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BONUS 116-PAGE ALTRONICS CATALOG $3.50 FEBRUARY 1991 NZ $4.95 :~L - AUSTRALIA'S DYNAMIC §~ELECTRONICS MAGAZINE~ SERVICING -VINTAGE RADIO - COMPUTERS - AMATEUR RADIO - PROJECTS TO BUILD IR David Reids have the best prices possible. Even one of their competitors seem to think so. Have a look/Ill/ Model 1122 lntergrated Telephone/Answering Machine Telephone Features: * Ten easily programmable memories * Last number redial * Tone/Pulse switchable dialing * Pause button * Three position ringer switch Answering Machine Features: * Variable length outgoing message * Play back of outgoing message * Voice activated for incoming messages * Call screening * LED indicators and tone verifications * 30/39 MHz eal for watching a video in the bedr ving to move your complete VCR s tension cables runing from one end Output channel: UHF30 Transmitting distance: 10 mtr. Complete with connecting cables and power supply. * Last number redial * Mute operation * 2-way intercom * Table or wall mounted Range approx. 250 mtrs * non-Watch" Wireless Baby Monitor Transmits all sounds in the room up to 300 ft away. normally $99.95 ARLEC Remote Control Door Chime A portable door chime you can place anywhere in the home. Range: 20 meters. only$69.95 wire ty * 8mtr. $7 *15mtr. $ Bargain !!!!! * Water level sensor mounted on a suction cup for easy level adjustment. * Also has floor water flood sensor on main unit to detect over-spills. only$9.95 Multi-Lingual Pocket Translator Telephone Extension Bell with 10 mtr. cord Instant word conversion of ENGLISH, FRENCH, GERMAN, SPANISH and ITALIAN. * 1400 words per language. This product allows you to hear your telephone ring up to 10 meters away from an exi~ting telephone outlet on/y$49.95 only$19.95 Gas Leakage Detector * Detects Propane, Butane and Methane gases. * Inbuilt visual and audible alarm. * N.0./N.C. output for alarm systems. $79.95 Heat Detector * Fixed temp. <at> 60 deg. C * Switch rating up to 30V DC<at>300mA * No voltage required * Suit many alarm systems * Easy to mount only$9.95 CITIZEN ED-3800 ELECTRONIC DIARY Store Telephone No's, Names and Addresses, Memo function, Schedules, 12/24 hr. Clock and Alarm, World Time, Calender, Calculator, Metric Conversion. * 10KB memory. * 3 lines with 18 characters. -..... CITIZEN ED-4500 CITIZEN ED-7800 ELECTRONIC DIARY ELECTRONIC DIARY Telephone Directory with Names and Addresses, Calender, Memo, Schedules, Calculator, Metric Conversion. * 32KB memory.* 6 lines with 13 characters. Telephone Directory, Schedules, Memo, 12/24 Clock with Alarm, World Time, Calender, Metric Conversion, Currency Exchanger, PC link. * 32KB memory. * 6 lines with 32 characters. .. ,,., • < ~ ., ~ ", ~, . .... , * 147 X 62 X 18mm ~ ' ' ·~ ~ only $129.95 *154 PRECOMPUTER1000 -A-----Ju11ior talking computer thatstimulates creative learning * 9 "Floppy" Discs * * * with over 1000 multiple choice questions on Science, History, Health and Safety, Trivia, Maths. 18 Activities including Spelling, Math, Music, and More! Multi-Level Games and Quizzes 1 and 2 player modes. Large Screen with animated dot matrix graphics. X 82 X :, • ,, .• », , ; , ~ " , " "' ~ ~ 19mm ,, . , ¥ ' " ' only $295.95 + AM/FMRADIO and DIG d PORT.A.GU.ARD Portable Security Sensor A portable PIR security system with built-in Alarm/Chime and light. Take it with you anywhere. E.g. from room to room, take it on holidays to secure your hotel/motel room, caravan or tent. Monitor children, or use it as an automatic light when the user gets up out of bed at night. * Detection distance: 15ft. * View of field: 30deg. horiz. * - - ---------... . ·~ "'"'',.,, ,;:-::~:"~"";:.:... . . ,.. ,, ." MS-110 SWR METER for 27MHz * SWR Meter * Power Meter * AM Modulation Meter * FM Deviation Meter * Antenna Matcher * 1watt/10watt/100watt switchable : 15deg. vert. Operates on 1 x 9V 216 battery and 2 x AA cells. ~ 24KT GOLD SAPPHIRE BLUE AUDIO CABLES WORKSHOP /HOBBY TOOL KIT * 1 RCA x 1 RCA 6' $9.50 * 2 RCA x 2 RCA 3' $11.00 * 2 RCA x 2 RCA 6' $12.00 * 2 RCA x 2 RCA 18" $13.50 * 2 RCA x 2 RCA 3' $16.00 ( with ground terminals) * 2 RCA x 2 RCA 6' $19.50 Contains: 1 x jewellers screwdriver set 1 x 120mm long nose pliers 1 x 110mm side cutters on/y$9.95 ( with ground terminals) DarldR•ld El•ctronlcs 127 York Str••~ SYDNEY 2000 PH: (02) 267-1385 24hr. FAX: (02) 261-8905 February 1991 THIS DC-AC INVERTER will let you run a fluorescent lamp from a 12V car battery. There are 3 versions for 16W tubes, 20W tubes & 40W tubes - see page 46. FEATURES 8 Electric Vehicles, Pt.2 by Gerry Nolan Energy storage - an Eldorado for innovators 14 A Practical Approach To Amplifier Design by David Eather How to design the output & driver stages 92 The Story Of Electrical Energy, Pt.7 by Bryan Maher Tasmania's hydroelectric power system PROJECTS TO BUILD YOU CAN ENJOY wideband stereo AM sound with this superb new stereo AM tuner. Details page 22. 22 A Synthesised Stereo AM Tuner by John Clarke Features pushbutton tuning & digital frequency readout 46 Three Inverters For Fluorescent Lights by Otto Priboj Use them to run fluorescent tubes from a 12V battery 54 Build A Low-Cost Sinewave Oscillator by Darren Yates Simple circuit can be built from junkbox parts 62 Fast Charger For Nicad Batteries by John Clarke & Greg Swain Pt.2: all the construction details SPECIAL COLUMNS 37 Computer Bits by Jennifer Bonnitcha Why it takes so long to turn on 40 Vintage Radio by John Hill One thing leads to another 76 Serviceman's Log by the TV Serviceman Now look what ya gorn an' done! REVERSED POWER SUPPLIES can cause all sorts of problems in electronic equipment. This month, the Serviceman relates two tales of woe. Turn to page 76. 82 Remote Control by Bob Young Galloping ghost & the evolution of proportional control 86 Amateur Radio by Gany Cratt Oscillators - which type suits your application? DEPARTMENTS 3 Publisher's Letter 4 Mailbag 20 Circuit Notebook 58 Back lssue.s 73 Product Showcase 2 SILICON CHIP 99 100 102 104 Subscription Page Ask Silicon Chip Market Centre Advertising Index LAST MONTH, we gave you the circuit details our our new Fast Nicad Charger. This month, we show you how to build it - see page 62 PUBLISHER'S LETTER Publisher & Editor-in-Chief Leo Simpson, B.Bus. Editor Greg Swain, B.Sc.(Hons.) Technical Staff John Clarke, B.E.(Elec.) Robert Flynn Darren Yates Reader Services Ann Jenkinson Advertising Manager Paul Buchtmann (02) 979 5644 Mobile: (018) 28 5532 Victorian Representative Hugh Anderson Ply Ltd (formerly McDonald Woodside & Associates Ply Ltd), 119 Market St, South Melbourne, Vic 3205 . Phone (03) 696 5411. Contact: Ian McDonald. Extolling the virtues of fluorescent lights In this month's issue we are presenting a compact inverter for running fluorescent lights from a 12V battery supply. There are three versions , catering for the very small fluoro tubes, up to those rated at 36W or 40W. We think that they will be popular for people who want to use fluorescent lights on boats, caravans and recreational vehicles, and on homes and farms which are far from the mains supply. The particular attraction of fluorescent lights in these applications is that they are so highly energy efficient - much better than incandescent lamps. All of which begs the question as to why fluorescent lamps have fallen so much out of favour as far domestic use is concerned. Why is it so? From our viewpoint, it seems as though there has been a concerted campaign by architects and interior decorators in home improvement magazines to deprecate fluorescent lights. They have been criticised because they put out a "harsh" light and have ugly fittings. And it is true that most fluorescent tubes do have a bluish light which gives a far from true colour rendition, compared to ordinary daylight. It is also true that most fluorescent light tubes emit a small amount of ultraviolet light which is regarded as undesirable (although it is far less than the amount of UV in daylight. When it is all added up, fluorescent lights have had a "bad press". It is about time they were put back into perspective. For a start, they are very efficient - about 5 or 6 times more efficient than typical incandescent lamps. They also last about 15 to 20 times longer than incandescents. But the potential energy and money savings are even bigger when you see the inefficient downlight fittings which are now advocated in kitchens and family rooms. The lamps used in these fittings are not only expensive but they tend to overheat and have a short life. In fact, it is now not unusual to walk into a modern kitchen which may have 600 to 700 watts of incandescent downlights on and yet still be poorly lit - so much for the vagaries of fashion. If you compare the cost of operating a twin 40W fluorescent light fitting with an equivalent amount of incandescent lamps (say 400 watts, 15,000 hours, 8 cents per kWH), the potential cost saving is around $600 if you include the cost of replacement incandescent lamps. Which means that the current kitchen lighting fashions are pretty silly. Leo Simpson Regular Contributors Brendan Akhurst Jennifer Bonnitcha, B.A. Garry Crall, VK2YBX John Hill Jim Lawler, MTETIA Bryan Maher, M.E., B.Sc. Jim Yalden, VK2YGY Bob Young Photography Glen Cameron Editorial Advisory Panel Philip Watson, MIREE, VK2ZPW Norman Marks Steve Payor, B.Sc., B.E. SILICON CHIP is published 12 times a year by Silicon Chip Publications Ply Ltd. All material copyright©. No part of this publication may be reproduced without prior written consent of the publisher. Printing: Magazine Printers Ply Ltd, Rozelle, NSW 2039; Macquarie Print, Dubbo, NSW 2830. Distribution: Network Distribution Company. Subscription rates: $42 per year in Australia. For overseas rates, refer to the subscription page in this issue. Liability: Devices or circuits described in SILICON CH IP may be covered by patents. SILICON CH IP disclaims any liability for the infriflgement of such patents by the manufacturing or selling of any such equipment. Editorial & advertising offices: Unit 39, 5 Ponderosa Pde, Warriewood, NSW 2102. Postal address: PO Box 139, Collaroy Beach, NSW 2097. Phone (02) 979 5644. Fax (02) 979 6503. ISSN 1030-2662 FEBRUARY1991 3 MAILBAG The great CD green pen controversy I am writing regarding "The Great CD Green Pen Controversy ", published in the December 1990 issue of SILICON CHIP. A CD analyser is intended to measure the loss of data caused by physical imperfections on a disc. In order to do so , the mechanism must be extraordinarily accurate and stable to eliminate errors caused by mistracking. Such a mechanism would be very expensive to produce and would not be found in domestic CD players. In this case, a trade-off between cost and performance is made, and so domestic CD players benefit from stabiliser rings and Sorbothane damping , having already a significant interpolation rate due to inadequacies in design. CD ROM players cannot afford to lose large chunks of data and so are more expensive. A high quality mechanism is unlikely to be affected by stray light and vibration anywhere near as much as a cheaper one. It is therefore no surprise that the green pen apparently made no difference in your tests. In order to determine whether or not the green pen is effective, it is necessary to modify your experiment. The test should be repeated, if possible, using a standard CD player mechanism connected to the data processor section of a disc analyser. As your test currently stands, you have proved that the green pen .does not eliminate physical flaws on a disc. You need a test which demonstrates the effect of the green pen on the tracking accuracy of the scanning mechanism of the average run-of-themill CD player. Only then will your data be conclusive. In support of this argument, it is claimed that damping rings, green pens and Sorbothane feet benefit all players, but that the effect is proportionately less on high quality machines. Note too, that CD Stoplight has produced data obtained from Hewlett-Packard analysers showing an improvement in S/N ratio due to 4 SILICON CHIP thei,r green pen. Application of the pen dramatically reduces visible reflectivity of the disc , indicating effective absorption of visible light (IR is, however, another matter). Does it work or doesn't it? The question hinges now on whether you can take an ordinary CD player to Disctronics and hook it up . P. Edwards, Ainslie, ACT. PS: valiant effort, bravo! Comment: we ain't gonna do any more tests. If you refuse to accept the evidence we have already presented, the chances are that you or other readers will cast doubt on subsequent tests and thereby consider the question still open. And on a practical basis, neither we nor Disctronics Ltd can afford the considerable cost and time involved in these tests. Having said that, the disc analysers used in the tests were connected to a number of standard CD players. Two of them were "broadcast" machines which differ only in their cueing facilities - in other respects they were bog standard. If you consider that the CD analysers (with supposedly superior tracking mechanisms) showed no improvement with the green pen treatment, then what chance at all is there of any improvement with a cheap CD mechanism? And although we have not done any tests, we very much doubt whether stabilisers or Sorbothane feet give any measureable or audible improvement to CD players. In our opinion , they come under the same heading of audio quackery. In a practical sense, we think that audible improvements to CD players can only come from improved digital to analog converters, together with improved digital and analogfiltering. Half a disc better than none at all! I read with interest your story on "The Great CD Green Pen Controversy" (December 1990 issue). I too was amazed and sceptical when the adverts for this product SILICON CHIP, PO Box 139, Collaroy Beach 2097. appeared but was too lazy (and mean) to buy one and try it for myself. As I expected, your tests show that there is nothing to them. However, I suspect you will be bombarded by golden -eared experts who will swear they can hear the difference. If the claims made by the manufacturers are true, then a double blind A-B test using identical discs on identical players should show up a noticeable improvement. I appreciate your comments on the difficulty of obtaining identical discs and players. So how about making the disc act as its own control? Treat half of a disc's circumference with the pen, leaving the other half untouched. Then (particularly if the disc chosen is recorded right up to the edge) the laser beam will alternately be swept through an area of maximum "improvement" for half the time, and for the other half will play a reference untreated signal. As the disc rotates at about 500 rpm when playing the outer tracks, the signal should be modulated at about 8Hz by the improvement factor. If this is as great as the manufacturers claim, there should be an audible - and measurable? - flutter. Of course, this won't show if the sound is actually improved, only that there is some change caused by putting green ink on the disc edge. My bet is that there won't be any effect whatever. This is a test anyone can perform in the privacy of his own home, without the expense of complex analysis equipment. And if you can't hear it, it ain't there. R. Mercer, Kelmscott, WA. Perhaps the pen should be another colour? You missed the point with the CDXP GREEN pen. It should have been BLUE! Another article perhaps? I enjoyed the one in green very much. Keep up the excellent work fellas! M. J. Vincent, Golden Beach, Qld. Availabls Soon/ ALL NEW 2M VHF FM TRANSCEIVER This outstanding high performance FM transceiver can be used as either a mobile or base station on the 144-148MHz amateur band. It must be one of the easiest transceivers of its kind to build yet it comes loaded with advanced features. s399es Features like - • • • • • • • • • Full PLL frequency synthesis 24 memory channels with repeater shifts 25W or 5W switchable output 5kHz or 25kHz tuning steps Microprocessor control system Excessive SWR safety shut-down circuitry 0.15uV sensitivity at 12dB SINAB 30kHz selectivity at -60dB -60dB image rejection At this price you can afford to take the challenge! Kit includes all components, hardware, heatsink and a pre-8unched silk screened front panel. Microphone is not supplied. YAESU D-211 or D-2105 are recommended. Cat K-6400 <at>-Feb'90 ~ QQQ ALARM SIREN MODULE TRANSISTOR TESTER Need an extra module for your home or car alarm? This is the perfect addition. Some car and house alarms can be disabled simply by cutting the power off. But not this one! It monitors its supply voltage for fluctuations. If the external supply is cut, or varies excessively, the siren is triggered. You can add this module to your existing system or use it as a stand alone unit. (Horn speaker not supplied) This low cost instrument will become an invaluable piece of your test equipment! • Tests bipolar transistors, diodes, F.E.T.s, S.C.R.s & P.U.l.s • Powered by a 9 volt battery (not supplied) • Includes 50mm meter, all components, pre-punched & screened front panel, and case ~ Cat K-3052 ~ July '78 Cat K-8250 s12ss Q <at>oct'90 s39es Q Was $46.95 Before Christmas! Limited Stocks! EGG TIMER DUAL TRACKING +/- 5OV POWER SUPPLY N~ ~ QQQ [1] VIDEO MODULATOR rzi Convert your video or computer output to VHF TV signal with this single module. Cornes aligned and pretuned plus -it's output is switchable to either VHF Ch.1 or Ch.0. Can be PCB mounted, includes a built-in voltage regulator and RCA output socket. A data sheet for this product is available on request. Degree Of Simplicity Cat K-6043 sges Originally $19.951 _ LZJ Kits marked with this symbol involve mains power wiring. Take extreme care when working with this equipment . Q Simple QQ Intermediate QQQ Detailed SCOPE 1so wattSOLDERINC superscope IRONS S Select the temperature you want and the Superscope will deliver it from cold in just 6 seconds! Uses a 5 C□ PE non-corrosive stainless steel barrel fo.r longer life_and comes with a spare tip and element. Requires a 3.3V<at> 30A transformer Cat T-1692. Cat T-1605 'l'()()I s se4ss 10·70 w att Miniscope Lightweight, fingertip control gives precise temperature adjustment. Comes with a spare tip & element and requires 3.3V <at> 30A transformer CatT, -~1~69;2~.::::::~~::=;::::::--CatT-1660 _ . ~ L. · . . .... Heat ·n Str·1p Cun A great tool to have around the house. Ideal for heatshrink work, removing old paint, drying ... you'll find hundreds of uses for the Arlec Heat 'N Strip gun. It's mains operated & light and easy to use. CatT-4845 ssgss Easy Etch Engraver With the Arlec Easy Etch Engraver you can easi ly and quickly mark your tools, stereo IIIJIDllllllllllllllll equipment and household goods with a :;__:,:~ permanent identification. Steel bits let you v.J v · · engrave on metal , plastic, or wood . It's -~: easy to handle and comes complete with a ··-:.-·· ----~- 12V plug pack and long cord. iiiiiI::: 0\1o;:.,.....,., ~ cat T-4753 $ -::;>==-~~iiiiiiii--_.;;;;iiiiiii!'--=-- 3.3V<at> 30A Transformer 3 gss A ~ow voltage transformer for Scope soldering irons. Includes an electronic shield for extra protection. Cat T-1692 s79ss Perfect For PCB work! ARLEC Supertool 12 Volt superscope The Arlec Supertool takes the hassle out of working on PCB's. It sands, it polishes, it drills, it engraves, it mills. Comes complete with wire brush, milling cutters, grinding wheel, high speed drills, chuck collets, eraser sticks and plug pack adaptor-all in a handy carry case. CatT-4754 A 30-150 watt iron that connects to your car battery and heats in just 3 seconds! Comes with a 6m lead with alligator clips. Current drain is 45A. Cat T-1635 s94ss s,gss Replacement tip packs T-1601/3 Only $1095 SCREWDRIVER BIT SET Push-Action The One Tool That Does It All! • 6 & 8mm flat blades • No.1 & 2 Phillips heads • 2 hole reamers • • • • CatT-4512 sgss ~ Magnetic • • • • 3·IN·1 Modular TOOi Fully insulated with magnetic head~;.;;e,..4.5 & 6mm flat blades ~ No.1 & 2 Phillips heads No.1 & 2 Pozidrive heads Cat T-4505 sgss 5 Bit Set ~ • Large rubber handle for extra grip , • 1.2, 6, 6.5 & 7mm flat blades • No.1 & 2 Phillips heads . Cat T-4500 $595 It's a drill plus drill bits It's a Soldering Iron plus solder It's a Screwdriver plus drivers And it's rechargeable too! Cat T-5712 Unbeatable value at s79 9 s l 0===4·· - -- - .·· '.·<· . universal Bit set • • • • For manual or electric drivers 4.5 & 7mm flat blades No.1 & 2 Phillips heads No.1 & 2 Pozidrive Cat T-4518 $395 T·Bar Magnetic screwdriver • With 6 magnetic bits & plastic holder • 2 Phillips, 2 flat, and 2 Torx bits CatT-4515 ssss tB1 088/TI - - Fluke 73 The Incredible Fluke 87 Uncompromised quality at an affordable price. The superb autoranging FLUKE 73 is just the thing to withstand the rough and tumble of everyday use. • 3.5 digit, 3200 count multimeter • 31 segment bargraph • Autoranging & automatic polarity • High energy overload protection • Every feature on one rotary dial! Cat Q-1 602 You 'll wish that all your test equipment could perform so well , last so long, and give you so much flexibility! • 4.5 digit & Analogue Bargraph readout • Auto & manual ranging • Frequency & true RMS • Capacitance • Minimax average recording • Overload protection Cat Q-1610 • Continuity & diode testing • Touch hold • Back-lit display plus lots more! $179 3YEAR WARRANTY! S699 Fluke 75 Fluke 77 With al l the features of the FLUKE 73 plus cl iode and audible continuity testing! The feature packed FLUKE 77 is the top of the line 70 series multimeter with advanced features like Touch Hold • 3.5 digit multimeter and superior accuracy (0.3% for 3.2 to 320V). • 31 segment bargraph • Autoranging & automatic polarity • Autoranging & automatic polarity • 3.5 digit plus 31 segment bargraph • Audible continuity testing Cat 0-1606 • Touch Hold with 'beep' indicator • Diode test • Continuity & diode test • Dirt and moisture resistant case • Superior accuracy across most ranges Cat 0-1604 • Hand carry holster S289· s399 Genuine Fluke Accessories----------------Universal Temperature Probe Air Probe For air and other gases. Protected probe with perforated stainless A P-N junction probe. st eel baffle. Range: Converts any DMM to a -196°C to 816°C. thermometer. Air, surface and liquids from -50 °C to Cat 0-1686 150°C. Switchable °C and °F. ~ $119 Immersion Probe High Voltage Probe AC Clamp Meter AC/DC Clamp Meter For liquids and gels. Fully protected by lnconel sheath. Range: -196°C to 927°C. Extends your measurement capabilities up to 40K volts using a division ratio of 1000 to 1. cat o-16go Hal I-effect clamp metre accessory with its own battery. Measures currents from 1 to 400A and fits co~ductors up to 30mm d1a. CatQ-1670 Battery powered Halleffect meter for conductors up to 30mm dia. Measures currents from 5 to 400A at frequencies up to 400Hz. Cat Q-1672 S159 ~2~,89 [iJ •199~ ~ ~ Deluxe Test Lead Kit Industrial Test Lead Set Soft Case Standard shrouded banana plug leads with interchangeable tips in a 1.6m silicon insulated test leads with soft carry pouch. Comes with interchangeable stainless steel test alligator clips, spade lugs, standard probes and safety alligator clips. pointed tips, and one retractable Cat Q-1652 hook tip. Cat 0-1658 Store Locations _ __ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ s59gs s799s NSW • A lbury 21 8399 • Bankstown Square 707 4888 • Blacktown 671 7722 • Brookvale 905 0441 • Bondi 387 1444 • Campbe ll!ONn 27 2199• Chatswood Chase 4111955 • Chullora 642 8922 • Gore Hil\ 439 5311 • Gosford Protective case for FLUKE meters. With water resistant zipper and pockets for leads. Even fits FLUKE holster! Holster With lead and probe pouch plus tilt stand and bel) hook. Suits any of the FLUKE 70 series DMMs. ~~?r:~; ~fsn~~~i~,N~~=tl~u~~tv~1:~s~J: ; ~~:~~~s3~2;P~i~~~~ ':s~~• .M~~~~~ ~~ ~~~ ----------• • Railway Square 211 3777 • Sydney City 267 9111 • Tamworth 66 1711 • Wollongong 28 3800 • ACT • Belconnen (06) 253 1785 • Fyshwick 80 4944 • VIC • Ballarat 31 5433 • Bendigo 43 0388 • Box Hill 890 0699 • Coburg 383 4455 • Dandenon g 794 9377 • East B righton 592 2366 • Essendon 379 7444 • Footscray 689 2055 • Frankston 783 9144 • Gee long 232 711 • Melbourne City 399 Elizabeth St 326 6088 and 246 Bourke SI 639 0396 9 5 2 ; ft:1c~m~fJe 33;:;2;~r~n~~~a~~t 2ii Js~~g:C~~i! ~~~~C~~ ~ 4 9033 •TOONOOmba 38 4300 •Townsville 72 5722 • Underwood 341 0844 • SA • Adelaide City 223 4122 • Beverley 347 1900• Elizabeth 255 6099 • Enfield 260 6088 • St. Marys 277 8977 • WA• cannington 451 8666 • Fremantle 335 9733 • Perth City 481 3261 • Midland 250 1460• Northbridgc 328 6944 • TAS• Hobart3 1 0800 • NT • Stuart Park 81 1977 ;~t~33.d~~~~~~~ S299 ;i~:,i~~g~ Cat Q-1664 s499s Cat Q-1663 s3295 • ectr,c he size, weight, shape and technical characteristics of the energy source affect almost every other vehicle attribute. Energy density is the most important consideration but choice of the energy source will depend on a host of factors including: power density, cycle life, initial cost, maintenance cost, energy efficiency, output voltage, internal impedance, charge rate, byproducts, shelf life, temperature characteristics and overall safety. However, energy density is what really matters. This is simply the total source energy divided by the source weight to give a result in watt-hours per kilo~ gram (Wh/kg). Naturally, the source weight must include any subsystems required by the source, such as cooling fans and so on. Table 1 shows the energy densities of various fuels and other energy sources and makes it clear how very low the energy densities of man-made sources are. The values listed are nominal and may vary considerably under certain conditions but the much lower energy densities of the man-made sources relative to the natural sources are obvious. It is also important to realise that energy density may vary considerably with the rate at which the energy is used. For example, an energy density of 60Wh/kg may be claimed by the manufacturer of a particular type of T By GERRY NOLAN When you consider that one kilogram of petrol stores the equivalent of 12,000 watt-hours of energy, any electric storage medium falls a long way short. The best alternative is the aluminium-air fuel cell which has an energy density of up to 360 watt-hours per kilogram, so it is obvious that the field of energy storage is wide open to innovation. 8 SILICON CHIP battery weighing 30kg, so we would expect to obtain 1800Wh of energy. What the manufacturer may neglect to tell us, however, is that if we use the energy at double the normal rate, the energy density drops to 45Wh/kg, giving us a total energy availability of only 1350Wh. The moral of this, of course, is to specify energy density at a specific power level. As anyone reading this article probably already knows, the most common energy source for electrical vehicles is the lead acid cell. The currently obtainable energy densities of these is up to 50Wh/kg. Other batteries, fuel cells and flywheels are shown in Table 2 along with their theoretically obtainable energy densities. Power density vs acceleration An energy source with a very high energy density is highly desirable but, as with conventional engines, the rate at which the energy may be used is also very important. This rate is determined by the power density which is measured in watts per kilogram. A good example of a battery with a high energy density but a low power density is the aluminium-air fuel cell developed by Alupower in Ontario, Canada. Because it takes up to half an hour to reach its full power capacity, it needs to be used with lead acid cells which supply short term demands. Pt.2: energy storage - THE GENERAL MOTOR'S IMPACT car uses high-power sealed-lead acid batteries & shatters the perception thai electric vehicles are slow-moving golfbuggies. During trials, it beat a Nissan 300ZX in 0-100km/h acceleration tests. Power densities of up to 150W/kg may be obtained from lead acid batteries , around 200W /kg for nickel zinc, 100W /kg for nickel iron, 65W / kg for zinc chloride, 160W /kg for lithium iron and up to 200W /kg for sodium sulphur. On the basis of this comparison, the ordinary lead acid battery isn 't too bad. Replacement cost How many times can you charge and discharge (cycle) the batteries before they have to be replaced? The General Motors Impact car is designed to be powered by 32 10-volt batteries. These have an expected life of about 40,000km and a replacement cost of around $3500, or a little less than nine cents per kilometre. This is a much higher cost than the energy itself, which could be taken from the power grid for as little as 0.3 cents per kilometre. Increasing cycle life will obviously reduce the replacement cost per kilo- metre and research over the past decade has greatly improved the number of cycles possible, in some cases almost doubling it. Now lead acid batteries have a cycle life approaching 800 cycles, up from 500 in 1980, while nickel iron and sodium sulphur may be cycled (ie, fully charged and fully discharged) more than a thousand times. Another factor which needs to be taken into consideration when selecting an energy source is cell voltage , which will determine how many cells need to be hooked up and the type of array to obtain the voltage necessary to run the motor and battery efficiently. The available voltage will also be affected by the internal impedance, which generally increases as charge decreases. Battery maintenance is also an important consideration from time, material costs and skills points of view - your average EV user may not feel too comfortable topping up the battery with some exotic electrolyte every second day. Flat batteries One of the things that will worry EV users , at least until there are enough recharging stations handy, is the fear of the batteries going flat without warning. In your present vehicle, a glance at the fuel gauge and a quick mental calculation will ef\able you to work out roughly how far you can go before you need to stop for fuel. However, replacing the fuel gauge Table 1 Energy Source Nominal Energy Density (Wh/kg) Petrol 12,300 9,350 Natural gas Methanol 6,200 Hydrogen 28,000 Coal 8,200 Lead-acid battery: up to 50 Sodium-sulphur battery: 150-300 an Eldorado for innovators FEBRUARY1991 9 ELECTROLYTE STORAGE TANK \ LEAD-ACID BATTERY PACK ELECTRIC DRIVE ALUMINIUM-AIR HYBRID ELECTRIC PROTOTYPE - because the aluminiumair battery takes half an hour to build up to peak power, a lead-acid battery pack is used to supply start-up and acceleration energy. Excess energy from·the Al-air battery can then be used to recharge the lead-acid pack while the vehicle is moving. with a "charge gauge" is not such a simple matter in an electric vehicle. The definitions of a fully charged battery and the way to measure its charge vary considerably with the type of battery. The no-load voltage level may give a reasonable indication in some cases but will vary with the history of the battery, temperature and so on. Measuring the electrolyte specific gravity also gives an indication but few EV users would appreciate the inconvenience. A type of "charge gauge", which integrates the current into and out of the battery to give an actual state-ofcharge, would be a great comfort. An additional selling point would be a "range-at-present-speed" readout. Charge acceptance The capability of the energy source to take a charge is also an important ALUMINIUM-AIR CELL - an aluminium-air cell usually has 20 individual cells, a condenser and a heat exchanger at the centre of which are located the pump motor and air blower. The condenser removes oxygen depleted air from the system and the heat exchanger keeps the electrolyte temperature at about 60°C. The blower circulates air through the cathodes. 10 SILICON CHIP consideration, as it should be able to absorb high rates of energy input (eg, under regenerative braking) without exceeding acceptable temperature levels. Nickel-cadmium batteries, in particular, are able to handle high charge rates and Audi is using these in a hybrid 4-wheel drive car. The front wheels of the "duo" are driven by the normal Audi 2.3 litre, 5-cylinder petrol engine and the rear wheels by a pack of 49 nicad cells, each of 1.2 volts, powering a 9.4kW electric motor which fits into the transmission tunnel. Safety considerations The sheer weight of batteries, especially when lead acid cells are used, requires special strengthening in the design and construction of EVs from scratch or when converting conventional vehicles to EVs or hybrids. 400kg of batteries suddenly coming loose during a crash stop would be a major hazard, to say the least. "Gassing" and high temperatures during charging can also lead to problems, particularly at high rates of charge, and effective ventilation must be built-in. Silver zinc batteries Twelve of the first 13 cars in the recent World Solar Challenge used silver zinc batteries, while roughly the same number of vehicles used DUAL POWER FOR AUDI - a 180kg, high performance nickel-cadmium battery pack fits into the spare wheel-well of the Audi 100 to power the 9.4kW electric motor which fits into the transmission tunnel. Because the petrol engine is retained to drive the front wheels, a 4WD vehicle with two completely independent drive systems is the result. lead acid batteries. Although they are much more expensive than lead acid batteries, with their high energy density (100Wh/kg), superior power density and lighter weight, silver zinc batteries give an electric vehicle a decided performance advantage. So far we've talked mostly about batteries and their close relatives, fuel cells, but flywheels have been around for a long time, much longer than batteries in fact, and could conceivably have even greater potential than batteries or fuel cells as energy storage systems for EVs. Flywheel research Your silky smooth BMW, Mercedes, even the Rolls, would run very roughly, if at all , without a flywheel to maintain the crankshaft rotation through to each ignition stroke. Apart from smoothing out the staccato power delivery of the piston engine, flywheels have also been used in vehicles for energy storage since the 1930s in everything from torpedoes to draglines and helicopter hoists. Archaeologists have found one in the Middle East that they believe was used as a potter's wheel in ancient Ur of Chaldea 5,500 years ago. As far back as 1973 , researchers were predicting energy densities of 870 watt-hours per kilogram using fused silica as a material for super flywheels. What some people didn't seem to Exotic Energy Storage For EVs Zinc-hydroxide, aluminium-air, vanadium and sodium-sulphur electro-chemical batteries and fuel cells, some being recharged simply by replacing the electrolyte, are all current areas of research . Energy densities of up to 200Wh/ kg are being claimed for the zinchydroxide electrochemical cells which are being researched by a team headed by Jim Evans at the Lawrence Livermore Laboratories near San Francisco. Zinc is often used as a material for electrodes - remember the zinccopper-acid cell we all experimented Table 2 Source Lead acid Nickel zinc Nickel iron Nickel cadmium Silver zinc Zinc chlorine Energy Density (Wh/kg) Now Available Theoretical 110 50 90 60 30 100 500 90 High Temperature Batteries Lithium metal sulphide: Sodium sulphur: 170 300 Fuel cells Aluminium air: Flywheel (steel): Super flywheel (fibre): realise until much more recently was that, while the energy storage capacity is directly proportional to the mass , it is proportional to the square of the rotational velocity - so triple the speed ofrotation and you get nine times the energy storage capacity. Concentrating the mass near the circumference, where the rotational velocity is highest, also increases the energy storage capacity for a given overall weight. For a time, lightweight high-speed flywheels appeared to have real potential and a great deal of research was carried out during the early 70s with at school? - but it is generally in the form of a sheet or slab. By using the zinc as particles, the slurry of anode and electrolyte can be continuously replaced from a reservoir with the used material being stored for later replacement and recycling at a "service station". The aluminium-air cells being developed by Alupower have a claimed energy density of 360Wh/kg. Alupower is an Alcan subsidiary which is combining its technology with Moli Energy's rechargeable lithium battery knowledge. Alupower's fuel cell generates electricity by an electrochemical reaction between aluminium and oxygen , using an alkaline solution or saltwater as an electrolyte. An air 350 12-30 up to 40 870 when the Middle East put up oil prices. Unfortunately, when oil prices dropped again, flywheel research lost its momentum. Now, although research is gaining speed again, the high expected energy densities haven't materialised. Nevertheless, the availability oflight, high-tensile fibres such as Kevlar, magnetic levitation bearings, high vacuum enclosures and electronic commutation and control have enabled densities of more than 40 watthours per kilogram to be obtained. Because they are so light, relatively maintenance free and could be made stream is blown through the cell stack to supply the oxygen for the electrochemical reaction, while the electrolyte is pumped through the cell stack between the aluminium anodes and air cathodes. Electricity is produced as the alu minium oxidizes, forming aluminium hydroxide as a byproduct which precipitates out and is collected in a sump. This can be collected and recycled back into aluminium, making it a clean and non-polluting renewable power source (see illustration). Some of these research paths will be blind alleys, others will lead to developments in directions quite different from that originally intended, but that is the way of research. FEBRUARY1991 11 i THE CLEAN AIR TRANSPORT LA301 - a 4-passenger or 2-seat microvan - uses lead-acid batteries & an aluminium-air fuel cell to power an 11.9kW DC motor. It also has a propane-fuelled auxiliary power unit to achieve a maximum range of 240km and a top speed of lO0km/h. for change over at service stations instead of waiting for a recharge, the possibilities for fruitful research are very high. Another advantage of the lightweight fibres is that if the flywheel disintegrates, perhaps because of overspeeding, it just becomes a pile of fluff instead of potentially lethal chunks of high grade steel. Where are we going? One of the mistakes EV designers and builders seem to be making is to compete head on with existing fam- ily cars by designing for ranges of at least 100km at speeds up to 100km/h. You may remember from last month's article that 90% of all daily one way trips are less than 35km long. So why not design for a trip range of 50km at speeds of up to 80km/hr, at least until the technology_ is more widely accepted. For a start, this would reduce battery weight to less than half. Less than half? Yes - with a lighter battery load and the consequent reductions in strengthening required - the overall vehicle weight would be much EXPERIMENTAL ELECTRIC vehicles have been produced in Australia. This one is a converted Mazda utility powered by a tokW forklift motor & a 48V battery bank. Solar cells on the roof top up the batteries during the day. less and not so much energy would be required to push it around. The combined results would be reduced manufacturing, running and maintenance costs, making EVs a much more immediately attractive alternative, thereby greatly accelerating their acceptance by the public. sc Outside chamber liquid-filled for cooling Fibre-glass shielding · Contra-rotating flywheel rotors Gimball ing spring assembly Electrical leads to motor/generator 12 SILICON CHIP THE ADVENT OF THE "ENERGY WH~EL" an energy pack of super flywheels built as a combined motor/generator with electronic commutation and magnetic levitation bearings, running in a high vacuum, would provide very efficient energy storage. Because of the enormous speed at which the flywheels rotate, the energy would be used to power an electric motor to drive the wheels, rather than using a mechanical drive train. The pack would be self-contained so that it could be quickly replaced by a fully charged one when discharged. 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Tax exemption certificates accepted if line value exceeds $10.00. BANKCARD, MASTERCARD, VISA, CHEQUES OR CASH CHEERFULLY ACCEPTED A practical approach to amplifier output stage design There are many requirements for a successful amplifier design. One of the least understood is how to design the output and driver stages to remain within their safe operating areas. Faulty design here can be more than just expensive; the smoking remains are down right embarrassing. By DAVID EATHER Many cope with this task by copying from other designs. This is a limiting approach and almost invariably leads to designs with a certain sameness about them. Also, bad design is perpetuated. There is a better way. This article shows a practical approach to amplifier output stage design and covers the calculation of power supply voltages, output load . lines, derating transistor SOAR curves and heatsink selection. You get nothing for nothing so before you start there is a fair swag of calculations to be done. You also need access to a power transistor data book. The payoff is reliable amplifiers with output. power levels customised for your needs. There are no definitive answers as to exactly how many or what type of transistors you have to use in your 14 SILICON CHIP design; a lot depends on taste. At the same time, there are certain design rules that should not be transgressed. My method is a simplified approach the overall aim has been to achieve a reliable design without too much pain. What has been shaved off one area is generally compensated for elsewhere. For illustration, I will be designing the output and driver stage of a general purpose amplifier capable of 25 watts into 8Q. The circuit is a simple 10-transistor design as shown in Fig.l. After a general discussion on each step, I will provide some specific results, so you can check your understanding of the principles being discussed. Assuming you already know how much power output you want, the first step begins with calculations to find the peak voltage and peak current delivered to the load. Use the following formulas. Vmax load = ✓ (2 x P x Z) lmax load = ✓ (2 x P/Z) For my amplifier this works out as: Vmax load= ✓ (2 x P x Z) = ✓ (2 X 25 X 8) = 20 volts Imax load= ✓ (2 x P/Z) = ✓ (2 X 25/8) = 2.5 amps Emitter resistors At this point, I will give a quick mention of the emitter resistors, Rl and R3, on Fig. l. These resistors help provide thermal stability of the output stage bias current and in designs with output transistors in parallel they help to ensure equal current sharing. The higher the resistance the better the thermal stability and current sharing but the more power they waste. The final value is a compromise. As a guide, you would normally try for about 0.6 volts across the emitter resistors at lmax load. For this design, 0.22Q should prove adequate. The resistance is a little low but I would not expect any problems for the following two reasons: (1) there is only one output transistor for each rail so there is no current sharing; and (2) I don't intend to set a high quiescent current. The next step is to work out the required supply voltage (±Vee). You must consider the requirements of Vmax load, the voltage drops caused by the driver and biasing circuitry and the voltage drop caused by the emitter resistors in the output transistors, and lastly the ripple voltage (hum and audio signal) on the supply rails (±Vee). At this stage, refer to back to Fig, 1. , - - - -.....- - - - - - - - - - - - . - - - - - - . . . . . - - - + V C C R1D R9 01 ? 09 BC547 R17 07 BC549 R9=R10=2R8 C4 06 -YCC+1.4Y BC639 RB ...__ _ _----,.__ _ _ _ _...__ _ _ _ ___.____ _ vcc Fig.1: the circuit for a general purpose 10-transistor audio amplifier capable of delivering about 25W into 8Q. Note that the design uses split supply rails and complementary output stages. Notice that the bias voltages applied to the bases of Q5 and Q6 are equal. Notice also that the outputs, drivers and pre-drivers are mirror images of each other (R5, Q5, Q2 and Ql vs R6 , Q6, Q4 and Q3). This is a common situation and allows calculation for ±Vee by considering just the positive side. In cases where the quiescent biasing varies for the positive and negative sides, the ±Vcc rails are worked out separately. Depending on the design, use the larger value for both supply rails. In this example (see Fig.1 again), there is 1.4 volts across the base-emitter junction of Q5 and R3. We will assume that at full power, the same voltage of 1.4 volts appears between the collector of Q5 and +Vee, 0.55 volt peak (Imax load x Rl) across Rl, and 1.6 volts across the base-emitter junctions of Ql and Q3. This gives a total overhead of 3.55 volts. Power supply ripple Next, you have to make an estimate for the ripple on the power supply. For this I like to use what I call Eatber's rule of thumb. Stated as a formula it looks like this: Vripple = 6300 X lmax load/Cwhere Vripple is the peak to peak voltage ripple on the power supply and C is the filter capacitor size in microfarads. The capacitors should be a minimum of 100-200µF per watt of output power for a class B amplifier with a full wave rectifier. (Actually, Eather's rule of thumb is not just a whim of mine but is a condensation of the maths for capacitor-input power supplies). For this example, I have elected to use two 2500µF capacitors for each power supply rail: Vripple = 6300 X lmax load/C = 6300 X 2.5/2500 = 3.15 volts The value for ±Vee is: ±Vee= Vmax load+ Vripple + circuit overhead For my design this becomes: ±Vee= Vmax load+ Vripple + circuit overhead = 20 + 3.15 + 3.55 = 26.7 volts This can be safely rounded off to ±27 volts. Transistor load lines OK so far? The next step is to figure out the transistor load lines. We are not going to bother with the load lines for resistive loads. These are straight lines and not really the problem for amplifiers. We are concerned with reactive load lines. These show the instantaneous voltage and current flowing through the transistors when driving a complex load impedance such as a speaker. To do this you need the output power, Imax load and ±Vee. You also need the value of the emitter resistors in the output stage (Rl, R2 in my case), the power output of the amplifier and the load impedance, Zl. Before leaping into the computations , we need to make an estimate of the maximum phase shift caused by the inductive portion of the speaker load. 45° seems to be the accepted standard in many electronics magazines and is the value we shall use FEBRUARY1991 15 20 " "- .... le = lmax load x sin(wt - 0) Write down each result in turn for the value of wt. Next is Vee using the more complex formula: Vee = Vee - Imax load X Zl X sin(wt) - le x RE The column for Ppk(W) is calculated by multiplying the collector emitter voltage Vee by the collector current le: Ppk(W) = V ce X le Table 1 shows the results for the amplifier under discussion. I'\ 10 .... " I'-- ~ 1 ", 1" I Sn LINE "-.... \ -........I'- V I '\ I \ \ \ \ Load variations I I I 0.5 I 0.3 0.2 I \ \ \ \ \ I I \ I 3 I 20 10 30 60 Vee (VI Fig.2: the 4Q & an load lines for the output transistors of the amplifier. These curves were plotted using the data shown in Tables 1 & 2 respectively. Note that the load lines should be fully enclosed by the DC SOAR curve of the selected transistor as shown here. here. However, if you intend to use your amplifier with highly reactive loads such as electrostatic speakers or line transformers, 60° would be a better choice. Drawing up a table Now we draw up a table with five columns and 13 rows. The columns are labelled: (wt - 0), wt , le, Vee and Ppk(W). Theta (0) is the electrical phase shift caused by the speaker. The term "wt" is the instantaneous phase of the signal frequency and is expressed in degrees. le is the instantaneous current through the collector of th e output transistor. Vee is the instantaneous voltage across the output transistor. Ppk(W) is the instantaneous power dissipated by the output transistor. The (wt - 0) column starts at 0 and steps up to 180° in 15° increments. Down the wt column write the corresponding value of wt. This is the same as adding the selected value of 0 (45° in our case) to the adjacent value of (wt - 0). This leaves the wt column with values starting at 45° and ending at 225 °. Start the calculations with le, using the formula: 16 SILICON CHIP Now take a deep breath. A general purpose amplifier could drive all sorts of speakers, some with only a very nominal 8Q impedance. For amplifiers in this situation, it is normal to design the amplifier so that it can safely drive into half the nominal load impedance. This may not be necessary if the amplifier is to drive a known speaker impedance or if using electronic limiting. If electronic limiting is not done carefully though, the amplifier may produce objectionable distortion if pushed hard into a nonresistive load. The rule of thumb for estimating power output into half the nominal load impedance is that the amplifier will produce about 50% more power. This won't apply if the amplifier has a well regulated power supply and large filter capacitors, in which case the power output will be closer to double. Conversely, if the power supply has poor regulation and small filter capacitors, the amplifier may only deliver a few percent more power into half its nominal load impedance. First, assume your amplifier will deliver 50% more power. Then you have to check that your amplifier will really deliver this power into the new load. Why? Because if it can, it will have to dissipate a lot more power and we need to know that the transistors can stand this extra stress. Work out the required value for Vee for the increased power output. This means going through the same procedure you did before, finding the required voltage across the load, the amplifier overhead and the power supply ripple using the new load impedance. A required value for Vee much larger than that available from your power supply means that the amp1ifier won't be able to deliver the extra 50% power, except maybe for short peaks. If the required value for Vcc is less than the actual supply, the amplifier will deliver a bit more than an extra 50%. Most times, allowing 50% gives a close estimate of what will actually happen. If, in your case, the value you came up with for Vee was very different, adjust your estimate of output power and go through the checking procedure again. For my amplifier, half the load impedance equals 4Q and I expect the amplifier to deliver about 37 watts. The calculations for Vmax load and lmax load give 17.3 volts and 4.33 amps respectively. The amplifier overhead goes up by 0.4 volts to 3.95 volts due to the higher current through the emitter resistors. The ripple on the supply also increases to 5.45 volts. So the Vcc needed is still about 27 volts. The next step is to calculate another load line for the new load impedance. Use the new values for Zl and lmax load. My results for output into a 4Q load are tabulated in Table 2. We can now draw some conclusions about the possible output transistors. The output devices must have an le rated higher than Imax load. The Vce must be twice Vcc and the power rating should be at least 50% greater than the largest value for Ppk(W) for most designs. In suggesting 50% more for the power rating of the output transistors, I am assuming power dissipation is the limiting factor and not secondary breakdown. It is just a ballpark figure and may need adjustment. Output transistors For your design, you should be able to make an educated guess about what output transistors or combination of transistors you will need to use. For my job, I will need the output transistors to have an le of more than 5 amps, a Vee of 60 volts or more, and a power rating of around 100 watts. I c;an now select some possible devices. For my design, transistor pairs such as the MJE3055/MJE2955, TIP3055/ TIP2955, 2N3055/MJ2955 or MJ15003/MJ15004 could all be suitable. I won't use the TIP and MJE pairs because the packages are not pin compatible even though they are of- HEAVY DUTY TV/SPEAKER WALL-CEILING BRACKETS Table 1 rot-0 0 15 30 45 60 75 90 105 120 135 150 165 180 rot 45 60 75 90 105 120 135 150 165 180 195 210 225 Vee le 12.858 9.537 7.406 6.611 7.205 9.148 12.308 16.469 21.347 26.611 31.901 36.858 41 .142 0.000 0.647 1.250 1.768 2.165 2.415 2.500 2.415 2.165 1.768 1.250 0.647 0.000 Ppk(W) 0.000 6.171 9.258 11 .687 15.600 22.091 30.770 39.769 46.218 47.042 39.877 23.848 0.000 rot 45 60 75 90 105 120 135 150 165 180 195 210 225 Vee le Ppk(W) 14.753 11.754 9.794 9.006 9.445 11.080 13.800 17.420 21 .692 26.326 31.007 35.414 39.247 0.000 1.121 2.165 3.062 3.750 4.182 4.330 4.182 3.750 3.062 2.165 1.121 3 0.000 0.000 13.172 21.204 27.576 35.418 46.343 59.755 72.858 81.344 80.605 67.129 9.687 0.000 ten sold as being interchangeable. The mounting tab is on opposite sides when placed into a PC board. This has the potential for mistakes during construction or repairs. Also, the power rating for these transistors is a bit low (only 90 watts). They could work but I will look around for something else. The 2N3055/MJ2955 pairs have a higher power rating for only a few cents more. This higher power rating could-lead to cost and size savings by enabling the use of a smaller heatsink. The MJ-15003 /15004 pairs are nice but relatively expensive. Compared to the 2N3055/MJ2955 pair, they do offer a better current gain-bandwidth product (ft) and would give slightly berotated 360 degrees ~:~ ~1H i1 li1 _, 1 as well as being swivelled up or down to any viewing or listening angle. The metal platforms have predrilled holes for mounting and are easily adjusted with a large alien key supplied with the unit. ~~ Imparted 1111d distributed by: Table 2 rot-0 0 15 30 45 60 75 90 105 120 135 150 165 180 The M83 and MB5 are heavy duty two platform mounting brackets designed for securing small TV's and speakers to walls, ceilings, desks or bench tops. When mounted both units can lower distortion. Also the much higher power rating means I could possibly get away with quite a small heats ink. Overall, the 2N3055/MJ2955 pairs should perform satisfactorily in my circuit so they are my first choice. At this stage, the choice of output transistors is no more than an educated guess. It is possible that the transistors may not be suitable. The graph of the load lines, transistor SOAR curves and the heatsink calculations will confirm the final choice. This is the time to check your transistor data book closely. Enlarge or redraw the safe operating area (SOAR) graphs for the transistors until they are a convenient size. Then plot the ~ ELECTRONICS Available through the fol/owing retailers: David J Reid All Electronic Electronics. Components. 127 York Street. 118 Lonsdale St. Sydney. 2000. Melbourne. 3000. NSW. (02) 267-1385. Vic. (03) 662 3506. SOUND AUSTRALIA Your P.A. Accessory Specialist Electronic Component Specials 555 Timer 4001 4007 4011 4013 -15volt regulator LED's 5mm Red, Green, Orange, the same price V28 7MHz $0 .1 0ea $0.15ea $0.15ea $0.15ea $0.15ea $0 .15ea Yellow All $0 .1 0ea $7.95ea HEAVY DUTY CARPETED ROAD CASE 4 Unit $100.00 6 Unit $115.00 8 Unit $135.00 10 Unit $155.00 12 Unit $175.00 Rack cases can be made to order in any size and any carpet colour. HANDLES 6" Strap $1.95 s· Strap 10• Strap $4.95 s· Nylon Briefcase Style Chest Handle Metal Recessed Spring Handle [Z] $ 2.45 $ 2.95 $ 2.95 $ 5.95 $12.95 - Please Call for a catalogue SOUND AUSTRALIA 28 Walker St. Dandenong, VIC, 3175 Telephone: (03) 791 1622 FEBRUARY1991 17 10 wt-e wt 0 15 30 45 60 75 90 105 120 135 150 165 180 45 60 75 90 105 120 135 150 165 180 195 210 225 Table 3 Vee 12.858 9.537 7.406 6.611 7.205 9.148 12.308 16.469 21 .347 26.611 31 .901 36.858 41 .142 I le Ppk(W) 0.000 0.032 0.063 0.088 0.108 0.121 0.125 0.121 0.108 0.088 0.062 0.032 0.000 0.000 0.309 0.463 0.584 0.780 1.105 1.538 1.988 2.311 2.352 1.994 1.192 0.000 '- '\ '\ \ ~ 0.1 ~ \ '\\ ' I I\ I I \ .01, 1 \\ 10 100 Vee (V) wt-e wt 0 15 $0 45 60 75 90 105 120 135 150 165 180 45 60 75 90 105 120 135 150 165 180 195 210 225 Table 4 Vee 14.781 11 .789 9.834 9.048 9.486 11.117 13.831 17.442 21.705 26.328 30.997 35.394 39.219 load lines for the amplifier using the points you calculated above. Fig.2 is my plot for the 4Q and 8Q loads using the data in Tables 1 & 2. You may be used to seeing these load lines in text books on graphs with a linear scale and think mine look a bit strange. Don't worry, they are the same type of graph only the scales arf) logarithmic. Notice how the 2N3055 SOAR curve fully encloses the load lines. If this were not the case, then the amplifier may die on the first occasion it is required to give a big burst of power. Make sure the load line~ are fully enclosed by the DC SOAR curve of your transistor. The fully enclosed load lines show that the selected 18 SILICON CHIP le Ppk(W) 0.000 0.056 0.108 0.153 0.187 0.209 0.216 0.209 0.187 0.153 0.108 0.056 0.000 0.000 0.659 1.062 1.382 1.774 2.319 2.987 3.639 4.060 4.021 3.348 1.979 0.000 power transistor can work in the design. Driver transistors Now we come to the driver transistors. The first step is to calculate the load impedance presented to the driver transistors. In my case, it is simply the speaker impedance multiplied by the minimum beta of the output transistor over the range of currents of interest (0 to lmax load). For the 2N3055, the minimum beta is 20. Calculate lmax for the driver by dividing Imax load by the beta of the output transistor. If your circuit calls for it, make sure you add in any Fig.3: these curves show the load lines for the driver transistors & were plotted using the data shown in Tables 3 & 4. As with the output devices, the load lines must be fully enclosed by the DC SOAR curve of the transistor. other currents the driver transistor must supply. Now calculate points for the load lines for the driver transistors in the same way as for the output transistors . Remember to do this for half the nominal load impedance if applicable. My results are tabulated in Tables 3 and 4 while Fig.3 shows the plotted load lines. Note that, as with the output devices, these load lines must be fully enclosed by the DC SOAR curve of the selected transistor. Go through the same selection procedure as you did for the output transistors. For my case, a look down the tables on this page shows a peak power dissipation of 4.06 watts and a maximum current of 216mA. Notice that even at these modest power levels, small signal transistors like the BC546/7 /8 aren't able to cope. Be wary of designs that suggest they will. I will try a BD139/BD140 pair for the driver transistors. Next month, we will see if a pair of BD139/BD140 transistors is up to the task of being driver transistors in the circuit of Fig.1. I think that they will but we'll find out for sure, next month. See you then. SC SHERIDAN ELECTRONICS We Want Your Business 68705 (Motorola) 6805 Processor with Eprom $11.50each IC SOCKET PACK 30 ASSORTED SIZES $2.95 PER PACK SUPER CAPS .047 5.5v KEEP THE VOLTAGE IN YOUR MEMORY 80cents each OTHERS SELL THESE FOR $3.95 TYTEL KEYPAD COMPLETE WITH LCD DISPLAY, AND SPEAKER $4.95ea 5" 24 WAY IDC HEADER CABLES $2.00ea 3 CORE MAINS LEAD AND PLUG GREAT FOR ANY MAINS PROJECT $2.50ea DISK DRIVE POWER SUPPLY 360k D/S DISK DRIVE TRANSMITTING VHF/UHF VALVE 2C39BA AIR COLLED 250 WATTS 50 WATT RE CUT SUITS XT or AT IBM Compatibles $49.95 $30.00 each NEW Just about as cheap as a Cleaning Kit NORMAL PR/ TRANSFORMER 12.5v plus 12.5v<at> 1.5amp 8v<at> 3amp PRIMARY: 2x110v 19.95ea ELECTROLITIC CAPS 91000 uF 15v $6.00ea 14000uF 25v $4.00ea b MALLORY 75ohm BNC CABLES NEC 432156-10 CRIMP PLUGS ON BOTH ENDS 62256 STATIC RAM WE HAVE THE CHEAPEST PRICE IN TOWN 0.. ·. . 3 M$~-~5ea 6 Metre $5.50ea $8.50ea · · H SCORE MATIC CADDY Replace your pen and score cards forever with this handy mini computer. You can keep tally of up to 4 players and can save your game for later recall. Many other features. Runs of two l;>atteries whi.Gh are supplied 240v MOTOR BY JAPAN SERVO CO. 80mm x 80mm x 75mm 1800 rpm 100mA with 3uF STARTER CAP THERMALLY PROTECTED $14.95 $19.95 each Great Gift Advertised elsewhere for $39.95 SPECIALS LIST MAGNETS 25mm x 10mm 22 uF 100v PCB ELECTRO'S 3v LITHIUM PCB BATTERY MINI MICRO SWITCH WITH LEVER MOC8042 OPTO COUPLER VARISTER 88JL .01 uF 50v MONO CAP 5-6v ZENERS 400mw Z80 OTC SCOOP PURCHASE TYTEL TELEPHONES HANDSFREE DIALING , 12 MEMORY, TONE OR PULSE, LED DISPLAY plus many other features. THESE PHONES ARE BRAND NEW 17 volt 3.4A, 8.5 volt 6.8A $110.00 each BRAND NEW $19.95 NORMAL RETAIL PRICE $425.00 SHERIDAN ELECTRONICS, 328 ELIZABETH ST, (Cnr Kippax St. opp. Central Station & Dental Hospital) SURRY HILLS, NSW, 2010 TELEPHONE: (02) 281 7727 Zl1~1 ~ $0.20ea $2.00/10 $0.50ea $0.50ea $0.50ea $3.45ea $2.00/50 $1.00/20 $1.00ea SHER.IDANS WILL BUY YOUR SURPLUS STOCK SHOP HOURS: MON - FRI SAT 9.00am - 5.30pm 9.30am - 12.00pm FEBRUARY1991 19 CIRCUIT NOTEBOOK Interesting circuit ideas which we have checked but not built and tested. Contributions from readers are welcome and will be paid for at standard rates. +9V 0.15 02 560k S1 o.11 J. 100 10VW TO FREQUENCY METER 1k LX 1k 1k OV .,. ,:J Q3 2N3904 VR1 5k LIN. + + 2500 m,J S2 LED1 GREEN 1k 270k 27k ov E 27011 1W .,. ►9V chosen because its unity gain bandwidth is greater than 3MHz, because of its high slew rate, and because it This economical inductance meter costs less than $3.00. IC1a operates is based on a wide-range oscillator with a gain of two and drives a freand can measure inductances from 3 quency meter. It also drives IC1b microhenries up to to 100 henries. which, together with diodes D1-D3, Transistors Q1 & Q2 form the wide- operates as a precision rectifier and range oscillator which is capable of drives a 300µA meter. covering from 10Hz to 30MHz. These The 300µA meter is used to inditwo transistors are emitter coupled, cate the onset of oscillation. Germwith the collector of Q2 fed back to anium diodes were selected for D1the base of Q1. The unknown induc- D3 because their forward drop is less tance, together with one of three ea- than 0.15V, which means that the . pacitors selected by S1 (.0lµF, 0.1µF meter will still operate at 3MHz when & 1µF), forms a tuned load which sets the gain of the ampl!.fier is reduced to the oscillator frequency. unity. The inductance meter can be caliA constant current source based on Q3 and ZD1 feeds the emitters of both brated against inductances of known Q1 and Q2. This current can be var- value. If you use a digital frequency ied by means of VR1 and S2, and is meter, you can produce frequency to used to set the emitter resistance of inductance conversion tables. AlterQ1 and Q2 and thus the gain of the natively, if an analog frequency meter oscillator circuit. In operation, the is used, its face can be calibrated to constant current source is adjusted so give a direct reading. Power for the circuit is obtained that the circuit just oscillates. The oscillator output level is self- from a mains transformer which limiting and has an amplitude of drives a bridge rectifer to obtain ±9V about 0.6V p-p. It is coupled to the supply rails. LED 1 provides power pin 3 input of non-inverting ampli- · indication. fier IC3a, which is half of a dual JFET The test procedure is as follows: op amp package. This device was (1). Connect the inductance to the Wide range inductance meter 20 +9V SILICON CHIP 2500 2500 ..gv test terminals and set all controls anticlockwise so that the 1µF capacitor is in circuit, VR1 is set to give maximum base voltage, and the 270kQ emitter resistor is selected. If the meter shows an indi-cdtion, then rotate VR1 clockwise to reduce the meter reading to say 5µA and read the frequency meter. (2). If the meter gives no indication, switch S2 to the next lowest value until the meter gives an indication , then rotate VR1 clockwise until the meter drops to 5µA and read the frequency meter. (3) . If, having selected all the resistors in the emitter, you obtain no reading on the meter, set S2 back to the 270kQ position and select the next lowest capacitor using S1. Repeat the above procedure until you obtain a reading. (4). Note that the same inductance can be, measured using several capacitor settings. If the meter cannot be brought down to about 5µA with the 270kQ emitter resistor in circuit, connect a 68kQ resistor to the test terminals in parallel with the unknown inductor. Victor Erdstein, Highett, Vic. ($35) .068 Mid-frequency tone control Adding a mid-frequ ency control to the standard Baxandall bass and treble controls is not an easy task. This circuit adds two op amps to provide the midrange control, leaving the bass and trebl e controls as normal. IC1b acts as a vo ltage follower with its input coming from the 100kQ midrange control which is connec ted across the existing feedback network for IC1d. The outp ut of IC1b then feeds IC1c which is connected as a bandpass filter, to feed and bias the non-inverting input of IC1d . Overall midrange control is claimed to be ±10dB in the range 450Hz to 2kHz, with a -3dB bandwidth of 350Hz, depending on the setting of VR4. While the circuit is shown using a TL064, it could be used with a TL084 14 o-f---- OUTPUT INPUT 0.15 or TL074, with the latter giving a lower noise figure. From "Electronics World+ Wireless World", October 1990. 02 •/J~,~~OONM 0-----<I-N"-+--- - - - - - - - , SWITCH 1N4002 68!1! +9Vo--------------------------------. IC3 555 01 18k 1N4148 470!1 01 BC559 c~i~~TO--Hlf-+-1+---+----f 470~10•·~---t + 47 IC2 555 + 1000+ Coolant level alarm for cars Unless you own an air-cooled VW, this idea could save you a lot of money and your engine as well! The circuit monitors the coolant level in the radiator and w·hen it gets below a certain level, an alarm sounds . The sensor used is a Ford part, XF 10K889A, as some of the bigger Ford's have provision for this to be fitted to the radiator. The circuit works as follows: While there is sufficient coolant to cover the sensor, which is essentially an insulated stainless steel pin, the non-inverting pin of the LM324 op amp (IC1), wired as a comparator, is held at +O. 7V by the input diode (D1), and the output of the op amp remains low. Once the coolant level drops, the 470µF capacitor at the non-inverting input charges up via the 18kQ resistor. Once the voltage across the capacitor reaches ½Vee, the output of IC1 goes high. Visual indication that something is wrong is provided by LED 1. This output is then fed to the input stage of a 555 oscillator (IC2) which has a frequency of 1Hz, as set by the 3.9kQ and 1.8kQ resistors and the 1000µF capacitor. The output from pin 3 is fed to an inverter/driver stage consisting of Ql and Q2. Q2 switches in another 555 oscillator (IC3) which provides an audible alarm to drive the loudspeaker. VRl allows the alarm volume to be adjusted. Glen Host, Doubleview, WA. ($25) FEBRUARY1991 21 A synthesised stereo AM tuner If you have the right equipment, stereo AM radio can sound fantastic. This new stereo AM tuner will really deliver the goods. It's based on a stereo AM receiver chip and features pushbutton tuning and digital frequency readout. By JOHN CLARKE & GREG SWAIN In September 1989, we published a 2-Chip Portable AM Stereo Radio based on Motorola's new high-performanc e MC13024 IC. That design is very popular but, since publication, there has been a steady stream of requests for a mains powered version with digital readout. This new tuner is our response to those many pleas. It's very easy to Despite its "high-tech" design, the new tuner is easy to build. Most of the parts are mounted on two PC boards which are soldered together at right angles. This view shows the completed assembly, before installation in the case. 22 SILICON CHIP build and align, yet boasts many impressive features such as 6-station memory, synthesised tuning with microproc essor control, digital readout and, of course, AM stereo decoding. It delivers low-distortion wideband stereo sound which, as far as most people are concerned, is every bit as good as FM stereo sound. One of our main concerns in producing a "high-tech" design such as this was that the unit had to be easy to build. This has been achieved by mounting most of the parts on two PC boards which are then soldered together to give a neat assembly. This assembly then fits into a slimline rack mounting case to give the tuner a modern appearance. All the control switches, the indicator LEDs and the digital displays are mounted on the display board. The switches and indicator LEDs protrude through holes in the front panel while the four digital displays are located behind a red perspex window. You don't have to get involved in too much metal bashing though - at least one kit supplier (Dick Smith Electronics) will be supplying a kit with a fully pre-punched front panel that will feature screen-printed gold lettering. A bevelled pers pex window that slots into place in the front panel cutout will be included as part of the deal. Front panel controls Let's take a look at the front panel layout. At the extreme left is a pushbutton on/off switch, whi le immediately to its right are a 5-LED signal strength indicator, the frequency display window and a stereo indicator LED. Next in the lineup are pushbutton switches for station seek and memory enable, and then the six station memory buttons. Finally, at the extreme right, there are two pushbutton switches for down/up tuning. 522·1629tllz FREQUENCY DISPLAY FERRITE ROD TUNED CIRCUIT 3.6MHz OSCILLATOR AUDIO AMPLIFIERS AND 9kHz _....__ NOTCH FILTERSLEFT r----'-----.VARICAP ERROR ~Sm'fE OlJTF-==---t MICROPROCESSOR CONTROLLER MUTE STOP LOCAL OSCILLATOR 972-207!111Hz 450kHz 1ST IF MIXER BUFFER 450kHz CERAMIC FILTER CQUAM STEREO DECODER AGC R 450kHz 2ND IF AGC STATION MEMORY SWITCHES AND LEDS SEEK, UP, SIGNAL LEVEL LED METER DOWN, TUNING MUTE CONTROL Fig.I: block diagram of the Stereo AM Tuner. It operates on the superheterodyne principle, which means that the local oscillator always runs 450kHz higher than the tuned RF (radio frequency) signal. The tuning is fully synthesised & is controlled by a microprocessor chip which also drives the LED displays. Most of the tuner functions shown are contained in a single IC - the MC13024. These controls are all easy to use. For example, when the Seek control is pressed, the tuner automatically scans up the frequency band and locks onto the next available station. The Memory Enable control allows you to store pre-selected stations in any one of the six memories. You simply tune to the desired station, then press the Memory Enable and the desired Memory switch to store the station setting. If the station switch is not pressed within five seconds, the Memory Enable LED extinguishes. Of course, you can tune manually if you wish and that function is provided by the Down/Up pushbuttons. When these buttons are pressed, the tuner steps up or down in 9kHz steps. If either button is held down, the tuner scans at a fast rate until the button is released. The stereo indicator LED lights whenever a station is received in stereo. Ferrite rod antenna For ease of antenna adjustment, we opted for a ferrite rod assembly instead of a long wire loop antenna. This is installed on an adjustable mount on the rear panel and provides excellent signal pickup compared to a balanced loop configuration. The antenna coil is a commercial unit by the way, so you don't have to go to the trouble of winding it. Nor do you need any special equipment to align this tuner - just a couple of plas- tic alignment tools and a multimeter. The alignment procedure is carried out using off-air stations and by measuring the AGC voltage. Block diagram Take a look now at Fig.1 which is the block diagram of our new tuner. It operates on the superheterodyne principle which means that the local oscillator frequency is always 450kHz above the tuned radio frequency (ie, the station frequency) . Both the RF and local oscillator stages are tuned using varicap diodes. These diodes are connected in parallel with inductors to form tuned circuits and vary their capacitance according to a control voltage. The microprocessor controller plays a very important role in the operation of this circuit. In addition to driving the front panel display, it also provides synthesised tuning for the AM tuner front end plus audio output switching and the station seek function. There are several inputs to the _microprocessor which control its operation. These include an input from the local oscillator, a Stop input from the station detector, and various inputs from the front panel switches (Up/Down tuning, Memory switches, Memory Enable and Seek). Basically, the microprocessor functions as a phase lock loop consisting of three sections: a reference frequency oscillator, a programmable divider and a phase comparator. In operation, the value of the programmable divider is set by inputs from the external switches. Depending on these inputs, it divides the external 4.5MHz crystal frequency to provide a reference frequency in the range 5221629kHz. This reference frequency is always some multiple of 9kHz, which corresponds to the station spacing. Inside the microprocessor there is also a counter which subtracts the 450kHz offset from the local oscillator. The resulting frequency is then compared with the reference frequency from the programmable divider. This produces an error output voltage which is then fed to the varicap diodes to lock the tuner to the desired station. In addition to frequency synthesis, the microprocessor also has outputs which drive the 4-digit frequency display and the memory enable and memory selection LEDs. These displays are all multiplexed. There is also a Mute output and this is used to switch out the audio amplifiers during tuning to eliminate noise. Tuner section Although shown as separate blocks, most of the AM tuner section of the circuit is contained in a single IC - the Motorola .MC13024. Those parts inside the chip include the local oscillator, the mixer, the two IF stages, AGC circuitry, a stereo pilot tone detector and a C-QUAM stereo decoder. To these, we have added the necessary tuned circuits for the RF and IF stages, plus signal strength indication, a station detect function and audio output stages. FEBRUARY1991 23 elude 9kHz notch filters. The notch filters remove any 9kHz whistles which can be generated by adjacent stations beating with the received station. Main circuit J The ferrite rod is installed on a small PC board along with its varicap tuning diode & a few other parts. This assembly in turn mounts on an adjustable bracket on the rear of the chassis, so that the ferrite rod can be oriented for best signal pickup. Following the mixer, the signal is fed to the 1st IF stage and thence to a wideband 450kHz ceramic filter. This filter has a response which is only 6dB down at ±12kHz but is then sharply rolled off to be 35dB down at ±20kHz to reduce noise. The output from the filter is then fed to the 2nd IF stage and thence to the stereo decoder. The output from the 2nd IF stage is also fed to a narrow band station detector block. This block consists of a narrow band ceramic filter, a gain stage and a comparator. Because the ceramic filter has a very narrow bandwidth (about 2.5kHz), the output of the comparator goes high only when the tuner is locked to the exact station frequency. This high is applied to the Stop input of the microprocessor and ensures that the tuner locks to the next available station when the Seek function is used. Stereo decoding An AM stereo transmission consists of an L+R (left plus right) mono signal plus a phase encoded L-R signal. To decode the L-R signal, the CQUAM decoder compares the phase changes in the 450kHz IF signal with a reference signal. This signal is derived from a 3.6MHz oscillator, which is divided by eight internally to give the required 450kHz reference. In operation, the decoder compares th e phase changes in the IF signal 24 SILICON CHIP against the reference and derives an error voltage using a PLL circuit. This error is then used to adjust the 3.6MHz oscillator, to bring it into lock with the IF signal. The phase fluctuations in the IF signal are interpreted by the IC as L-R stereo information. Once this signal is extracted, all that remains is to add and subtract it to the L+R mono signal to get the required left and right stereo outputs . The MC13024 will not switch into stereo mode on just any signal, however. The signal has to be confirmed as a genuine CQUAM stereo signal by detecting a 25Hz pilot tone in the L-R signal. If this tone is not present, the decoder will remain in mono. AGC voltage In addition to stereo decoding, the CQUAM decoder also derives an AGC (automatic gain control) voltage from the recovered audio. This voltage is used to control the gain of the preceding mixer and IF stages, so that the audio output level remains constant regardless of signal strength. The AGC voltage is also used to drive a signal level indicator. In thi_s circuit, the signal level indicator is a bargraph made up of five rectangular LEDs. Finally, the left and right outputs from the MC13024 IC are fed to audio amplifier stages. These stages boost the output from the IC and also in- Now take a look Fig.2. This shows the main tuner circuit diagram. While the circuit looks rather daunting at first glance, it's really not that bad. If you look at the centre of Fig.2, you will find the MC13024 (IC2) and this does most of the work. As we 've already pointed out, it is virtually a complete stereo AM tuner on a single chip. The remainder of the circuitry provides the narrow band station detect function (Q2, CF2 & IC4a-b), the signal level indicator (IC6, IC7 & LEDs 2-6) and the audio output stages (IC3ad). The incoming RF signals are picked up by antenna coil 11 which is tuned to resonance at the signal frequency by varicap diode VC1. A 4.7pF capacitor is wired in parallel with VC1 to provide the extra capacitance required to cover the high frequency end of the band. Another varicap diode, VC2, is used to tune local oscillator coil 12. This varicap is connected in parallel with trimmer Cl which is used to adjust the local oscillator so that it is always exactly 450kHz higher than the signal frequency. This 450kHz difference is equal to the intermediate frequency (IF) of the tuner. The series 470pF capacitor reduces the capacitive effect ofVC2 by up to a factor of 2 at the low frequency end. This is done because the local oscillator tuning range from 972-2097kHz is a 2.16 ratio , while the tuning range of the L1/VC1 antenna circuit from 522-1629kHz represents a 3.12 fre quency ratio . The tuning voltage for the varicap diodes is derived from the microprocessor-based control circuit. This voltage is applied to VC1 via a 100kQ isolating resistor and to VC2 via a 1MQ isolating resistor. In practice, VC1 , its two associated capacitors (.0lµF and 4.7pF) and the ferrite rod antenna are installed on a small PC board which is mounted on the back of the chassis. The output is taken from the secondary winding on the ferrite rod and fed to the RF input (pin 10) via a length.of shielded cable. DISK DRIVES AT RIDICULOUS PRICES (-------- - ------------ -- - - - -- - - -------, · Hard disk drive package deals with savings of up to $500 NEC 45 Mb AT BUS (IDE) Special Package deal for both the Drive and an IDE/FDD controller card NEC 42 Mb MFM Hard Disk Drive and MFM Hard Disk Drive Controller Card Only $495.00 Normally $695.00 You Save $200.00 This month only $549.00 Normally $795.00 You Save $250.00 NEC 115 Mb AT Bus IDE Drive and IDE/FDD Controller Card Reduced to only $995.00 Normally $1495.00 You Save $500.00 . ~-- - - ---- ------- -- - -- --------- ---------J SAVE $50.00 ON EACH OF THESE FLOPPY DRIVES Now is the time to add a second floppy drive to your system 1.2 Mb Floppy Disk Drive 1.44 Mb Floppy Disk Drive only $125.00 only $135.00 Normally $175.00 Normally $185.00 ~ ------------------- - --------- ---------, Notebook Computer - smaller than a ream of A4 paper 1 80C286 6/12Mhz 286 Weight only 3.2 kgs 1 1 I In such a small package you will find many of the features of desktop computers. VGA display which can emulate CGA, EGA, MDA and Hercules mode, as well a fast 25ms 20Mb Hard Disk Drive and 3.5" 1.44Mb I floppy disk drive. There is 1Mb of RAM on the motherboard which can be expanded to 8Mb. The built in battery gives more than three hours operation with a built in low battery warning lamp, can also be powered I from the mains . As well there are 2 x RS232 serial ports, parallel printer port, external 16 bit expansion port, I external VGA socket and external 1.2Mb FDD port. \, sx 16Mhz, 40 Mb HOD Available April 1991 Only $3995.00 1 •; I I I I · -···--··~··--·········--·····--·· i . /J ;\,"::,.~, ·1:.E:l .. ___ ______ ______________ _______________ IAN'S PERSONAL GUARANTEE * All products carry a 14 day money back guarantee ( except software and hard disks). * All prices include sales tax. * All cards come with full documentation All motherboards carry a full 12 month warranty. * All other products carry a full 3 month warranty. * Due to Technical advances, products we supply may in some cases vary from those pictured. In all cases the produ,cts supplied are guaranteed to perform to an equal or higher standard than those pictured - WHOLESALE ENQUIRIES WELCOME I VlSA I r------------------- 1 Send us this coupon to receive your FREE 1991 Catalogue: Electronic Solutions 5 Waltham St Artarmon 2064 PO Box 426 Gladesville 2111 Telephone: (02) 906 6666 Fax: (02) 906 5222 I Mr/Mrs/Ms:_ _ _ _ _ __ __ _ _ _ _ __ I I Address:_ _ _ _ _ _ _ _ _ _ _ _ _ _ __ I Suburb:_ _ _ _ _ _ _ _ _ State: Postcode:_ __ I I. Note: Please do not send back this coupon if you purchased from us in 1 990 or returned the previously issued card to be included on the mailing list (you will receive the catalogue automatically) . 02 /91 I I ·--------------------------· PARTS LIST 1 black rack-mounting case, 44mm high 1 bevelled red Perspex sheet for front panel 1 PC board, code SC01101911, 352 x 120mm 1 PC board, code SC01101912, 341 x36mm 1 PC board, code SC01101913, 101x11mm 1 SPOT plastic.rocker switch 10 black pushbutton switches 4 20-way Molex pin strips 1 dual RCA panel socket 1 mains cord & plug 1 cord grip grommet 1 Ferguson PC-mounting transformer, PL 12/5VA 1 4 rubber feet 2 solder lugs 1 150mA 3AG fuse 1 piece of Elephantide insulation (352 x 120mm) 1 panel mount fuse holder 5 5mm spacers 1 TO-220 heatsink 13 PC stakes 3 small cable ties 1 4.5MHz parallel resonant crystal 2 5kQ miniature horizontal trimpots 2 10kQ miniature horizontal trimpots Semiconductors 1 017106-227 microprocessor (IC1) 1 MC13024 AM stereo receiver (IC2) 1 LF347 quad op amp (IC3) 1 LM339 quad comparator (IC4) 1 4066 CMOS quad bilateral switch (IC5) 1 LM324 quad op amp (IC6) Note that the shielded side of the cable connects to the 1V reference of IC2 so that the RF input is biase d correctly. The output from the local oscillator tuned circuit is fed to pin 9 of IC2 via a l0Q isolating resistor. It also feeds buffer transistor stage Ql via a 47pF capacitor. The buffe red oscillator output appears at the collector of Ql and is fed to the local oscillator input (pin 18) ofICl. It is this frequency that is compared with the reference frequency derived 26 SILICON CHIP 1 LM358 dual op amp (IC?) 1 UA9667 Darlington driver (IC8) 1 4049 hex inverter (IC9) 2 BC548 NPN transistors (01,02) 5 BC328 PNP transistors (03-07) 2 BC549 NPN transistors (08,09) 2 B8212 double varicap diodes (VC1,VC2) 1 B8809 varicap diode (VC3) 4 common anode ?-segment LED displays (red, 13mm high) 13 red rectangular LEDs (LED1-13) 1 LM317 3-terminal regulator (REG1) 2 7805 5V regulators (REG2,REG4) 1 78L05 5V regulator (REG3) 61N4002 diodes (01-04,014,015) 10 1N4148 signal diodes (05-013, 016) Inductors & Filters 1 3/8-inch dia. x 100mm ferrite rod 1 prewound AM broadcast band antenna coil (L 1) 1 A7BRS-T1080UH Toko 7P coil (L2) 1 A7NRES-T1341AYN Toko 7P mixer coil (L3) 1 A7NRES-T1340AYN Toko 7P IF coil (L4) 1 A 119ANS-18287RS Toko 7P coil (L5) 1 SFP450D Murata ceramic filter (CF1) 1 SFZ450C Murata ceramic filter (CF2) Capacitors 1 2200µF 25VW axial electrolytic 2 4 70µF 16VW PC electrolytic 1 100µF 16VW PC electrolytic 2 47µF 16VW PC electrolytic from ICl (the microprocessor), as described previously. The error output from the microprocessor controls the tuning voltage and this in turn adjusts the capacitance of VCl & VC2 so that the tuner locks to the station . Normally though , a PLL circu it inside IC2 w ould control the local oscillator. However, as w e h ave just stated, the local oscillator in this circuit (insi de IC2) is controlled by a tuning voltage derive d from the microprocessor (ICl ). This has been 1 33µF 16VW RBLL electrolytic 1 22µF 16VW PC electrolytic 3 10µF 25VW PC electrolytic 10 10µF 16VW PC electrolytic 1 3.3µF 16VW RBLL electrolytic 1 2.2µF 16VW PC electrolytic 5 1µF 16VW PC electrolytic 1 0.4 7µF 16VW PC electrolytic 1 0.1 µF metallised polyester 1 .068µF metallised polyester 2 .047µF 2% metallised polyester 16 .01 µF ceramic 2 .0012µF metallised polyester 1 .001 µF ceramic 1 470pF polystyrene 8 270pF 1% polystyrene 1 120pF polystyrene 2 100pF ceramic 2 47pF ceramic 2 22pF ceramic 1 4.7pF NP0 ceramic 2 1.8-22pF trimmers Resistors (0.25W, 4 1.8MQ 9 1MQ 21MQ1% 1 330kQ 1% 1 180kQ 1% 1 180kQ 2 150kQ 7 100kQ 4 68kQ 1% 2 68kQ 2 47kQ 4 33kQ 218kQ 1 15kQ 5%) 6 10kQ 1 8.2kQ 1% 54.?kQ 7 3.3kQ 1 2.?kQ 2 2.2kQ 1 1.8kQ 9 1kQ 6 680Q 2 220Q 1 120Q 2 1000 7 47Q 4 10Q Miscellaneous Shielded cable (1 metre), machine screws & nuts, heatshrink tubing, hookup wire. achieved by using a high-Q tuned circuit for the local oscillator. IF stages The signal from the RF input is amplified and mixed w ith the local oscillator signal to produce an intermediate frequenc y (IF) signal of 450kHz. This appears at pin 11 and is resonated in the tuned circuit based on coil L3. A low-impedance tapping on L3 is then used to drive the SFP450D ceramic filter. TMl102C Sweep/ Function Generator Has Built-In Frequency Counter Metrix DMMs First To Offer New Level of Safety · lftll Metrix have announced that their popular MX50 Series digital multimeters have been tested and approved to safety standard VDE411, Class 2. <at> [g] They are the first manufacturer in the world to gain this approval. The MX50 Series now carries the VDE logo ind icating their compliance to the standard which requires protection against hazards such as electric shock or burn, excessive temperature, liberated gases and explosion or implosion. Among the safety features of the MX50 Series are fuse protected current ranges - even on the 10A range, totally sealed case (to IP66 standard) and a unique battery and fuse compartment accessed via the front face of the instrument. To gain access it is necessary to disconnect the safetydesigned test leads and Secur'XTM adaptor, thereby protecting the operator from accidental contact with hazardous voltages. il Goldstar Release 100MHz, 3 Channel Scope Under $2000 The new OS-81 oo 100MHz scope joins the popular Goldstar low cost oscilloscope range. It offers 3 channel, eight trace capability using a new 150mm rectangular CRT with internal graticule. Key features of the OS-8100 include high sensitivity (1 mV max) and a bandwidth limiting circuit. For X-Y phase measurements the bandwidth can be expanded. Trigger view is also incorporated together with single sweep.'B' sweep sampling enables improved observation of critical parts of waveforms. A variable 'Hold-Off' circuit and TV sync separation circuits are also provided. The Goldstar OS-8100 is very competitively priced at $1950 ex tax .. .Joins Popular Scope Range Goldstar also produce 20MHz and 40MHz dual trace and a 20MHz readout oscilloscope with measuring cursors. • 0.02Hz to 7MHz in 7 ranges • Multifunction Output with Sweep • Built-In 4 Digit Counter • External Sweep Control • CMOS/TTL Output • <0.5% Distortion from 10Hz to 20kHz • Variable DC Offset Order TMIT102C $340 ex tax Low Cost Topward Bench Supplies Have Extensive Metering • Tough aluminium cases for good heat dissipation • Constant Voltage & Constant Current Modes • Short Circuit Protection • Single & Triple Outputs • Two or Four Meters • Compact Design Model 2303 4303 Outputs 30V 3A Dual 30V, 3A plus fixed 5V, 3A Australia's Leading Test & Measuring Instrument Company NEW SOUTH WALES 18 Hilly Street, MORTLAKE · P.0.Box 30, CONCORD NSW2137 Tel. (02) 736 2888 Fax: (02) 736 3005 VICTORIA 12 Maroondah Higl1way, RINGWOOD P.O.Box 623, RINGWOOD VIC3134 Tel· (03) 87~ 2322 Telex: AA30418 Fax: (03) 870 8972 QUEENSLAND 192 Evans Hoad, SALISBURY P.O.Box 274 SALISBURY OLD4107 Tel. (07) 875 1444 Fax . (07) 277 3753 SOUTH AUSTRALIA 241 Churchill Road, PROSPECT P.O.Box 154 PROSPECT SA5082 Tel. (08) 344 9000 Telex. AA87519 Fax. (08) 269 641 'I W. AUSTRALIA 32 Teddington Road, VICTORIA PARK, WA 6100 Tel: (09) 4701855 Fax: (09) 470 31 73 Metrix 40 Series Ideal For Harsh Industrial Applications ~~ !di] • Exceptional All-Weather Performance • Four Year Warranty • 4000 Count Resolution . • Autoranging with Manual Override • Hold & Peak Functions • True RMS AC or AC+DC • Safe to IEC348 Class 11 from $220 ex tax 4.7k 100k 47pF 220n SEEK SET C2 2-22pF +5V +12V + + 101 16VWJ 10 16VWJ .01! 10ll .01! -:- 1°1T 01---1. 100k 120pF STYRO L5 18287 10!2 OUT 11 MIXER 16 IF IN 91VCLOt :::.>":---.--'wll.--"1 A1 ,. 01J .,. 22 REF 19 IF OUT L1 FERRITE ROD ANTENNA PLAIN PLL 3 TUNINGF- - 0UT osc IC2 MC13024 7 AGC>-- - - ;.- 10 RF IN .01 15 +1V REF PILOT 25Hz OUT 24 25Hz IN 1M 1% +5V 180k 1M 1% R OUT 20 L OUT LOCK 13 23 10 + 16VWI: 330k 1% 1% .01 -I +1V 01r 01+ .047 2% 8.2k 1% 10 16VW+ MUTE----+---..--- 100k +12V -:- TUNING VOLTAGE LOCAL OSCILLATOR OUT F1 150mA A D1-4 4x1N4002 A 100k IC5b 1 16VW - 10 + 16VWJ 1M No----~ EO>--~-, CASE 01 CASE 470 16VWJ .,. 6□ •12 •• 4• • 3 L2-L5 STEREO AM TUNER 28 SILICON CHIP VIEWED FROM BELOW + The ceramic filter contains four coupled resonant elements and these provi de an almost rectangular bandpass characteristic of 450kHz ±12kHz at the -6dB points. Its output is amplified by the 2nd IF stage (inside IC2) , the output of which is tuned to 450kHz by coil L4 and its associated internal capacitor (pin 19). A lO0kQ resistor across the coil damps it sufficiently to give the required ±12kHz bandwidth . 1000 .01 4.7k STOP 10k .sv 10k' 100k . 1M 6800 10n • 12v 01+ 15k 2.2k Stereo decoding A STEREO LED1 1M 'A 6800 4.7k .,. 1M 6800 .12v TP1 •1.3V-0.9V 1M 680 \l 3.3 .12v • 01l 16VW.J .12v ~ .,. 1M 68k 1% SIGNAL LEVEL DISPLAY 68 k 16VW 21orJ 100pFl 2% 10k s? ·rs 1 LEFT OUTPUT lk 270pF 10 • 16VWJ .12v--- 2% 270pF 2% The output of the IF amplifier is internally connected to an envelope detector, much the same as in a conventional (mono) AM radio. Wh en the MC1 3024 is in monaural mode, the output from the envelope detector is the L+R signal and this is fed to both audio outputs . The stereo decoder components comprise the 3.6MHz oscillator, a 25Hz pilot filter, and a lock filter at pin 13. The 3.6MHz reference oscillator is at pin 22 and is tuned by coil L5 and its parallel 120pF capacitor. Further tuning of th is stage is provided by varicap di ode VC3 which provides the small frequen cy shifts necessary to lock the 3.6MHz oscillator to the 450kHz IF signal when a stereo signal is present. The tuning voltage for VC3 is provided by the PLL output at pin 7 of IC2 an d, as stated previously, is derived by comparing the phase of the divided 3.6MHz oscillator with the 45 0kHz IF signal. Wh e n phase lock has been achieved, the deco der will switch to stereo provided th e 25Hz p ilot tone is present in th e demodulated L-R signal. In order to detect this pilot ton e, the L-R signal is first fed internally to. pin 8 an d filtered using a l00kQ resistor and .068µF capacitor. This re- - -+ 10 16VW: r 68k 68k 1% 1% 1 14 270pF .,. 10k 10 + 16VWJ 270pF 2% 270pF 100pF! '~ RIGHT Fig.2 (left): the main tuner diagram. Most of the work is done by IC2 which is virtually a complete stereo AM tuner on a single chip. It is tuned by varicap diodes VCl & VC2 which vary their capacitance according to a control voltage from the microprocessor circuit. Q2, CF2, IC4a & IC4b form the narrow band station detector, while IC6a-d & IC7a,b form the signal level meter. FEBRUARY1991 29 STEREO AM TUNER - CTD moves most of the audio but the pilot tone is still too small to be recognised at this stage. To overcome this problem, the filtered signal is buffered by an amplifier with a gain of two, between pins 5 & 4, and then fed to a high-Q 25Hz bandpass active filter between pins 1 & 24. This effectively extracts the 25Hz pilot tone from the low frequency noise. The output of the 25Hz bandpass filter at pin 24 goes to the MC13024's pilot tone detector. If the 25Hz tone is present for more than seven consecutive cycles, the decoder switches into stereo mode. When a new station is selected, the decoder immediately drops out of stereo and then returns to stereo again when the new pilot tone is detected. Because it takes 300ms to cciunt seven cycles of a 25Hz signal , there is a slight time delay before the stereo mode switches in. IC2 's pin 3 output is used to drive the stereo indicator circuit. When no station is present, pin 3 is at +5V. However, if a station is detected, the voltage on pin 3 drops to about 3.5V and, finally, to 0V if a stereo signal is decoded. Thus, when a stereo signal is detected , pin 9 of comparator IC4c is pulled low and so its pin 14 output goes low and drives stereo indicator LED 1 via a 3.3kQ resistor. The associated 15kQ and 4. 7kQ resistors set the voltage on IC4c 's inverting input to 1.2V. This ensures that pin 14 can only switch low when pin 3 of IC2,is at 0V; ie, when stereo is detected. Station detect circuit Q2, CF2, IC4a & IC4b form the narrow band station detect circuit. Its job is to stop the microprocessor from scanning further up the band as soon as a station is detected, when the tuner is in the seek mode. A tapping on IF coil L4 provides the signal drive for the station detect circuit. This signal is coupled to the base of common emitter amplifier stage Q2 via trimmer capacitor C2 which sets the sensitivity of the seek function. The amplified signal is taken from the collector of Q2 and is applied to 30 SILICON CHIP narrow band ceramic filter CF2. Its output drives the inverting input of comparator stage IC4a. When the input signal exceeds 20mV p-p, IC4a's output swings between the +5V and 0V supply rails. This signal then charges a .0lµF capacitor on pin 4 of comparator IC4b via diode D16. Two 10kQ resistors set the bias on pin 5 of IC4b to +2.5V, while the lO0kQ feedback resistor sets the hysteresis to about ±240mV. When the voltage on pin 4 drops below +2.26V (due to the .0lµF capacitor charging up), pin 2 switches high and delivers the stop signal to IC1. If there is no signal out of CF2 (ie, when tuning between stations), IC4a's output remains high and the .0lµF capacitor discharges via a 68kQ resistor. Signal level meter In addition to controlling the gain of the IF and mixer stages, the AGC voltage developed by the MC13024 is made availabl e at pin 17 and is used to drive the signal level indicator. This AGC voltage is first buffered by op amp IC7a which then drives a comparator chain consisting of op amps IC6a-d & IC7b. These drive the five signal level LEDs via 3.3kQ current limiting resistors. A resistive divider chain is used to set the voltages on the non-inverting comparator inputs, ranging from 0.8V on pin 6 of IC7b to 1.2V on pin 3 of IC6a. Thus, all the LEDs will be on for AGC voltages of less than 0.8V, indicating a strong signal, while all the LEDs will be off for AGC voltages of greater than 1.2V. For voltages in between these values, one of more of the LEDs will be lit to indicate the relative signal strength. The 1MQ resistors connected between the outputs and non-inverting inputs provide a small amount of hysteresis for each comparator. This is done to prevent the LEDs from flickering at the threshold points. Audio output stages The audio outputs appear at pins 20 & 23 of IC2 and are shunted by .0lµF capacitors to filter out high frequency noise. The left and right channels are then fed to op amps IC3a & IC3b via CMOS gates IC5b & IC5a re- spectively. These CMOS gates switch the signal through when the mute signal from the microprocessor is high (ie, when a station is detected) but go open circuit to mute the output when the control input is low (ie, during tuning and at power up or power down). IC3a & IC3b both operate with a gain of 11, as set by their 10kQ & lkQ feedback resistors. A .0012µF capacitor across each 10kQ feedback resistor sets the upper frequency rolloff to about 13kHz. Immediately following the amplifiers are the twin-T filter networks, based on IC3c, IC3d and their associated close-tolerance RC networks. These twin-T filters provide a sharp notch at 9kHz, to filter out signal beats from adjacent stations. VR1 & VR3 allow the total resistance in the bottom leg of each twin-T filter to be adjusted to the correct value, while VR2 & VR4 allow precise setting of the notch frequency. The 100pF capacitors on the noninverting inputs of IC3c & IC3d are there to prevent instability in the twin-T filters, and to provide a small amount of high frequency cut above 12kHz. Control circuit Now let's take a look at the control circuit for the new tuner, shown in Fig.3. At the heart of the control circuit is IC1 which is a standard NEC tuner control chip. Among other things, it provides the tuner control voltage and drives the 7-segment LED displays and memory LEDs in multiplex fashion. The Sa-Sg outputs drive the display segments and memory LEDs via Darlington buffer IC8 (UA96677), while the D1 -D5 outputs drive inverter stages IC9b-IC9f. These in- Fig.3 (right): the control circuit is based on microprocessor ICl. It's basically a phase lock loop that compares the local oscillator signal with a divided reference frequency & produces an error voltage at pin 8. This error voltage is then buffered by QB to give the tuning voltage for the varicap diodes in the tuner front end. ICl also drives the LED displays & decodes the switch inputs. ~ ... ..... co co ..... >-<: > :i:l c:: :i:l ~ t%J !:Cl I + 10 25VW! B SEEK ~o D13~ 1N4148 + IN 7 10 25VW+ A I I I 4 t 44 lk2 43L ~ + "T 29IFM STOP -:- I D1 4 1N4DD2 MUTE +5V DISPLAY p INT 5 voo 17 12 CE 2 MUTE 18 AM osc 13 STOP X1 ..,. GN0 9 5=+R" 0 XTA 4.5M LOCAL OSCILLATOR ":' 100 16VWI vv• 22pF I ?? t r-M"' I I I 33kl I"'~ "-~ I """% I - '-~- UP ~ ~ r-.~ 421Ko -:- GN0 10 IC1 D1710G-227 7 31 6 1 .01 '""' ':' J: 470 16VWI 1.8k 1 +12V 08 BC549 -f .,. D.47 + 16VW I 220 .,. i'.'N D TP2 TUNING VOLTAGE I t g 05 1N4148 I t D6 1N41 48 05 BC328 COM 3,8 DISPLAY 3 I '-Y 04 BC328 t /c /b COM 3,8 - d- 1/ ., a OISPLAY 2 IN I 4xZ-4145 COMMON ANODE DISPLAYS 07 1N4148 CDM 3,8 DISPLAY1 03 BC328 10 g 9I +5V~ 1_~ _ _.,u, ... _... 15 1e 14 4C 6b 7a 2d 7!~?P· 13 4 7kf 1 16VW -:- IC8 UA9667 TUNER CONTROL ME 20 D1 02 52 03 51 D4 50 D5 49 VDD 1 ~ I t1 '""~ 34 35 36 37 38 4D 41 a b C d e I g 12 ~o OUT B EOc I! l6 GN0 '~"' ~ .P. VIE WED FROM BELOW R ~ +5V DISPLAY OISPLAY 4 This view shows the completed tuner, minus its silk-screened front panel. It's easy to build & delivers superb stereo AM performance. verters then drive transistors Q3-Q7 which switch the display digits and the memory LEDs. ·The ME or 'memory enable' output drives the ME LED via inverter IC9a and a 1kQ resistor. In addition to driving the display segments, the Sa, Sb, Sc , Se, Sf & Sg outputs drive the switch matrix via isolating diodes D8-D13. The other sides of the switches are connected to the K0-K3 inputs of IC1, which are normally pulled low via 33kQ pulldown resistors. However, if a switch is pressed, one of the segment outputs will pull the corresponding K0K3 input high and the switch function is then decoded and executed by the microprocessor. Also connected to the Kl & K2 inputs are feature selection diodes D5D7. These are driven by the D1 & D2 outputs of 1C1 and are used to select various options; eg, 9kHz or 10kHz station spacing, discrete LEDs or a 7segment display for memory indication, etc. Because IC1 is designed to control both AM and FM tuners, it always comes on in FM mode when power is initially applied. Since we want to control an AM tuner only, Q9 has been included to automatically switch IC1 back into AM mode. It works quite simply. When power is first applied, pin 29 of IC1 goes high and turns on Q9 after a brief delay, as set by the 2.2µF capacitor. This in turn allows Sf to pull the K3 input high, which is the command 32 SILICON CHIP for IC1 to switch to AM control. A 4.5MHz crystal (X1), connected to pins 3 & 4, provides the timebase for the IC1 and this is loaded by two 22pF capacitors to ensure optimum operating conditions. Pin 8 (EO1) is the error output and this drives buffer stage Q8 via a 10kQ resistor. The output appears at the collector of Q8 and, after filtering, provides the tuning voltage for the varicap diodes in the tuner front end. The .01µF capacitor reduces high-frequency noise on the collector of Q8, while the series 1.8kQ resistor and 1µF capacitor form a low-pass filter. Other inputs and outputs are the stop input (pin 13), the local oscillator input (pin 18) and the mute output (pin 2). The oscillator input is derived from buffer stage Q1 on the main tuner circuit (Fig.2) as discussed previously, while the mute output controls CMOS switches IC5a & IC5b. Power supply Power for the AM Stereo Tuner is derived from a mains transformer which provides 12VAC at 5VA (see Fig.2). This drives bridge rectifier D1D4 and the resulting DC output filtered by a 2200µF capacitor to give an unregulated supply rail of about 17V. This 17V rail is then used to drive a number of 3-terminal regulators. For the main tuner circuit, the 17V rail is switched by S1 and fed to adjustable 3-terminal regulator REG1 to derive a regulated +12V supply rail. This +12V supply is used to power most of the op amp and comparator circuitry and also supplies the collector of Q8 via a 4. 7kQ resistor. It also drives REG4 which provides a +5V rail to power IC2, IC4 & IC5. Note the 470µF capacitor across the 1kQ voltage adjust resistor on REG1. This ensures a slow turn on to prevent large thuds in the audio output when power is first applied. (You can't get slow turn-on from a 7812 but with a capacitor on the ADJ terminal, you can with an LM317). The 0.1µF capacitor connected between chassis and circuit earth is necessary to keep the circuit earth at the same AC potential as the chassis. Without this capacitor, the sensitive 25Hz pilot detector in IC2 would be overloaded by 50Hz mains signal and there would be no stereo reception. Two separate supplies are used to power the microprocessor chip (IC1) - see Fig.3 again. First, a +5V supply is derived via REG3 from the unswitched side of S1 and this is applied to pins 5 & 17 via D14. This standby supply is on permanently (unless the mains is switched off at the wall socket) and keeps the microprocessor powered up to maintain the station memories when the tuner is switched off. If the mains supply is interrupted (or the tuner is switched off at the wall), the 33µF low leakage capacitor at pins 5 & 17 maintains the standby supply for several hours, to ensure that station settings are not lost. Diode D14 prevents the 33µF capacitor from rapidly discharging back into the regulator if the mains supply does fail. To compensate for the voltage drop across this diode, diode D15 jacks up the output of REG3 to 5.6V. The second +5V supply rail for the microprocessor is derived from the switched side of S 1 and is fed to the chip enable (CE) input via REG2. This supply rail is also used to power the LED displays. At first glance, the use of four separate regulators may seem unnecessary. Why not just use two: one to provide the +12V rail and another to power all the +5V circuitry? The answer is that separate +5V regulators are necessary to keep the multiplex noise generated by the control circuitry out of the sensitive tuner circuits. That's all we have space for this month. Next month, we will continue with the full construction details. SC COMPUTER BITS BY JENNIFER BONNITCHA Why it takes so long to turn on Ever wondered why your computer takes so long between the time you turn it on and the time when it is actually ready to do your bidding? This month we explain why. Start-up is a very busy time in the day-to-day life of your PC. One of the most important activities is the POST (Power On Self Test) which is a series of program routines, buried in the motherboard ROM (Read Only Memory). POST tests all the main system components at power-on time and is th,e reason why there is some delay between turning the computer's power on and actually using it; all tests are executed before the computer loads the operating system. The procedure tests all the primary computer components such as the CPU (Central Processing Unit - the "brains" of your computer), ROM, motherboard support circuitry, memory and major peripheral devices such as printers. However, the tests are brief in nature, to the extent that the POST process can provide error or warning messages when a faulty component is encountered, either by sounding a tone and/or displaying a message. Almost all manufacturers also display the system memory as it is tested. The last number you see (eg, 640KB OK) is the amount of memory correctly tested and the number should agree with the total amount of memory installed in your computer. Alternatively, you may see "conventional" then extended memory tested and reported as separate amounts. Watch next time you boot your computer and note also that expanded memory is not tested by the POST, nor does it count in the numbers reported. For a discussion of PC memory usage, refer to Brian Richard's article in the December 1990 issue of SILICON CHIP. POST error codes POST error codes usually provide tones with varying combinations of beeps to identify the faulty compo- Table 1: Error Tones TONE PROBABLE FAULT No beep Continuous beep Repeating short beeps 1 long, 1 short beep 1 long, 2 short beeps 1 short beep, bad/no display 1 short beep, no boot sequence Power supply Power supply Power supply Motherboard Video adpator card Video cable &/or display Disc cable, adaptor drive nent. If an error is detected during the POST procedure, an error message displays. These messages are usually in the form of a numeric code several digits long and will again depend on your computer's manufacturer. Normal POST completion sounds one short beep when the system starts. If any problems are encountered, you will probably get the tones shown in Table 1 but, as always, watch the screen and check the manual: In addition to the POST, general diagnostics and advanced diagnostics are available for most PCs. Diagnostics discs The manufacturer's System Diagnostics Disc (or equivalent) enables you to test various parts of your computer system, including the system unit and many installed options such as the expansion unit, keyboard, display, printer and so on. You often need to boot from the diagnostics disc to run the programs since a special version of DOS (Disk Operating System) resides on the disc. Of particular interest is the suppression of system parity checking during the boot process using this disc. A normal system may be continually locked up with a memory parity-check error. By disabling the check, a defective system may be able to "limp" through the diagnostics. For "technician level" diagnostics, the Advanced Diagnostics or the equivalent provide the "real" diagnostic programs which produce error messages in the form of numbers. Since many manufacturers offer their own versions of diagnostics programs, you should use those provided. If your system does not have this type of manufacturer support, you can generally use the IBM diagnostics. FEBRUARY1991 37 COMPUTER BITS - CTD Nearly all PC error codes for the POST are represented by the device number followed by two digits other than 00. The device number plus 00 is used to indicate successful completion of a test. Typical error codes are shown in Table 2. The Advanced Diagnostics do a good job with the system components, however these programs fall short when testing disc drives. Drives are the cause of the vast majority of problems in computer systems, so it is worthwhile finding a program to test not only the disc's data but also characteristics such as the drive's alignment. While many programs can evaluate the condition of, say, a floppy disc, not many can evaluate the condition of the drive itself. To do this, you need a disc created by a specially calibrated machine. This disc, which contains certain known errors, can then determine the capabilities of the drive against the disc in conjunction with the appropriate software. Errors can include sectors that are progressively further from the precise track centre, so the ability of the drive to read these intentionally off-centre sectors is used to guage the drive 's alignment. Basic booting As the computer initialises, ROM performs the POST and reads the contents of the Basic Input/Output System (BIDS). The function of the BIDS.SYS file is to talk to the system's peripherals. The IBM PC of old also contained Cassette BASIC, so if all else fa iled, you could play around with BASIC. Placing a small, but very essential part of start-up procedure in ROM allows the computer to boot itself automatically and yet remain flexible for future changes. While an in-depth knowledge of the various kinds of ROM is useful perhaps to a programmer, at some stage it is likely you may need to know which version of ROM is installed in your computer. New ROM ANTRIM ~ TRANSFORMERS versions deal with the ability to interface to the enhanced 101 keyboard, 5.25-inch 1.2Mb drive, 3.5 -inch 720Kb and 1.44Mb drives, hard disc types etc. Subtle differences hidden in your system can often be the cause of some strange problems. ROM version can be tracked through programs such as Norton Utilities and at a basic level through observation at boot time. For example, Phoenix Software manufactures compatible ROM BIDS chips for compatible motherboard manufacturers. A typical display is as follows: Phoenix 80286 ROM BIDS Ver. 3.05TB Copyright (c) 1985,1986 Phoenix Technologies Ltd. All Rights Reserved. If the display changes too quickly for you to read the information, try pressing AS (hold down Ctrl and press the letter S) or the Pause key on the 101 enhanced keyboard. Disc duties Having satisfied itself that the POST memory and hardware tests are complete, the next phase in the boot sequence is to search for a system disc with the operating system on it. A E-1 LAMINATED POWER TRANSFORMERS PCB MOUNT STOCK RANGE TRANSFORMERS, ILABLE PCB mount ex-stock in sizes from 2.5VA to 25VA with secondary voltages from 2 x 6V to 2 x 20V. Triple output models also available for logic circuits. Chassis mount manufactured to order in sizes from 2.5VA to 1KVA in E-1 and C core. CHASSIS MOUNT TO ORDER We are the largest ex-stock supplier of toroidal power transformers in Australia. Our standard range consists of the U.K. manufactured AN,:_RIM range in 10 VA sizes from 15VA to 625VA. All have a single 240V primary and dual secondary windings ranging from 2 x 6V to 2 x 55V. Our local manufacturing facilities supplement this range by manufacturing specials to order. Models are available from stock to suit most project kits. Comprehensive data sheets are available on request. Enquiries from resellers and manufacturers are welcomed. Prices are extremely competitive and generous trade discounts apply for quantity. 38 SILICON CHIP 90 George St., HORNSBY NSW disc qualifies if it has a boot record on the first track of the disc to indicate the presence of the hidden system files 10.COM and DOS.COM - machine language COMmand files. Should the first available disc not contain these two hidden files - you accidentally leave a disc in Drive A, for example - a NON SYSTEM DISK message displays. The first hidden file is 10.COM (or IBMIO.COM if you have the real article). This file contains extensions to the ROM BIOS routines and so by interfacing with it, can pass instructions to the processor and so determine equipment status, initialise peripherals, etc. It also loads the COMMAND. COM file into its allotted memory address. The second hidden file is MSDOS.COM (IBMDOS.COM). This file contains the DOS service routines which are the next level of system software up from ROM BIOS. Its functions include performing 1/0 (input/ output) operations to various devices, initialising the working tables of DOS, and performing its interrupt functions. Additionally, DOS.COM determines the lowest available address for COMMAND.COM to be loaded into Random Access Memory (RAM). CONFIG.SYS file Next, the contents of the CONFIG.SYS file are read from the system disc. SYS files are used by the operating system and they can hold software routines that control and communicate with the computer's devices or peripherals. This file generally contains default values for the operating system and information on required device drivers. The command processor COMMAND.COM is the highest level of DOS and its job is to interpret the commands a user enters through the keyboard and control the internal DOS commands. The internal commands are frequently-used DOS commands such as COPY, DIR, DEL etc that are kept in RAM. COMMAND.COM can't control external commands such as FORMAT, CHKDSK, etc and they must be loaded into memory from a disc whenever they are issued by the user. Executable files COM files are machine language command files. Thus, whenever you type a DOS command, DOS searches Table 2: Typical Error Codes CODE DESCRIPTION 01x 02x 1x~ 2xx 3xx 4xx 5xx 6xx 7xx 9xx 10xx 11 XX 12xx 13xx 14xx 15xx Undetermined problem Power supply System board Memory (RAM) Keyboard Monochrome Display Adaptor (MDA) Colour Graphics Adaptor (CGA) Floppy drive/adaptor 8087, 80287 or 80387 math co-processor Parallel printer adaptor Alternate parallel printer adaptor Asynchronous communications adaptor Alternate asynchronous communications adaptor Game control adaptor Matrix printer Synchronous Data Line Control (SDLC) communications adaptor Display emulation (327x, 5520, 525x) Fixed disc 1/0 expansion unit 3270 PC attachment card Binary synchronous communications (BSC) adaptor Alternate binary synchronous communications adaptor Cluster adaptor Enhanced Graphics Adaptor (EGA) XT/370 errors AT/370 errors 3278/79 emulation adaptor Colour/graphics printer Primary PC network adaptor Secondary PC network adaptor Compact printer errors General Purpose Interface Bus (GPIB) adaptor Data acquisition adaptor Professional graphics controller Voice communications adaptor 3.5-inch external disk drive IBM Expanded Memory Adaptor (XMA) Music feature card 16xx 17xx 18xx 19xx 20xx 21xx 22xx 24xx 26xx 27xx 28xx 29xx 30xx 31xx 33xx 36xx 38xx 39xx 71xx 73xx 85xx 89xx the disc and any path you set for a file with that command name. If the search fails, DOS then searches for a file with the same name and an EXE (EXEcutable) extension. You could say that binary notation EXE files are second-level command files since they are used less frequently· than the COM files. Finally, if an AUTOEXEC.BAT file is found, the information contained within is processed and the computer is ready for use. Next month, we'll have a look at the CONFIG.SYS and ANSI.SYS files, together with a whole host of environment settings you can try on your computer. But be warned: the earlier your DOS version, the less you can try. SC FEBRUARY1991 39 VINTAGE RADIO By JOHN HILL One thing leads to another It's funny how one simple act can lead to a series of events that probably would not have otherwise happened. In my case, these so-called events were well overdue and it was about time something was done anyway. It all started when I was looking for a potentiometer. I have hundreds of these items in various shapes and sizes and while looking for one particular pot I kept finding others. I was surprised to discover that I had so many wirewound types and these were put to one side rather than mix them up again with the other potentiometers. I eventually found what I was looking for and put the wirewound as- sortment into a box to be inspected at a later date. As my potentiometer collection is mostly secondhand, such pots need a thorough clean and checkout before they can be put back into service. In many cases, they don't make the grade. This particularly applies to old and used wirewound potentiometers. Not only are they secondhand but they are also often well worn, dirty and clogged up with dry grease. Checking and reconditioning these old pots seemed like a good idea for they would then be ready to use when needed. Wirewound potentiometers were used as volume controls in early superhet receivers up to about the mid-1930s, before the advent of AVC (automatic volume control) . The usual setup was to place the volume control in the cathode circuit of the intermediate frequency amplifier valve(s) and, in some instances, the frequency converter valve as well (but not in an autodyne). A variable resistance in the cathode circuit alters the cathode bias (effectively the grid bias) of the valves and, therefore, controls the gain or volume of the receiver. It was also normal practice to connect the aerial to the unused end of the volume control. This gave a secondary control of the volume because as the resistance in the cathode circuit increased, the resistance between aerial and chassis decreased. Two volume controls This 1936 model Radiola has two volume controls, one in the cathode circuit of the IF amplifier valve and the other in the audio section of the receiver. This arrangement is especially useful if the set is operated close to a powerful transmitter, since cutting back the gain ahead of the detector stage helps prevent overloading the audio stages. 40 SILICON CHIP Some pre-war superhets actually had two volume controls. One control was, as previously explained, in the cathode circuit of the IF amplifier valve, while the other was in the audio section of the set. Such an arrangement can be an advantage if the set is operated close to a powerful transmitter. Cutting back the gain ahead of the detector stage helps prevent overloading the audio stages. A local station switch has much the same effect but lacks variable control. Superhet design moved away from these early ideas, with the advent of AVC, and the volume control was eventually placed in the control grid circuit of the first audio valve only. When this is the case, a cheaper car- Resurrection Radio Vintage Wireless Specialists Repairs - Restoration - Sales Our skilled technicians offer QUALITY repairs and restoration. We also have a large stock of Bakelite and Timber radios fully restored and for SALE. This is just part of the author's potentiometer collection. Many old pots require cleaning and lubrication before they can be put back into service. One certainly collects lots of parts in the vintage radio business! Parts are available for the enthusiasts including over 900 valve types, high voltage capacitors, transformers, dial glasses, knobs, grille cloth etc. Circuit diagrams for most Australian makes and models. Send SAE for our catalogue. WANTED · Valves, Radios, etc. purchased for CASH Call in to our Showroom at: 51 Chapel Street, Windsor,Vlc 3181 PO Box 1116 Telephone: (03) 529 5639 control knobs only. That problem can be easily overcome, however. Extension shaft A few hours work was all that was required to restore these old wirewound potentiometers. Many old radios from the 1920s and early 1930s used wirewound potentiometers as volume controls. bon potentiometer is used. The need for a wirewound volume control in those early superhets is because larger currents flow in cathode circuits than in control grid circuits. However, in some instances, a carbon potentiometer can be used as a replacement for a wirewound type. If the volume control only alters the cathode bias on one valve, there is every chance of getting away with it. If it controls the bias on two valves, then a carbon pot may not be able to carry the current. Anything greater than a 0.25W load might be asking too much from a carbon potentiometer, although the larger old types were rated at one watt over the whole element. The wirewound pot was originally used for good reason. Dick Smith Electronics and other electronics outlets sell nice new wirewound potentiometers, including 5kQ and 10kQ, types that are ideally suited to early superhets. There is, however, one disadvantage with these modern replacements: they seem to be only made with an extremely short splined shaft which is suitable for metric style If these modern potentiometers are to be used for vintage radio applications, then they will require a neatfitting extension shaft. Because I have a lathe in my workshop, tailor-made extensions are no problem. Without the lathe, difficulties could be encountered because the extension shaft needs to be a very close fit in order to maintain reasonable alignment of the shaft. An ordinary commercially made extension may not fit these extremely short shafted potentiometers. When using modern wirewound potentiometers, remember that the wiper arm is insulated from the control shaft whereas in the older types this was not usually the case. This simply means that the arm is not automatically earthed when the pot is installed in the chassis by its securing nut. Therefore, the wiper arm connection may require earthing. As I like to keep my vintage radios as original as possible, I prefer to use a similar potentiometer if there is a FEBRUARY1991 41 Modern wirewound potentiometers usually have very short control shafts. A suitable extension will thus be required if you intend using this type of potentiometer as a replacement in a vintage radio. need to replace one. Hence the reason for reconditioning all those wirewound pots that had been put aside. Many of these volume controls are quite reusable but they do require a particular maintenance routine if they are going to work smoothly again. In this case, the word "smoothly" has two meanings: smooth mechanically and smooth electrically. Watch the needle To see how rough some of these old pots are, one only has to connect an ohmmeter and watch the needle dance up and down the scale as the wiper arm is turned around. Dusty or corroded contacts will cause the meter needle to fluctuate, a fault that will result in considerable noise if the component is used as a volume control. Making up suitable extensions for wirewound pot shafts is a fairly straightforward job if you have access to a lathe. Alternatively, you may be able to find a suitable commercial shaft extender. Worse still is the possibility that the fine resistance wire element has a break in it which will render the control pretty useless. A continuity check should be one of the first steps when repairing old wirewound potentiometers. Checking the overall resistance often shows a variation in the specified resistance ofup to 20%. For example, it is common for a 10kQ pot to measure as low as 8kQ or as high as 12kQ when checked with an ohmmeter. Modern wirewound potentiometers are made more accurately - not that it really matters in a volume control. Restoring old pots Cleaning up an old wirewound pot can only be done properly if the whole unit is stripped first. The bearing part of the shaft needs to be thoroughly Background To Volume Control The very early superhets used an autodyne type local oscillator/ mixer. The circuit values in these were quite critical and so they could not be included in the volume control system. With only one stage under control, overload on strong signals was a serious problem. The local/distant switch was the first solution but, because it relied on the user switching it in or out, was not always successful. Connecting the antenna to the unused end of the variable cathode resistor was a major improvement, provided the resistor value 42 SILICON CHIP was carefully selected. The development of the pentagrid converter was the next major step and allowed both valves to be controlled . Then, with the advent of AVC, the volume control was moved to the audio stage. Some people did object to AVC in the early days. One reason for this was the increase in noise between stations, particularly on the very sensitive sets that were popular in those days. Another reason, probably arising out of the first one, was the belief that sets with AVC "picked up more static". cleaned and regreased so that it will work smoothly. The electrical cleanup may require more time and effort. If the wire element is in good condition, it can be cleaned with a toothbrush or a blast of compressed air. However, all too often, years of wear and tear have almost worn the wire through. Even those types of potentiometer where the wiper arm presses a metal disc onto the wire can be worn to almost breaking point. Pots that employ a direct contact wiper arm are even more likely to wear the wire through. Now if the worn track is still in one piece, the potentiometer can usually be salvaged simply by removing the resistance winding and turning it over so that the opposite side of the coil is brought to bear on the wiper arm. This operation varies from being fairly easy to quite difficult, depending on the type of construction. Some types may not allow the wire element to be reversed. Naturally, reasonable care needs to be taken when repairing potentiometers in the manner just described, for it can be a delicate task. In most instances, wirewound volume controls can be completely restored by reversing the resistance element and cleaning and relubricating the mechanicals. This treatment costs absolutely nothing whereas a new pot costs around $8 and requires an extension shaft. The best part of an afternoon pased before I finished repairing my collection of wirewound potentiometers. Only two were discarded. It was a job that had been put off for quite some Vintage Service Tip Checking Early Pickups Depending on design and condition, many wirewound potentiometers can be restored by cleaning them and by reversing the wire resistance element so that a fresh section of track is brought to bear against the resistance arm. time and now they were all ready to use. As a matter of fact, I could even think of where I could use one straight away. Modifying an Airzone One of my radio treasures is a 193 7 5-valve console model Airzone. Although a 1937 model with octal based valves, it had a wirewound volume control in the cathode circuits of the first two valves. This control had developed a particularly bad spot where it made a lot of noise and the volume level jumped noticeably. It seemed like a good time to swap it over for one of my reconditioned units. When removed, the pot was found to be in excellent condition and it was repaired and put back into serv- Many early pots had their working parts exposed to the dust and grime. Cleaning the resistance element and lubricating the mechanicals (particularly the wiper arm) often restores the unit to working condition again. ice again instead of being replaced. The main problem with this particular potentiometer was a dob of gunk on the wiper track which effectively isolated a number of turns on the resistance element - hence the noise and the jump in volume. However, this simple repair was about to lead onto a more ambitious project. While the set was on the workbench , it seemed like a good opportunity to look at other things. The old Airzone has no AGC (Automatic Gain Control; also known as AVC or Automatic Volume Control). It is one of those receivers which requires two hands to tune in order to avoid "crashes" on the stronger local stations. Automatic gain control was one of the really good innovations to come out of the early 1930s. Why the Airzone was made without AGC is a bit of a mystery. Perhaps receivers without AGC were a little cheaper and the Airzone was a budget priced model? Perhaps some people liked them that way - who knows? What I proposed to do was add AGC to the old Airzone. It is a good receiver with a very attractive timber cabinet and the addition of AGC would most certainly improve an already excellent radio. I had been thinking about such a conversion for quite a while and now seemed like the ideal time to do it, even if I had to remove the volume control that had only just been fitted. A number of modifications would be necessary to convert the receiver to AGC. To begin with, the set would Old crystal & magnetic pickups can be quickly checked by connecting them to a set of high im pedance headphones and then rubbing a finger across the needle or stylus. The scratching should be clearly heard in the headphones. The relative output can be checked by comparison with a known good unit. Other then being open circuit, faults in early magnetic pickups are mainly confined to misalignment or drying out of the rubber armature dampers. In the latter case, repairs can be effected by using bicycle valve tubing. Cut off a length slightly less than that required and split it lengthwise. In most cases, the top (blade) rubber will also have hardened or disintegrated. Replacement of this is essential as it not only provides damping but also stops the armature hitting the magnet pole faces. Th is damper will have to be handshaped from sheet rubber of suitable resilience. Watch out for shorts in the old shielded cable used in these pickups. This often has rubber compound insulation which also cracks & hardens. Vintage Radio Service Tip is supplied by Resurrection Radio, 51 Chapel St, Windsor, Vic 3181. Phone (03) 529 5639. have to be changed to diode detection and the volume control shifted from the present cathode circuits and placed in the control grid circuit of the first audio valve. Finally, the AGC voltages would have to be connected to the control grids of the first two valves. Unfortunately, we have run out of space, so the AGC story will have to wait for some other time. If the conversion turns out OK (and there is no reason why it shouldn't), I know what it will lead onto next. The old Airzone isn't the only set in my collection that would benefit from such a modification, so the operation will be repeated a number of times. SC FEBRVARY1991 43 ~~ - ~ 1· ~ <at>1 < ~, DIGITAL MULTI METER HC -4510 DISPLAY:41/2 DIGIT ~I BASIC ACCURACY: 0.5% DC V DC VOLTAGE: 0-1000V DC CURRENT: 0-10A AC VOLTAQE: 0-750V AC CURRE~T: 0-10A RESISTANCE:' 0-20M OHMS CONTINUITY TEST, DIODE TEST DATA HOLD \ C ' I 20 MHz DUAL TRACE OSCILLOSCOPE · 013030 ........... 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(02) S19 3 868 (03) S43 2648 $1 • $9.99..........$3.00 $10 • 24.00 ........$3.50 $25 • $49.99......$4.50 $50 $99 99 $6 00 $100 • $199 .......$7.00 $200. $500 .......FREE $500 Plus .........FREE 335757 TOLL FREE MAIL ORDER t-lOTLINE FOR C~ ED;T ·~~~D ORDERS~. ~~.? 1·~.• -~ \ '\~\,__, , ,%~ --<~~ r ;\\v ~C ~ ~~ ,· .4 ~\ d ~ t / . ,- ' _c-~ ~ ~ - · ~ _f ~ • "'~) W/ /~ ~ ~ Three inverters for fluorescent lights Battery powered fluorescent lamps are commonly available as a feature of some torches but they are flea-power units. Here we present three DC-AC inverters, suitable for fluorescent lights rated up to 40 watts. Design by OTTO PRIBOJ Fluorescent tubes are one of the most efficient forms of electric lighting but because of their high voltage requirements, they are rarely used unless 240VAC mains power is available. Yet there are many applications where the high efficiency of fluorescent tubes could be highly useful. These range from portable emergency lighting to lighting for recreational vehicles, caravans, boats and farms. In fact, if a pinpoint light source or a 46 SILICON CHIP concentrated beam is not required, then fluorescent lighting should be the first choice, because of its efficiency, glare-free light and freedom from shadows. This series of three inverters provide the necessary high AC voltage to drive a fluorescent tube from a 12V DC supply and at a high efficiency. Not only that, the circuits are low profile and use readily available components. DC to AC inverters intended for driving fluorescent tubes have two quite different requirements. First, they must generate sufficient voltage to fire the tube. Once the discharge is established through the tube, it becomes a negative resistance which means that unless there is some means of current limiting, the tube will destroy itself. In conventional mains powered fluorescent lamp fittings, the ballast performs two duties. First, in conjunction with the starter bulb, it produces the voltage to fire the tube arid then, its inductive reactance limits the current through the tube to a safe level. This is a very effective and time proven circuit which is used in billions of fluorescent lamp fittings throughout the world. But using a ballast to limit the lamp current in a battery-powered fluores cent circuit is not practical because of the relatively high losses involved (about 10 watts for a 40 watt tube). This is too much to tolerate for a battery operated circuit. Fortunately, as the saying goes, "there is more than one way of skinning a cat". When designing a transistor driven inverter, it is desirable to make it run at a high frequency. This enables a very compact ferrite cored transformer to be used and also allows losses to be minimised. Using a high frequency to drive the fluores cent light fitting then gives a further advantage - we don 't have to use a conventional inductive ballast. Instead, we can use a capacitor. This will limit the current but the capacitor will have very low interna l losses which translates to higher efficiency. As well, the capacitor will be more compact and cheaper than an inductive ballast. It is also possible to design the inverter to have a higher internal impedance in order to limit the discharge current through the fluorescent tube but that tends to lead to higher losses and hence, higher current drain. Let's now have a look at the ci rcuit. The circuit Simplicity is the byword for this circuit although as with many ostensibly simple circuits , there is more to it than at first meets the eye. As shown in Fig.1 , the circuit is essentially a straightforward push-pull transistor inverter. The positive DC supply connects to the centre-tap connection on the primary winding of the transformer and the collectors of the two power transistors are each connected to the ends of the primary winding. When one transistor, say Ql, turns on, it saturates and applies the full 12V DC across half the transformer primary winding. By transformer action, thi s applies 12V (in opposite polarity) to the other half of the transformer winding , so that we have a total of 24 V across the full winding. The current builds up in the transformer winding associated with Ql until it reaches its maximum value whereupon Ql is suddenly forced to turn off and QZ turns on. Why? Because transformer action also applies to the other windings of the transformer and this means that the base drive voltages for Ql and QZ are generated by the associated 2-turn windings. When the current pulled by Ql reaches its maximum value, it effectively becomes DC and since transformers don't work on DC, the base drive voltage to Ql suddenly drops to zero. +12V Rx 1W 470 16\/V\' , + 0.47 TO FLUORESCENT TUBE ov ; BCE RX 40W Cx 120(2 + 22U .001 600VACl/.001 600VAC 20W 330\l 7-16W 680!1 .001 600VAC// .001 600VAC .001 600VAC 01 02 TIP3055 TIP3055 MJ E3055 VERSATILE FLUORESCENT INVERTER Fig.1: the circuit is a straightforward transistor inverter which steps up the 12V DC battery voltage to about 1000V AC to fire the fluorescent tube. Capacitor Cx limits the tube current to a safe value while flyback diodes D1 & D2 protect the transistors from voltage spikes when each one turns off. This causes Ql to turn off and since the current pulled by Ql is no longer DC but rapidly dropping to zero, transformer action now generates base voltage for QZ which then turns on fully. This reverses the 24V across the full primary winding and so the current pulled by QZ climbs to its maximum value whereupon the cycle begins again. The voltage across the transformer primary is 24 volts peak or approximately 12 volts RMS. (Actually, it will usually be higher than that, depending on the condition of the battery). This voltage is then stepped up by the 500-turn secondary winding to aro und 1000 volts RMS. This is enough to fire any fluores cent tube currently available. It will even fi re the 1.5-metre long 58 watt tubes. Once the discharge current through the tube is established, capacitor Cx in series with the tube limits the current to a safe value. Starting the inverter Balanced inverters such as the one depicted in the circuit of Fig.1 will usually not start by themselves. They need a fixed bias so that one of the transistors can turn on and start the switching cycle described above. This bias is provided by resistor Rx and the ZZQ 0.5W resistors in series with the bases of Ql and QZ. When power is first applied, both transistors try to turn on but the one with the highest current gain (beta) wins the race and starts the cycle. Diodes Dl and DZ are flyback protection diodes, included to protect the transistors from the peak voltages that are developed when each one turns off. Air gap in ferrite core All three versions use the same transform er but the gap between the ferrite cores is varied to set the current drain. This concept may be novel to some of our readers so we'll explain the principle. Normally the transformer used for DC-AC inverters is constructed without any gap which means that the core permeability is very high. This means that a relatively small magnetising force (ie, ampere-turns) is required to saturate the core. This results in a squ are hysteresis curve and a very square AC waveform in the primary and secondary windings. Such a waveform though is not really suitable if the current limiting element for the fluorescent tube is to be a capacitor - all it will let through will be very narrow current spikes FEBRUARY1991 47 which will not let the tube operate at normal brilliance. No, for the capacitor to correctly limit the current through the tube, the voltage waveform from the transformer should be more rounded, like a sinewave. This is achieved by having an air gap between the two halves of the ferrite transformer core. The oscilloscope photo accompanying this article shows the voltage waveforms which can be expected from the transformer. Note that they are nothing like square waves but much more like sinewaves. Having an air gap means that the inverter also draws a substantially higher current and that means the exact dimension of the air gap is quite important. We'll have more to say about this later. Construction All three inverters can be built using the same PC board which is coded PARTS LIST 16W Version 1 PC board, code SC11103901, 99 x 45mm 1 L-shaped mounting bracket (110mm in length) 1 TO-220 heatsink mounting kit 1 Siemens ETD29 transformer bobbin, N27 core & clips 1 25-metre length 0.2mm ECW 1 5-metre length 0.25mm ECW Semiconductors 2 MJE3055 NPN power transistors 2 1N4002 200V 1A power diodes Capacitors 1 470µF 16VW PC electrolytic 1 0.47µF 63VW metallised polyester (WIMA MKS, 5mm lead spacing) 1 1000pF 600VAC polypropylene (WIMA FKP 1) Resistors (5%) 1 6Bon ;w 2 22Q 0.5W Miscellaneous Hookup wire, screws, nuts, washers, solder, etc Note: ECW = enamelled copper wire 48 SILICON CHIP DV - TO FLUORESCENT • ~ ~ - TUBE Fig.2: all three versions of the inverter are built on the same PC board but some of the component values are different, as are the transformer winding details (see Fig.I). The completed board is mounted on an L-shaped bracket which is used for heatsinking but note that Qt & Q2 must be electrically isolated from this heatsink as shown in Fig.4. SCl 1103901 and measures 95 x 40mm. When you buy or make the board and before you commence construction, check it for breaks or shorts in the tracks. If there are any, correct them now. The table in Fig.1 shows the values for Rx and Cx for each model of the inverter. It also indicates that TIP3055s are used for the smallest inverter while the more rugged MJE3055s are used for the 20 watt and 40 watt models. After checking the board, you can install the wire link, the resistors, diodes and the capacitors. Make sure that you have the electrolytic capacitor inserted correctly. Winding the transformer when you rattle or crumple them them). You can now begin winding the second layer of another 100 turns, after which you repeat the above process. Continue doing this until you have wound fiv e layers of 100 turns, making up the 500 turns of the secondary winding. Note that if you are building the 16W version, only 400 turns are required. Once you've completed the last of the five windings, wind on five to six layers of polypropylene foil to ensure isolation. Now for the primary and base windings. The primary winding (that is the winding to the transistor collectors) contains two windings of six turns which are tapped in the middle. The gauge of the wire in this case depends on the inverter you are working on. For the 7-16W version, the wire is 0.35mm and 0.5mm for the other versions. The base windings are two wind- Before you continue any further with the board, you should begin winding the transformer. Fig.3 shows where the windings should be terminated on the former, as well as giving the correct number of turns for each inverter. Begin by winding on 100 turns of 0.2mm enamelled copper wire (or 0.25mm for the 40 watt inverter). This should get you from one side of the core to the other. Now, using a small brush, apply an even coating of petroleum jelly (Vaseline) to the winding. Once this has been applied, cover the winding with a layer or two of polypropylene foil. A This oscilloscope photograph shows the voltage good source of this is waveforms that can be expected from the those freezer bags you transformer. At top is the 200V p-p tube voltage can buy from your local while the bottom trace shows the 30V p-p supermarket. (These bags waveform which appears on the transistor collectors. The frequency is 17kHz (approx). are crinkly and noisy y X B rl-ol Lr-r-r , 2 31 A 0 0 0 O h ol 0 bifilar (ie, with two wires together) but in this case bifilar winding has not been used. When all the windings are complete, the starts and finishes must be cleaned of enamel, tinned and then terminated to the various pins of the bobbin. Before the wires are terminated, it is a good idea to fit some sleeving over them. Setting the air gap I C 1-2,2-3 A-B,B-C X-Y 40W 2T, 0.35mm ECW 20W 2T, 0.35mm ECW 6T, 0.5mm ECW 6T, 0.5mm ECW 7-16W ZT, 0.35mm ECW 6T, 0.35mm ECW 500T, 0.25mm ECW 500T, 0.2mm ECW 400T, 0.2mm ECW Fig.3: terminate the transformer windings exactly as shown here. The step-by-step winding details are given in the text. Be sure to use the correct gauge of wire & number of turns on the secondary for each version. ings of two turns each, again tapped in the middle. The wire gauge here is 0.35mm throughout. Note that some inverter transformers have the primary windings wound With the windings completed and terminated, the two ferrite half-cores can be placed into the bobbin and held in place by the spring clips. Before the second core half is placed though, the air gap needs to be set. Actually, it is not an air gap but a space between the two core halves, set by a given thickness of insulating material which may be paper or plastic. For the 7-16W inverter, the gap is 0.1mm; for the Z0W and 40W models, 0.44mm. How do you obtain a suitable thickness of material for that gap? If you have vernier caliper or micrometer, then it is simply a matter of measuring some plastic sheeting or paper and then folding it to give the right thickness. If you don't have one of these instruments, a single thickness of a page PARTS LIST 20W Version 1 PC board, code SC11103901, 99 x 45mm 1 SOT-93 transistor heatsink mounting kit 1 L-shaped mounting bracket (110mm in length) 1 Siemens ETD29 transformer bobbin, N27 core & clips 1 30-metre length 0.2mm ECW 1 1-metre length 0.5mm ECW 1 1-metre length 0.35mm ECW Semiconductors 2 TIP3055 NPN transistors 2 1 N4002 200V 1A diodes Capacitors 1 470µF 16VW PC electrolytic 1 0.47µF 63VW metallised polyester (WIMA MKS, 5mm lead spacing) 2 1000pF 600VAC polypropylene (WIMA FKP 1) Resistors (5%) 1 330.Q 1W 2 22.Q 0.5W Miscellaneous Hookup wire, screws, nuts, washers, etc Note: ECW = enamelled copper wire Below: the switching transistors are bolted to the L-shaped bracket to ensure adequate cooling. This is the 16W version which uses MJE3055 transistors. FEBRUARY1991 49 INSULATING MICA WASHER -~jl SCREW r ~ ----CASE 1 T0220 DEVICE Fig.4: mounting details for the switching transistors. Smear all mating surfaces with heatsink compound before bolting each transistor to the heatsink, then use your multimeter to confirm that its metal tab is correctly isolated. of this magazine is close to .05mm. A single page of a newspaper is close to .08mm while standard 80gsm photocopier paper is 0.1mm. With a combination of these materials, you can obtain the right thickness of material for the transformer gap. By the way, you can obtain a very cheap plastic set of vernier calipers for as littl e as $3.50. See your local hardware store. Now that you've completed the transformer, you can ins ert it into place on the PC board. Use the overlay diagram to make sure you have connected it up correctly. Check again for any solder splashes on the board as it will not be possible to do this after the two transistors have been mounted on the heatsink. Heatsink bracket As you can see from the photos, the prototypes had the two transistors I. ' li.J 0 mounted on an L-shaped aluminium bracket. The two transistors are insulated from the aluminium bracket with mica washers, insulating bushes and heatsink compound, as shown in Fig.4. The L-shaped bracket also has the PC board mounted on it, as you can see. Before you mount the transistors on the bracket, solder them into position on the board; then, using four mounting screws, spacers and nuts, secure the board to the bracket. Note that the 40W version of the inverter needs an additional finned heatsink mounted to the back of the aluminium bracket. Use a larger heatsink than the one shown in our photos, as our prototype ran a little too hot for our liking. When the transistors are mounted, switch your multimeter to the ohms range and make sure that both transistors are correctly isolated from the aluminium bracket. You should get an open circuit if you _measure between the bracket and the transistor tabs. Ideally, the whole board and bracket assembly should be mounted inside a standard fluorescent light fitting but before you do that, it's time to check the circuit operation. You will need a 12V power supply or battery capable of delivering sufficient current to suit the inverter model. When operating correctly, the inverters will draw the following currents: 7-16W 20W 40W 0.9A 1.4A 3.2A When connecting the power supply to the inverter, make absolutely sure you have the correct supply polarity. If you don't, you are liable to 00---. • OP-010 FLUORO INVERTER You can use this full-size pattern to etch your own PC board and to check your finished board for possible defects. 50 SILICON CHIP PARTS LIST 40W Version 1 PC board, code SC11103901 , 99 x 45mm 1 SOT-93 transistor heatsink mounting kit 1 L-shaped mounting bracket (110mm in length) 1 single sided finned heatsink (see text) 1 Siemens ETD29 transformer bobbin, N27 core & clips 1 30-metre length 0.25mm ECW 1 1-metre length 0.5mm ECW 1 1-metre length 0.35mm ECW Semiconductors 2 TIP3055 NPN transistors 2 1N4002 200V 1A diodes Capacitors 1 470µF 16VW PC electrolytic 1 0.47µF 63VW metallised polyester (WIMA MKS, 5mm spacing) 2 1000pF 600VAC polypropylene (WIMA FKP 1) Resistors (5%) 1 120Q 1W 1 22Q 1W 2 22Q 0.5W Miscellaneous Hookup wire, washers, screws, nuts, solder, etc. Note: ECW = enamelled copper wire damage the transistors. When you are connecting the fluorescent tube, you will find that it has two pins at each end. These pins are for the heater filaments which are not used in this circuit. You can make the connection at each end to either filament pin - it does not matter which. When power is applied, the tube should immediately light up and then abruptly increase its brilliance after about one or two seconds. There is no flickering as with conventional starter/ballast fluorescent lights. Note that fluorescent tubes do not reach their full brilliance when they are first turned on. Depending on the ambient temperature, they make take 10 minutes or longer to reach full brilliance. Even so, if you are a making a di- BARGAIN PRICED LASER A spacial purchase ol lllls tuba, which Is priced at a fraction ol Its real value allows us ID offer Ibis mains (240¥) powered KIT SPECIAL. Use 11 lor disco affects, holography, axparlmanling, ale, ale. Includes a la111a 2·3mW HE-NE tuba, translormar, PCB, and all components, amins plug and lead plus Illa mains switch: Everything except the case. IMPORTANT: This product carries lethal voltages and Is not for kids. Strlctty during February and Man:h, or until stocks run out at this unrepeatable price ol: ONLY $249.90 !! The price even includes Certified P&P. Don't tell your friends because you could miss out yourself! This view shows the 20W version of the inverter. Note the mica washers & insulating bushes used to isolate the switching transistors from the L-shaped aluminium bracket (see also Fig.4). The completed converter should be compact enough to mount in a standard fluorescent light fitting. LASER SCANNER DRIVER KIT This PCB and all romponents kit can be driven using an audio source or an electret microphone, to produce magnificent visual displays which are synchronised to music. Drives speakers with mirrors attached, or professional X-Y scanner. Makes provision possible driving from a romputer (with rorrect software). The kit includes the PCB, all onboard components, battery holde, external potentiometer, and even an electret microphone for ONLY $20.00 Professional X-Y scanner: $220 Small front surfaced aluminium mirrors: $9.00ea (These are to attach to the front of speakers) SEE IN THE DARK! A large finned heatsink (preferably slightly larger than the one shown here) should be fitted to the 40W version to stop the switching transistors from overheating. Although rated for driving 40W tubes, this version can also be used with the 36W slimline tubes, while the 20W version above can be used with 18W slimline tubes. rect comparison between a fluorescent tube powered by one of these inverters and an identical tube powered from a conventional mains fitting, you will find the brilliance of the inverter-powered tube slightly down. This is normal and is the compromise we came to for best efficiency. If you find that your inverter-powered lamp is not as bright as it should be and the inverter is drawing less current than it should be, it is likely that the transformer gap is not correct. Increasing the air gap by adding another thickness of paper should increase the brightness and the current drain. However, the current drain should not be appreciably higher than the values we show above, otherwise the inverter transistors will rapidly overheat. When normal operation is confirmed, you can mount the inverter inside a standard fluorescent light fitting and the job is finished. Finally, you can use the n ewer slimline tubes with these inverters. The 20W inverter will happily driv e an 18W slimline tube while the 40W job will drive a 36W slimline tube. sc with our INFRA RED NIGHT VIEWER at a SPECIAL price of ONLY $349.00 Only while stocks last, . . .• . and during March and April only we will include a high quality round IR filter which is 3mm thick and has a diameterof75mm. Can be easily cut down to suit your torch We have good stock of the 6032A tubes. This is your opportunity to build your own night viewer. A product which commercially usually costs 1000's of dollars at a fraction of the price. We supply the electronic kit, a 6032A Image Intensifier tube, and the case components. The 6032A iubes are BRAND NEW and pertorm well wi1h a good infra red torch. Torch and Lenses are not supplied I VISA I OATLEY ELECTRONICS PO BOX 89, OATLEY, NSW 2223 Telephone: Fax No: (02) 579 4985 (02) 570 7910 Certified p&p $4-$6 Aust. NZ add $2 Melbourne Distributor - Electronics World (03) 723 3860 or (03) 723 3094 FEBRUARY1991 51 AL TRON/CS ELECTRONICS COMPONENTS YOURS FREE with this month's Silicon Chip and CATALOGUE Electronics Australia Magazines 1991 OR Send $1 to cover P&P to: AL TRON I CS MAIL ORDER, PO Box 8350, Perth Stirling Street, Perth WA 6849 Our 1991 Catalogue has even more fantastic new products and greater value than last year's. 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Suitable for Hi Fi ~~~~~~~ A.._ 3K to 40kHz f~ C 8100 $~NOW $10 RECTANGULAR HI FI-PA PIEZO 144.8 x 84mm. Speaker - suitable for HI Fi and Sound Reinforcement. Full 90 deg . horizontal dispersion angle. F19q. Ree. 3K to 40kHz Bene. 110dB • 2.8V. TELEPHONE EXTENSION CORD C 8120 S,,., NOW $10 A very handy 5 metre length. Superb lightweight HI FI stereo headphones. Super comfortable foam ear muffs. 29mm semarlum cobalt speakers. HIGH PERFORMANCE MINI HEADPHONES POt91$r $7.00 C9002S~ C.B. POWER MICROPHONE For professional 2 Way radios on aircraft, boats, vehicles and also industrial PA syatems. _c 033a s,..S $20 \ . STEREO AUDIO MIXER This brilliant little mixing console is absolutely packed with features. Allows blending of microphones, two phono Inputs and either two tape or tuner Inputs. • Right and left VU meters. • Separate baaa and treble controls. • 5 slide level controls. • Fader control between phono plckups for profeaalonal cueing. • Headphone monitor switch. • Talkover facility. 240V Maine Operated A2550 u-1160 quency e er UNBELIEVABLE VAL K 2515 WAS $299 NOW $ 249 SAVE $50 (See Silicon Chip Nov '87, Jan '88) This superb 1GHz Frequency Meter will out perform many other instruments twice its price. FHlulff Include: • Professionally machined and screen-printed red perspex front panel • Easy to assemble • Bright Hewlett Packard 8 digit display • Electronic switch latching • High performance IC's • High Quality components. Speclfleatlono: Operational Modes: Period frequency to 100MHz freq . to 1GHz freq. Range: 100Hz to 1GHz (1 .7GHz typical) in frequency mode; 10Hz to 2.5MHz (5MHz typical) in period mode. Gating times: 0.01, 0.1, 1.0 and 10 seconds (10MHz and 100MHz ranges): 0.128, 1.28, 12.8 and 128 seconds (1GHz range). ·· You can use this =~~:r:r;\~~ f.1~/~t~i'l'ited information system. Each unit contains a Telecom approved modem and information decoding circuits. The single PCB is a goldmine of quality components for the enthusiast, including the fantastic valuable SAA 50.!0 and SAA 5050 chips. ~ k8J :ir. :rJ>J:EW nt rtsl (See ETI April '80) Invaluable for testing all your audio projects. • 250 milli watts output into 4 Ohms • Runs off single 9V supply • Can give 0.5 watts when run on 12V + heatsink • Complete kit housed in "ABS" jiffy box . VIATEL VIDEOTEX MODEM DECODER Three models to choose from; Each with a numeric keypad. TWIN RANGE LED TACHO (See ETI Aug '80) 0-1000 RPM/ O/ 10,000 RPM This unit is suitable for 1, 2, 3, 4, 6 and 8 cylinder vehicles, both 2 stroke and 4 stroke. Fully compatible with conventional COi and transistorized iqnition systems. Includes protection circuitry to prevent noise and high voltage spikes over-revving occurs. Only requires 3 connections to the electrical system . s.)rl'o $20 X 1000 with RF output $~5 $25 X 1002 with RF o/p & telephone handnt $ ~ $29 X 1004 with RF and RGB video o/p PIN POINT ULTRASONIC CLEANER K 4324 Normally $32. DC ELECTRONIC FU value at only $20 . SAVE $12. (See EA Nov '87) Calling all servicemen and bench technicians This unit simply clips across the DC Fuse holder. Olfers protection adjustable from 0-10A in two ranges. In essence it's an adjustable DC circuit breaker. BONANZA NI-CAD SALE! Premium Grade - Good tor up to 1000 rechargell Charge rates: 45-50mA for AA, 20mA for AAA, 1015mA for 9V 120mA Will even clean your teethl Earns its cost hundreds of times over in cleaninjj connectors, PCB's, switches, Jewellery, glasses, watches, drafting pens, etc. Awarded the Good Product Design Award for CETOC in 1987. FHtureo: Fast blow - slow blow setting . K 2535 Normal Price 11 $39.50 Thll Month $34.50 THIS MONTH Cat No. S S S S 5020 5021 5022 5023 1-9 AA 1.2V 500mAh $2.50 AAA 1.2V 180mAh $3.50 C 1.2V 1.8Ah $8.00 D 1.2V Massive 4Ah $12.00 10+ $2.00 $2,90 $7.00 $10.00 TRANSISTOR TESTER (See EA Aug '83) Checks transistor in circuit "NO NEED TO UNSOLDER SUSPECT TRANSISTORS" Feature, : • Tests both NPN and PNP transistors in circuit at the touch of a switch . • Tests Diodes and SCRs as well . • No need to switch between NPN and PNP - its automatic . • LED indication to show condition of device. LOW COST RESETTABLE CIRCUIT BREAKER • WIii hold 100% of rated current Indefinitely at 25° C. • Will trip within 1 hour at 125% of load at 25° C. • WIii trip within 4-40 seconds at 200% rated load. . 8 8 8 8 5503 5505 5510 5515 S 5520 S 5525 3 Amp 5 Amp 10 Amp 15 Amp 20 Amp 25 Amp ~ $29 BATTERY OPERATED PORTABLE P.I.R. INTRUSION ALARM Ward off thieves and intruders at home and when travelling. Thi• month even more fanta1tlc Manual reset button. LED fuse tripped Indicator. Operates off 1 single 9V battery (not supplied). Two current settings easily adjustable via a pot and calibrated scale. Sorry no warranty at this price. • Mains Transformer - = / 1~4V 300ma • Line isolation Transformer Telecom approved 600/600 Ohm or 600/ 150 Ohm impedance• Video/RF Modulator (Channel 0) • Low profile 12V 5A SPOT Relay• Capacitor - 2.0uF 440V AC • Crystals • 6MHz and 4.43MHz • TTL, CMOS, Liniar and LSI ICs SAA 5020, SAA 5050, 2516 and many more• Voltage regulators• Bridge rectifiers • Trimpots and capacitors • Filter capacitors • Flatpack heatsink 1 Plus much, much more! BENCH AMPLIFIER K 2105 Altronics has recently purchased this quality stock auctioned by the liquidator of DTX Australia LTD. This super handy, go anywhere P.1.R. alarm system is great for shop, office, caravan, boat, garage and whenever you are travelling. Extremely .___ Hlf to /nIte//. ' • A 0100 Top Value Normally $199 FEATURES: ./ • Exit delay • Entry delay • Large coverage - up to 100 square metres • Low battery LED ind icator• 9V Alkaline battery (not supplied) lasts many months. ONLY $149 thl1 month S5305"9'$49 THE PROTECTOR ALARM KIT (See SC Feb '88) This relined car burglar alarm has about every feature you could possibly want to keep would-be thieves away. Fealulff: Internal and External Sirens. Dash Lamp Flasher. Battery back-up. Delayed and Non-delayed inputs. Easy to build and install. K 4370 W■1 $129 $119 Now a GrHt Speclal at BCNUS OFFER We will include a aet of 4 Car Alarm WARNING stickers ($3.95 value) ABSOLUTELY FREE with every Car Alarm Kit ordered this month . SUPER GUARD HOUSEHOLD ALARM SYSTEM • Easy to operate Simplicity itself - Just select the switch ALL $3 Heh. ~~~~~eAO:J ~c~~~y as .. exlVentry delay allows you to vacate and/or re-renter your premises and disarm ew updated ircult corporates cllltles for sting ransistors FET's nd Zeners etc. EATURES: Gain• ~=~=x~;n oltages • Zener ltage • larlt - ~o~~ ~.,:it~h::~; ~~bons to push . Thus the system is ideal for families e9en the kids can operate this system. • Facility for external siren.• Battery backup (battery 8 'C' cells not Included) Syatem Contente: • Master Control unit • Front Door Bell Switch • Panic/Emergency Switch • Three Window/Door Reed Switches • Mounting Hardware • 20 Metres Wire • Instruction Manual. Compl Build this low-cost sinewave oscillator This small PC board allows you to build a low distortion sinewave oscillator using only junkbox bits. It runs off a 12V plug pack, gives a low-impedance output signal of up to 6V p-p and costs peanuts to build! By DARREN YATES Sinewaves are as fundamental to electronics as resistors and ICs, but unless you're willing to pay big bucks for the generators currently available, professional low distortion sinewave gear is out of reach for most of us. However, it's only on very rare occasions that you need the wide frequency selection from DC to daylight that these expensive boxes provide. For example, when you see an operational amplifier quoted in some databook, they'll quote a distortion figure at some particular frequency, usually lkHz. Most power amplifiers that you buy or see described in magazines, usually provide distortion measurements at selected frequencies. Often, these include lO0Hz, lkHz and lOkHz. To fill in this present gap, we've designed this project for low distortion (.015% or better), low cost (about $15-$20), and the ability to run from This is the 10kHz version of the sinewave oscillator but versions for other frequencies look exactly the same (only a few component values are changed). Take care with component orientation when installing the parts on the board. 54 SILICON CHIP a standard 12VDC plug pack. We've also given you the choice of three very common frequencies: lO0Hz, lkHz or lOkHz. Circuit theory So, how do we go about making low distortion sinewaves? Well, in the end, there are two ways of doing this. You can either start out by making the best oscillator money can buy or you can start with a so-so one and improve the signal coming out of it. We chose the second option because it was easier to do, and a lot cheaper into the bargain! Block diagram Fig.1 shows how it is done. First of all, we start off with a Wien bridge oscillator, which is one of the oldest circuits around, and then we take the output signal from that and run it through a fairly brutal low-pass filter. This removes a large amount of the unwanted multiples of the fundamental frequency or "harmonics" which make up what we call "distortion". It does this by increasingly attenuating higher frequencies but allowing the frequency of interest to pass through. These higher frequencies are knocked off at the rate of 24dB/octave. This means that if we started with a lkHz signal, then the 2kHz harmonic present at the output will be about 24dB below or about 1116th the amplitude of the lkHz signal. The 4kHz harmonic would be 48dB below or 11250th the amplitude of the lkHz signal, and so on. The result is a dramatic improvement in distortion. For example, if we start with a sinewave that has about 0.5% distortion, we would end up with a sinewave that has only .01 % distortion after filtering - and improvement of 50 times! The circuit The circuit diagram is shown in Fig.2. It only requires an LF347N quad -- WIEN BRIDGE OSCILLATOR 4TH ORDER BUTTERWORTH LOW-PASS FILTER LOW DISTORTION i----- SINEWAVE OUTPUT Fig.1: block diagram of the sinewave oscillator. It consists of a modified Wien bridge oscillator driving a 4th order Butterworth low-pass filter. The low pass filter atlenuates harmonics above the wanted frequency at the rate of 24dB/octave & this drastically reduces the distortion. op amp , a couple of signal diodes and a few passive components. You will probably already have some of or all of these components lying around in your spare parts bin or junkbox. ICla & IClb form the Wien bridge oscillator while IClc & ICld form the 4th order low-pass Butterworth filt er. This 4th order filter actually consists of two 2nd order filt er sections connected together. Butterworth filters are easy to calculate and have the advantage of having a flat respons e across the passband. You will notice that there are several components on the circuit that have no specific values. If you look at Table 1, these components have different values, depending on the frequency you want. When assembling the unit, you simply go to the frequency you want and read off the corresponding component value. Looking at the circuit, ICla and IClb form an unusual Wien bridge in that resistor RZ is not returned to ground as in conventional designs, but forms part of the unity-gain inverting amplifier formed by IClb. This provides gain compensation and helps stablise the output amplitude. Diodes Dl and DZ also do this job but because they are non-linear in their response, the more they interfere with the signal, the more distortion they produce. Most designs use a thermistor or small 12V light globes for this job. We chose the diodes because suitable thermistors can be expensive and hard to get while lamps require extra current and , because of their slow repsonse, take some time to reach their final resistance. This results in a sinewave which has a fairly long settling time, particularly at low frequencies. The diodes speed up this process and because of the high value of resistor R6 (470kQ to 1.ZMQ) in series, they only have minimal affect on signal distortion. The gain of ICla is set by resistors R4, R5 & R7. Resistor R7 sets the gain of ICla just enough for the oscillator to start. If we have too much gain, the oscillator starts OK but introduces heaps of distortion; if we don't have enough gain , then it won't start at all! The Wien bridge itself is formed by components Rl, RZ, Cl & CZ. The frequency of the sinewave pro duced is: F = 1 /( 21tR1C1) . The sinewave produced at the output of ICla [pin 1) will have a total harmonic distortion of about 0.5% to 1 % - which is certainly nothing to write home about. Low-pass filter The signal from pin 1 ofICla is DCcoupled to the first stage of the filter formed by ICld and its associated components. This section has a 3dB cutoff frequency set to the frequency of interest - whether it be 100Hz, lkHz or 10kHz - by selecting the correct components from Table 1. This leaves us with a problem, though. To get maximum effect from the filters, we need to set their cutoff frequency at our frequency of inter- 470 U R2 OUTPUT LINK SEE TEXT R3 100k .,. +12V 01 220k 220k-:- 2x1N914 10 16VW I 100k .,.. 02 16VW! +12V 0.1 0.1 u - - -- -,__--e-_ __ _ _,__~ov ":' SPOT FREQUENCY SINEWAVE GENERATOR Fig.2: the final circuit is based on a single LF347 quad op amp package. ICla & IClb form the Wien bridge oscillator, while IClc & ICld together make up the 4th order Butterworth filter. Note that some of the resistor & capacitor values are selected to give the desired frequency. FEBRUARY1991 55 your application. If you wish, you can replace the wire link at the output with a 22µF 16VW electrolytic capacitor to provide DC isolation. You can also reduce the output signal amplitude by changing the 4700 and 10okn output resistors with a potential divider of your own. For example, with two lkQ resistors , the output would be reduced to half. Power supply est. But this results in about 3dB attenuation of the signal. By the time it has gone through both sections, we would then get 6dB attenuation. In other words, the signal is reduced to half its original amplitude. To overcome this, we give each section a gain of roughly 3dB (or 1.42), so in the end, the filters have unity gain at the frequency we want. By the time the signal comes out of ICld, its distortion is of the order of .05% to 0.1 % - an improvement, but we can still go better than that! In giving the filters extra gain, we are also amplifying the harmonics, but since they are still being attenuated at the rate of 24dB/octave, the relative amplitude of the wanted frequency to those we don't want remains unchanged. In other words, it doesn't make the distortion worse. The final signal is taken from the output of IClc (pin 8) where the distortion has now dropped to around .015% for the 100Hz and lkHz versions, and to about .005% for the 10kHz version. We have set the output impedance of the circuit at 4 70Q with the resistor at the output but you can increase this to 600Q or any other value to suit Table 1: Component Values A1}- 100Hz 1kHz 10kHz Resistors 56 R2 R3 R4 R5 R6 R7 R8 R9 R10 R11 R12 R13 15kQ 100kQ 10kn 470kQ 330Q 18kQ 27kQ 560kQ 18kQ 27kQ 560kQ 1.2MQ 4.7kQ 1.8kQ 3.3kQ 47kQ 1.8kQ 3.3kQ 47kQ 820kQ 470Q 470Q 470Q 5.6kQ 1.5kQ 2.7kQ 5.6kQ Capacitors C1 C2 C3 0.1µF 0.1µF 0.1µF .0015µF .0015µF 0.1µF .001 5µF .0015µF .015µF SILICON CHIP Power is provided by a 12V DC plugpack which drives a 7812 3-pin 12V regulator. Even though this regulator requires a couple of volts of headroom to operate correctly, typical 12V DC plugpacks provide about 16-17V DC when lightly loaded and and so will work perfectly well with this circuit. Extra decoupling and filtering of the power supply is provided by the 100µF and 470µF electrolytics, as well as O. lµF greencaps. Construction All components for the oscillator are mounted on a PC board which is coded SC04102911 and measures 104 x 57mm. This can also be housed in a standard zippy box, measuring 130 x 68 x 41mm. As there are no controls to mount on the front panel, it is a simple case of drilling two holes, say for an RCA socket for the output signal and a DC socket for the power supply. Before you start assembly, check the board carefully for breaks or shorts in the tracks. If there are any, it's best to correct them now. Once you're happy that everything is OK, take a look at the wiring diagram. This shows you where each component fits into place. Begin by installing the wire links and the resistors. Some of the colour bars on the resistors may be difficult to distinguish, in which case, use your multimeter to make sure of the correct value. Again, make sure that you have the correct resistors and capacitors for the selected frequency from Table 1. Now install the diodes. It's best to do this now while the flat components only are on the board, otherwise they become difficult to put in. It doesn't matter which way round you put the two diodes in, as long as they face in opposite directions. We suggest that you put them in as shown on the wiring diagram. PARTS LIST 1 PC board, code SC04102911, 105 x 57mm 1 12VOC plug pack 4 PC stakes Semiconductors 1 LF347N quad FET-input op amp (IC1) 1 7812 +12V regulator 2 1N914 signal diodes (01, 02) 0 SC04102911 Fig.4: compare your PC board against this full-size artwork before installing any of the parts. Next, solder in the PC stakes. You may need to hammer these in, depending on the type of pins you get, or you can enlarge the holes using an appropriate drill. The capacitors can now be installed. Make sure you get the polarity of the electrolytics correct, particularly those in the power supply, otherwise they could quite easily pop. All that should be left is the two ICs. Solder in the 7812 regulator first and then the LF34 7. Testing Now check over the board again and compare it to the wiring diagram. When you're sure the board is correct, you can hook up the power sup- CAPACITOR CODES 0 0 0 0 Value IEC Code 100n 0.1µF .015µF 15n .0015µF 1n5 EIA Code 104 153 152 ply. When you do so, put your multimeter, switched to a DC milliamps range, in series with the power supply and the circuit. The current drain sho uld be no more than about 20mA. If you get more than this, then it is possible you have a short circuit somewhere. If you have a CRO, monitor the output and check that you get a stable sinewave at the frequency you selected. If you don't have a CRO, just connect it up to an audio amplifier (turn the volume control down first). If you hear a tone when you turn the volume up, it's a good bet that the circuit is working correctly. If you don 't get any signal, first check that there is 12V at the output of the regulator. If that's OK, check that it appears across pins 4 and 11 of IC1. If the voltage is there, try touching both sides of the diodes with your finger. If the signal appears and then dies away when you remove your finger, then it is probably due to the fact that IC1a doesn't have enough gain to keep oscillating. To fix this , Capacitors 1 470µF 25VW PC electrolytic 1 100µF 25VW PC electrolytic 3 10µF 25VW PC electrolytic 4 0.1 µF metallised polyester (greencaps) 4 .0015µF metallised polyester Resistors (0.25W, 5%) 1 1.2MQ 1 4.7kQ 2 220kQ 2 3.3kQ 10 100kQ 2 1.8kQ 2 47kQ 1 470Q Miscellaneous Solder, hookup wire etc Note: This parts list is for the 1kHz version . Other versions will require different resistor & capacitor values - see Table 1. change R7 to the next highest standard value; ie, if it was 330Q, make it 390Q instead. Once the circuit is working, you may like to house it in a zippy box to keep the dust and bugs away from it. For those who may have access to the necessary equations, you may like to try to work out other frequencies as you need them. The LF347N should be capable of producing a clean sinewave at well above 20kHz. SC RESISTOR CODES 0 0 0 0 0 0 0 0 0 No Value 4-Band Code (5%) 5-Band Code (1%) 1 2 10 2 1 2 2 1.2MQ 220kQ 100kQ 47kQ 4.7kQ 3.3kQ 1.8kQ 470Q brown red green gold red red yellow gold brown black yellow gold yellow violet orange gold yellow violet red gold orang~ orange red gold brown grey red gold yellow violet brown gold brown red black yellow brown red red black orange brown brown black black orange brown yellow violet black red brown yellow violet black brown brown orange orange black brown brown brown grey black brown brown yellow violet black black brown 1 FEBRUARY 1991 57 May 1988: Optical Tachometer For Aeromodellers; High Energy Ignition For Cars; Ultrasonic Car Burglar Alarm; Walkaround Throttle For Model Railroads, Pt.2; Designing & Build· ing RF Atten uators; Motorola MC3334P High Energy Ignition IC Data. October 1988: Stereo FM Transmitter (Uses Rohm BA1404); High Performance FM Antenna; Matchbox Crystal Set; Electro nic House Number; Converting A CB Rad io To The 28MHz Band; Queensland's Powerful Electric Locomotives. July 1988: Stereo Control Preamplifier, Pt.2; Fitting A Fuel Cut-Off Solenoid ; Booster For TV & FM Signals; The Discolight Light Show, Pt.1; Tone Burst Source For Amplifier Head· room Testing; What Is Negative Feedback, Pt.3 ; Ameren MA-1200 Power Amplifier Review; Amplifier Headroom· Is It A Con? November 1988: 120W PA Amplifier Module (Uses Mosfets); Poor Man's Plasma Display; Automotive Night Safety Light; Adding A Headset To The Speakerphone; How To Quieten The Fan In Your Computer; Screws & Screwdrivers, What You Need To Know; Diesel Electric Locomotives . August 1988: Building A Plasma Display; Unive rsal Power Supply Board; Remote Chime/ Doorbell ; High Performance AC Mil livoltmeter, Pt.1; Discolight Light Show, Pt.2; Getting The Most Out Of Nicad Batteries ; Data On Insulated Tab Triacs. December 1988: 120W PA Amplifier (With Balanced Inputs), Pt.1; Diesel Sound Generator; Car Antenna/Demister Adaptor; SSB Adaptor For Shortwave Receivers; Electronics & Holden's New V6 Engine; Why Diesel Electrics Ki lled Off Steam ; Index to Volume 1. September 1988: Hands-Free Speakerphone; Electronic Fish Bite Detector; High Perform· ance AC Millivoltmeter, Pt.2; Vader Voice; Motorola MC34018 Speakerphone IC Data; National Semiconductor LM12 150W Op Amp Data & Applications; What Is Negative Feedback, Pt.4. January 1989: Line Filter For Computers; Ultrasonic Proximity Detector For Cars; Simple Computer Sound Repeater; 120W PA Amplifier (With Balanced Inputs) Pt.1; How To Service Car Cassette Players; Massive Diesel Electrics In The USA; Marantz LD50 Loudspeakers . February 1989: Transistor Beta Tester; Minstrel 2-30 Loudspeaker System; LED Flasher For Model Railways (uses LM3909); Build A Simple VHF FM Monitor (uses MC3362), Pt.1; Lightning & Electronic Appliances; Using Comparators to Detect & Measure . March 1989: LED Message Board, Pt.1; 32· Band Graphic Equaliser, Pt.1; Stereo Com pressor For CD Players; Map Reader For Trip Calculations ; Amateur VHF FM Monitor, Pt.2; Signetics NE572 Compandor IC Data; Electronics For Everyone - Resistors. April 1989: Auxiliary Brake Light Flasher; Electronics For Everyone: What You Need to Know About Capacitors ; Telephone Bell Monitor/ Transmitter; 32-Band Graphic Equaliser, Pt.2; LED Message Board , Pt.2. May 1989: Electronic Pools/Lotto Selector; Synthesi sed Tom -Tom; Biofeedback Monitor For Your PC; Simple Stub Fi lter For Suppress- Use this handy form to order your back copies ,---------------------------------Please send me a back issue for: O September 1988 0 October 1988 O February 1989 o March 1989 o July 1989 o August 1989 O December 1989 0 January 1990 O May 1990 o June 1990 O October 1990 0 November 1990 O May 1988 O November 1988 O April 1989 o September 1989 O February 1990 O July 1990 0 December 1990 0 July 1988 0 December 1988 0 May 1989 o October 1989 0 March 1990 0 August 1990 O January 1991 Enclosed is my cheque/money order for $_ _ ____or please debit my: 0 Bankcard Card No. $5.00 each (includes p&p). Overseas orders add $1 each for postage. NZ orders are sent air mail. Signature _ _ _ _ __ __ __ _ __ Card expiry date_ _ /_ _ Name _ _ _ __ __ __ __ _ _ _ _ __ _ _ __ _ __ _ Street _ _ _ _ _ _ _ __ _ _ _ __ _ _ _ __ _ __ __ Suburb/town-~- -- -- - - - - - - - -- Postcode _____ _ 58 --7 0 August 1988 0 January 1989 0 June 1989 O November 1989 O April 1990 O September 1990 SILICON CHIP 0 Visa Card 0 Master Card Detach and mall to: SILICON CHIP PUBLICATIONS PO BOX 139 COLLAROY BEACH NSW 2097 Or call (02) 979 5644 & quote your credit card details. Fax (02) 979 6503 x I I ~-,--, .,J,-1. ' . .. ;~ .. ing TV Interference; LED Message Board , Pt.3 ; Electronics for Everyone - All About Electrolytic Capacitors. June 1989: Touch-Lamp Dimmer (uses Siemens SLB0586) ; Passive Loop Antenna For AM Radios ; Universal Temperature Contro ller; Understanding CRO Probes; LED Message Board , Pt.3 ; Coherent CW - A New Low Power Transmission Technique. July 1989: Exhaust Gas Monitor (Uses TGS812 Gas Sensor); Extension For The Touch-Lamp Dimmer; Experimental Mains Hum Sniffers ; Compact Ultrasonic Car Alarm ; NSW 86 Class Electrics; Facts On The PhaxSwitch Sharing Your Phone Line With A Fax Machine. August 1989: Build A Baby Tower AT Computer; Studio Series 20-Band Stereo Equaliser, Pt.1; Garbage Rem inder - A 7-day Programmable Timer; Introduction To Stepper Motors ; GaAsFet Preamplifier For The 2-Metre Band ; Modern 3-Phase Electric Locomotives. September 1989: 2-Chip Portable AM Stereo Rad io (Uses MC13024 and TX7376P) Pt.1; Alarm-Triggered Telephone Dialler; High Or Low Fluid Level Detector (uses LM1830N); Simple DTMF Encoder (uses Texas TMC5089); Studio Series 20-Band Stereo Equaliser, Pt.2 ; Auto-Zero Module for Aud io Amplifiers (Uses LMC669); A Guide To Hard Disc Drives. October 1989: Introducing Remote Control; FM Rad io Intercom For Motorbikes (Uses BA1404 And TDA?000) Pt.1 ; GaAsFet Preamplifier For Amateur TV ; 1Mb Printer Buffer; 2Chip Portable AM Stereo Radio, Pt.2 ; Installing A Hard Disc In Th e PC; A Look At Australian Monorails. November 1989: Radfax Decoder For Yo ur PC (Displays Fax , RTTY and Morse) ; Super Sensitive FM Bug; Build A Low Cost Analog Multi meter; FM Radio Intercom For Motorbikes, Pt.2; 2-Chip Portable AM Stereo Radio, Pt.3; Floppy Disc Drive Formats & Options ; The Pilbara Iron Ore Railways . December 1989: Digital Voice Board (Records Up To Four Separate Messages , Uses Texas TMS3477NL and 256K RAMs); UHF Remote Switch; Balanced Input & Output Stages ; National Semiconductor LM831 Low Vo ltage Amplifier IC Data; Install A Clock Card In Your PC ; Index to Volume 2 (Jan-Dec 1989). January 1990: Service Tips For Your VCR ; Speeding Up Your PC; Phone Patch For Radio Amateurs; High Quality Sine/Square Oscillator; Active Antenna Kit ; The Latest On High Definition TV ; Speed Controller For Ceiling Fans ; Designing UHF Transmitter Stages. February 1990: 16-Channel Mixing Desk ; High Qu ality Aud io Oscillator, Pt.2 ; The Incredible Hot Canaries ; Random Wire Antenna Tuner For 6 Metres; Phone Patch For Radio Amateurs, Pt.2; PC Program Calculates Great Circle Bearings . March 1990: 6/12V Charger For Sealed LeadAcid Batteries ; Delay Unit For Automatic Antennas; Workout Timer For Aerobics Classes; 16-Channel Mixing Desk, Pt.2 ; Using The UC3906 SLA Battery Charger IC; Digital Waveform Generation Using a PC ; The Controls On A Model Aircraft. Apri l 1990: Dual Tracking ±50V Power Suppl y; VOX With Delayed Audio ; Relative Field Strength Meter: 16-Channel Mixing Desk, Pt.3 ; Simple Service Tips For Your Microwave Oven ; Model Aircraft Aerodynamics; Active CW Filter For Weak Signal Reception. May 1990: Build A 4-Digit Capacitance Meter ; High Energy Ignition For Cars With Reluctor Distributors ; The Mazzie CW Transceiver ; Waveform Generation Using A PC , Pt.3 ; 16Channel Mixing Desk, Pt.4; What To Do When Your Computer Goes Bung , Pt.1; Electronic Load For Checking Power Supplies. June 1990: Multi-Sector Home Burglar Alarm; Low-Noise Universal Stereo Preamplifier; Load Protection Switch For Power Supplies; A Speed Alarm For Your Car; Design Factors For Model Aircraft; Fitting A Fax Card To Your Computer; What To Do When Your Computer Goes Bung , Pt.2. July 1990: Digital Sine/Square Generator, Pt.1 (Covers 0-500kHz) ; Burglar Alarm Keypad & Combination Lock; Simple Electronic Die ; LowCost Dual Power Supply; Inside A Coal Burning Power Station; What To Do When Your Computer Goes Bung , Pt.3 ; Digital Waveform Generation Using A Computer, Pt.4. August 1990: Hig h Stability UHF Remote Transmitter; Universal Safety Timer For Appl iances ; Horace The Electronic Cricket; Digital Sine/Square Wave Generator, Pt .2; The Tube Vs. The Microchip (Two Shortwave Receive rs Compared); What To Do When Your Computer Goes Bung , Pt.4. September 1990: Music On Hold For You r Telephone; Remote Control Extender For VCRs; Power Supply For Burg lar Alarms ; LowCost 3-Digit Counter Module; Voice Mail For Your Computer; Simple Shortwave Converter For The 2-Metre Band ; How To Make Dynamark Labels. October 1990: Low-Cost Siren For Burglar Alarms ; Dimming Controls For The Discolight; Surfsound Simulator; DC Offset For DMMs; The Dangers of Polychlorinated Biphenyls; The Bose Lifestyle Music System ; Using The NE602 In Home-Brew Converter Circu its. November 1990: Low-Cost Model Train Con troller; Battery Powered Laser Pointer; A Really Snazzy Egg Timer; 1.5V To 9V DC Converter; How To Connect Two TV Sets To One VCR ; Introduction To Digital Electronics ; Simple 6-Metre Amateur Transmitter. December 1990: DC-DC Converter For Car Amplifiers; The Big Escape; Wiper Pulser For Rear Windows ; Versatile 4-Digit Combination Lock; SW Power Amplifier For The 6-Metre Amateur Transmitter; The Green CD Pen Controversy. January 1991: Fast Charger For Nicad Batteries; Have Fun With The Fruit Mach ine; TwoTone Alarm Module ; Laser Power Supply (For Tubes With Ratings Up To 10mW) ; LCD Readout For The Capacitance Meter; How Quartz Crystals Work; The Dangers When Servicing Microwave Ovens; Electric Ve hicles - The State Of The Art. PLEASE NOTE: All issues from November 1987 to April 1988, plus June 1988, are now sold out. All subsequent issues are presently in stock. For readers wanting articles from issues out of print, we can supply photostat copies (or tearsheets) at $5 .00 per article , including postage. When supplying photostat articles or back copies, we automatically supply any relevant Notes & Errata, at no extra charge. _J FEBRUARY1991 59 SAFE CARD POWER FAIL PROTECTOR ,, '1,,i., The revolutionary Safe Card Power Fall Protector. This little gem takes away ..._, IA all the risk of losing hours of important '/I' work when the power dips or fails. Ideal for areas where power is a problem or data Integrity Is vital. The need for a huge bulky In-line back-up system Is now eliminated by the single slot 1/2 Card. Introductory offer for this Australian promoted product is $595 and only available from us. X11118 .....................................................$595. T with SUPER VGA Colour monitor (1024x768 • 42 MEG HO 28ma ,.os1-1EE't • 1.2 MFDD ff\EE DON'T PAY $19 • tM RAM v;of\O • (16 MHz LANDMARK; so sl'::oe ssof\ • SUPER FAST 21M LANDMARK • 512K VGA CARD • 2MB RAM • MASSIVE 85 MEG HO 18ms • 1.2 M FLOPPY • MINI CASE & 200W PS • 2 YEAR WARRANTY • SUPER VGA (1024 x 768) COLOUR MONITOR • SERIAL, PARALLEL & GAMES PORTS •101 EXTENDED KEYBOARD iii AUSTRALIA'S TOP SELLING NOTEBOOK! PC-4741 COMPACT NOTEBOOK. . • • Triple super twist LCD (640 x 400) with 4 shades of grey • 8088 compatible processor with 10MHz clock speed (~ocket for 8087 coprocessor) • 40 MB hard disk drive wtth 29ms access time • 3.5" 1.44MB high denstty floppy disk drive • 640 Kb Internal RAM expandable to 1.6 MB • Weighs only 3.8 Kg • Battery or mains operated X20004 .................................................................................$3499 (Available to order) The GS·C105 Colour scanner scans any colour or Black & White Image Into your IBM PC AT, PS·2 or compatible system without loss of hue. FREE SOFTWARE! The powerful Colour Maestro allows you to scan an Image and then do colour editing In colours you can create yourselfl You can draw different shapes; modify objects, alter colours and edit a palette of 256 colours by using the commands on your pop•up menus. You can oven design you r own font type size. SPECIFICATIONS: • 105mm scan width, multl•scan up to 300mm • 100·400 DPI selecable in steps of 10 DPI for 2,8, & 16 colours • 64 shade levels • Scanning speed: 3.5 ms/llne ................... ............ . .............................: ., $895 Colour Scanner Sharp Invented the colour scanner and we have scooped a batch of their A6 size units for you. Compatible with the Apple Mac II and with IBM or equivalents this Impeccable unit brings quallty scanning within easy operational and financial rea ch. For IBM the RPP ( Including MS Windows and Mouse) Is $1499, and for the Mac $1299. SPECIFICATIONS: Type: Flat Bed Resolution : 200 dpl Image Size: 100mm x 160mm Colours: 262, 144 Grey Levels : 64 Colour range: 6 bit Colour Accuracy: 6 bit Interface: RS232C Supplied Software: Mac II: Chromascan 100 IBM: Microsoft windows with mouse, Colour Lab 100 IBM X19905 ...................................................$1499 rallel Interface Extender , \~ ·•7 the real world of Interfacing mputers to parallel printers, It Is '-: O en very usful to extend the ~GE UP ~I ta nee over the normal 1o foot R~ ,-.e.rfl-E itation. Para link II is the • xpenslva and effective way to do an external po s. It's ultra high speed nsrr.ls3ion rate produces parallel- complete with receiver & 50 f a speed. It Is compatible with all through RJ-1 . are & hardware & Installs In MAC X19907 ..................................................$1299 'ill . 008 335757 TOLL FREE MAIL ORDER HOTLiNE FOR CREDIT CARD ORDERS! i~ ~ ~;~ ~ J ~ ~~ l ~ ~ &\. ~ \ \ <-. ·"'~;. j"J - ~"~ ~;) Ufl ( ~~ ~ I ~ \ A , / '--- I G ~ 1'\\" - C Turn your computer into a Fax Machine. with tha NetComm PC Fax Cardi Send and receive facimlle documents over the phone. • Multi speed, multi standard. • PSTN Dial up • 12 months warranty • Australian design & manufactured • Telecom approved INCLUDED WTIH FAX CARD: • Users manual • Telephone cord • Size · 116 x 66 x 34mm · Mouw- Driver Software included, allowmg you 10 inslall with ell popular software packages. Also included 1s the handy Pop-up menu software that allows the user to integrate the mouse wlth the keyboard, 00S. and other popular 1oftware pack• "software. .: ..card •_T_h_r_e_e_5_1_/4_ft_o_p_p_y_d-is_k_s_c_o_n_t_al_n_ln_g __ •• _P_C_f_a___,x X19091 .............................................. $595 ~ CHECK OUT OUR HUGE RANGE OF IBM CARDS AVAILABLE. MOTHERBOARDS 1 l ~, 21 MHz ALL IN ONE AT MOTHERBOARD WITH THE LOTI All you have lo do Is add a Graphics card. Thi& Ultra :~~~i~rln;~7;~;c~~!ti;o:;;~r~a~~:see state the art ACER technology & surface mount design for the best performance & reliability. • 16 MHz O wait state CPU (21 MHz landmark speed rating)·· • Up to 4MB of RAM on the Motherboard O Ram fitted 1 ~~sx ~r5 :;::~s: : :~:~x'::'a~~tfo~ slots • 2Serlal & 1 Parrallel Port ) , • Dallas real time clock fitted life expectancy 10 years ,! • IDE 40 pin· connector for hard disk Interface (You need to add an lmbedded hard disk drive) '.,, •just Floppy disk controller on board • You only have to add a Graphics card. of XT HD CONTROLLER ....... $129 AT HD CONTROLLER .. ;..... $199 RS 232 SERIAL CARD ..•.•• $49 RS232 /SERIAL/ CLOCK .. $59 MONO/ COLOUR CARD.... $96, ' MULTI 1/0............................ $99 512K RAM .......................... $59 DIAGNOSTIC..................... $849 ~ TTL/ PRINTER ................... $89 RAM 2M AT EXT/EXP.•••••.• $225 · SM AT EXT/ EXP................ $325 4 PORT SERIAL................. $89 ., VGA 256K .......................... $179 ~ VGA 512 K ••••••• .. •• .... •••--•••.... $249 :.--,. . VGA 1 MEG ........................ $ 395 ~ ~ VOICE MAIL CARD •••...••.... $199 PRINTER CARD................. $ 3 S ' EGA CARD......................... $139 2 WAY FDD CONT. (360K). $49 ~ GAMES CARD $29 · {• ; ! r--- :· '.. : 9 ~~~ :Ls: ATM• 110 Touch Mouse tor IBM PC/ XT/ ~~c:: o~~,m:i~:!\:s~:~r~ nd8 r 1 ;~: FEATURES . Users tmger movements on the 58 X 48mm front panel ot the touch mouse control the ~ .0 3 Compallble w11h all existing mouse software 10 , ,, I'I·: 4 WAY FDD CONT. (360· 1·44 M) ........................ $ 129 CLOCK CARD.................... $49 SMART DRIVE ADAPTER . 1DE / FDC............................ $S9 I FREE SOTWARE INCLUDED!~ ~5~5iR~R~~~~ . DEMO PROGRAM HIGH LEVEL LANGUAGE INTERFACE ROUTINE: ·~PM 1a-co■•,o..1t.ectc•.Microaolt Fortran. Quick B■atc. Turt>o C ~ 1· SMART DRIVE ADAPTER IDEI/OFDC ........................ $119 88 POP-UP MENU JDR.HALOIUGRAPHICSSOFTWARE ~ ..__ _ _ _ _ _ _ _ _ ___. ._____ _ _ _ _ _ _ _ _ _ _ _____., X19960 •••..•.•....•.••....••••..•••••••••.••...• X18198 ..............................................................$595 ~ ~ ~8- . • 1 l • b• 0J • Processor 80386·33 Cache Controller 882385, 32 Bit Peripheral • Memory 32KB Cache memory (35 ns) • Expansion alots: 1 x 32 bit, 3 x .8 bit, 4 x 16 bit • Intel' Combo Chip set: 82230, 82231 • Shadow RAM C&T 82C206 lntergrated peripherals Controller <• ) •, • • • • • , I LEO display for speed Indication Ability to run OS/2, MS/DOS, XENIX Real time clock/calender with battrey back up Baby AT' size board Reset button Connector Keylock button connector Speaker connector X18112 ............................................ $2495 • Processor: 80386SX-16MHz (0/1 wait atate) • Co-proceaoor: 80387SX-16 (optional) • CHIPS & TECH NEAT chipseta • (SMT) Surface Mount Technology for chlpseta & CPU • Supports up to 2MB on board, (Sixteen 44256 and Eight 41256 sockets) • Three 8 BIT alota • Five 16 BIT alota • Meo mti ory Expansion Slot rd • p onal 2-8MB memory ca S rte LOTUS~NTEL MCROSOFT (UM) E nded • Spee. (EMS) v~alon 4.0 xpa • Supports Page lnterleaw Mode ualng 100NS DRAM • BIOS: AMI or PHOENIX • Turbo Light and Hardware Reset connector • Keyboard or H.ardware Reset connector rd • Power Good Signal on board • Baby alze mail' ,..:;::::;'ry 11°• X18094. OK RAM .................. .,.,_ I ~). ~ . \.~\ r::::~g M OTHERB~ -ARD M:::~~~::~ ~ 1' $1 Q9 · The .• FREE Telepaint disks which allows the user to. :perform high resolution graphics with th<> mouse. $6951 X19951 , ,~~ j\\\Y ~ ~ 119 A oos . 33s~ ,~ ~ La:. F::REe~ttA'~ oRo~~R~oTLl~t;,roR cR~ l~fA~D,9 RDERsJ ? J';, \\! V") I I I I productivity. the most out of your computer and enhance yo..It gives you the ability to expand the I·veraitility of your co~puter through the use of · ·graghic software a11ch as paint, draw and CAD · · II programs. super mouse 2 allows you to run programs like GEM and Window• which makea al operations of the computer easier and faater. Many popularSpreadsheeta, databases, word I.processors and other programs can also be wor with the Super Mouse 2.. 1I '. ~~:!;~~~ltF;!~~~:~uter compatible. • Free Software with Pop-up Mcnua I . .Also Life time War{anl}I · supplied with the Syper Bus Mouse 2 are~ C ~~\D~ ~ ~ ;~,~c~:e~a~t:~~rt;u0cvhe:~:~e requires ~ no desk space to, movement I :~~::.~~~rg:;:~rt: a~~tdh: ~:e~~ :~:!.~~ace ~I• · :;~;:,;,~;~~:t~~;~ laptops. ..J'T I the touch mouse sa,es on desk spac~ AT S/P GAMES CARO....... $35 . } \ A liFi~ ~ . ~ /J,,I ~ 7 / ~ FAST CHARGER NICAD BATTER! Last month, we introduced our new Fast Nicad Charger & described the circuit. In this issue, we give you all the construction details. By JOHN CLARKE & GREG SWAIN Despite the circuit complexity, this project is very easy to build and there are just two simple adjustments. Most of the parts are mounted on a single large PC board coded SC14101911 (167 x 222mm) and this is housed in a plastic instrument case. A large finned heatsink is bolted to the metal rear panel and this provides heatsinking for the Mosfet switching devices (Ql-Q4) and for the rectifiers (D4 & D5). Begin construction by checking the copper pattern of the PC board for any shorts between tracks or open circuit tracks (compare it with the published pattern). A quick check at this stage can save hours of troubleshooting later on. Fig. 7 shows the parts layout on the PC board. Before installing any of the parts, check that the board mounting holes are large enough to accept the self-tapping mounting screws. Similarly, check the mounting holes for diode D1 and for the transformer (Tl). Begin the PC board assembly by installing PC stakes at all the external wiring points, then install the wire links, diodes and resistors. Be sure to use the correct diode at each location and check that they are all installed the right way around. It 's a good idea to install the zener diodes with a loop in one of the leads (see photo) to relieve any stresses due to thermal expansion. The two 0.22Q 5W resistors should be stood off the board by about 2mm so that air can freely circulate beneath them for cooling. This done, install the ICs , small signal transistors and the stud-mount diode (D1). Be sure to install the star washer for D1 on the copper side of the board, as this "bites" into the copper pattern and ensures a good contact. The electrolytic capacitors can now all be installed, followed by the four Mosfets (Ql-Q4) and the two power diodes (D4 & D5). These last six components should all be mounted at full lead length. Inductors This close-up view shows how power diode D1 is mounted. Be sure to install the star washer on the copper side of the board, as this bites into the copper pattern & ensures good electrical contact. Note also the stress loop in one of the leads from zener diode ZDl. The other zener diodes are installed in similar fashion. 62 SILICON CHIP Inductors Ll and L2 are each wound using 9 turns of 1.25mm enamelled copper wire (ECW) on the same Neosid iron powder toroid. These windings are wound on opposite sides of the toroid and in opposite directions to each other (see Fig.7). Scrape Pt.2: The Construction Details FOR ES The Nicad Fast Charger features a very reliable automatic switch-off circuit when operated in fast-charge mode. This prevents overcharging which could ultimately lead to expensive cell damage. the enamel from the ends of the windings and tin them before installing the unit on the PC board. Winding the transformer The transformer is supplied as a bobbin with two E cores, one for the top and the other for the bottom. These cores are held together with a U-shaped clamp which is installed after the transformer is wound. Now take a look at Fig.6. This shows how the primary and secondary windings are terminated on the transformer bobbin. Note that the 4-pin side of the bobbin terminates the primary leads, while the 5-pin side is for the secondary windings. To wind the primary, you will need 1-metre of1.25mm ECW. First, scrape the enamel from one end and solder it to the S1 pin. Now, starting from the bottom, wind on 8.5 turns in a clockwise direction, with the windings laid side by side as you progress up the transformer bobbin. When you have wound on the 8.5 turns, run the lead directly down the side of the bobbin (ie, at right angles to the winding), trim to size and terminate the end on the Fl pin. Wrap a layer of insulating tape tightly around the winding to secure the turns firmly in place. The other half of the primary wind- S1 F1 S2 FZ S3 PRIMARY S4 F3 SECONDARY T1 WINIHNGS Fig.6: the transformer windings must be terminated exactly as shown here, otherwise the inverter circuit won't work. Step-by-step winding details are given in the text. F4 ing starts at S2 and is wound in the same direction directly over the top of the first. Wind on 8.5 turns as before and terminate this winding cin the F2 pin. Another layer of insulating tape is then used to secure this winding. The two secondary windings are wound in exactly the same manner, except that each winding consists of 17.5 turns. Begin the first winding at the S3 terminal, wind on 17.5 turns of 1.25mm ECW and terminate at the F3 pin. Secure this using another layer of insulating tape then, starting at S4, wind on another 17.5 turns and terminate this winding at F4. Install a final layer of insulating tape to secure this last winding, then fit the top and bottom cores to the bobbin and clamp the transformer assembly to the PC board. Tighten the clamp nuts firmly but don't overtighten them, otherwise you'll crack the ferrite cores. Finally, solder the various transformer pins to the PC pattern. FEBRUARY1991 63 RESISTOR COLOUR CODES 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 No. 2 5 2 12 1 2 2 5 3 1 1 2 4 2 Value 4-Band Code (5%) 5-Band Code (1%) 2.2MQ 470kQ 220kQ 100kQ 47kQ 33kQ 22kQ 1% 20kQ 1% 15kQ 10kQ 6.8kQ 4.?kQ 4.?kQ 1% 3.3kQ 1.5kQ 1kQ 820Q 680Q 47Q 10Q 1Q1W 0.22Q 5W red red green gold yellow violet yellow gold red red yellow gold brown black yellow gold yellow violet orange gold orange orange orange gold not appli cable not applicable brown green orange gold brown black orange gold blue grey red gold yellow violet red gold not applicable orange orange red gold brown green red gold brown black red gold grey red brown gold blue grey brown gold yellow violet black gold brown black black gold brown black gold gold not applicable red red black yellow brown yellow violet black orange brown red red black orange brown brown black black orange brown yellow violet black red brown orange orange black red brown red red black red brown red black black red brown brown green black red brown brown black black red brown blue grey black brown brown yel low violet black brown brown yellow violet black brown brown orange orange black brown brown brown green black brown brown brown black black brown brown grey red black black brown blue grey black black brown yellow violet black gold brown brown black black gold brown brown black black silver brown not applicable The PC board now can be fitted into the case. Note that it will be necessary to trim the threaded portion of the stud-mounting diode using a hacksaw so that it doesn't foul the bottom. In addition, some of the internal pillars will have to be shortened using an oversize drill so that they don't foul the board. Installing the Mosfets Once the PC board fits correctly, you can mark out the mounting positions for the Mosfets and power diodes on the heatsink and rear panel. Note that the two outside Mosfets (Ql & Q4) mount on 93mm centres so that their mounting screws fit between the fins of the heatsink. The two inner Mosfets, QZ & Q3, are on 27mm centres so that their mounting screws intercept the flat area between the two sets of heatsink fins. Note: if you use a different heatsink to the one specified, you will have to adjust the positions of the mounting holes accordingly. It's best to mark out and drill the holes in the heatsink first and then use this as a template for marking out 64 SILICON CHIP the Mosfet mounting holes in the rear panel. Position the four holes so that they are 28mm from the bottom of the heatsink and make sure that the heatsink is centred vertically on the rear panel so that it clears the top and bottom panels of the case. The holes for the two power diodes , cordgrip grommets and the fuseholder can also be marked out on the rear panel at this stage. After drilling , carefully deburr all holes using an oversize drill to ensure a smooth mounting surface for the transistors and diodes. The four Mosfet transistors and the two power diodes (D4 & D5) must be insulated from the case using mica washers and insulating bushes. Fig.8 shows the mounting details. Smear heatsink compound on the mating surfaces before screwing each assembly to the rear panel and note that it may be necessary to bend the leads of each device slightly so that it lines up with its mounting hole. As each device is mounted, use your multimeter to confirm that its tab has been correctly isolated from the rear panel. If you do get a short CAPACITOR CODES 0 Value IEC Code EIA Code 0 0 0 0 0.1µF .022µF .01µF .001µF 100n 22n 10n 1n 104 223 103 102 circuit, clear the problem before proceeding further. Final assembly If you don't already have a predrilled front panel, you will have to use the accompanying artwork or a self-adhesive label as a drilling template. If you have a self-adhesive label, it's best to attach this to the front panel before drilling the holes. Drill small pilot holes for the switches initially, then carefully ream them out to the correct size with a tapered reamer. Once this has been done, you can mount the switches and LEDs and complete the wiring as shown in Fig. 7. All wiring to the front panel METAL REAR PANEL ~FUSE '\~1HOLOER TO NICAO BATTERY CORO CLAMP GROMMET - 02 G• O •S • ...___G_•o_; .. I ~ ~ZD3~ 'D3 ~ \L I) - ri·• 0.47uF +,( D ........ ........ 0 Q) 0 0 e3 0 0 •2' 0 0 •,/ FRONT PANEL Fig. 7: check that all polarised components are correctly oriented when mounting the parts on the PC board. Be sure also to use the correct transistor type & zener diode at each location. The pinouts for the Mosfet transistors (Ql-Q4) & the two power diodes (D4 & D5) can be obtained from the main circuit diagram (Fig.5). Note that the metal tabs of these parts must be electrically isolated from the metal rear panel, as shown in Fig.a. The front panel wiring can be run using light-duty hookup wire but use heavy-duty (10A) cable for all rear panel wiring. FEBRUARY1991 65 INSULATING MICA WASHER ~,~jl SCREW r rnllllil(3 -------- CASE 1 T0220 DEVICE Fig.8: mounting details for the Mosfet transistors & fast recovery diodes. Smear all mating surfaces with heatsink compound before bolting each assembly together. The four Mosfet transistors and the two fast recovery diodes (D4 & D5) are all soldered directly to the PC board at full lead length & then bolted to the metal rear panel using TO-220 insulating kits. Check that the mounting surfaces are smooth & free of metal swarf before installing these devices. can be run using light-duty hookup wire but be sure to use heavy-duty (10A) wire for all wiring to the fuseholder, 12V battery and nicad battery. The leads to the 12V battery can be fitted with large automotive battery clips while the output leads should be fitted with a polarised socket to match the plug on the battery pack. Testing Initially, set VR1 and VR2 about 90% anticlockwise, set the Fast/ Trickle switch to FAST, and set the The PC board is secured to integral plastic standoffs moulded into the bottom of the case. Note that it will be necessary to cut off part of the threaded portion of the stud-mounting diode so that the board will fit. 66 SILICON CHIP Battery Select switch to 6V. Now connect a 12V power supply and check for the correct supply voltages on all the ICs. Check also that the pin 1 output of IC3a is at +5V and that the pin 7 output of IC3b is at +9.55V. If you strike problems, switch off immediately and clear the fault before proceeding further. If everything is OK, press the Start switch and check that the Charging LED lights. This LED should then extinguish after a few seconds and the Error and End Of Charge LEDs should come on. Now disconnect the power supply and connect the unit to a 12V car battery. Press the Start switch again and immediately check the output voltage of the charger (ie, check across the output leads to the nicad battery). You should get a measurement of about 24V or higher, since the output terminals are open circuit. Now short the output terminals, press the Start switch once more and check the voltage across the paralleled 0.22n 5W resistors. Adjust VR1 for a reading of 0.66V. This sets the charging current to 6A. Similarly, switch to Trickle charge and adjust VR2 to set the standard charge rate for your nicad cells. For 1300mAh cells, this will be 130mA (ie, C/10). This means that the voltage across the 0.22Q resistors must be set to 14mV (ie, V = IR where I = 130mA and R = 0.11n). At this stage, your Nicad Fast Charger is ready for work but a few final checks are in order. Connect the charger to a discharged battery pack, select fast charge and the appropriate voltage range, and press the Start button to begin charging. Now check that the voltage across the 0.22Q resistors Fig.9: this is the full size artwork for the PC board. It is a good idea to carefully check this pattern against your etched board before mounting any of the parts, as it is easier to spot any errors at this stage. In particular, check for breaks in the copper pattern & for shorts between adjacent tracks. FEBRUARY1991 67 (.!) ~ • 0 z (.!) a: <C J: (.) I- Cl) ::::> (.) > C\I • > • me ,- I- (.) w w U) >• o::t' co >. C\I ...J Cl) • > a: w ~ • CD > I'- > a: w_ U) • a: w (!} a: • <( J: <C J: (.) LL 0 (.) Cl t- z w <( LL I- en • C <( (.) a: ~ CJ) z I w I- CJ) ,....., <C .,, ' LL 1-:u:· 1•••• • , ' llttu•" :::::: ······· ··1····,::· 1111~1 II 68 ~fi~I SILICON CHIP • ~a a: CD I-a:- (.) a: Ww w (.!) ...J zw <((/) w J: (.) (.!) a: 0 ...J :::ii::: (.) a: I- - The output leads should be fitted with a polarised plug to match the battery pack. This will prevent you from connecting the leads the wrong way around. is still 0.66V. Also, check the voltage across the nicad battery pack - it should gradually rise towards its final end point voltage of about 1.8V per cell. While the battery pack is charging, check that the DAC output follows the battery voltage by monitoring pin 1 of IC7. This should rise as the nicad battery voltage rises. Similarly, check that pin 5 of IC8 is 80mV less than pin 1 of IC7. Finally, continue monitoring the nicad battery voltage until it reaches a plateau and begins to fall. The charger should automatically switch off as soon as the battery voltage falls 80mV below its peak value. Custom cell packs The custom selection on the Battery Select switch is provided for special applications; eg, you may want to charge 24 cells in series. As stated earlier, this involves winding more turns on the secondaries of the transformer. In addition, you will have to choose a value for ZD7 (see Fig.5) to suit your particular application. When winding the transformer, you have to provide at least enough turns to give 1.8V per cell. This means that for 24 cells, enough turns must be wound on to give 44V. In this design, each turn on the secondary gives about 1.38V. Thus, a 44V output requires 32 turns, to which we add an extra three turns to provide a reasonable margin. This brings the total to 35 turns on each half of the secondary (ie, an output of about 48V). Note that you will now have to use 0.8mm ECW instead of the 1.25mm wire so that the windings will fit on the bobbin. ZD7 is selected so that the voltage fed to pin 3 of IC8a is less than 8V when the cells are fully charged. For 24 cells , we expect 44V and from this we can subtract the 1.8V drop across LED 1. Thus, 44 - 1.8 - 8 = 34.2V, which means that ZD7 can be a 35V 1W zener diode. Finally, note that the charging current cannot now be adjusted for 6A, as the maximum power that the charger can deliver is limited to 100W. In this case, you will have to settle for a current of about 2A (ie, 100W/48V = 2.08A). SC Fig.10 (left): this artwork can be used as a drilling template for the front panel. You can also use it to make up your own artwork if you don't wish to purchase a commercial panel. I PRODUCT SHOWCASE I Portable PC has automatic power save Sanyo has just released the MBC17NB "Notebook" portable PC. It has an inbuilt 20Mb hard disc drive and a floppy drive as well. The display is a backlit blue LCD panel which is claimed to be NCQ - near colour quality. As well, there is a standard port for connection of a full size VGA monitor, quite desirable for those users who want a portable but need the good quality display. The automatic power save lets the user nominate a time delay up to 127 minutes , after which the power to LCD screen, keyboard and hard disc is suspended without affecting the work currently being processed. The clock speed is also dropped to 6.5MHz to conserve the batteries. When the batteries do discharge, they can be fully recharged within one hour. Sanyo says the MBC-N17B outperforms some 386SX machines. It features an 80C286 processor and 1Mb standard memory expandable to 5Mb. There is also an IDE connector and an optional internal modem. For further information , contact Sanyo Office Machin es Ply Ltd, 384 Eastern Valley Way, East Chatswood, NSW 2057. Phone (02) 498 2799. Midi system has CD player & Dolby noise reduction These days, if you are looking for a good midi-sized hifi system under $1000, you will almost always find that the cassette deck does not have Dolby noise reduction. This is ludicrous really since all recorded music cassettes feature Dolby. However, this new release from Akai does have Dolby. The Akai M-393 features a power amplifier cum graphic analyser rated at 30W per channel , although by some imaginative mathematics they manage to claim that it can deliver 600W peak music power. One of the nice features about these midi systems is their comprehensive infrared remote control which the Akai M-393 has as standard. It controls most of the wanted facilities and, in particular, the volume leve l via a motorised volume control. The AM/FM tuner offers a total of 12 preset stations (six AM and six FM), as well as automatic station scanning. The dual cassette deck offers a continuous listening mode for uninterrupted music and both a normal and high speed dubbing facility. Furthermore, a "synchro" recording feature permits synchronised starts when recording from one tape to another. The CD player is a 16-bit twice over-sampling digital .filter unit with up to 16 program selections. It has all the standard playback features . The record turntable is a 2-speed belt-drive unit (33 & 45 rpm), while the tonearm has a ceramic cartridge and has manual cueing and automatic return at the end of play. Recommended retail price for the Akai M-393 is $899 and it has a 12-month warranty. For furt her information , contact your local Akai hifi dealer. FEBRUARY1991 73 Battery eliminators for communications gear Melbourne based manufacturer Setec has available two power supplies that also double as battery chargers. The model BCEl has a 13 .65V regulated DC output at currents up to 10 amps. The model BCE2 supply provides a 27.6V rail for powering 24V equipment at currents of up to 5 amps. Both supplies are switchmode types with high efficiency, low noise and compact size. Both are fully protected against overload and output short circuits. With communications equipment IEEE-488 controller board for the Mac This board, from Elmeasco Instruments, w ill turn your Maclntosh SE/ 30 into an IEEE-488.2 bus system, capable of transferring data at rates up to lMb/sec. It can control up to a maximum of 14 separate devices or instruments. Applications for this can include lab- PHONE LINE AND MAINS FILTER/SURGE PROTECTOR :ZijProtection for t•Answering machines •Cordless phones , •Facsimiles '. .computers '•Modems '•Telex The Arista model CPE P- 1 ensures that lightning, power surges and spikes do not reach your costly communication equipment as it constantly monitors the PHONE line and the MAINS power line. Simply connect to any existing power point, plug in your fax, phone, video, Hi Fi or any other 240 VAC operated equipment and a series of indicators shows the status of the mains power point while several MOV's and gas arrestors prevents access to damaging energy sources. The CPEP-1 is fully Telecom and Dept. of Minerals and Energy tested and approved. Imported and distributed by: AIUSTI\ ELECTRO NICS Available through the following retailers: Telegrafax PIL. 305-307 Sailors Bay Road. Nor1hbridge. 2063. NSW. (02) 958 5137 74 Geoff Wood E/ec. 229Burns Bay Road. Lane Cove. 2066. NSW. (02) 427 1676. SILICON CHIP and a battery connected to the supply, the installation gives a measure of power fail protection. Under normal conditions, the supply powers the equipment and float charges the battery. Then; when the mains power fails, the battery supplies the equipment but it will be disconnected before it is heavily discharged. This ensures longer battery life and allows the equipment to run unattended with a minimum of service calls. Each unit is available in panel mount, rack mount or PC board versions and all come with a 5-year waroratory testing, production testing and process monitoring, as well as communicating with engineering, scientific and medical equipment. The board itself uses Turbo488 and NAT4882 custom chips. These are designed for the job and are extremely reliable. The unit comes with National Instruments Corporation's NI-488 software driver for the Mac system and requires no configuration jumpers as it's all done by software. For further information, contact your nearest Elmeasco office or phone Sydney (02) 736 2888 or Melbourne (03) 879 2322. Ind us try standard IEEE-488 interface card Electronic Solutions has just released an industry standard IEEE-488 card which is one of the cards available to implement the entire IEEE488 standard. It provides all the hardware to interface a PC to the IEEE-488 bus and has all the software in ROM. Complete documentation is provided, so that programming for special applications can be done. ranty. For further information, contact Setec Pty Ltd, 6 Holloway Dr, Bayswater, Victoria 3153 . Phone (03) 762 5777. No additional operation is required for operation with Basic or Turbo ~ascal while Basic A, Basic Compiler and Quick Basic are supported as standard. For further information, contact Electronic Solutions, 5 Waltham St, Artarmon , NSW. Phone (02) 906 6666 or fax (02) 906 5222. Monolithic 20-bit DIA converter , a A01862 Analog Devices Inc has announced the first monolithic 20-bit digital to analog converter designed specifically for high performance digital audio applications such as electronic musical instruments. Measured according to EIAJ standards, the AD1862 achieves a signal to noise ratio of 119dB and 96dB (.0016%) total harmonic distortion+ noise (THD+N), and a minimum dynamic range of 102dB. Gain linearity is very good with an error of ±ldB at -90dB. Packaged in a 16-pin DIP, the monolithic converter employs proprietary digital offset circuitry to enhance low- DMM checks inductance, frequency & temperature This 4000 count multimeter, the TES 2360, measures just about everything ever found on a multimeter except perhaps for transistor beta. As well as measuring the normal volts AC & DC, AC & DC current up to 10 amps and resistance up to 40 megohms, it has four ranges each for capacitance and inductance. In fact, it is the first multimeter we have come across with inductance ranges. Its inductance ranges are 4 millihenries, 40mH, 4 Henries and 40 Henries, making it a very useful instrument just for these ranges alone. As well, it will measure frequency and temperature, both Fahrenheit and Celsius. A Jaycar Electronics import, it is well worth considering at $179.00. ELECTRONICS WORLD 5p1:c1•LS USED 'AA' 700mAH NICAD BATTERIES $ 0.50 TEMPERATURE CONTROLLED SOLDERING STATION $135.00 UNIVERSAL NICAD BATTERY CHARGER $ 29.95 Can do 4 at a time (AA, C, D, or 9V Nicads) 40 CHANNEL AM CB RADIO $ 79.00 SMOKE DETECTOR $ 49.95 PIEZO SIREN WITH BACKUP BATTERY $ 59.95 Ideal for Car Alarms level signal linearity and eliminate the need for deglitching circuitry. An external midscale trim pin is provided for applications requiring the best possible distortion performance for small signal amplitudes (<60dB). For further information, contact the distributor for Analog Devices, NSD Australia. Phone (03) 890 0970. Probe for dielectric measurements Hewlett Packard has introduced a dielectric probe kit that simplifies measurements of materials used in the food, chemical and electronics industries. The HP 85070A kit includes a probe and software, designed to work with a network analyser and computer. Together they form a system that measures the complex permittivity, including the dielectric los& factor of materials at radio and microwave frequencies. To measure liquids or semi-solids , the probe is immersed into the sample. No special fixtures, containers or sample preparations are required. For solids, a smooth flat surface on the material is required for contact with the probe. The system then measures parameters as a function of frequency. Frequency coverage is determined by the material properties, the network analyser and the probe, which operates up to 20 Gigahertz. The HP 85070A comes as standard equipment with PC-compatible software running under Microsoft Windows. The kit is priced at $6600 .. Complete systems, including network analyser, computer and probe kit, start at $59,000 .. For further information, contact Hewlett Packard Australia Ltd, 31-41 Joseph St, Blackburn, Vic 3130. Phone (008) 033 821. SC DIGITAL DISPLAY AM/FM STEREO CAR RADIO $ 49.95 PORTASOL GAS SOLDERING IRON $ 35.00 ARLEC SUPER TOOL KIT $ 69.50 LOGIC PROBE $ 35.00 SCANNER FANATICS FREQUENCY REGISTER OF VIC. $ 24.95 PHILIPS INFRARED REMOTE CONTROL $ .35.00 COMMON CATHODE 7-SEGMENT DISPLAY $ 1.00 VIDEO DUBBING KIT $ 15.95 ARLEC 2 SPEED CORDLESS DRILL AND SCREWDRIVER $ 69.95 2-CHANNEL FM WIRELESS INTERCOM $ 89.95 SINGLE CHANNEL UHF TRANSMITTER KIT $ 18.00 SINGLE CHANNEL UHF RECEIVER KIT $ 34.90 VULTURE CAR ALARM KIT $ 39.90 INFRA RED NIGHT VIEWER KIT $239.00 .I.E...;. t■t;it:■11: RCS Radio Pty Ltd is the only company which manufactures and sells every PCB & front panel published in SILICON CHIP, ETI and EA. 651 Forest Road, Bexley, NSW 2207. Phone (02) 587 3491. TALKING ELECTRONICS ULTIMA FM BUG KIT $ 12.50 Mail Orders Welcome 30 Lacey St, Croydon VIC, 3136. Telephone: Fax: (03) 723 3860 (03) 723 3094 (03) 725 9443 FEBRUARY1991 75 SERVICEMAN'S LOG Now look what ya gorn an' done! We don't hear that expression much these days but it was a popular one years ago. It was reserved for those occasions when someone committed a careless act which resulted in serious - and sometime irretrievable - damage. These days we tend to use the more economical expression, "Oops". Either way, the implication is the same; somebody has goofed and done a lot of unnecessary damage in the process. And since we have all done it at times, it doesn't do to be too cocky when someone else docs it. But we can take heed and be warned. I have two such stories this month. One situation was retrievable, even though it looked a bit sticky for a while. The other one ... ? The first story concerns a Hanimex 18cm monochrome TV set, model HTV7 . It was a brand new set, belonging to a colleague who is one of the lo ca l antenna installers and with whom I work quite frequently. The set was bought specifically for this job, to be used when doing survey work in difficult areas, particularly involving SBS on UHF. It could operate from either the 240V AC mains or a 12V battery. In the latter mode, it used a lead fitted with a lighter plug at one end and a so-called DC plug at the other, this mating with a PC board socket in the set. For those who may not recognise the DC plug by that name, a brief description might help. The best al ternative term that comes to mind is a female plug - a contradiction in terms perhaps, but that is what it is; a plug shaped device for lead termination which is, in the conventional sense, a socket. And the male mating device, designed more like a socket for chassis or PC board mounting, is in the conventional sense a plug. 76 SILICON CHIP While these devices are not often found in everyday TV and . video equipment, they are used extensively on plugpacks, small chargers for nicad battery operated devices, and such like. (An article in an English technical magazine some years ago suggested that, in order to avoid confusion, such devices should be referred to as "sugs" and "plackets". Fortunately, the idea did not catch on). Anyway, battery operation was one TETIA TV TIP Sanyo CTP5604 Symptom: no sound or picture. Higher than normal voltage appears on the line output transistor collector and a faint squeal can be heard from the power supply circuit board. Cure: R473 (100Q 0.25W) open circuit or dry jointed. This resistor is a vital part of the line oscillator and without it the set can never start up. The squeal is the power supply running in its self-oscillating mode, at a much lower frequency than normal. TETIA TV Tip is supplied by the Tasmanian branch of The Electronic Technicians' Institute of Australia. Contact Jim Lawler, 16 Adina St, Geilston Bay, Tasmania 7015. of the main advantages of this device and the owner had purchased a small sealed lead-acid 12V battery to go with it, making the whole assembly compact enough to carry around with an exp loratory antenna, even onto a roof if necessary. To accommodate this battery, he had removed the cigarette lighter plug, shortened the lead somewhat, and bared the ends to fit the screw terminals on the battery. Which was all very clever and logical. Except that this was where he came to grief. The original lead was fitted with a fuse and his first mistake was to remove this from the modified lead. His second mistake was confuse the polarity of the battery leads after he had removed the lighter plug. He assumed - perhaps not unreasonably that the centre connection of the DC plug would be positive whereas, had he taken the trouble to check the original setup, he could have determined that the reverse was the case. In fact, there is a noticeable lack of standardisation in this regard. Some manufacturers favour one arrangement, others the opposite. I'll have more to say about this later. The inevitable disaster So there was a disaster waiting to happen. And, of course, it did happen. The first I knew of all this was when the set was pushed across the counter, together with a brief synopsis of the above events and a plaintive plea from my colleague. He had planned to survey a difficult VHF area that morning; could I have & quick look and perhaps get the set going? He couldn't have picked a worse time. It was a Monday morning and the weekend's pile-up of problems was being unleashed. The phone seemed to be ringing every few minutes and other customers were breasting the counter. And I didn't even have a circuit of the set. Granted, I had a fair idea of what to look for. Most devices designed for external battery connection use a protective circuit of some kind. The usual arrangement is simply a power diode, reverse connected across the supply leads, so that it is open circuit with correct polarity. Then, in the event of reversed polarity, it is effectively a short circuit, and takes out the aforementioned fuse in the battery lead. Thus alerted, the user can take appropriate action. But, without a fuse, what would happen? An ohmmeter check confirmed that there was a short across the battery leads, but was this simply a damaged diode, or was it something more serious? I tried running it in the 240V mode but it was just as dead. This tended to confirm my worst fears. I opened the set with the aim of finding the diode and working from there. But that was easier said than done. Thme was no diode anywhere near the input socket and my efforts to trace the path through the maze of other tracks on a compact board proved fruitless; it seemed that every time I was half way through a trace there was an interruption of one kind or another. Finally, even my colleague realised that we were battling against the wind; there was no way we were going to .a chieve a quick fix in such an atmosphere. The survey would have to be done without it. So I suggested that he leave it with me and go back to the dealer from whom he bought it, and get either a manual or, at least, a circuit. Then, with a more leisurely approach, we might get somewhere. And so I put the set aside. No circuit I heard nothing more from my colleague for about three weeks, then he turned up with the news that, after much chasing and duck shoving, he had been advised that Hanimex could not even supply a circuit. So we were on our own. The owner wasn't particularly happy about the situation. He had spent around $130 for a set which had never been used and now he feared it might be a write-off. I wasn't that pessimistic but I was worried. While I assumed that there was a protective diode, I wasn't sure. And if there wasn't, the likely damage was anybody's guess. So, at the first convenient slack period, I tackled the set again. And strangely, without all the pressures of the previous occasion, I found the elusive diode without too much trouble. Of course, it was nowhere near the input socket or on/off switch; I suspect manufacturers do this deliberately. Anyway, the diode was found, checked , and proved to have a very short circuit! Replacement was simple enough, any power diode with a rating of lA or better being suitable. Then I set to and re-arranged the customer's lead, clarifying the polarity, and fitting a fuse holder and fuse. That done, I connected the lead to a 12V battery, crossed my fingers, and switched on. Splat! The fuse went instantly and I thanked my lucky stars I had taken the precaution of fitting it. But what was wrong? Once again I had horrible thoughts about what damage might have been done with the reversed connection, in spite of the protective diode. Nor was I at all consoled when I put the ohmmeter across the battery leads and found, not the short circuit of a faulty diode, but still a very low resistance, amounting to only a few ohms. Fortunately, further checking revealed that this low resistance was present even with the set switched off, which left only a short track between the input socket and the on/off switch on the volume control to check. There wasn't much to suspect here. There could, in theory, be a leakage between tracks but this seemed most unlikely. More realistically, the only likely component was the input socket, mounted on the PC board. Closer examination suggested that it looked somewhat misshapen, so I unsoldered it for a closer look. And it was misshapen all right; in fact, it was well and truly cooked. More importantly, removing the socket had removed the short from the board. Of course, there could be other, more subtle damage yet to be revealed, but I was feeling more hopeful. This optimism proved to be justiFEBRUARY 1991 77 - .. SERVICEMAN'S LOG ~ CTD · · . · I). fi ed . I patched a pair of leads directly into the board, connected a battery with due regard to polarity - and gingerly switched on. And, for the first tim e. the set came to life; sound immediately and a picture a few seconds lat er. Well, that was a relief. No serious damage had been done and all I had to do was fit a new input socket to put th e set back into new condition. Serviceman's goof Well, this was where I goofed. The simple truth is that I was not as familiar with DC plugs as I thought I was. I had handled them often enough , as part of various pieces of equipment including some ofmy own - but I had never had occasion to actually work on them in the service sense. For a start, I blissfully imagined 78 SILICON CHIP that I could nip down the street to my local electronics store and purchase a new socket for 80c or so. No dice. They had the plugs and they had mating sockets for lead termination or for chassis mounting, but not for PC board mounting. "Sorry, we don't get much call for them." No problem really. A phone call to one of my regular bits and pieces suppliers confirmed that they had good stocks. I ordered one and was assured that it would go in the post immediately. And they were as good as th eir word; it arrived in the mail the next day. It took only a few minutes to fit it to the board, then I reached for the battery lead to plug it in and give the whole setup a final test. I imagine some readers are way ahead of me; yes, my face was red. I had failed to appreciate that these devices come in two sizes; a 2.1mm pin and a 2.5mm pin. And, apparently, the 2.5mm version is the more commonly used one so, in the absence of any specifications from me, my supplier had as sumed that this was what I wanted. Need I add that the set used the 2.11mn version? And so it took another phone call, another hastily arranged postal delivery, and another solder job on the board. And that finished the job. But what a chapter of accidents and confusion. As it was, I made on ly a nominal charge for the job - much less than was really justified. But then, my colleague has done me a few favours and I owed him one. So everyone was happy, particularly my colleague who had mentally written the set off. But he is also a lot wiser and realises it could have been much worse. Not all devices carry protective circuitry and not all protective circuitry works every time. When you're mucking about with any powe.r leads - even low voltage ones check and double check the polarity. Finally, some thoughts on the polarity conventions used with DC plugs. I happened to relate the above story to an amateur friend, including my embarrassment over the DC plug sizes. He grinned, "Oh yes, I was caught that way myself the first time; it's a common trap." (Now he tells me!) But he was also able to demonstrate a typical conflict of standards in regard to plug and socket polarity. He produced a popular 2-metre hand held transceiver; a Yaesu Musen model FT-23R which, by all accounts, is a very nice little unit. As is typical of such devices it operates from a slide-on nicad battery pack, 7.2V in this case, although a 12V pack is available. The pack is fitted with a 2.1mm phono socket (not exactly the same as the DC plug, but similar) which accepts a plug from a charger. And moulded into the case is a schematic portrayal of the socket, with polarity markings clearly indicating that the centre conductor, which becomes the tip of the plug, should be positive. Fair enough. As well as the battery pack proper, there is also a dummy battery pack available as an accessory. It is similar to the real one but empty, its purpose being to provide access to an externa l power source, such as a car's 12V system. This is fitt ed with the same type of socket ·to take the lead from this source - except that (yes, you've guessed it) this connection uses the opposite polarity. Why this distinction? I have no idea. As far as I can sec, there is no advantage one way or the other. Nor does it matter, provided the difference is appreciated. But wou ldn't there be less chance of accidents if both connections were the same? Anyway, that's my "Oops" for the month. But here's another one from my regular contributor, J.L. from overseas in Tasmania. Here's how he tells it. Crossed wires This story is being written on a 6year-old BBC micro-computer. It's now an old-fashioned machine, with only 32K of user memory. But with its operating system and the word processor routine both in ROM , th e machine has proved more than adequate for the jobs I us e it for. Coupled to the machine is a dual single sided disc drive, a Star Gemini printeJ, an English Nightingale modem and a Thomas green screen monitor. All in all, it represents $2500 worth of computer equipment and I'd be totally lost without it. Alongside me as I write is another, far less fortunate BBC computer, the subject of the photos on the following page. It suffered from the careless machinations of a would-be serviceman and is now a part of $2500 worth of junk. The photos tell most of the story in graphic detail. What more need I say? It seems that the owner of the machine wanted to operate it at a distan ce from th e nearest power point so he asked his '·' friend" to make up an extens ion power lead for him. The so-called fri end did so, but crossed over the active and earth leads, with very expensive results. The 240V AC was appli ed to the computer via the earth line and blew the lids off most of the !Cs on the main board. At the time of writing, it seems that only the keyboard escaped total destruction. But that's not all! The 240V found a path out of the main board to the monitor, disc drive and modem lin es, and played merry hell with all of their Is Your Product Or Service Getting The Exposure It Deserves? 25,000 consumers will read this page. They need to see your advertisement if you want them to buy your product. Contact Paul (018) 28 5532 or Ian (03) 696 5411 to reserve this space. semiconductors along th e way. The resultant current finall y went through the printer, leaving a charred and very exp ensive mess behind it. If it had been my computer, I'd be weeping tears of blood. But then, I would have made up my own extension lead and I would have been more carefu l with the active. neutral and earth leads , wouldn't I? (A lat er investigat ion showed that even th e keyboard did not esca pe entirely. Three chips. three resistors and several diodes were totally cooked . The key switches did survive and they have been salvaged for possible use in mv machin e at a later date!) Well. that's J.L.'s story and, as they say in the classics . that was a fair dinkum, no-mu cking-about. kind of "Oops". Belting a VCR Finally, here is a short story which, as well as highlighting th e tendency of some servicemen to assume th e worst, may also provide a coup le of helpful comments fo r other readers. It was inspired by problems with a Hitachi video recorder, mod el VT-33E. TV TEST EQUIPMENT THAT WILL EARN YOU MORE MONEY (AUSTRALIAN MADE) 12 Months Warranty SHORTED TURNS TESTER Built-in Meter to check EHT transformers including split diode type, yokes and drive transformers. $78.00 + $3.00 p&p HI-VOLTAGE PROBE Built-in meter reads positive or negative 050kV. For checking EHT and focus as well as any other Hi-tension voltages. $98.00 + $5.00 p&p LOW VOLTAGE PROBE Ideal for checking microwave ovens and TVs. The ranges are from 0 to 5kV Negative and from 0 to 10kV Positive. Double insulated for safety. $8_4.00 + $5.00 p&p $75.00 10.00 p&p + <:...... _.. .~ DEGAUSSING WAND 7,700 apere turns. Strong magnetic field, larger than usual coil with multicore centre . Double insulated for safety with momentary on/off switch. 240V NC 2.2 amps. This one is just about as important as having a soldering iron in your toolbox! REMOTE CONTROL TESTER (INFARED OR ULTRASONIC) j""'~ "-· -~·.:} $85.00 + $4.00 p&p TUNER REPAIRS TV . Designed to test any lnfared or Ultrasonic control units. With the extension lead you can also test infared units which cannot be placed in front of the testing unit. Requires a 9V battery.· Output is via the LED diode and piezo speaker. trom only $11.00 + p&p . Cheque Money Order Bankca;d or Masterca~d We also repair most tuners on an exchange bas,s. "• • 11JNERS~216 Canterbury Road , Revesby, ~ NSW, 2212, Australia Telephone (02) 774 1154 FEBRUARY1991 79 This is what 240V AC can do to a computer motherboard. These burnt & melted chips were fed with mains voltage after the active & earth leads were swapped on an extension cord. This model is about eight years old and appears to have been very reli able. I have encountered few faults until recently; just the odd minor one or a routine head clean, etc. But lately I have encountered several with what appeared, initially, to be quite puzzling "funnies". In fact, all were due to the same basic cause, albeit with variations. It's the drive belts that case all the problems. There are no less than six belts in this machin e and failure of any one can produce a range of (sometimes) puzzling symptoms. Five belts are on the underside of the machine, while one is on the top side. On the underside, two belts run from the capstan motor which carries two pulleys. One of these pulleys is about 12mm diameter and engages a wide belt which drives the capstan shaft via an 80mm pulley. The other pulley is about 20mm diameter and engages a longer belt which then drives a larger pulley (about 40mm diameter). This latter is on an intermediate shaft which carries a second pully, about 18mm diameter, and from this another belt drives a second pulley, again about 40mm diameter, on the idler shaft. This carries the tyred idler wheel which drives the takeup or supply reel, according to the operating mode. Also on the underside is the loading motor and this drives the two arms which extract the tape from the cassette and wrap it around the drum. The link between the motor and the loading mechanism is via two belts. 80 SILICON CHIP It looks like a bombed-out factory in World War II. This is another section of the main circuit board of the BBC microcomputer after someone connected 240V AC to the PCB earth track. The loading motor pulley is about 10mm diameter and drives an intermediate pulley of about 20mm diameter via the first be lt. A second (12mm) pulley on the same shaft is then coupled via the second belt to a 20mm pulley on the loading mechanism shaft. That accounts for five belts. The sixth one , above the chassis, couples the takeup reel to an impulse generator which feeds the microprocessor. Its function is to confirm that the takeup reel is functioning. Faulty diagnosis The recorder came to me with the story that it sometimes refused to run a tape. It had been taken to another service organisation whose diagnosis was that it was a microprocessor fault and that, as an old machine, it was not worth fixing. I opened it, confirmed that no belts had been changed, then put it through the load function. It appeared to load normally; the tape actually starting to run. Then everything stopped. Acting on experience, I applied gentle pressure to the last pulley in the loading mechanism chain. It moved a fraction and - bingo! - the tape began to play. It was a classic fault. Both of these belts are prone to go spongy and lose their elasticity. Then they will no longer drive the loading arms fully home; nearly, but not quite - and not hard enough to activate a protective sensor. So the machine shuts down. (I admit that this one tricked me for a while, the first time round). Another rather alarming symptom of this condition is that, as the system attempts to load, it will produce a violent screeching sound; something which sounds exactly like a dry bearing about to sieze. That noise is simply due to one of the pulleys spinning against the belt. The cure was simp le; a complete set of new bolts and a now idler tyre, plus a routine clean and lubricate, restored the machine to first class condition. So much for the "it's not worth fixing" diagnosis. A more obvious belt fault involves the top belt coupled to the takeup reel. This sometimes breaks and, while the machine will load, it will not run. The microprocessor knows the takeup reel is not functioning, and shuts the machine down. Fortunately, this is easy to pick. I have also encountered a broken belt in the drive from the capstan motor to the idler wheel - the larger one in this case. Again , while the machine will load, it will not run, because the microprocessor is being told - genuinely - that the takeup reel is not functioning. This is also easy to see, but a slipping belt in this chain could create more puzzling symptoms if it failed only momentarily, in the middle of a run. All of which adds up to a simple piece of advice. Any VCR of this age and the VT-33E in particular - which exhibits similar symptoms, may well have a belt problem. And don't muck about; change all the belts. If one is dead the rest are dying. SC OUR FIRST AFTER STOCKTAKE CLEARANCE SALE You get the bargains at never to be repeated prices Universal wire wrap card Code:IF054 External Floppy drive controller card, including case and cables Code: oc122OE Designed for engineers and other technical developers and is fitted with universal decoding component and a user prog ramable 1/0 chip (PAL 16L8). This has board 4000 wire wrap holes which are plated 1 through for easy prototyping and is a full length card, with a D25 connector femal connector. For use on IBM PC/XT/AT or compatibles. This is an intelligent floppy disk controller card for external drives. It can be used with existing internal controller cards and supports all standard drive formats. For use in IBM XT/ AT/ 386-AT or compatibles. $199.00 Save $26.00 only $99.00 Enhanced EGA graphics adaptor Normally priced at $125.00 Code:VCEGA Suitable for IBM PC/XT/AT with a full 256kB video memory. The card has light pen interface • and external DIP switch for easy display mode selection. Only uses a short slot. Also features auto-switch utility and will support 132 column text mode .. Provides 640 x 480 extended EGA resolution. Super Special only $50.00 STOCK CLEARANCE BUT ONLY LIMITED QUANTITIES ON THE FOLLOWING ITEMS Adaptor tray for 3.5" FDD Single height 5.25" external drive case . Will fit in a 5.25" slot. These have a black front panel CAEX5 - These come complete with cables and a high quality metal case. Quantity : 13 only only $5.00ea Quantity: 4 only only$20.00 Normalprice $25.00 Normal Price $99.00 Removable hard disk case CAPO - Now you can remove your hard disk without having to pull your machine apart. Has key lock. Quantity: 4 only Fastcard for 8088 - IF286S Upgrades your 8088 machine to perform at the speed of an AT. Now there is no need to throw out that old maachine of yours. Quantity: 12 only only .$50.00 Normal Price $199.00 Multifunction 3.5MB / RS232 x4card Quantity: 7 only RC2350 - Expand your machine up to 3.5MB as well this card has 4 -RS232 serial interface for control of modems or serial printers. Also has a parallel printer port and game port. RAM not included. Now only $75.00 Normal Price $299.00 only $99.00 Normal Price $495.00 3.5" external drive case Quantity: 9 only Save$74.00 only $15.00 5.25" external drive case - CAEX52 Quantity: 7 only Save $100.00 now onlv $25.00 SEE OUR OTHER ADVERTISM£NT IN THIS ISSUE FOR YOUR FREE 1991 CATALOGUE OFFER Electronic Solutions 5 Waltham StArtarmon 2064 PO Box 426 Gladesville 211 1 Telephone: (02) 906 6666 Fax: (02) 906 5222 -[Z] Due to Technical advances, products we supply may in some cases vary from those pictured. In all cases the products supplied are guaranteed to perform to an equal or higher standard than those pictured REMOTE CONTROL BY BOB YOUNG Galloping ghost - the missing link in the evolution of proportional control These days, modellers take proportional control systems for granted, without realising just how much better they are than the systems they made obsolete. This month, we take a look at a system which was popular before digital electronics took over. . Over the past few months, we have discussed much in relation to the modern radio control system but we have yet to answer some vital questions: "what exactly is digital proportional control; why is it so good; and how did it evolve?" All of these questions will be answered in the following series of articles. However, before progressing further, I would suggest that the reader refresh his memory with the first article in this series, published in the October 1989 issue, for much of the history of the developments leading up to this system was covered there. For those who missed that article, it is sufficient to state that prior to proportional control, the typical multi-channel R/C system was usu- 1 • ally some sort of audio tone system using either filters or tuned reeds for decoding. Tuned reeds were by far the most popular and successful system, certainly in this country and in America. Now the point here is that these systems only gave two to three simultaneous controls (usually two) but, most important of all, they only gave neutral, full clockwise and full anticlockwise control positions. No intermediate positions were available. This was not really satisfactory for any form of modelling but despite these shortcomings, the best flyers could give demonstrations which would be hard to distinguish from those given by flyers today using · modern proportional control equipment. 01-lsec , I ~-A ~ ~ ~ ~ DOWN MAIN AERODYNAMIC FORCE= NEUTRAL Fig.1: the inertia of the model plus the elasticity of the air will average out a rapidly oscillating control to give smooth flight. If the control oscillates symmetrically about the neutral position as shown here, the result will be neutral control. 82 SILICON CHIP We learned to adapt and we learned all the tricks. A separate servo was used for elevator trim , one which could be nudged into the correct position and left there until retrimming was required. A similar type of servo was used for throttle as well. Pulsed controls Controls could be pulsed to average out the aerodynamic effects and short pulses only gave small control throws. Long pulses gave about half throw and the lever held full on gave full throw of course. The pulses never showed up in the manoeuvres and all looked perfectly smooth - in the hands of an expert that is. The average flyer, which included myself, never really knew what to make of all of these shortcomings and thus we never really learned to feel comfortable with this system. Believe me, I crashed many a good model trying to master this system. Something had to be done, and we all knew what it was. But the burning question was how? This problem, like all problems when solved, turned out to be easy so easy as a matter of fact, that I was stunned at the time at just how simple and effective the system really was. But let me tell you that the problem occupied many of the finest minds in the electronics world and baffled most of them until the early 1960s when two Americans, Don Mathers and Doug Spreng, developed the proportional system as we now know it. So complete was their approach that to this day little has been changed except the technology applied to solving the practical problems. However, we are now a little ahead of our story, I TONE OR CARRIER ONI CONTROL POTS REPETITION RATE ~1 J ONI I 0.1-1sec #I J I 50% MARK/S PACE RATIO _.,. B1 1 !.i... -T B2 , !.i... Fig.2: the "Galloping Ghost" system used mark-space/pulse rate encoding & decoding. In this scheme, the decoded pulses controlled a relay & this in turn was used to rapidly switch a small electric motor first in one direction & then the other. The model thus responded to the mean aerodynamic position of the control surface. having missed that important step mentioned earlier. The Galloping Ghost What on earth was the Galloping Ghost? I can hear the readers now: "this lad has finally flipped for real and is now seeing apparitions". Sorry to disappoint you, but "Galloping Ghost" is the name given to that missing step in the proportional control story. Earlier, I mentioned that the inertia of the model and the elasticity of air will average out rapidly oscillating controls and give a smooth result around the averaged control positions, as shown in Fig.1. Now this phenomenon has two very important uses: (1). If interference or weak signal areas are encountered, then random noise intruding into the servo amplifier will strike some sort of average which may be anywhere from full down to full up. This average is changing rapidly but, combined with the occasional snatch of uncorrupted control data, will often keep a model flying until full control is restored. This is the factor that made PPM such an effective system and which renders the concept of "fail-safe" (neutralised flying controls) invalid. (2). It's also useful in the Galloping Ghost type systems of constantly flapping servos, in which the rapid flutter is deliberately introduced and averaged out to a mean aerodynamic value by virtue of a controlled encoder. This is our missing link in the chain of development leading to true digital proportional control. The basis of the Galloping Ghost system was the concept of markspace, pulse-rate decoding. In this system, a small electric motor was connected directly to the terminals of a relay which was switched by an encoder. This encoder was controlled. through gimballed joysticks driving potentiometers, suitably arranged to vary the mark-space, pulse-rate ratios of the relay switching. Oscillating control surfaces The name "Galloping Ghost" came from the franti c appearance of the constantly thrashing control surfac es. To hear a model gliding overhead controlled by this system was a real experience - the noise was unbelievable. Of course, the motor armatures and brushes didn't take too well to this sort of treatment. Nevertheless, the system was remarkably reliable considering the strain on the motors and relays. The block diagrams in Fig.2 show the theory behind this truly incredible and very primitive system. Fig.3 gives the timing diagrams for various combinations of mark-space ratio and pulse-rate. For a modern modeller, versed in the art of digital electronics, the following system will seem almost incomprehensible, yet it formed a major link in the chain of development and some really satisfying flying was done using this system. It also serves to indicate just how difficult the prob- lem of achieving proportional control really was and just how powerful the techniques of digital electronics are today The electronics revolution has largely been possible due to digital concepts an d it is difficult for modern readers to realise that in 1960 very few of us had even heard of the term , let alone had any knowledge of the techniques involved. Fig.4 shows the way the two separate control outputs are taken from the servo drive disc, one for the elevator and one for the rudder. The series of diagrams in Fig.5 shows the way in which the mean aerodynam ic force is generated for the two controls; in other words, the decoded output. The system worked as follows : · The transmitter was a conventional single-channel type using either tone modulation or straight carrier switching. A mark-space, pulse-rate encoder controlled the transmitter and delivered to the receiver a coded signal carrying two streams of data. One stream cons isted of a signal with a mark-space ratio varying from 20-80% to 80-20% Is Your Product Or Service Getting The Exposure It Deserves? 25,000 consumers will read this page. They need to see your advertisement if you want them to buy your product. Contact Paul (018) 28 5532 or Ian (03) 696 5411 to reserve this space. FEBRUARY1991 83 50-50 0.5sec 50-50 0.25sec 50-50 1sec n n 25-75 0.5sec LJ LJ 75-25 0.5sec 40-60 1sec Fig.3: these timing diagrams show various combinations of mark-space ratio and pulse-rate for a proportional control system. The second stream was carried in the coded signal generated by the variation of speed at which this markspace signal was repeated, commonly termed the pulse rate. This rate was usually varied from approximately 0.ls to 0.8s. The exact rate depended upon the transit time of the servo motor. Both these signals were of course superimposed upon one another and needed to be separated at the receiver end. Now the logical and modern thing to do would be to use , solid state, mark-space, pulse-rate detectors and this was eventually done in some systems, but once this constantly variable DC voltage is generated, what do you do with it? Remember, this is in the days long before ICs and those nice little op amps. This was in the electronic dark ages and electronic solutions were prohibitively expensive. I can remember buying my first transistor around this time; it cost me 25 shillings and I bled for a week. However, we are ahead of our story again. Motor decoding Modellers, being by nature a tight fisted lot, came up with a primitive 84 SILICON CHIP but effective system using a single electric motor for decoding. Fig.4 shows the mechanical arrangement of the basic mark-space, pulse- rate decoder. The mark-space decoder is simply a slotted yoke mounted and pivoted at a suitable point to allow the control pin to accomplish almost one complete revolution (80% of a revolution to be exact). This yoke is usually connected to the rudder of the model, neutral being at the 12 o'clock position. If the motor rotates clockwise, the rudder will turn right, for example, and if the motor rotates anticlockwise, it turns left. In practice, the relay is switching constantly between open and closed at a mark-space ratio determined by the transmitter encoder. Thus, we now have a yoke which will deliver to the control surface a deflection which is rapidly and equally varying around neutral if the mark-space ratio is exactly 50%. If the mark-space ratio is varied, then the avtJrage position will shift from neutral in an amount directly proportional to the mark-space variation (Fig.5d & 5e) . Fig.4 also shows the arrangement for the pulse rate detector, which is simply another yoke set at right angles to the first and again pivoted suitably to all9w the control pin to rotate freely over 80% of a revolution. If the pulse rate is taken to its highest, the motor oscillates quickly about the 12 o'clock position and the averTO ELEVATOR DRIVE PIN age deflection is considered to be "up" elevator. (The rate control was usually connected to the elevator in the model). As the rate was slowed, the motor had more time to rotate and the average position moved towards the "down" position. At the slowest rate, the elevator was in the full "down" position. Note here that, in effect, full down is really neutral elevator. Fig.5c shows the timing of the arcs involved. However, the dwell time at servo reversal added to the down elevator effect and the trimming of the model biased the system to account for the rest. In this way, we achieved two proportional controls from a single channel receiver - quite a step forward but well short of the requirements for a model aircraft, in which four simultaneous controls are tL~ minimum required for full control. Note also that the decoding was far from perfect, with a great deal of mixing between controls occuring (Fig.5 illustrates this quite clearly). Theoretically, the transmitter joystick should have been positioned in the centre of a square hole, but in order to overcome some of the problems of the control mixing, which occured mainly at control extremes, there were some strange configurations at the borders of this no longer square hole. In fact, you had to learn to fly not to the spring centre of the sticks but to the feel of the model. If it was going where you wanted it, then it really did not matter much where the stick was. You never had time look at that anyway. Believe me , it was all you could manage to keep the model airborne. It was ingenious, simple, cheap and diabolically primitive. However it worked, and worked well and gave many of us a taste for a much more professional system, if only we could work out how to do it, that is. New developments RUO.OER NEUTRAL DRIVE DISK ON MOTOR OUTPUT SHAFT Fig.4: this diagram shows the arrangement of a mechanical markspace/pulse rate decoder. The markspace decoder consisted of a slotted yoke connected to the rudder, while the pulse-rate detector used a second yoke (connected at right angles to the first) to control the elevator. There were several important developments that followed on from this basic system. One was the system marketed by Dr Walter Good in which two audio tones were transmitted simultaneously, each modulated for mark-space, pulse rate. This gave four simultaneous proportional (galloping) channels. Motor control was achieved through a trimable (positionable) servo driven ~ t ,_ 0 " ~ ™ O o~: +~J, - ~:,H" """'""'""'""''" 01.~i ~ ~ ol~. 1 ~ 0 RUDDER {/ \) I.~ 0.25sec ~h\/ EFFECTIVE --Fi~,;::;,;:;,_,_EL_EV-AT_O_R 't'.f" ~ ,Jj - ~,--- lsec NEUTRAL MIXING OR~:RFECT DECODING EFFECT Fig.5: this series of diagrams shows the way in which the mean aerodynamic force is generated for the two controls; in other words, the decoded output. Note how the rudder moves away from the neutral position for mark-space ratios other than 50:50, while the elevator position varies according to the pulse rate. from a pulse om1ss10n detector on each of the two tone channels - one for high throttle and one for low. This was a very sophisticated and complex system for its time and held us all in awe whenever the very occasional example showed up on one of our fields. Here was a taste of what was soon to come. The feel of the transmitter was marvellous and those twin proportional sticks felt just right, compared with the five cumbersome lever switches on our reed transmitters. Never mind that the performance of the rest of the set was as primitive as it is possible to imagine. A model fitted with three flapping controls was a sight to behold but at the time, we thought it was great. They were exciting days and it is impossible for modern modellers to comprehend the degree of yearning that the dream of true, simultaneous control generated in us. One must remember that at that time, a transistorised anything was rare on our fields, for many of us were still flying single channel valve sets. As a matter of fact, I did not stop producing valve super-regenerative receivers until around 1969, long after I began producing a solid state superhet 6-channel digital system. Even then, the only thing that stopped me was the difficulty in obtaining valves and 22.5V batteries. The demand for a valve system was always there. In this respect, a trip to the flying field was always very interesting, for one would see operating, side by side, valve super-regen single channel systems, superhet reed, 8channel audio tone, Galloping Ghost, Walter Good dual Galloping Ghost, and a host of home-made systems using many and varied approaches. The final step in the mark-space systems came with the development of solid state mark-space, pulse rate decoders. These delivered a DC output proportional to the input. From here the difficult part began. Just what could you do with this sort of output? These days, a DC-coupled, closed loop feedback servo would be possible but this was well before op amps. The answer in those days was to feed this power into a magnetic actuator. This device consisted of a circular magnet inside a coil wound at right angles to the magnetic field. This was lightly spring-loaded for return to neutral. Thus, with the polarity aligned in one direction, the magnet would begin to deflect clockwise and with the current flow reversed, in the counter clockwise direction. The greater the power fed into the coil, the more deflection obtained. They were not very powerful, giving about 3-5 oun,ces on a spring balance, but this was enough for a lightlyloaded, slow-flying aircraft. They were quite accurate and gave true and smooth proportional control, free of the gallop and decoding mixing associated with the "galloping ghost" systems. They were, however, not the answer we were looking for. That had to wait until two very gifted Americans made their contribution to the field of radio control and that story will be told in next month's issue. See you then. SC FEBRUARY1991 85 AMATEUR RADIO BY GARRY CRATT, VK2YBX Oscillators - which type is best for you? Last month, we discussed the operation of quartz crystals. Following on from that article, we discuss the different types of oscillators that can be used in amateur equipment, both crystal and free running types, and the advantages of using particular types. Without going into the detailed circuit theory behind oscillator design, there are two basic conditions that must be fulfilled in any design before oscillation can occur: (1). the amplifier around which the oscillator is based must have a gain of more than one; and (2). positive feedback must be applied between output and input. Fig.1 shows the block diagram of a basic oscillator. As can be seen, there is a feedback path from the active device output to its input, leading to ACTIVE DEVICE INPUT NETWORK -7 t ! the conclusion that the oscillator is essentially a feedback amplifier that supplies its own input. There are many types of oscillator designs, each with a particular advantage depending upon the application. In some applications (eg, the local oscillator in a superheterodyne receiver), it is necessary to use an oscillator design having good spectral purity and stable frequency characteristics. Other applications require a design that will be rich in harmonics; eg, a circuit requiring the use of an overtone crystal, Frequency stability is also often an important factor, as several stages of frequency multiplication may be used after the oscillator to reach the output frequency. There is also the added complication of temperature stability. Because temperature changes can affect the operating frequency, care must also be taken to maintain a stable temperature. 1 ~I __J Fig.1: block diagram of a basic oscillator. Note the feedback network from active device output to input. 86 SILICON CHIP Hartley oscillators Fig.2 shows the circuit of a Hartley oscillator. The frequency of oscillation is determined by L1 and Cl. The amount of feedback is determined by the ratio of the reactance of Lla and Cl (the volt- .---------ovcc RL C2 r----il_----, _ _ _ _ _ _O V0UT Fig.2: the Hartley oscillator. This type of oscillator exhibits a constant output voltage over its tuning range. age divider network within the tuned circuit), and the feedback energy is returned to the tuned circuit by the current passing through Llb and C3. This type of oscillator is most commonly used in VFO circuits due to its constant output level over the tuning range. However, this oscillator type has one major disadvantage and that is the high level of harmonics. As can be seen from Fig 2, the reactance of Ll increases with the output frequency. This means that harmonics of the fundamental frequency are developed in the tuned circuit and returned to the input, then being further c;tmplified before appearing, along with the fundamental, in the output. Thus, in order to use a Hartley oscillator sucessfully, a bandpass filter is required after the tuned circuit. Alternatively, a double tuned collector tank could be used. Colpitts oscillator The most common type of oscilla- ,---------ovcc ,------.----ovcc R1 C4 01 CJ CJ v~ o---------..J R2 .,. Fig.3: in the Colpitts oscillator, the emitter of the transistor is connected to the junction of two capacitors (Cl & C2). The main advantage of this configuration is low harmonic content in the output. tor using an inductive divider network is the Colpitts oscillator - see Fig.3. This circuit differs from the Hartley oscillator in that the emitter of the transistor is connected to the junction of two capacitors (Cl & CZ), instead of tapping the inductor. The voltage divider is formed by Ll & Cl. Typically, Cl is three times the value of CZ to ensure reliable oscillation. Changing the value of Ll or CZ will change the frequency, while changing the value of Cl will vary the output level. Colpitts oscillators are used because of their high spectral purity. Because the feedback voltage is developed across a capacitor, the reactance of which decreases at harmonic frequencies, the harmonic content is low. However, the main disadvantage of this type of oscillator is the difficulty in varying the output frequency without varying the output level. In fact, it is necessary to vary both capacitors, whilst maintaining the ratio between them. The Clapp oscillator is a variation of the Colpitts design, where a series variable capacitor has been added to the tank coil (Ll). This provides improved stability and allows tuning of the oscillator. If the value of the trimmer is low compared to the value of Cl & CZ, then the feedback ratio will be largely unaffected when the oscillator is tuned. Fig.4 shows the details. Crystal oscillators Although the previous designs can Fig.4: the Clapp oscillator is similar to the Colpitts configuration but employs a variable capacitor (VCl) in series with the tank coil (Ll). This provides improved stability and allows tuning. Quartz Crystal Oscillators C1 R1 .--------0vcc C2 .,. Fig.5: quartz crystal oscillators are used when good stability & high Q are required. This Hartley oscillator uses crystal Xl as the active resonant element. .,. Fig.6: a crystal controlled Colpitts oscillator. VCl allows some adjustment of the output frequency. be used in many applications, a-quartz ing the inductance of the crystal and crystal oscillator is inevitably used Cl, while the energy to maintain oscillation is returned via CZ. where good stability and a high Qare required. Figs.5 & 6 show how a crysIn addition to fixed frequency ostal can be used as the active resonant cillators, circuits are available to alelement in both Hartley and Colpitts oscillators. If an addi,-------vvcc tional degree of stability is required, the Pierce oscillator design shown in Fig. 7 can be used. VC1 CJ The conditions to sustain osl---0 OUTPUT cillation are present only at the frequency which makes the crystal behave as an inductive reactance. Hence the crystal replaces the inductor in the circuit. Variable capacitor VCl allows a small adjustment to be niade to the output frequency. The circuit operation is identiFig.7: a crystal-controlled Pierce cal to that of the Colpitts oscillaoscillator. It operates in exactly the same tor. The feedback voltage is deway as the Colpitts oscillator but offers improved stability. veloped by the network comprisFEBRUARY1991 87 .-------0+12V RFCrr+gv 100pF 1mH x1I' ~ - - --- - - 22pF 12MHz c, 100k .00 1 D1 .01 1N4148 22pF .,. Fig.8: these two variable frequency oscillator (VXO) circuits can be run at 12MHz and subsequently multiplied to 144MHz for use in a 2-metre transmitter. ,-----------------<J+9-12V 47k 01 OUTPUT VC1 220pF .,. Fig.9 this modified Colpitts oscillator uses diode switching to select between three different crystals (Xl, X2 & X3). 270U MWA120 2xHOT CARRIER 4.lk oUTPuT(J') 50U 'I L1 1uH L2 1uH 5-60pF+ Fig.10: experimental oscillator circuit based on the Motorola MWA-120 MIC (microwave integrated circuit). low crystals to be "pulled" in frequency, allowing as much as 8kHz to l0kHz of frequency change to be achieved. These circuits are called 88 SILICON CHIP variable frequency crystal oscillators or VXOs. In a 2-metre transmitter, if a crystal oscillator followed by several stages of frequency multip lication was used, it can be seen that at least 100kHz of frequency adjustment would be available at the output frequency. Two circuits that can be used at 12MHz (and subsequently multiplied to 144MHz) are shown in Fig.8. A buffer stage should always be used after a VXO to eliminate frequency pulling. VXOs are a compromise between cost (simplicity) and full band coverage. However, if only a small segment of an amateur band is of interest, such circuits can be used. In addition, a scheme to switch crystals covering segments of the band could be implemented as shown in Fig.9. Here, a Colpitts oscillator has been modified to allow diode switching of a bank-of crystals. A superior approach is to use a VFO circuit, some of which are capable of operation over several megahertz at VHF or UHF. Without going into design detail, VFOs for HF tend to use large plate variable capacitors and rely on mechanical stability and vernier gearing to give good stability and adequate frequency coverage. These units often only need to cover 500kHz, as the output can be mixed up to any HF band. VFOs designed specifically for VHF/UHF work tend to be PC board mounted and varicap tuned, relying on multiturn potentiometers or optocoupled controls for stability and frequency coverage. Also of interest to amateurs working at VHF is the advent of MICs (microwave integrated circuits), which these days form part of many RF systems. The most common MIC is the cascade amplifier, often designed with 50-ohm input and output impedances. Provided a resonant net- work with a phase shift of 180° at the desired operating frequency and some form of current limiting external to the MIC are used, output levels of around 6dBm are achievable. Fig.10 shows the experimental circuit used, based on a Motorola MWA-120. Finally, Fig.11 shows a series of circuits using an MMIC, illustrating the simplicity of oscillator design using these devices. 56-27DpF! (FUNDAMENTAL) Fig.11 (a) Further reading (1). Oscillator Design Handbook; (2). ARRL Handbook; (3). VHF/UHF Manual - G.R. Jessop, G6JP; (4). Es- Fig.11 (C) Fig.11: these three circuits illustrate how simple oscillator design can be using MMICs. They include a basic 70MHz oscillator (a), a 210MHz 3rd overtone oscillator (b ), & a 330MHz fundamental oscillator (c ). IC1 uPC1651G One of the most comprehensive publications on RF oscillator design has recently been released by Cardiff Publishing Company, 6300 S. Syracuse Way, Suite 650 Englewood, Colorado 80111. Called "Oscillator Design Handbook", it is available from the publishers for around $20. References IC1 uPC1651G IC1 uPC1651G L1 f56pF .07uH.,. (3RD OVERTONE) Fig.11 (b) sentials of Communication Electronics - Slurzberg/Osterheld. Footnote: The MWA-110/120 & MWA-310/320/330 MICs should be available from Motorola stockists (VSI Electronics, etc). The uPC1651 MMIC is available from Dick Smith Electronics. SC PC INSTRUMENTATION FOR THE 90s Australia's widest range (over 10,000 items) of PC/XT/AT/'386 based engineering/industrial and scientific hardware and software. 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BOSTON TECHNOLOGY PTY LTD EAST COAST PO Box 415 Milsons Point NSW 2061 Ph: (02) 955 4765 Fax: (02) 922 1118 WEST COAST PO Box 1093 West Perth WA 6005 Ph: (09) 321 2899 Fax: (09) 321 2891 FEBRUARY1991 89 ll CPF CONTINUOUS POWER FILTEA SPIKE ARRESTOR The Fortron CPF F1l1ered Electronic Spike Protector p ro vides a prolectlve eleclromc barrier IOf microcompu1ers prmters. telephone sys1ems anel modems elec1romc typewriters. audio and stereo s-ys1ems and other sens1hve e tectromc equ1pmen1 The C PF provides protec11o n trom dangerous electrical spikes that can caIJse anything from obvious damage (llke 1mmed1ate equ ipment !a1!ure) to less obvious harm that can dras11cany shorten a system 's hie CPF's superior c1rcu11ry design and sem i conductor technology resp:,nds in stan tly !O any potentially dam aging ove1-vollage. ensuring safe trouble free opera11on l\e "•· .1-·· f l---.l 2&4WAY RS232 DATA TRANSFER SWITCHES THE BUTTON SPIKE PROTECTOR A simple way of monitoring RS232 interface lead actrvIty Interface powered. pocket size !or c1rcuIt ~et~~g~aT~~~:;a r e g~a~~~ng 2 spares 24 sw11ches enables you to break oul cucuits or reconfigure an:1 pa1ch any or all the 24 active pos,11ons SPECIFICATIONS : Connectors : D825 plug on 80mm nbbon cable and D825 socket Indicators : Tricolour LED·s for TD. RD. RT S. CTS . DSR. C D. TC. AC. OTA. (E)TC Jum per Wires : 20 tinned end pieces Power : lnter1ace power Enclosure : Black. high Impac! plastic Dimensio ns : 85 x 95 11 30mm X 15700 .... .... $119.95 g <> ~ Surges and spikes are caused no1 only by lightning strikes and load switching but also by other equIpmen1 being switched on and off . such as fluorescent lights . electric motors. fridge freezers. ai r cond1t Ioners. e1c For eflect1ve protection such spikes must be stopped before they reach your equIpmen1 Simply plug The Bunon ,nto an outlet and it will protect all equ,pmenl plugged mto ad1acen1 outlets on the same branch c1rcuI1 The Button employs umque metal oiude vari ster technology and wi ll d issipate 150 Joules ot electri.ca l energy (nearl y twice that ot comparable surge arresters I SPECIFICATIONS, ¥g!:len:r~~VR~~~nf~o Joules Response T1me 1Ons Protec1to n Level 350V peak $36.95 Addlhonalfy. C PF s hltenng capabihty helps ehm1na1e 1roubtesome and annoying inter1erence . general hash cre.ated by sm all mo to rs. l tuoresceni lamps. and the hke that threaten the per1ormance and stx>rt en equIpmen1 life of unprotected elect ronic componenl s SPECIFICATIONS : Electrical rating : 220- 260 volts (AC) 50Hz 10 Amp Spike/RF! Pro1ec1ion : 4.500 amps tor 20m second pulses M8i im um clamping v oltage : 275V d1fferen11al mode Cat.X1 0088 $69.95 ENCLOSED PRINTER STAND • Keep"> your paper ,l nel pr1nt-01,h neal and ord ert v • Transpar ent cov(•r 1n.ike~ 1! ed..,\I to check on papPr ... upply • Pape, can be fen 1rom thf' cenl re or the , ear acctirdma to the de">,QP o t the printe, · • RPmova b!e dr,,wer which allow.., pape1 robe cn,rnqed wIt11ou! moving thf" pi, n1e1 • AetractablP rf" ,tr b,1~ke1 mrlk ~.., prIn1-ou1collpUic,n ta st ;ind convenient • Su11able frn mu ... 1 printer~ . ... .. COMPUTER PAPER Ouallty paper at a low pr1Ce I 2.000 shee! s ot 70 gsm bond paper Cat C21003 11 • 9 12 · Ca t C21005 15 , 11 · $67.95 $44.95 KEYBOARD EXTENSION LEAD 5 Pin Din plug and socket Pl 9038 ..... .... ....... .. . $9.95 HEAD CLEANER DISKS It o n! )' takes a minute am o unt o f dust , dirt o r ma gn eti c ox ide p a rticl es o n your drive h ea d s t o cau se pro blems: erro r s, d ow ntime o r a n ex pensi ve se r vice ca ll . Regu l a r u se of a h ea d cl eaner will k eep your d ri ve free of troub l e cau sing d i rt and h elp k eep your system up a nd runnin g . T h ese disk clea n er s are simpl e t o use, an d include cl eaning sol utio n and instru ctio n s. • :{ 1/ 2" C 12560 ....... ...........$6.95 • S 1/ 4 " C l2 55 5 ...... .. ...... ... .S6.95 9 PIN TO 25 PIN CONNECTOR ADAPTORS NE W' The ,deal sotut•nn' Fea1ures '~;~e~;n:~~~ 1 20 only 4 WAY Cal X19125 only 2 $39 $49 2&4WAY CENTRONICS DATA TRANSFER SWITCHES Save time and ha ssles of constantly ~~~~~~r ;~tt ~i •; ;e~~~~~ ~~v:~~fa switches These data sw1lches suppon the 36 pm cen1romc 1nter1ace used by Centromcs . Printron1cs. Data Products. Epson. M1cromcs Star. and many other printer manufactu rers. • No power required • Speed and code 1ransparent • Two/Foui pos11Ion rotary sw,tch on front pa nel • Three,F,ve interface conne<J1ons on rear panel • Sw,lch comes standard with female connector • Bale locks are standard 2 WA Y (X19130) only$49 4 WAY Ix191 3s1 onIY$59 UV EPROM ERASER Erase your EPROMs q u ick ly and safely. This unit i s t he cost effective solut ion to your proble ms. It will erase up to 9 x 24 pin devices in complete sa fety, in about 40 minutes (less lime for les s chips) • Chip drawer has conductive foam pad • Mains powered • High UV intensity al c hip surtace ensures EF'ROMs are t horoughly erased Without timer X14950 .. ...... .. .... •.. .. $129 W ith built-in timer X14955 .... .. ... ....... ... $159 $69.95 -~~ II you have rwo or lour compattble devices that need to share a third or filth. then these inexpenSJve data transfer sw11ches will save you the hme and hassle of constantly changing cables and leads around • No power required • Speed and code transparent • Two/Four posI1 Ion rotary switch on lront panel • Three/Five 1nl ertace connections on rear panel • Switch comes slandard with DISK NOTCHER DELUXE PRINTER STAND • Rr~lore~ 01c.1er !O youi work area without occupying eictra space • c eeds and 1etolds paper lJnder tt1e prin ter automat1ca11,,. • Atl1u~table pape1 deflector~ ensure ~moolh flo w ol pr1pr1 • Made 01 moulded plastic • Suita ble IOI most prIn1cr~ C210S8 (80 column I $69.95 DUST COVERS Co n ve rt s 5 1/ 4 " sing l e sided n o ppy d isk s t o d o ubl e si ded , by p l ac in g an appropriat e n o t ch i n I he fl oppy d i sk jac k et. c 210?0 .... ..............s s.oo X 1S6b8 DB9 Plug tu D8 25 Socke1 X 1565q DB9 5ockE>1 to 0B25 Plug $8.95 DUST COVER Keep your computer and accessories free ot dust and gri me whi le not In u se MAGIC STAGE A working bench tor your Mo use . •High qu-, ity A BS plast ic and an li-stati c rubberise d Pop •S1a1ionary holder •Includes pull-ou l s he ll tor Mouse -1• ." XT HO CONTROLLER $129 AT HO CONTROLLER $199 RS232/ SERIAU CLOCK ..... ..................... $59 MONO/ COLOUR CARD igs MULTI 110 ....••.............•.•• $99 512K RAM ...................... $59 OIAGNOSTIC................. $849 nu PRINTER. ...............$99 RAM 2M AT EXTIEXP ..$225 SM AT EXT/EXP ........... $325 POCKET AUTO AB SWITCHES • Pocket s ize , auto -sca nning • All ows 2 PCs to share one Printer XT' Cover Set C21066 .............•... .$14.95 AT' Cover Set C21068 ...... ...•....... •$16.95 Serial mod el: MS-20 1 - Host-powered X19150 .... .. ..... .. .....$79.95 Parellel model: MP-201 Pro toc ol transparent X1 9 155 ...... ............ $89.95 LEADS VOICE MAIL................ .. $245 PRINTER CARD ....... ...... $35 EGA CARD .................. ... $139 2 WAY FUD CONT. (360K) ............................ .. $49 RS232 SERIAU CARO .... ························· S49 GAMES ............................ $29 AT SIP GAMES .............. S35 41•1AY FOO CCINT. (3S0·, .<4M)....................:$129. 2 WAY FOO CONT. (3GO•U 4M) ····· $80 CLOCK CARO........ . ... $49 SMART DRIVE ADAPTER IOEIFDC..........$89 SMART DRIVE ADAPTER IOE 110 IFDC ... $119 P 1904 5 $99.95 3 'h" FLOPPY DISK DRIVE EXTENSION CABLE • IBM" compatible • 0837 Male 10 34 IDC c:onnec ior • I enqth O ~ me1re-. P1 9046 $99.95 6 PROTECTED POWER OUTLETS Ideal for protecting personal com puters, video equipment, colour TVs. amplifiers. tuners, graphic equalisers, CO players etc SPECIFtCATIONS : • Electrical ra1ing : 240V AC , 50Hz, 10A • 3 x Me1al Oxide Varistors (MOY) • Maximum clamping Vo ltage : each MOY: 710 volts at SO am ps • Response time : Less than 25 Nanoseconds. Xl 0086 ..................... $69.95 RS232 GENDER CHANGERS • Saves mod1tymg or replacing non-ma1 Ing RS232 cables • All 25 pins w ired straight lhrough Cat X 15650 Male to Male Cal X1 5651 Male to Female Cat X15652 Female to Fema le Norm ally $14 95 each Only $8.95 MOTHERBOARDS XT 10M MINI ...................... $120 XT 31M................................ $199 XT 12M STD. SIZE............. S199 SU NTEC AT 12M................$375 80386-25••• .~.£~.~!!!'..... $2,695 80386- 33 •.• ~1:!!~!1!\ .... $2,995 Stanmore. 2048. RS232 MINI TESTER • Male 10 fem ale connections • All pm wired straight lhrough • Dual colour LED 1nd,ca1es actcv1ty and d1rec11on on 1 Imes • No battenes or power , equ1 red T D Transmit Data D S A Data Set Ready A D Receive Data C D Carner Detect A T S Reauest 10 Send D T R Data Terminal Ready C T S Clear to Send Cat X 15656 No rmally $39.95 s COPYHOLDE7 (YU-H32) /4 • Adju s tab~~ ar~s allows easy p o s111onmg • Copy are■ 91 12" • 11 " • Sliding line guide • Cla m p mounti ng C21062 .•.•. ..... .$39.95 Phone (02) 519 3134 Fax 102) 519 3868 MELBOURNE: 48 A·secken St Phone (03) 663 6151 NORTHCOTE, 425 Htgh St Phone (03) 489 8866 CLAYTON , 56 Aenver Ad Phone (03) 543 7877 MAIL ORDER& CORRESPONDENCE : P.O. Box 620. CLAYTON 3168 Order Hotline . 008 33 5757 (Toll free. str1ctly orders only) lr1qu1r1es · (03) 543 7877 Telex: AA 151938 /Fax· (03) 543 2648 MELBOURNE PEA\ ERS MICRODOT 177 SPRINGVALE ROAD NUNAWADtNG. Ph.BIM 1255 GREENSBOROUGH COMPUTERS 17 GRIMSHAW ST (an Howard at) Ph : 434 8161 BRISBANE DEALER YRC COMPUTER SERV1CE 1547 LUTWYCHE RD LUTWYCHE, <030 ADELAIDE DEALER ..CROTRONICS 305 MORPHETT ST ADELAIDE, 5000 All sales tax exempt orders and wholesale inquiries to: RITRONICS WHOLESALE. 56 Renver Road. Claylon Phone: (03) 543 2166 (3 lines) Fax : (03) 543 2648 PRINTER LEAD • Suils Only S24.95 RODIRVING ELECTRONICS SYDNEY , 74 Parramana Ad SURGE BUSTER • IBM " compa!1ble • 083 7 Male to 34 way eoae connector • I ength O S me1res CENTRONICS GENDER CHANGERS • Female lo Female • Saves modifying or replacing non-malmg Centromcs cables • AU 36 prns wired stra1 ghl through Cal X15663 Male to Male Cat X 1566 1 Male to Female Cat X1 5664 Female to Female Normally $33 95 . "illi 4 PORT SERIAL .............. $89 VGA 2561<. ...................... $199 VGA 512K. ...................... $299 VGA 1 MEG ......... $495 SPECIAL. ONLY $32.95 qoln plated pin"> eac h . IBM• PCI XT, compatibles • 25 pin " O" plug (computer end) to Centronics 36 pin plu!'.J RIPPER STRIPPER Rem ove ugly paper feed edges qu ickly and cleanly with lhis sim ple lillle gadgel C21085 ... ............ ... $14 .95 •1.8 metres P19029 ..•.......•. ...... $14.95 • 3 metres Pl 9030 .... .............. $19.95 • 10 metres Pl 9034 ................ .. $39.95 Errors and omtss1ons eicepted. Prices and specifications subject to COPY HOLDER • Copy a1e! W ,.,;H,J,~l • Sliding hne guide • FIa1 metal base C2 1060 ........ ..... . $39.95 change. IBM· PC' Xl ". Al" •• ••19$1ertldtradoem.-,kS OI In1~ 11 Busonns M.ch ·~ ,s 1 lrade<naf\. "Denol1$ reg,s1ered tr.clm¥1<sol """rr11P8(tl\1 0W.....-S rl'jllls!..-tld f C-1 BNC PLUGS AND SOCKETS BNC MALE PLUG 1-9 10.99 100. P10S14 $2.SO $2.25 $1 .50 _ BNC PANEL SOCKET I IC SOCKETS HEATSINK COMPOUND Heatsink compound is applied to the base and mounting studs of transistors and diodes. II maintains a positive heatsl nk seal !hat improves heat transfer from the Hevice to the heatsink , thus increasing overall efficiency. H11800 .. 10g ...... $2.00 H11810 .. 1 .... $14.95 p 1-9 10 99 100 . Pl0516 $2.50 $2 .25 $1.50 .. 1:· BNC CRIMP PLUG 1-9 P105JO $2.85 10 -99 10('1. $2.75 $2.00 ~ BNC SOLDERLESS TWIST ON PLUG 1-9 10 -99 100. p10531 n .50 s2.2ss2.oo CANNON PLUGS AND SOCKETS CANNON TYPE 3 PIN CHASSIS MALE 1-9 TRANDUCERS Designed to transmit at 40kHz (L 19990) and recieve at 40 kHz (L 19991 )with up to 20V 1/P on the transmitter. These units can't be heard so are ideal for TV remote control's , water level detectors, burglar alarms, motion detectors and information carriers a~ they can be either pulsed or used in a contlnuos wave mode. ·Transmitter 1·9 10+ L 19990 ..... $3.95 $2.95 · Receiver L 19991 .... $3.95 $2.95 10+ 100+ P10862 $3.50 $2.95 $2.50 ffl GJL=- CANNON TYPE 3 PIN LINE FEMALE 1-9 10+ 100+ P10864 $3.95 $3.50 $2.90 t'CB MOUNTING SCREW TERl,flNALS CANNON TYPE 3 PIN CHASSIS FEMALE 10+ 100+ P108M $4.95 $4.50 $3.50 . '"" .. 1-1 10+ 25< 30< 26< 26< 35< 30C 40< 35< 30< • P10521 so.so 3way SO. 70 $0.60 10+ 100+ COMPUTER CABLES each $8.95 SO .BO t-----------11 I---.,.,..,.,.,=.,.,.=.,..--= ----- HAVE YOU RECEIVED YOUR DEfil"__J1 .0Q NEW 1A8 PAGE RO 10+ IRVING ELECTRON! s1.oo CATALOGUE FLAt.!ftNG ~OS · red 5mm 210159 1.9 suo WITH 32 PAGES OF DATA~ WIRE WRAP SWITCHES IC SOCKETS Jt you have 2 or 4 compatable devices that need to share a third or fi fth , then these inexpenci vedata !ranter will These quality 3 level wire wrap sockets are tin-plated phosphor 1 ::::~:~ ~t~/i;;,:~;i~;::!~s and leads around . No power required Speed and code tranparent · Two or four position rotary switch on fron t panel. Switch c omes standard with female connectOr. RS232- 2 way ..................... $39 RS232- 4 way ..................... $59 RS232- X over .................... $69 RS232- 2 way auto ............. $69 Centronlcs- 2 way .............. $49 Centronics- 4 way .............. $69 Centron ics- X over ............. $69 Centronics- 2 way auto ..... $79 bronze. 1-9 10+ P10579 8 pin 1.50 P10580 14pin 1.85 P10585 16 pin 1.95 P10587 18 pin 1.95 P10590 20 pin 2.95 P10592 22pin 2.95 P10594 24 pin 3.95 P10596 28 pin 3.95 P10598 40 Din 4.95 1.40 1.70 1.80 1.80 2.75 2.70 3.50 3.50 4.50 IDCPLUGS AND SOCKETS FREE WITH 'f • RECTANGULAR LEDS 1-9 10.99 100+ RED 20c 15c 12c GREEN 20c 15c 12c YELLOW 20c 15c 12c ORANGE 20c 15c 12c 1-9 10+ P12166 100 . plug $2.95 $2.50 $2 .00 • DA15P 1Splnplug TRANSFORMERS $3.50 $3.00 $2.50 •• $,C.50 $195 $3.SO D TYPE ICC SOCKETS 9 pin 1ocket 1·9 10. · OE9S 100• P12167 $2.95 $2.50 $2.00 15 ~n eocke1 • DA 15S 2155 10+ 1-9 240V 6-15V 1A ea, M12155 $8.95 010500 010502 010504 010510 010518 010520 MU45 MU45 MU45 MU45 MU45 MU45 0-1m A $12.50 50l50uA $12 .50 0-100uA$12.50 0-5A $12.50 0-1A $12 .50 0-1A $12 .50 Cat M16672 $12.95 $11 .95 AA 450mAH $1.95 $1 .75 $1 .50 C HORNS $12.50 $14.50 MU52E 0-5A $14.95 MU45 VUP $14.95 MU65 0-50uA $16.95 MU65 0-1mA $16.95 MU65 0-'100uA$16.95 MU650--20V $16.95 , SUPER HORN TWEETER Requires no crossover and handles up to 100 Watts · Sensitivity : 100dBI 0.5 m · Frequency response : 3kHz-3-0kHz Independence: 8 ohms. · Size 96 m diameter Normally .................... $12.95 SPECIALS 2SJ49 2SJ56 2SK134 2SK176 1-9 $7.50 $10.00 $6.90 $9.50 ONLY .................... $9.95 10+ $7.00 $9.50 $6.50 $8.90 10W HORN 25 pin aoc:kat · Plug P 12200 10, $3.95 100. $3 .00 $2 .95 • Sor:ket P1 :no 1 10 . 100. $3.95 $3.00 $2 .95 ~~ ., _•• . SPEAKERS While durable plas1ic . 8 ohms P12171 $4.50 $3.95 $3.50' ICC CENTAONICS 36 WAY PLUG & SOCKET 1 2 A H $9.95 $9.50 $8.95 1 2 A H $9.95 $9.50 $8.95 0 MOSFET $4.50 $4.95 2860 240 V 15VCT 250m A Cat M 12860 S4.95 S4.50 6672 240V 15 30vc 1A tapped NICADS ~ $3.95 P12169 $3.50 $3.00 $2.50 . oe2ss 010533 010535 010538 010540 010550 010560 2851 240V 12-6V CT 250mA CatM121151 $1.10 $1 .20 Save a fortune on expens ive thiow away batteries with these quality Nicads and Rechargers! Size Desc . 1-9 10+ 100+ We have a great range of panel meters at great prices! $7.95 $4.95 < I•Nhililt ~ PANEL METERS GALORE 2156 240V 6-15V A2 Cat M12156 S13.95 $12.95 2840 240V 9VCT ea, M12840 I. ' S11010 O.P.O.T $1.20 S11020 O.P.O.T $1.30 010525 MU45 0.20V 010530 MU52E 0.1A · DE9P • pin ' t-----------t ~ t - - - - - - - - - - - f TOGGLE SWITCHES 1-9 10.99 1-----------1 P12170 The perfect solution! Features gold plated pins X15668 D89 Plug lo D825 Socket X15669 089 Socket to D825 Plug. $0 .80 $0 .80 P10880 Z10150(R)so.u so.10 $0. 10 Z10151 (G)so.:io S0.1 $ $0.12 Z10152(Y) $0.211 S0.l 5 $0. 12 DATA. , 0825P 25 pin plug ADAPTORS 100+ P10905 0825P $1.00 P10905 0825S $1.00 ORDERS OVER $100. P1216a 9 PIN TO 25 PIN CONNECTOR 10,88 $0.70 $0.70 $0.80 S0.80 P10895 OA15S $1.00 $0.80 P10902 0B25C $1.00 $0.80 A10452 ......... ...... $99 100+ !S0.60 $0.50 S0.40 «::::Ji P10860 $4.50 $3.50 $2.50 RECIEVER SPECS, H;< 30< 1--1 10+ 1·9 $1.00 $ 0.70 P10890 OA15P $1.00 P1089 1 OA15S $1.00 P10892 OA15C $ 1 .00 P10880 DA15P $1.00 10G+ ,QUALITY SMM LEDS Receiver freq : 37.1MHz Output level : 37mV(max) Receiving sys : Super crystal oscillation Power sup : 9V battery Volume control : Tuning Led Dimmensions :115x32x44mm Weight : 220grams 25• 22< 1!Ml8 Z10140(R) .... $0.15 $0.12 $0.10 Z10141(G) .... $0.20 $0.25 $0.12 Z10143(Y) .... $0.20 $0.15 $0.12 Z10145(0) ... $0.20 $0.15 $0.12 Transmitting Frequency : 37 .1MHz Transmilting system : Crystal oscillation . Microphone : Electret condenser Power supply :9V battery Range : 300 feel in open field 120 10C 18< 15< , 1.. TheN terminal• feature lnter1oc:king end ■ to form any number ot conectlone. Standard 5mm apaclng pine • P10520 2 way CANNON TYPE 3 PIN LINE MALE 1-9 ,_, ,, ...... ,se 8 pin 14 pin .... 20f 16 pin .... 20f 18 pin ... :30e 20 pin .... 35< 22 pin .... 3Se 24 pin. ... 35< 28 pin .... ,SC 40 pin .... '5< P10885 OE9S QUALITY 3MM LEDS RECIEVER MICROPHONE SPECS, Save a small fortune on these " Direct Import" low profl~ le sockets! PCB mounling solder lall. All tin plale<f phosphor bronze or berryllium and dua l wipe lor reliability. 0B25 CONNECTOR . SPECIALS ===I~ MICROPHONE & LOW PROFILE IC SOCKETS P105SO P10560 P10565 Pt0S67 P10568 P10S69 Pt0570 Pt0572 Pt0575 ====1.r; ====11r. ( CRYSTAL LOCKED WIRELESS (INTERLOCKING ENOS) ~ 1-9 ,ma Cat. No. Descript ion ULTRASONIC - LEDS Cat. C12010 12V DC FANS 80 x 80 .: 25 .4mm 12 V DC . 1.7 Watt . 0.14 Amps T12469 .... $12.95 10+ fans only S11 .95 each FANS Quality. lans lor use in power amps. compulers . hotspot cooling e1c . Anywhere you nffd plenty et air. 240V 458" T12461 .. $12.95 '15V 45 8" Tl 2463 .. $12.95 240Y 3 1 2" T12465 .. $12.95 115V 312"T12467 .. ·$12.95 MAIL ORDER & VOLTAGE REGULATORS BARGAINS D••crlptlon 7B05UC 7812UC 7815UC 71105UC 7912UC 7915UC 78L05 78L12 LM324 555 741 1-9 $0.50 $0.50 $0.50 $0.60 $0.60 $0.60 $11.40 $0.40 $1.00 $0.40 $0.50 All sales tax exempt orders and wholesale inquiries to: RITAONICS WHOLESALE . 56 Renver Road. Clayton Phone. (03) 543 2166 (3 Imes) Fax· 03 543 2648 Normally Sl I 95 CORRESPONDENCE P.O. Box 620, Cloyton, 3168 Order Hotline: 008 33 5757 [Toll F,- Sb1ctly Ol'"der11 onty) 10+ $0.45 $0.45 $0.45 $0.55 $0.55 $0.55 $50 • $99.99 ...... $6.00 $0.30 $100 • $199 ••••••. $7.00 POSTAGE RATES $1 • $9.99 .. . ....... $3.00 $10 • 24.00 ........ $3.50 $25 • $49.99 ...... $4.50 $11.30 $0.110 $0.38 $0.45 f $200 • $500 ....... REE;, $SOU Plus ......... FREE Err , Pnc change. 1BM· PC· xr· AT· a,e, "IP, 1• tntematQl'l.i 8u- s s Mach •~Sle!tcl !r ~ 11r; • ua,o,nan, sot1fWl,,,,espec1tve -~ ~ '-f The Story of Electrical Energy, Pt.8 The largest hydroelectric machines in Tasmania are in the Gordon River underground power station, in the rugged south western region. The subject of much controversy in the past, it is an impressive project by any standard. By BRYAN MAHER Exposed to the never-ending moist gales of the roaring forties , the southwest corner of Tasmania boasts Australia's wettest temp erate climate , with 200 rainy days each year. Flora and fauna, direct relics of ancient times , still thrive in the cold rainforests . Rugged parallel mountain .5es lying in a north west to south easterly direction and broad valleys cut by inaccessible gorges posed a nearly impossible task for the surveyors and engineers. Although recognised since World War 1, the hydroelectric potential of the Gordon River was not thoroughly investigated until 1961. In March of that year, a hydrology analysis station was established on the Serpentine River. Measurements of precipitation and runoff predicted that 500 to 1000MW could be generated from the Gordon, Huon and Serpentine rivers. That was easier said than done! Just reaching the site, let alone bringing in heavy machinery, was a major effort. A rough access track, suitable only for tracked vehicles , was constructed in 1960 to McPartlan Pass. Helicopters were necessary to build research stations on Lake Pedder and the upper Huon River. The region was accessible only in summer, when snowfalls and driving south westerly gales usually abated. To verify the choice of dam site on the Gordon (1.5km upstream from the Serpentine confluence), a camp was ·established. Here intensive surveying, geological mapping, exploratory tunnelling and drilling occupied the summers of 1963 and following years. Approval by parliament in 1967 of the $185 million scheme started construction destined to increase the state's electricity supply by 23 %. The ambitious plan involved a 140-metre high dam blocking the precipitous gorge on the Gordon river. The 260 square kilometres of Lake Gordon thus formed would join an elevated version of the existing Lake Pedder to create Australia's largest fresh water storage. After a road was built to the dam site in 1969, diversion tunnels were the next to be built. River diversion Taken when the Gordon Dam was almost complete, this photo shows the extreme curvature of the structure - a classic concrete arch dam. 92 SILICON CHIP To enable the building of the Gordon Dam, the river had to be temporarily diverted. This was done in two stages in 1969/70. First, a reinforced concrete coffer dam was built upstream from the main dam site. The water thus impounded flowed through a 350 metre long tunnel bored through the gorge cliff, exiting well down stream. Then a second stage diversion was built closer to the dam. Subsequently, the first diversion tunnel was sealed with a concrete plug and the coffer dam demolished in --:-·-~· <t~' )'t j, ·~ !i ""' Most dam projects require at least two dams, one a temporary coffer dam which lets construction start on the main dam. This upstream photo of the Gordon Dam during construction shows the remains of the coffer dam after it had been demolished. FEBRUARY1991 93 The arched design transfers most of the water force onto the steep rock cliffs which form abutments on each side. Begun in 1972, the dam was completed in 1974, but it took 4 years to fill. The weight of water exerts a pressure of 1.4 megapascals (ie, 14 kilograms per square centimetre) at the base of the dam wall. As the dam's security depends on the stability of the abutments, electronic transducers were buried within the concrete wall. Computers in Hobart monitor the electrical readings to constantly assess the conditions. At the same time as the dam was being constructed, an 80-metre high intake tower was built with an access bridge above spillway water level. At the top of the tower are controls for the 75-tonne cylinder gate valves, located at the bottom, which control the bulk water flow to the power station below. The flow of water (415 cubic metres/sec) can be totally stopped, if need be, by the cylinder valves in only 20 seconds. Water falls via the 8.23m diameter shaft, then runs horizontally to the turbines, as the cross section diagrams show. The 356-metre power tunnel was completed in 1973 and the following year the dam began to fill. Underground turbine room This photo shows the underground Gordon power station during construction. The inlet valve and turbine casing for the No.2 machine can be clearly seen. 1970. Similarly, the Serpentine River was diverted so its dam could be commenced. As the region was totally uninhabited, Strathgordon Village was built to house the workforce, while design of a twin 220kV power line to the east commenced. The proposed site of the underground power station proved to be unsuitable because of unfavourable rock structure. The geology of south west Tasmania consists of 700 million-year-old sandstone with limestone outcrops and ancient lava intrusions up to 300 metres thick. A quarry and cement plant was built on a knob hill overlooking the river and roads were built to the bottom of the 400-metre deep gorge. Roads and an overhead cable way 94 SILICON CHIP carried men and equipment to the dam site. Using twin haulageways and four tower cranes, by 1972 the first concrete was being poured in the Gordon Dam structure. The following year, the excavation of the re-sited underground power station began. The Gordon Dam Rising 140 metres above its foundations (higher than Sydney Harbour Bridge), the Gordon dam is a classic reinforced concrete arch; the largest of its kind in the southern hemisphere. Only 200 metres long, it tapers in thickness from 17.68 metres at the base to 2.74 metres at the top. Containing 280,000 tonnes of steel and concrete, the dam is constructed with its convex curvature facing upstream. The construction of a power station within the bowels of a mountain tests the expertise and experience of engineers to the limit. The procedure used was to excavate the underground turbine room from the top downwards. The artificial cave was first dug out down to crane rail level. The crane runway structures were set into the rock walls, then the cranes assembled and operated. The work then consisted of digging out the floor using tracked hydraulic boring equipment until the full 32metre depth was reached. As machinery was set in place, tiling contractors then lined the ceiling. The walls were faced and lighting was set in place. Various floor levels were then constructed; above and below the alternators, at basement and above the turbine runner height. Reinforced concrete busbar troughs were built around the walls to house the generator output conductors which run from each machine to the vertical shaft, thence up to the aboveground substation. The final appear- tured in Germany by Siemens and assembled on site. The heaviest component is the 269-tonne rotor; so heavy that it was lifted into place in sections by the two overhead travelling cranes. The 22-pole stators for each machine , weighing 168 tonnes when assembled, were lifted into position by both cranes. When fully assembled, the total 314-tonne weight of the rotor, turbine and coupling shaft hangs on one vertical thrust bearing and is aligned by a number of guide bearings. So accurate is the alignment and so smooth the lubricated bearings that two men can turn the total rotating mass by hand (at a very slow speed of course). Having done its work in turning the turbine, the water falls through the fabricated steel outlet draft tube to the tailrace tunnel. This huge conduit , 9 metres in diameter, carries the Hydroelectric alternators are very big machines, especially compared to those driven by steam turbines. This is one of the stators in the Gordon Power Station. ance of the main floor of the power station, high above the lop of the alternators, is shown in one of the photos. Only the exciters are visible from the operating floor; stairways give access down to all other levels. Simultaneously with the turbine room construction, the boring of the inlet and outlet water tunnels proceeded. As already noted, the inlet shaft has a diameter of 8.23 metres. This main water conduit and the branchings to each turbine are lined with concrete and a great deal of trouble was involved in obtaining smooth contours throughout. Smooth contours Smooth pipe contours are necessary to obtain laminar water flow with minimum turbulence. Turbulent flow implies a severe energy loss which must be avoided for best efficiency and least wear in the tunnels and turbines. The cross section diagram of the power station shows the water pathway. Controlling the flow through each turbine is a 2.8-metre diameter hydraulically operated rotary inlet valve. The station's two 90-tonne capacity cranes were used in tandem to lift these 116-tonne valves into place during construction. From each valve, the water flows into the tur- MAX . LA~f LE VEL $ .L. 30 &m bine at a rate of 86 cubic metres per second. Francis turbines Each 150MW Francis vertical shaft water turbine consists of a welded steel spiral casing in which the turbine runner rotates. The 100-tonne spiral casings were fabricated in the HEC workshops and were then lifted into position and embedded in concrete. In op eration, the water enters the spiral casing at the large diameter end. Flowing around the spiral towards the small diameter end, th e water is forced to flow through the turbine runner before falling downwards. The water thus rotates the turbine and the direct coupled alternator above. Each 3-metre diameter turbine runner, the most critical mechanical component, was cast by Fuji in one piece of stainless steel. These 23tonne castings must have smooth blades polished almost to mirror finish to reduce water friction and enhance efficiency. The chromium component in the stainless steel alloy inhibits pitting and corrosion which would otherwise increase losses. Each turbine runner is coupl ed by a long 22-tonne vertical shaft to the rotor of the alternator above. These 144MW generators were manufac- LAKE GORDON GAU. EI-H•' .... -•·· ~---,J~ GHOUl ,/ /.,,j COfHAIN t -. .,. ·-!--··· ORAINAG E I CURTAINS l The cross section of the Gordon Dam shows it to be a very thin structure, relative to its height. Note that it is curved vertically and horizontally. FEBRUARY1991 95 This photo really does show the scale of the Gordon hydroelectric scheme. This is the 8.23-metre diameter inlet water tunnel with the three raceways running off lo Lhe left. Note how smooth the concrete is, to minimise turbulence. total outlet water from all machines 1.6km downstream to the lower Gordon River. Scale working model To test the performance of the turbines and verify the design , the Fuji Electric Co of Japan constructed a true 118th scale working model. This model turbine used water flow and full load to ascertain the efficiency, speed characteristics , stresses, strains and the extent of cavitation. In any turbine of the Francis or Kaplan types (as with ships' propellers), water flow patterns are critical. Cavitation means a non-ideal action wherein the turbine or propeller generates bubbles of water vapour close to the steel blades. As this water vapour is compressable (whereas liquid water is not), less than ideal forces act between turbine blade and bulk 96 SILICON CHIP water. The result is that full power transfer cannot be realised from the machine. Thermodynamic theory shows that there will always be some cavitation. However, this effect can be minimised by optimum design of blade dimension, shape and contour. In operation, the generator runs at 272.7272 RPM (long term average). But as with all generators, the sudden application of a heavy load must cause a momentary reduction in speed until the water valve opens incrementally to compensate. Load reduction causes the reverse. However, the very heavy rotating mass of large hydroelectric generators provides a great spinning reserve of energy, helping to maintain system frequency during changes in load. The 18kV 5000A 3-phase output of the alternators is carried by hollow square aluminium busbars through a 190-metre vertical lift shaft to the aboveground substation. Here the power is stepped up to 220kV for transmission to Hobart. Each transformer weighs 194 tonnes, so heavy that a special technique was used to transport them to the site. Carrying frames Instead of an enormous trailer being used (which would be too long for manoeuvrability) a special pair of carrying frames were built. Each 160MVA transformer was supplied by the manufacturer, Reyrolle-ParsonsWilson, complete with special transporting frames . After being lifted from ship to wharf, the triangular frames were bolted to the front and rear of the transformer casing. Multiple road wheels supported each triangular frame, while a heavy Pacific prime mover hauled the assembly. The switchyard and power line in the Gordon regions were designed to _________ 23 · 165 METRES ,ii! ___, UHF HIGH GAIN ANTENNAS !I if ii H f/ ROCK BOLTS antenn existing systems triangul powder coated receiving elements ensures excellent UHF reception compared to other UHF antennas of similar size and price. Two models are available: the TVA 14 for Band Four and the TVA 15 for Band Five UHF reception. Both models are supplied with back reflectors to prevent ghosting as well as a waterproof entry box designed to accept 75 ohm coaxial cable without the need for addittional baluns. They also have predrilled holes for securing the tilt adjustable metal mounting bracket in either a horizontal or vertical position. 90 .i 10 T ON TWIN OVERH EAD C:__l'! A"'_~S ~········-····· , __;r~J?~s12y· l,ll IIJ ...cc w :lF 0 (jt 0 Imported and dlatrfbuted by: M ARIS'& ELECTRONICS Aval/able through the following retallera: Ritronlcs. 56 Renver Rd. Clayton. V/ctoria. 3168. (03) 543 2166. Bernys. Brldgepoint. Military Road. Mosman. 2088. NSW. (02) 969 1966. DRAFT TUBE ··- GATE CHRISTIAN BLIND MISSIQ~ ·d Re$toti~t t~~~,, M,~ This cross sectional diagram of the Gordon Power Station shows the scale of the project. The station capacity is 432MW, with provision for two more machines. blend as much as possible with the scenic surroundings. ACSR (Aluminium Conductor Steel Reinforced) conductors 25mm in diameter were used for the twin power feeders, using an average span length of 450 metres. In the sensitive Gordon River regions, towers were constructed of a special steel. This develops a uniform stable rust coating which inhibits further corrosion. The dark colour blends successfully with natural surroundings. The first two generators were completed and commenced supplying load in 1978. Full load commercial operation was achieved in 1978/79. After 3½ years work and an expen- diture of $38 million, the installation of the third turbogenerator at Gordon Power Station was completed in 1988. This raised the total station capacity to 432MW. The station still has provision for two more machines. If installed, these would raise the available peak load output. However, the total output in a year would not be increased as this is limited by the rainfall and snowfall within the catchment area. Lake Pedder To supplement the water storage of Lake Gordon, the level of Lake Pedder was raised by the Serpentine and Scotts Peak dams and the small Edgar COUPON Please cut and send to: CHRISTIAN BLIND MISSION INTERNATIONAL, P.O . .Box 5, 1245 Burke Road, KEW. Vic. 3101 Phone: (03)817-4566 e D Please send me further information about CBMl's work. As long as it is possible for me, I will help: monthly D quarterly D annually D to prevent blindness D to restore eyesight D to rehabilitate the blind Enclosed is my gilt of S _ _ _ _ _ __ D Mr/ Mrs, Miss, Street , __ . . City , _ _ .. . . P051code, FEBRUARY1991 97 The third machine, installed in the Gordon Power Station in 1988, raised the station's maximum output to 432 megawatts. levee. Though much smaller than the Gordon, these two additional dams are an integral part of the scheme. The Serpentine Dam, on the river of the same name near Mt Sprent, is a 38-metre high mass of concrete-faced rockfill 131 metres long. Much bigger is the Scotts Peak Dam, just over a kilometre in length but only 43 metres high and containing about a million tonnes of rockfill under its concrete skin. These two small dams, with the Edgar levee, impound the Lake Pedder catchment, raising the water to approximately the same level as Lake Gordon. The McPartlan Pass Canal, 2.66km long, was cut to allow water to flow either way between the two lakes. Normally water flows from Pedder to Gordon but flood rains in the Gordon catchment can also be stored in Lake Pedder. The Tasmanian parliament and the Hydro Electric Commission recognised that the intrusion of man into previous! y inaccessible wilderness regions must cause adverse effects. Certainly the flooding of the small but beautiful original Lake Pedder provoked serious environmental controversy. The Gordon power station contributes a large percentage of the total state power loading which reached an all-time peak of 1.4505 Gigawatts in June 1989. The control of the entire Tasmanian hydroelectric system requires many factors to be taken into account. Not only must power be immediately available at all times but also water resources must be carefully husbanded. Accurate weather forecasts must be taken into account. These factors and other Tasmanian dams and power stations will be investigated in a later chapter of this series. References (1). Tasmanian HEC literature. (2). "Australia the Beautiful Wilderness"; Bob Brown. (3). "Australia's Wilderness Heritage" Vol.1; Geoff Mosley. (4) . "Australia the Greatest Island"; Robert Raymond. Acknowledgements Big alternators require big transformers and these cause big headaches in transportation. This photo shows the solution used for the Gordon power station transformers - a special carrying frame hauled by a heavy prime mover. 98 SILICON CHIP Grateful thanks to the Tasmanian Hydroelectric Commission and to Liz Emson for data, photos and permission to publish. SC ORDER FORM -- USE THIS FORM FOR ALL YOUR SILICON CHIP ORDERS SUBSCRIPTION: 0 a RATES: NEW SUBSCRIPTION: Month To Start._ _ _ _ _ _ __ RENEWAL: Sub No. _ _ _ _ _ _ Start In, _ _ _ _ __ Q GIFT SUBSCRIPTION: Month To Start_ _ _ _ _ _ __ ,,::c o GIFT SUBSCRIPTION DETAILS Mr/Mrs/Ms: _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ __ (PLEASE TICK ONE) 2 YEARS (24 ISSUES) 1 YEAR (12 ISSUES) Australia Australia With Binder NZ & PNG (Airmail) Overseas Surface Mail Overseas Airmail □$A84 □$A105 □ $A13O □ $A13O □SA24O □$A42 □$A53 □$A65 □$A62 □$A12O -I 0 (") ,, 0 Address: _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ __ SPORTS SHIRT < -I ::c iii _ __ _ _ _ _ _ _ Postcode,_ _ _ _ _ _ _ __ "II Please send me _ __ _ _ Sports Shirt(s) <at>$A24.95 I SILICON CHIP BINDERS Size: _ _ _ _ S, M, L, XL, XXL Total $A_ _ __ including postage (NZ add $A3) 0 "II ~ Yes! Please send me. _ _ _ SILICON CHIP binder(s) at $A 14.95 each C Cl 0 (including postage) TOT AL$ _ _ _ __ _ _ __ _ __ z ~ (Overseas Orders add $A3 each for postage) _ SLOPPY JOE Please send me, _ _ __ _ Sloppy Joe(s) <at>$A27.95 including postage (NZ add $A3) Size: _ __ _ S, M, L, XL, XXL Total $A,_ _ __ ::E iii ::c ti BACK ISSUES: ISSUE $A5.00 each (includes postage). Overseas orders add $A 1 .00 per issue for postage. YEAR ISSUE YEAR ISSUE YEAR ISSUE YEAR (") C -I -I ::c ,.'"3: ,. c:, TOTAL $A !::! z '" Enclosed is my cheque/money order for $..c.. , _ _ _ _ __ or please debit my Card No . Ill O I V/S4 1 rmi lri. I~ [ Mr/Mrs/Ms: _ _ _ _ _ _ _ _ _ _ _ _ _ _ __ Address:. _ _ __ _ __ _ _ _ _ _ _ _ _ __ Card expiry date Signature· _ _ _ _ __ _ __ _ _ _ _ __ _ _ Postcode: _ _ _ _ _ _ __ 24 Hour Fax Service Subscription Hotline (02) 979 6503 Send the coupon with your Credit Card Details. 24 Hours, 7 Days a week. Telephone (02) 979 5644 9am-5pm Mon-Fri and quote your Bankcard, Visa Card or MasterCard No. and expiry date. Detach and Mail to: FREEPOST 25 SILICON CHIP PUBLICATIONS PO BOX 139 COLLAROY BEACH NSW 2097 No stamp required in Australia FEBRUARY1991 99 ASK SILICON CHIP Got a technical problem? Can't understand a piece of jargon or some technical principle? Drop us a line and we'll answer your question. Write to: Ask Silicon Chip, PO Box 139, Collaroy Beach, NSW 2097. Sick Jaguar needs better spark I have built and installed the High Energy Ignition System (described in May 1988) on my Renault and I am very happy with it. Now, I am considering installing a similar system on my 1983 Jaguar since it has not been performing as well as it should of late. However, before I proceed, I need some additional information. The Jaguar handbook makes reference to the system having a 6V coil, and then later on, to a 12V coil. I am confused and the Jaguar people here do not seem to be able to give a clear answer. The coil also seems to get very hot. On some occasions the car has refused to pull away from a stop Big bang for big bucks Having just read about the DCDC converter featured in the December 1990 issue of SILICON CHIP, you have just filled one of the many holes in my limited electronics knowledge. It has urged me to find out more. At present I am looking down the barrel of an $800 subwoofer setup to complement my highpowered Alpine car audio system. This leads me to my ponderings: How would a famous brand 10inch woofer (22Hz-12kHz, 89db/ WIm, unknown R) for a car compare with a Dick Smith 12-inch driver (25Hz free air resonance, 96dB/W/0.5m, 8Q), both driven by a bridged 200W car amplifier? I have noticed that some home style drivers look quite wimpy in the magnet department when up against their road-going counterparts. Is this to compensate for the lack of damping provided by the voluminous Aussie car boot? My second component hurdle is the crossover. I have a copy of 100 SILICON CHIP and has even stalled. It then starts iar with Jaguar ignition systems and and drives as normal. A new coil is get it fixed. You could be asking for a very expensive, by the way, at around . lot of trouble in hooking up the SILI$200.00. CON CHIP ignition design to a car Hence, my thoughts about chang- which already has a breakerless igniing the ignition system. Will the high tion fitted and one which has a repuenergy ignition system work with a tation for using specialised parts. 6V coil? And how do I hook it up to the breakerless distributor on the car? Ignition kill switch to (J.E., Melbourne, Vic). • In the past, we have been asked be triggered by oil loss whether the High Energy Ignition I have an idea for using a normally System will work on 6V cars and our closed relay to switch the line to the reply has been that, as far as we know, ignition system in the event of oil it will work without modifications. pressure loss. One side of the relay In your case, however, we must urge coil would be connected to the posicaution. tive side of the ignition coil primary We really think that, in spite of the winding while the other side would expense, your best approach is to con- connect to the oil pressure light on sult an auto electrician who is famil- the dash. Richard Kaufman's "Enhanced Sound" in which he almost enticed me into building a 112Hz asymmetrical crossover but to my horror, it had to have a dual polarity supply for the three TL072s involved. How can I substitute the TL072s for 12V single polarity ICs and still be as simple as in the book? Your DC-DC converter story mentioned a 100W amplifier module from a previous edition of your magazine. I assume that when this amplifier is matched to your converter, the 100W rating is into 8Q. What would happen when this combination drove a 4Q speaker, as used in car audio? (C. A., Babina, Qld). • OK, we'll answer your questions in order. The problem with comparing different speaker drivers is that you are comparing apples and oranges. Both may sound (taste?) pretty good when installed in the correct enclosure and it becomes important to ask about power handling and efficiency. Car speakers are often quite inefficient but, as you have noted, they often have really big magnets and a stiff suspension to make up for the lack of correct baffling. Converting your crossover circuitry to 12V single supply operation happens to be quite easy in this case. All you do is connect two 22kQ resistors in series across the 12V supply and a 22µF capacitor from the centrepoint to the OV line. This then becomes a bypassed 6V supply to feed the non-inverting (+) inputs of op amps IC1 and IC2. The 100W module referred to in the DC-DC Converter article was the one described in the December issue of SILICON CHIP and it delivered that power into a 4Q load from ±40V rails. The Studio 200 stereo power amplifier used the same modules but with higher rated transistors and ±50V rails and was rated at 100W into 8Q loads. Depending on the power supply regulation, it can deliver up to 190 watts into a 4Q load. Having said all that, we suggest you hang off for a bit on your subwoofer project. We hope to do one in the next four or five months. A diode would be connected in series with the relay coil to prevent Difficult reception in the oil pressure light from getting a remote Tasmania 'false' ground through the ignition coil and points. A pushbutton switch also I live in a north/south valley needs to be included to allow the only about 20km west from Hovehicle to start, because the oil presbart's. Mt Wellington (as the crow sure is zero when the motor is staflies) where all the TV transmittionary. The button has to be held in ters are located. But my TV recepuntil the oil pressure light goes out. tion is lousy on all three channels, What do you think of the idea? (A. both VHF and UHF, because my M., Browns Plains, Qld). house is on the eastern slope at • To be brutally honest, we don't think almost the lowest point in the valmuch of the idea at all. For a start, it ley. requires the use of a pushbutton to All the TV antenna and antenna disable the relay while the vehicle is installation books in general deal being started. This may be OK when with "line of sight" installations you are starting the engine at the beonly. I am sure there must be literginning of a journey. But what hapally hundreds of TV users around pens if the vehicle stalls in traffic and Australia in the same predicament you suddenly need to restart the enas myself. There are hills on the gine? You could easily forget to press opposite side of the valley which that button and thereby be subject to bring in good reception from the a considerable amount of hassle. top. I don't want to install about a Second, what happens if the oil kilometre of cable plus supply pressure switch itself fails? In our experience, this is actually more common than a loss of oil pressure. Sometimes too, it is possible to have building a traditional timebase. A a momentary loss of oil pressure while crystal oscillator running in a temperature stabilised oven may well under heavy braking or during fast cornering. Would you want the en- have a frequency stability of a few parts in 10 million but isn't that a bit gine to stop then? With a normal car, if the- oil pres- old hat? Why not go a lot better and sure switch fails or if the engine does strive for the accuracy of a Caesium lose oil pressure, you can at least keep . beam clock - 3 or 4 orders of magnidriving until it is safe to stop and tude better? Most, if not all, television networks check the problem. With your scheme, the engine would stop whether you in Australia are tied to a Caesium beam clock. This means that if you liked it or not. If you are really concerned about measure the colour subcarrier freloss of oil pressure, we suggest that quency (4.43361875MHz) from your you install a pressure gauge and per- local TV station when it is connected haps an audible alarm which could to the National network, you have a be connected to the oil pressure frequency reference of excellent acswitch. That way, even if the oil pres- curacy. All you need is a small colour sure switch does malfunction, the oil TV set and a circuit to buffer the pressure gauge will tell the true story. 4.43MHz crystal oscillator. If enough of our readers are interested in such a project (write and tell Wants to build us), we'll do it. a stable timebase I am interested in building a very stable timebase which could operate at 1MHz or 10MHz with a stability of at least one part in 107 • Has SILICON CHIP ever published such a project and if not, do you have any plans for such a project? (G. E., Dorrigo. NSW). • We have not published any circuits along these lines and do not have any plans to do so at present. We also wonder if there is much point in UHF converter for old TV set I have recently acquired an old colour TV set that does not receive the UHF band. I want to watch SBS and so need a UHF to VHF converter. I know that such units are commercially available but building is more fun and perhaps a wee bit cheaper. I do hope that you can service this cable for line boosters. At that cost, I'd be better off opting for "space TV". Could one install a reflector and what size and type would be best? Is there any other option? (P. T., Tullah, Tasmania). • You are right that there are many people in your predicament but in your case, there does seem to be a chance of a solution. You mention a hill on the opposite side of the valley where there is good reception. Why not use the hill as your reflector? Aim your TV antenna directly up to the top of the hill. If the signal up there is strong, you may well find that sufficient signal is reflected down to you to give reasonable reception. There is nothing new in this technique and it is often used by antenna installers in difficult hilly areas. request as I do like to watch SBS. (R. J., Balmain, NSW). • We have not described a UHF converter and we are not inclined to think that such a project would be popular. The reason? First, not enough people with old TV sets want to watch programs on UHF and second, most people have a VCR anyway. And that is probably the cheapest and best way to get a converter, since just about all VCRs have a UHF tuner as standard. We suggest you get a new VCR (or even an old VCR with a worn out transport mechanism) and your problem will be solved. Expander for tape player I built the CD Compressor described in the March 1989 issue of SILICON CHIP and it worked first time. In fact, it works so well that I use it not only to compress from CD to tape but to compress the vocals in our band. Are you considering bringing out an expander so we can pla.y our tapes on the hifi and so bring back the original dynamic range? I built a compressor expander many years ago but the distortion was abysmal. Thank you for replying to my previous letter about feedback (see "Curcontinued on page 104 FEBRUARY1991 101 MARKET CENTRE Cash in your surplus gear. Advertise it here in Silicon Chip. r-------------------------7 I I I I I I I I I I FOR SALE CLASSIFIED ADVERTISING RATES WEATHER FAX programs for IBM XT/ ATs *** "RADFAX2" is a high resolution, shortwave weather fax, Morse & RTTY receiving program . Needs CGA, SSB HF radio & Radfax decoder. Also "RF2HERC", "RF2EGA" & "RF2VGA", same as RADFAX2 but suitable for Hercules, EGA & VGA cards respectively. $35. *** "SATFAX" is a NOAA, Meteor & GMS weather satellite picture receiving program. Uses EGA & VGA modes, needs EGA or VGA colour monitor & card, plus "WEATHER FAX" PC card . $45 . *** All programs are on 5.25-inch or 3.5-inch discs (state which) & include documentation . Add $3 postage. ONLY from M. Delahunty, 42 Villiers St, New Farm, 4005 Old. Phone (07) 358 2785 . Advertising rates for this page : Classified ads - $7.00 for up to 15 words plus 40 cents for each additional word. Display ads (casual rate) - $20 per column centimetre (Max. 10cm). Closing date: five weeks prior to month of sale. If you use a PO Box number, you must include your permanent address and phone number for our files. We cannot accept ads submitted without this information. To run your classified ad, print clearly on the lines below or on a separate sheet of paper & send the form together with your cheque or credit card details to : Silicon Chip Classifieds, PO Box 139, Collaroy Beach , NSW 2097. Or fax the details to (02) 979 6503. BWD OSCILLOSCOPE, 35MHz Dual Trace , Model 830. As brand new. Paid $1600, sell for $900 (no offers) . Contact Claude on (086) 28 2435 anytime . MY AUSTRALIAN DESIGNED lowcost super-fast Z80 micro-controller development system has gained acceptance already with educational institutions. Pop it on the end of any PC MS DOS or Z80 machine and away you go. Boards, EPROM and 360K disc $76 including postage for a short form kit. Gee, I wish I had this when I was a IIT MATHS COPROCESSORS Enclosed is my cheque/money order for $_ _ _ _ or please debit my 0 Bankcard O Visa Card O Master Card Card No. Signature_ _ __ _ __ _ _ _ _ Card expiry date___/_ __ Name _ _ _ _ _ _ __ _ _ _ _ _ _ _ __ _ _ __ _ __ Street _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ __ _ _ _ _ _ __ Suburb/town _ _ __ _ _ _ _ _ _ _ _ Postcode_ _ _ _ __ X I I I I I I I I I I L------ ------------------~ 102 SILICON CHIP 2C-08 2C-10 2C-12 2C-20 2C87- 8MHZ 2C87-10MHZ 2C87-12MHZ 2C87-20MHZ """'&r. ~,s> ""o $330 $359 $430 $490 ~< ~<S'.s, $640 3C-1_6 3C87-16MHZ 3C-20 3C87-20MHZ $680 3C-25 3C87-25MHZ $840 3C-33 3C87-33MHZ $990 These pices include Sales Tax. Stocks are limited at this price, so order early. FIVE YEAR WARRANTY CAD CONNECTION PHONE (02)957 6719 FAX (02)954 5550 CONNECTION CAD MEMORY EXPANSION SIMM & SIP 9 x 256 9 x 4MB ·120ns ·100ns · 80ns · ?Ons · 60ns -100ns · sons · ?Ons · sons · ?Ons • sons N/A 23.00 23 .80 24.70 30.00 79.00 81.50 89.50 76 .50 82.00 528.00 DRAM/DIP 4164 41256 41464 4 x 256 1MB -100ns · sons · 80ns · sons • sons 2. 10 2.40 2.50 7.65 7.65 9 x 1MB 8 x 1MB(MAC) Prices At Sept. 13, 1990 CO-PROCESSORS INTEL 8087-2 80287-10 80C287-1 2 387SX· 16 387DX-16 387SX-20 387DX·20 387DX-25 387DX·33 175.00 308.00 390.00 435.00 478 .00 490.00 538.00 680.00 835.00 CYRIX 400.00 490.00 750.00 387SX-16 387DX·20 3870X-33 TOSHIBA LAPTOP TIOOOSE T1600 T3100E T3100SX T3200SX T3200 T5100 T5200 2MB 515 .00 2MB 340.00 2MB 340.00 2MB 340.00 2MB 340.00 3MB 570.00 2MB 340.00 2MB 340.00 COMPAQ 386-20. 386-25. 386·20E , 386-S, 386-33 4MB MOD ULES 680.00 4MB BOArds 798.00 TOROID POWER TRANSFORMERS From quality UK manufacturers. Available from stock at discount prices, 15VA to 625VA. Send SSAE for data & prices to: Transformer Discounters, PO Box 542, Wahroonga 2076. IBM PS/2 PELHAM WEITEK 3167-20 3167-33 4167-25 4167-33 820.00 1010.00 1500.00 1780.00 30/286.50 70E61 ,121 70A21 2MB 2MB 2MB 250.00 280.00 280.00 Sales Tax 20%. Overnight Delivery. Credit Cards Welcome 1st Floor, 100 Yarrara Road , Pennant Hills , NSW 2120. Tel (02) 980 6988 Fax (02) 980 6991 MAX 1/0 Board Kit $169.00 Buitl & Tested $269.00 • • • • • • 7 x Relays SPST 2 amps each 8 x Switch inputs (TTL) 1 x DAG (Digital to Analog converter) 1 x ADC ( Analog to Digital converter) 4 x Motor Drive outputs (40mA ea.) 1 x Programmable timer output. MAX includes a 20 page manual with all schematics, parts layout etc., a 360K PC compatible floppy with diagnostic and sample software in GW-Basic. MAX runs from a PC compatible Printer pert for full compatibility with a large range of computers. Same day dispatch of orders. Credit cards or personal cheque welcome. Phone: (08) 332 6513 or Fax: (08) 364 0902 (24 hours) ELECTRONIC TOY SERVICES, PO BOX 491, NOARLUNGA CENTRE, SA 5168. Phone: (08) 382 8919 LOOP ANTENNA Improve signal strength & quality with this portable antenna. Kit $44.00. Built and Tested S69 00 COMPACT INDOOR FM ANTENNAS Two models to choose from, Terk FM2000 a passive loop FM antenna for $69 .95 or the Terk Pl2 powered FM antenna with wideband low noise filter for S199.00. KIT REPAIRS We can also provide assembly facilities for small production runs at competitive prices Kits repaired from all magazines. PCs and peripherals also repaired Ring anytime 9am - 9pm JILOA (TECHNIKIT DIVISION) EEM ELECTRONICS LEARN WITH UCANDO TRAINING COMPUTER ANIMATED VIDEOS 10 Bouverie Place Epping Vic. 3076 (03) 401 1393 PC Computers 36 Regent St,Kensington, SA, MODEL TRAIN CONTROLLER project Silicon Chip November 1990, $19.95 plus $2.50 p&p. Plugpack, 12VAC, 1.7A, suitable for the above (use rectifier), $29.95 plus $4.00 p&p. Kits built & repaired. Prototype production board supplier to the hobbyist & supplier of SILICON CHIP project PCBs. ACTIVE SHORTWAVE ANTENNA SILICON CHIP, JAN 1990. Complete kit S59 00, Built and Tested $119.00, Case $10.00. FIX-A-KIT $20.00 PER HOUR LABOUR 3 MONTHS WARRANTY ON REPAIRS 12 MONTHS WARRANTY ON CONSTRUCTION Service to most types of electronic equipment TECHNICAL ASSISTANCE HVCAL INSTRUMENTS Design. Manufacture & Repair of Electronic Equipment Trading Hours 8am to 3pm, Monday to Friday (02) 633 5897 PO Box 73, Glenhuntly, VIC 3163. Telephone: (03) 571 6303 VT201 53 Mins DC Circuits VT202 71 Mins AC Circuits VT203 54 Mins VCR Maint. VT204110 Mins VCR Repair VT205 47 Mins Semiconductors VT206 55 Mins Power Supplies VT207 54 Mins Amplifiers $75.42 $79.54 $75.42 $114.97 $75.42 $75 .42 $75.42 Mastercard/Visa/NZ Cheque to : Electronics Assembly Company PO Box 21191, Christchurch, New Zealand. Phone (03) 79 5570 Price includes postage & packing. kid. For more information, send a 43c stamp to: Don McKenzie, 29 Ellesmere Crescent, Tullamarine 3043. CREATE YOUR OWN DIGITAL WAVEFORMS FOR SALE: 5mW LASER. Fully built power supply. $350. (02) 728 4768. As described in SILICON CHIP in March 1990, May 1990 & June 1990. The software can also be used for the similar project (Simple PC Function Generator) described in Electronics Australia in January 1989. ANTIQUE RADIO Software & PC Board: $39.95 incl. p&p. Software only: $32.50 incl. p&p. Money Order or Cheque. Guaranteed delivery within 14 days. ANTIQUE RADIO restorations. Your one-stop electronic repair shop. Specialising in restoring vintage radios including chassis rewiring, quality new parts, valves, valve sockets, speakers, transformers, cabinet restoration. Quality secondhand radio dials & parts for most brands & models. About 400 radios in stock for restoration & parts. M. Radvanyi, PO Box 49, Kingswood, NSW 2749. Every restored wireless is covered by a 2-year warranty on parts & service. French polishing of timber cabinets available. Vintage car radios in valve & transistor types available for restora- tion. Repairs done on tape decks, amplifiers, TVs & videos. Open Sat. 10am-5pm; Sun. 12.30-Spm. 109 Cann St, Bass Hill, NSW 2197. Phone (02) 645 3173 BH or (02) 7261613AH. SC FEBRUARY1991 103 ASK SILICON CHIP - CTD FROM PAGE 101 Advertising Index Altronics .............................. 52-53 ing Feedback with Equalisation", p106, August 1990). I have decided to take your advice on frequency shifting the whole signal slightly with a "Howl Round Stabiliser", though the pitch shifting chips (MC1495) are rather hard to find. (S. P., Melville, WA). • We have not considered doing an expander although the circuit is not much different from that of the compressor. We'll put it on the list of projects for 1991. How about that? The Motorola MC1495 should be available from VSI Electronics (Australia) Pty Ltd in Perth. Try them on (09) 328 8499. Volume control needs better matching I have built two Studio 200 Stereo Control Units, as described in the June and July 1988 issues of SILICON CHIP. Both work well but they both have the same problem. When I want to listen at very low levels, when the rest of my family is asleep, I find that one channel is louder than the other. Is there a design fault in the circuit or is there a modification I can make to improve the problem? (M. K., Stanmore, NSW). • What you are experiencing is not a design fault but the normal lack of matching between sections of the volume control when it is set at very low levels. Just about all controls on stereo amplifiers have the same problem unless a higher cost, specially matched vo lume control has been install ed. Japanese firms such as Alps do manufacture closely matched dual ganged volume controls but they.are not cheap or readily available. It might also be possible to purchase such a volume control as a replacement part for a Japanese amplifier. One other way around the problem would be to put in an extra switch to reduce the gain for low level listening, similar to a Mute switch. That way, you could listen at low levels but have the volume contro l set to say, 9 or 10 o' clock, where the control matching is reasonable. This could be achieved by switching a 22kQ resistor in series with each section of the Balance control. Another way could be to wire one pair of the Source inputs for lower gain. If you listen to CD most of the time, connect a 120kQ resistor from the CD input to the Aux 2 input, in each channel. Then when you select Aux 2, you can listen to CDs with a higher setting on the volume control. Arista ......................... ..... 17,74,97 Back Issues .. .. ....... .......... ..... 58,59 Boston Technology . ... . .. ... .. ... ... 89 Cad Connection ... ... .. ... .. ... .... 102 Christian Blind Mission ............ 97 David Reid Electronics ........ IFC ,1 Dick Smith Electronics ........... . 5-7 EEM Electronics .. ... ... .. ... ... .... 103 Electronic Solutions ............ 25,81 Electronic Toy Services .......... 103 Electronics World ......... ... ... ..... 75 Elmeasco . ... .. ... .... ... .. .. ... ... .... .. 27 Geoff Wood Electronics . .... ... .. 13 Harbuch Electronics .. .............. 38 Hycal Instruments ...... ... ..... ... . 103 Jaycar Electronics ..... ........... 33-36 69-72 Jiloa ............. ........... .... ............ 103 J.V. Tuners .... .. ... ....... .............. 79 M. Radvanyi ...... .... .... ..... ....... 103 Oatley Electronics ...... ..... ......... 51 PC Computers . .... ... ... .... .. .. ... 103 PC Marketplace ... ...... .... ... .... IBC Pelham ............... .. ........ .. ....... 103 RCS Radio .. .. ... .... ... .. ... ... ... ... .. 75 Resurrection Radio .. .. .... .. ... ... .. 41 Rod Irving Electronics ....... ... 44,45 60,61,90,91 Sheridan Electronics .... .. ... .. .. .. . 19 x r-------------------------, Silicon Chip Binders ...... ........ OBC SILICON CHIP BINDERS Subscriptions . .. .... ... ... ... ... .. .. . .. 99 To: Silicon Chip Publications, PO Box 139, Collaroy Beach, NSW 2097, Australia. Yes! Please send me _ _ _ SILICON CHIP binder(s) at $A11 .95 plus $A3 p&p each (NZ $A6 p&p). Enclosed is my cheque/money order for $_ _ _ _ _ or please debit my O Bankcard O Visa Card 0 Master Card Card No . Signature_ _ _ _ _ _ _ __ _ _ _ Card expiry date_ _ _,/_ _ _ Name _ _ __ _ _ _ _ __ _ _ _ _ _ _ __ _ __ _ _ __ Street _ _ _ _ _ _ _ _ __ _ _ _ _ _ _ __ __ _ _ __ _ Suburb/town _ _ _ _ _ _ __ _ _ _ _ Postcode_ _ __ _ __ L _________________________ J 104 SILICON CHIP Sound Australia .. ... ... ... ... ... .. .. . .. 17 Transformer Discounters ...... 103 PC Boards Printed circuit boards for SILICON CHIP projects are made by: • Electronic Toy Services, 2/111 Glynville Drive, Hackham West, SA 5163. Phone (08) 382 8919. • Jemal Products , 5 Forge St, Welshpool, WA 6106. Phone (09) 350 5555. • Marday Services, PO Box 19-189, Avondale, Auckland, NZ. Phone 88 5730. • RCS Radio Pty Ltd, 651 Forest Rd, Bexley, NSW 2207. Phone (02) 587 3491. ml llilDmlmlllilmlmlmlmlmJ[IEIIIIDIIDIIDI SUPER SPECIALS FLOPPY DISK CONTROLLERS TO SUIT AT ONLY / BRAND NAME 360K 5.25" DISK DRIVES"" / WITH 3 MONTHS WARRANTY e 1 FOR $69 e 2 FOR $120 e 3 FOR $165 e 4 FOR $200 MOTHERBOARDS WAS NOW 8088 8088 8088 8088 8088 8088 80286 80286 80386 80386 ,80486 12Mhz 12Mhz 640K installed 12Mhz 1Mb installed 31Mhz 31 Mhz 640K installed 31 Mhz 1Mb installed 12Mhz 16Mhz NEAT 25Mhz Cache 33Mhz Cache 25Mhz Cache $129.00 $250.00 $300.00 $225.00 $335.00 $385.00 $350.00 $649.00 $1995.00 $2495.00 $109.00 $199.00 $235.00 $189.00 $279.00 $319.00 $299.00 $449.00 $1495.00 $1795.00 $4395.<>9 WAS ,r $199.00 $299.00 $399.00 $499.00 880K Macintosh series 164K Apple 11E 164K Apple 11Gs 720K Amstrad PC 1512/1640 1.44 Amstrad PC 2000 360K Amstrad PC 2000 1.2 Amstrad PC 2000 1.2 Amstrad Portable 720KAtariSt 360K/720k 40/80 Atari ST 880K Amiga 500/1000/2000 360K Amiga 500/1000/2000 720K IBM 1.44 IBM 360K IBM 1.2 IBM 1.2 IBM PS11 360K Toshiba/portables 1.2 Toshiba/portables ,r WAS WAS WAS / NOW $329.00 $209.00 $229.00 $249.00 $309.00 $249.00 $249.00 INTERNAL FLOPPY "' DISK DRIVES 3.5HH 3.5HH 3.5HH 5.25 5.25 WAS NOW $ 99.00 $245.00 $245.00 $299.00 $199.00 $79.00 $199.00 $199.00 $279.00 $149.00_. pricing. WAS Serial I/O Card 4 port Serial 1/0 Card 8 port Games card 2 port Parallel printer card Serial 2 port XT Serial 2 port AT Serial/Par/Games XT/AT 2Serial /2Parallel Multi 1/0 S/P/G/C/F XT/AT Proto Board with decoder \_Slot Extension Kit NOW KEYBOARDS / WAS Mono PC/XT/AT CGA _. ... \. WAS NOW $129.00 $199.00 $55.00 $99.00 $139.00 $175.00 $245.00 $220.00 $119.00 $99 .00 $179 .00 $39.95 $79.00 $99.00 $149 .00 $199 .00 $199.00 $99 .00 e :;~~:~~ $299.00 WRITE OR PHONE FOR FREE CATALOGUE PHONE OR FAX TODAY/ .... ._ """W"'~""'4i --- . I"◄ VISA SERVICE IS THE DIFFERENCE "" -=•- ..--·-~"'1111111!!!!1• MillJ ~;ii~ l!D1i 0 SERVICE IS THE DIFFERENCE • SERVICE IS THE DIFFERENCE $69.00 $99.00 DEALER ENQUIRIES WELCOME- . PERSONAL COMPUTER MARKETPLACE Pty ud PHONE (02)4186711 Include $10 with order fur all normal items - heavy items, e.g. monitors add $16. FAX (02)4186713 14 day money back guarantee Mail Order Address: Order by phone (use credit card), by fax or by mail. P.O. Box 1100 Lane Cove Unless insurance is declined it will be charged at 1% of total purchase. This is fur your protection. NSW2066 PRICES CURRENT FOR MONTH OF PUBLICATION OR WHLE STOCKS LAST. NOW \."'----------~ CONTROLLER CARDS FOG 360/720/1.2/1.4 x4 FOG 360K to 2.88Mb X4 FOG 360K INT/EXT x4 FOG 360/720/1 .2/1.4 x2 HOG MFM -PG/XT HOG/FOG MFM PG/XT HOG/FOG MFM AT HOG MFM AT Go-Existant FOG 2 Drives $109.00 $109.00 ~:~it 256K :~:~:~ VGA 16 bit 512K $449.00 FREIGHT CHARGES e GRAPHIC CARDS ' I ~~: ' WAS $109 .00 NOW $89.00 ' $199.00 $179.00 $449.00 $429.00 $ 29.50 $25.00 $ 24.95 $19.95 $ 55.00 $35.00 $ 65.00 $40.00 $125.00 $62.50 $ 75.00 $50.00 $125.00 $99.00 $149.00 $99.00 $199.00 $149.00 _. -~~-----------~ 101 Enhanced keyboard ( $125.00NOW $99.00 $199.00NOW $149.00 " NOW MOUSE/ACCESSORIES ' WAS $185.00 $285.00 $249.00 $299.00 $249.00 $299.00 $409.00 $309.00 $369.00 _. NOW $160.00 $169.00 $265.00 $69.00 $149.00 ... Mouse for PC/XT/AT/PS11 $119.00 $99.00 Mighty Scanner $399.00 $379.00 ~Sound Blaster $399.00 $349.0~ '- $379.00 $249.00 $279.00 WAS $199.00 $199.00 $299.00 $149.00 $179.00 INTERFACE CARDS a huge range of cables, adaptors, swithboxes and chips Call today for very competitive / 720K 1.44 4MB 360K 1.2 '- MEMORY CARDS TRY PC MARKETPLACE SUPERFAST MAILORDER - Pfii{ (jfeeson 's $205.00 $499.00 $849.00 $649.00 $399.00 $699.00 $999.00 '- WAS \. / ' NOW 14" White/Amber/Green $239.00 $535.00 14" Philips CGA $899.00 14" Multisync VGA $695.00 14" Colour VGA $499.00 Olympia NP30 Centronics Olympia NP80/24 Centronics $779.00 Olympia N P136/24 Centronics $1395.00 $349.00 $249.00 $269.00 $269.00 $329.00 $329.00 $329.00 $399.00 $269,00 $299.00 $199.00 $299.00 $299.00 $329.00 $299.00 $329.00 $449.00 $349.00 $399.00 POWER SUPPLIES 150W XT Power Supply 200W AT Power Supply ' MONITORS/PRINTERS EXTERNAL FLOPPY DISK DRIVES "' 3.5 5.25 5.25 3.5 3.5 5.25 5.25 5.25 3.5 5.25 3.5 5.25 3.5 3.5 5.25 5.25 5.25 5.25 \.5.25 NORMALLY $99.00 SUPER SPECIAL $49.00 SAVE $50.00 HURRY LIMITED STOCKS Memory card PC/XT 576k "" Memory card 2Mb AT Memory card 2Mb XT NOW Memory card 32Mb XT/AT $149.00 {lam card for Amiga $250.00 $299.00 We also stock $399.00_. CASES XT Case 4 Drives 150W P/S AT Case 3 Drive 200W P/S Minitower Case 200W P/S. \... Maxitower Case 200W P/S WiH support up to 2 driws of 360172().11 .2/1.44 includes cables for both 5.25" and 3.5" drives e SERVICE IS THE DIFFERENCE