ing. Just for once the computer is adapted tothe needs of the operator, rather than viceversa.

The program in Listing 1 provides oneexample of using the lightpen in just themanner described. This is by no meansrepresentative of the best that can beachieved with the BBC Micro/lightpencombination; instead it illustrates the typeof facilities which can be provided byprograms of quite modest length. The pro-gram is still a little longer than is usual inthis column, so a few notes of explanationas to the way it works, as well as how it isused, are appropriate.

PROGRAM DESCRIPTION

The program is effectively split into fourmajor sections: setting up (lines 10-180), themain loop (lines 190-310), exit (lines 320-360), and subroutines (lines 380-580).

An assembler routine is provided in lines50-70 to read the current value of thelightpen register from the CRTC. The char-acteristics of the standard 'beep' are thenredefined in lines 90-120, and various parameters set up for controlling the operationand characteristics of the program. Userdefined character definitions, and the for-mat of the screen windows are establishedin lines 130-180.

The main program loop starts by allowingthe user to select a pen colour from thepalette displayed on the left edge of thescreen. This selection is performed usingthe lightpen. Once selected, a bar of thechosen colour replaces the palette, and ashort 'beep' is also emitted. There is then adelay (set in line 100) to allow the pen to be

moved to the required start position fordrawing on the white sheet area provided.This should be done before the second beepsounds to show that the pen is now active;otherwise an unwanted smear may wellresult. Thereafter the pen's position on the

Listing 1: Drawing Tablet Program

1020

304050

60708090

100110120130140150160170180190200210220230240250260270280290300310320330340350360370380390400410420430440450460470480490500510520530540550560570580

REM Lightpen Drawing TabletREM

ON ERROR GOTO 330DIM P% 30(.pen LDX 1,16:STX &FE00: LOX BFE01LDA41017:STA *.FE00:LDA &FEO1:RTS:]

Corr% -1542: *FX210.0Delay% -200: *FX212.136Smooth% -8: *FX213.200MODE 2: *FX214.3GCOL 0,135: COLOUR 135: CLSA-24: B-60: C-126: D-60VDU 23.254.A.B.C.C.C,C.B.AVDU 23.255.D.D.D.D.D.D.D.DVDU 28,0.31.0.0VDU 23.1.0:0:0:0:: VDU 5

REPEAT PROCaelecr_colourTemp-INKEY(Dela4'%): VDU 7PROCpen_poa1tionCurrX%-XX: CurrY%.Y%REPEAT PROCpen_poeitiondXX-X%-CurrX%: dY%-Y%-CurrY%CurrX%-CurrX%.(dX% DIV Smooth%)CurrYX-CurrY%,(dY% DIV Smooth%)MOVE CurrXX.CurrYX: VDU 254Temp-INKEY(0)UNTIL Temp -32UNTIL FALSE

VDU 23.1.1;0:0:0:: *FX212.144MODE 7: *FX213.101*FX214.7END

DEF PROCpen_position: *FX19Poe%-(USR(pen)AND &FFFF)-Corr%X%.16*(Pos% MOD 80)Y%-1024-32*(Poe% DIV 80): ENDPROC

DEF PROCaelect_colourVIDU4: COLOUR 135: CLSFOR colour -0 TO 7COLOUR colour128VDU 32,255.255IF colour<>7 VDU 32NEXT colour*FX 21,0REPEAT PROCpen_positionKey-INKEY(0)UNTIL (X%<128) OR Key -33

IF Key -33 CLG: GOTO 440VDU 7: colour -7-(Y% DIV 128)GCOL 0.colour: COLOUR colour.128CLS: VDU 5ENDPROC

Fig. 1. Sample results from Listing 1

screen is followed by the program, whichprints the character defined as ASCII 254(line 150). This character may be redefinedto be larger or smaller as required; see page384 in the User Guide to see how this isdone. To produce a smooth response, asoftware filter is included in lines 250-270.Readers will have noticed with the demon-stration last month that the pen produces avery jittery response unless some form offiltering is introduced. The smoothing fac-tor for the filter is adjustable, and is set inline 110; larger values increase the timeconstant.

To change colour (or just lift the pen), thespace bar is pressed. This stops the drawingprocess, and causes the palette to be re-displayed. The user may then select anothercolour (or re -select the same colour) usingthe lightpen as before, and the whole opera-tion then repeats as just described. As analternative to selecting another colour, thedrawing sheet may be wiped clean bypressing the "!" key; the program thencontinues by displaying a blank sheet andthe palette. Exit from the program is bypressing ESCAPE; the cursor and beepcharacteristics are reset to their normalvalues by the exit routine in lines 320-360.

The first of the two subroutines is forreading the X -Y coordinates of the lightpen,and for converting the CRTC values tographics coordinates for use by the PLOTcommand. The second routine is for dis-playing the colour palette and allowing theuser to select the pen colour. The palette isdisplayed using a one character wide textwindow.

RESULTS & ENHANCEMENTS

A simple example of the results which canbe obtained using this program is shown inFig. 1. In use, it will soon be found thatmany improvements may occur to you forincorporation into this basic program. Theprogram just described is still relativelysimple, but is offered here as a starting pointfor experimentation. One of the first im-provements which could be considered is toadd a facility to overcome the wrap -aroundeffect that occurs when the pen approachesthe right edge of the screen.

The next improvement could be to elimi-nate the need to use the keyboard at allduring the operation of the program. Oneway of doing this would be to make use of amicroswitch mounted on the pen barrel,and connected to one of the fire buttoninputs on the analogue port. This simplyrequires one extra wire to be brought to thepen, as shown in Fig. 2. Thus, the lightpencould be configured to draw only when thisswitch is held down. This means that theswitch really needs to be mounted conve-niently under the artist's finger as the pen isheld, but this should not be too much of aproblem. An alternative could be to consid-er touch pads connected to one of the ADC

36 Practical Electronics December 1985

inputs to detect the resistance of a finger asthe switching event.

As mentioned before, the uses to which atool such as a lightpen may be put arelimited mainly by the imagination of theprogrammer. Anyone looking for furtherideas for directions in which to developtheir lightpen applications may like toconsider trying to emulate some of thecapabilities of the Reekie Image Plotter asreviewed in September's PE. Another usefor a lightpen is in applications where theuser is not familiar with entering choicesfrom the keyboard (e.g. with young chil-dren, who prefer to point). Here it is oftenmuch better if a menu of choices can bedisplayed, and the actual choice made bypointing at the appropriate symbol or col-oured area on the screen. In this type ofapplication, it should always be remem-bered that the lightpen responds best towhite areas, and not at all to black areas ofthe screen.

Happy experimenting!

PEN BARRELPUSH BUTTON

SWITCH

orA-- ComerAfter two month's absence, Book Corner

returns to look at what could perhaps bedescribed as a programmer's atlas to theBBC Micro's built-in software. Within theBBC Microcomputer by Roger Cullis ispublished by Losco Ltd., PO Box 4, Cran-leigh, Surrey GU6 8BQ at f 11.95 plus f1.80P&P. A spiral bound book of around 260pages, this is a reference manual for theserious assembler programmer and hard-ware designer. It contains descriptions andexplanations of the principal ROM rou-tines, memory maps, tables of RAM usage,ROM routine entry points, page zero loca-tions, and JMP/JSR and lookup referenceorigins. It covers OS 1.2, Basic 1&2, DFS0.90, NFS 3.34, 6502 2nd processor OS 1.1,and DNFS/Econet Tube communications.

It must be said that this is not for the mostpart a book to be re-commended for light

TWISTED LEAD

Fig. 2. Switch addition. The internalcircuit for the SD4324 appeared lastmonth

'P669961

06 03 06 OS 04 03

PSI015 014 13 012 011 010 9

ANALOGUE PORT CONNECTOR( SOLDER SIDE)

reading, since it is moreof a reference book inthe true sense of theword. That said, how-ever, there is much in-teresting material con-tained in the descrip-tion which introduceseach of the types ofROM. For example,there are 13 pages de-voted to an outline de-scription of the MOS interms of its principleroutines. This is thetype of material whichis not easily to be foundelsewhere.

Each ROM is dealt with in a similarfashion, which considerably eases the taskof finding your way around the book. A titlepage gives basic information about theROM in question, such as the title string,the assembly address, relocation and work-space requirements. This is followed by amemory map of the ROM, giving the basicstructure of the code, in typically just overhalf a page. After this is a map identifyingwhich of the first 256 bytes of RAM (pagezero) are used by the ROM. Descriptions ofthe main routines in the ROM then follow,accompanied by a gazetteer of their entrypoints. The areas of RAM used are thenidentified, and each section is concluded bytables giving the sources of subroutine calls,unconditional jumps and lookupreferences.

It must be said that these latter tables arelikely to be of interest only to anyone who isactually trying to use the routines within theROM. This section of each ROM's descrip-tion would benefit fom a few words ofexplanation as to the significance and use-fulness of the information presented. A fewexamples would also help to illustrate theseparts of the book, which otherwise left yourreviewer little the wiser. In general, thebook would benefit from a few illustrationsand hints as to how to use the data which isso carefully. clearly and thoroughlyprovided.

Verdict: A useful reference guide, full ofmuch valuable information, which may bethe answer to many a prayer. However, youwill need to know what you want to do withthe information presented in order to makeMI use of it.

NEXT MONTH:The RS423 port is explored.

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Practical Electronics December 1985 37

At the end of 1977 PE and EE were separated and the editorialoffices of PE moved to Poole in Dorset. I took over responsibilityas Editor of PE with the January '78 issue-that month we hada mistake on the front cover, not the best start for a new Editor.Fortunately things could only get better!

the virtues of the Z8000 architecture, but Zilog wanted to get allelectronics engineers interested and there's only one way to dothat, isn't there? Yes of course, they gave the Z8000 its very owncomic bookl Enter Captain Zilog, alias systems designer NickStacey, who is given the gift of "Zilog power" by an extra-terrestrial being who hauls him bodily through his VDU screen.

Moulded in the fine tradition of Superman and Captain America,Captain Zilog hurls himself into adventures such as "The doom ofDoctor D" and "Battle beneath the architecture" in a desperate(and of course successful) attempt to foil the dastardly plans ofDoctor Diabolicus who intends to conquer Earth with the aid of hissuper main-frame computer. Liberally laced with comments suchas: "Stick it in your Index Register Diabolicus" or "Dancin' data"and "Leapin' logic", the new Zilog comic book is a must, if youcan get one!"

We spent more than a year describing most of the availablemicroprocessor chips during '83 in Micro -File written by RayColes. The work has proved to be well accepted and together

. makes an invaluable reference to microprocessors. The serieswhich has now been updated will be available in a book fromNewnes in the near future.

More recently we have turned our attention to explaining how touse microprocessors and the new series Introduction to Micro-processor Systems is an example of this policy.

ENTER ZXScience of Cambridge was the company name, Clive Sinclair the

driving force and the ZX80 the breakthrough product. It wasavailable in kit form for £79.95, and PE's Mike Abbott reviewed itin July '80 with the following conclusion:I see the ZX80 in the classroom, and in workshop controlapplications. Perhaps even hidden in the executive's top drawer,to be pulled out at lunch times to resume training. For these

YEARS OF ELEcnein

MICROSAs microcomputers developed into the hobbyist area and

prices started falling a number of designs were being produced bycontributors and offered to the hobby magazines. Apart from thePE Champ which we published in Sept. '77 PE resisted thetemptation to carry these designs while developments wereracing ahead. However by mid '79 various realistic systems hadbeen built around chips like the Z8 and 6502 and we took theplunge with Compukit UK101. This design was arguably the mostsuccessful kit to be published in a UK hobby magazine and while,as has often been the case with microcomputers, there were earlysupply problems the design took off in a big way. Success wasmainly due to the use of Microsoft BASIC and a realisticspecification for an all in price of around £200.

Interestingly we had published a microcomputer printer usingelectrosensitive foil paper and a 40 column, 5 x 7 dot matrix printhead made by Mastsushita a full six months before UK 101-thecost of constructing the printer was about £90. In Feb '79 welooked at "Home Computers . . . the Microprocessor Miracle!"and such machines as the Commodore PET, Tandy TRS80, AppleII, Research Machines 380Z and Nascom 1 were featured-it'ssurprising how long some designs have been around!

We reviewed bubble memories in April '79 and expected themto make an impact fairly quickly, the article said "Already a 64Kdevice has been passed in the laboratory by a 256K devicewhich should enter production before 1980. In the USA chipsas large as 1M have been made and operated and chips fourtimes this capacity have been projected by the early1980's . . . it is hoped that over the next few years circuitdesigners will come to regard magnetic bubble devices asjust another integrated circuit package."

Zilog were shouting about their new 16 bit micro the Z8000around the end of '79 and we reported on their Captain Zilogcomic:"Now, one way to tackle the publicity task would be tocommission some technical articles and advertisements extolling

situations, the machine is excellent, and eminently suited toteaching children the art of computer programming. It is of littleuse scientifically at present, with only integer capability and nomathematical functions, and this to some extent wastes theboasted processing speed of the machine.

At the time of writing it seemed appropriate to advise that a firm de-livery date be secured before purchasing the D(80 microcomputer.Some things do not change much do they?

Of course the ZX80 soon gave way to the much moresuccessful ZX81 and then the Spectrum. None of the later modelswere offered in kit form. Clive Sinclair-later Sir Clive-has come along way since those early ads in 1980 but the Spectrum was totake him away from the electronics hobbyist and firmly into thenew area of home computing.

The Compukit UK 101. A 6502 based single boardcomputer. This 8K machine was published in August'79 and proved to be one of our most popular projects

38 Practical Electronics December 1985

FE);#34CTRONICp

g ItGE

9v Stabilised P.S.U. va.

The Jan '78 front cover, can you spot the mistake?-Itwasn't deliberate!

PROJECTSOver the years the editorial staff of the magazine have built up a

general knowledge of what projects are likely to be the mostpopular and of course those which are often requested byreaders. One such project was an Ultrasonic Cleaning Bath-adesign which had often been requested but which had alwayseluded us because of transducer and stainless steel bath supplyproblems. A project was published in the Jan '80 issue and a kitwas available for £68. With the help of a friendly componentsupplier the problems had been solved; a little ingenuity resultedin a canteen food dispensing dish being used as the bath.

About 20 kits were sold over the next few months-a very poorresult especially when the design had often been requested. Latera fire destroyed the stock of components and the designinformation for the special coils used-truly a fated project andone which is occasionally requested by readers; even now we stillhave to disappoint them. (We cannot supply any information orassistance on projects that are more than five year old anyway.)

Other project landmarks in '79 were an Accoustically CoupledModem, PE Magnum Metal Locator and PE Teletext. We pub-lished a sound board for Compukit and a Speech Synthesiser.Support for Compukit continued through Micro Prompt-thehardware and software exchange point for PE computer projects-and in the Interfacing Compukit series which ran in 1981.

CB was big at that time, PE allowed readers to listen to theillegal a.m. transmissions with a 27/28MHz converter for carradios. Of course it was illegal to even listen to those transmis-sions but that was up to youl Later the same year we published abooklet entitled Introduction to Legal CB and, at the same time,commenced a short series describing the construction of a rigdesigned to meet the newly introduced CB laws, the PE Ranger.

The Ranger design annoyed some established amateur radiomagazines as they argued it could not be type approved by theHome Office. The kit was moderately successful but the CBbubble soon burst and readers could buy a ready-made full spec.rig for less than the £60 it cost to build the Ranger.

1981 was quite a year for projects and PE scored further hitswith the Genesis Robots-designed by Richard Becker then adirector of Powertran-and with the PE Car Computer-probablystill an unsurpassed design capable of many in -car calculations.Both these projects went on to be marketed around the world, ashave many other PE designs over the years.

A few projects never seem to die and the PE Scorpio IgnitionSystem was one of these. In '82 we published a miniature versionof the unit that was first introduced to readers in 1974; once againit proved to be very popular.

Practical Electronics December 1985

FAMEJust a couple of items we have described to readers have made

it to BBC's Tomorrow's World. The first was XEE described lastmonth; the other was the Telectric, an electricity cost monitorfeatured in March/April '82.

Telectric behaved itself perfectly well, though just what hap-pened to the food being cooked in a conventional and amicrowave oven is a mystery-my guess is the cameramen gotthere first.

One or two other projects have made it to various local radioprogrammes and some readers may have heard me describingthem rather nervously to presenters; Micrograsp was one fea-tured late in '82.

It would be easy to go on at length about various projects overthe years but as we come more up to date readers will rememberwhat has been done. Many projects had their associated prob-lems, some gave us more than a few headaches-notably someof the various robots that have been featured.

Projects changed with the times; we published logic analysers,digital lighting effect units, a computer terminal and many add-onsfor various computers-in fact just the subjects you will find in PEtoday. Where do we go next? What about surface mounteddevices and are we moving towards an android type robot? Whoknows, perhaps that is what makes it all so exciting.

HUMOURPE has not been the place for much humour. Right or wrong we

have always felt that the serious matter of technology at areasonable level of understanding does not readily mix with offthe cuff remarks and the "cheap sell" approach. However wehave "bent the rule" a little on various occasions and sometimesthis has rebounded on us.

"I had the pleasure of spending a day with the Tomorrow'sWorld team during '82, seeing how the programme is puttogether and watching Judith Hann fall off a pair of Japanesemotorised roller skates that were also being featured."

39

In April 1980 we were pleased to find BBC Wales interested indoing a programme based on an item in Semiconductor Circuits,but imagine their red faces when we had to explain the whole pagewas an April Fool. Llyis Electronics exploits were reported such:

"ZMOS F.E.T. (X520, X530)All the rage in UK discos later this year will be the new

range of ZMOS f.e.t.s from the Welsh firm of Llyis Electron-ics. At last the unflagging research efforts of this energeticyoung company have come to fruition, and there will be nostopping them now. Working with only limited capital andoutdated equipment, the back -room boys at Llyis have takenon the might of giants like Texas Instruments and Motorola,beating them at their own game with radical and innovativetechnology of the very highest standard. Llyis make their ownsilicon because they have found imported material to containtoo many impurities, and with the confidence encouraged bya bulging order book, they have now found it possible to takeup their option on a section of Prestatyn beach, thus ensuringa ready supply of raw material for years to come.

The new ZMOS power transistor family is typical of Llyisproducts. Designed primarily for high current, high powerapplications in disco power amplifiers, the new ZMOS familymanages to combine the best of bipolar, MOSFET and valvetechnology in one easy to use "HEX -NUT" package. TheZMOS X520 for example, is very sensitive to static chargesand requires a high current drive source, and yet it has thehighest "on" resistance in the industry and runs from a 200Vh.t. supply. All the ZMOS range feature industry -standard

This tongue-in-cheek news pieceappeared in the April issue this year

LAST CHANCEFOR 11 YEARSIn these times of regular space travel most ofus know what weightlessness 'looks' like hav-ing witnessed much television coverage of theSpace Shuttle crews.

It is a little known fact, however, that oncein every eleven years we can actually ex-perience a level of weightlessness right here onearth.

At exactly 8.17 a.m. on Monday 1st Aprilthe planet Pluto will pass directly behind theplanet Jupiter, bringing about a strong, albeitmomentary, increase in the combinedgravitational pull. At the precise momentwhen the planets are in exact spacial align-ment, a sense of elation can be felt. Indeedjumping into the air at this exact moment willbring about a real sensation of weightlessness.

This phenomenon was originally discoveredin 1899 when a Mr. Y. S. Dilloss made anincredible high jump of 3.47 metres, a recordincidentally that has never been broken.

6.3V a.c. heaters and unique "disco safety" circuits whichrender the amplifier harmless during transient musical pas-sages which might otherwise lead to auditory damage. The4kW per channel (typical using 4 x X520S) or 8kW perchannel (typical using 4 x X530S) is higher than anythingunleashed in discos before, and has forced Llyis to developcompanion loudspeakers with leather cones. Every devicecarries a government health warning, but under extremeconditions the "disco safety" circuit will cause the outputdevices to self-destruct before the 160dB pain threshold isexceeded.

The novel ZMOS "HEX -NUT" package features ports forstandard microbore central heating pipes, and for evaluationpurposes a domestic radiator and central heating pumpsystem topped up with ice water before a session will beabout ready to brew coffee two mind blowing hours later. Forserious applications a thirty gallon header tank will beneeded, a full quadrophonic system can provide centralheating for an average street if used just four hours per day.Nice one boyos!"

We presume BBC Wales were worried about the beachdisappearing!

We have carried other April fool pieces over the years and '85was no exception, the item shown was carried in News & MarketPlace, April issue.

One reader suggested that with so many people in the UKjumping at once it might put the world off balance, but unfortuna-tely our Australian readers must have been heavy enough tocounteract the effect. Only a small tremor was felt in the editorialoffice and that mainly due to IPC staff trying to beat the record!

As its title would signify, PracticalElectronics was an addition to the fam-ous family of periodicals created bypublishers George Newnes.

A word of acknowledgement to thefather of the "Practical Group" will notbe out of place here. F. J. Camm is aname that will be remembered by thou-sands of readers, and certainly by thosewith radio interests. Founded in 1932,Practical Wireless became the largestselling publication of its kind.

Fred Bennett joined Practical Wirelessin 1962, shortly after to become Assis-tant Editor. Two years later he wasassigned to work on a new publicationthat would cater for all electronics en-thusiasts. Early in 1964 the PracticalGroup moved from their original homein Tower House, just off the Strand,London to nearby Catherine St. (nextdoor to Theatre Royal, Drury Lane) andthis was to be the birthplace of PE andits home for the next few years. In 1970the Practicals moved once again, thistime into the City, to Fleetway House,Farringdon St.

During the launch period Roy Smith,then Advertisement Manager of PWtook on similar responsibility for thenew magazine. He was assisted byDavid Tilleard. Within a few months,David Tilleard was appointed ad. man-ager, a post he has held throughout tothe present day.

The first recruit to the PE editorialteam was David Barrington, an estab-lished member of the Practical Group,who commenced his early training withthe Company under F. J. Camm. Henow holds the position of AssistantEditor (Production) on PE and sisterpublication Everyday Electronics.

Gordon Godbold joined the editorialteam in 1965 and with the establish-ment of the PE workshop he becameresponsible for testing and evaluatingprojects submitted by readers, as wellas creating numerous designs himself.

Gordon was Assistant Editor from 1977to 1982.

Jack Pountney was appointed ArtEditor and continued in this role until hisretirement in August 1985. Jack wasresponsible for the design of lastmonth's front cover, celebrating 21years of PE-his last for PE.

MOVE TO POOLEWith the publication of the December'77 issue, an era closed. This was thelast issue of PE to be produced inLondon and the last to be edited by FredBennett who had held this officethroughout from the launch of the mag-azine in 1964.

The editorial department moved to anew location at Poole, Dorset and MikeKenward was appointed editor. Nonewcomer to PE, Mike joined the staffof this magazine in 1968. When a sisterpublication Everyday Electronics wascreated in 1971 he was chosen to beAssistant Editor and held this post untilleaving the company in early 1977, onlyto return six months later.

Everyday Electronics remained in Lon-don under Fred Bennett. The "sisters"had been separated and each publica-tion went its own independent way. Aswas to be expected, some rivalry devel-oped between PE and EE and the de-marcation between areas of interestmay have become a little less distinctthan before, however, the original edi-torial policy laid down for each maga-zine was, in general, maintained.

A further domestic upheaval tookplace in 1984, with the relocation ofEveryday Electronics to Poole. Thus PEand EE were re -united once more underone editor, this time Mike Kenward.Fred Bennett remained in London, act-ing as Consultant Editor until his retire-ment in September 1985.

Fred's last published work for PE wasthe first part of this feature, a fitting endto 21 years involvement with PE.

40 Practical Electronics December 1985

Just for interest the idea was one that Dr Patrick Moore-now aPE contributor-tried out on a radio programme some yearsearlier, apparently with much success! Patrick was kind enough tolet us use it in PE.

GIFTSFor many years PE produced and gave away a number of free

plastic gifts. 1979 was no exception, with two excellent toolsbeing cover mounted free with the May and October issues. Thetools were an IC Insertion Tool and an IC Removal Tool whichproved so popular with readers that both gifts were repeated acouple of years later.

Probably the most successful gift we have ever given was theInstrument Case presented free with the May '81 issue-a similarbut improved case is now sold by Maplin for £1.25, but PE wasresponsible with Lascar Electronics for its inception. The casewas cover mounted, it took up half the cover and was twice asthick as the magazine so it gave us a number of problems with dis-tribution of the issue.

We published six projects designed by Lascar to go into thecase and later other contributors used it to house their projects.The case was so popular it proved difficult to follow, and furthergifts have been mainly of the paper variety-charts like the one inthis issue, and data sheets for logic etc. Once again these havebeen very well received and we feel are of more value than a verysimple plastic item. Of course if we can come up with somethingrather special again you will benefit-we are working on it!

COVERSFor many years PE covers were virtually always given over to

depicting projects. A change was introduced in April '83 withmore wording and a split photo -approach being adopted. Thisnever worked to our entire satisfaction and we gradually movedback to the original ideas until a complete departure wasinstigated with the February issue this year.

Our covers are now mainly formed from abstract photos takenin the electronics industry, exciting covers that are in keeping withPE's standing and readership. We will continue to produceexceptions to these like this month's specially commissionedartwork of Halley's Comet which ties up with Patrick Moore'sarticle.

The Micrograsp robot with interface and 2X81-a verypopular low-cost system introduced in Dec '82

THE NEXT SEVEN YEARSOver the last few months there have been many changes in the

market place. Magazines like Electronics and Computing, Digitaland Micro Electronics and Electronics Monthly have changed,disappeared or been merged with others (Electronics Monthly hasbeen bought by IPC and merged with our sister publicationEveryday Electronics). Some companies have not withstood therecession and disappeared, with very few newcomers to replacethem.

PE has weathered the storm well and recently we have beenable to increase our page size while still introducing economies tokeep the cover price at a reasonable level-we are still cheaperthan our direct opposition and believe we represent better valuefor money.

From a firm base with many new ideas we will again moveforward with the next generation of hobbyists and engineers whomay well be designing and building with surface mountedcomponents and more I.s.i. than ever before. Stay with us-itshould be interesting.

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Practical Electronics December 1985 41

1 I

I I I I

I I I

IN

INN

IA Micro-ScopeComputerised circuit tester for audio to visualdisplay on Commodore PET or BBC

THERE are many readers who periodically build some of thepublished projects and who would ideally like to use an

oscilloscope to give a visual display of circuit activities duringtesting. Although there are low cost oscilloscopes available, theexpense is not necessarily justified if projects are only builtinfrequently. However, many people who take an interest inelectronics, probably have a computer that can be quite readilyused with an interface circuit and suitable program to give such adisplay at a considerably lower cost.

WHAT IT'S FORPrincipally this interface unit has been designed for use with the

Commodore Pet series 2, 3 and 40 -column 4, C64 and the BBC,but should be usable with any micro having an 8 -bit parallelsocket, with only minor modifications to the program given later.

The capabilities of this unit allow the sampling and display, inoscilloscope fashion (Photos G, I, J), of audio frequencies of lessthan 1Hz to greater than 70KHz, with an input amplitude rangeswitchable from 1mV up to 25V in three steps. The program hasbeen written so that in addition to waveform display, there is aread-out of peak to peak signal voltages, of the fundamentalfrequency being sampled, and also a bar graph display of a .c. ord.c. voltage levels so enabling the unit to act as a voltmeter (PhotoH). The unit will not totally simulate equipment dedicated to thesefunctions but the accuracy is sufficiently close to provide arealistic use of a computer as an electronic test aid. All figuresquoted are subject to normal component tolerance variations.

A -D CONVERTEREssentially the unit is no more than an analogue to digital

converter with variable input gain, but the inclusion of panelcontrolled biasing, and switchable frequency division givesgreater flexibility than with just an A -D on its own. IC2 is thebusiness end of the unit and is a high speed successiveapproximation A -D chip which produces an 8 -bit binary outputnumber that is relative to the analogue voltage present at its input.

Upon receipt of a convert pulse from the computer, the chipsamples the voltage level whereupon an internal oscillator, thefrequency of which is set by C4 to about 1MHz, then clocks thechip through 8 cycles. During each cycle it assesses whether thebinary bit associated with that cycle should be high or low. At theend of the eighth cycle the conversion approximation ceases and

the DAV output goes high signalling that the chip has asatisfactory answer available. The computer is programmed totake note of the DAV signal, where upon it reads the output of IC2via its eight data lines. After processing the sampled byte, thecomputer signals back to the chip to proceed with the nextsampling.

SAMPLING PARAMETERSIt will be apparent that this sampling is not instantaneous. The

maximum rate depends on the conversion clocking procedurewhich takes approximately 8 microseconds with a 1MHz clock,and the computer takes about another 50 microseconds toprocess the data. During this time the signal amplitude at the inputto IC2 has probably changed its level by the time that the nextsampling takes place. The result is that there is a step betweenthe level of each sample, and so the read out display given by thecomputer will not be a smooth waveform slope as found with anormal oscilloscope, but a succession of cliffs and platforms, theplatform representing the actual sampled voltage, and the cliff thegraph line displayed linking each sample (Photo E).

This naturally places an upper limit upon the frequency that canbe sampled. The minimum number of samples that can be used torepresent a particular frequency is two, either the signal is low or itis high, resulting in binary 0 or greater than binary 0 (Photo F). Fora better waveform approximation at least three samples perwaveform are better so that intermediate points can be plotted,and so the clocking rate should preferably be at least three timesthe sampled frequency. Here, with the computer program runningat about 15kHz sampling rate, 5kHz is about the maximum inputfrequency that will still show a resemblance to its actualwaveform. (Photo B). As the more dominant audio frequencies liebelow 5kHz this limit is quite adequate for most signal tracingtests. For input frequencies of less than 5kHz the number ofsamples per cycle will increase and so a better waveform shapecan be approximated. (Photo A). Frequencies greater than twicethe sampling frequency will still be sampled, but each samplingwill take place on different frequency cycles, and so the resultingdisplay will effectively show harmonic waveforms related to theratio of the input and sampling frequencies (Photos C, D).

The reference voltage at IC2 is set by an internal zener to about2.5V and the total number of binary output variations from the8 -bit output is 256 (29, so each bit represents a 10mV step, up to

42 Practical Electronics December 1985

TEST GEAR PROa maximum level of 2-5V. The amplitude of the input signal thoughcan be increased or decreased before it reaches IC2, and so awider input voltage range can thus be sampled.

FROM INPUT TO OUTPUTThe signal is brought in from JK 1 and can be selected by S2a for

either d.c. or a.c. coupling via Cl. S1a then selects whether thesignal comes direct from S2a with no attenuation, or via R1 andVR1 which are set for an attentuation to one tenth of the originallevel. The overall impedance at the input is about 100k, so thatthe unit will offer very little load to the circuit being examined.

IC 1a is a high impedance buffer and gain stage, where the gainis switch selectable by Slb. In positions 1 and 2 the gain is set byVR3 for x1, and position 3 via R4 and VR2 for x10. The three posi-tions of Si thus allow for a gain range of x0.1, x1 and x 10. FromIC1a the signal is routed to IC2 directly, or via the frequencydivider circuit, as selected by S4. On the latter route, the signal isgiven maximum gain by the open loop amplifier IC1b. Withsufficient gain from the preceding IC 1a, the output from IC1b willbe a full line to line swing square wave of about 10 volts peak topeak. This is suitable for driving the decade counter IC3, which

IN

BIA

tr°DAC /DC

0

AC /DC

BUFFER +0

Ode.°

RANGE

A-I)

-CONTROL OUT

-DATA X 8 OUT TO COMPUTER

-CONTROL INIREovcsl

Fig. 1. Block diagram

divides the frequency by ten and produces an equal mark -spacesquare wave at its output. R2 and R6 attenuate the output swingto a level low enough not to embarrass IC2. It is not intended thatwaveform shape should be retained at IC3, and this part of the cir-cuit is included primarily so that frequencies higher than 5kHz canbe measured by the computer. A visual display will still take place,but of course it will only be a square waveform. (Photo F(. In thismode the frequency readout should be multiplied by 10.

INPUT

JP1

0 0

22p

FS1A

R4

100k

520 51a

RI100k

VR I

25k

+ V

ICIbIL 082

0

0

D115 4148

.411),;

111MMENIINII

R7

10k

16

IC34017

11 1

R630k

S5a

+5V

OUT

C6 I 1C7 co. 01=C84706 220n 220n

CS

470p MP.

R5467

0v3,70

IC47805

C2

Min 22p

R11

200k

RIO20k

V

100k

52b

VRS

100k R1210k

C3

4).17

R9 4763

+5V

R8390

IC228 448

BBC UserCBIPBOPB 1

PB2PB3PB4PB5PB6

R2 PB7CB2GND

62k

+5V

COMPUTERCONNECTIONS

ISM

6C DAV

1C DAO D101

2C 0A1 0102

3C DA 2 D103

4C DA3 21044

PC DA4 01053 :14c DA5 0106

DA6 D107II 16

C DA7 0108

4.-C ATN ATNX12,-

GND 050

6

C433p

PET

IEEE

DAV

Fig. 2. Circuit diagram

PET

USER

CA I

PA 0

PA I

PA 2

PA3

PA4

PA 5

PA6

PA7

CB2

GND

C64

USER

FLAG 2

PBO

PB 1

PB2

PB3

PB4

P85

PB6

PB7

PA2

GND

IRE 00ecsj

NV PP 251 A2 7611 1701C 28 DELAY

e

© U.

Practical Electronics December 1985

Fig. 4. Component layout

From S4 the signal goes to the input of IC2. Here therequirements for d.c. and a.c. voltage reading are different. Fora.c. waveforms these need to swing evenly from either side of amidway point so that the computer sees approximately decimal128 in the absence of a signal. For d.c. voltages, the computerneeds to see decimal 0 for zero voltage. Consequently separatebiasing panel controls are provided. VR4 is used in the a.c. modeto set a midway point, and VR5 is used in the d.c. mode to set azero point. S2b selects between the two. Diode D1 ensures thatonly positive levels reach IC2.

NV , 259

rI..

0 di

Al LEN SYNC tS DELAY II 'liar air

POWER SUPPLYIC2 requires about 25mA of current

and so the unit has its own mainspower supply to ensure stability. Thepositive rail uses a standard full waverectifier circuit with the level regulatedto +5V by IC4. The negative rail drawshardly any current and is producedfrom a half wave rectifier circuit cou-pled to the other winding of Ti. D3drops the rectified level to -5V, withC5 and C2 ensuring adequatesmoothing.

PORTS AND PROGRAMLOCATION

The computer program has beenwritten to be automatically used any-where in memory for a CommodorePet, C64, or BBC2. On the Pet it can beused either with the IEEE 488 Port, orwith the user Port. For the C64 and BBCit is only for use on the user Port. Foruse with other machines on their IEEEor user ports, sufficient information isgiven for the relevant memory codes tobe readily changed, The program itselfis totally relocatable, and will automati-cally place itself in the highest availableRAM area and reset the memory point-ers and its own branch codes accord-ingly. It can be used in the presence ofTool Kit and Super Chip, and probablywith other programming aid chips. Thedata output socket should be selectedand wired to suit the computer beingused.

When typing in the program remem-ber to change Line 150 give the com-puter type otherwise the wrong datastatements will be read. Experiencedprogrammers can omit data lines notrelated to their machine. Note that if thecontrol unit is on the same control linesas other equipment such as disc drivesor printer, S5 must be switched off ifthose other items need to be usedotherwise IC2 will affect their correctoperation. With S5 off IC2 is in highimpedance.

A full description of the program isbeyond the nature of this article, andonly brief function descriptions can begiven. Closer examination of the pro-gram itself will reveal more of whathappens.

BASIC STARTThe BASIC program first checks to see if the existing top of

memory pointers need to be reset, and if so resets them. It thenloads the relevant data statements into the reserved area ofmemory. These data codes are the machine code routines that dothe main sampling and display. When the data has been stored inmemory, the program goes straight into the scope display routine

1.1V M 4211 DE (MD SYNC le DELAY 1.11

%. r0

NV. 1275

44 Practical Electronics December 1985

COMPONENTS ...

ResistorsR1, R4R2R3, R7, R12R5R6R8R9R10R11

100k (2 off)62k10k (3 off)4k730k39047k20k200k

All resistors !W 5%

CapacitorsC 1 , C2,C3C4C5, C6C7, C8

22p 16V electrolytic (2 off)4p7 63V electrolytic33p polystyrene470p 25V electrolytic (2 off)220n polyester (2 off)

PotentiometersVR1, VR3 25k skeleton (2 off)VR2 100k skeletonVR4, VR5 100k mono rotary (2 off)

SemiconductorsD1, D2 1N4148 (2 off)D3REC1IC1IC11C2

IC4

SwitchesS1S2, S3, S5S4

5V1 400mW Zener1 A bridge rectifier4017TL082ZN4487805

3 pole -4 waymin d.p.d.t. (3 off)min s.p.d.t.

MiscellaneousFuseholder; p.c.b. clips (4 off); 1A fuse; knobs (2 off);MAINS NEON; PCB247A; 8 -pin i.c. socket; 16 -pin i.c.socket; 18 -pin i.c. socket; mono jack socket; T' former 2x 6VA secondaries.

Constructors' NoteThe full kit of parts is available from Becker-Phono-sonics, 8 Finucane Drive, Orpington, Kent BR54ED. Price £44.50 + VAT. Postage and packing £1.50extra. The p.c.b. on its own costs £3.33. W. 0689 37821.

Copies of the following software are available on requestfrom Practical Electronics (Poole office). Please send SAE230 x 300 mm.1) Full Combined Program for PET, C64, BBC2) Optional Assembler

MVP 214 1411 SYNC D DEL V 253 M . Le ,42 )4 SYNC DU DELAY DI

al

without any synchronisation or sampling rate correction factors.A prompt is displayed if the computer thinks that the control unitis not fully switched on. If the prompt display remains on checkthat both power switch S3 and DAV switch S5 are switched on.

SAMPLING ROUTINEAs soon as the program goes to the machine code routine a

pulse is sent out on the ATN line to IC2 triggering it into itsconversion routine. Upon completion of the conversion a pulse issent back to the computer on the DAV line. During the conversionthe computer waits for this change, and upon its detection and forthe next 255 samplings, the computer successively reads theincoming binary data, stores it in successive memory locations,each time sending back another convert pulse to IC2. When all256 samplings have been stored, another routine is started inwhich any previous data on the screen is erased, and the correctsampling step points and their connecting lines are calculated anddisplayed. The maximum lines are limited to 24 vertically, 1 lessthan the maximum screen height, and 40 columns across, themaximum screen width. The remaining stored bytes are ignoredby the screen. They are, however, used in the next routine towhich the program then jumps.

FREQUENCY COUNTINGIn this routine the progam counts the number of times that the

stored number goes above and below the midway decimal 128mark. The answer is stored and becomes the base for calculatingthe main dominant frequency. The number of crossovers withinthe 256 byte block will be related to both the input and samplingfrequency rates. The latter may vary between computers and theactual position in memory. The timing factor "T" in line 230 hasbeen given a nominal value of 59, representing the 59 micro-seconds for the computer to acquire and store one byte of data. Ifthe screen readout shows a frequency that is significantly outwhen checked against a signal generator, this factor can be resetaccordingly. Do not expect precision and the figures should onlybe treated as a guide line.

NEXT MONTH: More information on the use of the Micro-scope. How to wire it up, and computer connector details.

Practical Electronics December 1985 45

THE LEADING EDGEPERILS OF PATENTING

In a separate item (see August issue) I

looked at how the public records of theBritish Patent Office tell an interestingstory about the history of Sir Clive Sin-clair's plans for wafer scale integration.The patent records also tell somethinginteresting about Sir Clive's work on theC5 car.

Under current British patent law (sincethe late 70s) patent applications are pub-lished while still pending. Before the 1977Act, pending applications stayed secret.They still do remain secret in America.

Many inventors, and firms, still have notwoken up to what the new British lawmeans to them. They get hot under thecollar when people who know the patentsystem do a simple patent search, andread technical details of an invention whichthe firm would prefer to remain secret.

Sir Clive Sinclair is well aware of theperils of patenting. He got caught early onwhen a French language patent applicationon his flat TV tube was published earlierthan he expected. Suddenly his secret waspublic knowledge. Since then Sinclair hasbeen wary about filing patent applicationsunless he is sure that the product will beready to launch by the time the applicationis published.

For a while it looked as if Sir Clive hadslipped up on his electric car. In May 1983he filed a patent application on a motorvehicle. This was due to be published onNovember 6, 1984, but even by the end ofthe year there was still no sign of thedocument. There was also still no sign ofany official launch of the vehicle.

Advance publicity from Sinclair thenpromised an unveiling of "The Sinclairelectric vehicle" on January 12. The pub-licity showed a "top secret" wrapping ona box, which we now know contained theC5 trike. Even by the day of the launch,there was still no sign of any publishedSinclair patent.

UNEARTHING THE SECRETSMysteriously the Official Register of the

Patent Office gave no clue as to why theapplication was still unpublished. The fullanswer, which I can assure you has takenquite a bit of digging to unearth, is asfollows. It's important, especially to any-one who keeps an eye on the patentrecords, to see what a competitor is doing.

The Patent Office routinely publishes allpending applications unless there are spe-cial circumstances. These special circum-stances could be routine print delays, butslippage is usually only a few weeks. If theGovernment thinks that an inventiontouches on national security then it canprohibit publication. The Sinclair C5 isunlikely to be in this category! More often,non -publication is because an inventor haswithdrawn the patent application, to pre-vent it being seen.

Until Spring 1984 the Patent Officepublished lists of patents that had beenwithdrawn (or refused by the Office) and itentered this information in a public regis-ter. But on 26 April 1984 a brief note in theOfficial Patent Office Journal said bluntlythat this practice had stopped.

Only those who are closely in touch withPatent Office matters will have seen andnoted the importance of this notice. WhenI questioned the Department of TradePress Office (which acts as spokesbodyfor the Patent Office) they knew nothingabout it.

The nitty-gritty is that the Patent Officeis now interpreting the British laws asforbidding it to give any information onpatent applications until they are pub-lished. In catch -22 fashion they can't saywhy a patent application hasn't beenpublished!

In the case of the Sinclair patent, all thesigns are that Sir Clive filed an applicationon an electric vehicle and then withdrew it,either because the technology claimedturned out to be old or because his launchschedule was delayed and he did not wantthe press to be able to read his secretsbefore the official January unveiling.

So the patent application was neverpublished and the Patent Office is not ableto say why. A casual searcher, lookingthrough the Patent Office records could betrapped into thinking the case is still pend-ing, because there is no mark in the publicregister to say it is dead.

Anyone who uses the patent system,for instance to keep an eye on whatcompetitors are doing, should note thiswell. They may also like to note that thereis one remaining loophole. If you wait untila patent application should have beenpublished and then file a form called acaveat (official fee E7) you can ask thePatent Office to tell you whether or not ithas been published. If the case has beenwithdrawn (rather than held up) the PatentOffice will state the simple fact that it hasnot been published. This 'tells an astutesearcher all he or she needs to know.

ENDOCRINOLOGYEveryone knows how easy it is to start

feeling drowsy at the wheel of a car, on along journey. Sadly we all know, if onlyfrom press reports, what can then happen.

Over the years there have been severalideas put forward for waking people upbefore they have a chance to go to sleep.For instance, a mercury switch can beattached to the head of the driver. It willbridge contacts and sound an alarm whenthe head nods down. But obviously it is

better to alert the driver before the headstarts dipping. The key to this, is skinresistance.

For a long time people have known thathuman skin on the volar surfaces (that'sthe palms of hands and soles of the feet)

exhibit a curious characteristic. Their elec-trical resistance falls as we become morealert, and rises as we become drowsy. Theobvious thing then is to monitor thisresistance and use any sudden rise totrigger an alarm.

At first sight, this looks easy. You juststrap an electrode to a finger or toe, andconnect it to a resistance -measuring cir-cuit. When the resistance rises above apre-set threshold, it closes the circuit to ableeper.

Recently a doctor, who specialises inendocrinology (the science of glands)showed the press a prototype of a circuit,which he calls Dormalert. Dr. Gerald Swyerreckons that it overcomes the kind ofpractical problems which people encoun-ter when they try to build a volar alarm.

The first problem is that different hu-mans have a different nominal skin resis-tance. It can be as high as 4 megohms oras low as 5 kilohm. So it's obviouslyimpractical to use the same alarm sensorthreshold for everyone.

Also there is a settling -in period. Whenthe electrode is first attached, the resis-tance starts high, and then falls, over aperiod of 10 minutes, before bottomingout. To be reliable, the alarm must have a10 minute delay and then self -adjust tonominal skin resistance. On Swyer's pro-totype, a knob then sets the alarm thresh-old at anything between 50 per cent and32 per cent above the nominal resistanceafter settling in and self -adjustment.

Swyer is now trying to sell the idea toany electronics firm who will manufactureit. Reading between the lines he hasn't yethad too much success, and the pressconference was obviously called to stimu-late publicity. As a gadget for car owners,it's surely a lot more useful than noddingdogs for the back seat and stickers for thewindow to obscure the driver's view.

JUDGEMENT TIMEHats off to Swyer for suggesting some

other novel uses. The volar alarm wouldkeep sonar and radar operators awake, forinstance in air traffic control. It would alsostop people in charge of oil and chemicalplant process controls from dozing off.

I particularly like Swyer's suggestionthat it would be useful to keep audiencesand committee members awake duringboring meetings. When the House of.Lords is televised, half of them seem to beasleep.

Judges, too, might be interested. For-mer Lord Chancellor, Lord Elwyn -Jones,said recently, "One of the dangers of sittingon the woolsack is falling asleep." Quitehow people will react to the sound andsight of a judge in court suddenly bleepingand sitting bolt upright remains to be seen.

BARRY FOX

46 Practical Electronics December 1985

all in your

JANUARYissue!

LOW COST...

SpectrumSPEECH

Synthesiser& 8 Bit I/O Port

It only takes £18 and a hot iron to make a Spectrumtalk, and the boys to do it are the SP0256AL2 and the280A PIO. They can persuade ZX81s, too!

MODULAR MIXERModular design permits countless combinationsof mono or stereo signal controllers. Featuresinclude voltage controlled signal paths, selectivefiltering andpanning facilities.

o/c.,

.INPUT LE vi.

LOW

MicroelectronicsEducation ProgrammeThe MEP was established in 1980 to assist education to prepare children for life in anera of microelectronics. We take a look at MEP-what it is doing, why and how.

ELECTRONICSROBOTICS MICROS - ELECTRONICS INTERFACING

JANUARY 1986 ISSUE ON SALE FRIDAY, DECEMBER 6

Practical Electronics December 1985 4

U.K. £13.00Overseas f15.00

COMPLETEAND POST

THISORDER FORM

TODAY!

PRINTED CIRCUIT BOARD SERVICEPrinted circuit boards for certain PE constructional projects arenow available from the PE PCB Service, see list. They are fully .

drilled and roller tinned. All prices include VAT and postage andpacking. Add Cl per board for overseas airmail. Remittancesshould be sent to: PE PCB Service, Practical ElectronicsEditorial Offices, Westover House, West Quay Road,Poole, Dorset BH15 1JG. Cheques should be crossed andmade payable to IPC Magazines Ltd.

Please note that when ordering it is important to give project title,order code and the quantity. Please print name and address in BlockCapitals. Do not send any other correspondence with your order.

Readers are advised to check with prices appearing inthe current issue before ordering.NOTE: Please allow 28 days for delivery. We can onlysupply boards listed here.

PROJECT TITLE OrderCode

Cost

Spectrum Autosave MAR '84 403-01 £2.90

Sustain Unit 405-02 £2.90Audio Signal Generator MAY '84 405-03 £4.28

405-04 £2.90

Cross Hatch Generator JUNE '84 406-01 £3.52

Simple Logic Analyser I 407-01 £7.73EPROM Duplicator JULY '84 407-02 £3.74Alarm System 407-03 £3.19Oscilloscope Calibrator 407-04 £4.23

Comm. 64 RS232C Interface 408-01 £3.02Field Measurement AUG '84 408-02 £3.19

408-03 £2.90Simple Logic Analyser II 408-05 £2.93

Parallel to Serial Converter 409-01 £2.92Through the Mains Controller SEPT '84 409-02 £2.90

409-03 £2.90Logic Probe OCT '84 410-01 £2.90Computer DFM Adaptor NOV '84 411-01 £2.90Ni-Cad Charger DEC '84 412-01 £2.90Outrider Car Computer (Set of 2) JAN '85 501-01/2 £9.10Modular Audio Power System

Pt -1: Power Amp Board FEB '85 502-01 £4.19Spectrum DAC/ADC Board 502-02 £3.69

Modular Audio Power SystemPt -2: Pre-Amp/Line Driver

Main BoardHeart Beat Monitor MARCH '85

Main Circuit BoardDetector

Low Cost Speech Synthesiser

503-01503-02

503-03503-04503-05

£5.00£5.12

£8.90£6.62£3.42

Power Control Interface 504-01 £3.36Disc Drive PSU 504-02 £6.54Modular Audio Power System APRIL '85

Pt -3: Test Signal Source 504-09 £4.20Power Supply 504-10 £4.17

Amstrad Synthesiser Interface 505-01 £4.23Rugby Clock Pt -2 504-03 £24.22

504-04 £9.06MAY '85 504-05 £5.12

504-06 £9.54504-07 £5.40504-08 £10.24

CBM64 Music KeyboardKeyboard JUNE '85 506-02 £4.55Main PCB 506-03 £3.50

MTX 8 Channel A to D JULY '85 507-01 £3.92Voltmeter Memory Adaptor 506-01 £3.28Envelope Shaper AUGUST '85 508-01 £3.73Car Boot Alarm SEPT '85 509-01 £2.90RS232 To Centronics Converter 509-03 £4.95Touch control PSU 001 £3.17Exp. with Robots (double -sided) OCT '85 004 £16.91Modulated Syndrum 005 £3.80CBM User Port Expander 006 £3.93Model Railway Track Control 010 £5.44Bytebox: ROM Board (double -sided) 002 £12.75

ZIF Socket NOV '85 003 £2.90RAM Board 007 £4.95Battery Backed RAM 008 £3.74EPROM Board 009 £2.93'Special Price -Complete set of 5 boards 00A £23.00

Model Railway Track ControlReceiver Board -A 016 £3.90Receiver Board -B DEC '85 017 £4.86Receiver Board -B Ext. 018 £3.93Test Load 019 £2.90

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4 ti Practical Electronics December 1985

IZIVI) POWER AMPLIFIER MODULESPRICES INCLUDE V A T * PROMPT DELIVERIES * FRIENDLYSERVICE * LARGE S A E. 28p STAMP FO_R CURRENT LIST

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OMP100 Mk II Bi-Polar Output power 110watts R.M.S. into 4 ohms, Frequency Res-ponse 15Hz - 30KHz -3dB, T.H.D. 0.01%.S N.R. -118dB, Sens for Max output500mV at 10K, Size 355 115 65mm.PRICE £33.99 - £3.00 P&P.

OMP MF100 Mos-Fet Output power 110watts R M.S. into 4 ohms. Frequency Res-ponse 1Hz - 100KHz -3dB. Damping Factor80, Slew Rate 45V uS. T H D Typical0.002%, Input Sensitivity 500mV, S.N.R.-125dB. Size 300 123 . 60mm. PRICEPRICE £39.99 - £3.00 P&P.

OMP, MF200 Mos-Fet Output power 200watts R M S into 4 ohms, Frequency Res-ponse 1Hz - 100KHz -3dB. Damping Factor250. Slew Rate 50V 'uS. T.H.D. Typical0.001%. Input Sensitivity 500mV. S.N.R.-130dB Size 300 x 150 x 100mm. PRICEPRICE £62.99 + £3.50 P&P.

OMP/MF300 Mos-Fet Output power 300watts RIM S into 4 ohms. Frequency Res-ponse 1Hz - 100KHz -3dB, Damping Factor350, Slew Rate 60V uS. T.H.D. Typical0.0008%. Input Sensitivity 500mV. S.N.R-130dB, Size 330 >, 147 102mm. PRICEPRICE £79.99 £4.50 P&P.

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voice coil Res Freq 35Hz Freq Resp to 4KHz Sens 92dB PRICEL33 49 - /2 00 P&P ea12 300 WATT R.M.S.Disco/Sound re -enforcement etc.

.oice coil Res Freq 35Hz Freq Resp to 4KHz Sens 94dB PRICE/41 49 - f3 00 P&P ea

SOUNDLAB (Full Range Twin Conel5' 60 WATT R.M.S. HiFi, Multiple Array Disco etc.1" voice coil Res Freq 63Hz Freq Resp to 20KFir Sens 86dB PRICE (999 (1 00 P&P ea6'2" 60 WATT R.M.S. Hi-Fi, Multiple Array Disco etc.1" voice coil Res Freq 56Hz Freq Resp to 20KHz Sens 89dB PRICE /10 99. (1 50 P&P ea8" 60 WATT R.M.S. HiFi/Multiple Array Disco etc.

'," voice coil Res Freq 38Hz Freq Resp to 20KHz Sens 89d8 PRiCE 2 99 - (1 50 P&P ea10" 60 WATT R.M.S. Hi-Fi/ Disco etc.

voice cod Res Freq 35Hz Freq Resp to 15KHz Sens 89dB PRICE I16 49 - 00P&P

BURGLAR ALARMBette, to be 'Alarmed' then terrifiedThandar's famous 'Minder' Burglar Alarm System.Superior microwave principle Supplied as three unitscomplete with interconnection cable FULLYGUARANTEED.Control Unit - Houses microwave radar unit. rangeup to 15 metres adjustable by sensitivity controlThree position. key operated facia switch - off - test- armed 30 second exit and entry delay.Indoor alarm - Electronic swept freig siren.104dB OutputOutdoor Alarm - Electronic swept Freq. siren 98dBoutput. Housed in a tamperproof heavy duty metalcaseBoth the control unit and outdoor alarm contain re-chargeable batteries which provide full protectionduring mains failure Power requirement 200/260 VoltAC 50/60Hz Expandable with door Sensors. panicbuttons etc Complete with instructionsSAVE t 138.00 Usual Price £228 85BKE's PRICE .£89.99 + f4.00 P&P

Why buy a crtttection of self assembly boards,

IDEAL for Work-shops. Factories.Offices. Home.etc. Suppliedready built.

k)MP LINNET LOUDSPEAKERSThe very best in quality and value. Made specially to suit Today,need for compactness with high sound output levels Finished inhard wearing black vymde with protective corners. grille and carryhandle All models 8 ohms Full range 45Hz 20KHz Size 20"15" 12" Watts R M S per cabinet. Sensitivity 1W lmtr dB

OMP 12-100 Watts 100dB. Price f 149.99per pair.OMP 12-200 Watts 102dB. Price f199.99per pair. Delivery Securicor £8.00 per pair

4

19" STEREO RACK AMPS 1 K -WATTWSLIDEDIMMER

* Control loads upto 1 Kw* Compact Size

Professional 19" cased Mos-Fet stereoamps. Used the World over in clubs, pubs,discos etc. With twin Vu meters, twintoroidal power supplies, XLR connections.MF600 Fan cooled. Three models (RatingsR.M.S. into 4ohms). input Ser,s, 775inV

MF200 (100 + 100)W. £169.00 SecuricorMF400 (200 + 200)W. £228.85 DeliveryMF600 (300 + 300)W. £274.85 £10.00

* Easy snap in fix-ing through panel/cabinet cut out* Insulated plasticcase* Full wave con-trol using 8 ampmac* Conforms to

BS800 Suitable for both resist-ance and inductive loads In-numerable applications inindustry. the home. anddisco's. theatres etcPRICE £13.99 - 75p P&P4

zelb.

BSR P295 ELECTRONIC TURNTABLE Electronic speed control 45 & 33' P m PiusMinus variable pitch control Belt driven * Alu-minium platter with strobed rim Cue lever * Anti'Skate (bias device) * Adjustable counter balanceManual arm Standard cartrige fixings *Supplied complete with cut out template D.0Operation 9.14v D.C. 65mA

Price £36.99 L3 00 P&P.

ADC 04 meg cartnd e for above Price £4.99 ea

PIEZO ELECTRIC TWEETERS MOTOROLAJoin the Piezo revolution The low dynamic mass Inc voice coil) of a Piezo tweeter produces animproved transient response with a lower distortion level than ordina.y dynamic tweeters As acrossover is not required these units can be added to existing speaker systems of up to 100 watts(more if 2 put in series) FREE EXPLANATORY LEAFLETS SUPPLIED WITH EACH TWEETER.

TYPE 'A' (KSN2036A) 3" round with protective wiremesh, ideal for bookshelf and medium sized Hi lespeakers Price /4.90 each - 40p P&PTYPE '8'1KSN1005A) 3'2" super horn For generalpurpose speakers. disco and P A systems etc Price

5.99 each 40p P&PTYPE 'C' (KSN6016A) 2" , 5" wide dispersionhorn For quality Hi-fi systems and quality discos etcPrice £6.99 each - 40p P&PTYPE '13' (KSN1025,41 2" -,6" wide dispersionhorn Upper frequency response retained extendingdown to mid range I2KHz) Suitable for high qualityHi-fi systems and quality discos Price £9.99 each- 40p P&PTYPE 'E' (KSN1038A) 33," horn tweeter withattractive silver finish trim. Suitable for Hi-fi monitorsystems etc. Price /5.99 each 40p P&PLEVEL CONTROL Combines on a recessed mount ing plate, level control and cabinet input lack socket85 85 mm Price £3.99 - 40p P&P

PAOITItt HOBBY KITS. Proven designs including glassfibre printed circuit board and high qualitycomponents complete with instructions.

FM MICROTRANSMITTER MUG) 90/105MHz with very sensitivemicrophone. Range 100/300 metres. 57 x 46 x 14mm 19 Yoh)Price: (8.62 + 75p P&P.3 WATT FM TRANSMITTER 3 WATT 85/115MHt varicap controlledprofessional performance. Range up to 3 miles 35 x B4 x 12mm112 volt) Price: /14.49. 75p P&P.SINGLE CHANNEL RADIO CONTROLLED TRANSMITTER/RECEIVER 27MHz Range up to 500 metres. Double coded modulation.Receiver output operates relay with tamp/240 volt contacts. Ideal formany applications. Receiver 90 x 70 x 22mm 19/12 volt) Price:(17.82 Transmitter 80 x 50 x 15mm 19/12 volt). Price: (11 29P&P - 75p each. S.A.E. for complete list.

t'411 14 -

3 watt FMTransmitter

POSTAL CHARGES PER ORDER £1.00 minimum. OFFICIALVISA ORDERS WELCOME. SCHOOLS, COLLEGES. GOVERNMENT

BODIES. ETC PRICES INCLUSIVE OF V.A.T. SALES COUNTERVISA ACCESS. C.O.D. ACCEPTED.

STEREO DISCO MIXERSTEREO DISCO MIXER with 2 - 5 band L &R graphic equalisers and twin 10 segmentL E D Vu Meters Many outstanding features5 Inputs with individual faders providinguseful combination of the following -3 Turntables (Magi 3 Mics, 4 Line plus Micwith talk over switch Headphone MonitorPan Pot L & R Master Output controls Out-put 775mV Size 360. 280 x 90mm

Price £1 34.99 - (3 00 P&P

AU citAuf,410

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UNIT 5, COMET WAY, SOUTHEND ON -SEA,ESSEX. SS2 6TR TEL: 0702-527572

Practical Electronics December 1985

A complete fantasy adventure gamemagazine for the young and young atheart!To play the game you just need dice,pencil and paper, plus lots ofconcentration and luck.Exciting, entertaining and absorbing.Bound to keep the kids quiet forhours!

FREEfull -colour

POSTE(approx. 40x 29 cms)

ANDPAIR OF%DICEBritain's leastexpensivefantasy adventuregame magazine.

THE MINES OF MALAGUSIN PROTEUS No. 2

Practical Electronics December 1985

INDEXJANUARY 1985 TO DECEMBER 1985

VOLUME 21

CONSTRUCTIONAL PROJECTS

A to D Converter, MTX 8 -Channel July 11Alarm, Car Boot Sept 22Alarm, Radar Security Jan 49Amplifier, Modular Power System Feb 10, Mar 40,

April 23Amstrad Synthesiser Interface by R.A. Penfold May 10Analogue/Digital Waveform Generator by Tom Gaskell

BA(Hons) CEng MIEE June 22Audio Power System, Modular... Feb 10, Mar 40, April 23Automatic Fish Feeder by Mike Abbot Aug 28Auto Shut -Dawn Multiple Regulator by Tom Gaskell

BA(Hons) CEng MIEE Mar 19

BBC Disc Drive PSU April 18BBC Speech Synthesiser Mar 31, June 49Bytebox by Ray Stuart Oct 10, Nov 26

Car Boot Alarm by D. Stone Sept 22Car Computer by S.H. Cousins BSc PhD and P.D.

Wilson BEng Jan 24CBM64 Music Keyboard by R.A. Penfold June 26Chorus Flanger, Mono/Stereo Jan 10, Feb 59Clock, Rugby Controlled April 47, May 53Commodore User Port Expander by R.A. Penfold... Nov 50Computer Envelope Shaper by R.A. Penfold Aug 10Cylinder Thermostat by Mark Stuart May 38, Oct 9

DAC/ADC Board, Spectrum Feb 15D.C. Motor Drivers Feb 31Digital Delay & Sound Sampler by John M.H. Becker

June 40, July 44, Aug 38, Sept 50Digital Timer by Tom Gaskell BA(Hons) CEng MIEE Aug 50Disc Drive PSU by J.R.W. Barnes April 18, Sept 9Disco Lights Controller by John M.H. Becker Nov 45,

Dec 9, 24

Envelope Shaper, Computer Aug 10Experimenting with Robots by Mike Abbott Sept 10,

Oct 46, Nov 42, Dec 10

Fish Feeder, Automatic Aug 28Flanger, Mono/Stereo Chorus Jan 10, Feb 59F -V Converter, Signal Generator and Feb 34

Heart Beat Monitor by P. Leah Mar 10Hi-Fi Stereo VCA System by Tom Gaskell BA(Hons)

CEng MIEE July 16High Performance Stepping Motor Driver Dec 10

Increasing Lamp Life by E. W. Hunter July 20Interface, Amstrad Synthesiser May 10Interface, Power Control April 10Interface, Serial to Parallel Sept 46Interface, Teleprinter May 26Interface, 5 -Channel General Purpose Sept 10,

Oct 46

Keyboard, CBM64 Music June 26

Lamp Life, Increasing July 20Lights Controller, Disco Nov 45, Dec 9, 24Low Cost BBC Speech Synthesiser by A. Foord Mar 31,

June 49

Memory Adaptor, Voltmeter July 28Mentor and Neptune Robots Feb 49, Mar 48

Microcomputer "Watchdog" Timer by Tom GaskellBA(Hons) CEng MIEE Jan 61

Microprocessor Controlled D.C. Motor Drivers byTom Gaskell BA(Hons) CEng MIEE Feb 31

Micro -Scope by John H. Becker Dec 42Model Railway Track Control by J. Mi/ne Nov 10,

Dec 32Modular Audio Power System by M. Tooley BA and

D. Whitfield MA MSc CEng MIEE Feb 10, Mar 40,April 23

Modulated Syndrum by R.A. Penfold Oct 32Mono/Stereo Chorus Flanger by John M.H. Becker Jan 10,

Feb 59MTX 8 -Channel A to D Converter by R.A. Penfold July 11

Neptune and Mentor Robots by Richard Becker &Tim Orr Feb 49, Mar 48

Noise Gate and VCA, Stereo May 14

Power Control Interface by R.A. Penfold April 10Power Supply "Watchdog" by Tom Gaskell

BA(Hons) CEng MIEE April 58PSU, Disc Drive April 18, Sept 9PSU, Touch Control Oct 28

Radar Security Alarm Jan 49Railway Track,Control, Model Nov 10, Dec 32Regulator, Auto Shut -Down Multiple Mar 18Remote Sensing Thermometer by Tom Gaskell

BA(Hons) CEng MIEE May 22Robot Eyes, Squint Nov 42Robots, Experimenting with Sept 10, Oct 4:'Robots, Neptune and Mentor Feb 49, Mar 48Robots, RUR Hobby June 10, Aug 16RS232 To Centronics Converter by Tom Gaskell

BA(Hons) CEng MIEE Sept 46

Signal Generator and V -F Converter by John M.H. BeckerFeb 34

Sound Sampler and Digital Delay June 40, July 44,Aug 38, Sept 50

Spectrum DAC/ADC Board by R.A. Penfold Feb 15Speech Synthesiser Mar 31, June 49Stepping Motor Driver, High Performance Dec 10Squint Robot Eyes Nov 42Stereo Noise Gate and VCA by John M.H. Becker May 14Syndrum, Modulated Sept 37

Teleprinter Interface by B. Drake May 26Thermometer, Remote Sensing ' May 2?Thermostat, Cylinder May 38, Oct 9Timer, Digital Aug 50Timer, Microcomputer "Watchdog'. Jan 61Touch Control PSU by R.A. Penfold Oct 28Track Control, Model Railway Nov 10, Dec 3?

User Port Expander, Commodore

VCA, Stereo Noise Gate andVCA System, Hi-Fi StereoVoltmeter Memory Adaptor by Jan Erik Borge

Waveform Generator

8 -Channel A to D Converter, MTX

Nov 50

May 11July lsJuly 2R

June 22

July 11

Practical Electronics December 1985 51

GENERAL FEATURES

Alarm Systems --DIY Buyer's Guide by Brian ButlerSept 25

BBC Micro Forum by D. Whitfield MA MSc CEngMIEE Mar 36, April 40, May 44, June 34, July 24,

Aug 44, Sept 36, Oct 50, Nov 55, Dec 36BBC Micro Printer Software by Michael Tooley BA &

David Whitfield MA, MSc CEng MIEE May 46

Cellular Radio by Barry Fox Jan 44

Electronics At The BBC by Chris Kelly May 32

Halley's Comet by Dr. Patrick Moore 28

INGENUITY UNLIMITED Jan 40, Feb 42, Mar 26, June 39,July 50, Aug 52, Oct 40,

Accented Beat Metronome Jan 42

Bar -Graph Display Jan 41

Din Lead Tester Feb 44Dual LED Logic Probe Jan 42

Electronic Dice Jan 43Electronic Seismograph Mar 50

Intelligent Level Crossing Warning LightsController July 50

Interval Timer Aug 52

Logic Recorder Feb 43

Op -Amp Sign Changer June 39

Shop Counter Bell Mar 26

Telephone Bell Ringer Oct 40Telephone Monitor Aug 52Thermister Thermometer Feb 42Video Timer Interface Jan 40

Wide Range High Current Supply Jan 40

ZX Spectrum Buffered Input Port (6 Bit) Feb 43

7 -Segment Logic Probe July 51

Introduction To Microprocessor System .. Oct 20, Nov 20,Dec 16

IVAX Review by Phil Dane Oct 42

Lasers and Holograms by Richard Barron Jan 30

Mars Electronics by Richard Barron Mar 22Micro Bus Jan 67, Feb 65Microwriter by Tom Gaskell BA(Hons) CEng MIEE Feb 22Modems by M. Tooley BA and D. Whitfield MA MSc

CEng MIEE June 14, July 32, Aug 24, Oct 9

Printers -Buyer's Guide April 30Plotter Review by D. Whitfield MA MSc CEng MIEE Sept 20

Robotics Review by N. Clark July 27, Aug 46, Sept 19,Oct 26, Nov 18, Dec 20

SEMICONDUCTOR CIRCUITS by Tom GaskellBA(Hons) CEng MIEE Jan 59, Feb 28, Mar 17,

April 56, May 19, June 19, July 14, Aug 47, Sept 44Baud Rate Generator (4702B) Sept 44

Data Converter (ZN435) June 19

Power Op -Amps (TCA365 and TCA2365) ...Feb 28Programmable Delay Timer (LS7210) Jan 59Programmable Voltage Detectors ICL8211CPA and

ICL8212CPA April 56

Quad Supply and Line Monitor (UC 3903) .... Mar 17

Temperature Sensor (LM35) May 19

Universal Timer (HEF4753B) Aug 47

Voltage Controlled Amplifier (dbx2150A) July 14

Sequential Logic Techniques by M. Tooley BA andD. Whitfield MA MSc CEng MIEE Jan 18, Feb 55,

Mar 54, April 14Serpent Review by Dick Becker & Roger Gay Sept 39Speech 64 Review by R.A. Penfold June 37

Vernon Trent at Large Jan 54, Feb 67, April 54

Why Fibre Optics by Eric Hoffman July 40

21 Years of Electronics by Fred Bennett &Mike Ken ward Nov 32, Dec 38

NEWS AND COMMENTBAZAAR . . ... Jan 16, 33, Feb 18, 48, Mar 16, April 29,

May 49, June 33, July 31, 43, Aug 35, Sept 35, Oct 19,Nov 41, Dec 23

BOOK REVIEWS July 38, Oct 36

EDITORIAL ....Jan 7, Feb 7, Mar 7, April 7, May 7, June 7,July 7, Aug 7, Sept 7, Oct 7, Nov 7, Dec 7

INDUSTRY NOTEBOOK Jan 17, Feb 21, Mar 59,April 52, May 50, June 24, July 19, Aug 15, Sept 18,

Oct 16, Dec 15

LEADING EDGE by Barry Fox Jan 64, Feb 25, Mar 31,April 44, May 58, July 49, Aug 36, Sept 16, Nov 16,

Dec 46

NEWS AND MARKET PLACE Jan 8, Feb 8, Mar 8,April 8, May 8, June 8, July 8, Aug 8, Sept 8, Oct 8,

Nov 8, Dec 8

PCB SERVICE.. Jan 57, Feb 68, Mar 60, April 60, May 59,June 52 July 52, Aug 53, Sept 53, Oct 52, Nov 58,

Dec 48

POINTS ARISINGJan 9, Feb 9, Sept 9, Oct 9, Nov 9, Dec 9

Automatic Bilge Pump (Oct '84-I/U) Jan 9Cylinder Thermostat Oct 9Disc Drive PSU Sept 9Disco Lights Controller Dec 9Modems Oct 9Ring Modulator (Dec '84) Feb 9Rugby Clock Nov 9

READOUT Sept 52, Oct 18, Nov 52,

SPACEWATCH by Dr. Patrick Moore OBE ..Jan 56, Feb 40,Mar 52, April 28, May 24, June 32, July 30, Aug 34,

Sept 34, Oct 38, Nov 40, Dec 22

STRICTLY INSTRUMENTAL by K Lenton-Smith Jan 66,June 50,

SPECIAL OFFERSCrotech Oscilloscopes Mar 28, April 26 Quasar Cassette Deck Jan 27

52 Practical Electronics December 1985

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0356 LA1240 5.75 STK014 £625 TA7201 02.00 UPCI185H £220 2SBI56A £0.95 2SC79I £1.75 2SC2570 E035LM2917N £175 co co

BA313 5.75 L41320 550 STK015 OM TA7202P 12.00 UPCI186 EOM 25E1171 £120 2SC792 F215 2SC2577 £1.90BA318 £130 LA1365 E120 STK016 £4.75 TA7203P 510 UPCIIB7V ELM 208172 MAO 2SC799 £1.75 2SC2578 £220 '''''''.5 '''''''' '''' a 70 , 'oar, , -, ..1,84 As A.° h."' ''''''''''BA402 0175 LA1368 ELM STK0213 £4.50 TA7204P E1.10 UPC1230H 5-50 208173 E035 200828 £029 2SC2579 C2.20 Meese ado alp post and paciongl'and Own MO 15% VAT to totalBA511A ELIO LA1460 £1.95 STK022 525 TA7206AP £1.10 UPC1350c. £120 208187 10.45 204839 £035 2SC2580 f2.20 Caters or appantmont oponen9 on,.. Wom 5pm Mon in 9 12 SotsBA5I4 5.75 LA2200 £1.75 STK041 5.50 '7472076 £150 UPC1353C £1.75 2S8341V £2.60 2SC840 5.50 20024 5.50 Missed Bane Hoklays)

64521 E1.75 LA3101 £1.60 STK077 (3.95 TA7206P 550 UPC1363C 550 25E1364 5.80 2SC856 5.60 2SD72 5.60VISA.ACC£55BA527 5.50 LA3155 £0.95 STK078 650 TA7210 6.00 UPCI365C 6.00 258365 580 2SC867 £2.75 20E1170 5.60

BA5328A536

£150E215

143I60IA3201

£13.93

f0.95STK080STK082

E720£1.15

TA72I4P7472156

E250£1.110

UPC1485C660277

£1190550

20E4370

20E3405£0.90£0110

2SC900204923

5I5£050

2S0187250313

5.660£0.95

TMNACCEPTEELEPHONED

mu) )50) T. POWELL,BA6I2 ELIO LA3300 £1.40 STK006 1325 TA7217AP E1.20 2013407 E2.65 2SC928D200315 E1.80BAI310 E1.75 LA3301 £120 STK433 01.75 1472206 61.75 TRANSISTORS 2SB422 foio 2509290 £030 200325 f0.65 16 PADDINGTON GREEN,BAI320841330

£1.25£1.75

LA33501.43361

£120E1.10

STK433STK435

5.50510

TA7222APTA7223P

£120£135

2SAI22SA15

5.50550

2SB4262513449

UME3.70

2SC93302SC931D

£033£225

2SD348250352

14505.60 LONDON W2 1LG

CX0642CXosse

£050f2.50

LA40306LA40316

E200£1.40

STK436STK437

5.00530

TA7224PTA7225P

amMO

2SA522SA70

E050f0.75

2013463

208467535£1.95

2SC9452SCI030

ELM0.35

250371200389

"3°£395

Tel 01-723 9246 (Answerphone)CX0758 1220 LA4032P E1.40 STK439 5.50 TA7226P £220 2SA71 £0.60 258468 1325 2SC1034 E3.75 20046713 E033 ITEMS DESPATCHED WITHIN 48 HOURS

5 A MO n MOSFET AMPLIFIERS

UNBEATABLE PRICES!!!

sorion AP 100 SLAVEr

' T EIEID API00

SLAVE MODEL

AP100 100WRMS £69AP200 200W RMS £89

2 INPUT GENERAL PURPOSEMODEL

AP100SAP200S

* TREBLE/BASS EACH CHANNEL * INDIVIDUAL* MASTER PRESENCE

Write or phone for a FREE BROCHURE onthese incredible amplifiers

P.E HYPERCHASER

£79

P.A. MODEL* 6 INPUTS* 3 CHANNELS* ECHO IN/OUT

VOLUMES

AP 100M £99AP 200M £119

£84.9514 CHANNEL PSEUDO INTEWGENT

LIGHT UMTI* 16 Programmes or Manual Flash Buttons* ManuaLAuto Programme * Strobe Ouputs

1* Individual Dimming * Sound To LightNot lust a light unit but a sophisticated & comprehensive effects unit A full kn of parts includingP.C.B., Facia, Case, etc. Repnnt of article on request

P.E.STAR DESK £2098 + 4 CHANNEL UG1R MIXING DER(

*8 Channel Twin Preset Mixer * Strobe Outputs*4 Independent Channels * 4/8 Channel Sequences* 8 Programmes * Manual Rash Buttons* IKW Output/Channel Ican be boosted to 2KW/Ch)* Timed Crossfade * Soft/Hard Sequence

A truly magnificent unit ideal for clubs, groups, drama, etc. A full kit of parts inc. PCB, Facia, Case,etc. Reprint of article on request

BENSHAM RECORDING LTD327 Whitehorse Road, Croydon, Surrey CRO

(01) 684 8007 gam-5pm. Mon -Sat.All prim inlcucle VAT and Post & Packing. Please allow 14 days for delivery

You can depend on

to supply the finerange of test &measurement

gear by

FREE 44 PAGEPRICED ANDILLUSTRATEDCATALOGUE ONREQUEST Over 6000 items stocked

C

counters multimeters scopes signalgenerators etc.

ELECTROVALUE LTD 28 St. Jude's Road. Engletield Green, Egham.Surrey TW20 OHB Phone Egham (0784) 33603 Telex 264475

North Branch. 680 Burnage Lane. Manchester M19 1NATelephone 061 432 4945

Please mention this publication when replying

BRITAINS FOREMOST QUALITY COMPONENT SUPPLIERS

Practical Electronics December 1985

When replying to ClassifiedAdvertisements please ensure:

(A) That you have clearly statedyour requirements.

(B) That you have enclosed theright remittance.

(C) That your name and addressis written in block capitals,and

(D) That your letter is correctlyaddressed to the advertiser.

This will assist advertisers inprocessing and despatching orderswith the minimum of delay.

RECEIVERS AND COMPONENTS

BOURNEMOUTWBOSCOMBE. Electronic components special-ists for 33 years. FORRESTERS (NATIONAL RADIOSUPPLIES). Late Holdenhurst Road. Now at 36. AshleyRoad, Boscombe. Tel. 302204. Closed Weds.

TURN YOUR SURPLUS capacitors. transistors, etc into cash.Contact COLES HARDING & CO., 103 South Brink.Wisbech, Cambs, Tel. 11945 584188. Immediate settlement.

OMEGA SERVICES97 Stricklandgate, Kendal. Cumbna LA9 RA4

Resistor e t 4 wan CF 54. 100 plus 1pFensos e 4001 20p 4011 20pMemories a 2764 22.10 6264 LP15 24.50 6116 LP15 21.70Regulators a 7805 39p 7842 29p 27128 25 133.50

27256 250 29.70 4164 15 90pPresets a 10K HOZVRT 10p0 SUFI le 25W sociset angle 22.30Eurocard a 32W ',rug arge 21.03IC Sock a 14W 14p 28W 28pPSU a 500rnA Reg. Adis 9. 25.00

Pnces ph. 60p cars plus VATTelephone 0539 32132 (also Indust supplier)

SMALL ADSThe prepaid rate for classified advertisements is 36 penceper word (minimum 12 words), box number 60p extra.Semi -display setting £12.00 per single column centimetre(minimum 2.5 cms). All cheques, postal orders etc., to bemade payable to Practical Electronics and crossed"Lloyds Bank Ltd". Treasury notes should always be sentregistered post. Advertisements, together with remittanceshould be sent to the Classified Advertisement Dept.,Practical Electronics, IPC Magazines Limited, King'sReach Tower, Stamford St., London SE1 9LS. (Telephone01-261 5846.)

NOTICE TOREADERSWhilst prices of goods shownin classified advertisements arecorrect at the time of closingfor press, readers are advised tocheck with the advertiser tocheck both prices andavailability of goods beforeordering from non -currentissues of the magazine.

RECEIVERS AND COMPONENTS - CONT.

Carbon Film Resistors VrW E24 series 0.5IR to 10M0 - 1p

100 off per value - 759 IMO oft in even hundreds per value - E7

Metal Film 1/4W 10R0 to IMO 5% El2 series -2p I% E24 senes -3pBC107/8/9 - 12p 8C547/85 - 7p 13C557/0/9/ - 7p BC182L, 1841. - 10pBEY5135152 - 20p 263055 - 50p TIP31A, 32A - 25p TIP42 - 40p

Tantalum bead subminiature electrolytics (MtdsNotts)0.1/35, 0 2235. 0 47.35 1 035. 3 116, 4 716 - 14p 4.7,35 - 15p

2235, 4.7.25, 10'6 - 159 4 735, 6.816 - 169 10/18 226 - 209

Aluminium Electrolytics (MfdsNolts)150, 2.250 4.7/25, 4.7/50, 1816, 10/25, 1850 - 59 22/16, 22/25 - Eip2250, 47/16, 47/25, 47150 - 6p 100/16, 10525 - 7p 10850 - 12p100/100 - 14p 220/16 - 148 22025, 22050 - 10p 47416, 470.125 - 1 1 p

100825 25p 103135. 100840. 2200125 - 35m 4700 25 70p

Miniature Polyester Capacitors 2508 Why. Vertical Mounting01, 015..022, .033, 047..068 - 4p 0 1 58015.224804148Mylar Capacitors 100V Why. Vertical Mounting E12 Series1000p to 8200p 3p 01 to .068 4p 01 5p 0 15, 0 22 69

Subminiature Ceramic Plate 100V Wkg. E12 Series Vertical Mounting29, 1P8 to 47P 39 56P to 320P -- 4p 10-, 390P to 470P 4p

Polystyrene Capacitors 63V Why. E12 Series Axial Mounting10P to 820P 39 1000P to 10,000P 4p 12,000P 5p

194148 - 2p 194002 - Op 1814336 - 6p 165404 14p W01 bridge -

25p 0A91 - 6pZener diodes E24 series 3V3 to 33V 400mW - Bp I wan - 12pL.E.D's Red. Green 8 Yellow 3mm 8 5mm - 10p 8mm - 35p20mm fuse 0.IA to 5A quick blow - 5p 5P Anti Surge - OpHigh Speed drills 08mm, 1.0mm. 1.3mm, 1.5mm, 2mm - 25p Machines12V - E6Nicads AA - 110p HP11 - f2 PP3 [4.20 Universal Chargers - EaGlass reed switches single pole make contacts - Op Magnets - 12p

VAT inclusive. Return postage 10p (free over 151. Lists free.

THE C.R. SUPPLY CO.,127 Chesterfield Road,

Sheffield S8 DEIN Tel 557771.

RESISTORS FOR SALEHigh quality imported carbon film resistors for saledirect to users/manufacturers.

0.25W mixed = 45p per 100 or E2.95 per thou0.50W mixed = 65p per 100 or E4.95 per thou

+ VAT + p&p (Discount for quantity)Most values ex stock - Phone for.list

SHAH ELECTRONICS LTD.,6 Stratheden Parade, London SE3 7SX.

01-858 4210 or 01-853 3307 (24 hrs)

HOME SECURITY

CENTURIONAL ARMS-1

Manufacturers ofProfessional AlarmEquipment, for DIY& the TRADE. Sendnow for our New 16 -page Brochure, Fullof Information & theLowest prices.

VISA

Tel (0484)

21000or 35527 24 hr.

CIPAUPUIVALAMO

01161.11000

CENTURION Dept PE93 Wakefield Rood,Huddersfield.HD5 9ABW. Yorks.

N. CENIUPION s a Pegrsteiea liademors of Centutqn

ORDER FORM PLEASE WRITE IN BLOCK CAPITALS

Please insert the advertisement below in the next availble issue of Practical Electronics for

insertions. I enclose Cheque/P.O. for E(Cheques and Postal Orders should be crossed Lloyds Bank Ltd. and made payable to Practical Electronics)

NAME PRACTICAL ELECTRONICSClassified Advertisement Dept., Room 2612,

ADDRESS King's Reach Tower, Stamford Street,London SE1 9LS Telephone 01-261 5846Rate:38p per word, minimum 12 words. Box No. 60p extra.

Company registered in England. Registered No. 53626. Registered Office: King's Reach Tower, Stamford Street, London SE1 9LS. 12/85

Practical Electronics December 1985

COURSES

FULL-TIMETRAININGCOURSES

2 YEARB-TEC National Diploma (OND)

ELECTRONICS &

COMMUNICATIONS ENGINEERING(Television & Computing)

15 MONTHSB-TEC National Certificate (ONC)

ELECTRONIC EQUIPMENT SERVICING!Television & Video,

15 MONTHSB-TEC National Certificate (ONC)

COMPUTING TECHNOLOGY

9 MONTHSB-TEC Higher National Certificate (HNC)

COMPUTING TECHNOLOGY

& ROBOTICSHIGH PERCENTAGE OF COLLEGE BASED

PRACTICAL WORKSHORT COURSES WITH PREVIOUS

KNOWLEDGENO EXTRA CHARGES FOR OVERSEAS

STUDENTS

Prospectus from:

LONDON ELECTRONICS

COLLEGE

Dept: AA, 20 Penywem Road,London SW5 9SU. Tel: 01-373 8721.

SERVICE SHEETS

BELLS TELEVISION SERVICES for service sheets of Radio, TV,etc £1.50 plus SAE. Colour TV Service Manuals on request.SAE with enquiries to B.T.S., 190 Kings Road, Harrogate.N. Yorkshire. Tel. (0423) 55885.

FOR SALE

11110LP-3 for sale all new f1.75 each; 100 or more f1.50 each.P.P. 50. Mr Potts, 23 Newport Grove. Chesterton. Newcastle.Staffs. Tel. 11782 564037.

PROMS - EPROMS - PALsEPROMS from E3.25 (2716/2732/2764 etc)

PROMS from E1.50 (13P/82S/63 series etc)PALs from £4.25 112H6/16C1/16L8 etc)Full Programming Service availableSAE for full price list (incl. RAMs etc)

Any i.e. supplied - if it exists we will find itPUS, 16 Wordsworth Drive, Cheam, Surrey SM3 811F.Phone 01.644 8095 (usually manned 0800-2000 hrs)

Private and professional enquiries welcome.

EPROMS 2516. 2716. 2532, 2732 ex. eq. £1 each. O. 1p.F 400Vcapacitors 20 for f 1.470µF 50V capacitors 10 for LI. IttF 250Vcapacitors 5 for fl. 4mm cable plus 10 for fl. Monitor ampboards f2.50. Free P&P. C.W.O. please. B. Smith. 15 FarlandsDrive, E. Didsbury. Manchester M21) ODD.

MISCELLANEOUS

THE SCIENTIFIC WIRE COMPANY811 Forest Road, London E17. Telephone 01-531 1568

ENAMELLED COPPER WIRESING 1 lb 8 oz 4 oz 2 oz8 to 34 3.63 2.09 1.10 0.88

35 to 39 3.82 2.31 1.27 0.9340 to 43 6.00 3.20 2.25 1.6144 to 47 8.67 5.80 3.49 2.7548 15.96 9.58 6.38 3.69

SILVER PLATED COPPER WIRE14 to 30 9.09 5.20 2.93 1.97

TINNED COPPER WIRE14 to 30 3.97 241 1.39 0.94FluxcoreSolder 5.90 3.25 1.82 0.94Prices include P&P VAT. Orders under E2 add 20p.

SAE for list of copper and resistance wire.Dealer enquiries welcome.

MISCELLANEOUS - CONTD.

CLEARING LABORATORY, scopes, generators, P.S.U.'s, bridges,analysers. meters. recorders etc. Tel. 0403-76236.

FREE MEMBERSHIP to new national electronics club. Fordetails and a free gift of components worth over 110 send onlyfl P&P to NCC, Woodside. Doesett Lane, Ramsden Heath.Essex CMI I LIL.

READMIT UK SPARES AND SERVICE CENTRE Cedar Electron-ics, Una 12. Station Drive, Bredeon, Tewkesbury. Glouces-tershire. Tel. (0684) 73127.

BURGLAR ALARM EQUIPMENT. Ring Bradford (0274) 308920for our catalogue or call at our large showroom, oppositeOdsal Stadium.

CABINET FITTINGSFretcioths. Coverings. Handles. Castors.Flight Case Locks & Parts, Jacks. XLRs.Bulgins, Reverb Trays. P & N mic Stands,ASS Glasstibre Horns.CELESTION POWERSpeakers

Send30p cheque'

PO for illustratedcatalogue Adam Hall (PE Supplies),

Unit G, Carlton Court, Grainger Road,Southend-on-Sea.

SUPERB INSTRUMENT CASES by Bazelli, manufactured fromPVC. Faced steel. Vast range. competitive prices start at alow £1.50. Punching facilities at very competitive prices.BAZELLI, (Dept. 23), St. Wilfreds, Foundry Lane, Halton,Lancaster LA2 6LT.

RACK MOUNTING CABINETS AND KITS. Suitable for instruments,amplifiers and general purposes. Back anodised, various sizes.heavy guage front panel with handles. with ventilation slits.Kits for.audio. CB control power supply etc at discount prices.Send large SAE for details, trade welcome. MIA Develop.ment, 68 Pearl Road, London Ell 40Z.

PROTOTYPE P.C.113, single and double sided to your artwork byreturn of post. Technical Services, 3 Westdene Way. Wey-bridge, Surrey. Tel. Walton -on -Thames 242840.

PRACTICAL ELECTRONICS KITSModel Railway Track Control Type "A" £31.95 Nov PEModel Railway Track Control Type "B £42.55 Nov PEP.E. Syndrome October PE £23.25Touch Control Power Supply October PE £28.95 * El p8pCar Boot Alarm September PE E11.90Article Reprints 609 P&P 60p unless specified

ALL PRICES INCLUDE VAT

CPL ELECTRONICS8 Southdean Close, Helmington, Middlesbrough,

Cleveland TS8 9HE. Tel: 0642 591157.Overseas 0 postage. Moe repents 60p SAE Ice pncebst ot other

avertable kiln COnlecnents. loots mi./lowers etc

To Advertise onThese PagesPhone Mandi01-261 5846

, ... 1/11

* BAKER *GROUP PA. DISCOAMPLIFIERS post £2 0 0 0 0 ' me. ... nm .1.

150watt Output, 4 input Mixer pre -amp. Illustrated E99150watt Output, Slave 500 mv. Input 3 Speaker Outputs . ER0150+150 wan Stereo. 300 watt Mono Slave 500 rev Inputs E125150 watt PA. Vocal. 8 inputs. High/Lcnv Mixer Echo Socket E129100 wan Valve Model, 4 inputs, 5 Ouuts. Chassis only E9960 watt Mobile 240v AC and 12v DC. 4-8-16 ohm+ 100v line 139Roved, Unit for Microphone or Musical Instruments E36 PP El.Electronic Edio Machine for mic/etc 135 PP El. Deluxe CM.

DISCO CONSOLE Twin Decks, mixer pre amp f145. Carr E10Ditto Powered 120 wan E198; or Complete Disco 120 watt E300.150 wan £360; 300 watt f410. Carr 130.DELUXE STEREO DISCO MIXER/EQUALISER plus L.E.D. V.U.displays 5 band graphic equaliser, left/right fader, switchableinputs for phone/line. mikeline.Headphone Monitor. Mike Talkover Switch E129 PP E2As above but 3 Deck inputs, 4 Line/Aux inputs. 2 Mk. inputs, 2Headphone Monitors, Steno Graphic + LED Display E146.P.A. CABINETS (empty/ Single 12 EU; Double 12 f40. carr E10.WITH SPEAKERS 75W 156; 90W E75; 150W (34; 200W (32.HORNEIOXES 200 Watt £32, 300 Wan 138. Post £4.COMPACT SYSTEMS 100W £90; 200W (100; 400W £150. PP E10.PAID -N -TOP 300 Watt141044 -TOP System complete £125. Can. E12.MOTOROLA PIM BEC7101110 NOM TVISTEIL 941in. square El102 Witte No crossover required 4-6-16 ohm. 74.8x31Ain E1111

CIIIMSOVERS. 1110 -WAY 3:03 cis 40 wan TIM 60 wan ES 100 watt Efi.3 wiry 30 cps/30X cps. 60 watt £151 60 watt El. 103 wan EX

FAMOUSlin MOBIri roV81117

5 n 205i4 n 6051/2 0 5till612

: 602,

6/2 n 15

6y2 in 35612 n 338 n 20

8 in 25

8 n 30

a ri 33a in 50

8 in 408 n 60

8 n 00

S in 60

0 n 30

0 n 50

0 n 15

0 n 20

0 n 500 in 500 in 600 in 3332 n 30

2 n 451 in 402 in 75

2 n 103

2 n 1202n 103

2 in ice2 n 1502 in 2m2 in X03.8 10

5 n 10)5 in 100

5n Ill5 n 2508 in 2308 n 250

METAL GRILLES

LOUDSPFJJEERS - SPECIAL PRICESMIS (PITYS/CAL =IS MANNA/ MAX FRAME DIMENSION)IT,. Mail APPLICA11001 PIKE POST

a8 Goodman Ford Car Redo CS

SoundLab th 5 Twin Cone lid Range CIOAudi. Baenne Cane Woofer C10.50

Sr

Sound. Lab wib 00,Ft .144n,

0.50Cone Full Range fit

or 15 EMI Woofer 0.50Auden Bannne Carle woofer 07.90

roGoodans Twin Coot Fir F, FA Wow CMFar East Tee Cone. H. Ft Ful Woes 133Goodroare Woofer £710Wharfedale Rol Surround vi. h. is/index M h Wooer UMI M F Ribbed Benne Cone Woder noAudlia Hi F Woofer Bea tune Cone 0650Auda, H. ri Wooler Bemire Cone 0950Sound Lab Mr Fr Twin Cone Foil Reno. 04Goodman PA A 8 Fr Systems Ele

Of 8 Far East Bass Woofer, Hr h 04SEAS Bass Woofer Hr F1 L1952limonda General Purpose 0

or 16 Coleman Desco-PA (150116 Baker Deco -Gone -PA Ellor 16 Ceiesnon Deco -PA 01

Sound Leh hen 6041. NI Range E1950wEM Woofer 06

or 8 Of 16 Baker Ten Cone fire Wad 810or 8 or 16 Ball, Deco Guear-PA MI

Baker Bass Wooer LWor 8 or 16 Baker Deco -Gum -PA 172

GOOdONVIS Woofer CMOf 16 Goceknans Deco -Grew -PA CM

H El PA 09or m Baker Deco -Gutter -PA C28

Caureaon Daco-Bess Garay rasH+ H PA -Deco enWEM Woofer Oa

Of 8 EMI 14501 WOOlOf well Tweerer C5

Ceesten Deco Group LWor 16 Baker DISCO-GUM1111 -PA 09or 8 or 16 H H Deco. Group E4950

Goodmans Disco + Group 04GOOdf.f13 Deco Group EI7

0 16 Celesoon Deco + Group 010

8in E300, 10in. 13.50, 12in. £450, 15in. ELM,18in. E7.50. Loudspesker Covering Vynak etc- Samples. S.A.E.

DISCO SOUND / LIGHT COIBTROLLERReady Built Deluxe 4 Channel 4,000 watt sound chaser +

+arme controls EM. Mk.2 16 programmes, £19. PP 12"PASTY UTE", Sound Flashing, Ught Show, 4 lamps, sea

contained unit 240v AC No other connections needed OUL PP El

MAINS TRANSFORMERS Price Post250-0-250V 80mA. 6.3V 3.5A. 6.3V 1A. E7.00 £2350-0-350V 25OrnA. 6.3V ack CT (12.00 Shrouded E14.00 E2220V 25rnA. 6V 1 Amp f3.00 220V 45mA. 6V 2 Amp f4.00 El250V 60mA. 6.3V 2A. 13.00 EtLow voltage tapped outputs available1 amp 6, 8, 10, 12, 16. 18, 20. 24, 30, 36, 40, 48. 60 EOM £2ditto 2 amp £10.50 3 amp £12.50 5 amp E16.00 £231-26-0-26-31 volt 6 amp £14.00 £2LOW VOLTAGE MAINS TRANSFORMERS E5.50 each post paid91/, 3A; 12V, 3A; 16V, 2A; 20V, 1A; 30V, 1%2A; 33V. 5A+ 17-0-17V,2A; 35V, 2A; 20-4660V, 1A; 12-0-12V, 2A; 20-0-20V, 1A; 50V, 2A.

01.50 post 50p MINIMULTI TESTERPocket sire instrument. DC volts 15, 150, 500, 1000.AC volts 15. 150, 500, 1000. DC 0.1ma, 0-150ma.Resistance 0 to 100K. De -Luce Range Doubler Meter,50,000 o.p.v. 7 v 5 or 2in. Resistance 20 meg in 5ranges. Current 50tua to 10A. 025V to 1000V DC 10Vto 1000V AC. £25.00 Post El

PANEL METERS 509A. 100pA. 5nraiA, lmA. 5mA. 100mA. 500mA.1 amp, 2 amp, 5 amp, 25 volt. VU 21/4x 2 x 11/4in. E5.50 Post 50P

ii ..'4 iPillilrx 21 ' .0.Bre 6111741 Cvl ?ltd. D.80; T8 ; 5 x2iinn. £4.00;11 x 6 x 3in. £9.50;113.4 x 6 x Sin. 01.00; 15 x 8 x 4in. E12.00.ALUMINIUM PANELS 10 s.w.g. 12 x 12in. 11.10; 14 x Sin. 11.75;6 x 4in. 569; 12 x Bin. (1.30; 10 x 7in. IIIIp; 8 x gin. 10p; 14 x 3in.72p; 12 x Sin. 10p; 16 x 10in. 2.10; 16 x Bin. E1.30.ALUM/MUM BO M& 4 x 4 x rAllin. ELM; 7 x 5 x 21/2in. CIO;3 x 2 x lie. ET; 4 x 21/2 x 2in. E1.20; 4 x 4 x 11/2in. E1.50:6 x 4 x tin. E1.110; 6 x 4 x 3in. 020; 8 x 6 x 3 in. 0.00;10 x 7 x 3in. C.O. 12 x 5 x 3in. OM; 12 x 8 n 3in. 14.30.10 x41/2x 3in. 12.110; 4x51/4x21/2in. 11.50; 4x231Ix11/2in.-1120,

HIGH VOLTAGE ELECTROLYTCS 20+20350V .16,450V 50p 2260400t1 12 32+32/500V .. 75A20/500V 75p ,8 + 8/500V El 32+32/350V .. so.32/350V 469 8+16/450V 75p 32+32+32/460V. £132/500V 95p 16+ 16f350V 75p 16+32+32/500V ....0

SINGLE PLAY RECORD DECKS. Post £2.Make Drive Model Cartridge PriceBSR Belt 12 Volt Ceramic £22BSR Rim P207 Ceramic E22AUTOCHANGER BSR Ceramic £22AUTOCHANGER GARRARD Ceramic E24

DECCA TEAK VENEERED PLINTH space for small amplifier1300O1 cut for BSR or Garrard 1B7/ein. o 141/4in. x Ain. £5. Piet El

* * * 'STOP PRESS' * * *H & H 1000 Watt stereo/mono. Professional Power

Amplifiers S5000 Reconditioned, guaranteed. £275, carriage ES

RADIO COMPONENT SPECIALISTS

OeM 3, 337, WHITEHORSE ROAD, CROYDONSUNNY, U.K Tel: 01-6114 16115iI AEI Peel Me Pilisewes. Callen Warw... [ VISA ]

Sam Ow isepeick. Eiesell Wed. Lisa Ile.

Practical Electronics December (985

a

The latest developments and a review of the AR 2002

-,rroIRER

PLUS* Christmas Presents

Radio accessories, tools and testequipment for the radio amateur.

* Broadside and Endfire AntennaSystems Part 2: the use of half -waveelements or radiators.

DECEMBERISSUE

OUT NOW

IOC KL1P

Aversatilelogisting

deviceat

budget

Attractive pocket-size unitprovides clear and simple'hands -free' operation

Simultaneously monitors the interaction of up to16 points or nodes via numbered LEDs.

Simple connection using standard 4 -point I.C. clipsupplied or a combination of clips interfaces. grabbersand probes supplied as optional extras.

Power supply taken from test circuit, either TTL (operatingvoltage +5V) or CMOS (4.5-18V).

Logic state at test point indicated by -

Logic 1 (high) LED on

Logic 0 (low) LED off

Display face of unit can be temporarily marked, using achinagraph pen. to describe circuit layout or I.C.pin-outs.

Separate overlay supplied with unit for marking alternativelayouts. Additional overlays available to facilitate build-upof 'library'.

Uses include Development testing maintenance. training

1OHNSONS (LEIGH) LIMITED

100/102 Glendale Gardens, lsigh-on-Sea, Essex SS9 2AY

INDEX TOADVERTISERS

Adcola Products Cover IIAlcon Instruments 41

Audio Electronics 31

Bensham Recordings 53

B.K. Electronics 49

B.N.R.E.S 5

Bull,J 56

Clef Products 37

Cricklewood Electronics 4

Crofton Electronics 5

Croydon Discount Electronics 5

Cybernetic Application 14

Electrovalue 53

ESR 4

G.C.H.Q. 35Grandata 4

ICS Intertext 37

Johnsons (Leigh) Ltd. 56

Maccon Systems 37

Magenta Electronics 21

Maplin Supplies Cover IVMarco Trading 35

Phonosonics 27

Powell, T 53

Powertran Cover Ill

Radio Component Specialists 55

Riscomp Ltd. 27

T.K. Electronics 4

Tandy 6

Universal Semi -ConductorsDevices 14

Watford Electronics 2, 3

BAKER'S DOZEN PACKS

Pack 04No1

2

3.

5

6

1-

£1 EACH OR 13 FOR £12All new goods. Please add

5 13 amp nng main 'unction boxes5 13 amp nng main spur boxes

25 13 amp fuses for nng mainssurface mounting switchesflush switches whitein flex line switchesin flex line switches with neons80 watts brass cased elementsmains transformers with 6v la secondaries

0 - mans transhonners well 12v Ile secondanes1 - extension speaker cabinet for 61/2" speaker2 - octal bases for relays or valves3- 1 glass reed switches4 - OCP 70 photo transistors6- tape heads, 2 record. 2 erase7 - ultrasonic transmMers and 2 dmo recovers8 - 15030 mid computer capacitors9- i d r similar ORP 12

20- duff micro switches21- mains interference suppressors22 - 25 wan crossover units23 - 40 wan 3 way crossover unit25- of each wafer switches - 6p 2 way.

4p 3 way. 2p 6 way, 1p 12 way26 - tape deck counters27 - 6 digit counter 12v28 - 6 digit counter mains voltage29- BOAC in flight stereo unit Is hi30- NICAD banery chargers31 - key "welch with key32- humidity switches33- aerosol cans of ICI Dry Lubricant34 - 96 x 1 metre length colour -coded wires35 - 4 battery operated model motors36- 2 air spaced 2 gang tuning condensors37 - 2 solid diaelectnc 2 gang tuning condensors38 - 10 compression trimmers39- I Long & medium wave tuner kit42. 6 rocker switches 10a mains SPOT45. I 24 hour time switch mains operated ISW)46 - 1 6 hour clockwork time switch47 2 2 lever switches 4 pole changeover up and

dino down48 - 2 6v operated reed switch relays49 - 10 neon valves - make good night lights50- 2 x 12v OC or 24v AC 3C 0 relays

£1 post if order under £20Pack StyNo.51 t x 12v 2C 0 very sensitive relay52 1 e 12v itC 0 relay53- 2 mains operated relays 3 x Ba changeovers

Isecond handl10 rOws of 32 gold plated IC sockets natal 320

socketsl1 miniature Uniselector with circuit for

electric jigsaw pale57 - 5 dolls house switches58 2 telephone handsets59 2 flat solenoids to make current

transformer etc60- 5 ferrite rods 4" x 5" - 16' Ma61 5 ferrne slab aenals LW 6 MW62- 4 200 ohm ear pieces63 - 1 Mullard Thyristor trigger module64 - 10 assorted knobs 1,4 spindles80172 10 12v 6w oulbs Phdrps m e s00174 2 End of travel ryo switches mounted on

metal plate 10A 250v80175 I 203 rpm motor. mains operated. 2wBD176 4 Heavy duty push switches ideal for foot

operation 3A 250vBD177 5 Lilloput bulbs 12v130178 3 Oblong amber indicators with lilliputs 12vBD/ 79 3 Oblong amber indicators with neons 240v80180 6 Round amber indicators with neons 240v80181 100 P V C grommets for 341" hole60182 1 Short wave tuning condenser 50 pf with I/4"

spindle130183 1 Two .gang shoe wave tuning condenser

with 1/4' spindle80124 1 Three gang tuning condenser each section

500 pf with trimmers and good length 191"spindle

B0185 4 Ferree rod aerials 2" e 38" rods with longand medium wave coils

00186 I 3 wafer switch 10 pole 2 way, 12 pole 3 way,9 pole 4 way. 6 pole 6 way. 3 pole 12 way.your choice

00187 2 2 water switches 8 pole 2 way, 8 pole 3way, 6 pole 4 way. 4 pole 6 way, 2 pole 12way any 2 your choice

1 Plastic box sniping metal front, size160,95nen average depth 45mm

6 B C lamp holder adaptors

54

ss

BDIM

80191

You can order night or day: 'phone 0444 454563

J.BULL (Electrical) Ltd.(Dept. PE), 34-36 AMERICA LANE,HAYWARDS HEATH, SUSSEX RH16 3QU.

Established30 YEARS

56

Published on approximately the 7th of each month by IPC Magazines Limited, Westover House, West Quay Road, Poole, Dorset BHI5 I1G. Printed in England by Ma.'orgunciale MagazinesLtd.. Andover, Hants. sole Agents for Australia and New Zealand - Gordon and Gotch (Asia) Ltd., South Africa - Central News Agency Ltd. Subscriptions INLAND E13 and OVERSEAS 1:15payable to IPC Magazines Ltd., "Practical Electronics" Subscription Department, Room 2816, King's Reach Tower, Stamford Street. London SE I 91..S. PRACTICAL ELECTRONICS is soldsubject to the following conditions. namely that it shall not, without the written consent of the Publishers first having been given, be lent, resold, hired out or otherwise disposed of by way of Tradeat more than the recommended selling price shown on the cover, and that it shall not be lent, resold, hired out or otherwise disposed of in a mutilated condition or in any unauthorised copier by wayof Trade or affixed to or as part of any publication or advertising, literary or pictorial matter whatsoever.

I .1\ 1

ROBOTICSPowertran's"Hebot II" and"MicroGrasp" kitsoffer unrivalledvalue for moneyto

colleges,schools andindividual enthusiasts.Put the kit together,your micro and oHebot II cvarie

SICpendent

lashing "eyeretractable pComplete kit £ 9.95Universal computer intboard kit £5.50 + VAT

a bewilderingns u control ofp am. Fea res includ.ntrol if two eels,two- hoot r and a

lpfiNciAr\-\

0E

I

Powertran's range of isuality auproducts offers top quality at tlrw, lowprices. All the products are finisrugged metal cabinets suitarack mounting or as fr t g units.

Hea honlifr2 x 3 sets s reophon s from either ortwo it uts. £20 + VAT(Metal rk and PC only)

Synth MixStereo keyboard mixerwith 3 aux sendseach of its 6 in s£30 + V(metalwork

only)

MicroGraspis a fullyprogrammable

electric robot arm with closeloop feedback for po

positioning.can

Robot k withpower s pply£150 + ATUniversinterfaceboard kit£42 + VA

kits are 'mple downnut and b It, wit' easy-

embly in tructi s.

Cortex II. 16 Bit r.

Cortex II off-

.eed and power oftrue 16 ssing at the same priceth- t pay for some of the 8 -bit

machines on the market.he standard kit has interfaces for TV.

cassette and RS232 - others areavailable as optional extras. Add disc

rives, printer and a monitor for a fully -edged business system. Price:

£199 + VAT

gliffilTRANCYBERNETICS LIMIT D

MPA 200 100 watt mixer -ampComplete kit £40 + VATSP2 200 2 -channelComplete kit £Chrom5-

00t sho nt

e kit £40 + ATDelay Line dio

o 1,...6s delay £95 + Vatchb416 pairs of jacksr stage. 6?0 + VAT

amplifi

ality effects

or studio

1 MIDI- ntro d sampling unit -uble a hig uality effects unmpl e £2 + VAT

Send f de

Our Dopplerintruderenou toprotectio two

POWEATRANORA nR

udur hdr-ne reald kit including

ers £70 + VATra transmitters £23 + VAT

Ctadar Alarenou

ecial offer: extended kit includingfour transmitters £84 + VAT

n ation mple some of the sounds available £2.50 + VATTo Powertran Cybernetics Limited, Park Road, Crowborough, Sussex

Pleasioseetcerr; following kitsenclos heque/Postal Order, value £ (Don't forget to add V.A.T )

e Address

Please allow 21 days for delivery. Offers subject to availability. Prices apply to UK only. are exclusive of V A Ta and correct at time of gong to press. Overseas customers - please contact our Export Department

MO =IP I1 111=1. INV =. MEI .11101MI .MFAccess/Visa cardholders - save time - order by phone: 08926 64222

111=12ll

WELCOME ToTHE MAPLINADVENTURELANIN 1981..The new Maplin catalogue for 1986 is a real adventureland for theelectronics enthusiast. With hundreds of new lines and details of Maplin'snew low low prices, it's the one event in the electronics year that no-oneshould miss. Packed with data and information on all the latest electronicproducts. Pick up a copy from any branch of W.H. Smith for just £1.45.Alternatively you can order your copy by post for just £1.85. For overseascustomers the prices are as follows: Europe surface mail £2.50; Europeair mail £3.75. Outside Europe surface mail £2.50; Outside Europe airmail depending on distance £4.25/£5.50/£6.25. For surface mailanywhere in the world you may send eleven International Reply Couponsfor payment in full.

Post this coupon now for your copy of the 1986 catalogue.Price £1.45 + 40p post and packing. If you live outside the U.K.send £2.50 or 11 International Reply Coupons. I enclose £1.85.

Name

Address

PE 12.85

MAPLIN ELECTRONIC SUPPLIES LTD.Mail Order: P.O. Box 3, Rayleigh, Essex SS6 8LR. Tel: Southend (0702) 552911SHOPS BIRMINGHAM Lynton Square, Perry Barr, Tel: 021-356 7292. LONDON 159-161 King Street, Hammersmith, W6. Tel: 01-748 0926. MANCHESTER 8 Oxford Road, Tel: 061-236 0281. SOUTHAMPTON 46-48 Bevois Valley Road, Tel: 0703 225831. SOUTHEND 282.284 London Rd, Westcliff -on-Sea, Essex. Tel: 0702-554000Shops closed all day Monday.