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SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.altronics.com.au Vol.7, No.4; April 1994 FEATURES   4 Electronic Engine Management, Pt.7 by Julian Edgar Other input sensors THE THROTTLE position sensor plays an important role in your car’s engine management system. Find out how this & other sensors work by turning to page 4. 36 Microcontrollers With Speed by Darren Yates The new PIC series from Microchip 56 PC Product Review: The Video Blaster by Darren Yates Imports PAL or NTSC video signals into your PC 70 Spectrum Analysis With The Icom R7000 by J. Lloyd & J. Storey It operates under computer control 80 G-Code: The Easy Way To Program Your VCR by Leo Simpson Just enter the numbers in your TV guide & that’s it! PROJECTS TO BUILD 16 Remote Control Extender For VCRs by John Clarke EVER WANTED to operate your VCR from another room while watching the picture on a second set? This Remote Control Extender relays signals from the handpiece to an IR LED located near the VCR – see page 16. Lets you operate your VCR from any room in the house 22 Sound & Lights For Level Crossings by John Clarke Companion unit to the Level Crossing Detector 29 Discrete Dual Supply Voltage Regulator by Darren Yates Provides regulated supply rails from ±5V to ±12V 32 Low-Noise Universal Stereo Preamplifier by Darren Yates Use it with a magnetic cartridge, cassette deck or microphone 60 Build A Digital Water Tank Gauge by Jeff Monegal Displays water level & can automatically activate a pump SPECIAL COLUMNS 40 Serviceman’s Log by the TV Serviceman ADD REALISM TO your model railroad layout with this Sound & Lights module. It mates with the Level Crossing Detector & flashes lights & produces a realistic bell sound when a train approaches. Construction starts on page 22. A couple or real stinkers 54 Computer Bits by Darren Yates Experiments with your games card, Pt.5 86 Vintage Radio by John Hill Bandspread tune-up for an Astor multi-band receiver DEPARTMENTS   2   3 10 53 84 Publisher’s Letter Mailbag Circuit Notebook Order Form Back Issues 80 90 93 94 96 Product Showcase Ask Silicon Chip Notes & Errata Market Centre Advertising Index THIS DIGITAL GAUGE will keep tabs on the water level inside a tank & can turn on a pump when the water falls below a preset level – turn to page 60. Cover design: Marque Crozman April 1994  1 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, B.Sc. Reader Services Ann Jenkinson Sharon Macdonald Marketing Manager Sharon Lightner Phone (02) 979 5644 Mobile phone (018) 28 5532 Regular Contributors Brendan Akhurst Garry Cratt, VK2YBX Marque Crozman, VK2ZLZ John Hill Jim Lawler, MTETIA Bryan Maher, M.E., B.Sc. Philip Watson, MIREE, VK2ZPW Jim Yalden, VK2YGY Bob Young Photography Stuart Bryce SILICON CHIP is published 12 times a year by Silicon Chip Publications Pty Ltd. A.C.N. 003 205 490. All material copyright ©. No part of this publication may be reproduced without the written consent of the publisher. Printing: Macquarie Print, Dubbo, NSW. Distribution: Network Distribution Company. Subscription rates: $49 per year in Australia. For overseas rates, see the subscription page in this issue. Editorial & advertising offices: Unit 34, 1-3 Jubilee Avenue, Warrie­ wood, NSW 2102. Postal address: PO Box 139, Collaroy Beach, NSW 2097. Phone (02) 979 5644. Fax (02) 979 6503. PUBLISHER'S LETTER Should we reduce our mains voltage to 230V? Recently, there have been moves afoot to standardise much of the Western world’s electricity supplies, transformers, ma­chines and appliances. If Australia goes along with it, our domestic mains voltage would be reduced from a nominal 240 to 230 volts AC. This suggestion came originally from the International Electrotechnical Commission (IEC) in 1983. As far as Europe is concerned, the move to standardise on 230 volts, or any other figure for that matter, is probably a good one. Presently, Europe has a range of mains voltages – 220, 230 and 240 volts – and it makes sense to standardise on the one voltage in the long term. Britain, which now uses 240 volts, is going along with the idea but the USA, as is their usual conser­vative stance in these matters, will stick with its 110 volts at 60Hz. However, any suggestion that Australia should automatically follow Europe should be treated with cynicism. Dr David Sweeting, chairman of the Australian Institute of Engineering’s 230-volt working group, is quoted in the Sydney Morning Herald (March 5th, 1994) as saying “It is going to improve the opportunities for the electrical equipment we produce, opening up the world to our industry”. Oh really! Let’s face it, any Australian manufacturer who wants to export is already meeting the standards of world markets or they should be. If they want to sell a product in an overseas market, it has to meet the standards of that market and it will not make one whit of difference whether Australia has the same electrical standard or not. On the other hand, it might make it easier and cheaper for importers of electrical equipment and, heaven knows, Australian manufacturers don’t need any more competition from imports. In virtually every field of endeavour, Australian manu­facturers have heavy competition from aggressive importers. Do we really want to make it easier for the importers and thereby put our balance of payments in even more jeopardy? Remember also that if we change to 230 volts AC for domes­tic use that automatically means a change to the 3-phase distri­bution standard of 415 volts AC to 397 volts. So all the equip­ment designed to run at 415 volts will be slightly less effi­cient, as will 230 volt equipment. The 230-volt working group referred to above estimates the reduction would add about 0.5% to the cost of electricity. I would question that figure too. If the voltage is reduced by a nominal 5% from 240 to 230VAC, the I2R losses in the distribution system will be more like 10%. And when you consider that a great deal of the domestic distribution network actually runs at 250 volts AC or more, the distribution losses would be more like 15% if the change was fair dinkum. That is a huge cost to Australia, for the doubtful bene­fit of being in line with a European standard. I could go on poking holes in the argument but I think I’ve made the point. Should we reduce our mains voltage to 230 volts AC? We’d like to hear from you. Leo Simpson ISSN 1030-2662 WARNING! SILICON CHIP magazine regularly describes projects which employ a mains power supply or produce high voltage. All such projects should be considered dangerous or even lethal if not used safely. Readers are warned that high voltage wiring should be carried out according to the instructions in the articles. When working on these projects use extreme care to ensure that you do not accidentally come into contact with mains AC voltages or high voltage DC. If you are not confident about working with projects employing mains voltages or other high voltages, you are advised not to attempt work on them. Silicon Chip Publications Pty Ltd disclaims any liability for damages should anyone be killed or injured while working on a project or circuit described in any issue of SILICON CHIP magazine. Devices or circuits described in SILICON CHIP may be covered by patents. SILICON CHIP disclaims any liability for the infringement of such patents by the manufacturing or selling of any such equipment. SILICON CHIP also disclaims any liability for projects which are used in such a way as to infringe relevant government regulations and by-laws. Advertisers are warned that they are responsible for the content of all advertisements and that they must conform to the Trade Practices Act 1974 or as subsequently amended and to any governmental regulations which are applicable. 2  Silicon Chip MAILBAG Information on guitar amplifiers With reference to the “IF Generator Is Nifty” letter from L.T. of Eaglehawk, (Ask SC, December 1993), he(?) asked for a course on antique musical instruments, specifically guitar amplifiers. In 1989, I purchased a paperback book from McGill’s bookshop in Melbourne, called “The Tube Amplifier Book II” by R. Aspen Pittman. As far as I can tell, it is published by Groove Tubes, 13994 Simshaw Avenue, Sylmar, California 91342, USA (my edition was published in 1988). There are 400 pages to this book and it has 32 pages of photos of various guitar amplifiers and a few other items. There is a considerable rundown on the history and technical details of many amplifiers, including 10 pages listing valve types used in various makes and models. There is a small cross reference list of US/industrial/ European type equivalents, a list of Groove Tube companies and instrument manufacturers (worldwide list) and, most importantly, 277 pages of circuits of all the big name guitar amplifiers. If this book is still available, it should be just what is needed. As a regular reader, let me compliment you on your excellent magazine. I am a collector of early radio equipment and a technician by trade, so I read the Vintage Radio and Serviceman’s Log columns first, followed by the rest of the magazine articles. I am a member of the Historical Radio Society of Australia and a local vintage radio club (The North East Vintage Radio Club). About 17 of our members went across to see John Hill’s museum in Maryborough a few weeks ago. How I wish I had as many of my radios restored and somewhere to display them like that! E. Irvine, Benalla, Vic. Environmental concern I am writing to you because of concern I have about the Engine Management feature in the January 1994 issue of SILICON CHIP, in which Julian Edgar explains how to “Change The System”. My concern is that with the environment now being such an import­ant issue, is it really the proper thing to do to explain to people how to increase the performance of their car which can lead to increased fuel consumption and an increase in exhaust pollutants? Also something which Julian omitted from his article and which I think is important is that, on some cars, the radiator cooling fan is controlled by the ECM. By changing the information the ECM receives from the coolant temperature sensor, the ECM “thinks” the motor is running cooler than it really is. This could lead to the engine overheating because the radiator cooling fan is not turned on. F. Loprete, Cabramatta, NSW. Comment: We accept your concern about increased performance leading to more pollution but we also think that is more useful to make this information available than to suppress it. We have also spoken to Julian Edgar on your concern about the ECM think­ing that the engine is cooler than it really is, leading to a danger of overheating. He agrees that your concern is valid. SILICON CHIP, PO Box 139, Collaroy, NSW 2097. the “high” or the “low” coding line on the PC board. The switch should just protrude through the case lid when the two halves are fitted together. The receivers then need to be coded in such a way that pressing the original button operates one receiver and pressing both operates the other. An example of this coding would be 1-low, 3-high, 4-low and, through the extra switch, 5-high. This would mean that the original button would operate a receiver coded to 1-low, 3-high and 4-low, while pressing both would oper­ate a receiver coded 1-low, 3-high, 4-low and 5-high (all other lines open). If the extra coding line is to be taken high, it may also be possible to switch the transmitter as well so that only one button is pushed for each receiver – I have not tried this, however. W. Sutton, Adelaide, SA. EFI cars have more poke I can’t let G. J. Hunt’s letter in the March 1994 Mailbag pages pass without comment. He reckons that his wife’s Daihatsu Charade is easily beaten by an 18-year old Mini. Just for inter­est, I’ve tabulated their comparative performance figures. Converting a UHF remote control to dual operation I recently built the UHF Remote Switch and the Garage Door Controller designed by Oatley Electronics, as described in the December 1993 issue of SILICON CHIP. I have found both units to be reliable and excellent value. Because I use the UHF switch to operate the central locking on my car, I need to have a remote controller for both the garage door and the locking system. Rather than carry two remotes, I cut a small (about 4mm) hole in the top of the transmitter case directly over the encoder IC. I then fixed (using several layers of double sided tape) a switch to this. In order to allow the switch to sit correctly, the legs needed to be bent outwards. The normally open contact of the switch was then connected to either 1993 Daihatsu Charade 1976 Leyland Mini 0-60km/h 4.4 seconds 7.5 seconds 0-100km/h 11.4 seconds 23 seconds Top speed 172km/h 125km/h The Charade test figures are from the September 1993 issue of “Motor” magazine while the Mini figures are from the April 1976 issue of “Wheels” magazine. E’nuff said? Julian Edgar, Para hills, SA. Comment: we are in no doubt that modern cars with engine manage­ment systems are far superior to 20-year old vehicles and your figures bear this out. It seems likely that the Charade referred to by G. J. Hunt might be the 3-cylinder version which is a little underpowered. April 1994  3 Electronic Engine Management Pt.7: Other Input Sensors – by Julian Edgar In addition to the airflow and exhaust oxygen sensors pre­viously discussed, engine management systems run other input sensors to allow the system to monitor changing engine and envi­ronmental parameters. For example, the temperature of various parts of the engine is another factor that influences fuel and ignition requirements. This is especially so at engine start-up, as a cold engine requires substantially more fuel to run satis­factorily. Temperature sensors The engine coolant temperature plays a major role in deter­ mining the amount of fuel enrichment. The lower the engine tem­ perature, the greater the fuel correc­tion applied to the base injector opening time. Sometimes this correction factor, which is A potentiometer type throttle position sensor. It meas­ures the precise amount of throttle opening and feeds this data to the ECM (electronic control module) to control fuel enrichment. 4  Silicon Chip also tied to idle speed, is applied in a series of discrete steps. As a result, the engine idle speed reduces in a corresponding series of abrupt steps as the water temperature rises. The coolant temperature sensor also plays a major role, even when the engine is up to operating temperature. In one system, for example, when the coolant temperature is over 95°C and the throttle position switch idle contacts are open (ie, the throttle is applied), fuel injection is increased by 10% over the base quantity. This enriches the mixture to counteract possible detonation. If the same high engine temperature exists at start-up, the fuel pressure is increased to avoid possible vapour-lock problems. The ignition timing control is also affected by the engine coolant temperature. For example, in one engine management sys­ t em, the ignition timing is advanced by about 7° when the coolant temperature is below 0°C. This allows greater time after ignition for maximum combustion pressures to occur. Pollution control mechanisms may also be influenced by coolant temperature. In one car, for example, the evaporated fuel from the fuel tank is purged from its absorption canister by being vented to the intake manifold –but only when the engine is sufficiently warmed-up to burn it without further emissions release. Inside a switch-type throttle position sensor – note the contacts for idle & full-throttle positions. The movable arm (centre) follows the track in the guide cam (see also Fig.9). Fig.1: cross-section of Holden VL Commodore optical crankshaft position sensor. It uses two LEDs and two matching photodiodes to sense slots cut into a rotating disc mounted in the base of the distributor. Other temperature sensing which may be carried out includes the intake air temperature (especially with engines running vane-type airflow meters), cylinder head temperature and – in some programmable injection systems – engine and gearbox oil tempera­ture. Invariably, temperature sensing is carried out by a ther­mistor mounted within a heat-conductive body. Road speed sensor A vehicle road speed sensor is also generally used to feed data to the ECM. This data may be used in several ways. First, many vehicles feature over-run fuel injector cut-off. This means that when the throttle is lifted, fuel injector operation ceases, resuming only when the engine rpm approaches idle speed. This reduces exhaust emissions and improves fuel economy. An example of fuel shut-off occurs in the Nissan 6-cylinder engine used in the VL Commodore. In this case, the fuel injectors are shut off if the throttle position switch contacts are closed (ie, if your foot is taken off the accelerator) at any engine speed above 2000 rpm. The proviso here is that the engine coolant must have reached normal operating temperature. Fuel injection resumes when the engine speed falls below 2000 rpm. In some cars, however, the injector-resume speed is as low as 1500 rpm and a slight jerk can often be felt by the sensitive driver when the injection starts again. The road speed sensor input is relevant here because injector cut-off operation occurs only above a certain speed – 8km/h in the VL Commodore. A second use for road speed data occurs in those cars which run a speed limiter as part of the engine man­ agement sys­tem. Its job is to cut off the fuel or ignition when a certain road speed is reached. This is often well above the speeds reached in normal conditions – even in the Northern Territory! However, domestic Japanese cars run either a 145 or 180km/h speed limiter. The road speed sensor is usually built into the back Fig.2: the rotating disc in the VL Commodore’s distributor has 360 1° slots around its periphery to provide a signal that’s proportional to engine speed. Also on the disc are six slots at 60° intervals to indicate the crankshaft posi­tion. The large slot at the top indicates the position of the number one piston. Fig.3: this diagram shows how the rotating disc & the optical sensor are mounted in the base of the distributor. April 1994  5 The crankshaft position sensor is often built into the base of the distributor, as in this Holden 4-cylinder engine. This distributor-based system uses an optical pick-up but an inductive pick-up system using a coil & a magnet to sense protrusions on a crankshaft sprocket can also be employed. of the speedometer and so uses the speedo cable to drive it. Other systems mount the sensor on the gearbox. Crankshaft position sensor One very important sensor is the crankshaft (or camshaft) position sensor. This provides vital inputs to the ECM so that it can provide the correct injection and ignition timing. Fig.1 shows a cross-section of the optical sensor used in the Holden VL Commodore engine. It uses two LEDs, two photodiodes and a rotating disc. The rotating disc is built into the base of the distributor and has 360 tiny slots near its outside edge (see Fig.2). These slots rotate between one LED and its corresponding photodiode and provide a signal to the ECM that’s proportional to engine speed. In addition, there are a further six slots in the disc but fur­ther towards the disc’s centre. Five of these are of the same size but the sixth is much larger. Fig.4: the Subaru Liberty uses an inductive pick-up sensor to determine the crankshaft position. This sensor consists of a magnet & coil assembly & is mounted close to a toothed crankshaft sprocket. 6  Silicon Chip These six slots are placed 60° apart and are used to signal the crankshaft angle (or piston position) to the ECM. The large cutout is used to show the position of number one piston. Fig.3 shows the whole assembly. Other manufacturers use an inductive system, whereby a crankshaft sprocket with specifically located protrusions rotates past a moulded pick-up containing a magnet and coil. Fig.4 shows the cross-section of the inductive sensor used by Subaru in the Liberty. Fig.5 shows the layout of the system. Note that the pick-up is separated from the toothed sprocket by only a small air gap. In operation, the magnet briefly magnetises the sprocket protrusion as it passes the sensor and a voltage is then induced in the coil as the air gap changes. An AC waveform (Fig.6) is emitted by the pick-up, with the pulses occurring at different crankshaft positions. Camshaft position sensors often work in the same way. Knock sensor Knock (or detonation) occurs when fuel in the combustion chamber ignites before the progressively-moving flame front actually reaches it. When this happens, a sudden increase in combustion pressure occurs and this blow to the piston is the “tinking” sound heard inside the car. The fact that this sound is produced by a detonation hitting the crown of the piston Fig.5: as each protrusion on the crankshaft sprocket passes the sensor, a voltage is induced in the pick-up coil. This voltage is then fed to the ECM to indicate the crankshaft position. This late 1980s Holden 4-cylinder engine is fitted with six major input sensors for the ECM plus three minor sensors. Fig.6: the shape of the output waveform from an inductive pick-up sensor. Fig.7: cross-section of a typical knock sensor. It uses a piezoe­lectric transducer as the sensing element. April 1994  7 Fig.8: the knock sensor control process, as developed by Bosch. A filtering & evaluation system is needed to differentiate detona­tion noise from ambient engine noises. deep inside the engine indicates the violence of this phenomenon! Detonation can occur because the ignition timing is too advanced, the fuel octane rating is too low, or the tur­ bocharger boost pressure is too high – or due to a combination of these factors. However, maximum efficiency is often gained by running engines very near to the onset of detonation and so knock sensors are now being used in some engine management sys­tems to prevent engine damage. Knock sensors employ piezoelectric elements, with elaborate filtering and Fig.9: the layout of switch-type throttle position sensor. The movable contact is controlled by a guide cam & closes with the power contact when the throttle is opened. comparison circuits to differ­ entiate knock from normal engine noise. Fig.7 shows a typical knock sensor, while Fig.8 shows the control process carried out by the ECM. The sensor itself is usually screwed into the block near to the head (some systems use separate knock sensors for each cylin­der but most road-going engines make do with one). When knock is sensed, the ECM usually retards ignition timing and then, when the problem has gone, slowly advances the timing back to its original figure. Knock sensors are notoriously A typical intake air-temperature sensor. It is bolted into one of the intake runners. Temperature sensors invariably use a thermistor mounted inside a heat-conductive body. 8  Silicon Chip prone to false-alarming. In one car, the fault-code indicating a problem with the knock sensor is almost sure to be registering – with no apparent fault present! Shielding of the input cable is generally used to prev­ent interference but problems have continued to plague this device in production cars. Throttle position sensors Throttle position sensors (TPS) do just that – they in­dicate to the ECM the opening of the throttle valve. In the past, these sensors were invariably simple switches, with contacts for idle and full load. Current cars can run switches of this sort or can use a combination of an idle-position switch and a potentiom­eter to indicate the precise throttle opening. Other cars use just a potentiometer. Fig.9 shows a switch-type throttle position sensor. Input data from the throttle position sensor is used to indicate when full load and/or acceleration injection enrichment is needed, and to signal injector cut-off on the over-run. This sensor also sometimes causes the air-conditioner clutch to be switched off under full throttle, thereby allowing maximum road performance. Those cars using a potentiometer TPS also often use an ECM that’s programmed to take note of the speed of the throttle opening, as well as its angle. Rapidly flooring your right foot will then give different ignition advance and fuel rates compared to gentle acceleration to full throttle. SC High Purchase Costs Taking a “Bite” Out of Your Budget? NOT AT MACSERVICE. WE HELP YOU STRIKE BACK BY OFFERING THE LOWEST PRICES AND GOOD OLD FASHIONED SERVICE - Just look at these SPECIALS BALL EFRATOM M100 Rubidium Frequency • Factory cal. certs. • Perfect for ISO    accreditation • GPS applications • Ruggedised military    design TEKTRONIX 5440 Oscilloscope • DC to 60MHz • 1mV - 100V/div (x 10) • Dual Trace • Dual Timebase • Large Screen TEKTRONIX 7603 Oscilloscope • Mil spec AN/USM 281-C • Triggers to 100MHz • Dual Trace • Dual Timebase • Large Screen SUPER SALE $850 GREAT VALUE $2950 (new) Video Dist Amp & Cable Equaliser   $100 ADVANCE PP7 30V3A DC Power Supply   $150 AVO MK.IV Avometer With Cal.   $275 BPL CB154/4 Electrolytic Cap Bridge   $450 B&K 1466A 10MHz Oscilloscope   $275 EH 129 Pulse Generator   $90 ELGENCO 603A White Noise Gen 5MHz   $200 ENI 503L RF Power Amp 40dB 510MHz $1025 FLUKE 102 VAW Cal Meter    $75 FLUKE 9010A Logic System Troubleshooter $1000 GR 1608 LCR Meter – Lab Standard $1500 HP 211B 10MHz Square Wave Generator   $275 HP 302A Audio Selective Level Meter   $145 HP 400L True RMS Voltmeter   $170 HP 410B Vacuum Tube Voltmeter   $130 HP 432A 10GHz Power Meter (c/w sensor)   $875 SUPER DEAL $950 HP HP HP HP HP HP HP HP I/S Elect. 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M36 $55 VCE 150 $120 CM 25 $45 SEPTEMBER SPECIAL TEKTRONIX 465M 100MHz Oscilloscope VCE-150 VCE-200 VCD-150 DI-10 DI-1 TDI-0.8 CM-25 CM-50 150mm/6" Electronic Digital Vernier in box $120 200mm/8" Electronic Digital Vernier in box $180 150mm x 0.02 Dial Vernier Caliper   $75 10 x 0.01mm Dial Indicator   $45 1" x 0.001" Dial Indicator   $45 0-0.8 x 0.01mm Test Dial Indicator   $95 0-25mm x 0.01mm Outside Micrometer   $45 25-50mm x 0.01mm Outside Micrometer   $55 The Name That Means Quality CM-75 50-75mm x 0.01mm Outside Micrometer   $65 CM-01 0-1" x0.001" Outside Micrometer   $45 MB-6 CZ-6C Magnetic Base Stand   $55 VC-150 Dual Scale Vernier Caliper 150 x 0.02mm/6" x 0.001"   $35 VC-200* Dual Scale Vernier Caloper 200 x 0.02mm/8" x 0.001"   $45 VC-600* Dual Scale Vernier Caliper 600 x 0.02mm/24" x 0.001" $250 HI-600 600mm/24" x 0.02mm Height Gauge $550 *WITH FINE ADJUSTMENT Affordable Laboratory Instruments SSI-2360 60MHz Dual Trace Dual Timebase Oscilloscope BRA BRAN D EQUIP NEW MENT ND EQUIP NEW MENT Bandwidth DC to 100MHz; Rise time <=3.5ns; Deflection factor 5mV/div to 5V/ div in 10 steps; DC accuracy ±2%; 2-channel display mode; Horizontal deflection - main & delayed timebases; A - 0.5s/div to 0.05µs/div in 22 steps; B - 50ms/div to 0.05µs/div in 19 steps; Trigger - main/delay sweep; Coupling AC, DC, LF Rejection, HF Rejection TOP VALUE $1150 • • • • • • 60MHz dual trace, dual trigger Vertical sensitivity 1mV/div. Maximum sweep rate 5ns/div. Built-in component tester With delay sweep, single sweep Two high quality probes $1050 + Tax PS303D Dual Output Supply • 0 to 30V and 0 to 3 amps • Four output meters • Independent or Tracking modes • Low ripple output $385 + Tax PS303 Single Output Supply PS305D Dual Output Supply PS305 Single Output Supply • 0 to 30V and 0 to 5 amps $430 + Tax • 0 to 30V and 0 to 3 amps • Two output meters • Constant current/voltage • Low ripple output $225 + Tax • 0 to 30V and 0 to 5 amps $260 + Tax IF IT’S NOT HERE WE CAN GET IT... CALL US FIRST OR CALL US LAST... BUT DON’T FORGET TO CALL US! MACSERVICE Australia’s Largest Remarketer of Test & Measurement Equipment 26 Fulton Street, Oakleigh Sth, Vic., 3167   Tel: (03) 562 9500 Fax: (03) 562 9615 **Illustrations are representative only 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. Battery-life indicator for radio microphones This idea came about because one of our local churches plans to increase the number of radio microphones in its sound system from two to six. The problem is that the transmitter batteries must be replaced at about nine hours as a compromise between reliable life expectancy and the possibility of a sermon or music item fading out if the batteries are left in too long. The present method of manually logging the transmission times of two channels is impractical for the impending array of six channels. What follows is a solution that combines non-vola­ tile memory of total elapsed transmission time for each Block signalling for model trains This project provides a realistic signalling effect for model trains. It sets a CLEAR signal to DANGER as a train enters a section and then resets it to CLEAR again as the train leaves the section. No modification of rolling stock is required. The project provides two independent block circuits which detect occupancy. They can be used anywhere on your layout to operate signals or simply to indicate on your control panel that a train is in a section. This makes it ideal for use on hidden sidings. Phototransistors are positioned under the rails, one at each end of a block section. One block uses photo­transistors Q1 and Q2, while the other uses Q3 and Q4. When the signal is green, the shadow of a passing train interrupts light falling on the phototransistor as it enters the section. This causes the circuit to switch the red signal on in place of the green. As long as the train remains in the section, the red will stay on. As it leaves the section, the 10  Silicon Chip micro­phone with excellent accuracy, simplicity and low cost. The design takes advantage of the fact that a 6V line from each VHF receiver becomes active during reception from its corre­sponding transmitter. A combination of a resistor and a LED drops the 6V to a working voltage of 1.5V to operate a common quartz clockwork mechanism as sold by some electronics outlets. The minute and second hands can be discarded and the hour hand cut short so that the clocks only take up a small amount of room in the sound desk console. Escutcheons need to be made up for the clocks with numbers from 1 to 12 hours and access to the mechanisms must be provided to enable manual resetting of each clock to zero when its transmitter battery is replaced. The LEDs can double as activity indicators. Glen Host, Doubleview, WA. $15 train’s shadow causes the circuit to switch back to green. IC1a and IC1b are arranged as an RS flipflop. When no train is present, light falling on Q1 and Q2 causes them to conduct and so pins 1 and 5 of IC1a and IC1b are low. When a train subsequently passes over Q1 or Q2, it turns off and the corresponding input to the flipflop goes high, causing it to change state. A green LED is connected to one output of the flipflop, while a red LED is connected to the other. This output (pin 4) is also used to control transistor Q5. When pin 4 is high, the relay is on (as is LED 1, since pin 3 of IC1a is low). Conversely, when pin 4 is low, the relay and green LED are off and the red LED is on. The basic circuit will operate colour light signals which use LEDs but not small grain-of-wheat lamps. To drive these, the relay is required. The second section of the circuit, consisting of Q3, Q4, IC1c, IC1d, Q6 and RLY2, operates in exactly the same manner and is used to control the second section of track. If your signals use lamps, you will need to build the com­plete circuit and use the relay contacts to switch the lamps. On the other hand, if you only intend driving LEDs, you can leave out Q5, Q6, R7, R10, D2, D3 and the relays. The MEL12 phototransistors are connected to the board with long leads. Note that the base connections are not used in this circuit. In most cases, the signal for a block will be near the first MEL12 so you will only need to run one wire for LED common, one each for the two LEDs, one for the MEL12 collector and one for the MEL12 emitter. If you get the wrong indication (ie, red instead of green), just swap the LEDs (the relay will now be activated when the red signal shows). You can use the LEDs as indicators on your control panel or you can use them for both signalling and indication by connecting an additional LED in series with the first. Don’t make the wires to the MEL12s and the LEDs any longer than absolutely necessary – some are over two metres long on my layout but if you make them too long, you are inviting interfer­ence problems. It’s a good idea to twist VHF1 RECEIVER +6V VHF1 RECEIVER 0V +6V 0V LED1  LED6  CLOCK1 CLOCK6 Simple 4-step voltage comparator IN +8-15V This circuit provides visual indication of DC input voltag­es over four steps. It can be easily adjusted to suit a range of input voltages simply by changing a few resistors. IC1 is an LM324 quad op amp IC which is wired to form a line of comparators (IC1a-IC1d). The inverting inputs are con­nected up to a resistor string which taps off a 5V reference from a 7805 regulator. This regulator also supplies the power to the circuit. The voltages at the tap-off points are shown on the circuit and, for the resistor values shown, range from 3.4V to 4.6V. The incoming voltage is divided by a 10kΩ trimpot (VR1) and two 10kΩ resistors and the resulting voltage applied to all the non-inverting inputs. When the voltage on a non-inverting input rises above the voltage on the inverting input, the LED for that comparator turns on. Thus, as the input voltage rises, the LEDs turn on in sequence. Conversely, as the input voltage goes down, the LEDs turn off. VR1 is adjusted to give the correct change-over points during the setting-up procedure. With the resistor values, shown the circuit can be easily adjusted to operate in 1V steps over the range 8-11V to serve as a low battery indicator in a car. Power to the circuit can be anywhere between 8 and 15V. The current consumption depends mostly on the number of LEDs that are lit but should be no more than about 25mA.. Darren Yates, SILICON CHIP. 10 16VW 7805 GND OUT 0.1 +5V 5.6k 3 +4.6V 2 4 IC1a LM324 1 560  LED1  5.6k 5 +4.2V 6 IC1b 7 560  LED2  5.6k 10 +3.8V Vin VR1 10k 9 IC1c 8 560  LED3  5.6k 10k 10k 13 +3.4V 12 IC1d 14 560  11 LED4 47k  The circuit for the 4-step voltage comparator is based on an LM324 quad op amp. D1 1N4004 R1 10k R2 10k R3 10k LED1 GRN R4 10k R5 680  14 1 3 IC1a 2 4001 Q1 MEL12  6 12V C1 100 16VW Q2 MEL12 IC1b 4  LED2 RED LED3 GRN  D2 1N4002 R6 680  R7 4.7k RLY1 Q5 BC547 9 Q3 MEL12 IC1c LED4 RED  R8 680  D3 1N4002 RLY2 R9 680  5   10 8  13 Q4 MEL4 12 IC1d 11 R10 4.7k Q6 BC547 7  each pair of wires to­gether to help in this regard. The MEL12s must be placed in natural or artificial light so that the shadow of a passing train switches the circuit. If they are in a tunnel, a source of light will be required (eg, a small lamp or an infrared LED placed high enough above the rails to clear the trains). As an option, you can use the relay contacts to control the supply to a short section of track immediately before the block. When a train enters the block, the supply is removed immediately behind it and is restored only after the train has left. This prevents another train from entering an occupied section. S. Oppermann, George Town, Tasmania. ($40) April 1994  11 SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: dicksmith.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: dicksmith.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: dicksmith.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: dicksmith.com.au Remote control extender for VCRs This simple device will allow you to operate your VCR via its IR remote control from another room in the house. It works by receiving the IR signal from the handpiece & then retransmit­ting it to an IR LED near the VCR via a 2-wire cable. By JOHN CLARKE Many families now have two colour TV sets, one usually located in the living room with a VCR and a second set in the kitchen, rumpus room or one of the bedrooms. But although it’s quite easy to link both TV sets to the VCR (via a 2-way splitter), operating the VCR from the same room as the second set is usually impossible. This Infrared Remote Extender solves that problem. It sits in the same room as the second set and picks up infrared signals from the VCR’s remote 16  Silicon Chip control. This signal is then converted to an electrical signal and sent down a 2-wire cable to an infrared LED located near the VCR in the living room – see Fig.1. Because the signal from the infrared LED mimics the signal picked up by the receiver, the VCR will now respond to any com­ mands from the remote control in the other room. Of course, the extender is not only limited to VCRs – it can be used to re-transmit virtually any IR signal (eg, for CD players or burglar alarms). As shown in the photos, the circuit for the Infrared Remote Extender is housed in a small metal case. An ACKnowledge LED on the front panel lights whenever a signal is received from the remote control, to let you know that the unit is working correct­ ly. There is just one control – an on/ off switch. The rear panel of the device carries two sockets, one for power (12V DC) and the other to allow the cable for the remote infrared LED to be plugged in. Before moving on to the circuit description, we should briefly mention the Infrared Remote Control Extender published in the September 1990 issue. This proved to be an extremely popular project but was not without problems. Based on numerous enquiries from people who had constructed the project, it was clear that the circuit required some component adjustments (mainly around the AGC section) so that it would operate reliably with a variety of infrared controllers. This completely new circuit solves the problems associated with the previous design. How it works Fig.2 shows the circuit schematic. It uses an infrared photodiode (IRD1) to receive the signals and a Plessey SL486 infrared remote control preamplifier (IC1) to amplify these signals. An elaborate AGC circuit based on IC2a provides gain control for the am­ plifier stage inside IC1, while in­verter stages IC3a-IC3e drive the infrared and ACKnowledge LEDs (IRLED1 and ACK). In greater detail, signals from the remote control trans­ mitter are picked up by IR photodiode IRD1 and converted to electrical pulses. These pulses are then filtered by a twin-T filter with a notch frequency of 100Hz to eliminate interference from mains-powered lights and then applied to the differential inputs of IC1 at pins 1 and 16. Normally, the twin-T filter is not required since IC1 provides sufficient attenuation at 100Hz when using its recommended capacitor values to produce a roll-off below 2kHz. However, we have altered the gain of IC1 at low frequencies so that the roll-off begins INFRARED EXTENDER INFRARED LED VCR SECOND RECEIVER MAIN RECEIVER VCR REMOTE CONTROL ROOM 1 ROOM 2 Fig.1: the basic concept. The IR extender picks up infrared light from the VCR’s remote control & converts it to an electrical signal. This signal is then sent down a 2-wire cable & drives an IR LED located in the same room as the VCR. at 666Hz. This is to allow the circuit to amplify signals from those transmitters with outputs centred on 1kHz. The 22µF and 220µF capacitors at pins 2 and 3 respectively of IC1 set the pi functions of two internal gyrator circuits. In low ambient light conditions, the gyrator circuit using the 22µF capacitor is switched into circuit, while in high light condi­tions, the gyrator using the 220µF capacitor takes effect. The remaining capacitors at pins 5, 6 and 15 provide roll-off at frequencies below 666Hz. This low frequency roll-off works in conjunction with Most of the parts are mounted on a small PC board & this must be fitted inside a metal case. Power comes from a 12V DC plugpack supply. April 1994  17 47  10 22 220 2 0.1 3 5 K 6 IC1 SL486  A 6.8k 6.8k OUTPUT 16 REG IN 0.47 15 0.22 TP2 +6V 7 1 IRD1 BPW50 22 10k 4 14 12 AGC 13 680  .015 IC3a 74C14 IC3b 12 13 9 8 IRLED1 CQY89A D2 1N4148 IC3d 100Hz NOTCH 3 100k 13 5 Q2 BC328 B 47 +6V AGC ADJUST VR1 10k FILTER BUFFER 3 5 10 0.1 9 IC2d 8 100k 6 4 IC2b 7 2 2.7k 1 IC2c INFRARED REMOTE EXTENDER Automatic gain control The automatic gain control (AGC) output at pin 8 is normal­ly connected to a 0.15µF capacitor. This filters the amplified signal and controls the gain of IC1 to prevent signal overload. Unfortunately, this AGC system is only suitable for remote controls which produce very narrow pulses of infrared light. In most cases, however, the transmission code consists of bursts of signal which can be anywhere between 1kHz and 100kHz in frequen­ cy. This type of coding produces too much AGC for IC1, thereby rendering the amplifier ineffective. For this reason, we have completely revamped the AGC cir­cuit so that the 18  Silicon Chip C 12VDC INPUT BUFFER S1 1M 1000 16VW D3 B A K A K AMPLIFIER Fig.2: each time an IR light pulse is received, pin 9 of IC1 switches high & drives IRLED1 via IC3a & IC3b. A sample of the output pulse from pin 9 is also fed to IC2a which works with IC2b, IC2c & IC2d to provide automatic gain control. the 100Hz twin-T filter to provide a high degree of attenuation for 100Hz signals. If this were not done, noise signals from mains-powered lighting could degrade the receiver’s sensitivity and reduce its effective range. +6V Q1 BC338 B E 22 BP DC OFFSET -6V TP1 +6V E C 3.3k 100k 11  0.1 14 IC2a LM324  K ACK LED2 6 680  A  D1 1N4148 12 220k IC3e 4 A K A 8 3.6k POWER LED3 680  IC3c 22 -6V 47k 10 7 9 .047 0.22 14 11 receiver will work with a wide range of remote control transmitters without the hassle of fiddly adjustments. The modified AGC circuit works as follows. First, the amplified output at pin 9 of IC1 is attenuated by about 20% using a voltage divider (47kΩ and 220kΩ) and applied to the non-inverting input of op amp IC2a. This op amp is connected as a unity gain buffer and simply provides current drive for an AGC filter consisting of D1 a 100kΩ resistor and a 47µF capaci­tor. In operation, IC2a and the AGC filter act as a peak detec­tor for the output signal that appears at pin 9 of IC1. Each time a signal is received, the 47µF capacitor charges via D1 and is then discharged by the 100kΩ resistor so that the filter output decays after a few seconds. This filtered signal is applied to op amp IC2b which oper­ates with a gain of 11, as set by the 1MΩ and 100kΩ E C VIEWED FROM BELOW 1N4004 ALL VOLTAGES MEASURED WITH RESPECT TO GROUND feedback resistors. The 22µF capacitor across the feedback path filters the output to provide the required AGC response time. Bias for the inverting input of IC2b comes from the AGC adjust pot (VR1) and is applied via unity gain buffer stage IC2d. IC2c and transistor Q1 together form a high-current buffer stage for the output of IC2b. A 10kΩ pullup resistor provides the collector load for Q1, while feedback is provided from Q1’s collector to the non-inverting input of IC2c at pin 3. The buffer is made stable by the 22µF capacitor at pin 8 of IC1, the capaci­tor effectively slowing down the open loop gain of the stage. Because IC2c and Q1 operate with unity gain, Q1’s collector voltage follows the voltage fed to IC2c. Thus, under no-signal conditions, pin 2 of IC2c is at ground and so pin 1 goes high and turns on Q1 (ie, Q1’s collector goes low). Conversely, when a signal is received, the voltage on pin 2 rises and Q1 progres­sively turns off. As a result, Q1’s collector voltage 12VDC A 47uF IC1 SL486 IC2 LM324 680  1 220uF 1 680  3.3k 22uF BP 680  Q1 LED2 K 1000uF 0.1 22uF 0.1 22uF D3 D2 IC3 74C14 .015 3.6k 0.22 0.22 1 K A Q2 TP2 100k A K IRD1 1M LED3 2.7k K TP GND K 22uF 100k 10uF VR1 0.1 47k .047 6.8k 0.47 6.8k 220k S1 100k D1 K K LED3 LED2 A A 10k 47  TP1 K A IRLED1 Fig.3: here’s how to wire up the IR Remote Extender. Take care with component orientation & note that IRD1 is mounted with its leads untrimmed so that it can be adjusted to line up with its viewing hole in the front panel. The board must be fitted inside a metal case which is connected to the circuit via the solder lug (at the top of the diagram). rises so that it remains equal to the voltage on pin 2. The output from this buffer stage is fed to the AGC pin (pin 8) of IC1. This pin has a low input impedance but Q1 provides sufficient drive to overcome the internal AGC level. The AGC action works like this: when the output signal from IC1 at pin 9 exceeds the voltage preset by VR1, the AGC voltage increases on pin 8. This reduces the gain of IC1 and so the signal level is reduced. Conversely, when the output from IC1 falls below the preset AGC voltage, the AGC voltage at pin 8 falls and the gain increases. Signal drive The resulting signal from pin 9 of IC1 is squared up by Schmitt trigger IC3a and inverted by IC3b. This then drives the infrared LED (IRLED1) via a 680Ω resistor. Thus, each time a pulse of infrared light is received, IC3b’s output switches high and pulses IRLED1. LED 2 (ACKnowledge) and its associated circuit provide visible indication that a signal has been received. However, LED 2 cannot be driven by IC3b because the pulses from this stage are so short. To overcome this problem, IC3a’s output is inverted by IC3c and this drives a pulse extender circuit consisting of diode D2, a 0.1µF capacitor and 100kΩ resistor. Each time IC3c’s output goes high, the 0.1µF capacitor charges via D2 and buffer stages IC3d and IC3e drive the ACKnowledge LED via a 680Ω resistor. Conversely, when IC3c’s output goes low (ie, when no signal is being received), the 0.1µF capacitor discharges via the 100kΩ resistor and the ACK­ nowledge LED goes out. Thus, depending on the code from the transmitter, LED 2 will flicker on and off but at a much slower rate than IRLED1 due to the time constant formed by the 100kΩ resistor and the 0.1µF capacitor in the pulse extender network. Power supply Power for the circuit is derived from a 12V DC plugpack supply. This is applied via reverse polarity protection diode D3 and decoupled by a 1000µF capacitor. Note that the resulting supply lines have been labelled +6V and -6V, rather than +12V and 0V. This has been done to simplify the supply labelling for the rest of the circuit, particularly around the op amps. IC1 has an internal regulator which RESISTOR COLOUR CODES ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ No. 1 1 3 1 1 2 1 1 1 3 1 Value 1MΩ 220kΩ 100kΩ 47kΩ 10kΩ 6.8kΩ 3.6kΩ 3.3kΩ 2.7kΩ 680Ω 47Ω 4-Band Code (1%) brown black green brown red red yellow brown brown black yellow brown yellow violet orange brown brown black orange brown blue grey red brown orange blue red brown orange orange red brown red violet red brown blue grey brown brown yellow violet black brown 5-Band Code (1%) brown black black yellow brown red red black orange brown brown black black orange brown yellow violet black red brown brown black black red brown blue grey black brown brown orange blue black brown brown orange orange black brown brown red violet black brown brown blue grey black black brown yellow violet black gold brown April 1994  19 gives about 6V between the positive rail and ground. This 6V supply provides power for the rest of the circuit, with the exception of the LEDs. Transistor Q2 acts as a buffer stage for the regulator ground supply. Its emitter is effectively at ground (actually 0.7V), which means that the LED currents flow through Q2 to the -6V rail. This prevents the regulator inside IC1 from being overloaded by the LED currents (since these currents do not flow to ground). Finally, a 22µF capacitor is used to decouple the 6V sup­ply, while a 47Ω resistor and a 10µF capacitor provide additional supply line decoupling for IC1 to prevent noise from affecting the sensitive amplifier stages. PARTS LIST 1 K&W metal case, 127 x 68 x 39mm 1 PC board, code 15303941, 59 x 115mm 1 self-adhesive label, 63 x 33mm 1 self-adhesive label, 63 x 11mm 1 12VDC 300mA plugpack 1 2.5mm panel mount DC socket 1 2-pin panel mount DIN socket 1 2-pin DIN line plug 1 SPDT toggle switch (S1) 2 5mm LED bezels 1 10kΩ horizontal trimpot (VR1) 4 9mm tapped standoffs 1 solder lug 4 3mm dia. x 15mm long screws 5 3mm dia. x 9mm long screws 9 3mm nuts 1 10-metre length 2 x 14/0.19 twin cable 1 350mm-length twin rainbow cable 1 120mm-length twin hookup wire 1 100mm green hookup wire (for earth lead) 1 50mm-length 0.8mm tinned copper wire 12 PC stakes 4 small rubber feet Semiconductors 1 SL486 infrared preamplifier (IC1) 1 LM324 quad op amp (IC2) 1 74C14, 40106 hex Schmitt trigger (IC3) 1 BC338 NPN transistor (Q1) 1 BC328 PNP transistor (Q2) 2 1N4148, 1N914 signal diodes (D1,D2) 1 1N4004 1A diode (D3) 1 BPW50 infrared photodiode (IRD1) 1 CQY89A, LD271 infrared LED (IRLED 1) 1 5mm green LED (LED 2) 1 5mm red LED (LED 3) Capacitors 1 1000µF 16VW PC electrolytic 1 220µF 16VW PC electrolytic 1 47µF 16VW PC electrolytic 3 22µF 16VW PC electrolytic 1 22µF 50VW bipolar 1 10µF 16VW PC electrolytic 1 0.47µF MKT polyester 2 0.22µF MKT polyester 3 0.1µF MKT polyester 1 .047µF MKT polyester 1 .015µF MKT polyester Construction Most of the parts are mounted on a PC board coded 15303941 and measuring 59 x 115mm. Fig.3 shows the assembly details. Begin the assembly by fitting PC stakes to all the external wiring points and to the three test points (TP1, TP2 & TP-GND). This done, install the wire links, resistors and diodes. Be sure to use the correct diode at each location and make sure that it is correctly oriented. Now install the ICs, transistors and capacitors. Note that the ICs are all oriented in the same direction. The 22µF bipolar capacitor can be installed either way around but take care with the orientation of the remaining electrolytic capacitors. Check the transistor type numbers carefully when install­ing these parts Resistors (1%, 0.25W) 1 1MΩ 1 3.6kΩ 1 220kΩ 1 3.3kΩ 3 100kΩ 1 2.7kΩ 1 47kΩ 3 680Ω 1 10kΩ 1 47Ω 2 6.8kΩ Miscellaneous Heatshrink tubing, solder, insulation tape, etc. + + + ON ACK POWER + INFRARED LED SOCKET (CENTRE ANODE) INFRARED REMOTE EXTENDER 12VDC POWER INPUT (CENTRE +) ▲ Fig.4: here are the full-size artworks for the front & rear panels. 20  Silicon Chip Left: bend the leads of the infrared photodiode (IRD1) so that its face lines up with the matching front-panel cutout but make sure that its leads don’t short against the metalwork. The infrared LED (IRLED1) is mounted at the end of the 2-wire cable. It can be installed in a small case or taped in some inconspicuous location near the VCR. Note that the anode lead of the LED goes to the centre pin of the DIN plug. on the PC board. Q1 is an NPN type while Q2 is a PNP type, so don’t get them mixed up. Push the transistors down as far as they will comfortably go before soldering their leads. The board assembly can now be completed by installing the infrared photodiode (IRD1). This device should be mounted with its leads untrimmed so that it can later be bent into position to align with the hole in the front of the case. Fig.1 shows the pin connection details for photodiode. Final assembly A standard K&W metal case measuring 127 x 68 x 39mm is used to house the PC board. Attach the front and rear panel labels to the case (see photos), then drill out the mount­ing holes for the power switch (S1) and for the Power and ACK LEDs. The square cutout for IRD1 is made by first drilling a small pilot hole and then filing this to shape with a small three-cornered file. This done, attach a short piece of insulating tape to the inside of the case beneath the hole to prevent IRD1’s leads from shorting to the metalwork – see photo. Moving now to the rear panel, the two sockets must be mounted high up to provide sufficient clearance to the PC board. Again, use small pilot holes to begin with, then enlarge these to size using a tapered reamer. A three-cornered file will be required to provide the final shape for the DC socket. Once the sockets fit their respective holes, mark and drill the four holes for the mounting screws. The PC board is mounted in the case on four 9mm-long stand­offs. Use the board as a template for marking out its mounting holes, then drill these holes to 3mm. You will also have to drill a mounting hole for the earth solder lug – see Fig.3. Fig.5: check your etched PC board against this full-size artwork before installing any of the parts. Before installing the PC board in the case, you will need to wire up and install the power LED (LED 3). Use twin rainbow cable for the LED wiring and insulate the leads with heatshrink tubing to prevent shorts to the underside of the PC board. This done, secure the earth solder lug to the case and solder a short length of hookup wire to it. The PC board can now be installed in the case and the wiring completed using light-duty hookup wire. Check your work carefully against Fig.3 to prevent any mistakes. The remote IR LED (IRLED1) is connected to the receiver via a long length of light-duty speaker cable. This LED can be either mounted in a separate small case or taped to an inconspicuous location near the VCR. Be sure to connect the anode lead of the IR LED to the centre pin of the DIN plug. Testing To test the circuit, apply power from a plugpack and check that the power LED lights. Assuming all is well, check the vol­tage between TP2 and the GND terminal – the meter should read between 5.9V and 6.5V DC. Next, activate the remote control transmitter and check that the ACK­ now­ledge LED flickers when a button is pressed. If it does, connect your multimeter between TP1 and GND, activate the remote control, and adjust VR1 for a reading of 2V. This adjustment sets the AGC level. The maximum range for the receiver can now be checked. This will vary according to the remote control transmitter but you should be able to achieve at least five metres. Finally, plug in the lead to the infrared LED and check that it correctly activates your VCR in the other room each time a transmitter button is pressed. Note that the infrared LED should be placed within one metre of the VCR’s sensor for best results. For some remote controls, you may need to tweak the AGC level (using VR1) to obtain the maximum range. This should be done on a trial and error basis, although the final setting should not be too far from the setting arrived at earlier. In some cases, it may also be necessary to move the receiver away from the TV set to prevent interference from the line flyback pulses which can desensiSC tise the front-end circuitry. April 1994  21 Sound & lights for level crossings This Sound & Lights module is intended to be controlled by the Level Crossing Detector published last month. It drives LEDs or miniature incandescent lamps for the level crossing signs & produces a most convincing bell sound as an accompaniment. By JOHN CLARKE Apart from the lifelike effect of flashing lights, the particular attraction of this project is the uncanny sound of the bell. Anyone who has stopped at a level crossing on a rainy or foggy night will recall the eerie sound of the bells as their rate of ringing wavers up and down. This circuit reproduces this effect and thereby greatly adds to the realism. The Sound & Lights module comprises an on/off control, a lamp flasher and circuitry to generate the bell sound, as depict­ed in Fig.1. The on/ 22  Silicon Chip off control (IC2) prevents the circuit from operating unless its input is low. The lamp flasher alternately flashes the two lamps at a rate of about twice a second which is close to the rate used on typical level crossing lights. The bell sound circuitry is more complex and comprises a ringing oscillator which provides the bell tone, a bell rate oscillator which determines the rate at which the bell is struck, and a warble oscillator to vary the rate of the bell rate oscillator. The ringing oscillator produces a pure sinewave whenever the bell rate oscillator pulses its input. The sine­wave starts with a high amplitude which dies away in volume until the next pulse from the bell rate oscillator. The amplifier stage (IC3d) boosts the signal to a suitable level for the loudspeaker. It produces only a small amount of drive, just sufficient to make the bell sounds audible when you are close to the speaker which will be concealed under the layout close to the level crossing. The sound level must not be too loud, otherwise it will be “out of scale” with the rest of the layout and would quickly become annoying. Now have a look at the complete circuit of the Sound & Lights module, as shown in Fig.2. We’ll discuss the flasher section first. It employs IC1, a 4093 quad 2-input Schmitt NAND gate package. IC1a is used as a conventional Schmitt trigger oscillator and its frequency is determined by the 47µF capacitor at pins 1 & 2, together with the series 2.2kΩ resistor and 50kΩ trimpot VR1. IC1c inverts the output of IC1a so that the two Schmitt triggers constitute a two-phase square wave oscillator with the outputs fed to gates IC1b and IC1d. These two gates are enabled or disabled by IC2a which can be thought of as the master switch; it is part of the on/off control referred to earlier. When pins 9 & 12 of IC1 are pulled low by IC2a, their out­puts at pins 10 & 11 are high and the circuit is effectively disabled. When pins 9 and 12 are high, the alternating square wave signals from pins 3 & 4 are fed through to transistors Q1 and Q2 to drive the level crossing lights. Note that there are four lights in total, two for each side of the crossing, and they must be cross-connected so AMPLIFIER IC3d BELL RATE OSCILLATOR IC3a ON/OFF IC2b,c RINGING OSCILLATOR IC3c WARBLE OSCILLATOR IC3b ON/OFF CONTROL INPUT SPEAKER IC2a LIGHTS LAMP FLASHER Fig 1 Fig.1: the Sound & Lights module uses three oscillators to produce the bell sound and another for the lamp flasher. Fig.2 (below): just three ICs are used in the circuit for the Sound & Lights module. One of the op amps in the LM324 package drives the loudspeaker directly via a 68Ω resistor and 1µF capacitor. +10V 0.1 10 10 OSCILLATOR ADJ VR 3 500W 100k 100k 100k 10k 100k 6 5 IC3b LM324 10 100k 100k 10 IC2c 11 RATE VR2 50k 11 2 8 27k +10V 10 IC2b 8 .0047 100k 10k 14 9 6 +11.5V D1 1N4004 2.7k 12V INPUT IC2a 4066 1 68  1 IC3d 12 1M BELL STRIKER RATE OSCILLATOR 10k 3 14 .0047 47k +10V 13 10 33k IC3c D2 1N418 100  WARBLE OSCILLATOR 8 IC3a 9 100k 10k 4 12 3.3M 7 10k 68  +10V ZD1 10V 1W 1000 16VW 2 13 7 INPUT +10V 1 1 IC1a 4093 IC1b 13 3 2 FLASHER RATE VR1 50k 12 5 2.2k IC1c 4 8 6 B 47 A K 9 C VIEWED FROM BELOW 14 IC1d +11.5V 2.2k 11 22k 10 22k B Q1 BC557 7 2.2k E B Q2 BC557 C 1 LAMP 1A LAMP 1B LEVEL CROSSING LIGHTS AND BELL E C 2 LAMP 2A LAMP 2B 1 LED 1A LED 1B A A  K 2 LED 2A LED 2B A A  K OPTIONAL LED LIGHTS   K K 1k 1k April 1994  23 Fig.4: the wiring diagram. Note that IC3 is oriented differently to the other two integrated circuits. D1 1uF 22k 2.2k GND 100k 2.7k PARTS LIST 1 PC board code, 15203932, 150 x 97mm 1 10-way PC mount screw terminal block 1 4-way PC mount screw terminal block 1 small 8-ohm loudspeaker 2 50kΩ horizontal trimpots (VR1, VR2) 1 500Ω horizontal trimpot (VR3) Semiconductors 1 4093 quad NAND Schmitt trigger (IC1) 1 4066 quad analog switch (IC2) 1 LM324 quad op amp (IC3) 2 BC557 PNP transistors (Q1,Q2) 1 1N4004 1A diode (D1) 1 1N4148 diode (D2) 1 10V 1W zener diode (ZD1) 4 2mm red LEDs (see text) Capacitors 1 1000µF 16VW electrolytic 1 47µF 16VW electrolytic 4 10µF 16VW electrolytic 1 1µF 16VW electrolytic 1 0.1µF MKT polyester 2 .0047µF MKT polyester Resistors (1%, 0.25W) 1 3.3MΩ 5 10kΩ 1 1MΩ 1 2.7kΩ 8 100kΩ 3 2.2kΩ 1 47kΩ 2 1kΩ 1 33kΩ 1 100Ω 1 27kΩ 2 68Ω 2 22kΩ 24  Silicon Chip 2.2k D2 22k 10k 10k TO LAMPS 1 and is connected to the threshold voltage input 2x.0047 (pin 10) of IC3a via a 3.3MΩ TO LED CATHODES VR1 VR3 Q2 resistor. This slightly varies the threshold voltage of the bell striker oscillator (IC3a) 100k 1k 2.2k to provide a small variation 1k in the pulse rate. The resulting pulses from IC3a drive the centre leg of that each pair of lights on the level a T-section filter connected across the crossing signals flash alternately. 1MΩ feedback resistor of op amp IC3c. The circuit can be made to drive This op amp is adjusted using trimpot red LEDs rather than miniature incan- VR3 so that it is just on the verge on descent lamps. We have shown the oscillation. As a result, each time it alternative connection for LEDs with receives a pulse from IC3a, it briefly a 1kΩ current limiting resistor for each bursts into oscillation. cross-connected pair. This effect can be seen in the oscilloscope photograph of Fig.3. The top Bell oscillators trace of this photograph shows the The bell circuit comprises op amps very brief pulses which trigger IC3a IC3a-IC3d. IC3 is an LM324 quad into operation, while the lower trace op amp and IC3a is connected as a shows the bursts of oscillation which Schmitt trigger oscillator to provide come at varying intervals. the bell strike rate. It operates as fol­ Amplifier stage lows. Initially, the 10µF capacitor at pin Op amp IC3d functions as an am9 is discharged and the output of plifier to drive the loud­speaker. As IC3a is high. Pin 10 of IC3a is held at explained previously, only a modest about +6.6V by the 100kΩ resistors power output is needed and so an op to ground, to the +10V supply and amp is quite adequate. to the op amp’s output (pin 8). When IC3d is biased at half supply via the power is applied, the capacitor begins two 10kΩ voltage divider resistors at to charge via diode D2 and the 100Ω pin 3, with bypassing provided by resistor. When its voltage reaches the 6.6V threshold, the output at pin 8 goes low and pin 10 now drops to about +3.3V (due to the loading effect of the 100kΩ resistor to pin 8). The 10µF capacitor now discharges via the 47kΩ resistor and trimpot VR2 until it reaches the 3.3V threshold, at which point the op amp output again goes high. Thus, we have an oscillator which produces very short pulses at a rate of about twice a second (depending on the setting of trimpot VR2). Fig.3: the top trace of this photograph IC3b is also set up as a Schmitt shows the very brief pulses which trigger oscillator and this charges and trigger IC3a into operation while discharges the 10µF capacitor at pin the lower trace shows the bursts of 6 via a 100kΩ resistor. The oscillator oscillation which come at varying output in this case is a square wave intervals. 47uF 33k VR2 ZD1 IC1 4093 2x10uF 1 1M 1 10k IC3 LM324 10uF 100k 0.1 47k IC2 4066 100  + +12V TO SPEAKER 3.3M + GND Q1 1 100k SPARE INPUT 10k GND 100k INPUT 100k 10uF 68  27k 68  10k 100k 100k 100uF TO LAMPS 2 Fig.5: actual size artwork for the PC board. Check your board carefully against this pattern before mounting any of the parts. the asso­ciated 10µF capacitor. IC3c is also biased from this voltage divider, via trimpot VR3. The bell signal from IC3c is fed to IC3d via analog switch IC2b which is closed while its pin 6 is high. Since pin 6 of IC2b is controlled by the same signal line which enables the flasher circuitry, it ensures that the two circuits switch on and off at the same time. One analog switch has not been mentioned so far and that is IC2c which is connected between the inverting and non-inverting inputs of IC3d. IC2c is closed (ie, conducting) whenever IC2b is open. Thus, when the bell signal is not being fed to IC3d, switch IC2c ensures that the amplifier stage is fully muted. IC3d drives the loudspeaker via a 68Ω resistor which limits the current, while the 1µF capacitor prevents any DC from flowing through the loudspeaker’s voice coil. Construction All the components for the Sound & Lights module are assem­bled onto a PC board measuring 150 x 97mm and coded 15203932. Before you begin any soldering, check the board thoroughly for any shorts or breaks in the copper tracks and repair any faults that you do find. This done, install the resistors, link, PC stakes (if used) and ICs. Note that IC3 is oriented differently to the other ICs. Now install the transistors, zener diode and diodes, making sure that they are all oriented correctly. The trimpots and capacitors can be mounted now, taking care with the orientation of the electrolytic capacitors. Finally, if you are using terminal blocks, mount these as well. Once the PC board has been assembled, it is ready for testing. Note that the power for the PC board should be obtained from a 12V DC supply. If you built the Walkaround Throttle de­scribed in the April & May 1988 issues of SILICON CHIP, or the IR Remote Controlled Throttle described in the April, May & June 1992 issues, you won’t need a separate supply as this facility is already provided. Make sure that you have your multimeter handy, so that you can measure the DC voltages on the PC board. Connect an 8Ω loud­speaker and two lamps (or LEDs) to the board in their designated positions. Now apply power and check that the voltage across ZD1 is close +10V. If not, switch off and find the fault before applying power again. Even though the voltages are all correct, the circuit should not be operating unless the you have a jumper wire in the input terminal block, to connect the input to GND. With the input connected to GND, the lamps should be flash­ing alter- nately and you should be able to adjust the rate of flashing with trimpot VR1. The correct rate is about twice a second. You will probably also find that the loudspeaker is howling and this can be stopped by rotating trimpot VR3 clockwise, after which it should sound like “dink dink dink dink ..”. By carefully rotating VR3 anticlockwise, you will reach a point where the loudspeaker sounds just like a bell. You can also adjust the rate at which the bell is struck by rotating trimpot VR2 but after doing that, you may need to tweak VR3 again for the best effect. With the board complete and running, you can install it underneath your layout and operate it with a switch when required or have it controlled by the Level Crossing Detector board de­scribed last month. Finally, we should comment about the size of the LEDs used for level crossing signs. Ideally, these should be as small as possible. If you have an HO-scale layout (1:87), even 3mm LEDs are too large as they will “scale out” to a diameter of 261mm. Ideally, you should use 2mm LEDs as made by Hewlett Packard (they make them in red, orange, yellow and green). You can purchase these miniature LEDs from HT Electronics, PO Box 491, Noarlunga Centre, South AustralSC ia 5168. Phone (08) 326 5590. April 1994  25 SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.altronics.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.altronics.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.altronics.com.au Need a dual supply regulator in a hurry but don’t have any LM317 or 7805 3-terminal regulators handy? This simple circuit can provide regulated supply rails from ±5V to ±12VDC at up to 800mA. I F YOU’RE NOT in the component buying business, then you’ll probably be unaware that there has been a severe world-wide shortage of parts during the last 12 months – particularly 3-terminal regulators. Now since these devices get a guernsey in just about every project designed, we recently decided to see if we could come up with some sort of replacement based on readily available components. Since doing this work, the supply situation has vastly improved but we still feel that the design may be suitable for many applications. The fact that it uses only junkbox parts is a major plus. All the parts for the regulator are built onto a small PC board. This contains everything necessary to convert the AC voltage from a centre-tapped mains transformer to regulated plus and minus DC supply rails, including a bridge rectifier and filter capacitors. It will provide an output voltage of between ±5V and ±12V DC at currents up to 800mA. Circuit diagram Fig.1 shows the circuit diagram for the Dual Regulated Power Supply. It uses four power diodes, an LM358 dual op amp, a zener diode, a couple of transistors and sundry resistors and capacitors. Power is derived from a 12-24V centre-tapped mains transformer. Its output is fed to a bridge rectifier consisting of diodes D1-D4 to produce positive and negative rails which are then filtered using two 470µF electrolytic capacitors. These rails are then fed to the collectors of transistors Q1 and Q2 respectively and are also used to power the dual op amp (IC1). Discrete dual supply voltage regulator By DARREN YATES The assembled PC board can form the basis of a simple variable power supply or can be used to provide fixed regulated supply rails from ±5V to ±12V DC. April 1994  29 R2 10k 6 4x1N4004 A 240VAC N D4 R1 10k D1 5 F1 2A 6-12V Q1 BD139 8 7 100  IC1a LM358 B E D4 .047 1N4148 1k C +VOUT 0V 6-12V D3 470 25VW D2 10 16VW ZD1 4.7V 400mW 470 25VW Fig.1: the regulated positive supply rail is derived by using ZD1 to set a reference voltage on pin 5 of inverting amplifier stage IC1a. This in turn drives current amplifier stage Q1. Inverting amplifier stage IC1b & current amplifier Q2 are used to derive the negative rail. GND PLASTIC SIDE 100k 470 25VW E C 470 25VW 100k -VOUT .047 2 B 1 IC1b 3 100  4 F2 2A B Q2 BD140 E C DUAL REGULATED POWER SUPPLY IC1a and its associated zener diode (ZD1) form the heart of the regulation circuit. This op amp is connected as a bootstrapped-diode reference source and drives current amplifier stage Q1. IC1b, on the other hand, simply functions as a unity gain inverter stage; it drives current amplifier Q2 Zener diode ZD1 functions as the reference element and is part of a positive feedback path around IC1a. This feedback path may not be all that clear at first glance – it starts at the output of IC1a (pin 7) and goes via the 100Ω resistor, the base-emitter junction of Q1, diode D4 and the 1kΩ resistor, before ending at the non-inverting input (pin 5). This loop ensures that the output voltage remains constant. The 10µF capacitor across ZD1 filters out any noise on the line and improves the regulation. Note that it is necessary to include the transistor (Q1) in the feedback loop so that the op amp can compensate for the voltage drop across the base-emitter junction to give the required output voltage. Setting the output voltage for the positive rail is now just a case of selecting the negative feedback network to set the gain of IC1a. This feedback network consists of two resistors (R1 and R2) connected in the usual way; ie, one from the output to the inverting input (pin 6) and the other from the inverting input to ground. 30  Silicon Chip The formula for the output voltage is: Vout = 5.3V x (R2 + R1)/R1 where the 5.3V reference is equal to the voltage across ZD1 plus the voltage across D4 (ie, 4.7 + 0.6 = 5.3V). With the current values, IC1a’s gain is set to two and so the output voltage is set to 10.6V. However, this can be easily PARTS LIST 1 PC board, 04103941, 107 x 53mm 6 PC stakes 2 M205 (2AG) fuse clips 2 M205 2A fuses 2 Micro-U heatsinks 1 centre-tapped mains transformer to suit (see Table 1) Semiconductors 1 LM358N dual op amp IC 1 BD139 NPN transistor 1 BD140 PNP transistor 1 4.7V 400mW zener diode (ZD1) 4 1N4004 rectifier diodes 1 1N914 signal diode Capacitors 4 470µF 25VW electrolytic 1 10µF 16VW electrolytic 2 0.047µF 63VW MKT polyester Resistors (0.25W, 1%) 2 100kΩ 1 1kΩ 2 10kΩ 2 100Ω altered by changing the value of R1, R2 or ZD1. The negative rail is much simpler to produce because all we need do is invert the output of the positive rail. This is done by feeding the voltage on the emitter of Q1 to the inverting input (pin 2) of IC1b via a 100kΩ resistor. As previously mentioned, IC1b functions as a unity gain inverting amplifier. Its output at pin 1 drives PNP power transistor Q2 via a 100Ω current limiting resistor. As before, the output transistor is included in the feedback loop to ensure that its base-emitter voltage is compensated for. In this way, the negative rail mirrors the voltage on the positive rail. The two .047µF capacitors connected across the base-emitter junctions of Q1 and Q2 reduce the sensitivity of the circuit to noise or glitches and improve the regulation. The final outputs are taken from the emitters of Q1 and Q2 and filtered by two 470µF capacitors. A maximum of 800mA can be supplied by both sections. Construction All of the components for the Discrete Power Supply, including the two 2A fuses, are installed on a PC board coded 04103941 and measuring 107 x 53mm. Before you begin construction, it’s a good idea to check the PC board TABLE 1 1k R2 10k F1 D1-D2 470uF 0V IC1 LM358 D3-D4 470uF AC2 D5 470uF ZD1 R1 10k AC1 .047 100W Q1 10uF 100k +VOUT 0V 100k 470uF -VOUT Q2 Fig.2: install the parts on the PC board as shown here & note that small finned heatsinks should be fitted to Q1 & Q2. Resistors R1 & R2 are selected to set the required output voltage – see text. Fig.3: this is the full-size etching pattern for the PC board. for any shorts or breaks in the tracks. You can do this by carefully checking your etched board against the full-size pattern. Generally, there won’t be any problems here but it’s always a good idea to make sure. Begin the board assembly by installing the two wire links, followed by the resistors, diodes and capacitors. Be sure not to confuse the zener diode with the rectifier and signal diodes. After that, install the IC and power transistors. Be particularly careful with these components – check the orientation of the IC carefully and note that the transistors are installed with their plastic faces towards the adjacent .047µF capacitors. Transformer 5V 12V CT 6V 15V CT 8V 18V CT 12V 24V CT .047 100  F2 DC Output (V) Note also that Q1 is an NPN transistor while Q2 is a PNP type, so be sure to use the correct transistor at each location. Finally, solder in six PC stakes at the external wiring points, install the fuse clips and bolt two small finned heatsinks to the power transistors. There’s no need to isolate the transistors from the heatsinks but don’t let them short against any of the other parts on the board. To test the circuit, you need a centre-tapped mains transformer (or you can use an AC plugpack supply with a centre tap). Table 1 shows the transformer input voltage you need for a given DC output voltage. Wire up the secondary windings of the transformer to the PC board as shown on the overlay diagram and the primary to a mains terminal block. Warning: use extreme caution when installing the mains wiring – 240VAC can kill! The transformer and the PC board should be mounted inside a metal case and this must be securely earthed. Cover all mains connections with heatshrink tubing to avoid the possibility of electric shock. Before applying power, check your wiring carefully for any wrong connections. Once you’re sure that everything is OK, switch on and check the output voltage with your multimeter. If you have used the values shown on the circuit, you should get a reading of about 10.6V on both rails with respect to ground (this will depend on the exact voltage across the zener diode). If need be, you can substitute a trimpot for resistor R2 and trim the output voltage until it is exactly what you require. A variable supply By replacing R2 with a 20kΩ linear potentiometer, you can make a simple dual-tracking variable power supply capable of covering the range from ±5V to about ±12VDC. The circuit could thus form the basis of a very useful benchtop power supply for powering experimental lash-ups. For lower output voltages, you could replace ZD1 with a number of signal diodes. If only one diode is used, the output voltage will be about ±2.4V. Remember, the formula for the output voltage is: Vout = (VZD1 + VD4) x (R2 SC + R1)/R1. RESISTOR COLOUR CODES ❏ ❏ ❏ ❏ ❏ No. 2 2 1 2 Value 100kΩ 10kΩ 1kΩ 100Ω 4-Band Code (1%) brown black yellow brown brown black orange brown brown black red brown brown black brown brown 5-Band Code (1%) brown black black orange brown brown black black red brown brown black black brown brown brown black black black brown April 1994  31 This universal preamplifier can be easily constructed for use with a magnetic cartridge, cassette deck or a dynamic microphone. It uses a single dual op amp IC & has very low dis­tortion. By DARREN YATES Low-noise universal stereo preamplifier T HIS PROJECT WAS borne out of the recent news that National Semiconductor has discontinued its LM380 series of stereo pream­ plifier ICs. These have been around since the early 1970s and have been popular with enthusiasts for all sorts of projects. In fact, these devices were not all that good by today’s standards which is another reason to produce an up-to-date design. Our little universal preamp uses the industry standard LM833 dual op amp IC which has very low noise and distortion. Perhaps the prime use will be for those people who have an in­tegrated stereo amplifier which they are quite keen on but which has a phono or tape preamp which could be improved. And that applies to the phono preamps in a great many amplifiers. They weren’t designed to 32  Silicon Chip give the minimum noise, minimum distortion and the greatest overload margin. In fact, about the best thing you can say about the preamplifier stages in many older amplifi­ers is that they are still working. By comparison, the performance of the design presented here is far better than most preamplifiers in most stereo amplifiers – that’s a pretty ambitious statement but it is true nonetheless. How do you decide whether it would be worthwhile to upgrade your amplifier’s preamplifier. That is fairly easy to determine, pro­viding you still listen to vinyl records. Just set your amplifier’s controls to their normal settings and listen for hiss with no record playing. Can you hear hiss from the loudspeaker (or headphones) at your normal listening position? If so, does this hiss greatly reduce or disappear when you rotate the volume control to its minimum setting? If the answer to both questions is yes, then it is likely that your existing preamplifier produces more than its fair share of noise. This new design is extremely quiet so you are sure to hear a reduction in hiss. Even if you don’t need to upgrade your existing amplifier’s preamplifier, you may still have an application for the design presented here. For example, you may want to run two turn­tables. If your amplifier only has one pair of phono inputs, you could use this external preamplifier for the additional turntable and then feed its outputs to one pair of the line inputs of the stereo amplifier. Alternatively, you may have an audio mixer which does not have a phono preamplifier or you may wish LEFT INPUT +15V L1 150  100k 47 BP 3(5) 100pF 100k 2(6) 8 1(7) IC1a LM833 0.33 1M 4 L1 : 4T, ENCU WIRE ON PHILIPS 4330 030 3218 FERRITE BEAD 100  LEFT OUTPUT -15V IC PIN NUMBERS IN BRACKETS ARE FOR RIGHT CHANNEL R1 16k R2 200k C1 .0047 C2 .015 R4 390  47 BP R1 0W +15V +15V R3 3.6k C3 .015 R1 0W R2 200k R4 200  47 BP 0.1 GND 0V 0.1 -15V R2 200k -15V R4 390  C2 22pF 47 BP UNIVERSAL PREAMPLIFIER Fig.1: the circuit is shown with three different feedback networks: one for a magnetic cartridge (top); one for tape or cassette decks (centre); & a third for microphones (bottom). The inductor, series resis­tor & 100pF shunt capacitor at the input form a filter circuit to remove RF interference signals. to incorporate it into a public address system. We have also shown how this preamp could be used with a tape deck which does not have its own playback electronics or where the existing tape preamp is unduly noisy. Finally, this design can function as a high-quality micro­phone preamplifier for use with cassette decks (which normally don’t have microphone inputs) or in a public address system. We’re presenting this universal preamp as a PC board only, leaving you with the opportunity to install it anywhere you have space for it. The major rule is to keep it away from any mains wiring or transformers. This will reduce any hum pickup. The circuit The circuit shown in Fig.1 looks a little odd but we’ve presented it this way to avoid having to show three completely separate versions. So we have shown just one channel of the preamplifier with three different feedback networks: one for magnetic cartridge, another for tape or cassette decks and a third for microphone. For the magnetic cartridge function, IC1a not only has to amplify the signal but must also apply RIAA equalisation. It takes the low level signal from the moving magnet cartridge (typically, a few millivolts) and applies a gain of 56, at the median frequency of 1kHz. Higher frequencies get less gain while lower frequencies get considerably more, as shown in the accompa­nying equalisation curve of Fig.2. To be specific, a 100Hz signal has a boost of 13.11dB while a 10kHz signal has a cut of 13.75dB. The phono signal is fed directly April 1994  33 from the input socket via inductor L1, a 150Ω resistor and a 47µF bipolar capacitor to the non-inverting input (pin 3) of IC1a. The inductor, series resis­ tor and shunt 100pF capacitor form a filter circuit to remove RF interference signals which might be picked up by the phono leads. The 100pF capacitor is also important in capacitive loading of the mag- PARTS LIST (Magnetic cartridge version) 1 PC board, 01106941, 80 x 78mm 8 PC stakes 2 Philips ferrite beads 4330 030 3218 Semiconductors 1 LM833 dual op amp (IC1) Capacitors 4 47µF 50VW bipolar electrolytic 2 0.33µF 63VW MKT polyester 2 .015µF 63VW MKT polyester 2 .0047µF 63VW MKT polyester 2 100pF ceramic Resistors (0.25W, 1%) 2 1MΩ 2 390Ω 2 200kΩ 2 150Ω 4 100kΩ 2 100Ω 2 16kΩ Miscellaneous Shielded cable, screws, nuts, tinned copper wire. +20 20Hz (7950uS) netic cartridge. Most moving magnet (MM) cartridges operate best with about 200 to 400pF of shunt capacitance. The 100pF capacitance in the preamp input circuit plus the usual 200pF or so of cable capacitance for the pickup leads will therefore provide about the right shunt capacitance. For its part, the 47µF bipolar capacitor is far larger than it needs to be as far as bass signal coupling is concerned. If we were merely concerned with maximising the bass signal from the cartridge, then an input coupling capacitor of 0.47µF would be quite adequate. At 20Hz, a capacitor of this value would have an impedance of around 15kΩ which is considerably less than the nominal 50kΩ input impedance of the preamp. But having a large capacitor means that the op amp “sees” a very low impedance source (ie, the DC resistance of the car­tridge) at low frequencies and this helps keep low frequency noise, generated by the input loading resistors, to a minimum. RIAA/IEC equalisation The RIAA equalisation is provided by the feedback compon­ents, R1, C1, R2 and C2, between pins 1 and 2 of IC1a (or pins 6 and 7 of IC1b, in the other channel, which is not shown). These equalisation components provide the standard time constants of 3180µs (50Hz), 318µs (500Hz) and 75µs (2122Hz). The phono pream­ plifier also adds in the IEC recom- mendation for a rolloff below 20Hz (7950us). This is provided by the 0.33µF output coupling capacitor in conjunction with the load represented by the follow­ing amplifier’s volume control and input circuitry (which is likely to be around 50kΩ). There is also a further low frequency rolloff, at around 9Hz, caused by the 47µF capacitor in series with the 390Ω resis­tor. The 390Ω resistor sets the maximum AC gain at very low frequencies while the 47µF capacitor ensures the gain for DC is unity. This means that any input offset voltages are not ampli­fied, which would inevitably cause trouble with asymmetrical clipping and premature overload in the preamplifier. Actually, the magnetic cartridge version of the circuit just described is identical to the phono preamplifier of the Studio 200 Control Unit, published in the June and July 1988 issues. Incidentally, the mention of RIAA/ IEC equalisation above refers to two different disc recording standards. The RIAA stan­dard was originally set by the Record Industry Association of America in 1953. The later IEC variation was recommended by the International Electrotechnical Commission in the 1970s. Tape equalisation In the tape equalisation version, the value of R2 is identi­cal to that of the phono preamplifier but R4 is changed to 200Ω and R1 is replaced by a wire 50Hz (3180uS) DECIBELS +10 2.12kHz (75uS) 0 500Hz (318uS) -10 -20 2 10 20 100 HERTZ 1k 10k Fig.2: this graph shows the RIAA/IEC equalisation characteristics provided by the feedback components for the magnetic cartridge preamplifier version. 34  Silicon Chip 20k 0.33 47uF 1M R2 R1 47uF 47uF 0.1 IC1 LM833 1 C1 L1 100k LEFT OUTPUT 100pF 1M R2 R4 GND 100  100k 0.33 0V -15V R1 150  GND +15V C1 0.1 L1 R3 150  RIGHT INPUT C2 R4 100pF 100k GND 100  GND LEFT INPUT C3 100k R3 RIGHT OUTPUT C2 C3 47uF Fig.3: refer to the main circuit diagram for the values of R1-R4 & C1-C4 & install these parts to suit your application. link. C1 and C2 are omitted and replaced by R3 and C3. Microphone version In the microphone version, R2 and R4 are the same as in the phono preamp while R1 is a short circuit and C1 is omitted alto­gether. The microphone preamp has a gain of 513, making it suit­able for low impedance microphones. If less gain is required, it is simply a matter of changing the ratio of R2 to R4. For exam­ple, if you want a gain of 100 times, make R4 470Ω and R2 47kΩ. Power supply The required power supply is a regulated source of ±15V DC at around 10mA. This could come from 7815 and 7915 3-terminal regulators or derived from supply rails in your existing equipment. If you want a PC board for this job, refer to the “Universal Power Fig.4: check your PC board before installing the parts by comparing it with this full-size etching pattern. Supply Board for Op Amp Circuits” published in the August 1988 issue of SILICON CHIP. (This issue is now out of print but we can supply photostat copies of the article for $6. Alternatively, you could use the discrete regulator design published elsewhere in this issue. Construction All the input circuitry for the universal preamp goes onto a small PC board measuring 80 x 78mm and coded 01106941. Before you begin construction, check the PC board carefully for any shorts or breaks in the tracks. If you find any, correct the problem before installing any parts. When you’re happy that the board is OK, you must decide which version you are going to construct. In each case, make sure you know which resistors and capacitors numbers must be included and which must be left out or replaced with wire links. In any case, use the component wiring diagram of Fig.3 to carefully check the position of all components. Begin by installing the wire links, followed by the resistors and the MKT capacitors. This done, solder in the IC and then continue with the electrolytic capacitors. Once the board is fully assembled, check it for correct installation of all the components. You can now connect the ±15V supplies and check the DC voltages with respect to one of the PC stakes which is connected to 0V to GND. You should have +15V at pin 8 and -15V at pin 4 of the IC. You can also check the offset voltages at the outputs of IC1, pins 1 & 7. The voltage at these pins should be within ±100mV of 0V but will most likely be a lot less than this. If that is the case, the PC board is ready to be installed SC into your equipment. RESISTOR COLOUR CODES ❏ No. Value 4-Band Code (1%) 5-Band Code (1%) ❏ 2 1MΩ brown black green brown brown black black yellow brown ❏ 2 200kΩ red black yellow brown red black black orange brown ❏ 4 100kΩ brown black yellow brown brown black black orange brown ❏ 2 16kΩ brown blue orange brown brown blue black red brown ❏ 2 390Ω orange white brown brown orange white black black brown ❏ 2 150Ω brown green brown brown brown green black black brown ❏ 2 100Ω brown black brown brown brown black black black brown April 1994  35 Review: PICSTART Development System Microcontrollers with speed: the new PIC series The new PIC-series microcontrollers from Microchip Corpora­tion use new RISC architecture which contain as little as 33 instructions. We review these microcontrollers & the new PICSTART development system. By DARREN YATES Microcontrollers have taken off in the last few years or so, yet the internal structure of most of them is based on the 8-bit microprocessor system that dates back to the days of the Z-80. At the moment, there would hardly be a semiconductor house that doesn’t manufacture at least one micro­ controller. And most have at least a dozen or more in their range. Looking through the databooks, many are simply variations on the same theme with maybe just extra I/O ports. The PIC series from Microchip are radically different from the rest of the pack because of the RISC (reduced instruction set) architecture. There are only 33 instructions in the most basic unit but because each instruction is 12 bits wide, it gives each instruction a much greater degree of flexibility. What’s more, all instructions are single- or two-clock cycle, with most being one clock cycle. This makes time-related programming much simpler than most of the standard 8-bit controllers. The RISC architecture also enables PICs to run very fast. In fact, they can operate at up to 20MHz yet they are still low power devices. At 4MHz, the current consumption is less than 2mA at 5V and only a tiny 15µA at 3V for 32kHz operation, making them This is the initial screen displayed by the MPSTART system. This menu-driven package is used to program most of the PIC series microcontrollers. 36  Silicon Chip ideal for extended battery operation. Further, there are extra features to improve power consumption performance, including sleep modes and low-power clock oscillators. They are also guaranteed to operate down to 2.5V supply. Each device has on-board EPROM memory varying from 512 bytes to 2Kb for program storage, as well as between 25 and 72 8-bit registers for general use. There is also a code protec­tion fuse which can be blown once final code has been programmed in. One of the most useful programming features is the inclusion of an 8-bit real time clock\counter with a programmable prescal­er. This makes it easy to program the device to work as some clock type function. There are two main families of PICs – the PIC16CXX and PIC17CXX series which are tailored for different applications but all with the high-speed RISC system. PIC16C5X series The basic PIC series is the PIC16C54/5/6/7. The PIC16C54 is the simplest and smallest, and comes housed in an 18-pin DIP package, either ceramic or plastic. You can also get it in surface mount. It has 512 bytes of 12-bit EPROM, 32 bytes x 8 bit RAM and 12 I/O lines. The PIC16C55 is the same as the above 16C54 but with 20 I/O lines. It comes in a 28-pin package. The PIC16C56 is also based on the ’54 but with 1Kb of EPROM. The top of the range PIC15C57 has 2Kb of EPROM, 80 bytes of RAM and 20 I/O lines. For most applications, this makes the PIC the ideal single-chip computer since there is no external memory or driver hardware required. In all PICs, the RAM is individu- The PICSTART Development System comes with two manuals: the complete Microchip Databook & the Embedded Controller Handbook. ally addressable when programming whereas the EPROM is addressable in 512-byte pages. The I/O lines are banked in groups of eight so that they can be read as either single inputs or as a byte from say an 8-bit analog to digital converter (ADC). For mass production, the 16CXX series is available in erasable-UV form as well as OTP (one time programmable) for code protection once the device is in the marketplace. Second generation PICs The PIC16C71 is the start of the second generation of PIC micro­controllers which include 14-bit wide instruction sets and only 35 instructions. What sets this apart is the on-board 8-bit ADC. This ADC has four multiplexed analog inputs, sample and hold, 20µs/ channel conversion time and an external reference input. Accuracy is quoted at ±1 LSB. The PIC16C71 also has 1Kb x 14-bit EPROM, 16MHz clock speed, 13 I/O lines (each with individual direction control) and an external interrupt pin. All this is in a package that only has 18 pins. The has been achieved by multiplexing most of the pins to perform two functions. Depending upon the instruction, the pins are set to act as either inputs or out­puts. The I/O pins are capable of sinking and sourcing up to 20mA, which reduces the need for external drivers and helps to reduce the design cost. Power consumption for the ’71 is basically the same as the PIC16CXX series with slightly more current consumed with the ADC in operation. Other 16CXX series features such as power saving sleep mode, 8-bit real time clock/counter, power-on reset and watchdog timer are also included. The watchdog timer is basically a free-running RC oscilla­tor which has a nominal timeout period of 18ms but can be pre­scaled with a division ratio of up to 1:128 to produce a period of 2.5 seconds. Once the timer has timed out, it generates a RESET condition which can be used in programming to either reset the device or branch to another section of code. PIC16C84 All of the devices so far have used an EPROM which is UV-erasable. The 16C84 differs in that it contains a 1Kb x 14-bit electrically erasable PROM for program and a 64 byte EEPROM data memory. This could be used for entering external data which changes from device to device while the program code remains unchanged. It operates down to 2V and has a standby current consump­tion of less than 1µA. The package is an 18-pin outline with 13 I/O lines, capable of 25mA sinking and 20mA sourcing current. Maximum speed is 10MHz with a 400ns instruction cycle. Program interrupts are available from one of four sources – the external INT pin, real time clock overflow, toggling of one of the I/O lines and filling of the data EEPROM. The PIC17CXX series The PIC17C42 represents the latest step in RISC microcon­troller design with 16-bit wide instruction at up to 25MHz clock speed. What makes this device different is that it has four modes of operation: standard micro­­controller mode, secure microcon­troller mode, extended micro­con­troller mode with both internal and external program access, and microprocessor mode with exter­nal program access only. The 17C42 has 2Kb of 16-bit EPROM for internal stored programs or it can address a maximum of 64Kb x 16 memory space outside. In standard microcontroller mode, the 17C42 allows only internal program execution so that only the onboard 2Kb EPROM memory can be April 1994  37 Protect your valuable issues Silicon Chip Binders These beautifully-made binders will protect your copies of SILICON CHIP. They feature heavy-board covers & are made from a dis­ tinctive 2-tone green vinyl. They hold up to 14 issues & will look great on your bookshelf. ★ High quality ★ Hold up to 14 issues ★ 80mm internal width ★ SILICON CHIP logo printed in gold-coloured lettering on spine & cover Price: $A14.95 (includes postage in Australia). NZ & PNG orders please add $A5 each for postage. Not available elsewhere. Silicon Chip Publications PO Box 139 Collaroy Beach 2097 Or fax (02) 979 6503; or ring (02) 979 5644 & quote your credit card number. ➦ Use this handy form Enclosed is my cheque/money order for $________ or please debit my ❏ Bankcard   ❏ Visa   ❏ Mastercard Card No: ______________________________ Card Expiry Date ____/____ Signature ________________________ Name ___________________________ Address__________________________ __________________ P/code_______ 38  Silicon Chip used. Secure mode incorporates code and write protection so that your program code cannot be overwritten or copied. Extended mode allows the inclusion of external memory above 2Kb (between 2Kb and 64Kb) and the use of the internal EPROM below 2Kb. In microprocessor mode, the entire 64Kb memory is mapped externally and the internal EPROM cannot be used. Other features of the 17C42 include two high-speed pulse-width-modulation outputs with 10-bit resolution and 15.6kHz speed. These could easily be used with say an H-pack output drive circuit in part of a switching power supply, for example. There are 232 x 8-bit general SRAM registers and up to 33 I/O lines. As with the other PICs available, it also has a watchdog timer with its own internal RC oscillator as well as three 16-bit timer/counters. For those who require external control, there are 11 external/internal interrupts available as well. One of the more unusual features is the fully featured serial port (USART) which includes a baud rate generator. This can be configured for either full-duplex asynchronous or half-duplex clocked synchronous mode. An 8-bit dedicated baud rate generator which can be programmed is also included. Development system To help the PIC push into the marketplace, Microchip have come up with the PICSTART – a micro­controller development system which mates with any IBM AT. It contains a small PC board which has a connector for your serial port and a zero-force-insertion (ZIF) socket. As part of the system, the software package in­cludes a PIC device programmer called MPSTART; the MPALC Mi­crochip PIC Assembly Language Compiler; and MPSIM, a PIC simula­tor. All software supports the PIC16C54 to 84 devices and can be run on any PC with the following requirements: (1) 1.44Mb drive; (2) hard disc drive; (3) serial port; (4) 640Kb RAM; and (5) DOS 3.3 or higher. A text editor, VGA screen and mouse are highly recommended but not mandatory. The PC board requires a 9VDC 250mA power supply which can quite easily come from a 9VDC plug pack. The board is quite small at just 117 x 76mm and you also get two sample PICs to play with. All programs run under DOS and do not require Windows which is a great idea. The programmer, MP­ START, is activated simply by typing MPSTART<enter>. It’s a menu-driven package which automati­cally sets up the link between the PC board and the computer and warns you when the connection isn’t made, for example, if the power supply is not connected. It has context-sensitive on-line help in case you get into trouble at any stage, as well as normal file handling facilities. The program is completely menu-driven so you don’t have to remember any fancy command calls. MPALC The assembler, MPALC, is a command line driven program which requires your source code to be already in an ASCII format file. To assemble code, you simply add in the source code file­ name and the destination filename of the compiled code plus a number of option directives. For example, the /P option allows you to compile code for a specific device. Thus, “/P 16C54” would compile code specifically for the PIC16C54 controller. MPSIM The MPSIM simulator, which also runs from DOS, allows you to test program files by loading them into the simulator and checking the various registers and ports to check the program’s correctness. Programs can be tested by either single command stepping or execution up to a certain command or address in EPROM. Register values are maintained on-screen at all times. Overall, the PIC-series of micro­ controllers represent a big step forward in microcontroller design. They feature high speed and low cost in terms of both code development time and produc­tion. Watch out for the PICs to make big waves in the micro­con­troller industry. The PICSTART system also includes two manuals: the complete Microchip Databook and the Embedded Controller Handbook. The PICSTART is available from NSD Australia for the bargain price of just $250, which is peanuts compared to many other development systems. You can contact SC them on Sydney (02) 898 0133. SERVICEMAN'S LOG Nothing unusual happened this month I don’t have any stories from my own bench this month, since nothing sufficiently unusual has happened. So I have had to call on a couple of colleagues, who have come to the party with some really tricky ones. The first story comes from my colleague on the NSW south coast and it concerns a problem peculiar to his area. In fact, for readers not familiar with this area, it is necessary to set the scene in terms of the local TV channels. In the early days of TV, residents of Wollongong, about 80km south of Sydney, managed as best they could with signals from the Sydney channels. It was a chancey business. As well as the distance, they had to contend with less-than-favourable topography. Tall masts, high gain antennas and masthead amplifiers were the order of the day. Some managed reasonably well; others took what was there on a day-to-day basis and were grateful for it. Further south, around Nowra, Bate­man’s Bay and their surrounds, it was virtually hopeless. First relief for the area came with the establishment of a couple of VHF transmitters at Knight’s Hill, south of Wollongong. Today, the area is served entirely by five program sources in the UHF band, using five main transmitters and five translators. In order to appreciate my colleague’s story, it is neces­sary to set out these channels. The five main transmitters, at Knight’s Hill, use channels between 53 (701-708MHz) and 65 (785792MHz), while the translators use channels between 30 (540-547MHz) and 48 (666-673MHz). So, against that background, here’s my colleague’s story, more or less as he related it to me. The fussy Rank The set was a Rank-NEC model C-1413. It was brought in many months ago by one of my lady customers with the complaint that “the picture goes funny on some of the channels only”. Well, I’ve had worse descriptions although, as it turned out, it was AUSTRALIAN MADE TV TEST EQUIPMENT 12 Months Warranty on Parts & Labour DEGAUSSING WAND Great for computer mon­­­­­­it­ ors. Strong magnetic field. Double insulated, momentary switch operation. Demagnetises colour picture tubes, colour computer monitors, poker machines, video and audio tapes. 240V AC 2.2 amps, 7700AT. $85.00 + $10.00 p&p Cheque, Money Order, Visa, Bankcard or Mastercard. Phone for free product list SHORTED TURNS TESTER Built-in meter to check EHT transformers, in­clud­­­­ing split diode type, yokes & drive trans­ formers. $95.00 +$3.00 p&p TV, VCR TUNER REPAIRS From $22. Repair or Ex­change 216 Canterbury Rd, Revesby, NSW 2212, Australia. Phone (02) 774 1154 Fax (02) 774 1154 40  Silicon Chip accurate enough; it just wasn’t very helpful. In cases like this, one of the points I have to watch in this area is the need to determine, right from the start, which transmit­ters a customer uses; the main transmitters, the translators, or even combinations of both in odd cases. This fine distinction is usually lost on most people; they think in terms of names – ABC, SBS, Prime, etc – with little appreciation of how the program comes to them. But some careful questioning in this case finally pinpointed the main transmitters on Knight’s Hill as the signal source. So that was where we started. The model C-1413 is one of a series of sets which use essentially the same circuit and appear under several brand names. As a Rank, it also appears as the C-1414 and C-2020 (among others) but it also appears under the GE label as GE482 and under the General label as GC205. I have most of these circuits, including the C-1413 and the C-2020. As luck would have it, the 2020 came out of the file along with the 1413 and I left it out. As far as the symptoms were concerned, the lady was right and the pictures from Knight’s Hill were “funny”. And that wasn’t such a silly term either. The effect isn’t easy to describe; my best attempt would be random pulling and rolling, with the sug­gestion that this might have been hum related. The lady was also right in that there was no sign of the trouble on the translator channels. In fact, I explored this aspect very thoroughly to make quite sure. OK, so we had a frequency related problem. That meant trou­ble somewhere in the front end; probably in the UHF tuner itself. This set uses two mechanical tuners; the UHF tuner which down-converts to VHF, and a VHF tuner which then down-converts these signals to the IF. Of course, it can process off-air VHF signals as one carrying the supply rail, the AGC, AFT and chassis connections, one for the IF lead, and one for an auxiliary network for the UHF tuner RF bias control. With the two sets close together, there was enough lead length to allow the suspect tuner assembly to be replaced with the known good one, without any need for mechanical demounting. I was fully confident that this would confirm that there was a tuner fault. If so, it would make things easy because I had a couple of spare tuners from junked sets and a replacement would be a cheap and easy solution. But no – the set behaved exactly the same with the replace­ment tuner assembly. This was a really revolting development; any complacency I had allowed myself up to this point was completely dispelled. I had a real stinker on my hands, defying all the rules. If the fault was in the main circuit, which was carrying nothing higher in frequency than the IF, then how did it know when the set was tuned to something above 700MHz? And if use of the word “know” sounds a bit way out, it was no more so than the fault itself. Caffeine fix well. It’s all quite conventional really and I imagined that the job would be fairly routine. The first thing I tried was feeding in a signal from the colour bar generator. This happened to be set to channel 36 (575-582MHz) in the translator group and, as expected, it produced a perfectly steady picture. I then reset the generator to channel 67 (799-806MHz) in the transmitter group, fully expecting that I would be able to observe the fault under controlled conditions. But not a bit of it. The colour bar signal was just as steady on this channel as it had been on the lower one. It was a nasty setback. OK, so it was back to the real world. I switched to one of the Knight’s Hill transmitters and confirmed that the fault was still very much alive. So what next? Well, luck was with me; I had another identical set in the workshop at this time. There wasn’t much wrong with it and I could use it for a spot of swapping. In particular, I had in mind to swap the tuner assemblies, thus either confirming or rejecting this section as being at fault. It was a simple exercise. The tuner assembly is connected via three plugs, After I’d had a caffeine fix and calmed down a little, I had another thought. Could it be a power supply fault? A long shot surely – how could the power supply be involved? It was just about as far removed from the frequency selection process as anything could be. Yet I’ve had some very funny faults traced to power sup­ plies. We tend to forget that there are signal paths through or around all power supplies, usually involving capacitors other than the filter capacitors, and that failure of these can create faults a long way from the source. More to the point from a practical point of view, it took only a few minutes to patch the power supply from the other set into this one and settle the point once and for all. And it did – it made no difference. The next most likely possibility was distortion of the sync pulses. I could think of no way that such a fault could be fre­quency conscious but the idea could not be ignored. The IF signal from the tuner goes through an amplifier stage (TR201), a SAW filter (FL201), and thence to pins April 1994  41 Fig.1: the IF circuitry in the Rank C-1413 colour TV set. The IF input is at extreme left & feeds TR201, while C208 is below IC201, between pins 11 & 14. Note capacitors C221 and C222 from pin 11 to chassis. 1 & 16 of IC201 – see Fig.1. It emerges on pin 12 and a clear staircase waveform pattern is given for this point. So the CRO was hitched to pin 12 and the colour bar generator used to provide a stair­case signal. But, again, there was no cry of “Eureka” – or a triumphant dash down the main street. As far as I could see the waveform was perfect; exactly according to the circuit, with no hint of dis­ tortion or compression, from either a channel 36 or channel 67 signal. Nor did the signal level appear to matter. The generator can deliver a solid signal – stronger than most off-air signals in practice – and so I took this right down until the pattern dropped out of colour. The sync pulse remained perfect. Nor did varying the AGC adjustment have any effect. But what about off-air signals? I checked some of the transla­tor signals and the sync pulses appeared much the same as from the generator. The pulses from the Knight’s Hill transmitters didn’t look too bad either, although that “too bad” implies a qualifica­tion. Yes, the shape was still OK but one difference did catch my eye, although I still don’t know whether it was relevant. As I said, the shape was correct but there appeared to be some rub­bish, or noise, inside the pulse rectangle. It was nothing that could be resolved and is still a mystery. 42  Silicon Chip All I know is that it was only on the troublesome signals. Hard slog So now it was down to hard slogging and a lot of hope. I changed transistor TR201, the SAW filter, and even IC201. I changed the capacitors on the AGC line (pin 4), including C210 (4.7µF), C212 (0.01µF) and C209 (4.7µF), plus sundry resistors. None of these had any effect. By this stage, I had reached the point where I had to stand back and take a long hard look at the whole situation, not only technically but financially. I had spent a lot of time on it; somewhat more that could reasonably be justified for something which was now looking as though it might be a write-off. I contacted the customer and brought her up to date on the situation. She was quite co-operative, in that she was in no hurry to get the set back. To be truthful, I gained the impres­ sion that she was quite prepared to write it off. But she was prepared to spend up to $100 to get it working. So, at least the pressure was off. I had more pressing jobs to attend to and so the set was put aside in one corner of the bench. I had fully intended to get back to it reasonably soon but, as often happens, other jobs kept piling up and I kept putting it off. And so several months went by. But its mere presence provid­ed a nagging factor; every time I looked at it, I felt guilty – and apprehensive. I had no idea how I was going to tackle it. Eventually, when things slackened off over the Christmas/New Year break, I knew that the moment of truth had come. I fished it out again, determined to settle the situation one way or the other. Fortunately, I had scribbled a few notes and kept the com­ponents which had been changed, so I was soon back in the pic­ture. But I didn’t really have any fresh ideas. The best I could do was to continue replacing likely – or even unlikely – compon­ents and hope for a breakthrough. And that’s what happened. After a couple of false tries, which included capacitors C222 (47µF) and C221 (0.01µF) in paral­lel with it, I came to capacitor C208 – a 2.2µF tantalum electro­lytic connected between pins 11 & 14 of IC201. I hadn’t tried it earlier because it was hidden on the copper side of the board. Only its presence on the circuit diagram as part of the AGC circuit sent me looking for it. Its location may be significant, considering what followed. I pulled the capacitor out and checked it. It measured spot on but I replaced it anyway. Well, sort of – I didn’t have a 2.2µF capacitor handy, so I settled for 1µF. The result was quite dramatic; not a total cure but such an improvement that I could have almost let it go. There was just an occasional tendency to pull. My natural reaction, initially, was that if I fitted the correct value, it would complete the cure. It might have too, but a number of things happened to change my approach. To explain this, I have to make it clear that I had abso­ lutely no idea as to the function of this capacitor. I didn’t even know the function of pin 11; whoever drew the circuit had omitted to identify it. In hindsight, I could have easily worked it out by tracing the circuit but didn’t I realise this. But I was curious about C208. It was then that the C-2020 circuit stuck its nose in – see Fig.2. It had been updated, with pin 11 marked as VCC (the supply rail pin). On the C1414, it connects to the 12V rail via a 22Ω decoupling resistor (R223), bypassed by the previously noted C221 and C222. Suddenly, C208’s role became clear. It is a bypass capaci­tor for pin 14. Pin 14 is part of the internal AGC circuitry and, while I have no idea of its exact role, it is clear that it is held at around 7V by a 560kΩ resistor (R209) to chassis. And C208’s job is to peg this point, at RF, to chassis. Only it doesn’t go direct to chassis – it goes to pin 11. And pin 11 is pegged to chassis at all but DC by C221 and C222. It’s a rather roundabout route but a perfectly valid one – at least in theory. In the process of working all that out, I became aware that the pin 14 bypass circuit was quite different in the C-2020 circuit. In this case, the bypass capacitor, now designated C223 and reduced to 1µF, goes directly to chassis. In practical terms, this seemed to me to be a much more elegant approach and since someone a lot smarter than I had preferred it, why not try it? The rest is history, as our political commentators like to say; I made the changes and it was a perfect cure. I ran it for a couple of weeks before calling the lady and it remained rock steady. So we had a happy ending. But I realise that the story poses as many questions as it answers. While it is clear that the pin 14 bypass arrangement is critical – and that someone at engineering level must have discov- Fig.2: this is the IF circuit from the Rank C-2020. Note the changes on pin 11 & 14 compared with the C-1413. ered this – I still can’t explain why the fault was frequency conscious. But then I’m not an engineer; I’m only the poor bloke who has to try to make sense of these weird situations in the field. All I can do is learn from the experience and, by passing it on, perhaps help some other poor blighter from going round the bend – as I nearly did. Well, that’s my colleague’s story, and a good one it is too – as a story. But I can only sympathise with him over the anguish and frustration it must have caused. Nor can I answer any of the questions it poses. Any suggestions? A thorny problem And so to colleague number two; old faithful, J. L. from the island way down the bottom. Here’s his contribution. By all that’s reasonable, the old Thorn model 3504 should have been junked 10 years ago. It was released by AWA in early 1975 as the company’s first ever colour TV set. By 1984-85, the model was beginning to show its age and by 1990 most examples had succumbed to the years and were only to be found on the municipal tip. However, a few have survived and one of these came to my attention last week. I’ve been caring for this set for close to 15 years. I don’t know to what extent its longevity is related to my atten­ tions but I do know this – when I last worked on it about two years ago, it still produced a good picture. So when he called me last week and said that the picture had gone “...all purple” I wasn’t particularly worried. I was confident that it wasn’t the picture tube and fairly sure that it was going to be a simple electronic problem. I was even more convinced it was the latter when he said that thumping the cabi­net sometimes restored the picture to normal. A purple picture results from the loss of green content, so this problem had something to do with the green video output or the green gun. I firstguessed the former because, in the 3504, the video output load resistors are etched onto a ceramic sub­strate and I have found a number of these breaking down recently. In greater detail, the connecting pins break away from the ceramic where they are attached to the etched pattern. I’ve had no luck resoldering this connection; it is more practical to replace the printed resistors with discrete 10W units. Nowadays, I don’t have to resort to such subterfuge since I have a large collection of good boards taken from sets that have paid the supreme sacrifice. And so I decided it would be easier to do the job in the customer’s home, by simply replacing the suspect board with a known good one from this collection. And this did appear to be the answer; at least for a few moments after I had made the swap. But soon the green part of the picture disappeared April 1994  43 again and I had to admit that it was really a different fault. So where to start looking? I seem to have a habit of making the same mistake over and over again. The mistake this time was to forget to use my multi­meter. Circuit voltages are one of the best indicators of circuit performance, yet I always seem to make this my last test instead of the first! If I had made a quick check of the tube base board, I would have found that the fault lay with the screen (first anode) voltage, not with the cathode or grid voltages. So having done at last what I should have done at first, I set about trying to adjust the voltage on the green screen (pin 5). The result was uncertain – the green could be restored but it was erratic. It was hard to say exactly how it was varying, although the instability was seemingly related to the position of the screen potentiometer, R793. All of this made me think that we had a dirty screen pot. I’ve had these before and they usually respond to a 44  Silicon Chip squirt of contact cleaner. So, two or three squirts later, the picture came good and no amount of mechanical abuse would alter it. I let the set run for half an hour or so while I had a very welcome cuppa’ with the owner. The picture never varied and so, by mutual consent, we declared the job done. Pride commeth ... What is it that they say about pride coming before a fall? That night the owner rang to say that everything was back as it had been – no green, purple picture, and all! When I left the workshop next time, I made sure I had packed a complete convergence board. This panel carries not only the many convergence controls but also the three screen pots and their associated beam switches. My plan was to change over the whole board to make a quick and simple repair. What I had forgotten was that the “new” board had been set up for a different picture tube and would have to be completely readjusted. When I fitted it to the set, the picture came up with plenty of green but the convergence was grotesquely out of ad­ justment. I could see that it was going to be a long operation to do a complete convergence setup and I’d already spent as much time on the job as I could afford. So I decided to refit the original board and just change the doubtful pot for one of the good ones from the new board. And it was then that I found the true cause of the trouble. As I prepared to remove one of the screen pots from the new board, I noticed that the three beam switches were of two different types. Then I remembered! On a few occasions in the past, I have found that these beam switches develop internal shorts. It seems not to be a mechanical problem but an electrical one within the switch mate­rial itself. No amount of cleaning compound will cure the trouble – the only answer is to change the switch, something that I had obviously done on the new board at some time in the past. So instead of changing the screen pot, I changed the beam switch, S752. After a gray scale adjustment, we had as good a picture as any I’ve seen on a set this age. In fact, the colour, contrast and brightness were all excellent, as was the conver­gence. When I commented about the excellent picture on a set of such advanced age, the customer’s wife commented that they only used the set for a couple of hours at night. News and the early-evening soaps were all they ever watched and it was never on during the day. I made a quick calculation. Two hours a day, 365 days a year, for 18 years, makes over 13,000 hours! I seem to recall something about 10,000 hours being a reasonable life for a pic­ture tube. So this one is not only well past its presumed life­time but looks capable of going on for many hours yet! The only problem is that the set has only a VHF rotary tuner. However, the owner professes to have no interest in channels other than the ABC, so perhaps he really doesn’t miss the UHF facility. Thanks, J. L. – I hope you can keep the old clunker going for a few more years. As for the UHF channels, why not add a junked video recorder to the set to tune these stations; one in which the front end is still functioning? SC SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.jaycar.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.jaycar.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.jaycar.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.jaycar.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.jaycar.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.jaycar.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.jaycar.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.jaycar.com.au ORDER FORM BACK ISSUES MONTH YEAR MONTH YEAR PR ICE EACH (includes p&p) TOTAL Australi a $A7.00; NZ $A8.00 (airmail ); Elsewhere $A10 (airmail ). Buy 10 or more and get a 10% discount. Note: Nov 87-Aug 88; Oct 88-Mar 89; June 89; Aug 89; Dec 89; May 90; Aug 91; Feb 92; July 92; Sept 92; NovDec 92; & March 98 are sol d out. All other issues are currently i n stock. $A B INDERS Pl ease send me _______ SILICON CHIP bi nder(s) at $A12.95 + $5.00 p&p each (Australi a only). N ot avail abl e elsewhere. Buy five and get them postage free. $A SUBSCRIPTIONS ❏ New subscription – month to start­­___________________________ ❏ Renewal – Sub. 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Please have your credit card details ready ______________________________ Card expiry date________/________ Card No. Phone (02) 9979 5644 Signature OR Fax (02) 9979 6503 Fax the coupon with your credit card details 24 hours 7 days a week Mail coupon to: OR Reply Paid 25 Silicon Chip Publications PO Box 139, Collaroy 2097 No postage stamp required in Australia April 1994  53 COMPUTER BITS BY DARREN YATES Experiments with your games card, Pt.5 This month, we give some general information on the various games cards available & look at what you can and can’t do with them. We also present details on a simple games card break­out board. Most if not all PCs these days have the games/joystick port built into an “all-in-one” card which handles your hard drive, if it is an IDE (Intelligent Drive Electronics) type, as well as the serial ports and printer port. While this is a good idea and frees up a number of what would otherwise be used expansion sockets on your motherboard, the games port is not the “full quid”. What they in fact do is leave out the second joystick input, so you’ll find that while you can still plug your joystick in and shoot down the Red Baron, you won’t be able to run dual joysticks. What this means is that with a card of this type, you’ll only have two analog inputs and two digital inputs, rather than four analog and four digital inputs with a full games card. The easiest way to tell what type of games card you have is to open the lid of your computer and locate the card that con­ tains the joystick (DB15) socket. Next, unscrew the Phillips-head screw and remove the card. Make sure that you keep a record of which cables and plugs fit into which sockets, otherwise you’ll find yourself in a real spot. When you’ve removed the card, examine the ICs on the board. Somewhere near the joystick socket, you should find either a 556 or a 558 chip. The prefix will depend on the manufacturer of the device. It could be “LM” for National Semi­conductor or “NE” for Signetics/Philips. Whatever the case, if you have a 556 chip, then you only have the single joystick input. If you have a 558, then you have all available input functions. For the 556 version, pins 9-14 of the joystick connector are left disconnected and pins 1-8 function as normal. All of the experiments we have done so far require only the analog input of pin 3 or the digital (fire button) input of pin 2, so even if you only have the ‘half-joystick’ card, you can try out the programs we have developed so far. Full games cards are available from a number of retailers including one from Rod Irving Electronics which sells for only $29. For more details, contact Rod Irving Electronics in Sydney or Melbourne. Installing the games card The DB15 socket on the games breakout board allows you to use an existing DB15 extension cable to connect between the board & computer. 54  Silicon Chip If you’ve purchased a separate games card, it’s not just a case of plugging in the card into a spare slot and away you go. You first have to disable the games port on your IDE card before the separate card will function. The major problem you will find here is that there are a number of IDE cards available from different manufacturers and all have a different method of disabling the games section of the port. All IDE cards have a row of two or three-pin jumpers which are used to enable serial ports, hard disc drives, etc. Depending upon your card, there will be a jumper that will need to be either swapped to another pin or lifted or run your circuits off the games card 5V supply. Never mix the two or else you’re asking for trouble. Also don’t attempt to pull more than about 100mA from the card. It will probably handle more but we would caution against it as the sockets and tracks on the board are not designed to handle much current. One thing that should be considered as a rule is never let the end-user have the option of connecting into the computer’s 5V supply through your project. The possibilities for trouble are endless. Games breakout board The PC board has a patchboard area which will hold a number of ICs for simple projects & allow you to prototype designs as you go. off. Unless you have the manual for your IDE card, you’ll need to contact the company you purchased your computer from. This is where you can run into trouble if you purchased your machine from one of the discount stores rather than a specialised electronics dealer. Companies such as Rod Irving Elec­ tron­­ ics and Dick Smith Elec­ tronics are able to supply lots of information on the computers they sell but don’t expect the same sort of backup from a discount store. 5V supply One thing which we haven’t mentioned so far is the 5V sup­ply. Unlike the parallel printer port, the games card has a 5V supply rail located on pins 1 and 9. This connects through the expansion socket to your computer’s 5V supply rail. This supply rail must be treated with respect and caution for a number of reasons. Firstly, it is the main supply for the majority of your computer’s ICs. So if you somehow damage that supply rail, you risk damage to your motherboard – in fact, you risk just about all of the devices that are in your computer. Secondly, if you take of the lid off your computer, you’ll see that the power supply carries a number of specifications regarding output voltage and current. Your computer uses four supply rails and they are +5V, -5V, +12V and -12V. The +5V rail sup­ plies most of the equipment in your machine and is usually cap­ able of supplying around 15 to 20 amps, so be very careful. As a general rule, when you are interfacing with the games port, either use a separate supply for everything Fig.1: this is the fullsize etching pattern for the PC board. Be that as it may, we don’t want to frighten you all off – just make you aware of the possible problems. So to make things easier, we’re presenting a simple breakout board, which in many cases will be all that you need for some projects. The board has connections to all connected pins of the joystick port, including the 5V supply, with all pins marked on the copper side of the board. There is also a patchboard area which will hold a number of ICs for simple projects and prototype your designs. The main benefit is that the DB15 socket on the board allows you to use an existing DB15 extension cable to connect between the board and computer rather than having to make up a separate cable. DB15 male to male extension cables are available from Rod Irving Electronics (Cat. P-19016) for $30.95. You can make the board yourself by using the pattern pub­lished here. We will be using the board in the near future for a Nicad Battery Monitor for PCs. There are many circuits and pro­ jects which could use the joystick port as an input so if you come up with any using the breakout board, please write to us here at SILICON CHIP and let us know what you’ve done. Ok, that’s enough for this month. Over the last few months, we’ve given you enough information for you to get started with some experiments of your own. You can easily modify the STICK. BAS and BUTTON.BAS programs to suit your own application. Remember to optimise the execution speed and make sure you include the line “DEFINT A-Z” early in the program. This increases the speed, whether you using a QuickBASIC compiler or SC MS-DOS QBasic. April 1994  55 PC Product Review The Video Blaster is one of the lowest cost ways of entering the world of PC video. Import your PAL or NTSC composite video signal from a camera or VCR, then frame grab and create all sorts of visual effects. VIDEO BLASTER By DARREN YATES W HEN THE ORIGINAL Sound Blaster hit the streets a few years ago, few would have predicted its rise to prominence as the standard for PC audio. The 16-bit ASP model released a year or two later upped the stakes by bringing CD-quality audio to your PC – playing CDs through your PC via a CD-ROM became a reality. Now there’s a system that does for video what the Sound Blaster did for PC audio and, by no surprise, it comes from the same people at Creative Labs in the US. Features Here are some of the features: Supports NTSC and PAL systems; Software selectable video and audio input sources; • 16-bit card; • • 56  Silicon Chip • Supports PCX, TIFF, BMP, GIF and TARGA file formats in 640 x 480 res- olution; • Supports up to 2 million colours; • Live and still image zooming and scaling; • Freeze, save and load images; • Crop and resize images; • Windows® software (Video for Windows from Microsoft). The VB pack also includes manuals for all software packages, as well as instructions on installing both the card and software. For those who are running other equipment such as CDROMs, the I/O addresses, frame buffer base address and software interrupts are all selectable and a test program checks whether your choices are valid. Bundled software As much as the Video Blaster can do, it is remarkably easy to drive with a host of Windows-based software packages to allow you to make the most of its capabilities. Along with Microsoft’s Video for Windows, Tempra Special Edition allows you to edit video images with shapes and paint and supports all the usual file formats. Tempra SHOW is a multi-media presentation package that integrates audio, video, animation and still graphics into high-impact interactive presentations. ACTION from Macromind lets you import graphics from spreadsheet, paint and graphics programs and comes with over 100 templates for your own designs. System requirements • The basic system requirements are: IBM PC-AT or higher system; • • • Full length 16-bit slot; DOS version 3.1 or higher; VGA or multisync monitor running 50-70Hz with a scan rate of about 31.5kHz; • VGA card with a features connector; • Not more than 15Mb of system RAM. This last point may seem a little strange with the latest trends aiming for more and more system RAM but there is a very good reason for this. The VB card has 1Mb of RAM on board which it needs to overlay on to the system. This RAM is used to store the image and to display it as fast as possible to produce real-time video displays. The IBM PC-AT (or 286) has a 24-bit address bus which limits the maximum address RAM to 16Mb. Even on 386 machines, which are capable of addressing 4 gigabytes, the ISA bus limits the effective RAM to 16Mb. It turns out that the most efficient way to display the video image is to map this RAM into the system at the 15-16Mb boundary. However, this causes conflicts with any memory which exists so in order for the system to work correctly, no system RAM can use the 15Mb-16Mb addressing area – hence the 15Mb system restriction. This base address can be lowered for systems which have less than 15Mb of system RAM. Setting the system up This is a little more involved than you might think. To start with, you need a VGA card that has a feature connector on the top of the board. This is an edge connector similar to that found on 5.25-inch floppy drives. An internal-to-the-system cable connects from the VB card to the feature connector on your VGA card. A separate external cable then links the VGA output from your VGA card to the VB card. Your VGA cable then connects to the DB15 output socket on the VB card. What actually happens with the system is that it doesn’t really use the VGA card to produce the on-screen display. It uses a method called chroma-keying and is similar to the effect you often see on the evening news where the weather forecaster is seen standing in front of various meteorological photos and maps. The VGA card produces a blank colour screen which The Video Blaster allows either a PAL or NTSC composite video signal on any one of three inputs to be displayed on a VGA screen. This dialog box allows the user to select the video standard & the polarities of the sync signals. April 1994  57 the VB card uses to key in the video image. You can see this if you try to paste the screen image to the Windows Clipboard. When you go into the Clipboard, all you will see is a pink screen below the top menu. Installing the software Installation of the software is a much simpler affair. The Video Blaster driver software is loaded first under Windows and it automatically loads all the relevant files. You can change the destination drive and directory if you wish. Once the software is installed, you then have to run one of two setup programs to start the software drivers – there’s one for Windows and one for DOS. The Windows version is easier to drive and still allows you maximum flexibility. It automatically selects the correct I/O address and software interrupts. Real time video display After running the Windows setup program, you can then connect up your video source (either VCR or camcorder) to one of the video inputs, select it with the software selector and then click on the VIDEO KIT icon. After maximising the window, you should see the Windows menu routine at the top and whatever signal you have from the video source being displayed on the VGA screen. Tempra Show comes bundled with the Video Blaster software & is designed to incorporate sound & animation into the captured video images. This is the opening screen that appears when the program is loaded. The Video Blaster allows either a PAL or NTSC composite video signal on any one of three inputs to be displayed real time on a VGA screen. This is quite a breakthrough compared to some of the systems we have seen previously which have relied on small screen windows showing just a few frames a second. VB uses the full screen size for a much greater impact. What makes this all possible is a 16-bit nearly full-length card which not only contains stereo input mixing from a CD player or tape and output amplifiers to drive loads down to 4Ω but all the necessary circuitry to convert both NTSC and PAL signals with either negative or positive syncs. At any time while video is being displayed, you can select the freeze option in the main menu in VIDEO KIT, and grab a frame. The grabbed image is then frozen on the screen. To save the image, you just select one of the file formats, whether it be TIFF, BMP, PCX, GIF or TARGA and save it to disc. You can now import that image into either Windows Paintbrush or just about any desktop publishing program. Video for Windows The “slider bars” on this dialog box allow the picture colour to be quickly adjusted, either in continuous mode or in freeze frame mode. 58  Silicon Chip This package from Microsoft is fast becoming the basic standard for PC video and is a great addition to the Video Blaster package. It requires Windows 3.1 and it is capable of some pretty fancy effects. Among its features is the ability to capture real time video and audio using VidCap, however your machine needs to be quite good. The system requirements are: • 33MHz 80386 or better • 4Mb of 32-bit RAM minimum • 100Mb hard drive to hold reasonable amount of video – also must have a write capability of at least 320Kb per second. Video for Windows will handle S-video, RGB and digital video as well if you happen to have another video board capable of capturing these standards. It also comes with a CDROM full of captured video examples which you can look at and edit to your heart’s content. Even if you don’t have a CD-ROM, there’s quite a good little sample file on the distribution discs – at 1Mb, it gives you an idea of just how much space you need to capture a decent length of video! Conclusion Overall, the Video Blaster package is very impressive. The only thing which we feel they could have added is the ability to produce composite video of the edited capture. That would have made it the complete PC video system. Be that as it may, the package represents good value for money at $899. It is available from all Dick Smith SC Electronics stores. Do you have a water tank on your property? This digital gauge will let you keep tabs on the water level without having to look in the tank itself. It has the option of two digital dis­plays & is controlled by a microprocessor. By JEFF MONEGAL Build this digital water tank gauge W HILE MOST people on farms have large water tanks, they are now also becoming more common in the cities for people who want rain water to drink or for use on their gardens. On a farm (and now in the cities), water conservation is paramount and keeping a con­stant eye on water usage is mandatory. The problem arises when users need to take a reading of the present tank level. This usually involves trudging out to the tank with a calibrated measuring stick, manoeuvring a heavy manhole cover out of the way, then dipping the stick into the tank to read off the contents. It would be much easier to glance at a digital display in the kitchen; especially if your tank is 200 metres 60  Silicon Chip from the house and it is a freezing day. Freeze no more, this digital tank gauge will do the job. It has a 2-digit display which indicates the tank contents from zero to 99%. If you have access to a secondary water supply such as a bore, the project will also control a pump to maintain the level of water in the tank at a preset percent­age. The digital tank display consists of two parts: the main unit which sits out on the tank and the remote display which is situated in the house; it can be up to 800 metres from the main unit. The main unit contains most of the electronics, including the microprocessor. The remote display will normally be situated in the kitchen but a second display can be built in the unit at the tank. This is how the prototype was built and how it is shown in the dia­ grams and photos in this article. Like many projects, this one was borne out of necessity. The author lives on a property which uses a concrete water stor­age tank and so this project was produced, the result of many months of research and development. Four prototype installations were used and originally the project used many ICs (13 just for the main unit) to achieve the desired result. As time and the project evolved, 10 of the ICs were replaced with a micropro­cessor and more functions were added. Principle of operation Essentially, the circuit works by transmitting a pulse of ultrasonic en- Circuit description Fig.2 shows the main circuit of the Digital Tank Gauge while Fig.3 shows TRANSDUCER HEAD ASSEMBLY TANK LID OVER-FLOW OUTLET WATER INLET PIPE FROM HOUSE GUTTERING MAXIMUM WATER LEVEL 90mm PVC TUBE FITTED THROUGH HOLE CUT IN STRAINER BASKET CONCRETE OR STEEL TANK CABLE TO MAIN PCB 400mm ergy down a tube to the surface of the water. The pulse is reflected off the water surface back to an ultrasonic receiver. The microprocessor then com­­ putes the time period bet­ ween the initial pulse and the received pulse and then calculates the level of water in the tank as a percentage. Fig.1 shows the general installation with the transducer assembly mounted at the top of a tube which fits into the tank. You may wonder why the tube is necessary. There are two reasons. The transmitter only pulses the ultrasonic transducer very briefly but being a mechanical device, the transducer will continue to “ring” for some time after each pulse. Because of this, the system has a minimum range below which it will not function. Therefore, the transducer must be positioned so that the a minimum distance above the highest water level is 400mm. This means that the transducers must sit above the top of the tank. The tube acts as a support for the transducers, suspending them 400mm above maximum water level. The second reason for the tube is that it acts as a baffle. The surface of the water can be quite rough at times, especially when the tank is being filled from a tanker or during heavy rain. This rough water surface can result in readings which jump up and down by as much as 10%. By using the tube, the surface of the water inside is very smooth. One of the problems with the test units was a jittery dis­play. Software was then written to allow the microprocessor to store the last five readings and then only to update the display if they are all equal. This results in a much more stable display. Once conversion has been done, the microprocessor displays this value on its digital display and then transmits the reading to the remote dis­play. The microprocessor then compares the present reading against presettable upper and lower limits to see if a pump should be turned on or off. As well, diagnostic routines are written into the software. The reading is updated every few seconds and an alarm in the remote display will sound every half hour for a few seconds if the level in the tank drops below 20%. EXISTING PLASTIC STRAINER BASKET WATER LEVEL Fig.1: this diagram shows the general scheme for mount­ing the ultrasonic transducers in a tube above the surface of the water. The transducers must be mounted 400mm above the maximum water level in the tank. the circuit for the remote display. The entire cir­cuit is under the control of a 68705P3 microprocessor which has internal RAM and ROM. The latter memory stores the program which controls the transmitter and receiver circuits and drives the digital displays. Let’s start the circuit description with the ultrasonic transmitter which is shown at the top right-hand corner of Fig.2. Actually, the microprocessor (IC4) is the source of the transmitter signal. Its pin 16 delivers a 3-cycle burst at 40kHz which is fed to transistors Q2 and Q3 to drive the ultrasonic transducer X2. Q2 and Q3 are fed by an adjustable DC supply comprising transis­ tor Q1, trimpot VR3 and This is the transducer assembly for the Digital Tank Gauge. It consists of the two ultrasonic transducers (transmitter & receiver) plus a small light bulb which automatically switches on at night & serves as an anti-condensation heater. April 1994  61 62  Silicon Chip 100k VCC B CE 12-16V AC OR DC BR1 W04 LDR ANTI CONDENSATION HEATER D2 1N914 2.7k 1% ULTRASONIC RECEIVER X1 E CB  B E C 10 A 6 7 K B 47 .01 1k 2200 Q6 BC548 .0047 VR2 10k 10k 1% 1k 1% VR1 50k .01 VCC C E 10 5 3 +12V 1 8 .01 1.5k E C VIEWED FROM BELOW B LED1 LAMP Q7 BD139 IC3 555C 2200 2 4 27k 27k 27k  3 2 ZD1 10V 1 C 10k F 10k 27pF 22 E 10k D B 10k 10k A 10k 10k SET UP X3 3.58MHz IC1a LM358 2.2M 2.2pF 5 4 11 10 9 8 19 18 17 12 7 10k PC3 PC2 PC1 PC0 PB7 PB6 PB5 2 3 6 5 6 7 IC4 68705P3 VPP 4 IC6 LM741 220  1 VSS TMR/BT PB0 .01 4 3 SET VOLTS VR4 1k 6 1 9 IC9c 10 1 4011 3 6 5 7 LE A 7 4 b B 1 c 820  20 16 2 13 26 4.7k 1k E 100 Q5 TIP31 B BUZZER 8 Q4 BC548 C B 7.5k 15 21 E C VCC 2 GND VCC +12V 100k 7 0.47 IC9a 7x 470  16 4 a BI 6 D d IC8 4511 2 e 7 f 4 2 g a b 1 9 10 g 15 14 LT 1k 6 5 1 5 6 11 8 3 8 3 a LT 7 b B 1 c 10k 0.47 C 6 D d IC7 4511 2 B e Q2 BC548 7 f 4 2 g a b 1 3,8 e c d DIS1 MSD LC5611 6 B 68  C E f BI LE 9 10 4 E C VCC 100k Q8 BC548 RLY1 ULTRASONIC TRANSMITTER X2 Q3 BC559 0.47 16 4 5 IC9b g 15 14 6 5 VCC B D3 1N4004 +12V CRO TRIGGER E C 4.7k 1k 47k 13 12 11 10 9 A ALARM TX CLOCK TX DATA TX 100 7x 470W VCC 2 4 2 10 3 3 VCC E DIGITAL TANK GAUGE 3,8 e c d DIS2 LSD LC5611 6 f 8 IC5 MC3487 16 B Q1 BC548 0.47 13 12 11 10 9 C 7 1 100  28 RESET PB3 PA5 TP2 .01 14 VR3 1k 27 47k 10  IC2b 4093 5 10 9 VCC D1 1N914 TP1 VCC +12V 14 7 PA1 25 24 PA2 23 PA3 22 PA4 PA0 PB4 INT PB1 PA6 PA7 VCC PB3 IC1b 8 VCC 1M C ▲ Fig.2: the circuit of the Digital Tank Gauge is based on a 68705P3 microprocessor (IC4) which is programmed with software to provide quite a few functions. The microprocessor pulses ultraso­ nic transmitter X2 via Q2 & Q3 & counts the time until a return pulse is received at transducer X1. It then converts the count to a percentage reading for the 2-digit display. associated components. After sending the transmitter pulse, IC4 takes pin 6 of IC2b briefly low to allow for the ringing period of the transmitter. Then it goes high again, to enable the receiver circuitry. The reflected pulse is picked up by the ultrasonic receiver transducer X1 (see top lefthand corner of Fig.2). This is AC-coupled to trimpot VR1 and then fed to op amps IC1a & IC1b, which have a combined gain of about 3700 at 40kHz. Pin 7 of IC1b drives diode D1 which charges the .01µF capacitor at pin 5 of IC2b. When a pulse is amplified by IC1 and detected by D1, the voltage at pin 5 of NAND gate IC2b will go high. The other input of IC2b is high, as determined by the microprocessor. Hence, IC2b’s output goes low and pulls the interrupt pin (4) of the microprocessor low which is the cue for a number of events. First, it takes pin 6 of IC2b low. This effectively closes the gate. During the time between the transmitter pulse and the received pulse, the microprocessor counts pulses from IC3, a 555 timer connected in astable mode. The count is converted to percentage terms and sent to the local and remote displays. A couple of internal counters are now reset and the microprocessor waits for a few seconds and then does it all again. This photograph shows the main PC board in the local unit. The microprocessor is clearly visible at centre right & is mounted in a socket (sockets for the other ICs are optional). Note the heatsink fitted to Q5. A piezo buzzer connected to pin 15 of the microprocessor is used to communicate with anybody who wants to listen. Each time a reading is taken the buzzer will beep once. If the processor talks to the remote display, it will beep the buzzer again. If the setup link (pin 12, IC4) is in the setup position, then the microprocessor does not check the last five readings. It simply sends the last reading to the displays and gives a beep. If the link is in normal mode then the microprocessor will compare the last reading with the previous four readings and if they are all equal it will talk to the remote display as well as the local display. When it does talk to the displays, it will give another beep. What all this means is that if the buzzer beeps once then an echo was received after the last transmission. If the buzzer beeps twice, then an echo was received and the processor sent the reading to both displays. There is a third buzzer indication and that is six short beeps. This means that a burst of energy was sent but no echo was received within the time allowed for the pulse to go Local display The local display is driven by 4511 7-segment decoder/drivers, IC7 & IC8. Also on the local display PC board is Q8. If the upper and lower trigger points have been set, the microprocessor uses Q8 to drive relay RLY1. The relay supplied is rated at 10 amps and 240VAC. The local PC board is connected to the expan­sion plug on the main PC board via a standard 10way ribbon cable and IDC (insulation displacement connectors) connectors. The display board in the local unit is connected back to the main PC board via a 10-way cable fitted with IDC connectors. April 1994  63 The PC boards for the remote display unit fit inside a small plastic instrument case with a red filter at one end for the displays to shine through. The buzzer can be considered optional & can be left out of circuit. down to the bottom and return. This may mean that the calibration is not set correctly. Want to leave that buzzer out? Why not? Once you have the unit up and running, this buzzer is largely superfluous. Remote display data As noted above, you can have a remote display which can be up to 800 metres away. The 8-bit serial data is sent via standard 6-way telephone cable by IC5, a Motorola MC3487 RS422 line driver. The microprocessor sends data to pin 1, clock signals to pin 7 and any alarm information to pin 9. IC5 converts these single line digital signals to two-line antiphase signals and these are sent along the telephone cable to the MC3486 quad RS-422 line receiver chip (IC1, Fig.3) which converts them back into single line digital signals. Monostable IC3a & IC3d is triggered on the positive edge of the first clock pulse from IC1. Pin 3 of IC3 goes high while the BCD data is clocked into 8-bit shift register IC2. This takes about 4ms. About 5ms later, pin 3 of IC3 will go low and this signal is AC-coupled to the latch enable pins of the display driver chips, IC4 & IC5. The data sent by the microprocessor is then shown on the 7-segment displays. When pin 3 of the monostable goes 64  Silicon Chip low at the end of its time period, pin 11 of IC3d goes high and triggers a second monostable comprising IC3c & IC3b. Pin 10 of IC3c goes low and at the end of the timing period will go high again and reset the shift reg­ister ready for another 8-bit word from the microprocessor. The whole process then repeats itself. Alarm A third line into the remote display is for the alarm. If the contents of the tank drop below 20%, the microprocessor takes its pin 14 high. This high appears at pin 13 of IC1 on the remote display board; it enables oscillator IC6a and, via IC6b, removes the reset condition on counter IC7. IC7a’s output drives the blanking inputs of IC4 and IC5, causing the display to flash. Counter IC7 now starts to count the pulses from the Schmitt oscillator, IC6a. 2048 pulses later, its pin 1 goes high and triggers monostable IC6c & IC6d and at the same time resets itself via D3. Pin 11 of IC6d now turns on Q2 which drives the buzzer. Therefore, approximately every 30 minutes the buzzer will beep on and off for about 6 seconds. If the alarm condition is removed by filling the tank up above 20%, the buzzer will stop and the display will cease flashing. (Editor’s note: if you decide that having the display flashing is enough warning of a low tank, you could dispense with the buzzer and the components associated with Q1 & Q2). Transducer heater The circuit built around transistors Q6 and Q7 (Fig.2) turns on a light bulb which is situated on the same board as the two trans­ducers. During daylight hours, the LDR (light dependent resistor) has a low resistance which holds Q6 and therefore Q7 off. The result is that the lamp is out. When night falls the resistance of the LDR rises. At a point around dusk, Q6 will turn on. This will supply base current to Q7 and the lamp will light. The lamp supplies a little warmth to the transducers to keep condensation from forming on them. Finally, we come to the power supply. This uses op amp IC6 to control a Darlington transistor pair (Q4 & Q5). A 10V zener, ZD1, regulates the supply to IC6 and trimpot VR4 is used to set the output voltage, Vcc, to +5V. Not much more can be said about the circuitry itself except that if the remote display is less than 100 metres from the main unit, then power can be supplied down the main data cable by using 8-core cable. If the distance is further than that, a sepa­rate power source will be required. Assembly The alarm board in the remote display unit sits upside down on top of the main board, as shown in this photograph. When building this project you must decide whether or not to include the local display PC board. If you only want to have a display in the house of DISP1 MSD LC5611 VCC 16 16 9 7 CLK D Q0 5 7 4 1 Q1 IC2b 4015 Q2 3 10 Q3 RST 6 3 LT A f B 2 C 6 5 e IC4 4511 D d c LE 4 b BI a 1 ALARM 14 CLOCK 7 6 10 15 9 9 1 10 2 11 4 12 6 13 7 a f e c d DISP2 LSD LC5611 VCC IC1 MC3486 15 3 5 1 RST 13 D IC2a CLK 13 7 12 1 11 2 2 6 VCC 3 LT A g f B C e IC5 4511 D 5 8 d c LE 4 b BI a 7x 470  10 14 15 9 9 1 10 2 11 4 12 6 13 7 a f g e 5.6k 1 11 c 0.1 3 IC3a 2 VCC 0.1 0.1 8 IC3c 9 27k 3,8 D1 1N914 27k 1 b d 8 4001 14 13 IC3d 12 b 3,8 16 14 8 g 27k D2 1N914 2 15 14 8 16 12 4 DATA g 7x 470  10 VCC 5.6k 1 4.7k 5 IC3b 4 Q1 BC558 C 6 7 E B VCC BUZZER VCC IN GND 5 OUT 6 14 270k IC6b 4093 4 D3 1N914 10k IC6a IC6c 10 VCC 3 2 RST IC7 4040 16 10 Q12 12 IC6d 11 4.7k C B E D5 1N914 Q2 BC548 1 47k BR1 W04 CLK 8 220k 22 13 9 11 1 8 7 B E C VIEWED FROM BELOW D4 1N914 IN 12-16V AC OR DC 1000 4.7 7805 GND OUT 10 VCC .0033 DIGITAL TANK GAUGE REMOTE DISPLAY Fig.3: the remote display has data sent to it via an RS-422 link which is converted back to normal data by IC1. The data is fed into shift register IC2 & then decoded by IC4 & IC5. present tank contents and not a display on the main unit then you do not need the extra PC board. Alternatively, you may opt not to have a display in the house, thereby saving the prob­lems of running the data cable. In this case, all you need to do is install the unit as described and supply power at the tank. Normally the main pump is situated near the tank and from here you can get power. Depending on what type of installation you want, there can be up to five circuit boards to build. We will start with the main PC board. Go over the PC board with a magnifying glass to spot any track faults and fix any that you find. This done, insert the resistors, capacitors and trimpots. Next, insert all diodes and transistors, making sure that they are correctly oriented, then insert all remaining components but at this stage do not install the microprocessor. Check all your work to ensure that all components are in the correct positions and properly soldered. Now connect a DC or AC supply of 10 to 18V. LED1 should light. Using your multi­ meter measure the voltage at the emitter of Q5. Adjust trimpot VR4 until the meter reads +5V. Measure the voltage at the supply pins of all chips and ensure that +5V is present. Measure the voltage at the emitter of Q1. It should be somewhere between April 1994  65 SQ-40R X1 Fig.4: the component wiring diagram for the main unit with local display. Note that the local display is optional. SQ-40T X2 12V LAMP 0.47 2.7k D2 Q1 LAMP IC9 4011 0.47 Q8 0.47 D 1 D3 4.7k 1 TO RLY1 TO EXPANSION SOCKET ON MAIN BOARD 1 +8V and +15V. Adjust trimpot VR3 and make sure that the voltage reading varies. Reset the voltage to +8V for the time being. Before you can go any further a display must be built. Either the local or remote display will do. Our description will start with the local display. Insert all components into the PC board and solder them in. Ensure that the displays are insert­ed the correct way. Having completed the local display the system can be tested. Using the 66  Silicon Chip 100k TX F E BUZZER 1 2 100k 5 1uF SET UP ALARM TX RX EXPANSION CLOCK TX 1 DATA TX VR1 .01 27k B 27pF .01 1 A C IC4 68705P3S 10uF 1 LK2 X3 2.2M 27k 27k IC8 4511 6 47uF 2.2pF 10k 1 1 IC5 MC3487 .01 IC1 LM358 LK1 10k 10k 10k 10k 10k 10k 1M 10k IC7 4511 68  47k .01 TP1 Q7 LDR TP1 CRO TRIG 10  D1 470  TP2 10k 1 Q5 1 3 IC2 4093 Q6 Q2 0.47 1 4 VR2 1k 100uF 470  470  470  470  470  470  470  VR3 7.5k Q3 470  470  470  470  470  470  470  1k .01 1k 10k 100uF 100k 10uF VR4 22uF 1.5k IC3 555 DISP2 Q4 K 10k 1 LED1 A 2200uF DISP1 1 1k 47k .0047 820  10uF IC6 LM741 4.7k 2200uF 100  220  BR1 ZD1 12-16V AC OR DC assembled cable supplied, connect the local display to the main PC board expansion pins, insert the microprocessor and switch on. After a few seconds the buzzer should give six short beeps. There may or may not be anything on the display. Place the setup link in the setup position, furthest away from the microprocessor. This shorts pin 12 of IC4 to pin 7. The buzzer should beep six times, pause about a second, then beep six times again. This will contin­ ue as long as the transducers are not connected. Place the setup link in the normal position. The six beeps will now be followed by a 6-second gap. If everything is happening as described then your system will function correctly when the transducer assembly is connected. Transducer assembly The transducer assembly can be built now. Solder the two transducers into the PC board as well as the lamp holder. Next connect the cable. The cable used has to be 3-core shielded. D5 22uF D4 IC6 4093 IC7 4040 10k 1 220k D3 4.7uF 10uF 1 Q1 BUZZER 1 1 Q2 4.7k 47k 270k 4.7k Fig.5: the component wiring diagram for the remote display. This has three boards, the one at the top providing a tank level alarm. 1 7x 470  27k 0.1 .0033 1 7805 6 A BR1 1 D2 0.1 27k 5.6k 100uF 7x 470  1 27k IC3 4001 0.1 1uF IC4 4511 5 DISP2 1 1uF 1 4 IC2 4015 B DISP1 3 IC5 4511 IC1 MC3486 2 5.6k TO MAIN PCB MATCHING NUMBERS Solder two leads to the active sides of the transducers and the third lead to the positive side of the lamp. The earth braid goes to the earth track on the PC board. Be sure to remem­ber which cable went to which point as the transmitting and receiving transducers will not work properly if they are swapped over. Next, connect the transducer assembly cable to the corre­ sponding terminals on the main PC board. Place the setup link into the setup position, then place the transducer assembly over the 90mm tube in the tank and again supply power. This time after a few seconds the buzzer should beep twice then after a second or two beep twice again. This should then continue as long as power is connected. The display should show some number. Adjust the cali­bration trimpot VR2 and the reading should vary. If all is well, then measure the actual depth of water at the moment. Convert this to a percentage of the maximum level of water, then adjust the calibration trimpot VR2 until the reading on the display corresponds with the calculated reading. Do not worry if the reading jumps a digit or two either side of the value you want as this is quite normal. Now place the link in the normal D1 12-16V AC OR DC position and listen to the buzzer. This time the buzzer will beep once every six seconds. If it beeps a second time then the display is updated. The software remembers the last four readings and compares the last reading with these. If they all the same then the displays are updated and the buzzer is The light dependent resistor (LDR) is mounted on the top of the case & is connected back to its terminals on the main PC board via flying leads. It can be secured in position using epoxy resin. beeped a second time to indicate that the reading is correct and the display was updated. When in the setup mode this software checking of the last four readings is by­passed. The last thing to be done at the main PC board is to test the anti-condensation heater. Connect the LDR to the The display board in the remote display unit is soldered at right angles to the main board. Lightly solder tack the two outside connections first, then make any necessary adjustments before soldering the remaining connections. April 1994  67 PARTS LIST 1 PC board, code CE/93/DTG, 128 x 84mm, 1 PC board, 100 x 52mm (local display) 1 PC board, 70 x 32mm (transducer head assembly) 1 plastic utility case, 159 x 95 x 54mm (Altronics Cat H-0151) 1 3.579MHz crystal (X2) 1 SQ-40R 40kHz ultrasonic receiver (X1) 1 SQ-40T 40kHz ultrasonic transmitter (X2) 1 PC-mount piezo buzzer 1 MES lamp and holder 1 12V DC 500mA plugpack 1 U-shaped heatsink to suit Q5 (Altronics H-0502) 2 10-pin DIL header sockets 1 10-way cable for local display 1 50kΩ 10-turn trimpot (VR1) 1 10kΩ horizontal trimpot (VR2) 2 1kΩ horizontal trimpots (VR3, VR4) 1 1µF 16VW electrolytic 4 0.47µF monolithic 3 .01µF monolithic 1 .0047µF metallised polyester 1 27pF ceramic 1 2.2pF ceramic Semiconductors 1 TL072 dual op amp (IC1) 1 4093 quad NAND Schmitt trigger (IC2) 1 555 timer (IC3) 1 68705P3 programmed microprocessor (IC4) 1 MC3487 RS-422 line driver 1 741 op amp (IC6) 2 4511 7-segment decoder/drivers (IC7,IC8) 1 4011 quad NAND gate (IC9) 5 BC548 NPN transistors (Q1,Q2,Q4,Q6,Q8) 1 BC559 PNP transistor (Q3) 1 TIP31 NPN transistor (Q5) 1 BD139 PNP transistor (Q7) 2 1N914, 1N4148 signal diodes (D1,D2) 1 1N4004 silicon diode (D3) 1 3mm red LED (LED1) 2 LC5611-11 7-segment LED displays 1 W04 bridge rectifier (BR1) 1 10V 1W zener diode (ZD1) Semiconductors 1 MC3486 RS-422 receiver (IC1) 1 4015 dual 4-bit shift register (IC2) 1 4001 quad NOR gate (IC3) 2 4511 7-segment decoder/drivers (IC4,IC5) 1 4093 quad NAND Schmitt trigger (IC6) 1 4040 12-stage counter (IC7) 1 7805 3-terminal 5V regulator 1 BC558 PNP transistor (Q1) 1 BC548 NPN transistor (Q2) 1 W04 bridge rectifier (BR1) 5 1N914 signal diodes (D1-D5) Capacitors 2 2200µF 16VW electrolytic 1 1000µF 16VW electrolytic 2 100µF 16VW electrolytic 1 47µF 16VW electrolytic 1 22µF 16VW electrolytic 3 10µF 16VW electrolytic 68  Silicon Chip Resistors (0.25W, 5%) 1 2.2MΩ 1 1.5kΩ 1 1MΩ 5 1kΩ 3 100kΩ 1 820Ω 2 47kΩ 14 470Ω 3 27kΩ 1 220Ω 10 10kΩ 1 100Ω 1 7.5kΩ 1 68Ω 2 4.7kΩ 1 10Ω 1 2.7kΩ Remote display 1 PC board, 85 x 50mm (main) 1 PC board, 50 x 25mm (display) 1 PC board, 60 x 50mm (alarm) 1 plastic case, 120 x 60 x 30mm 1 buzzer (with internal electronics) Resistors (0.25W, 5%) 1 270kΩ 1 10kΩ 1 220kΩ 2 5.6kΩ 1 47kΩ 2 4.7kΩ 3 27kΩ 14 470Ω Capacitors 1 1000µF 16VW electrolytic 1 22µF 16VW electrolytic 1 10µF 16VW electrolytic 1 4.7µF 16VW electrolytic 1 1µF 16VW electrolytic 3 0.1µF monolithic 1 3300pF ceramic Miscellaneous Red perspex filter, screws, nuts, lock washers, hookup wire. appropriate terminals on the PC board and insert the lamp into the holder in the transducer assembly. Cover the LDR with a dark cloth. The lamp should light and then go out when the LDR is uncovered. The next thing to do is to waterproof the transducer head assembly. We simply poured Selleys “Kwik Grip®” into the assembly. Use enough to cover the PC board by about 3mm. Do not allow any glue to enter the transducers or lamp holder. Installation Installation involves laying a standard 8-core telephone cable from the remote display to the main unit at the tank. As well as this, a 90mm hole must be cut in the top of the tank. Normally this would be done in the plastic strainer. If you do not require the remote display inside the house, then installation involves only cutting the 90mm hole and supplying power to the unit. Calibration is done by adjusting trimpot VR2. Included in the software are a few diagnostic routines. These are activated using a clip lead with one end connected to Vcc while the other end is touched on pins soldered to the cir­cuit board. Bridging pin B to Vcc will put the unit in diagnos­tics mode. Pins C, D, E and F are now used to select the diagnos­tic routines. Pin C will cause the transmitter to give a burst of energy then wait just long enough for the returning echo before trans­mitting again. This routine makes it easy to test the transmitter and receiver sections as the whole Tx/Rx trace can be more easily viewed on an oscilloscope. Under normal operating conditions the Tx/Rx trace occurs for about 12ms every five seconds. This makes it difficult to check the operation of the receiver but if we use this diagnostic routine, the Tx/Rx waveform is easy to inspect. Pin D will cause the displays, both remote and local, to be clocked from 0 to 99 and then through to 0, then upwards to 99 again. This test routine is useful in testing the data transmit­ ter and remote display, as well as the cable. Pin E will turn the relay on if it is fitted and pin F will turn it off again. It should be noted that before the next rou­tine can be executed the unit must Kit availability This project will be available in kit form from CTOAN Electronics, PO Box 211, Jim­boomba, Qld 4280. Phone (07) 297 5421. Kit 1 contains the PC boards for the main unit and the transducer head assembly, plus all on-board components including the transducers, lamp holder, heatsink and a programmed microproces­sor (note: does not include the local display board or components). Price: $90.00 + p&p. Kit 2 is a complete local display kit containing displays, PC board and all other components, including a strip of red perspex and a pre-assembled connecting ribbon cable. Price: $26.00 + p&p. Kit 3 is a complete remote display including case, PC board and all components. The plugpack is not included. Price: $32.00 + p&p. Postage and handling on each kit is $5.00. CTOAN Electronics will also be offering the following back-up service on this project: (1) Fix any fault not including microprocessor replacement – $30.00; (2) Microprocessor replacement – $25.00; (3) Reprogram microprocessor with updated software – no charge. Note: copyright of the PC boards for this kit remains the property of CTOAN Electronics. be taken out of diagnostic mode by bridging pin A to Vcc. Now re-enter diagnostic mode and select a different routine. When in normal mode (the default mode at power-up), bridging pin C will display the presently set upper limit. Note that the power-up default for the upper limit is 99, while the lower default is zero. This effectively means that the relay is disabled when the unit is first turned on. Bridging pin E will advance the tens digit and pin F will advance the units digit. Once the required upper limit is on the display, bridge pin A. This will store the new upper limit and put the system back into normal mode. The lower limit is set in a similar fashion by bridging pin D which will display the present­ly set lower limit. Pins E and F will again advance the tens and units digits as before and pin A will store the new value and put the system back into normal mode. Be aware that the software does not check to see if the upper limit is higher than the lower limit and visa versa. You must ensure that this does not happen when you set the upper and lower limits. Once the limits have been changed from the default values, the pump will effectively be enabled. The pump relay will be energised when the level in the tank falls below the set lower limit and will remain energised until SATELLITE SUPPLIES Aussat systems from under $850 SATELLITE RECEIVERS FROM .$280 LNB’s Ku FROM ..............................$229 LNB’s C FROM .................................$330 FEEDHORNS Ku BAND FROM ......$45 FEEDHORNS C.BAND FROM .........$95 DISHES 60m to 3.7m FROM ...........$130 the level of water rises above the set upper limit. Remote display assembly There is nothing special about the construction of the remote display – just follow Fig.5 and make sure that your soldering is of a high standard. Once you have completed the remote display, connect it to the system via suitable cable. We used 8-way ordinary telephone cable. Power for the main PC board at the tank was supplied along two of the wires in the 8-way core telephone cable. The whole system was then powered by a 500mA plugpack. Power up the system and check the operation of the remote display. It should read the same as the local display. To test the operation of the alarm, raise the tube in the tank until the reading drops below 20%. This is best done with the setup link in the setup mode. The display should start flashing when the level reads 19% and 30 minutes later the buzzer should sound for about six seconds. One last point to consider is that the box that you use for the main PC board out near the tank must be made waterproof. Any water that gets in during rain will surely damage the unit. Also remember that the microprocessor is only rated to 60°C so do not leave the unit in direct sunlight. It should be in SC permanent shade. LOTS OF OTHER ITEMS FROM COAXIAL CABLE, DECODERS, ANGLE METERS, IN-LINE COAX AMPS, PAY-TV DECODER FOR JAPANESE, NTSC TO PAL TRANSCODERS, E-PAL DECODERS, PLUS MANY MORE For free catalogue call or write to . . . L&M SATELLITE SUPPLIES 33-35 WICKHAM RD MOORABBIN 3189 PH (03) 553 1763 April 1994  69 Using the Icom R7000 as a spectrum analyser The Icom-R7000 & similar receivers can be readily interfaced to a personal computer to form a simple, inexpensive spectrum analyser. The resulting analyser has 100dB of dynamic range & is capable of examining almost any section of the spectrum between 25MHz & 2GHz. Several different resolutions can be selected, from 2.8kHz to 150kHz. By JAMES LLOYD & JOHN STOREY* What makes this possible is that the Icom, like many modern receivers, incorporates a CPU-controlled PLL synthesiser. This same CPU controls the other functions of the receiver and can itself be controlled from the RS-232 port of a personal comput­er. The only modification required to the receiver is to tap into the AGC (automatic gain control) line to meas*School of Physics, UNSW, Kensington. 70  Silicon Chip ure the signal strength. Once this is done, all that is required is software to scan the receiver through the range of frequencies of interest, to record the signal strength at each frequency step, and to display the result. Receiver interface The interface between the PC and receiver is the “Icom Communication Interface V” (CI-V). The first thing needed is a small piece of hardware to convert the CI-V voltages to and from RS-232 levels. This little box is avail- able from Icom but in fact, it contains little more than a MAX-232 integrated circuit and would be easy to build. The Icom CI-V is a serial, half-duplex bus which has the advantage of being able to control several receivers. This actu­ally presents a few difficulties in interfacing to a PC. Firstly, the RS-232 standard is full-duplex (having a separate transmit and receive line) and has hardware hand­shaking facilities. This hardware hand­shaking allows the transmitter and receiver to agree when they are both ready to exchange data. The CI-V bus, however, consists of just a single data wire plus ground. The problem of bus arbitration (or agreeing who can talk and when) is tackled with the CSMA/CD (Carrier Sense Multiple Access with Collision Detection) protocol. This simply means that any device may try to use the bus at any time. Any collisions (more than one party attempting to transmit simultaneously) are detected and resolved by one of them waiting for the other to complete. This allows multiple devices on the one bus and is generally an efficient protocol if the bus is not over-committed. However, it does present some difficulties in implementation on a PC, since there is no readily available “carrier-sense” signal. We solved this problem by allowing all the communications between the receiver and the computer to be handled by a share­ware communications library. This tests for “line busy” by moni­toring the traffic in and out of the data buffers, thus emulating the “carrier sense” signal, equating carrier to transmission or reception of data. When the receiver detects a collision, it transmits a series of jammer codes which cause the software to stop sending. At the end of a command string the receiver transmits “acknowl­ edge” signals which are monitored to ensure reliable operation. The general command structure is a stream of bytes, con­sisting of two preamble bytes (to signify the start of the com­mand, each being the value FE hex), a destination or “to” address (08 hex is the default for the R7000), a sender or “from” address (default E0 hex for the controller), one or two bytes specifying the command number and an optional subcommand number, a variable number of data bytes and an-end-of-command byte (FD hex). The frequency data is sent as five BCD (Binary Coded Deci­mal) bytes, in least significant to most significant order. Binary coded decimal is a scheme whereby each decimal digit is encoded as a 4-bit nibble and thus a 2-digit number can be encoded in one byte. For example, the frequency 123.456789MHz would be sent as the bytes 89 67 45 23 01 (BCD). Since the tuning step is 100Hz, the first byte (1’s and 10’s of Hz) is ignored. The GHz digit is also ignored, since the 1-2GHz range of the receiver is set by manually pressing a button on the control panel. To “set frequency” the command number is 05, with no sub­command. To tune the receiver to the frequency 123.4567MHz, the command string would be FE FE 08 E0 05 00 67 45 23 01 FD. The receiver then sends a response, addressed to the controller, with a value in the command number field indicating the success (FB) or failure (FA) of the command. Thus, a successful command would return Fig.1: this buffer circuit was used to isolate the AGC line from the receiver and thereby avoid any loading effects from the PC. the string FE FE E0 08 FB FD. The complete process of stepping to a new frequency thus requires a total of 17 bytes. At 1200 baud, this takes approximately 120ms, plus the response time of the receiver CPU. The minimum step size of the synthesiser is 100Hz. Actually, the digital synthesis is done in 1kHz increments. The 100Hz steps are generated within the Icom with a D/A converter driving a VFO. However, for our present purposes this is of no consequence. The maximum step size can be anything you like and in fact the receiver could be hopped about in frequency in a completely random manner, though it’s hard to imagine why anyone would want to do so. Normally, one would choose a step Fig.2: this spectrum is the electromagnetic interference from a 33MHz 386 PC taken over the range from 50 to 100MHz. Radiation below 50MHz was found to be negligible. The 99MHz peak is most likely the third harmonic of the 33MHz internal CPU clock & the others are probably harmonics of the bus clock. April 1994  71 the same way as for the frequency commands. Extracting the AGC voltage To extract the AGC voltage, it is necessary to open the receiver, identify the relevant circuit connection and bring it out to a suitable socket. We chose to add a buffer amplifier to avoid any possibility of disturbing normal operation of the receiver. As shown in Fig.1, the buffer circuit uses an OP90 op amp as it has low power consumption, low offset voltage and operates from a single supply. The circuit has a gain of 2, to bring AGC voltage swing up to the full input range of the analog/digital converter. Icom are even kind enough to supply the R7000 receiver with a spare RCA jack on the rear panel, so no chassis work is re­quired. Measuring the AGC voltage Fig.3: this is the radiated spectrum of ABC channel 2 as received at Kensington, on the UNSW campus. This plot shows the structure of a television signal in the vicinity of the vision carrier (& should convince any doubters, if they still exist, of the reality of sidebands). The video signal is amplitude modulated onto the carrier & the dominant frequency component of this modulation is at the linescan frequency of 15.625kHz. The sidebands are thus located 15.625 kHz apart and extend symmetrically either side of the carrier. (Close in to the carrier the sidebands are expected to be equal. If the scan covered a wider frequency range the vestigial sideband character of the modulation would become apparent). The scan was performed with the “SSB” filter (FWHM of 2.8kHz), in 1.4kHz steps. size equal to half the filter bandwidth. This “Nyquist sampling” ensures the maximum amount of information is extracted from the spectrum. The settling time of the receiver tuning circuit is very fast. However, the AGC amplifier incorporates a time constant which is different for each of the receiver modes. In a moment we will show how we use the different modes to give the different filter resolutions. For the AM filter, the AGC time constant has been measured and found to be approximately 200ms. The AGC set­tling occurs concurrently with the transmission of the “acknowl­edge” signal, so it is not all “dead” time. Including all over­heads and settling time, reliable tuning of the receiver (to a signal stable within 0.5%) is 72  Silicon Chip achieved in approximately 500ms. Slight speed improvements could be made by increasing the trans­mission speed, or sacrificing stability in the signal. The resolution of the scan can be selected by choosing the R7000 receive mode which then selects the IF filter bandwidth. The filters have bandwidths of 2.8kHz (SSB), 6kHz (AM/FM narrow), 15kHz (AM/FM), 150kHz (FM wide). The receive mode (and hence filter bandwidth) is selected with command number 06 prior to beginning a scan, in a similar way to the frequency stepping mode. For example, selection of the AM filter (data field 02) would be done by the command string FE FE 08 E0 06 02 FD. The receiver responds in exactly In order for the computer to be able to read the AGC vol­tage, an analogto-digital (A/D) converter is of course re­quired. Almost any A/D would be suitable here, as the application is quite undemanding. We used a 12bit PC ADDA-12 card from ESIS in Sydney. This inexpensive unit works particularly well and has a conversion time of only 60 microseconds but care must be taken when using a fast computer. The card uses a monolithic successive-approximation con­verter which is clocked by strobing a register on the card. If this happens too quickly, the converter becomes confused and the accuracy drops dramatically. On the 386-33 PC that we used, we had to add delays in the code to prevent this from happening. The AGC voltage output of the receiver is highly non-linear with signal strength, as one might expect. Conversion of the raw AGC voltage to signal strength is achieved in the computer using a simple look-up table with linear interpo­lation between points. Creating the look-up table requires the use of either a calibrated signal generator or a signal genera­tor plus calibrated attenuator. The Icom R7000 receiver conveniently includes a 20dB switchable attenuator in the front end which could be used to get the calibration procedure off to a good start. Separate tables are needed for each of the SOLID STATE “PELTIER EFFECT” COOLER - HEATER Further to our advertisment somewhere else in this issue, we can offer a set of major parts needed to make a solid state thermoelectric cooler - heater. We can provide a large 12V-4.5A Peltier effect semiconductor, two thermal cutout switches, and a 12V DC fan for a total price of: $45 We include a basic diagram/circuit showing how to make a small refrigerator/ heater. The major additional items required will be an insulated container such as an old “Esky”, two heat­sinks, and a small block of aluminium. CAR ALARM We have purchased a good but limited quantity of this well known brand Australian made car alarm. It has been made obsolete because it doesn’t feature UHF remote control. But look at the features: voltage drop detection (wired directly or internal), pin switch detection for bonnet/ boot, piezoelectric movement sensor, optional passive arming via ignition switch, ignition disable via master switch if passive arming is not used, may be wired to existing door pin switches to act as a switch - sensing last door arming alarm, 30-second entry delay, 7-second entry delay, flashing LED - intrusion indicator provided, flashes vehicle indicators when alarm is sounding, extra negative output to power second siren or pager, colour coded wiring siren provid­ed, powerful 40 watt 125dB siren which employs a dynamic speaker: a sound that makes most car alarm sirens sound like toys!! $48 With the car alarm package we will also include a circuit and notes on how to modify the entry and exit times, and how to make it UHF remote controlled: our single channel UHF remote control is available: $17 for the transmitter, $34 for the re­ceiver. C.O.B. SOUND GENERATOR MODULES Stamp sized PCBs with an LSI sound generator IC that is surface mounted on them. Work from approximately 3V and have negligible standby current. Require a few external components to become complete sound generators: typically two resistors, one capacitor, one transistor and a speaker. FOUR TRAIN NOISES (excellent for model railways): $4 AMBULANCE, FIRE + POLICE SIREN, PLUS MACHINE GUN: $2.50 16 DOOR-CHIME TUNES: $4 CLASSIC DING-DONG DOOR CHIME: $3 IR “TANK SET” *** SUPER SPECIAL *** ON SPECIAL is a set of components that can be used to make a a very responsive infrared night viewer. The matching lens tube and eyepiece sets were removed from working military quality tank viewers. We also supply a very small EHT power supply kit that enables the tube to be operated from a small 9V battery. The tube emloyed is probably the most sensitive IR responsive tube we ever supplied. The resultant viewer requires low level IR illumina­tion. Basic instructions provided. The price is $120 for the tube, lens, eyepiece and the power supply kit. When ordering, specify preference for a wide angle or a telescop­ic objective lens. IR FILTERS A high quality military grade, deep infra red IR filter. Used to filter the IR spectrum from medium-high powered spo­tlights. Its glass construction makes it capable of withstanding high temperatures. Approx. 130mm diameter and 6mm thick. For use with IR viewers and IR responsive CCD cameras. Limited stock: $40 Ea. ARGON HEADS These low voltage air cooled Argon Ion Laser Heads are priced according to their hours of operation. They produce a bright BLUE BEAM (488nm) and a power output in the 30-100mW range: depends on the tube current. The head includes power meter circuitry, and starting circuitry. We provide a simple circuit for the supply. Limited supplies at a fraction of their their real cost: $500 - $650 FIBRE OPTIC TUBES In early May we will have some used single stage, first generation, “passive” image intensifier tubes in stock. These are US made, in excellent condition, and have 25/40mm diameter, fibre-optically coupled input and output windows. Both the tubes are basically cylindrical. The 25mm tube has an overall diameter of 57mm and is 60mm long, whilst the 40mm tube has an overall dia­meter of 80mm and is 92mm long. The gain of these is such that they would produce a good image in aproximately less than 1/4 moon illumination when used with suitable “fast” (low light lenses), but they can also be IR assisted with low level IR sources to see in total darkness. The superior resolution of these tubes would make them suitable for low light video pream­plifiers, high quality wild life observation, and astronomical use. Each of the tubes is suplied with a 9V/ EHT power supply kit and they are priced at an incredible: $125 .... for the 25mm intensifier tube/ supply. $190 .... for the 40mm intensifier tube/ supply. very interesting pattern displays from a laser beam. Includes two motors, two potentiometers, two Darlington transistors, two front surfaced aluminium mirrors, instructions and small hardware: most items that are needed to make a two motor laser deflection kit. $15 X-Y LASER SCANNER - KIT You could spend thousands of dollars buying commercial X-Y scanners for laser beam deflection. This X-Y scanner compromises by employing two suitable DC motors to achieve good results. With normal levels the motors don’t actually spin but simply vibrate around the set position. The PCB and components kit include rectification and filter­ing (power supply), audio preamplifiers, audio filtering, and two separate power amplifiers to drive the two deflection motors. The scanner is powered from a 16VAC-900mA plugpack. In one of the modes of operation the scanner can produce a totally random 2-dimensional display which is dependant on the actual music picked up by the electret microphone. A second mode of operation enables the power amplifiers to be driven from external oscillators and/or pre-taped signals recorded on a stereo cassette recorder. A short form kit of parts is available for the X-Y scanner. It includes a screened and solder masked PCB and all the on-board components, an electret microphone, two motors, and two light­weight mirrors. LASER POINTER Improve and enhance all your presentations. Not a kit, but a complete commercial 5mW/670nm pen sized pointer at a SPECIAL PRICE of: $120 DIVERGING LENS A high quality laser beam diverging (beam expander) glass lens, mounted on an aluminium plate, with mounting screws provid­ed. Dimensions: 25 x 25 x 6mm. Two of these cascaded provide sufficient expansion for use in HOLOGRAPHY. In conjunction with additional lenses these can also be used to diverge a laser beam. Great for experimenting with laser beams. $5 CRYSTAL OSCILLATOR MODULES These small TTL Quartz Crystal Oscillators are hermetically sealed. Similar to units used in computers. Operate from 5V and draw approximately 30mA. TTL logic level clock output. Available in 4MHz, 4.032MHz, 5.0688MHz, 20MHz, 20.2752MHz, 24.74MHz, 40MHz, and 50MHz. $7Ea. or 5 for $25 LED DISPLAYS National Semiconductor 7-segment common cathode 12-digit multiplexed LED displays with 12 decimal points. Overall size is 60 x 18mm, and pinout diagram is provided. 2.50 Ea. or 5 for $10 FM MICROPHONE Features a stainless steel case and a UNIDIRECTIONAL micro­phone insert, powered by two “AA” batteries. High quality at: $28 DYNAMIC MICROPHONE Stage quality unidirectional (cardioid) 600-ohm dynamic microphone in a black metal housing. Has on/off switch and Cannon connector. Prewired lead and clip provided. $39 FANS Brand new German made PAPST brand 115V-12W fans with metal blades. Overall dimensions 80 x 80 x 38mm. Use two in series to run off mains? LIMITED STOCKS. $14 PROFESSIONAL MICROPHONE CABLE High quality twin core flexible shielded microphone cable. Heavy duty construction, red in colour, overall diameter is 6mm, has a tightly woven shield and two 24-strand centre conductors (red and black). Uses lots of copper: the resistance of one of the centre wires is 2.4 ohms per 100 meters, which is lower than the resistance of one of the conductors in a typical 10A mains extension lead! The resistance of the shield is 1.4 ohms per 100 metres. Excellent for professional use in rugged environments and stage use. Also suitable for low voltage shielded power cables. Priced at a small fraction of its real value: $1.50 PER METRE SPEAKER GIVEAWAY One 3" tweeter, one 4" woofer, a non polarized crossover capacitor, plus a diagram: $10 for the set 2 sets (STEREO) for $18!! MEDIUM BRIGHTNESS LEDs With a luminous output of approximately 7mCds <at> 20mA, these 5mm LEDs are more than 10 times brighter than ordinary LEDs. Available in GREEN, YELLOW and AMBER, and priced below ordinary LED prices: 20c Ea. 10 for $1.80 or 100 for $15 For any mix of colours. OATLEY ELECTRONICS MOTOR DEFLECTION KIT This inexpensive kit can produce some PLEASE ALSO SEE OUR ADVERT ON PAGE 39 PO Box 89, Oatley, NSW 2223 Phone (02) 579 4985. Fax (02) 570 7910 Major cards accepted with phone & fax orders. P & P for most mixed orders: Aust. $6; NZ (airmail) $10. April 1994  73 monotonicly decreasing part of the curve, where there is only one signal value for a given AGC voltage. At zero and 10dB on the FM wide filter curve, there are two signal strength values for the one AGC value). Thus the system currently has a (software limited) sensitivity of 3 microvolts in the most sensitive bands. Software Fig.4: this is a spectrum taken of the FM band from 88 to 108MHz, taken with the FM WIDE filter (150kHz) in 75kHz steps. The anten­na was just a length of wire. The large peak at 107.3MHz is 2SER which is located on the University of Technology building in Ultimo and has a line of sight view to the Physics building at UNSW. The peak at 102.5MHz is 2MBS, with a transmitter located on the AMP building in Sydney, again very close and line of site to Kensington. Although the stations with powerful transmitters (2DAY 104.1, 2MMM 104.9, 2JJJ 105.7 and ABC 92.9) appear very weak, it should be noted that the vertical scale is linear and these stations are only a few dB below the most powerful. receiver filters and (at least in principle) for each of the four “front-ends” which the receiv­ e r automatically switches between as it changes bands. However, this variation of calibration with frequency is probably only a small effect and in many applications the system is only required to operate over a narrow frequency band. The data gathered by the calibration procedure is used to convert AGC voltage to signal strength, using a look-up table with linear interpolation. The discontinuities in the graph are an artefact of the signal generator used and occur at points where it switches circuits to alter range. Note the very wide dynamic range achievable, 100dB in the case of the AM filter. The soft­ware used only the The Icom R7100 Communications Receiver The Icom communications receiver pictured here is the R7100 model. This supersedes the R7000 model referred to in this article but it can be used for spectrum analysis in exactly the same way. Among its many features, the R7100 continuously covers the frequency spectrum from 25MHz to 2000MHz, has all-mode capability, 900 memory channels, and either direct keyboard entry or manual frequency selection. For further information, contact Emtronics, 92-94 Wentworth Ave, Sydney. Phone 211 0988. 74  Silicon Chip Depending on capabilities of the PC and on what your fa­vourite programming language is, the software can range from simple to complex. We wrote our program in C, with the following modules: (1) R7000LIB to handle the communications to the receiver, covering commands to set and read the frequency and receiving mode and interpret the responses for the receiver; (2) ADDALIB to perform the A/D conversions; and (3) AGCTOSIG to convert AGC voltages to signal strength using the data files generated from known signal strengths. Using these libraries, we built programs to perform auto­ mated scans, interactively scan, draw graphs and so on. The system can be used as a spectral analyser for virtually any application within the tuning range of the receiver (25-999MHz and 1025-1999MHz in the case of the Icom R7000). The main limitation is one of speed. Because of the time taken to scan across the spectrum, the result will only be meaningful if the spectrum is effectively unchanging during this time. The accompa­ nying spectrum plots demonstrate the capabilities of the system. Conclusion Computer interfacing to the Icom R-7000 receiver is straightforward and gives satisfying results. In fact, under computer control the extraordinarily good performance of these receivers in terms of versatility, stability, sensitivity and low spurious response levels becomes apparent. The spectrum analyser described here is just one example of what can be done once a PC is given control of the receiver and is able to monitor signal strength. Another interesting application for the avid SWL or DX’er would be to log the signal from various HF stations from around the globe. Why not become your own ionospheric SC prediction service? SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Rod Irving Electronics Pty Ltd SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Rod Irving Electronics Pty Ltd SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Rod Irving Electronics Pty Ltd SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Rod Irving Electronics Pty Ltd SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Rod Irving Electronics Pty Ltd PRODUCT SHOWCASE Kenwood K series midi sound systems Kenwood’s new K series midi lineup comprises the K-99M, K-88M, K-77M and K-66. Aside from their stylish lines, the new line-up has such features as Environmental Sound Enhancement, DSP, Omni-Directional speakers (optional), Graphic Equaliser/Spectrum Analyser, Dolby Pro-Logic Surround Sound, Dolby 3-stereo and Karaoke (K-99M). All systems are designed to be used as dedicated audio systems or to be integrated into the home video system. The DSP and presence circuits create the ambience of a number of “live” venues in the user’s own living room. Kenwood’s DSP (K-99M & K-88M) offer the choice of seven modes including Jazz Club, Church, Arena and Stadium, while the K-77M and K-66 offer similar effects through Kenwood’s ASP (Acoustic Sound Processor) circuitry. The AI (Acoustic Intelligence) features (eg, Auto Edit) allow the user to trim or rearrange songs so that a longer CD will fit on a shorter cassette. Addi- Crystal oscillator without an oven The trouble with traditional designs of crystal oscillator is that they require an oven to maintain high temperatures for stable output. This means that they are bulky, require a high current of typically 500mA and take as much as 20 minutes to warm up to temperature when switched on. GEC Plessey Semiconductors (GPS) has solved these problems with a new design of crystal oscillator, which uses digital tem­ perature compensation to achieve an ultra-stable output without the need for an oven. The OD9301 has no warm-up delay and the typical current consumption is less than 15mA. Also, as an oven is not required, the OD9301 is supplied in 80  Silicon Chip tionally, AI automatically checks the CD being played and creates the ideal equalisation curve to match it. These curves can also be stored in memory for later use (K-99M). The K Series midis can also be configured with several options including: turntable (all models), omnidirectional speakers, surround speakers and centre speaker (K-99M only), surround speakers and subwoofer a small package measuring only 36 x 26 x 12mm. The OD9301 allows for external frequency trimming and may be specified anywhere within the frequency range of 4-25MHz. The device uses a proprietary algorithm that enables it to give superb phase noise and short term stability performance whilst also meeting very tight frequency versus temperature specifications. The excellent frequency stability of ±0.3 parts per million (-10°C to +70°C) or ±0.5 parts per million (-40°C to +85°C) makes it ideal for use as a reference source in base stations for GSM, DECT and PCN or for military communications systems. For further details, contact GEC Electronics, Unit 1, 38 South St, Rydalmere 2116. Phone (02) 638 1888. (K-99M, K-88M), subwoofer (K-77M). Pricing is as follows: K-99M $3859; K-88M $3099; K-77M $2699; and the K-66 $2199. All models are covered by a 3-year parts and labour warranty with 12 months on the laser pick-up. If you would like further information on the K Series, con­tact Kenwood Electronics Australia Pty Ltd on (02) 746 1888 for your nearest Kenwood dealer. Dali 5A Mk2 loudspeaker Dali 5A Mk 2 is the largest in the range of Australian assembled Dali models. The Dali 5A Mk 2 features dual 18cm bass drivers with rubber suspension surrounds, textile dust­ caps and thick polypropylene cones. The powerful magnetic circuit features an aluminium short-circuiting ring in the pole piece which reduces second harmonic distortion. The use of two relatively small bass drivers within the one cabinet gives high sensitivity (93dB for one watt at one metre) with high power handling; amplifiers up to 120 watts per channel are recommended. The tweeter chosen for the speaker is a special design using a soft textile dome with a ferrofluid coiled voice coil. This is particularly well damped and has excellent transient response. The front baffle of the Dali 5A Mk 2 is Digital handheld clamp meter Meter International has released the MIC 2080W handheld, clamp-on, autoranging power meter. It is designed to measure various electrical parameters without the need to break the circuit. The meter features AC/DC current measurement to 1000A and true RMS voltage to 650VAC or 1000VDC. The MIC 2080W can measure true power to 200kW and frequency to 2kHz. The meter uses Hall Effect technology to measure true RMS current accurately, almost regardless of the waveform, to a crest factor of three. The measured value is displayed on a 3.5-digit liquid crystal display with an analog output provided for monitoring the current wave­form with an oscilloscope. The MIC 2080W is available from Computronics International, 31 Ken­ sington Street, East Perth, WA 6004. Phone (09) 221 2121. covered in “Acous­ti-Flock” absorbent material, in order to reduce edge diffraction and improve stereo imaging. Dali 5A Mk 2 is supplied with rigid steel spikes, which are claimed to couple the speaker securely to the floor and improve bass response and stereo imaging. Dali 5A Mk 2 is supplied in mirror-imaged pairs and sells for $1598 per pair. For further information, contact Scan Audio Pty Ltd, 52 Crown Street, Richmond, Vic 3121. Phone (03) 429 2199. Ultrasonic cleaner for small components Until you have used one of these ultrasonic baths for cleaning small components you don’t know how handy and effective they can be. They’re great for cleaning drawing pens, jewellery, small mechanisms, connectors, PC boards, camera bits and even (perish the thought) your dentures. Essentially it consists of a small stainless steel bath which has a piezoelectric transducer epoxied to its underside. The piezo transducer is driven ultrasonically and it agitates the cleaning fluid so completely that dirt, grease and grime just stream out of the components. This new model from Jaycar has four timer intervals of 4, 8, 12 & 16 minutes and its tank capacity is 570 millilitres. It runs from 240VAC, is priced at $169 and is available from all Jaycar Electronics stores and dealers. Model railway sound module Oatley Electronics has sourced a sound generator module that will directly appeal to model railway enthusiasts. Essen­tially it is an LSI chip bonded directly to a very small PC board measuring 29 x 16mm. This has 14 circuit connections brought to one edge and requires two external resistors, one capacitor and a battery pack, a loudspeaker and a 4-way switch to select one of the four available sound effects: whistle blowing, train chugging along, level crossing bell and train crossing a bridge. The module can be powered from a battery pack ranging from 2.4V to 6V although the sound effects are voltage dependent and to be honest, some effects are much more convincing than others. We have not had a chance to try modifications but it is possible to change the external components to modify the sound effects. Current consumption is very low: less than 1µA on standby and 0.2mA when operating. The cost is very cheap at just $4.00. Also available are three other modules: four sound effects (ambulance, fire, police siren and machine gun) for $2.50, a 16-tune door chime for $4.00 and a ding-dong door chime for $3.00. They are available from Oatley Electronics, PO Box 89, Oatley, NSW 2223. Phone (02) 579 4985. CALLING ALL HOBBYISTS We provide the challenge and money for you to design and build as many simple, useful, economical and original kit sets as possible. We will only consider kits using lots of ICs and transistors. If you need assistance in getting samples and technical specifications while building your kits, let us know. YUGA ENTERPRISE 705 SIMS DRIVE #03-09 SHUN LI INDUSTRIAL COMPLEX SINGAPORE 1438 TEL: 65 741 0300    Fax: 65 749 1048 April 1994  81 Product Review G-Code: the easy way to program your VCR Are you one of the millions of Australians who can’t or can’t be bothered programming your VCR to record? If you are, this new product, called G-Code, could make it a whole lot easier. By LEO SIMPSON G-Code is a small plastic box which you program with numbers from “TV Week”. The G-Code Instant Video Programmer then controls your VCR via its infrared LEDs and you no longer have to worry about the intricacies of programming. The G-Code Instant Video Programmer is claimed to work with any of 82  Silicon Chip 90 brands of VCR. The only proviso is that it must have an infrared remote control. G-Code controls the VCR by emulating the remote control functions of record, channel selection and stop. The G-Code Programmer looks like a small version of a port­able CD player and measures 99mm wide, 120mm deep and 32mm thick. Like a portable CD player, it has a liquid crystal display and a lift-up lid but instead of a CD compartment it has an array of pushbuttons, as can be seen in the photo below. There is an array of numerical buttons plus buttons marked Cancel, Review, Weekly, Once, Daily (M-F) and Add Time. Not shown in the photo is a row of seven smaller buttons which are used in the initial setting up of the unit. These are labelled Video, Cable/Sat, Channel, Clock, Alter, Save & Enter. When (and if) you buy the G-Code unit, you first have to tell it what brand of VCR you have. You do this by sitting the unit near your VCR which should be switched into the standby mode. You then enter the two digit code which is peculiar to your brand of VCR and press the ENTER button. For example, the code for JVC models is 21. That done, the VCR should turn on as it is addressed by the G-Code unit. You then press the SAVE button and continue to set G-Code unit’s clock with the date and time. Having set the date and time, you then have to tell it which TV stations are received on your VCR and what channel numbers are allocated to them. Again, this is a straightforward procedure, set out in the brief and well-written manual. Finally, you can run a test to make sure that everything is set up correctly. You place a blank tape in your VCR and turn it off, then key in the highest channel number your VCR is able to receive. For example, if your VCR can receive 15 channels, you key in 0015 and then hit the “Once” button. The G-Code Programmer flashes an orange LED to indicate that it is transmitting and it turns on your VCR, selects channel 15, makes a brief recording and then turns the VCR off again. From then on, the unit is ready to go and you can program it to make your VCR record at any time. Initially, the G-codes will be featured in “TV Week” magazine but it is expected that all major TV guides will quickly adopt the codes. The procedure is quite simple. Say you want to record a program such as “The Bill” on ABC TV. Look up “TV Week” and note the digital code – this can range from three to eight digits and appears to be quite random. Enter the code and the liquid crystal display will indicate the stored channel, time and date, and the length of tape required to record the program. At the appointed time, the G-Code unit will operate your VCR, and provided it has a blank tape cassette inside, it will record the program and then switch the VCR back into standby mode. Magic, eh? The G-Code Programmer can store up to 12 shows to be recorded at various times and you can review these times by pushing the Review button. You can program up to 27 days in advance. The unit will flag any clash between programs to be recorded and you then have the option of cancelling a particular program. You can also arrange to add extra time, in increments of 15 minutes, to cater for a program running over time. The G-Code Programmer runs from four AAA alkaline cells and battery life is estimated to one year under normal usage. When the battery is due to be replaced, a “LO BATT” message will be indicated on the LCD panel. We had a sample G-Code Programmer for this review and I set it up with my 7-year old Sharp VCR. The setting up procedure took about five minutes and it all went exactly according to the book. Indeed it is quite uncanny to see your VCR silently turn itself on and go into record mode when you know you have not touched the machine or its remote control and it is has not been programmed itself. Programming the G-Code Programmer is much easier than fid­dling with the itty-bitty buttons on your VCR, even to one famil­iar with the procedure. Instead of kneeling down and peering at poorly lit buttons on the VCR, you can sit at a table in good light, and simply punch in the numbers for each program to be recorded. So why have we had to wait so long for this product? It has been available overseas for some time under various names. In the USA for example, it is known as VCR-Plus. It was developed by Gemstar in the USA and is now being distributed exclusively in Australia by Philips Consumer Products. Initially, the G-Code numbers will be used in “TV Week” magazine and are expected to be eventually licensed to most major TV program guides. The G-Code Programmer comes with a cradle which can be positioned on top of your VCR, with the unit slightly overhanging the front. However, you can position the unit virtually anywhere in an average sized room since it has infrared LEDs aiming from its back corners as well as the front – this unit really does seem to have been well thought out. And if you get into any strife while setting it up or using it, Philips has a toll free number (131 124) to help you sort it out. The G-Code Programmer is priced at $129 and will be avail­able Australia-wide from department and electrical stores. It comes with a 6-month SC warranty. Subscribe now to the largest faults & remedies library in Australia ✱ ✱ 1994 manuals are now available. Our database is regularly updated with information supplied by technicians such as yourself. ✱ Exclusive backup service by qualified technicians. ✱ ✱ Over 10,000 faults and remedies on file with flow charts and diagrams. Covers Colour TVs and VCRs of all brands sold in Australia EFIL Phone or fax now for your FREE information package ELECTRONIC FAULT INFORMATION Reply Paid 4 P.O. Box 969 AIRLIE BEACH 4802 Ph 079 465690 Fax 079 467038 April 1994  83 Silicon Chip Designing UHF Transmitter Stages. February 1990: 16-Channel Mixing Desk; High Quality Audio 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. BACK ISSUES September 1988: Hands-Free Speakerphone; Electronic Fish Bite Detector; High Performance AC Millivoltmeter, Pt.2; Build The Vader Voice; Motorola MC34018 Speakerphone IC Data; What Is Negative Feedback, Pt.4. 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. December 1988: 120W PA Amplifier (With Balanced Inputs), Pt.1; Diesel Sound Generator; Car Antenna/Demister Adaptor; SSB Adaptor For Shortwave Receivers; Why Diesel Electrics Killed Off Steam; Index to Volume 1. 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; Build A Synthesised Tom-Tom; Biofeedback Monitor For Your PC; Simple Stub Filter For Suppressing TV Interference; LED Message Board, Pt.3; All About Electrolytic Cap­acitors. June 1989: Touch-Lamp Dimmer (uses Siemens SLB0586); Passive Loop Antenna For AM Rad­ios; Universal Temperature Controller; Understanding CRO Probes; LED Message Board, Pt.4. 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 Electric Locomotives. September 1989: 2-Chip Portable AM Stereo Radio (Uses MC13024 and TX7376P) Pt.1; Alarm-Triggered Telephone Dialler; High Or Low Fluid Level Detector; Simple DTMF Encoder; Studio Series 20-Band Stereo Equaliser, Pt.2; Auto-Zero Module for Audio Amplifiers (Uses LMC669). March 1990: 6/12V Charger For Sealed Lead-Acid Batteries; Delay Unit For Automatic Antennas; Workout Timer For Aerobics Classes; 16-Channel Mixing Desk, Pt.2; Using The UC3906 SLA Battery Charger IC. April 1990: Dual Tracking ±50V Power Supply; VOX With Delayed Audio; Relative Field Strength Meter; 16-Channel Mixing Desk, Pt.3; Active CW Filter For Weak Signal Reception; How To Find Vintage Radio Receivers From The 1920s. 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 A Computer. October 1989: Introducing Remote Control; FM Radio Intercom For Motorbikes Pt.1; GaAsFet Preamplifier For Amateur TV; 1Mb Printer Buffer; 2-Chip Portable AM Stereo Radio, Pt.2; Installing A Hard Disc In The PC. July 1990: Digital Sine/Square Generator, Pt.1 (Covers 0-500kHz); Burglar Alarm Keypad & Combination Lock; Simple Electronic Die; Low-Cost Dual Power Supply; Inside A Coal Burning Power Station; Weather Fax Frequencies. November 1989: Radfax Decoder For Your PC (Displays Fax, RTTY & Morse); 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. August 1990: High Stability UHF Remote Transmitter; Universal Safety Timer For Mains Appliances (9 Minutes); Horace The Electronic Cricket; Digital Sine/Square Wave Generator, Pt.2. December 1989: Digital Voice Board (Records Up To Four Separate Messages); UHF Remote Switch; Balanced Input & Output Stages; Data For The LM831 Low Voltage Amplifier IC; Installing A Clock Card In Your Computer; Index to Volume 2. January 1990: High Quality Sine/Square Oscillator; Service Tips For Your VCR; Speed­ing Up Your PC; Phone Patch For Radio Amateurs; Active Antenna Kit; Speed Controller For Ceiling Fans; September 1990: Music On Hold For Your Tele­ phone; Remote Control Extender For VCRs; Power Supply For Burglar Alarms; Low-Cost 3-Digit Counter Module; Simple Shortwave Converter For The 2-Metre Band. October 1990: Low-Cost Siren For Burglar Alarms; Dimming Controls For The Discolight; Surfsound Simulator; DC Offset For DMMs; The Dangers of Polychlorinated Biphenyls; Using The NE602 In Home-Brew Converter Circuits. Please send me a back issue for: ❏ April 1989 ❏ May 1989 ❏ October 1989 ❏ November 1989 ❏ March 1990 ❏ April 1990 ❏ September 1990 ❏ October 1990 ❏ February 1991 ❏ March 1991 ❏ July 1991 ❏ August 1991 ❏ December 1991 ❏ January 1992 ❏ May 1992 ❏ June 1992 ❏ October 1992 ❏ January 1993 ❏ May 1993 ❏ June 1993 ❏ October 1993 ❏ November 1993 ❏ March 1994 ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ September 1988 June 1989 December 1989 June 1990 November 1990 April 1991 September 1991 February 1992 July 1992 February 1993 July 1993 December 1993 ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ November 1988 July 1989 January 1990 July 1990 December 1990 May 1991 October 1991 March 1992 August 1992 March 1993 August 1993 January 1994 ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ➦ Use this handy form to order your back issues December 1988 September 1989 February 1990 August 1990 January 1991 June 1991 November 1991 April 1992 September 1992 April 1993 September 1993 February 1994 Enclosed is my cheque/money order for $­______or please debit my: ❏ Bankcard ❏ Visa Card ❏ Master Card Signature ____________________________ Card expiry date_____ /______ Name _______________________________ Phone No (___) ____________ PLEASE PRINT Street ________________________________________________________ Suburb/town ________________________________ Postcode ___________ 84  Silicon Chip Note: all prices include post & packing Australia (by return mail) ............................. $A7 NZ & PNG (airmail) ...................................... $A7 Overseas (airmail) ...................................... $A10 Detach and mail to: Silicon Chip Publications, PO Box 139, Collaroy, NSW, Australia 2097. Or call (02) 979 5644 & quote your credit card details or fax the details to (02) 979 6503. ✂ Card No. November 1990: How To Connect Two TV Sets To One VCR; A Really Snazzy Egg Timer; Low-Cost Model Train Controller; Battery Powered Laser Pointer; 1.5V To 9V DC Converter; Introduction To Digital Electronics; Simple 6-Metre Amateur Transmitter. December 1990: DC-DC Converter For Car Amplifiers; The Big Escape – A Game Of Skill; Wiper Pulser For Rear Windows; Versatile 4-Digit Combination Lock; 5W Power Amplifier For The 6-Metre Amateur Transmitter; Index To Volume 3. January 1991: Fast Charger For Nicad Batteries, Pt.1; Have Fun With The Fruit Machine; Two-Tone Alarm Module; Laser Power Supply; LCD Readout For The Capacitance Meter; How Quartz Crystals Work; The Dangers When Servicing Microwave Ovens. February 1991: Synthesised Stereo AM Tuner, Pt.1; Three Inverters For Fluorescent Lights; LowCost Sinewave Oscillator; Fast Charger For Nicad Batteries, Pt.2; How To Design Amplifier Output Stages; Tasmania's Hydroelectric Power System. March 1991: Remote Controller For Garage Doors, Pt.1; Transistor Beta Tester Mk.2; Synthesised AM Stereo Tuner, Pt.2; Multi-Purpose I/O Board For PC-Compatibles; Universal Wideband RF Preamplifier For Amateurs & TV. April 1991: Steam Sound Simulator For Model Railroads; Remote Controller For Garage Doors, Pt.2; Simple 12/24V Light Chaser; Synthesised AM Stereo Tuner, Pt.3; A Practical Approach To Amplifier Design, Pt.2. May 1991: 13.5V 25A Power Supply For Transceivers; Stereo Audio Expander; Fluorescent Light Simulator For Model Railways; How To Install Multiple TV Outlets, Pt.1; Setting Screen Colours On Your PC. June 1991: A Corner Reflector Antenna For UHF TV; 4-Channel Lighting Desk, Pt.1; 13.5V 25A Power Supply For Transceivers; Active Filter For CW Reception; Electric Vehicle Transmission Options; Tuning In To Satellite TV, Pt.1. July 1991: Battery Discharge Pacer For Electric Vehicles; Loudspeaker Protector For Stereo Amplifiers; 4-Channel Lighting Desk, Pt.2; How To Install Multiple TV Outlets, Pt.2; Tuning In To Satellite TV, Pt.2; PEP Monitor For Amateur Transceivers. August 1991: Build A Digital Tachometer; Masthead Amplifier For TV & FM; PC Voice Recorder; Tuning In To Satellite TV, Pt.3; Installing Windows On Your PC; Step-By-Step Vintage Radio Repairs. September 1991: Studio 3-55L 3-Way Loudspeaker System; Digital Altimeter For Gliders & Ultralights, Pt.1; Build A Fax/Modem For Your Computer; The Basics Of A/D & D/A Conversion; Windows 3 Swapfiles, Program Groups & Icons. October 1991: Build A Talking Voltmeter For Your PC, Pt.1; SteamSound Simulator Mk.II; Magnetic Field Strength Meter; Digital Altimeter For Gliders & Ultralights, Pt.2; Getting To Know The Windows PIF Editor. November 1991: Colour TV Pattern Generator, Pt.1; Battery Charger For Solar Panels; Flashing Alarm Light For Cars; Digital Altimeter For Gliders & Ultralights, Pt.3; Build A Talking Voltmeter For Your PC, Pt.2; Modifying The Windows INI Files. December 1991: TV Transmitter For VCRs With UHF Modulators; Infrared Light Beam Relay; Solid-State Laser Pointer; Colour TV Pattern Generator, Pt.2; Windows 3 & The Dreaded Un­ recov­erable Application Error; Index To Volume 4. January 1992: 4-Channel Guitar Mixer; Adjustable 0-45V 8A Power Supply, Pt.1; Baby Room Monitor/FM Transmitter; Automatic Controller For Car Headlights; Experiments For Your Games Card; Restoring An AWA Radiolette Receiver. February 1992: Compact Digital Voice Recorder; 50-Watt/Channel Stereo Power Amplifier; 12VDC/240VAC 40-Watt Inverter; Adjustable 0-45V 8A Power Supply, Pt.2; Designing A Speed Controller For Electric Models. March 1992: TV Transmitter For VHF VCRs; Studio Twin Fifty Stereo Amplifier, Pt.1; Thermostatic Switch For Car Radiator Fans; Telephone Call Timer; Coping With Damaged Computer Direct­ ories; Valve Substitution In Vintage Radios. April 1992: Infrared Remote Control For Model Railroads; Differential Input Buffer For CROs; Studio Twin Fifty Stereo Amplifier, Pt.2; Understanding Computer Memory; Aligning Vintage Radio Receivers, Pt.1. May 1992: Build A Telephone Intercom; LowCost Electronic Doorbell; Battery Eliminator For Personal Players; Infrared Remote Control For Model Railroads, Pt.2; Aligning Vintage Radio Receivers, Pt.2. June 1992: Multi-Station Headset Intercom, Pt.1; Video Switcher For Camcorders & VCRs; Infrared Remote Control For Model Railroads, Pt.3; 15-Watt 12-240V Inverter; What’s New In Oscilloscopes?; A Look At Hard Disc Drives. July 1992: Build A Nicad Battery Discharger; 8-Station Automatic Sprinkler Timer; Portable 12V SLA Battery Charger; Off-Hook Timer For Tele­phones; Multi-Station Headset Intercom, Pt.2. August 1992: Build An Automatic SLA Battery Charger; Miniature 1.5V To 9V DC Converter; Dummy Load Box For Large Audio Amplifiers; Internal Combustion Engines For Model Aircraft; Troubleshooting Vintage Radio Receivers. September 1992: Multi-Sector Home Burglar Alarm; Heavy-Duty 5A Drill speed Controller (see errata Nov. 1992); General-Purpose 3½-Digit LCD Panel Meter; Track Tester For Model Railroads; Build A Relative Field Strength Meter. October 1992: 2kW 24VDC To 240VAC Sine­wave Inverter; Multi-Sector Home Burglar Alarm, Pt.2; Mini Amplifier For Personal Stereos; Electronically Regulated Lead-Acid Battery Charger. January 1993: Peerless PSK60/2 2-Way Hifi Loudspeakers; Flea-Power AM Radio Transmitter; High Intensity LED Flasher For Bicycles; 2kW 24VDC To 240VAC Sine­wave Inverter, Pt.4; Speed Controller For Electric Models, Pt.3. February 1993: Three Simple Projects For Model Railroads; A Low Fuel Indicator For Cars; Audio Level/VU Meter With LED Readout; Build An Electronic Cockroach; MAL-4 Microcontroller Board, Pt.3; 2kW 24VDC To 240VAC Sine­wave Inverter, Pt.5; Making File Backups With LHA & PKZIP. March 1993: Build A Solar Charger For 12V Batteries; An Alarm-Triggered Security Camera; Low-Cost Audio Mixer for Camcorders; Test Yourself On The Reaction Trainer; A 24-Hour Sidereal Clock For Astronomers. April 1993: Solar-Powered Electric Fence; Build An Audio Power Meter; Three-Function Home Weather Station; 12VDC To 70VDC Step-Up Voltage Converter; Digital Clock With Battery Back-Up; A Look At The Digital Compact Cassette. May 1993: Nicad Cell Discharger; Build The Woofer Stopper; Remote Volume Control For Hifi Systems, Pt.1; Alphanumeric LCD Demonstration Board; Low-Cost Mini Gas Laser; The Micro­soft Windows Sound System. June 1993: Windows-Based Digital Logic Analyser, Pt.1; Build An AM Radio Trainer, Pt.1; Remote Control For The Woofer Stopper; A Digital Voltmeter For Your Car; Remote Volume Control For Hifi Systems, Pt.2; Double Your Disc Space With DOS 6. July 1993: Build a Single Chip Message Recorder; Light Beam Relay Extender; Build An AM Radio Trainer, Pt.2; Windows Based Digital Logic Analyser; Pt.2; Low-Cost Quiz Game Adjudicator; Programming The Motorola 68HC705C8 Micro­ controller – Lesson 1; Antenna Tuners – Why They Are Useful. August 1993: Low-Cost Colour Video Fader; 60LED Brake Light Array; A Microprocessor-Based Sidereal Clock; The Southern Cross Z80-based Computer; A Look At Satellites & Their Orbits; Unmanned Aircraft – Israel Leads The Way; Ghost Busting For TV Sets. September 1993: Automatic Nicad Battery Charger/Discharger; Stereo Preamplifier With IR Remote Control, Pt.1; In-Circuit Transistor Tester; A +5V to ±15V DC Converter; Remote-Controlled Electronic Cockroach; Restoring An Old Valve Tester; Servicing An R/C Transmitter, Pt.1. October 1993: Courtesy Light Switch-Off Timer For Cars; FM Wireless Microphone For Musicians; Stereo Preamplifier With IR Remote Control, Pt.2; Electronic Engine Management, Pt.1; Mini Disc Is Here; Programming The Motorola 68HC705C8 Micro­ controller – Lesson 2; Servicing An R/C Transmitter, Pt.2. November 1993: Jumbo Digital Clock; High Efficiency Inverter For Fluorescent Tubes; Stereo Preamplifier, Pt.3; Build A Siren Sound Generator; Electronic Engine Management, Pt.2; More Experiments For Your Games Card; Preventing Damage To R/C Transmitters & Receivers. December 1993: Remote Controller For Garage Doors; Low-Voltage LED Stroboscope; Low-Cost 25W Amplifier Module; Peripherals For The Southern Cross Computer; Build A 1-Chip Melody Generator; Electronic Engine Management, Pt.3; Index To Volume 6. January 1994: 3A 40V Adjustable Power Supply; Switching Regulator For Solar Panels; Printer Status Indicator; Mini Drill Speed Controller; Stepper Motor Controller; Active Filter Design For Beginners; Electronic Engine Management, Pt.4; Even More Experiments For Your Games Card. February 1994: 90-Second Message Recorder; Compact & Efficient 12-240VAC 200W Inverter; Single Chip 0.5W Audio Amplifier; 3A 40V Adjustable Power Supply; Electronic Engine Management, Pt.5; Airbags: More Than Just Bags Of Wind; Building A Simple 1-Valve Radio Receiver. March 1994: Intelligent IR Remote Controller; Build A 50W Audio Amplifier Module; Level Crossing Detector For Model Railways; Voice Activated Switch For FM Microphones; Simple LED Chaser; Electronic Engine Management, Pt.6; Switching Regulators Made Simple (Software Offer) PLEASE NOTE: all issues from November 1987 to August 1988, plus October 1988, January, February, March & August 1989, May 1990, and November and December 1992 are now sold out. All other issues are presently in stock, although stocks are low for some older issues. For readers wanting articles from sold-out issues, we can supply photostat copies (or tearsheets) at $7.00 per article (incl. p&p). When supplying photostat articles or back copies, we automatically supply any relevant notes & errata at no extra charge. April 1994  85 VINTAGE RADIO By JOHN HILL Bandspread tune-up for an old Astor multiband receiver As readers could well imagine, I have met a lot of fellow radio collectors over the years, particularly since I began writing Vintage Radio. My monthly column has brought about many meetings and, in some instances, long and lasting friendships. However, being a so-called “authority” on vintage radio does have its disadvantages, including the occasional knock on my door by complete strangers seeking advice on a particular receiv­er. In fact, it was a knock on the door that started this month’s story although, in this case, the owner of the receiver is well known to me. Gener- ally, he is quite capable of servicing his own radios and can usually track down an elusive fault and fix it. In this particular case, the receiver – a 1950 5-valve dual-wave Astor table model – had been repaired but the remaining problem was alignment. Not only was there an annoying double peak response when tuning but there was also the matter of three band- spread shortwave bands that were badly out of alignment. It seemed as though someone had tightened up all the adjustment slugs so that they wouldn’t fall out. In a past series of three articles, I covered receiver alignment fairly thoroughly but shied away from multiband short­wave tune-ups. After three consecutive months devoted to align­ ment, it seemed about time to change the subject. However, a multiband receiver such as this Astor offers different tune-up problems which should be discussed. Both the five and 6-valve versions of these Astors were popular radios back in the early 1950s and there are still a lot of them around. No doubt, a good many of them could do with a tune-up. In my opinion, a realignment of this type cannot be satis­factorily carried out without a radio frequency generator and an output meter. It was the owner’s lack of these items that led him to seek my assistance. IF transformers This particular style of Astor receiver was popular in the early 1950s. It was available in four, five & 6-valve ver­sions, some of which had three bandspread shortwave bands. 86  Silicon Chip The first step was to align the intermediate frequency (IF) transformers, particularly as a double-peak problem is usually the result of these devices being out of alignment. Un­ fortunate­ly, the IF alignment was not a straightforward job, as one of the adjustment slugs was stuck solid. To make matters worse, the adjustment slot in the soft iron core had been gouged out by a screwdriver blade. Nothing is ever as simple as first thought! Tuning the RF generator slowly across the IF showed up the double peak, with one peak being stronger to perfor­mance. It is definitely a better alternative to a double peak. Broadcast band alignment The wave change switch in the old Astor is surrounded by a bewildering array of components & wiring. However, a close exami­nation of the switch will reveal which coil is in circuit for each switch position. There are eight coils to adjust plus a trimmer. The shortwave coils are arranged in two clusters of three. Shown here are the coils that are switched (one at a time) into the oscillator circuit. The wave change switch controls a large number of components. than the other. The strong peak was at 455kHz while the lesser one was at 463kHz. When correcting a problem of this nature there are a number of options available: (1) replace the faulty IF transformer if a replacement is available; (2) add correcting trimmer capacitors to the base connections; or (3) compensate for the immovable slug by shifting the ones that will move to the frequency of the one that has stuck. I tried the latter option, as it seemed the easi­est solution. After setting the RF generator to 455kHz, the IF transform­ ers were readjusted to that frequency but there was no noticeable improvement. Readjusting the transformers to 463kHz produced a much sharper peak and, what’s more, without any hint of the previous double peak. Try doing that without an RF generator and an output meter! Not having a circuit diagram for the old Astor, I could only guess at what the IF was supposed to be but it would be unlikely to be anything other than 455kHz. While pulling the transformers off frequency a little is perhaps undesirable in theory, in practice it makes little or no difference The next step was the alignment of the broadcast band. The Astor is fitted with a nonadjustable aerial coil, an iron-dust cored oscillator coil and a trimmer on each of the tuning capacitor’s two sections. As there were pointer marks at each end of the dial, the pointer was adjusted to coincide with these marks. There were also marks at 600kHz and 1400kHz for alignment purposes. Starting at the low-frequency end of the band, a 600kHz generator signal was fed into the aerial and earth terminals and the oscillator coil adjusted for maximum output as shown on the output meter. As there was no adjustment provided in the aerial coil, it was necessary to rock the tuning capacitor while adjust­ing the oscillator coil slug so as to locate the aerial coil peak. This adjustment did not quite bring the dial pointer to the 600kHz mark and so the pointer was slid along the dial cord a couple of millimetres until it coincided. After injecting a signal of 1400kHz and transferring opera­tions to the other end of the dial, the pointer was found to be spot on its designated mark. If it had not been, the pointer position could have been moved by adjusting the oscillator trim­mer. All that remained was to adjust the aerial trimmer for maximum output at the 1400kHz position. It too was almost spot on and the screw required only a few degrees of rotation to peak the output meter. This completed the broadcast band alignment. Shortwave bands To the uninitiated, the 3-band, band­spread shortwave sec­tion with its array of six coils and adjustment slugs can be rather intimidating. However, taking one band at a time removes a lot of the mystery and two thirds of the coils. If one looks closely at the wavechange switch, it is not difficult to work out which pair of coils (three pairs altogeth­ er) are brought into circuit at each of the three shortwave positions. It helps if the coils are then marked: a simple 1, 2 and 3 to correspond to the switch positions is all that is need­ed. This is fairly important for there is nothing more annoying than April 1994  87 This photo shows the broadcast band coil (the large coil at bottom left) plus the three smaller shortwave coils that are switched into the aerial circuit. The three shortwave bands (19, 25 and 31 metres) are marked at the bottom of the dial. Note the clear frequency markings in MHz for each of these three shortwave bands. to move a previously aligned coil slug by mistake. These pairs of shortwave coils are adjusted in much the same way as those for the broadcast band. During the alignment procedure, one coil from a group of three is switched alternately into the oscillator circuit and its slug adjusted to give the correct frequency on the dial. The other three coils are switched into the aerial circuit and are adjusted for maximum output. There are no trimmers with this type of set up. In a bandspread receiver, such as the Astor, three of the more common shortwave bands were usually cho88  Silicon Chip sen. They are the 19, 25 and 31-metre bands. (Note: in a bandspread receiver of this type, a large fixed capacitor is connected in series with the tuning capacitor to restrict its tuning range. This is designed to make it easier to select stations without requiring a large step-down ratio in the tuning capacitor drive). 19-metre band Alignment of the 19-metre band was first. As the dial is also marked in MHz, a frequency of 15.4MHz was chosen because it is towards the high frequency end of the dial. The RF generator was set to this frequency and its output injected into the aerial and earth terminals. Selecting a frequency of exactly 15.4MHz on an RF generator is a difficult task without some assistance. The assistance in this instance was provided by a modern multiband receiver with digital tuning. All one has to do is tune to the required fre­quency on the synthesised receiver and place it near the RF generator. The RF generator is then adjusted until a squeal is heard in the receiver. By using this technique, almost any obscure frequency can be dialled up on the synthesised receiver and the RF generator adjusted to suit. Receiver alignment on the shortwave bands can be a hit and miss (mostly miss) affair unless the generator frequency is accurately set. All three shortwave bands required similar treatment; ie, adjustment of the oscillator coil slug to bring the frequency in line with the dial graduation, followed by aerial coil adjustment for maximum output. Everything went fairly smoothly in the shortwave depart­ ment, with no tight slugs to give trouble. The slug positions were held in place by re-melting the wax that was originally ap­plied to them for that purpose. Just re-melting the wax with a warm soldering iron was enough to shift the frequency a little and some readjustment was required on one band. It doesn’t take much to alter the settings on shortwave adjustments! If the receiver had been a 6-valve model with a stage of RF amplification, then there would have been additional coils requiring adjustment in the RF section. These would need to be adjusted for maximum output after the oscillator and aerial coils had been reset. Testing Testing the receiver was a bit of an anticlimax. It was midday in January and there was almost nothing to be heard on any of the three shortwave bands. It gave the impression that the shortwave bands had been completely detuned. Fortunately, after-dark reception was a completely differ­ent story and all three bands responded well to all corners of the globe. The Astor’s owner was very pleased. All things considered, the realignment of the old Astor was a relatively VINTAGE RADIO We are moving in February 1994 MORE SPACE! MORE STOCK! Radios, Valves, Books, Vintage Parts BOUGHT – SOLD – TRADED Send SSAE For Our Catalogue An RF generator is indispensable when aligning a shortwave receiv­er like the old Astor. The other essential item (not shown here) is an output meter. WANTED: Valves, Radios, etc. Purchased for CASH RESURRECTION RADIO Call in to our NEW showroom at: 242 Chapel Street (PO Box 2029), Prahran, Vic 3181. Phone: (03) 5104486; Fax (03) 529 5639 Radio and Electrical Books Almost any desired frequency can be set accurately on the RF generator with the aid of this Sangean ATS-803A synthesised receiver. The receiver dial reads 15.4MHz – a convenient align­ment point on the 19-metre band. It would be impossible to accu­rately set the RF generator to this frequency without the assis­ tance of the digital receiver. straightforward process. On the other hand, to attempt such a task without the aid of the RF generator and output meter would result in far from optimum results. Alignment fiddles Many of the valve receivers that we collect today are get­ting quite long in the tooth, this particular Astor being well over 40 years old. It is unreasonable to expect that someone at some time in the past hasn’t had a fiddle with the alignment adjustments. If they used the right equipment and knew what they were doing, OK. But that may not have been the case. I know from my own early alignment attempts that I’m guilty of mis­ aligning many a good receiver. I’m sure I’m not the only one to do so. Correct receiver alignment is an absolute necessity if the full potential of any radio is to be attained. A restoration is incomplete without a comprehensive SC tune-up to finish it off. 1914 Catalog Electro Importing Co ............$18 1936 Radio Data Book ...............................$15 Hammarlund Short Wave Manual (1937)....$11 Henley’s 222 Radio Circuit Designs ......$26.50 Neon Signs (1935) ................................$28.50 How to Become a Radio Amateur (1930) .....$7 How to Build & Operate Short Wave Receivers ...................................................$18 How to Build a Solar Cell ...........................$11 High Frequency Apparatus (1916) .............$29 Radio for Beginners ................................$6.50 Radio for the Millions .................................$20 Short Wave Radio Manual (1934) ..............$30 Television (1938) .........................................$7 Tesla Coil ....................................................$11 Tesla Coil Secrets .......................................$16 Tesla Said ...................................................$79 Construction of Large Induction Coils ........$23 The Wimshurst Machine How to Make .$19.50 The Wireless Man ......................................$27 Wireless Experimenter’s Manual 1920 .......$31 Electrical Goods & Radio Apparatus ..........$14 Electroplating (1911) ............................$17.75 Experimental Television How to Make ........$34 Meissner “How to Build” Instructions ........$22 How & Why of Radio Apparatus ...........$20.50 All prices include postage. Payment can be made by cheque or money order made out to Plough Book Sales, PO Box 14, Belmont, Vic. 3216. Phone (052) 66 1262. April 1994  89 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. Time signal generator wanted My brother-in-law is the president of a community radio station in country NSW and has asked me to design a time signal generator. The station often runs out of volunteer an­nouncers and they just leave a multi-disc CD player running. With the pips going to air the listeners would at least have an idea of the time. Building something is no problem for me but designing it is. I understand time signals in days gone by were synced to a PMG pulse generator and they had to be accurate for ships at sea and aircraft navigation. I don’t think aircraft or ships would be interested in any of the programs broadcast from this low-power community FM station. The only ideas I can come up with are three 555 timers, one counting down 59 minutes, then triggering another to count down 55 seconds and the third to count down the five seconds with six half second audio tone bursts, or pips. But how? Please help. (R. P., Toowong, Qld). • Your idea of using 555 timers Measuring soil conductivity Being an electronics enthusiast who has recently taken up hydroponic gardening, I was interested to read in my gardening literature that the nutrient strength (ie, the amount of dis­solved salts in the water base) is measured by a unit called the “Conductivity Factor”. To quote my source: 1 CF unit = 0.1 EC units; or 0.1 millimhos; or 0.1 millisiemens. This represents approximately 65 ppm. How do these figures relate to Ohms? Is it possible to measure CF with an ordinary ohmmeter? Could you please comment on this 90  Silicon Chip would not be very accurate and they would tend to drift as time went on. You really need to sync the generator with a source of accurate time signals such as from Radio VNG. The resulting circuit is not likely to be simple, however. Perhaps one of our readers has faced the same problem and has produced an easy solution. If so, we’ll pass the details on to you. UHF antenna for Tasmanian aggregation I have constructed UHF antennas from past issues of SILICON CHIP. Just recently, I’ve learnt that aggregation will occur in Tasmania in April and May of this year. A lot of translators will beam programs on UHF while some such as the Southern Cross net­ work will still be transmitting on VHF. Where we live at Sheffield, we will still receive Southern Cross on VHF and the ABC on UHF, as well as Tas-TV and SBS. This means that a combined VHF/UHF antenna will be required. As a future project, you may be keen to include an article on how to and consider the possibility of publishing a CF meter circuit if such an instrument would be economic? Thank you for a fine magazine. When will you be publishing the second part of your video fader unit? (C. G., Eden Hills, SA). • We are not aware of what an E.C. unit is although we assume that it refers to “electrical conductivity”. The “Siemen” is the unit of conductivity and supersedes the “mho” which is the recip­rocal of the unit of resistance, the “ohm”. One millisiemen is equivalent to 1000 ohms or 1kΩ. By the same token, 0.1 millisie­mens (0.1mS) is equivalent to 10kΩ. Yes, you can use your ohmmet­er or multimeter to measure these quantities. build a good long-range combined VHF/UHF antenna. I’m sure a lot of keen readers would welcome the challenge to build one as the prices they’re asking are very high. (R. P., Shef­field, Tas). • We’re not keen on the idea of building a combined VHF/UHF antenna as the time we would need to spend on design and evaluation could be prohibitive. We also wonder if it is really necessary. Presumably, you already have a VHF antenna which is quite serviceable. Why can’t you keep on using that together with a suitable UHF antenna and a VHF/UHF combiner which you probably also have? We also have doubts whether a combined VHF/UHF design would perform as well as separate antennas. We will be having another look at a UHF design soon though, so stay tuned. Queries on fluorescent lamp inverter I am writing about the high efficiency inverter featured in the November 1993 issue of SILICON CHIP. Being new to electronics and not having precision fault finding equipment, or the knowledge yet to operate them, I have to try to find other means to have a basic idea on what’s happen­ ing in a circuit. Looking at the circuit diagram, I wondered about the resis­tors in series and realised that this was to distribute heat loss more evenly. Then, after reading some of the text, I came across the two 150kΩ load resistors coming from the 680pF capacitor and it occurred to me that if a faulty connection or tube was pres­ ent, these resistors would take the load. If so, could an indica­tion lamp be combined with them or incorporated with similar resistances to allow you to monitor when the load has altered? And could an adjustment within safe limits be added to compensate for any tolerances that exceed the requirements? This would allow one to monitor on what side of the circuit a fault might occur, if one was able to do the same within safe limits on the feedback side. Is the feedback affected by low battery voltage and could this cause excessive switching in IC1? If so and if this could be damaging, is there a way to indicate when this happens or to protect the circuit? (J. C., Cooma, NSW). • The two 150kΩ resistors connected in-series are to allow equal heat dissipation in each. This is in preference to a higher wattage 330kΩ single resistor which is bulkier and more expen­sive. If there is a faulty connection to the tube, the circuit will revert to the starting pulse configuration whereby Q4 is driven with pulses from the Diac. There is no easy way to add indication that this is happening since a neon lamp connected between the 340V rail and the drain of Q4 via a suitable resistor will glow with similar brightness whether the fluorescent tube is lit or not. The circuit does not specifically shut down for low battery voltages. However, the ultimate fall in the +340V supply rail as the battery voltage drops below a critical level, whereby the feedback is no longer effective, reduces the tube current and consequently reduces the current drawn from the battery. Eventu­ally, the tube will extinguish due to loss of sufficient voltage to fire it and the circuit will revert to supplying starting pulses. In this condition, the circuit cannot be damaged by excess dissipation. Preamps & speakers for musicians I am writing in response to the letter by K. S. of Sellicks Beach in the March 1994 issue, regarding the guitar preamplifier and speaker. By way of introduction, I am a professional musician, audio engineer and electronics hobbyist, and I have spent the last five years specifically studying musical instrument amplifi­ ers (both solid state and valve), so I believe I am in a position to make a few suggestions. There are two problems with the mixer/preamp from the point of view of the average electric guitar. The first is that the input impedance of the circuit is too low at 10kΩ. This is fine with active pickups, as the article Artificial dawn for exotic fish Your November 1993 article on a high efficiency inverter for fluorescent tubes seems to be a good starting point for a type of lighting system needed by many people interested in keeping or breeding many kinds of animals and particularly fish. Apparently, fish dart around when the light is switched on and a zoologist friend of mine said he thought that this sudden brightness frightened them and possibly also shortened their life cycle. What is required is the ability to create a dawn and possi­bly a twilight cycle. This needs a flickerfree start at a low output; even 30% would be sufficient in an aquarium using two lamps as this is only 15% of the total. I believe that a commercial unit with a 10-volt stepless control is available (it goes from 1V to 10V for 20% output to full output) but it is expensive. If you could design the ballast, there would be a whole range of control systems. A simple multiple relay system using two tubes would probably be the cheapest way to go while the ideal approach would be to use a D/A converter in conjunc­tion with your Z80 computer in the August 1993 edition. (A. S., Moonah, Tas­­­­mania). • Our inverter circuit for fluorescent tubes cannot be easily adapted for dimming. The circuit as de- states, but for passive in­struments, or failed actives (batteries do run down at the most inconvenient moments, usually half-way through a song), this low impedance combined with the induction of the pickup coil forms a low-pass filter, which removes all of the nice harmonics of the instrument. The second problem is the tone control stage. This is a fairly standard 3-way Baxandall type, more at home with hifi and the processed sound of keyboards than guitars. This type of tone control works in frequency bands, with areas of maximum control and areas of minimum control. It just so happens that the area of scribed applies a filament preheat current before the tube starts and this is removed once the tube has fired. To enable reliable dimming of the fluorescent lamp, preheat current must be maintained after the tube has fired. In fact, it would be much easier to start the tube at full brightness and then dim down. Starting the tube reliably at a low brightness and then increasing the illumination would be impossible with the present circuit. Should you wish to pursue the idea, dimming ballasts are available from lighting suppliers which, in conjunction with a conventional light dimmer, can be made to dim the tubes over a limited range. The circuitry for this is supplied with the dim­ming ballast. As an alternative, you could use a conventional incandes­cent lamp which is designed to produce a daylight spectrum. These are available from lighting stores as Philips Daylight lamps. They have blue glass to filter out red light and a special fila­ment which emits light toward the blue end of the spectrum. The incandescent lamp can be dimmed using a standard dimmer. A fluo­rescent tube could then be lit later once the lamp is fully alight to provide the normal illumination. Be careful if you want to control the dimming using a D/A converter. This circuitry must be fully isolated from the 240VAC mains. minimum control between the mid and high bands corresponds to the part of the guitar’s frequency spectrum that provides all of the “bite” (not a techni­ cal term, but evocative enough). Since the sound with keyboards is already satisfactory and fiddling with components would change this, the simplest solution would be to add a switchable paramet­ ric equaliser module, such as the one available from Jaycar (Cat. KE-4724). As far as 4-way speakers (or quad boxes as they’re known in the trade) are concerned, the editors of SILICON CHIP may not recommend them but manufacturers like Marshall, Fender, April 1994  91 Query on Twin 50 stereo amplifier I am writing in reference to the “Studio Twin 50 Stereo Amplifier”. After carefully considering the circuit, I wrote to one of the Australian kit retailers asking whether individual parts would be available for the unit. They responded with a catalog and a recommendation that purchasing the entire unit would be cheaper. Preferring to construct, in “doit-yourself” fashion, at least the preamplifier portion of that design, I cannot fathom what kind of taper the balance control (VR5) is. The article specifies an “M/N” taper. Neither local retailers nor technicians at Clarostat Controls (a manufacturer or potentiometers) could help me. Can you help me identify what kind of control is intended for the balance section? Is it a custom-made unit available only with the kit, or is there a retailer, either in Australia or (better) the USA who carries a dual-gang 10kΩ M/N control? Anoth­er part that I cannot locate, and that even the Philips USA parts centre cannot identify Laney, Wasp, Trace Elliot, Hi-Watt and Peavey (to name but seven) cer­tainly do. There would be damping problems as mentioned if the boxes were designed for full range operation, but they are de­signed in such a way as to present a high mechanical impedance to frequencies below 84Hz (bottom “E” on a guitar; since this is the lowest note, why cater for anything lower?). Thus, most quad boxes are sealed and have a lower volume than you would expect for the same speakers in a hifi box. It is worth noting that the Marshall model 1969 quad, using 16Ω speakers, is switchable between series/ parallel (16Ω) or pure parallel (4Ω). There is no reason for not using the 10-inch speakers from Jaycar, although the maximum power handling would be only 130 watts at 8Ω single input, or 130 watts at 4Ω dual input. Dual input is possible for quad boxes and is an option on the afore­mentioned Marshall 1969. I hope that my observations will 92  Silicon Chip by the given part number, is L2 (an induc­tor at the phono input). In the parts list, it is identified as a “ferrite wideband choke”, Philips Ω4312-020-36760. Help? (M .F., Staten Island, NY, USA). • The M/N taper dual gang pot is a standard type used in balance controls in many Japanese amplifiers. As depicted on the circuit, each resistance element is short-circuit over half the wiper travel so that the gain in one channel does not increase once the wiper has reached the mid-point, while the other channel is reduced in gain as the wiper moves past mid-point. While it may not be of much help, Japanese manufacturers such as Alps make this pot as a standard item. Alternatively, you may be able to buy the M/N as a replacement item for an amplifier brand such as Sony, Panasonic, etc. Failing that, you could substitute a standard log/antilog dual gang pot. The Philips inductor is a standard part number taken from their Soft Ferrites catalog. However, it is not a critical part and you could substitute a small ferrite bead with a few turns of enamelled copper wire wound through it. be of some help to K. S. and to anyone else experiencing similar troubles. (T. N., Bal­main, NSW). Building a TV signal strength meter By utilising a secondhand tuner from a VCR, could not an ac­ceptable signal strength meter for siting TV aerials (in bad signal areas) be made? Commercial units are expensive. (B. P., Port Macquarie, NSW). • It would be possible to use a defunct VCR’s tuner as the basis of a signal strength meter but TV antenna installers who do not have a signal strength meter have a far more practical ap­ proach – they use a small portable TV set. This gives a good idea of signal strength and also gives an indication of ghosts. That said, we will have a look at the possibility of doing a signal strength meter as a project. Pointless ignition wanted I am interested in building and experimenting with a point­less ignition system for my lawn mower. Has your magazine the circuitry of these modules and if so, in what issue? (A. C., Benowa, Qld). • Unfortunately, we have no circuits for ignition systems for mowers. We understand that they are capacitor discharge systems with the capacitor charged by magneto. Similar systems are used on motorbikes and modules can be quite expensive to replace. Does any reader have more information? Debouncing needed for counter input I am a year 11 student at Benedict Senior College at Auburn and am studying a 1-unit electronics course. As a final project, I decided to build a 3-digit counter module, which is featured in your June 1990 magazine. However, when the button is pressed it advances three, four or even 10 numbers at a time. I understand that the problem is called debounce. I tried placing a 0.1µF greencap capacitor across the terminals of the pushbutton switch but there was no change; nor did larger capacitor values help. I also tried building a debounce circuit from a book. However, after much experimentation with all of these ideas, I have made no headway. Please help me. All I am after is a simple circuit diagram or any type of information that will solve this problem. (G. F., Auburn, NSW). • You will need to buy a 74C14 hex Schmitt trigger IC and build the circuit below – see Fig.1. The original project was designed to go with existing circuitry, not a pushbutton arrangement, +VCC 100k 13 0.1 74C14 14 12 7 TO COUNTER Fig.1: this simple debounce circuit will advance the count of the 3-Digit Counter Module by one each time the button is pressed. but this circuit will do the job. Make sure you connect pins 14 and 7 of the 74C14 to the supply lines of the 3-digit counter project. Speed control for a golf buggy Notes & errata Stereo Preamplifier with IR Remote Control; September, October and November 1993: on some units, the bass control is liable to become noisy and produce a scratchy sound from the loudspeakers when it is rotated. This problem is caused by a small DC voltage which appears across the bass control pot. This voltage is developed by the input bias current to pin 2 of IC6 and IC106. To prevent this problem, we recommend replacing IC6 and IC106 with OP27GP or LM627 op amps. These have signifi­ cantly lower input bias currents than the NE5534 op amps specified originally. Note that the 10pF capacitors between pins 5 and 8 for both IC6 and IC106 should be removed from the PC board since the replacement op amps are internally compensated. Finally, some early kits from Jaycar may have problems with the remote control not operating. The problem is due to a short between ceramic resonator X2 (on the main PC board) and ground, which prevents the oscillator inside IC23 from functioning. To cure the problem, go to the 4.7kΩ resistor side of the X2 pad and cut the copper between this pad and the adjacent ground track with a sharp utility knife. The problem has been corrected SC on later kits. SILICON CHIP FLOPPY INDEX WITH FILE VIEWER Now available: the complete index to all SILICON CHIP articles since the first issue in November 1987. Now you can search through all the articles ever published for the one you want. Whether it is a feature article, a project, a circuit notebook item, or a major product review, it doesn’t matter; they are all there for you to browse through. The index comes as an ASCII file on a 3.5-inch or 5.25-inch floppy disc to suit PC-compatible computers and you can use a word processor or our special file viewer to search for keywords. Now with handy file viewer: the Silicon Chip Floppy Index now comes with a file viewer which makes searching for that article or project so much easier. You can look at the index line by line or page by page for quick browsing, or you can make use of the search function. Simply enter in a keyword(s) and the index will quickly find all the relevant entries. All commands are listed on the screen, so you’ll always know what to do next. Note: requires CGA, EGA or VGA graphics card, IBM-compatible PC, MSDOS 3.3 and above. Disc size:   ❏ 3.5-inch disc   ❏ 5.25-inch disc ❏ ❏ ❏ ❏ ❏ ❏ ❏ Floppy Index (incl. file viewer): $A7 + p&p Notes & Errata (incl. file viewer): $A7 + p&p Bytefree.bas /obj / exe (Computer Bits, May 1994): $A7 + p&p Alphanumeric LCD Demo Board Software (May 1993): $A7 + p&p Stepper Motor Controller Software (January 1994): $A7 + p&p Printer Status Indicator Software (January 1994): $A7 + p&p Switchers Made Simple – Design Software (March 1994): $A12 + p&p Note: Aust, NZ & PNG please add $A3 (elsewhere $A5) for p&p with your order Enclosed is my cheque/money order for $­__________ or please debit my ❏ Bankcard   ❏ Visa Card   ❏ Master Card Card No. Signature­­­­­­­­­­­­_________________________ Card expiry date______/______ Name _____________________________________________________ PLEASE PRINT Street _____________________________________________________ Suburb/town __________________________ Postcode______________ Send your order to: SILICON CHIP, PO Box 139, Collaroy, NSW 2097; or fax your order to (02) 979 6503; or ring (02) 979 5644 and quote your credit card number (Bankcard, Visacard or Mastercard). ✂ I have a golf buggy which is driven by two 12V electric DC motors marked SWN 402-400V 12V/23, with one motor on each wheel. What I require is a circuit to control these motors. (G. R., Tura Beach, NSW). • The most practical approach would probably be to use the DC speed control published in our November & December 1992 issues. Unfortunately, we do not have any back copies of these issues but we can send you a photostat copy of the articles for $6 each including postage. You can also purchase a kit for the controller from Silvertone Electronics – phone (02) 533 3517. April 1994  93 MARKET CENTRE Cash in your surplus gear. Advertise it here in Silicon Chip. ANTIQUE RADIO CLASSIFIED ADVERTISING RATES Advertising rates for this page: Classified ads: $10.00 for up to 12 words plus 50 cents for each additional word. Display ads (casual rate): $20 per column centimetre (Max. 10cm). Closing date: five weeks prior to month of sale. To run your classified ad, print it clearly in the space below or on a separate sheet of paper, fill out the form & send it with your cheque or credit card details to: Silicon Chip Classifieds, PO Box 139, Collaroy, NSW 2097. Or fax the details to (02) 979 6503. _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ ANTIQUE RADIO RESTORATIONS: specialist restoration service provided for vintage radios, test equipment & sales. Service includes chassis rewiring, recon­ densering, valve testing & mechanical re­­furbishment. Rejuvenation of wooden, bakelite & metal cabinets. Plenty of parts – require details for mail order. About 1200 radios within 16,000 square feet. Two-year warranty on full restoration. Open on Saturday 10am-4.30pm; Sunday 12.30-4.30pm. 109 Cann St, Bass Hill, NSW 2197. Phone (02) 645 3173 BH or (02) 726 1613 AH. FOR SALE _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ THE HOMEBUILT DYNAMO: (plans) brushless, 1000 DC watt at 740 revs. $A85 postpaid airmail from Al Forbes, PO Box 3919 - SC, Auckland, NZ. Phone Auckland (09) 818 8967 any time. Rotor magnets (3700 gauss) kit now available. WEATHER FAX programs for IBM XT/ATs *** “RADFAX2” $35 is a high resolution, shortwave weather fax, Morse & RTTY receiving program. Suitable for CGA, EGA, VGA and Hercules cards (state which). Needs SSB HF radio & Radfax decoder. *** “SATFAX” $45 is a NOAA, Meteor & GMS weather satellite picture receiving program. Needs EGA or VGA plus “WEATHER FAX” PC card. *** “MAXISAT” $75 is similar to SATFAX but needs 2Mb expanded memory (EMS 3.6 or 4.0) Enclosed is my cheque/money order for $­__________ or please debit my ❏ Bankcard   ❏ Visa Card   ❏ Master Card ✂ Card No. RCS RADIO PTY LTD Signature­­­­­­­­­­­­__________________________ Card expiry date______/______ Name ______________________________________________________ Street ______________________________________________________ Suburb/town ___________________________ Postcode______________ 94  Silicon Chip RCS Radio Pty Ltd is the only company that manufactures and sells every PC board and front panel published in SILICON CHIP, ETI and EA. RCS Radio Pty Ltd, 651 Forest Rd, Bexley 2207. Phone (02) 587 3491 and 1024 x 768 SVGA card. All programs are on 5.25-inch or 3.5-inch disks (state which) & include documentation. Add $3 postage. Only from M. Delahunty, 42 Villiers St, New Farm, Qld 4005. Phone (07) 358 2785. MJ802 $6.00, B/rect CM3504 35A400V $3.00, WO4 $0.50, 1N5404 $0.12, SCR/C106DI (equiv.) $0.75, LM324CN $0.55, CD4001 $0.45, CD4071 $0.35, BC547/548 $0.07, BC547C/558C $0.08, BC327/337 $0.10, 5mm LEDs RED/GRN/YEL $0.15. Capacitors: 1000µF 35V RB $0.60, 1000µF 25V RB $0.50, 0.1µF 250V AC $0.35. 2-way PCB-mounting screw term blocks $0.40. Payment cheque, money order, Bankcard. Minimum order $10.00. Add $4.00 for postage. Fax: (049) 42 2984. LE Agencies, PO Box 770, Charlestown, NSW 2290. ROMLoader EPROM EMULATOR (EA Jan/Feb 92) - upgrade to handle 27128, 27256 EPROMs. Includes memory edit facility. 8051 Proto-Boards (EA Feb 93) also available. Send SAE for details. Tantau Australia, PO Box 1232, Lane Cove 2066. AH (02) 878 4715. PRINTED CIRCUIT BOARDS for the hobbyist. For service & enquiries contact: T. A. Mowles (08) 326 5590. SUBSTITUTE FOR A HANDFUL OF ICs: Parallax “BASIC STAMP”. A gen­er­al purpose small circuit module, it is really a 25 x 50mm board with a computer chip (4MHz PIC 16C56), EEPROM, 8 I/O pins, board space includes prototyping area. Program it on a PC (only 33 instructions) with development kit which includes one “BASIC STAMP” ($249 plus S/T & post), extra modules ($66 plus S/T & post). Send 45c stamp for more information. Parallax distributor and techni­cal support in Australia: MicroZed Computers, PO Box 634, Armi­dale, NSW 2350. Facsimile (067) 72 8987. MICASOFT Electronics and Computing tutor program, written in UK, ideal for TAFE, schools, or individual use. Now available in Australia. Send $1.80 in stamps for demo disk (tell us what size). MicroZed Computers, PO Box 634, Armidale 2350. UNUSUAL BOOKS: Electronic Devices, Fireworks, Locksmithing, Radar Invisibility, Surveillance, Self-Protection, Unusual Chem­istry and more. For a complete cat- Silicon Supply and Manufacturing 4002B 4010B 4011B 4012B 4013B 4014B 40150 4017B 4019B 4023B 4025B 4027B 4040B 4048B 4050B 4053B 4060B 4069B 4070B 4071B 4075B 4082B 4094B .86 .70 .86 .77 .82 1.53 1.55 1.88 .82 .67 .67 .67 2.13 1.15 .77 1.39 1.71 .69 .69 .69 .69 .69 1.31 74LS11 74LS12 74LS13 74LS14 74LS20 74LS21 74LS27 74LS30 74LS33 74LS49 74LS73 74LS74 74LS83 74LS85 74LS90 74LS92 74LS109 74LS126 74LS138 74LS139 74LS147 74LS148 74LS151 .60 .60 1.00 .65 .65 .50 .50 .50 .60 2.85 1.35 .55 .90 .75 1.10 1.45 1.10 .60 .75 .75 2.85 1.25 .60 74LS155 74LS158 74LS160 74LS164 74LS175 74LS191 74LS193 74LS196 74LS240 74LS241 74LS245 74LS257 74LS273 74LS366 74LS368 74LS373 74LS374 74LS393 74HC11 74HC27 74HC30 74HC76 74HC86 .60 .85 .90 .90 1.00 1.00 1.00 1.65 1.10 1.15 1.00 .75 1.00 .65 .75 1.00 1.05 1.05 .55 .50 .50 .65 .55 All prices include sales tax. Phone (02) 554 3114; Fax (02) 554 9374. After hours only bulletin board on (02) 554 3114 (Ringback). Let the modem ring twice, hangup, redial the BBS number, modem answers on second call. PO Box 92, Bexley North, NSW 2207. TRANSFORMER REWINDS ALL TYPES OF TRANSFORMER REWINDS TRANSFORMER REWINDS Reply Paid No.2, PO Box 438, Singleton, NSW 2330. Ph: (065) 76 1291. Fax: (065) 76 1003. SECONTRONICS COMPONENTS, COMPUTERS, ELECTRON TUBES S/H TEST EQUIPMENT, COMPUTER REPAIRS PC COMPATIBLE KEYBOARDS 101 AT:$39 I/O + IDE/FDD $35 RECYCLED EPROMS AT I/O CARDS $22 2716 $1.50 2SD1169 $2.00 2732 $1.50 2N3440 $0.80 2764 $2.00 2N3439 $0.80 27128 $3.00 2SC3157 $4.00 27256 $3.50 27C41 $0.80 27512 $3.50 7406 $0.20 27C101 $4.00 8250 $5     8251 $2 8259 $2    6809 $8 MC8050 $2 MCT275 $1.20 MOC3032  $2 VALVES: QQV07/50 $25 3D21   $8 12AU7   $6 6SG7   $8 6U8A   $8 1S2   $3 1T4   $6 CV553   $3 2C39A $30 2C40A $40 3A4   $8 5651   $6 5651A   $6 6AK5   $6 6J6WA  $7 6AM6  $5 6BA6  $4 SPECIAL: SURFACE MOUNT COMPONENT PACK – 180 RESISTORS, 40 ZENERS, 30 TRANSISTORS AND 2 ICs. $6.50 INC. PACK & POST PHONE OR MAIL ORDERS, CREDIT CARDS ACCEPTED FOR ORDERS $20 & OVER, DISCOUNTS FOR QUANTITY ORDERS. NOW AT SHOP 5, 79 RICKSTON ST, MANLEY WEST, QLD. 4179. OPEN TUES - FRID 9.30AM - 5PM, SAT. 9AM - 2PM. MAIL ORDERS TO PO BOX 34 CANNON HILL QLD. 4170. PHONE (07) 396 1859, FAX (07) 855 1014. MEMORY & DRIVES PRICES AT MARCH 7TH, 1994 SIMM 1Mb x 3 1Mb x 9 4Mb x 9 4Mb (72-pin) 8Mb (72-pin) 16Mb (72-pin) 70ns 70ns 70ns 70ns 70ns 70ns DRAM DIP 1 x 1Mb 256 x 4 70ns $8.50 70ns $8.50 IBM PS.2 50/55/70 70/35 90/95 2Mb 4Mb 4Mb $150 $265 $265 MAC 4Mb 4Mb x 80 80ns 6Mb P’Book $125 $420 $63 $72 $265 $265 $545 $985 CO-PROCESSORS 387SX to 25 387DX to 33 $105 $105 LASER PRINTER HP with 4Mb $260 TOSHIBA T3200SX T44/6400 T5200 4Mb 4Mb 2Mb $360 $305 $160 SUN SPARC 10/20 16Mb $1140 1Mb V2 BAT SRAM $230 2Mb V2 BAT SRAM $380 2Mb V2 FLSH SRAM $380 Sales tax 21%. Overnight delivery. Credit cards welcome. 5-Year Warranty Ring for Latest Prices 1st Floor, 100 Yarrara Rd, PO Box 382, Pennant Hills, 2120. Tel: (02) 980 6988 Fax: (02) 980 6991 alog, send 95 cents in stamps to Vector Press, Dept S, PO Box 434, Brighton, SA 5048. A WORD IS only worth a micro-picture. Need the full pic­ture? Send $2 in stamps, cash, or food parcels for Don’s 3.5-inch MS-DOS DEMO/PROMO disk. Covers all of my hardware kit projects. Don McKenzie, 29 Ellesmere Crescent, Tullamarine 3043. Phone (03) 338 6286. VALVE AMPLIFIERS: Australian made. Mono, stereo, guitar using 2A3, 211, 6L6 or 807 valves. Williamson reproductions. Parts available for DIY constructors. Circuit diagrams and construction details for many types of valve amplifiers. Valve equipment repairs. Lancroft Pty PELHAM Ltd, PO Box 439, Bexley 2207. Phone (02) 567 5390. SOSUTHERN CROSS SBC, accessories & EPROM emulator. See SC 8/93 & 12/93. Ideal for TAFE, schools & individual use. Alpine Technolo­gies, tel/fax (03) 751 1989. NETWORK YOUR PCs with “Little Big LAN”. Share disk drives and files (multi-user record locking), CD-ROMs and printers (with spooling). Connect PCs via serial or parallel ports, Arcnet and/or Ethernet cards. Supports up to 250 computers per network for only $95 ($100 for 3.5") for a whole network. Add $3 for postage in Australia. Works with MS-DOS, DR-DOS and Windows. April 1994  95 Software & Parts PC Voice Recorder V1.3 (SC 8/91) PC Talking Voltmeter V1.2 (10/91) Serious Guide to Building Kits V2.2 Transistor Specification Index V1.3 Op Amp Specification Index V1.3 $12 $17 $12 $15 $15 5.25 or 3.5" disc/PC CGA-VGA required LM3876T 50W amplifier IC $14 10 or more - 10% off Send Cheque/Money order to: Darren Yates, PO Box 134, French's Forest, NSW 2086. For more information, write to GRAN­ TRONICS, PO Box 275, Wentworth­ville 2145. Phone A/H (02) 631 1236. 68705 DEVELOPMENT SYSTEM: in-circuit simulator/emulator and pro­ grammer board for $250. Supports 68HC705C8/C4/J2/K1, 68705P3/U3/ R3 micro controllers and more. Contact Robert Priest­ley, PO 38/4 Illawong Village, Fowler Road, Illawong 2234. Phone/Fax (02) 541 0734. BINARY CLOCK - OCTOBER 1993: complete documentation supplied, includes introduction to binary, how it works, PLD source list­ings, conversion tables. Kit with PCB and all components $75 + $5 p&p. Optional Z frame stand (includes spacers and chassis DC connector) $25 + $5 p&p. Prototype Electronics, 1/29 Stewart St, Parramatta, NSW 2124. Phone (02) 683 3510; Fax (02) 630 3148. Pay by cheque, money order, credit card. FLUORESCENT INVERTER KIT (SC Feb 91) 12V or 24V/5W-21W.48V ver­ sion on request. Secondary wind, board plus components $30.00 plus ICL 286 Board Kits All in one board with two serial, printer, IBM keyboard, high density floppy & IDE mono video interface. Up to 4Mb RAM, 80286-16cpu, MS-DOS compatible, 130 page manual, small size 170mm x 255mm. Max I/O kit for PCs, 7 relays, ADC, DAC, stepper driver, TTL inputs, with software $169 PC I/O card with 8255 chip 24 I/O lines programmable as inputs or outputs $69 1.5 watt AM broadcast transmitter XTAL locked $49 2.5 watt FM broadcast transmitter 88-108MHz. $49 Digi-125 audio power amp (over 19,000 sold since 1987) 50 watt/8 $14 125 watt/4 $19 New 200 watt/2 version $29 Infrared relay kit $9 Remote control tester $4 $299 Ampo little PC All in one NEC V40 CPU board, MS-DOS compatible, high density floppy. SCSI hard disk, 2 serial, printer, solid state hard disk, IBM keyboard interface, (4W), CMOS single +5V rail, up to 768Kb RAM, 384Kb ROM, 145mm x 250mm, 98page manual. $299 P.C. Computers 36 Regent St, Kensington, SA. Phone (08) 332 6513. Altronics ................................ 26-28 Antique Radio Restorations.........94 A-One Electronics........................59 Av-Comm.....................................33 Ctoan Electronics........................96 David Reid Electronics ..............57 Dick Smith Electronics........... 12-15 Electronic Fault Info.....................83 Harbuch Electronics....................57 Instant PCBs................................95 CTOAN ELECTRONICS Low voltage lighting systems designed for your garden. Lights that dim up as the sun goes down create a great showpiece. Call us for your controlled garden lighting system. PO Box 211, Jimboomba 4280. Phone (07) 297 5421. Jaycar ................................... 45-52 JV Tuners.....................................41 L & M Video.................................69 Macservice....................................9 Nilsen Instruments.....................IFC P&P $4.00. Fluorescent inverter kit (SC Nov 93) 12V/24V/48V, 18W and 38W P.O.A. Solar battery charging regulator short form kit 12V or 24V (series) (SC Jan 94) employs Mosfet to switch solar array max current 10A $54.00 plus p&p $4.00. Additional Mosfet $8.00 and Schottky diode $5.00 to make 20A regulator. Cheques and postal money orders accepted with mail orders. Send orders to Otakar Priboj, PO Box 362, Villawood, NSW 2163, Austra­lia. Phone (02) 724 3801. KIT REPAIRS KIT REPAIRS and assembly. All work guaranteed. Phone (047) 51 5620. SILICON CHIP FLOPPY INDEX WITH FILE VIEWER Now available: the complete index to all SILICON CHIP articles since the first issue in November 1987. Now you can search through all the articles ever published for the one you want. The index comes as an ASCII file on a 3.5-inch or 5.25-inch floppy disc to suit PC-compatible computers and you can use any word processor or our special file viewer to search for keywords. Now with handy file viewer: the file viewer makes searching for that article or project so much easier. You can look at the index line by line or page by page for quick browsing, or you can make use of the search function.Simply enter in a keyword(s) and the index will quickly find all the relevant entries. All commands are listed on the screen, so you’ll always know what to do next. Note: requires CGA, EGA or VGA graphics card, IBM-compatible PC, MSDOS 3.3 and above. Price $7.00 + $3 p&p. Silicon Chip Publications, PO Box 139, Collaroy 2097. 96  Silicon Chip Advertising Index Oatley Electronics...................39,73 PC Computers.............................96 Pelham........................................95 Plough Book Sales......................89 RCS Radio ..................................94 Resurrection Radio......................89 Rod Irving Electronics .......... 75-79 Secontronics................................95 Silicon Chip Back Issues....... 84-85 Silicon Chip Binders..................IBC Silicon Chip Software..................93 Silicon Supply & Manufact...........95 Transformer Rewinds...................95 Yuga Enterprise...........................81 _________________________________ PC Boards Printed circuit boards for SILICON CHIP projects are made by: • RCS Radio Pty Ltd, 651 Forest Rd, Bexley, NSW 2207. Phone (02) 587 3491. • Marday Services, PO Box 19-189, Avondale, Auckland, NZ. Phone (09) 828 5730. • H. T. Electronics, 35 Valley View Crescent, Hackham West, SA 5163. Phone (08) 326 5590. Especially For Model Railway Enthusiasts Order Direct From SILICON CHIP Order today by phoning (02) 9979 5644 & quoting your credit card number; or fill in the form below & fax it to (02) 9979 6503; or mail the form to Silicon Chip Publications, PO Box 139, Collaroy, NSW 2097. This book has 14 model railway projects for you to build, including pulse power throttle controllers, a level crossing detector with matching lights & sound effects, & diesel sound & steam sound simulators. If you are a model railway enthusiast, then this collection of projects from SILICON CHIP is a must. Price: $7.95 plus $3 p&p Yes! Please send me _______ copies of 14 Model Railway Projects Enclosed is my cheque/money order for $­_________ or please debit my  Bankcard    Visa Card    Master Card Card No. Signature­­­­­­­­­­­­_________________________ Card expiry date_____/_____ Name _________________________Phone No (____)_____________ PLEASE PRINT Street ___________________________________________________ Suburb/town __________________________ Postcode____________