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Vol.7, No.3; March 1994 FEATURES FEATURES   6 High Energy Batteries For Electric Cars from ABB Review New sodium-sulphur batteries show promise 14 What’s New In Car Electronics by Julian Edgar THE DEVELOPMENT of highenergy batteries is critical if electric cars are to become a reality. Our article on page 6 looks at the progress being made. Latest Nissan uses head-up display 32 Electronic Engine Management, Pt.6 by Julian Edgar System operation – how it works 44 Switching Regulators Made Simple by Darren Yates Software does the design 80 Manufacturer’s Data On The LM3876 IC by Leo Simpson A high-performance monolithic audio amplifier PROJECTS PROJECTS TO TO BUILD BUILD 16 Intelligent IR Remote Controller by Ben Douchkov Works with almost any TV or VCR remote control 22 Build A 50W Audio Amplifier Module by Darren Yates HERE’S AN INTELLIGENT remote control that’s easy to build. It features both toggle & momentary outputs & works with just about any TV, VCR or universal IR remote control – see page 16. Uses a single-chip power module 38 Level Crossing Detector For Model Railways by John Clarke Adds realism to your model layout 56 Voice Activated Switch For FM Microphones by Darren Yates Provides audio muting of the transmitter section 62 Build A Simple LED Chaser by Darren Yates A low-cost project for beginners SPECIAL SPECIAL COLUMNS COLUMNS 50 Serviceman’s Log by the TV Serviceman We all make mistakes sometimes 60 Amateur Radio by Garry Cratt, VK2YBX Lowe’s HF-150 general coverage shortwave receiver THIS 50W AUDIO AMPLIFIER module is based on a single power IC that simplifies construction & eliminates quiescent current adjustments. Construction starts on page 22. 66 Computer Bits by Darren Yates A binary clock of the software kind 72 Remote Control by Bob Young How to service servos & winches 76 Vintage Radio by John Hill Refurbishing a Trio 9R-59D communications receiver DEPARTMENTS DEPARTMENTS   2   4 31 48 71 Publisher’s Letter Mailbag Order Form Circuit Notebook Book Reviews 84 86 90 94 96 Back Issues Product Showcase Ask Silicon Chip Market Centre Advertising Index ADD REALISM TO your model railroad layout with this level crossing detector. It detects the approach of a train, monitors its passing & provides an output to trigger an ancillary circuit to flash lights & sound a bell. Cover design: Marque Crozman March 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 It’s your magazine – tell us what you want No doubt many of you have filled in the reader survey which is included with this issue and will be in the coming March issue. It was also inserted into the January issue and the re­sponse so far easily exceeds the survey we ran late in 1990. If you have not filled in yours, please do so, either this month or next month since we want as many responses as possible. There is a good incentive to do so because prizes of Tektronix test equip­ment will be won by a few lucky readers. We need to run a survey such as this every now and again to make sure that we are meeting the needs of you, the reader. While we can’t be all things to all people, we can read what you say and take note. In the main, we expect that the result of the survey will enable us to enhance and fine-tune the editorial content of SILICON CHIP and thus make it more useful and enjoy­able to read. Some readers have been very thoughtful and have included letters with their surveys but in some cases we are not able to reply since they have not included their name and address. If you decide to write a letter as well as filling in the survey, please include your name and address so we can acknowledge it. While I am on this topic, many readers do send in letters which are ultimately featured in the “Ask Silicon Chip” pages, while others send in contributions to the “Circuit Notebook” pages and these are very welcome. However, relatively few readers are moved to send letters to the Editor which can ultimately appear in the “Mailbag” pages, although this month has been something of a purple patch and we have two pages of readers’ letters. We’re keen to receive letters for this page – it’s your chance to comment on events in the world of electronics or on topics in SILICON CHIP. Ultimately, SILICON CHIP is a distillation of the thoughts and needs of thousands of readers. You write or fax your letters in and we respond with technical articles and projects to meet your needs. In fact, in this issue alone, three of the articles – the Level Crossing Detector, the Voice Activated Audio Switch and the LED Chaser – have been presented in response to recent spe­cific suggestions from readers. And of course, some articles are directly contributed by readers, which is great. We acknowledge every letter we receive although some are inevitably delayed as monthly deadlines inexorably come around. So don’t be backward – if you want to ask a technical question, send in a Circuit Notebook contribution or express an opinion, please put pen to paper or fingers to the keyboard and make contact with us. We’d love 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 To help those using your stroboscope project featured in the December 1993 issue, I thought it would be useful to point out a small error in the use of this device that was stated in your article. The article instructs a user to “use the flash setting at which the line is brightest when it appears station­ary” as a point will appear stationary “if the strobe flashes at some exact multiple ... of the rev rate (eg, twice per rev)”. In fact, if the strobe is flashing at twice the rev rate a user will see two points (or double the number of spokes in a wheel etc.) This double pattern is the correct pattern to aim for when using a strobe. When a double pattern is first observed then the strobe will be flashing at exactly twice the revs of the rotating body. A single pattern cannot be guaranteed to be pre­cise. So to correctly use a strobe the user should start at the lowest flash rate and increase until a stationary pattern is observed. The flash rate should then be doubled continually until a double pattern is first observed. The flash rate is then halved and adjusted for a stopped pattern. This frequency will then be that of the rotating body. For this reason, the maximum rotational speed that a strobe can measure is half its maximum. S. Howell, Prahran, Vic. Mini Disc too expensive I would like to offer some comments and voice my disagree­ ment on a couple of matters in the October 1993 issue. Firstly, about that review of the Sony Mini Disc system. You say that this will eventually replace the compact cassette. Maybe, but how long might this take? Did you notice the prices? They range from $1400 to $2000! That’s more than twice the cost of my entire home sound system including radios and turntables. Now I know that things do tend to get cheaper with the fullness of time but can you imagine 4  Silicon Chip your proverbial average, out-of-work jogger being able to afford something like this? If the price came down to about one fiftieth then I just might consider it. Do you know that you can currently buy a Walkman-style cassette player for less than $40 from Dick Smith? And you get an AM/FM stereo radio thrown in. You also make some rather disappointing remarks about com­ pact cassettes. I acknowledge that my HF response isn’t what it used to be. And I agree that some of these cheap cassettes aren’t exactly crash hot. But if I copy a CD to cassette then apart from a little tape hiss I must say that I can scarcely tell the dif­ference. Even the player in the car isn’t all that bad. And another thing, as far as recording time is concerned. Cassettes come in one-, one-and-a-half and (I think) two-hour lengths which will easily accommodate even the longest CD. So there. (OK, I’ll concede the bit about random access.) End of subject. Next, the electronic engine management bit. The author says that power, performance, etc are greatly improved. Maybe he’s right but I’m not convinced. Throw another carby on the old Datsun and I’ll bet it wouldn’t be all that far behind. My wife’s car, the latest Daihatsu Charade, has fuel injection, multiple valves, hot & cold running everything but it’s still a gutless wonder. A friend’s 18-year old Morris Mini will leave it for dead at the lights. E’nuff said. G. J. Hunt, Frankston, Vic. Comment: We agree that the price of Mini Disc players is present­ly too expensive for most people, but that is no more the case than was the price of early CD players. As far as engine management and its virtues are concerned, we are adamant that all that is said in the article is true. While we cannot comment on your specific case, all things being equal, modern cars will not only blow their 20-year old counterparts into the weeds but they also don’t need engine tune-ups, don’t oil their plugs and never stall because of wet ignition. They are also much quieter and they produce a lot less pollution of the environment. Still need convincing? High efficiency inverter can drive other fluorescent tubes Regarding John Clarke’s article in your November 1993 issue, he has substantially underestimated the value of this circuit. As well as being able to drive the conventional tubular 18W 600mm long lamp and the 36W 1200mm lamp, the circuit will drive a whole range of miniature fluorescent lamps, which may have more convenient shapes for some purposes. The 18W version of the circuit will drive the 18W 225mm long miniature lamp such as the Philips PL18, while the 36W version will drive the 36W 415mm long tubes, such as the Philips PL36 and the Thorn 2D 205mm square lamp. With minor circuit changes (similar to those changes made to convert from 18W to 36W), the inverter should also run the fol­lowing types: 9W 165mm long, 11W 243mm, 18W 225mm, 24W 320mm, 36W 415mm long, 10W 91mm square, 16W 140mm square, 21W 140mm square, 28W 205mm square and 36W 205mm square. Thus, the inverter will run a far greater range of sizes and shapes of lamps than the standard 600mm and 1200mm tubular lamps. A word of warning though – it is essential to use the 4-pin versions of these lamps, which are designed for use with external starters. The 2-pin versions with inbuilt starter will not work, nor of course will the inverter run the miniature fluorescent lamps with inbuilt control gear designed to plug LUMINOUS EFFICACY Using the stroboscope SILICON CHIP, PO Box 139, Collaroy, NSW 2097. FIG.1 FREQUENCY kHz directly into a 240VAC incandescent lamp socket. With regard to the output of fluorescent lamps, their efficiency and light output improves with frequency from mains operation at 50Hz to approximately 30kHz – by which time the lamps is emitting 10% more light for the same power consumption (see Fig.1). Above 30kHz, the light output is constant, so the inverter causes the lamp to run at about 10% higher efficiency than if it were connected to the mains. There is also a minor error in the article. The rating of a fluorescent lamp is the watts consumed by that lamp and does not include control gear losses, so the inverter should be adjusted to have a power output of 18W or 36W, not an input of 18W or 36W. As cheap and inefficient ballasts consume around 10W, and high quality low ballasts about 5W, I would assume that operation with the inverter is probably more efficient than with the higher loss ballasts connected to mains. I suspect that John Clarke has done a better job than he thinks. A. Davies, Ainslie, ACT. Comment: as stated in the November 1993 article, the current through the lamps is set to approximately the same value as it would be if running in a conventional 50Hz ballast circuit. Therefore the power level in the tube will be the same as in a 50Hz ballast circuit. For this value of current from the invert­er, the tubes were brighter than if operated at 50Hz. LEDs have also gotten vastly cheaper and more reliable at the same time, so obviously some new production technique is being used. Another interesting point (not raised in your article) is that while early LEDs had a very low reverse breakdown voltage (typically 4.5V), in modern LEDs this is much higher (typically 20 to 40V). I still occasionally see technical writers cautioning about the hazards of applying more than 5V reverse potential to LEDs. This information would appear to be well and truly out of date! Keith Walters, Lane Cove, NSW. Comment: LED forward voltages do seem to be clustering around 2V or higher, although manufacturers’ published specs for some red LEDs still show 1.5V or thereabouts. All LEDs have higher forward voltages Which binary clock? I have just noticed that in your “One-Chip Melody Genera­tor” project (December 1993), you mention that a red LED is not suitable for LED 1 as they have a forward voltage drop of only “about 1.8V”. In fact, in my experience, all the visible LEDs I have bought in the past few years (apart from blue ones) seem to have the same forward voltage drop of about 2.2V. It is true that early red LEDs did have a very precise 1.5V forward voltage with a very sharp conduction “knee” but somewhere along the line this has become much more rounded. Impulse tacho driver works perfectly The circuit for the tachometer impulse driver featured on page 109 of the August 1989 works perfectly on a 6-cylinder Ford Cortina TE which I fitted with a High Energy Ignition System as published in S ILICON CHIP. However, the PNP transistor Q1 should be a BC327 not a BC337 (which is NPN). Jack Neighbour, Horsham, Vic. Comment: Thanks for your feedback on the tachometer driver. We have suggested this circuit to quite a few readers over the years but you are the first to tell us that it actually worked for your car. I was very interested to read your project on the Binary Clock in the October 1993 issue of SILICON CHIP. Are you planning to design another project related to an “analog” clock with LEDs in place of hands? I would like to suggest a clock having 12 blue LEDs (say) which represent the seconds, 12 red LEDs which represent the minutes and 12 green LEDs which represent the hours. After every 5 pulses (each of one second), the next blue LED becomes illumi­nated. After a total of 300 pulses, each successive red LED illuminates (representing 5 minute intervals). After a total of 3600 pulses, each successive green LED illuminates (representing hours). If you have any comments on the possibilities for the above project, I would be grateful to receive them. Bill Toussaint, Shelley, WA. Comment: Sounds OK to us. What do other readers think? More on making PC boards with a photocopier In the Mailbag section of the November 1993 issue of SILI­CON CHIP, D. Burke reported having difficulty in applying the photocopier/convection microwave method of making PC boards. I have enclosed some plastic transfers of my own use of the convection oven method and I think you will agree that 95% trans­fer success is a fair estimate, and these results are highly repeatable. D. Burke admits that the clothes iron method requires great care to prevent smudging of the transfer, and the correct amount of heat and heating time makes it all too tricky. Any electronically controlled precision oven would probably suffice, but D. Burke’s initial problem reveals that the calibra­tion of these convection ovens is not as good as expected, be­cause it sounds like he needed more heat and maybe more pressure. Enthusiasts will have to find the correct setting for their ovens, starting with 150°C. The correct setting will be that which is the hottest temperature before the copper starts to noticeably discolour and the plastic distorts. Improvements on my method described on page 92 of the May 1993 issue are as follows. I use two house bricks as a weight (one on top of the other and do not use the microwave oven ca­rousel for this load). Use 20 or 30 pieces of flat photocopy paper as the pressure pad as this does not crinkle as does news­paper. Go over “all” tracks with an etch resist pen carefully, heat up the ferric chloride etchant to almost boiling (not in plastic in a microwave oven) as this dramatically speeds up the etching process. Glen Host, Doubleview, WA. March 1994  5 High energy ba electric vehicle BMW’s electric car, the E1. It has a 32kW DC motor & an ABB high-energy battery rated at 120 volts & 160Ah. The E1 can easily hold its own in traffic. Fully charged, it has a range of 160 to 230km. Its top speed is 120km/h. 6  Silicon ilicon Chip hip at teries for es The development of high energy batteries is critical if electric cars are to seriously compete with conventional petrol & dieselpowered cars. In this article we report progress made by ABB in producing sodium sulphur batteries for electric vehi­cles. Electric vehicles, whether cars, minivans or buses, produce substantially less noise and emissions than their counterparts with conventional engines. In the past, electric car development has been hindered by the excessive weight of the battery; fully charged, a 400kg lead-acid battery allows a car to travel a distance of only about 50km. With a high-energy sodium-sulphur battery of only half this weight and assuming the same condi­tions, a modern electric car could travel about 150km. This means that there is now a realistic chance of emis­sion-free vehicles taking off in both private and public trans­portation. Not only does its better energy-to-weight ratio make the ABB high-energy battery superior to other types of battery. The use of sodium and sulphur as reactants has benefits which are unique to this battery, especially in the areas of design and application. The most important features of the battery are: • No self-discharge takes place in the cells. • The charging efficiency is 100%. This means that a cell needs only to be recharged with the amount of energy that it has discharged. Batteries with aqueous electrolytes, by contrast, require an excess charge to ensure that they are fully charged. This excess charge is consumed during the decomposition of water in the electrolyte. • The charge/discharge efficiency is high (about 90 percent for batteries in electric cars) on account of the 100% charg­ing efficiency. • Battery overcharging is essentially impossible. The internal resistance of the cells rises sharply at the end of the charging process, allowing them to be connected in series or parallel without risk. If a series-connected cell fails (short circuit), the internal resistance of another cell in the string will rise as soon as it has been charged by the parallel strings. In other types of battery, these conditions lead to electrolytic decomposi­tion of the water content, causing hydrogen and oxygen to form. This is why such batteries are usually not connected in parallel and why the capacity of the cells is always matched to the application. Sodium-sulphur batteries, on the other hand, can be built using cells of one standard type to obtain any required capacity. This gives the sodium-sulphur battery its flexibility and makes it economical to produce. Because of the battery’s 100% charging efficiency and the absence of electric self-discharge, its charge can be determined by simple current integration. The sharp rise in the internal resistance of the cell indicates when charging has ended. Every time the battery is fully charged, the starting point for the capacity is recalibrated. March 1994  7 The electric Cobus 200 EL, with three B17 batteries, carries 20 people. It has a top speed of 80km/h & a daily range of up to 200km. Since the cells are operated at a high temperature, the full battery charge is always available even under conditions of extreme cold or extreme heat. The thermal insulation of the batteries is very efficient, so that only a small amount of energy is required to maintain the temperature at the required level. The main advantages of the new generation of ABB high-energy batteries over their predecessors are their higher volu­metric and gravimetric energy densities. Their energy-to-weight ratio of 104Wh/kg makes them the lightest batteries available today for electric cars. This progress has been made possible by an improved cell and the use of liquid instead of air for cool­ ing. The same production technology is used for all the different battery sizes. The A08 cell has an outside diameter of 38mm and is 225mm long. Its capacity is 40Ah. A battery can contain up to 480 vertically mounted interconnected cells, arranged hex­ag­onally on 8  Silicon Chip a heat-exchanger. By using liquid instead of air for cooling, it is possible to utilise the heat dissipated by the battery at high loads for heating. A flat resistance heater heats the battery to the re­quired temperature and maintains it at this level. Operating temperature is between 300°C and 350°C The cells are enclosed, together with the heating and cool­ing systems, inside a double-walled casing. Good thermal insula­tion is ensured by evacuating the space between the walls. The only openings in the casing are for the power and measurement cables and the coolant tubing. As a result, the battery is very compact and heat losses are minimal. An insulating glass-fibre board in the evacuated space between the casting walls gives extra support. The result is a casing so strong that the battery can be mounted in the vehicle without having to use a tray. It can even be a factor in strengthening the vehicle’s body. During development of the new batteries, a large number of safety tests were carried out in collaboration with Germany’s technical inspectorate. Crash tests carried out by automobile manufacturers using their own cars demonstrated that the batter­ies meet the highest safety standards. ABB currently offers two standard batteries. Designated B16 and B17, they have 120 and 240 cells, respectively. A further seven customised batteries, of different sizes and with different energy contents, are also available. The batteries feature very good voltage stability over the full discharge range. Management system Reliable battery operation and efficient utilisation of the energy content depend on the battery management system. This has three primary functions: • To monitor battery conditions and ensure adherence to specifi­cations; • To transmit data to the processor in the drive control unit; and • To regulate the battery temperature. The main components of an electric car’s drive are the high energy battery with its management unit, the electric motor with its control and power sections, a protective circuit breaker and the battery charger. When the battery is cold, the circuit breaker is open and interrupts the battery management system’s power supply. In this condition, the battery can only be started when the battery management system is connected to a socket outlet. Power from this external source is used for the initial heating of the battery which cannot be operated until it is above the lower operating temperature limit. Heat-up normally takes about 24 hours. The monitor in the battery management system authorises operation as soon as the lower operating temperature limit has been reached. However, power is still not drawn from the battery until the drive system’s processor signals ‘ready to operate’ and the protective circuit breaker has closed. During charging and discharging, the monitoring unit checks the temperature, battery current, various voltages and the insu­ lation resistance. Any deviation from the specified data is signalled to the motor control system and initiates a programmed response (eg, a reduction of the discharge current). If this does not lead to the desired result and one of the limits defined for the specified operating values is exceeded, the monitor activates the circuit breaker. The monitoring system is necessary to protect the battery from inadmissible loads. In addition, safety reasons require the entire electrical power train to remain ungrounded under all operating conditions. The management system instantly disconnects the battery if a fault occurs in the insulation. During normal operation, the battery management system signals additional information, (eg, battery temperature, charge level, battery current, etc) to the CPU of the motor control system. By monitoring the battery independently, this CPU can respond before unwanted load shedding is initiated by the manage­ment system. The battery management system controls the battery tempera­ture by activating the cooling or heating system. If the tempera­ture becomes too high due to a high continuous current being taken from the battery, the coolant circulating pump is switched on. ABB’s standard sodium sulphur batteries, B16 on the right & B17 on the left. The leads protruding from the black cover on the heat-insulated casing are the power, measurement & heating cables. Behind this cover is the flange used to evacuate the double-walled casing. The coolant connections are at the back. The heat is either transferred, via a heat-exchanger, to a cooling circuit in the vehicle or via an air cooling system to the atmosphere. When the vehicle is stationary for longer periods of time, the heating system remains switched on to keep the temperature of the battery at its required level. The energy needed for heating is taken primarily from the AC mains but can be taken from the battery itself if there is no mains power available. This is possible for about a week, after which the battery is fully discharged and its temperature will drop below the minimum operating level. In this condition, the battery is unable to heat itself up unless it is connected to a power outlet. Such cases are expected to be very rare with electric vehicles, since they will normally be hooked up every day to the AC power outlet. Trial vehicles ABB has teamed up with major automobile companies in equip­ping electric cars with the high-energy battery. Small fleets of trial cars have already run up more than one million kilometres on public roads. New developments in the automotive industry are targeting the market for electric cars which will soon open in California. By 1997, 2% of all new vehicles in California will have to exhib­it zero emissions. Only electric cars can do this. The types of car involved range from modified production-line vehicles to new, purpose-designed electric cars, such as BMW’s E1. The designers of this “urban” car have put the ABB high-energy battery at the back of the vehicle, under the seats. It has 240 A08 cells, like the B17 battery, but has different dimensions. According to BMW, the car can accelerate from standstill to 50km/h in just six seconds, has a top speed of 120km/h and a range of between 160 and 230km. Electric vehicles with the ABB high-energy battery are also being used for public transportation. Minibuses (eg, the Cobus) are used for inner-city transportation as well as in recreational resorts and other zones reserved mainly for pedes­trians. These buses have three B17 batteries for a range of more than 100km. The batteries can be charged rapidly so it is possi­ble to double the range by interim charging SC during stops at terminals. Acknowledgement Our thanks to ABB Review for the photos and for permission to publish this article. March 1994  9 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 What’s New In Car Electronics? Latest Nissan uses HUD Recently released onto the Australian market, Nissan’s new Bluebird now includes a Head-Up Display (HUD) in the SSS sporty model. Claimed by Nissan to be a world first in a production car, the HUD panel is illuminated in the lower right-hand side of the windscreen. The green display comprises a digital speedometer, turn signal indicator arrows, door-ajar indicator, brake failure warning, and a master warning indicator which lights the word “Check” when activated. The HUD works by using a vacuum fluorescent display located behind the instrument cluster in the dashboard. It transmits the image onto a mirror, which reflects the information onto a “com­biner” panel. This in turn reflects the infor­mation to form a virtual image in front of the windscreen. The brightness of the image is ad­justable and it can also be turned completely off, if the driver desires. The HUD is in addition to the normal instrumentation pro­vided in the dashboard. 14  Silicon Chip WINDSHIELD COMBINER VIRTUAL IMAGE MIRROR HUD UNIT ANALOG INSTRUMENT CLUSTER VFD CONTROL UNIT Fig.1: how the head-up display is formed. A mirror reflects the image on a vacuum fluorescent display onto a “combiner” panel & this in turn reflects the infor­mation to form a virtual image. K ALEX BRAKE WARNING TURN SIGNAL INDICATORS DOOR WARNING The UV People ETCH TANKS ● Bubble Etch ● Circulating SPEED INDICATION MASTER WARNING Fig.2: this diagram illustrates the readings on the Head-Up Display (HUD) unit used in the new Nissan Bluebird. LIGHT BOXES ● Portuvee 4 ● Portuvee 6 ● Dual Level TRIMMER ● Ideal VDO upgrades plant PCB DRILL ● Toyo HiSpeed MATERIALS ● PC Board: Riston, Dynachem ● 3M Label/Panel Stock ● Dynamark: Metal, Plastic ✸ AUSTRALIA’S NO.1 STOCKIST ✸ K ALEX 40 Wallis Ave, East Ivanhoe 3079. Phone (03) 9497 3422, Fax (03) 9499 2381 Silicon Chip Binders VDO Instruments Australia, a major manufacturer of automo­tive instruments, has recently spent $2.5 million upgrading its Australian manufacturing plant by installing the latest in sur­face mount technology (SMT). “Clean” technology is being em­ployed, whereby the SMT system operates in a nitrogen atmosphere. This removes the need for chlorofluorocarbons (CFCs) to be used for cleaning the circuit board assemblies at the end of the manu­ facturing process. Cartridges containing 10-20 individual circuit boards are loaded at the beginning of the system, each marked with a bar code label determining the necessary procedures to be carried out during the manufacturing process. As each circuit board passes through flip stations, the board is turned so that components can be mounted on either side. A high speed “chip placer” inserts resistors, capacitors, diodes and transistors onto the solder paste, while a “chip shooter” is used for larger ICs. Cameras monitor the placement of components onto the boards, before they pass into a nitrogen curing oven. VDO has contracts to supply instrument clusters and fuel pump assemblies to German car-makers Mercedes-Benz and BMW, as well as supplying 70% of the local market. These beautifully-made binders will protect your copies of SILICON CHIP. They are made from a dis­tinctive 2-tone green vinyl & will look great on your bookshelf. Price: $A14.95 (incl. postage in Australia). NZ & PNG orders add $5 each for postage. Not available elsewhere. Send your order to: Silicon Chip Publications PO Box 139 Collaroy Beach 2097. Or fax (02) 979 6503; or ring (02) 979 5644 & quote your credit card number. March 1994  15 By BEN DOUCHKOV ❋ Circuit uses a microcontroller IC ❋ Features toggle & momentary outputs ❋ Works with any TV or VCR infrared remote control Build an intelligent IR remote controller This simple project allows you to add infrared remote control functions to your favourite equipment. It works with almost any TV, VCR or universal remote control. The idea for this project first occurred many years ago when the author owned an old colour TV that was not remote con­trolled. One feature that was really missed was a remote on/off control but that problem can be easily overcome using this in­frared receiver. It’s based on a 68HC705 micro­con­ troller and can be used to remotely switch appliances such as old TV sets, or to perform a range of remote control functions in other equipment. A few applications that come to mind include amplifier power control, speaker mute functions, model trains, 16  Silicon Chip controlling small motors, robot control, and lighting control. To make it as versatile as possible, the receiver features toggled DPDT relay outputs and two open collector (ie, transistor switched) outputs (designated output 1 & output 2). These outputs are controlled by the channel 1 and channel 2 buttons on the transmitter. The channel 1 button controls the relay outputs, while the channel 2 button toggles output 1. The other open collector output (output 2) is either held low while ever the channel 2 button is pressed (repetitive code transmitter) or briefly pulsed low each time this button is pressed (one-shot code transmitter). Output 1 could thus be used for power switching via a relay or solenoid, while output 2 could be applied to user-controlled functions; eg, slide projector advance or focus motor control. Note: some remote control transmitters only send the code once when a button is pressed and held down, while others will continuously send the code while ever the button is held down. There were two important goals set in developing this pro­ject: (1) it had to be inexpensive; and (2) it had to work with virtually any common TV, VCR or universal IR remote control transmitter. It also had to be flexible so that it could be used in a number of different applications and configurations. A circuit based on a single chip microcontroller was the natural choice and also offers the chance to 5 +5V R1 150k 8 IN+ D1 TFK186  4 F0 R11 10k 1 VCC C4 .01 R3 4.7k GND 6 5 C2 4.7 C1 0.47 3 OUT 2 C1 +5V R4-R8 3 C3 220pF 8 7 6 X2 4 2 F1 4 AC1 +DC D3-D6 4x1N4004 IN C9 1000 3 AC2 IRD 0V PA1 PB5 PA2 IC2 68HC705J2 PB0 OUT IC3 7805 GND PA4 PB2 PA5 PB3 PA6 PA7 PB4 5x10k OSC1 +5V OSC2 R16 R15 1k VIEWED FROM BELOW A K B Q3 BC337 A 17 4 16 3 15 2 14 1 TP 2 C 4 3 E AUX1 AUX2 AUX3 0V 13 12 11 GND 10 C6 22pF +DC +5V 4 5 1 B C R12 1k 18 RELAY 1 D2 1N914  R9 10M C8 4.7 +DC E 2 XTAL1 4MHz C7 22pF I GO PA3 PB1 1 1 0V VCC PA0 5 +DC RESET +5V 19 C5 4.7 7 INCD LED1 9 20 IC1 UPC1490 R2 10  R10 10k C1 NC1 C2 D8 1N4004 D7 1N4004 X1 R14 1k Q2 BC337 B NC2 R13 1k C E Q1 BC337 B +DC OUT C10 .01 2 OUTPUT 1 TOGGLE 3 OUTPUT 2 MOMENTARY C E 1 K +5V OUT 0V INFRARED REMOTE CONTROL Fig.1: signals from the IR transmitter are picked up by photodiode D1 & fed to IR preamplifier stage IC1. The signal from IC1 is then fed to IC2, a 68HC705J2 microcontroller with programmed ROM tables. Its outputs drive Q3 to toggle relay 1, while Q1 & Q2 provide toggle & momentary open collector outputs. tackle more complex applica­tions at a later date. The ability to use an existing TV or VCR remote control transmitter means that you do not have to buy another one. It also means that quite a number of different codes have to be recognised by the microcontroller. This is achieved by using code tables that reside within the microcontroller’s ROM. The ROM codes that were selected for each remote control are for channel 1 and channel 2. With the current version of the software, 10 different transmitter groups (five TV and five VCR) are recognised. Each of these groups covers a number of different manufacturers and models, which means that a wide range of trans­mitters can be used. Unfortunately, not all the popular manufacturers and models can fit within the limited amount of ROM available and so, for this reason, a general purpose learning mode is also included. This mode allows one remote control code to be learned when the project powers up or is reset. The learnt code is stored in RAM and is lost when power is removed. Note that, due to the limited amount of RAM within the microcontroller used, only one code can be learned and so the same button is used to control all three outputs simultaneously. Thus, if the receiver is using a learned code, pressing the transmitter button will toggle the onboard relay, toggle output 1 and either pulse output 2 or acti­vate output 2 for as long as the code is received. Although not guaranteed to work with all transmitters, this mode does allow the use of a lot of remote control transmitters that would otherwise be March 1994  17 XTAL 1 R16 C1 NC1 NC2 +5V R8 10k R7 10k R6 10k R5 10k R4 10k RELAY 1 C2 22pF 10M 1 0V 10k 1k 10k 4.7k IC2 68HC705J2 X1 4.7uF 1k 1k .01 IC3 7805 X2 150k 4.7uF F1 1k AC1 1 D2 AC2 +DC OUT 0V 0V AUX3 AUX2 AUX1 +5V OUT 22pF 1000uF A LED1 K Q1 0V OUTPUT 1 OUTPUT 2 Q2 +5V OUT +DC OUT .01 D8 D7 10  Q3 D3-D6 0.47uF 220pF 4.7uF D1 IC1 UPC1490 K A Fig.2: install the parts on the PC board exactly as shown here & be sure to use a socket for the 68HC705J2 microcontroller (IC2). Pin 1 of IC1 can be identified by the adjacent dot in its plastic body. Note that although shown here & in Fig.1, the auxiliary outputs are unused in this version of the project. unsupported. It also allows the user to customise the code to which the unit responds. Circuit description The circuit can be broken down into three blocks: a power supply stage, an infrared preamplifier stage, and the microcon­ troller stage. Fig.1 shows the details. The power supply consists of fullwave rectifier D3-D6, filter capacitor C9 and 5V regulator IC3. Because the project may be incorporated into a piece of equipment, an onboard fuse (F1) is also included. This fuse is nominally rated at 0.75A but can be changed to suit the external circuit being powered via the receiver. The power supply screw terminals (X2) provide easy termina­tion for the input power (AC1 and AC2). These terminals can accept either 9-20VAC or 12-30VDC (the polarity does not matter). In addition, the output from the bridge rectifier is fed to a +DC terminal and this could be useful for powering external circuits. The infrared preamplifier (IC1 – UPC1490) was selected for its ability to operate from 5V and because no external inductor is necessary. However, the key to any infrared receiver is the quality of the infrared detector (D1) and, after a number of experiments, it was found that a BPW90 photodiode gave good per­formance. Unfortunately, it appears that this photodiode is no longer manufactured and so an equivalent unit from Tele­funken, the TFK186, was used. In operation, D1 picks up the infrared pulses from the transmitter and applies the resulting current pulses to pin 8 (IN+) of IC1. R2 and C1 set the initial gain and low frequency Specifications Range ���������������������������8-15 metres (depending on transmitter used). Power supply �����������������12-30V DC or 9-20VAC. Outputs �������������������������DPDT relay contacts; two open collector outputs; 1 indicator LED. Codes (preset mode) �����Channel 1 toggles the DPDT relay; channel 2 toggles open collector output 1 and either pulses open collector output 2 low or holds this output low for as long as the button is pressed. Learned mode ���������������A single button toggles the DPDT relay, toggles open collector output 1, and either pulses open collector output 2 low or holds this output low for as long as the button is pressed. 18  Silicon Chip roll-off for the input amplifier inside IC1, while R1 sets the bandpass filter. These components were selected to provide a wide bandpass. C2 is the detector capacitor, while C3 is the inte­grating capacitor. These were selected to provide maximum sen­ sitivity but the receiver can be detuned if necessary by changing C3. The output from IC1 appears at pin 2. This is an open collec­tor output and so requires a pull-up resistor (R3). C4 provides additional pulse filtering. Microcontroller IC1 drives the PB5 (pin 3) input of IC2, an MC68HC705J2 micro­controller from the 68HC05 family. This device uses CMOS technol­ogy and has 2064 bytes of program space and 112 bytes of static RAM. The “J2” also has 13 input/output pins and an inbuilt timer. Resistors R4-R8 on lines PB0-PB4 are used to select the desired ROM code and are connected to either the 0V or 5V rails, depending on the transmitter – see Table 1. This means that the input port lines (PB0-PB4) are either pulled to 0V or 5V. A DIP switch could have been used here but as the configuration will probably be permanent, the cost of the switch was saved by using only resistors. It is worthwhile mentioning several important control lines for the microcontroller. These are the oscillator, reset and IRQ (interrupt request) lines. C5 provides the power-on reset pulse by holding pin 20 low for a brief period after power is applied. During this period, the oscillator starts and this operates at 4MHz as set by crystal XTAL1 between pins 1 and 2. When the receiver is switched on, the software goes through its reset routines. One of these routines is designed to flash an on-board LED (LED 1) four times each time power is applied. If the receiver has been con­figured for one of the ROM codes, the microcontroller will then sit in the main program loop, waiting for infrared pulse signals from the transmitter. When a valid signal is received, LED 1 pulses on and off in sympathy with the pulse code. This feature is useful for testing the range of the receiv­er. If the Learning mode has been selected, the microcon­ troller will sit in a program loop after power-up looking for the infrared code to be learned. Some codes are easier for the Mount the relay separately from the PC board if you intend using it to switch mains voltages. Alternatively, you can leave the relay on the board & use it to control a slave relay. TABLE 1: Mode Selection Transmitters Type Learning mode (only one code) Setting R8 R7 R6 R5 R4 0 0V 0V 0V 0V 0V mains appliances, mount the relay off the board or use it to control an external slave 240VAC-rated relay. Resistor R16 is used to limit the current through the relay coil when the output voltage from the bridge rectifier (D3-D6) is higher than 12V DC. This rectified voltage is measured across C9. The nominal coil current is 45mA so the value of R16 is calculat­ed using the formula R16 = (VDC - 12)/0.045. Table 2 shows a range of suitable resistor values. Outputs PA5 and PA6 drive transistors Q1 and Q2 and these respectively provide the toggled and momentary open-collector outputs (output 1 and output 2). Each output is used by connect­ing the load between the collector of the transistor and either the +5V rail or the +DC rail, depending on the application; eg, a relay could be connected between Q1’s collector and the +DC rail exactly as shown for relay 1 and Q3 (don’t forget the current limiting resistor for voltages greater than 12V - see Table 2). Diodes D7 and D8 are there to protect Q1 and Q2 from any high back- EMF voltages that may be generated by inductive loads. Note that Q1 and Q2 have a maximum current rating of 1A. Akai, Goldstar, Magnavox, Marantz, AWA/Mitsubishi, NEC, Samsung TV 1 0V 0V 0V 0V 5V Marantz, AWA/Mitsubishi TV 2 0V 0V 0V 5V 0V GE, Panasonic TV 3 0V 0V 0V 5V 5V Panasonic TV 4 0V 0V 5V 0V 0V Sony TV 5 0V 0V 5V 0V 5V Construction Hitachi, Pioneer, RCA, Toshiba VCR 6 0V 0V 5V 5V 0V Sony Beta, Zenith Beta VCR 7 0V 0V 5V 5V 5V Canon, GE, Magnavox, Memorex, Panasonic, Realistic VCR 8 0V 5V 0V 0V 0V Realistic, Sharp VCR 9 0V 5V 0V 0V 5V AWA/Mitsubishi VCR 10 0V 5V 0V 5V 0V The construction is straightforward since all the parts are mounted on a small PC board (code IRJ201, 105 x 58mm). Fig.2 shows the parts layout. No particular order need be followed when installing the parts on the PC board, although it’s best to leave the larger parts until last. Take care when installing the semiconductors and electrolytic capacitors, since these parts are all polarity conscious. The crystal (XTAL1) can be installed either way around; its leads should be bent through 90° so that it will lie flat against the PC board. IC1 can be soldered directly to the PC board, while IC2 should be mounted using a 20-pin IC socket. Pin 1 of IC1 can be identified by the small adjacent dot in the plastic body of the device. The cathode (K) of the photodiode (D1) can be identified by the bevelled edge along one corner (see the pinout diagram on Fig.1) The five 10kΩ resistors (R4-R8) on pins 4-8 of IC2 must be installed so that they select the required ROM code for your transmitter. As mentioned re­ceiver to learn than others, so several attempts may be necessary to teach the receiver the desired code. Outputs The PA7 output from IC2 toggles high or low on each succes­sive press of the channel 1 transmitter button and this output drives NPN transistor Q3. Q3 in turn switches relay 1 on or off to open or close the two sets of contacts. Relay 1 is ideally suited to switching low voltage circuits such as loudspeaker lines and 12V power supply rails. The relay contacts are rated at 240VAC 5A but, due to the close proximity of the contacts to the rest of the circuit, it is not recommended that the relay be used for directly switching mains appliances. If you do wish to switch 240VAC TABLE 2 Voltage Across C9 R16 12V Link 18V 120W 0.5W 24V 270W 1W 27V 330W 1W 30V 390W 1W March 1994  19 PARTS LIST 1 IRJ201 PC board 1 20-pin IC socket (for IC2) 4 plastic PC board standoffs 2 4-way screw terminals 2 2AG fuseclips 1 2AG 0.75A fuse (F1) 1 FBR621D012 12V relay 1 4MHz crystal (XTAL1) Semiconductors 1 uPC1490 IR amplifier IC (IC1) 1 68HC705J2 programmed microcontroller (IC2) 1 78055 5V regulator (IC3) 3 BC337 NPN transistors (Q1,Q2,Q3) 1 TFK186 infrared photodiode (D1) 1 1N914 silicon diode (D2) 6 1N4004 silicon diodes (D3-D8) 1 5mm red LED (LED1) Capacitors 1 1000µF 35VW electrolytic (C9) 3 4.7µF 16VW electrolytic (C2,C5,C8) 1 0.47µF 16VW electrolytic (C1) 2 0.01µF monolithic (C4,C10) 1 220pF ceramic (C3) 2 22pF ceramic (C6,C7) Resistors (0.25W, 5%) 1 10MΩ (R9) 1 150kΩ (R1) 7 10kΩ (R4 -R8, R10-R11) 1 4.7kΩ (R3) 4 1kΩ (R12-R15) 1 10Ω (R2) 1 R16 – 0.5W or 1W (see text & Table 2) Miscellaneous Two LEDs plus two 1kΩ resistors for testing open collector outputs; plastic case; red plastic window. Take care when installing the infrared photodiode (D1). It must be oriented so that its bevelled top edge goes towards diode D7 (see Fig.1 for case outline). The two large LEDs were installed temporarily to test the open collector outputs. previously, each resistor can be con­ nected to either the 0V rail or to the +5V rail. Table 1 shows the codes for a range of TV and VCR transmitters. By way of example, let’s assume that you have a Sony TV remote control. In that case, you would use setting 5; ie, R4 & R6 connect to the +5V rail, while R5, R7 & R8 go to the 0V rail. Similarly, if you have a Sharp VCR remote control, then setting 9 is the one to use (ie, R4 & R7 to +5V and R5, R6 & R8 to 0V). R16 must be selected so that when relay 1 is on, only 12V DC is applied across its coil. It should be left off the PC board for the time being. Testing Once the board assembly is completed, go back over your work carefully and check that all parts are correctly Where to buy the kit Parts for this project are available from Benetron Pty Ltd, PO Box 43, Quakers Hill, NSW 2763. Phone (02) 963 3868. Prices are as follows: (1). PC board plus all on-board components (includes programmed microcontroller but does not include case or power supply) .....................$55 (2). Preprogrammed infrared transmitter ...............................................$40 (3). Programmable infrared transmitter (controls up to eight receiv­ers; does not come pre-programmed) ..........................................................$55 Please add $5 p&p for receiver only or $10 p&p for receiver plus transmitter. Payment can be made via cheque, money order or credit card. Note: copyright of the PC board and the ROM code in the microcon­troller is retained by Benetron Pty Ltd. 20  Silicon Chip oriented. This done, connect a power supply to the AC1 and AC2 terminals. Either a 9-20VAC supply or a 12-30V DC supply can be used. It doesn’t matter which way around you connect a DC supply to these terminals because of the presence of bridge rectifier. Switch on and check that LED 1 flashes four times as the unit powers up. The LED will now probably continue flashing in a random fashion due to stray infrared signals from various sources (eg, fluorescent lights). This is quite normal and does not interfere with the operation of the unit. The next step is to measure the DC voltage across the 1000µF capacitor (C9). Resistor R16 can now be selected from Table 2 and installed on the PC board (switch the power off first). Re-apply power and check that the relay toggles each time you press the channel 1 button on the transmitter. If it does, then the unit is probably fully functional but you will need to wire up some LED indicators to verify the two open collector outputs (output 1 & output 2). This can be done by connecting a LED and a series 1kΩ resistor between each output and the +5V rail (LED anode to +5V). This done, check that the LED connected to output 1 toggles each time the channel 2 button is pressed. Depending on the remote control, the LED on output 2 should either flash briefly each time the channel 2 button Setting Up A Universal Transmitter If you purchase the Bondwell preprogrammed universal trans­mitter, it will have to be correctly set up before it can be used with the receiver. This involves programming an appropriate 2-digit code to match a particular TV set or VCR into the unit, as set out in the manual. Once this has been done, it’s then simply a matter of choosing the appropriate connection for resistors R4-R8 from Table 1. Alternatively, you can use a programmable transmitter (ie, one which learns its codes from existing TV and VCR transmitters). A suitable unit is available from the author that can control up to eight separate receivers. is pressed or remain on for as long as the button is held down. Troubleshooting Check the following points if the unit appears to power up correctly but fails to operate: (1). If the channel 1 and channel 2 keys don’t work, then try the other keys. The reason for doing this is that different manufac­ turers use similar codes but with different key assignments on their transmitters. (2). Some manufacturers use a number of different codes so, if the receiver doesn’t work with a particular transmitter, try another setting from Table 1. (3). If all else fails and you cannot find a ROM code for a transmitter, try the Learning mode. Remember, however, that the learnt code is stored in RAM and is lost if the power is switch­ ed off, as mentioned previously. Note that, due to the limited amount of RAM available, some of the longer codes that are used will not be sampled completely and the receiver may respond to other codes that match the limited sample stored. Keep other light sources to a minimum during the learn­ ing process and position the trans­ mitter close to the receiver so that it swamps out any interference from such sources. It’s surprising just how much 50Hz and 100Hz pickup there can be from mains-powered lighting! If you do strike problems here, a red window placed in front of the photodiode (D1) can help filter out some of the unwanted infrared signals. Failing that, the best procedure is to tempo­rarily disconnect the indicator LED and teach the unit the code in the dark. It’s simply a matter of pointing the transmitter at the photodiode and pressing the channel 1 and channel 2 buttons in turn. Performance If you don’t wish to use an exiting TV or VCR remote control, this Bondwell universal remote control can be used instead. It comes preprogrammed with a range of transmitter codes. The exact range is difficult to specify, as this will depend on the transmitter output. Generally, you can expect a range of about eight metres and this is what was achieved by the prototype when combined with a Bondwell universal transmitter. Installing the unit in a plastic case with a red plastic window in front of the photodiode reduced the range to about seven metres. Some transmitters, however, will give a range of up to about 15 metres, although it is necessary to earth the 0V rail to reduce interference from unwanted sources to achieve this figure. In some cases, this can be done by connecting the 0V rail to the earth rail of the equipment SC being controlled. March 1994  21 Looking for an easy-to-build audio power amplifier with more power than the 25W module in the December 1993 issue? This single-chip power module will provide 50W RMS continuous into 8 ohms with extremely low distortion. It’s a sign of the times and how far electronics has come when you can buy a 50W audio power amplifier on a single chip which has better specifications than many of the discrete modules currently available. This 50W amplifier module is based around the newly-released LM3876T from National Semiconductor. Not only can it deliver 50W RMS continuous into 8Ω loads but it has on-board protection and an input mute function. See the data article on this device elsewhere in this issue for the full details. This amplifier module is quite robust and requires no setting up – all you do is build it then use it. It will also run on a lower supply voltage, with no changes to the circuit required. Build this 50W audio amplifier module By DARREN YATES 22  Silicon Chip A glance at the specification panel in this article will show that this amplifier module has very respectable performance, better in fact than the Twin 50W power amplifier module pub­lished in the February 1992 issue of SILICON CHIP. In particular, note the very low distortion, excellent signal-to-noise ratio and very high damping factor. Circuit details Looking at the circuit diagram in Fig.1, you could be forgiven for thinking that the LM3876T is just a big power op amp – and that’s really all it is, although it has a lot of enhance­ments in the way of internal protection circuitry. A handful of passive components and a power supply complete the circuit. The input signal is connected to the non-inverting input at pin 10 via an RC network consisting of a series 1kΩ resistor and a 220pF shunt capacitor. This network is an RF attenuator to prevent pick-up of radio interference. The voltage gain of the module is set to 19 by a negative feedback network consisting of an 18kΩ and 1kΩ resistive divider and a 22µF capacitor. The 1kΩ resistor and 22µF capacitor togeth­er set the low frequency -3dB point to about 7Hz. Also connected to the output at pin 3 is a fairly savage Zobel network comprising a 2.7Ω resistor and 0.1µF capacitor. This RC network and the associated RL network consisting of a 10Ω resistor in parallel with a 0.7µH inductor ensure that variations in the load impedance at supersonic frequencies do not cause instability. F1 2A 220 63VW 1k 220pF INPUT 22k 10 1 9 IC1 LM3876 Construction All of the components for the 50W module except the heat­sink are installed on a small PC board measuring 83 x 58mm and coded 01103941. Before you begin any soldering, check the board thoroughly for any shorts or 2. 7  1W 22 16VW 8W 0.1 MUTE S2 27k F2 2A 220 63VW 22 63VW -35V 0.1 .01 250VAC T1 ALTRONICS M-3030 S1 A BR1 PW04 25V +35V 240VAC 25V 2200 63VW N GND E 2200 63VW -35V L1 : 10T, 0.4mm DIA ENCU WOUND ON 10  1W RESISTOR 1 11 50W AUDIO AMPLIFIER MODULE Fig.1: the module is based on IC1, an LM3876T audio amplifier IC with comprehensive internal protection circuitry. No setting-up adjustments are necessary. IC1 LM3876 1 22uF F2 220pF 220uF 1k 1k 0.1 TO S2 -35V GND +35V 18k 220uF 0.1 The power supply uses a 50V centre-tapped transformer feeding a bridge rectifier and two 2200µF 63VW electrolytic capacitors. This results in balanced supply rails of around ±35V, although the exact voltage will depend on the mains voltage and transformer regulation. To obtain the quoted power output of 50 watts, you will need a transformer rated at 80VA or more. We suggest the 80VA toroidal type sold by Altronics (Cat. M-3030). A cheaper alterna­tive would be the 44V centre-tapped 66VA transformer sold by Jaycar Electronics (Cat. MM-2010). This would reduce the module’s maximum power output to about 40 watts. 10  1W 4 1k 27k Power supply L1 0.7uH 18k Muting An optional feature of this module is the mute function at pin 8. We’ve shown pin 8 connected via switch S2 and a 27kΩ resistor to the negative supply rail. With the switch closed, the amplifier operates normally but with the switch open the audio signal is attenuated by 110dB (typical) which is near enough to completely off. The 22µF capacitor also connected to pin 8 provides a slow turnon feature. If you don’t want to use this feature, you can replace switch S2 with a wire link. The proto­type board, shown in the photo, was wired this way. 0.1 3 7 8 +35V 22uF 10 / L1 2. 7 0.1 F1 O/P 22k GND I/P GND Fig.2: the parts layout on the PC board. Make sure that all polarised components are correctly oriented. breaks in the copper tracks. These should be repaired with a small artwork knife or a touch of the soldering iron where appropriate. When you’re sure that everything is correct, you can install the wire links, followed by the resistors and capacitors. Make sure that you install the electrolytic capaci­tors correctly. March 1994  23 Fig.3 (above): the LM3876 IC is insulated from the heatsink using a mica washer & insulating bush (note: the pins on the IC are cranked differently to those shown here). Smear all mating surfaces with heatsink compound before bolting the assembly together. Fig.4 at right shows the PC artwork. L1 consists of 10 turns of 0.4mm enamelled copper wire wound onto a 10Ω 1W resistor and soldered at both ends. To wind it, scrape the enamel off the start of the copper wire and solder it to one end of the resistor. This done, neatly wind 10 turns onto the resistor body, scrape the enamel off the end of the wire, and solder it to the other end of the resistor. You then install the resistor-cum-inductor as you would a normal resistor. Following that, you can continue by installing the seven PC stakes and the PC mounting 2AG fuse clips. Note that these clips have little lugs on one end which stop the fuse from moving. If you install the clips the wrong way around you cannot fit the fuses. Finally, you can install the LM­ 3876T IC. Make sure that the tab of the device is lined up with the back edge of the PC board so that it can be properly mounted onto the heatsink. Once installed, you can add the four 15mm spacers and then line up the heatsink against the IC so that you can drill the hole for the mounting screw. After drilling, use a standard TO-3P mounting kit to mount the device to Performance measurements Output power .......................... 50W into 8 ohms, 55W into 4 ohms Frequency response ............... 15Hz - 110kHz ±1dB Input sensitivity ....................... 1V RMS (for clip point onto 8 ohms) Harmonic distortion ................ < .06% from 20Hz to 20kHz; typically <.002% Signal-to-noise ratio ............... 106dB unweighted (20Hz-20kHz); -114dB A-weighted Protection ............................... 2A fuses plus SPiKe (TM) Damping factor ....................... >150 (for 8-ohm loads) Stability ................................... unconditional the heatsink (see Fig.3) and make sure that the heatsink is electrically isolated from the device (use your multimeter switched to a high “Ohms” range). The heatsink used needs to be sub­stantial and should be rated at about 1.5°C/W or less. A suitable model is Altronics Cat. H-0580. If you use a smaller heatsink, the IC will run hotter and its internal protection circuitry will reduce the maximum avail­able power output accordingly. As presented in this article, the heatsink is attached to the PC board via the leads of the power IC. In practice, both the heatsink and the PC board should be attached to a suitable chas­ sis, together with the power supply. Testing To test the unit, first connect up the power supply and apply power. The supply rails should be around ±37V (no load condition). Now check the quiescent current. This can be done in one of two ways. The first is to remove one fuse (while the power is off) and connect your multimeter, switched to an “Amps” range) across the fuse clips. With no input signal and no load, the quiescent current should typically be around 30mA but may range up to RESISTOR COLOUR CODES ❏ ❏ ❏ ❏ ❏ ❏ ❏ No. 1 1 1 1 1 1 24  Silicon Chip Value 27kΩ 22kΩ 18kΩ 1kΩ 10Ω 2.7Ω 4-Band Code (1%) red violet orange brown red red orange brown brown grey orange brown brown black red brown brown black black brown red violet gold brown 5-Band Code (1%) red violet black red brown red red black red brown brown grey black red brown brown black black brown brown brown black black gold brown red violet black silver brown PARTS LIST Capacitors 2 220µF 63VW electrolytic 1 22µF 16VW electrolytic 1 22µF 63VW electrolytic 3 0.1µF 63VW MKT polyester Resistors (0.25W, 1%) 1 27kΩ 1 1kΩ 1 22kΩ 1 10Ω 1W 1 18kΩ 1 2.7Ω 1W Power supply 1 25V + 25V 80VA mains transformer (Altronics Cat. M-3030 or equivalent) 1 100V 6A bridge rectifier 2 2200µF 50VW or 63VW electrolytic capacitors 70mA. Alternatively, you can connect a 100Ω 1W resistor across the fuse clips and measure the voltage across it. For a quiescent current of 30mA, the voltage across the 100Ω resistor should be 3V DC. The DC voltage at the output should be within ±15mV of 0V DC. Next, connect suitably rated speaker and check that you get an output. If you touch the input PC pin on the PC board you should get an “audible” blurt from the loudspeaker. If you don’t, check that the mute circuit is disabled. To disable the mute facility, switch S2 must be closed or replaced with a wire link. If the circuit isn’t working, check all audio paths from the input through to the output for continuity. You should also make sure that the PC stakes are well soldered into position. Some brands don’t take solder easily and SC can cause dry joints. 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). ✂ 1 PC board, code 01103941, 84 x 58mm 4 10mm x 3mm machined screws 4 15mm x 3mm tapped spacers 1 125 x 75mm heatsink 1.5°C/W (Altronics Cat H-0580 or equivalent) 1 LM3876T 40W audio amplifier (IC1) 4 M205 PC-mounting fuse clips 2 2A M205 fuses 7 PC pins 1 30cm length of 0.4mm-dia. enamelled copper wire March 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. 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 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. No._______________   ❏ Gift subscription ☞ RATES (please tick one) Australia Australia with binder(s)* NZ & PNG (airmail) Overseas surface mail 2 years (24 issues) 1 year (12 issues) ❏ $A90 ❏ $A49 ❏ $A114 ❏ $A61 ❏ $A135 ❏ $A72 ❏ $A135 ❏ $A72 ❏ $A240 Overseas airmail ❏ $A120 *1 binder with 1-year subscription; 2 binders with 2-year subscription GIFT SUBSCRIPTION DETAILS Month to start__________________ Message_____________________ _____________________________ _____________________________ Gift for: Name_________________________ (PLEASE PRINT) YOUR DETAILS Your Name_________________________________________________ (PLEASE PRINT) Address___________________________________________________ Address______________________ _____________________________ State__________Postcode_______ ______________________________________Postcode___________ Daytime Phone No.____________________Total Price $A __________ ❏ Cheque/Money Order ❏ Bankcard ❏ Visa Card ❏ Master Card 9am-5pm Mon-Fri. 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 March 1994  31 Electronic Engine Management Pt.6: System Operation – by Julian Edgar The actual processes which occur within the ECM to allow the control of fuel injection, ignition timing, idle speed & so on are obviously complex. Various inputs trigger various outputs but what happens in between? The simplest to understand are engine management systems which use analog control processes. A good example of this type of engine management system is the Bosch L-Jetronic system which was developed back in the 1970s. This is a fuel-only system and so it can be more accurately referred to as an Electronic Fuel Injection (EFI) system. The Bosch L-Jetronic design was the first EFI system in common use and has now been largely dropped as more sophisticated engine management systems have been developed. Cars which used the L-Jetronic system (or variations of it) include many European cars from the 1970s (BMW, Mercedes Benz), many Japanese cars from the early-mid 1980s (Nissan, Toyota), and – in Australia – Ford and Holden with their first fuel injected cars (Falcon and Commodore) in the mid 1980s. The “L” in L-Jetronic is from the German word “luft”, mean­ ing air. Airflow measurement is critical in the operation of the EFI system and, as was subsequently proved, in all other engine management systems as well! The L-Jetronic ECM initially used discrete components, as was common in electronics at the time of its introduction. More recent versions of the L-Jetronic system use integrated circuits. Injector pulses An early Bosch L-Jetronic ECM. Note the use of discrete (& large) components in this mid-1970s Mercedes unit. Being an analog system, the ECM has no memory & doesn’t use an oscilla­tor. 32  Silicon Chip Fig.1 gives some idea of how the system generates its injector pulses. The ECM uses the ignition pulse as its starting point and this is derived from the low tension side of the igni­ tion coil. A pulse shaper is then used to generate rectangular pulses of the same frequency from this input. In this system, the injectors are fired simultaneously twice per engine cycle (two turns of the crankshaft). Because of this, it is necessary to divide the pulse train so that a single pulse is produced for each complete rotation of the crankshaft, regard­less of the number of cylinders. This is achieved by using a bistable multivibrator to divide the rectangular trigger pulses by two. The measured engine rpm and the Fig.1: how the fuel injector pulses are generated. A basic injection time (tp) is first of all derived according to engine rpm & airflow & this is then corrected for factors such as acceleration, engine temperature & battery voltage. signal from the vane air­flow meter are now used by the division control multivibrator to generate the base injection pulse width. This gives an injector opening time which is uncorrected for factors such as accelera­tion and engine temperature. A multiplier stage calculates a correction factor to take these aspects into account and this is added to the base injection time, giving an injector pulse width which is correct at the standard battery voltage. In practice, the response time of the fuel injectors is greatly in­fluenced by battery voltage, the latter varying during normal vehicle operation from about 11V to 14V. This gives rise to insufficient fuel delivery at low battery voltages, due to slow injector response times. To overcome this problem, a voltage compensation stage is used to appropriately extend the injector pulse width. This now gives the final injector opening time, with the injectors con­ trolled by power output transistors. Fig.2 shows a block diagram of the system. Analog systems are “programmed” using a hard-wired mathematical algorithm which is determined by the values of the components used. This means that the EFI computer is designed for a specific car and engine; changes have to be made by the manu­ facturer to the actual hardware before the ECM can be used in other cars. It also means that if fuel injection modifications are made with L-Jetron­ ic The Saab APC (“Advanced Performance Control”) is used to control turbo­ charger boost and ignition timing. This is also an analog ECM & was introduced in the early 1980s. March 1994  33 Sold in Australia only in the Ducati 851 motorcycle, this Weber-Marelli ECM has a 24Kb memory & a clock speed of 4MHz. This digital ECM is from a rotaryengined Mazda RX-7 Turbo & is typical of early 1980s Japanese designs. The clock speed is 4MHz & the memory capability is 12Kb. Motronic It was only a matter of time before the fully analog EFI systems like FULL ENGINE SPEED (IGNITION ENGINE SPEED (IGNITION PULSE)PULSE) PULSE SHAPING STAGE FREQUENCY DIVIDER systems, then analog circuit design procedures need to be undertaken. LOAD FULL LOAD SWITCH SWITCH BATTERY BATTERY VOLTAGE VOLTAGE FULL LOAD ENRICH VOLT CORR BATTERY BATTERY POSITIVE POSITIVE INJECTORS DIVISION CONTROL MULTIVIBRATOR (DSM) START ENRICH AIR AIR FLOW SENSOR FLOW SENSOR STARTER STARTER SIGNAL SIGNAL POWER STAGE MULTIPLIER FUEL CUTOFF IDLE IDLE SWITCH SWITCH ACCEL ENRICH AFTER START ENRICH WARM UP ENRICH COLD START CONTROL TEMPERATURE TEMPERATURE SENSOR SENSOR Fig.2: block diagram of the Bosch L-Jetronic EFI (electronic fuel injection) system, as used in mid-1980s Ford Falcons. 34  Silicon Chip L-Jetronic were replaced with digital systems, using microcomputers. These offer several important advantages, includ­ ing lower price, greater ease of programming, and more accurate control. The digital Bosch Motronic design is probably the most sophisticated engine management system currently in mass produc­ tion. Note that the “Motronic” name has been given to a number of different systems over the years – today’s Motronic is much more sophisticated than the system of five years ago. Fig.3 shows the basics of an early Motronic system, while Fig.4 is a block diagram of the ECM. Note that a large number of analog-to-digital converters are used on the input signals. This is because sensors such as the throttle position potentiometer, engine coolant thermistor and so on produce a varying voltage analog signal. This information must be converted to digital format before it can be processed. Other sensors – such as the crankshaft position and engine speed sensors – need to have their outputs fed through a pulse shaper before being fed to the microcomputer. The Motronic ECM calculates output data in two different ways. When in closed-loop mode, feedback signals are obtained from the exhaust oxygen sensor and the knock sensor. In this situation, the ECM uses digital Fig.3: diagram of a typical Motronic engine management system – 1 fuel tank; 2 electric fuel pump; 3 fuel filter; 4 pressure regulator; 5 electronic control unit; 6 ignition coil; 7 high-voltage distributor; 8 spark plug; 9 injection valve; 10 throttle valve; 11 throttle valve switch; 12 air-flow sensor; 13 air temperature sensor; 14 lambda (oxygen) sensor; 15 engine temperature sensor; 16 idle speed actuator; 17 engine speed sensor; 18 battery; 19 ignition switch; 20 air-conditioning switch. algorithms to calculate, in real time, the ignition timing and injector pulse width. Conversely, when in open-loop configuration (with the ECM not monitoring the results), the system uses a series of ROM-stored maps of informa­ tion. These are burned-in during manufacture but can be repro­grammed by after-market chip “cookers”. The sort of program information which is stored in the ROM is often shown in the form of 3-axis graphs. This ECM is from a 2.6-litre Holden Rodeo. Although it uses only a relatively small memory of 4Kb, this ECM shows current state-of-the-art construction with its VLSI chip. Its clock speed is 8MHz. March 1994  35 Extensive engine dynamometer testing is carried out by the manu­facturer to give precisely the best outputs at a variety of loads, engine speeds, engine coolant temperatures, and so on. Other systems This GM-Delco ECM is now used in all Holdens, whether they run 4, 6 or 8-cylinder engines. The program software is contained within a plug-in “MemCal” (memory calibration) unit, which is shown at the bottom of the picture. Fig.4: block diagram of the Motronic electronic control system. 36  Silicon Chip Almost all car manufacturers now use either Bosch compon­ents or technology in their engine management systems. However, the range of software and hardware available means that each manufacturer’s system is unique. Self-learning feedback is used in many systems, allowing changed engine parameters – like engine wear – to be compensated for. As an example of self-learning, when a fault has been fixed in some cars (and the fault code cleared), the car must then be driven for several kilometres before normal performance is restored. This is because the ECM needs to re-learn its new operating parameters! Another example of this self-learning process can be found in the Subaru Liberty. The Liberty uses an exhaust gas oxygen (EGO) sensor to monitor mixture richness, as is the case in most current cars. However, in many engine management systems, the EGO sensor is simply used to modify the base injector pulse width, which has been derived – according to engine load and rpm – from the memory. The greater the correction applied by the EGO feed­back, then the lower the control accuracy of the system. In the Subaru system, the air/fuel ratio correction factor is constantly memorised and is then applied directly to the base injector width, actually changing the stored base injec­ tion time. This process occurs after a few engine cycles. The subsequent correction to the mixture by the EGO feedback loop is therefore lowered, giving more accurate overall control. To put this another way, if the car is being driven hard on a hilly, open road, then rich mixtures will be required to give maximum power. The ECM will quickly “learn” that a wider than normal base fuel quantity is being required and so the need for feedback correction from the EGO sensor is lessened. When the car is once more being driven gently, the learned base fuel injector pulse will again shorten. Other cars also use self-learning procedures, all of which are aimed at realising optimal values quickly. SC Level crossing detector for model railways Add realism to your model train layout with this level crossing circuitry. It will detect the approach of a train, monitor its passing & provide an output to control circuitry to flash lights & sound a synthesised bell. By JOHN CLARKE Most model train enthusiasts will want to include at least one level crossing on their layout. Such a feature increases the realism since it is so commonplace on real railways and the effect is heightened if you have a convincing sound and lights display. This month we are presenting the level crossing detector circuitry and this will be followed next month with an accompany­ ing sound and lights module. This will flash the lights at a similar rate to the real live units and 38  Silicon Chip will even go so far as to simulate the distinctive ding ding of the bell, right down to the random variation in the bell ringing which is so characteristic of level crossing bells. The train detector circuit is suitable for both single and double track crossings and it also caters for situations where there are points to a siding in the track immediately before or after the crossing. This is often the case in rural areas. The circuit is designed to detect the train as it approach­es the crossing and start the lights and sound module. When the train has passed through the crossing, the lights and sound module is turned off. Two train sensors are required, one before the crossing and one after. They will need to be placed suffi­ciently far from the crossing to simulate realism. This will depend on the size of the layout, the length of trains being run and the operating speeds. The sensors are Hall Effect devices measuring 4.5 x 4.5 x 1.5mm and are placed directly between the sleepers of the train track. With typical ballast­ed track, they will be virtually invisible. They provide a signal in the presence of a magnetic field. At least two magnets must be concealed under each train, one under the leading locomotive and one under the last wagon at the end of the train. We expect that constructors will want to fit all their lo- ROAD LIGHTS 1A 2A TRACK SENSOR A SENSOR B 1B 2B LIGHTS MAGNET MAGNET REAR CARRIAGE Fig.1a (left): this diagram shows the general arrangement of a railway crossing with the sensors in place. Each sensor is placed at a realistic distance away from the intersection so that the crossing lights will provide sufficient warning of an approaching train. If the crossing also includes points, as shown in Fig.1b, a third sensor is required. MIDDLE CARRIAGE(S) ENGINE Fig 1a SENSOR C LIGHTS ROAD SENSOR B SENSOR A LIGHTS Fig 1b comotives and guards’ vans (cabooses) with magnets, as well as any wagons with end-of-train flashers. The circuitry is designed to count up to 15 magnets per train which should give a lot of versatility in how each train is made up. This will cater for double, triple and quadruple heading of locomotives. If the number of cars with magnets in a train exceeds 15, the circuit may briefly interrupt the sound and lights module while the train is passing through the crossing but this is unlikely to be noticed. Fig.1 shows the general arrangement of a railway crossing with the sensors in place. Each sensor is placed at a realistic distance away from the intersection so that the crossing lights will provide sufficient warning of an approaching train. If the crossing also includes points as shown in Fig.1b, a third sensor is required. Note that the level crossing detector will operate for A single PC board accommodates all the parts for the level crossing detector, except for the magnets & track sensors. trains travelling in either direction. If there are two tracks, then two separate train detector circuits will be re­quired and their outputs are connected in parallel. How it works Fig.2 shows the block diagram of the level crossing train detector. This shows three Hall effect sensors which detect the magnets under the train. The output from sensor A is amplified by op amp IC1a and then fed to a window comparator comprising IC2a & IC2b. Upon detection of a magnet by the sensor, the window com­parator clocks the DOWN input of counter IC3. Sensor B and sensor C, connected to op amp IC1b, are in parallel so that either sensor can detect the presence of a magnet. IC1b drives a window comparator comprising IC2c and IC2d which clocks the UP input of counter IC3. In effect, IC3 counts down the pulses from the first sensor and counts up those from the second sensor. As soon as the count of IC3 changes from zero (either up or down), zero detector circuit IC4 goes low, to turn on the sound and lights module. March 1994  39 RESET AMPLIFIER IC1a COMPARATOR IC2a,b SENSOR A COUNT DOWN COUNTER IC3 SENSOR B SENSOR C '0' DETECTOR OUTPUT IC4 COUNT UP IC1b IC2c,d Fig.2: the Level Crossing Train Detector uses Hall Effect sensors to detect magnets mounted under the train. The outputs from the Hall effect sensors are amplified & fed to two window comparators (IC2a,b & IC2c,d) which clock UP/ DOWN counter IC3. IC3 in turn drives zero detector stage IC4. Initially, IC3 is set to zero when power is first ap­ plied. As soon as a train is detected by sensor A, IC3 counts down by one and the zero detector switches to activate the sound and lights module. As each train magnet passes over sensor A, IC3 counts down by one. When the train passes over sensor B, IC3 counts up by one for each train magnet until the train has passed. Since the number of magnets which pass over sensor A must equal the number of magnets which pass over sensor B, IC3 will ultimately count back to zero and this will switch off the sound and lights module. In the unlikely event that there is some problem, there is a manual reset switch for the counter to be set back to zero. Now let’s have a look at the complete circuit for the train detector which is shown in Fig.3. The Hall effect sensors, A, B and C, are powered from 5V and provide an output voltage at their pin 3 which is about half supply. When the south pole of a magnet is brought near the labelled side of the sensor, the output swings high while for a north pole the output will swing low. Note that these Hall effect sensors are linear types without logic output circuitry. They have been specified because they have higher sensitivity. The sensors are AC-coupled to the following amplifier cir­cuits, IC1a for sensor A and IC1b for the B and C sensors. Trim­pots VR1, VR2 & VR3 provide facility to adjust the gain of the amplifier for each sensor so that the magnets can be detected reliably. The 0.1µF capacitors across the 1MΩ feedback resistors for IC1a and IC1b reduce the amount of noise at the amplifier outputs and prevent false triggering of the following comparator stages. IC1a and IC1b are biased at half supply by the 10kΩ voltage divider network at pins 3 & 5. As mentioned above, IC2a and IC2b comprise a window comparator. This is so-named because it has two voltage thresholds, the upper at +2.92V (pin 9) and the lower at +2.22V (pin 12). IC2a & IC2b have open-collector outputs and these are connected together and to a common 3.3kΩ pullup resistor. So when ever the commoned inputs at pins 8 & 11 are within the window, both com­ parator outputs are high. However, when the inputs are pull­ ed above +2.92V or below +2.22V, the commoned comparator output goes low and the negative transition is coupled to the COUNT DOWN input of IC3 (pin 4) via a 330pF capacitor. Both the upper and lower thresholds of the comparators have hysteresis, as set by 100kΩ resistors to pins 9 & 11. Thus, when the voltage at the output of IC1a goes above the 2.92V threshold of IC2a, IC2a’s output goes low. The 100kΩ resistor between pins 9 & 14 pulls pin 9 down to +2.72V so that IC1a’s output must go below this 2.72V threshold before IC2a’s output can go high again. This provides about 200mV of hystere­sis. Similarly, when the output of IC1a goes below the +2.22V threshold of IC2b, its output goes low and the 100kΩ resistor between pins 13 & 11 pulls the voltage at pin 11 down by a fur­ther 200mV. This again provides 200mV of hysteresis. Thus the commoned output of IC2a and IC2b goes low whenever the output of IC1a goes above +2.92V or below +2.22V. The window comparator comprising IC2c and IC2d works in exactly the same fashion. It drives the COUNT UP input of IC3 via a 330pF capacitor. Diodes D2 and D3 protect the count inputs of IC3 by clamping them to 0.6V above the 5V line, each time the window comparator outputs go high. IC3 is an up/down 4-bit binary counter which has a maximum count of 16. It is reset by a power-on reset provided by the 10µF capacitor and The position of the train is sensed by using two or more Hall effect sensors to detect magnets mounted in wagons at either end. The Hall effect sensors are mounted under the track, flush with the sleepers (see above). 40  Silicon Chip +5V 3.3k 100k 0.1 8.2k 0.1 +2.92V 1M 1 2 47 3 BP VR1 100k 2 3 SENSOR A UGN3503U 9 8 7 1 IC1a LM358 100W D2 1N4148 3 IC2a LM339 2.2k 14 LOAD 4 COUNT DOWN 100k 2.7k 13 IC2b RESET S1 12 +5V 14 COUNT UP 12 3 10k 8 CLEAR 100k C E VIEWED FROM BELOW 10k 10 8.2k B 5 +5V 10 +2.92V 2 VR2 100k 0.1 SENSOR B UGN3503U 2 7 100  47 3 BP SENSOR C UGN3503U D3 1N4148 7 6 QC QD 3 6 7 12 9 8 14 IC2c 2.2k 10 IC4b 4.7k 6 5 4 330pF 10k D1 1N4004 5 +2.22V VR3 100k 4 Q1 BC548 B C OUTPUT E 2.7k IC2d +5V IC4c 1 100k 1M +5V 1 6 IC1b QA 2 11 5 47 3 BP 1 100k 8.2k +5V B QB IC4a 13 4071 7 3.3k 1 9 D IC3 40193 11 LABEL SIDE 10 C +5V +2.22V 12 15 A 4.7k 4 11 16 330pF 2 180  0.5W +5V 12V INPUT 1000 16VW ZD1 5.1V 400mW 470 16VW 8.2k LEVEL CROSSING TRAIN DETECTOR USED ONLY FOR SWITCHED TRACK LAYOUTS Fig.3: the complete circuit for the Level Crossing Train Detector. When a sensor detects a train magnet, the output from its corresponding window detector goes low & clocks IC3 (the UP/DOWN counter). OR gates IC4a-4c detect the zero state & drive Q1 for all other counts. 100kΩ resistor at the clear input (pin 14). Switch S1, connected to the Clear input at pin 14, allows the counter to be reset at any time. The binary outputs of IC3 are monitored by 2-input OR gates IC4a and IC4b. These have a high output when any input is high. IC4a and IC4b are in turn monitored by OR gate IC4c. Its output goes high whenever any of the outputs of IC3 are high. Thus, the output of IC4c is low only when IC3 is reset or at “0”. IC4a drives transistor Q1 via a 10kΩ resistor. So let’s now recap on how the circuit works. The Hall effect sensors detect magnets under locomotives and carriages in the train as it passes. The magnets are counted up as the train passes over the first sensor and count­ ed down as they pass over the second sensor. The OR gate zero detector at the output of IC3 then determines whether the sound and lights module is turned on or off. Power is derived from a 12V supply via a 180Ω resistor and is regulated using 5.1V zener diode ZD1. D1 protects against reverse polarity connection and also provides isolation from ripple on the 12V supply which is decoupled using a 1000µF capacitor. Construction The train detector is constructed on a PC board measuring 140 x 79mm and coded 15203931. We used PC mounting terminal blocks for all external connections but PC stakes could be used as a cheaper alternative. Begin construction by checking the boards for any broken tracks or shorts on the copper pattern. Repair any faults that you do find, then install the resistors, link, PC stakes (if used) and ICs. Note that IC2 is oriented differently to the other ICs. Now install the transistor, zener diode and diodes, making sure that they are oriented correctly. The trimpots and capacitors can be mounted now but take care with the orientation of the electrolytic capacitors. The 47µF bipolar electrolytics can be mounted either way around. Finally, if you are using terminal blocks, mount these as well. Note that if you need to use a third sensor for points, you must install trimpot VR3 and its associated 47µF bipolar capacitor. March 1994  41 ZD1 2 2.2k 3.3k 100k 2.7k 100k 100k 10k 2.2k 1 IC4 4071 +12V GND GND + 1 3.3k 47uF BP D1 330pF 8.2k 8.2k 2 100 1 D2 4.7k 3 1 100k VR2 IC2 LM339 2.7k 1 IC1 LM358 0.1 2 D3 TO S1 IC3 40193 330pF 8.2k 1 100  1M 0.1 10k 47uF BP 3 SENSOR A 470uF VR3 1 SENSOR B 8.2k 10uF 100k SENSOR C 47uF BP 4.7k 3 1M 0.1 10k OPTIONAL PARALLEL INPUT Q1 SUPPLY OUTPUT 1000uF VR1 180  10uF Fig.4: install the parts on the PC board exactly as shown here & note that IC2 faces in the opposite direction to the other ICs. Once the PC board has been assembled, it is ready for testing. Temporarily connect the Hall Effect sensors (sensor A and sensor B) and switch S1. To see whether the output transistor Q1 is switching correctly, you will need a LED connected in series with a 2.2kΩ resistor from the collector to the +5V sup­ply. You will also need to connect up the power supply inputs (the +12V and GND terminals). Note that the power for the PC boards should be obtained from a 12V DC supply. If you built the Walkaround Throttle de­scribed in April & May 1988 or the infrared controller described in April, May & June 1992, you won’t need a separate supply as this facility is already provided. Before applying power, check that you have your multimeter ready to measure the DC voltages on the PC board. Set all trimpots to midway initially, then apply power and check that the voltage across ZD1 is close to +5V. If not, switch off and find the fault before applying power again. With power on, you can bring a magnet near one of the Hall sensors. The LED associated with Q1 should then light up. If all is operating satisfactorily, you can install the sensors beneath the track. We recommend that the wires for each sensor be bent at right angles and passed through holes on the lay- Fig.5: check your PC board against this fullsize etching pattern before mounting any of the parts. RESISTOR COLOUR CODES ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ No. 2 5 3 4 2 2 2 2 1 2 42  Silicon Chip Value 1MΩ 100kΩ 10kΩ 8.2kΩ 4.7kΩ 3.3kΩ 2.7kΩ 2.2kΩ 180Ω 0.5W 100Ω 4-Band Code (1%) brown black green brown brown black yellow brown brown black orange brown grey red red brown yellow violet red brown orange orange red brown red violet red brown red red red brown brown grey brown brown brown black brown brown 5-Band Code (1%) brown black black yellow brown brown black black orange brown brown black black red brown grey red black brown brown yellow violet black brown brown orange orange black brown brown red violet black brown brown red red black brown brown brown grey black black brown brown black black black brown This photograph shows how a magnet can be mounted on the bottom of a wagon. out. The sensors can be mounted flush with the sleepers and can be mount­ed with the label side up or down. Magnets can be attached to the underside of your locomo­ tives and carriages using glue or a screw and nut. For best results, try to mount all the magnets so that they are about the same height above the track. For some locomotives, there is very little room to mount a magnet on the underside. In some diesels, it should be possible to fit a magnet inside the fuel tank in place of the bottom sheet steel weight. In steam locomotive models, it may generally be easier to mount the magnet underneath the tender wagon. We used magnets from a variety of sources, including those supplied with cheap magnetic door catches. These can be cut down in size by firstly scoring a line where the break is required, then clamping the magnet in a vyce and breaking it at the score with a hammer. Use safety goggles when doing this, by the way. The magnets can be mounted with either their north or south poles facing down. Trimpots VR1 and VR2 for sensor A and sensor B (and VR3 for sensor C) will require adjustment for best results. To do this, connect your multimeter between ground and pin 1 of IC3 on the train detector PC board. Run the locomotive and carriages over the sensor and adjust the associated trimpot so that the multi­meter goes from a low to a high or from a high to a low once for each passing magnet. If the gain is too high (ie, the trimpot is too far anticlockwise), then the multimeter will go high or low several times per passing magnet. If the gain is too low (ie, the trimpot is too far clockwise), the multimeter may not change from PARTS LIST 1 PC board, code 15203931, 140 x 79mm 2 6-way PC mount terminal blocks 1 momentary contact pushbutton switch (S1) Magnets (minimum 2 per train), Tandy 64-1875 or salvage from magnetic door catches 1 20mm length of 0.8mm tinned copper wire 2 100kΩ horizontal trimpots (VR1,VR2) Semiconductors 1 LM358 dual op amp (IC1) 1 LM339 quad comparator (IC2) 1 40193, 74HC193 up/down counter (IC3) 1 4071 quad 2-input OR gate (IC4) 2 UGN3503U linear Hall effect sensors (sensors A & B) 1 BC548 NPN transistor (Q1) 1 1N4004 1A diode (D1) 2 1N4148 diodes (D2,D3) 1 5.1V 400mW zener diode (ZD1) Capacitors 1 1000µF 16VW electrolytic 1 470µF 16VW electrolytic 2 47µF 50V bipolar electrolytic low to high or high to low. Some final adjustments may be necessary once the PC boards have been incorporated in your train layout , so allow access to the trimpots during installation. These final adjustments will have to wait until the Sound and Lights 2 10µF 16VW electrolytic 3 0.1µF MKT polyester 2 330pF MKT polyester Resistors (1%, 0.25W) 2 1MΩ 2 3.3kΩ 5 100kΩ 2 2.7kΩ 3 10kΩ 2 2.2kΩ 4 8.2kΩ 1 180Ω 0.5W 2 4.7kΩ 2 100Ω Extras for switched track layout 1 3-way PC mount terminal block 1 UGN3503U Hall effect sensor (sensor C) 1 47µF bipolar electrolytic capacitor 1 100kΩ horizontal trimpot (VR3) Parts availability A kit of parts for this project should be available from Dick Smith Elec­ tronics, Jaycar Electronics and Al­ tron­ics. The UGN­3503U Hall Effect sensors are available separately from Farnell Electronics, phone (02) 645 8888. Magnets are available from Tandy Electronics or can be salvaged from the magnetic door catches sold in hard­ware stores. Module is built and involve running trains over the level crossing at various speeds. If any sensor fails to operate reliably, it’s simply a matter of adjusting its associated trimpot. The reset switch will come in handy during these adjust­ments should the circuit SC malfunction. March 1994  43 Switching Regulators Made Simple RO UN DE DG E 0 HB SOFTWARE DOES THE DESIGN National Semiconductor’s new range of “Simple Switcher” DC switching regulators are designed to take the hassle out of power supply design. What’s more, there is a software package available which can do it all for you. By DARREN YATES Yep, switching regulators are not new. They’ve been around for quite a long time, firstly as discrete designs using clock generators, comparators and output power devices. Then came IC packages such as the Texas Instruments’ TL497 and Motorola’s MC­ 34063 which contained all the circuit elements except the power devices. Now, National Semiconductor has gone one step further by combining all of this circuitry with an output power device inside a 5-pin TO-220 package. All you need to do is add an inductor, a fast-recovery diode and a few passive components to obtain a complete switching regulator circuit. These devices are classified into four series: (1) the LM2574/2574HV 0.5A step-down series; (2) the LM­ 2575/2575HV 1A step-down series; (3) the LM2576/2576HV 3A step-down series; and (4) the LM2577 3A step-up series. We used the LM2576-ADJ device as the basis of the 40V 3A variable power supply featured in the January 1994 issue of SILICON CHIP. These “Simple Switchers” are easy Fig.1: block diagram of the LM2576 step down converter IC. It comes in fixed & adjustable output versions. 44  Silicon Chip to get going and are capable of operating at an efficiency of over 80%. The step-down switchers require only four external components to make a com­ plete circuit, however all of the devices have a similar internal structure. The LM25 XX series have their own in-built oscilla­tor fixed at 52kHz ±10%. Having a fixed frequency allows for easy selection of filtering components. The frequency is also high enough to allow a small inductor to be very efficient. The LM25XX series also include thermal shutdown and current limit protection. Being in a TO-220 package they’re easy to mount onto a heatsink but in many cases, they don’t need one. Step-down circuit Fig.1 shows the block diagram of the LM2576 step down con­ verter. Let’s take a look at how it works. Unregulated DC is applied to pin 1 which is then regulated for the internal circui­try. This includes a 1.23V band-gap reference, which is fed into the inverting input of a fixed gain error op amp. The error signal is then fed to a comparator which produces a pulse width modulated (PWM) signal at 52kHz. The PWM signal then passes through a reset gate and onto the driver circuitry which also has an input from the thermal shutdown and over-current limit pro­tection circuits. The driver controls the 3A NPN output switch connected to pin 2. The internal switch drives a filter network consisting of inductor L1, capacitor C OUT and fast recovery diode D1. The resultant DC voltage across the load is directly monitored by pin 4 in the case of fixed output voltage versions (LM2574-LM­ 2577), while for the adjustable versions, pin 4 monitors the output voltage via an external voltage divider. The devices also include an external shutdown pin which, when taken to the supply rail, closes down the switching circui­try to leave a quiescent current of about 50µA. This is ideal for battery-operated circuitry which doesn’t always need to be pow­ered up. In normal circuit operation, the current drain is typically 5mA, with no load on the output. The range of output voltages available for the LM2574/2575/2576 stepdown series of switchers is as follows: 3.3V, 5V, 12V, 15V and adjustable (1.2V-37V). Vin(max) is 40V. For the LM2574HV/2575HV/2576HV series, the corresponding figures are: 3.3V, 5V, 12V, 15V and adjustable (1.2V-57V), with Vin(max) = 60V. Step-up converters The LM2577 step-up range of converters use slightly differ­ent circuitry and are available in a variety of packages includ­ing 5-pin TO-220 (straight or bent lead), 16-pin DIP, 24-pin surface mount and 4-pin TO-3 packages. They are typically used to step up from a 12V battery to some higher value. Because of their different operation, this series includes a soft-start function which reduces the initial inrush current into the load. Maximum input supply voltage is 45V while maximum output is 65V. Maximum switching current is 3 amps but the actual output current is less than this. The reason for this is twofold. First­ ly, because it is stepping up the voltage, it has to step down the current, and so we end up with less output current. The second reason is that in stepping up the voltage there has to be a current trade-off so that the maximum power dissipation of the device is not exceeded. Fig.2: diagram showing how the LM1577-ADJ/LM2577-ADJ is used as a stepup regulator. The switching device is an internal 3A 65V NPN transistor which operates at 52kHz. The PWM of the circuit is controlled by the feedback network connected to pin 2. This series doesn’t have a standby low current capability as do the step down converters. Instead, pin 1 is connected to an RC time constant which performs two functions. Firstly, it en­sures stability of the regulator and secondly, it forms part of the soft-start function. Block diagram Let’s take a look at the block diagram in Fig.2 and see how it works. Unregulated DC is applied to pin 5 which connects to a 2.5V regulator for the internal circuitry. The 3A 65V NPN switching transistor is controlled via the driver circuitry and runs at 52kHz. It switches current via the inductor and each time it switches off, the flyback voltage generated causes the high speed diode to conduct and charge capacitor COUT. The output voltage is monitored by pin 2 via an external voltage divider consisting of R1 and R2. The voltage at pin 2 is compared against a 1.23V reference by the internal error amplifi­ er. This amplified error signal is then Fig.3: the basic flyback arrangement. Both positive & negative rails which are greater or less than the input voltage can be derived. March 1994  45 Fig.4: higher output currents can be achieved by connecting two switching regulator ICs in parallel, with one slaved to the other. This circuit allows 5V to be stepped up to 12V with an output current of 1.5A continuous. Up to six regulators can be connected in this manner. fed to the inverting input of a comparator which compares it to the sum of the correc­tive ramp voltage from the 52kHz oscillator and a voltage propor­ tional to the switch current. The current sense voltage comes from the sense resistor which is in the emitter circuit of the 3A 65V NPN switching transistor. The output from the comparator, along with the cur­rent limit, thermal limit and under­voltage shutdown circuitry control the driver circuitry which in turn drives the output transistor. Undervoltage shutdown The undervoltage shutdown circuitry sounds like a good idea since it could be used to prevent the switcher from over-discharging a battery. Unfortunately, the shut-down voltage for all the 2577 series is typically 2.9V – too low to be of any use with most battery applications and there is no way of varying it. The input supply current under no load conditions is 10mA. The maximum duty cycle is 95% and the soft start current is only 5µA. At 3A switching current, the output device saturation voltage is typically 0.7V <at> 25°C. The efficiency of the switcher is quoted as 80% when stepping 5V up to 12V with an output load of 800mA. This is quite good for a step-up switcher with so few components. Flyback circuit Unlike the step-down switchers, the LM2577 is suitable for use in a flyback design as shown in Fig.3. In this mode, the output switching transistor is used to drive the primary side of the transformer. The feedback is derived from the rectified positive output on the secondary side of the transformer. Note the phasing of the primary and secondary windings – this is critical. Because of the high switching frequency, compact trans­formers can be used, keeping the overall size of the converter down. This flyback arrangement allows the generation of both positive and negative supplies greater or less than the input voltage. Parallel switchers But what if you need an output current which is higher than the available 3A? No problem. You can easily parallel up a couple of LM2577s and Software Offer Thanks to NSD Australia, we are making available copies of the “Switchers Made Simple” software package on a floppy disc which can be 3.5-inch or 5.25-inch format. System requirements are IBM PC or compatible, DOS 2.0 or higher and 512K RAM minimum. The cost is only $12 plus $3 for postage and packing. You can obtain a copy by filling in the order form on page 25 and sending it to Silicon Chip Publications, PO Box 139, Collaroy, NSW 2097; or you can phone (02) 979 5644 or fax (02) 979 5644 and quote your credit card details (Bankcard, Master­card, or Visa). 46  Silicon Chip there is no need for ballast or current sharing resistors at the output as is usually the case with conventional regulators. Fig.4 shows how to do it and the idea could easily be extended to include up to five or six devices in parallel for even higher currents. The circuit of Fig.4 allows 5V to be stepped up to 12V with an output current of 1.5A continuous, with one regulator slaved to the other. The control regulator’s feedback error amplifier is used to control the switching of both regulators, the slave’s feedback input being tied to ground. This works because the LM2577 is current-mode controlled and by tying both compensation inputs together via the same network, the slave regulator is forced to follow the control’s waveform quite accurately. The master regulator produces a voltage on its compensation pin which is proportional to the inverse duty cycle of the output switch. What this means is that the smaller the amount of time the output switch is off, the higher the compensation voltage. Hence, this inverse duty cycle is proportional to the output voltage and by feeding this master compensation voltage back to the slave regulator, it forces the slave’s duty cycle to match the master’s and so the output voltages will be very similar. In this way, both regulators share the load. The outputs from each regulator are then fed via separate fast recovery diodes to the same filter capacitor and the output is taken from there. As with any switching regulator, there are precautions to take to make sure that the regulator produces the least amount of electromagnetic interference (EMI). Layout is crucial in keeping down the level of voltage transients. The leads of any components which carry the switching current should be kept as short as possible and to reduce the effects of ground loops, single point or “star” earthing should be used. In many circuits, the length of the leads is not all that critical but here just a few centimetres can make a big difference, due mainly to the 52kHz switching frequency used. Component choice can also make a big difference as well, particularly in the output filtering stage. The amount of ripple voltage that appears across the output is a function of the equivalent series resistance (ESR) of the filter capacitor. The lower the ESR, the lower the ripple and hash. Unfortunately there is a trade-off. Using a capacitor with a very low ESR tends to make the circuits unstable, particularly if a capacitor with an ESR of less than 50mΩ (that’s 0.05Ω) is used. With small ESRs, the load pulse response worsens. This results in increased ringing or overshoot in the output at the switching point. By using a capacitor with a higher ESR, the pulse response is decreased and so the amplitude of the high frequency transients is reduced. Another method of reducing the amount of ripple in the output is to add a second LC low pass filter at the output. By setting the cutoff frequency to a tenth of the switching frequen­cy (ie, to 5.2kHz), the amount of ripple is reduced to around a tenth of that from a single stage filter. All you have to do is type in the required input parameters & the program automatically generates the relevant component values (shown at right). This is the circuit diagram generated by the program for the above input parameters. In this case, we have a flyback converter which generates ±12V rails at up to 0.5A. Design software National Semiconductor has put all of the design equations and procedures into an easy-to-use software package. It contains all the necessary data to design any type of switcher using the complete range from the LM2574 to the LM2577 and features boost, flyback, buck and buck-boost circuits. Boost converters step up the input voltage; flyback converters can either step up or down, or invert the input voltage via a coupling transformer thus provid­ing isolation for the output; buck converters step down the voltage; and buck-boost converters create a negative voltage from a positive one, either higher or lower in magnitude. The software will tell you everything The software can also be used to design standard step-up converter circuits, as shown here. This circuit generates a 12V rail from a 5-7V input. you need to know, including the device to use and the component values. It will also tell you the maximum switching current for a given output load current and even the junction temperature of the device under the user-specified conditions. Finally, the software generates an on-screen circuit diagram (see above) which can SC be printed out via your printer. March 1994  47 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. Resistance & capacitance meter 1M 10M 10k 1 This circuit will measure capacitors and resistors in four ranges selected by a rotary switch: Range Resistance Capacitance 1 0-10MΩ 0-0.001µF 2 0-1MΩ 0-0.01µF 3 0-100kΩ 0-0.1µF 4 0-10kΩ 0-1µF 100k 3 2 S3a R S1b C S1a C The circuit is based on two 555 timers. IC1 is wired in astable mode and its output at pin 3 is a train of brief negative pulses which are fed to pin 2 of IC2 via a 0.47µF capacitor. IC2 is wired in monostable mode so that it delivers a series of positive pulses from its pin 3 output. The length of these pulses is determined by the RC network connected via switches S1a and S3 to pin 7. In capacitance mode, S1 connects switch S3a and the four range resistors into circuit. The meter reads the average voltage of the pulses at pin 3. Transistor Q1 is connected as a Vbe to clip the pulses to a constant amplitude. When used in resistance mode, 3 0.1 48  Silicon Chip 560  1 .001 .01 2 S3c Q1 BC549 47k 1 2 VR3 4.7k 1 IC2 555 2 S3b BATT VR2 4.7k 3 4 M1 1mA FSD VR1 4.7k 1k S4 +9V 120k 4 8 100 0.47 3 7 680  5.6k GND IC1 555 6 2 1 0.22 reference capacitors are connected. The circuit otherwise operates in the same manner. The circuit runs from a 9V battery and draws about 10mA. Power switch S4 is a pushbutton because if the circuit is powered up without a device on its test leads, the meter will be deflected off scale. For best accuracy, use 1% resistors throughout the circuit. To calibrate the circuit, short the wipers of S3a and S3b together and turn the unit on. You can now adjust trimpots VR1 to VR4 to set the meter to fsd on each range. A. Chin, Heidelberg, Vic. ($25) +12V Adding latched outputs to the IR train controller The AUX1 and AUX2 outputs for the Infrared Railpower (April, May & June 1992) are momentary, which go low only as long as the remote control switch is pressed. This cir­ cuit converts a momentary output to a latched output by adding a D-flipflop (IC1). The momentary output is coupled into the clock input of IC1 via a 0.1µF capacitor. Each time IC1 receives a positive-going pulse, the Q output changes state. D1 protects 3 6 4 1 10k 8 7 R TEST LEADS VR4 4.7k 4 0.1 1k 10k 10k 10k D1 1N4148 LED1 100k FROM AUX OUTPUT 1 OR 2 R 13 D IC1 Q 4013 11 12 Q CK S 8 the clock input from being forced above the +12V line. The Q output drives Q1 to provide the latched LATCHED OUTPUT 10 14 9 .01  1k Q1 BC337 7 output which is indicated by LED1. Alf McKeon, Browns Plains, Qld. ($20) 33k 4 8 7 33k Q1 BC557 IC1 7555 6 2 3 10k Q2 BC547 GND 100k 10k 1 .001 Q3 BC557 2.73.3V +5V 3mA ZD1 5.1V 400mW 470 16VW Q4 BC557 4.7 16VW 100k Low power voltage booster This voltage doubler converts a 3V input to 5V at currents up to 3mA. It is useful for powering a 5V Mosfet in a CMOS circuit which operates from a 3V supply and for doubling the voltage of a battery power supply. IC1 is a CMOS 7555 timer. It oscillates at about 14kHz and drives a power amplifier comprising Q1 and Q2. These transistors provide buffering and voltage level translation for a charge pump circuit consisting of a 4.7µF capacitor, transistors Q3 and Q4, and a 470µF capacitor. Both Q3 and Q4 are used as diodes which have very low forward voltage drop between the collector and emitter terminals. This improves the voltage doubling efficiency over conventional charge pumps which lose about a 0.7V across each diode. Q3 and Q4 are biased on via their 100kΩ base resistors. The circuit operates as follows. Initially, the 470µF capacitor is charged up to the battery voltage via Q3 and Q4 and supplies power for IC1. When pin 3 of IC1 is high, Q2 is on and the 4.7µF capacitor charges up to the battery supply via Q3. When pin 3 of IC1 goes low, Simple quiz game adjudicator Many of the quiz game circuits published in the past re­quire several ICs and diodes. This circuit requires only three relays and four diodes to provide the basic functions. The addition of the usual pushbutton switches and indicating lamps for each player, plus a buzzer, go to make up a complete quiz game circuit. The circuit sounds the buzzer whenever one of the pushbutton switches (S1-S3) is pressed. The first button pressed will light up the associated lamp (LP1-LP3) and prevent any further lamps from being lit until the reset switch (S4) is pressed. The circuit operation is as follows. Initially, all the relays are off (un­ powered) and the positive supply is coupled through the normally closed contacts of RLY3, RLY2 and RLY1 to switches S1, S2 and S3. When any one of the switches is pressed, its associated lamp (LP1-LP3) and relay are energised. The con­tacts now Q1 turns on and the charge on the 4.7µF capacitor is transferred to the 470µF capacitor at the output via Q4. Ultimately, the voltage across the 470µF capacitor is double that of the battery. Zener diode ZD1 limits the voltage to 5.1V. Power for the circuit can be from three nicad cells, two dry cells or a single lithium cell. It will operate down to a 2.7V input. The circuit will voltage double on higher supply voltages (up to 15V), provided the 470µF capacitor is suitably rated for twice the input voltage and ZD1 is removed. James Moxham, Urrbrae, SA. ($15) S4 D1 1N4002 S1 D2 1N4002 S2 D3 1N4002 S3 C1 470 LP1 RLY1 LP2 RLY2 LP3 RLY3 D4 1N4002 BUZZER This quiz game adjudicator is about as simple as you can get & can be built from junkbox parts. change over to latch on the relay and disconnect power to the pushbutton switches. This prevents any further relays from being energised via the pushbutton switches. At the same time, the diode associated with the powered relay drives the buzzer momentarily via capacitor C1. These diodes prevent current flow back to the remaining two unenergised relays. The circuit is reset by pressing switch S4. This discon­ nects power to the energised relay and the circuit returns to its initial state with all relays off. E. Hermann, Taranaki, NZ. ($20) March 1994  49 SERVICEMAN'S LOG Well, we all make mistakes sometimes If there is a common theme in this month’s notes, it is the significance of the phrase “if only” – once described as the most tragic phrase in the English language. While not tragic in this context, it does emphasise that there are always lessons to be learned. Dealing with irate – and unreasonable – customers seems to be on the increase, at least in my neck of the woods. In my December notes, I told the story of one such character who called down the curses of the damned on both the set manufacturer and yours truly – simply because the set failed under warranty. This month’s story is almost an exact replica, at least as far as the abuse is concerned; almost word-for-word in some cases. As with the first incident, it involved another Samsung set but there the similarity ends. They were quite different model sets and the technical problem was quite different. Some of the preliminary events occurred before I was in­volved, so I am only assuming some aspects of these. 50  Silicon Chip It concerns a Samsung CB-515F colour set and, as some readers may recall, I related a story about this model some time ago. This involved, among other things, a modification to the horizontal output circuitry around the pincushion transformer (T402). More specifically, inductor L401, capacitor C414 and a diode/resistance package designated RH01, needed to be replaced, the soldering around them carefully checked, and the board checked for possible burn damage. As well as circulating their various service personnel, Samsung published a recall notice, advising owners of this model to contact their nearest Samsung dealer or service centre to have these modifications carried out under warranty. Apparently, this is where it all started; the customer re­ sponded to the recall notice by ringing Samsung’s headquarters and asking where the set should be taken for this to be done. As it happens, the customer lives some distance from me and so was directed to Radio Rentals in an adjacent suburb. Radio Rentals duly made the modifications and returned the set to the customer. Unfortunately, a couple of days later, the set developed a fault; the picture was rolling downwards very slowly. At this point the customer “did his lolly” as the saying goes. Instead of contacting Radio Rentals, he rang Samsung and demanded that his set be repaired immediately or that he be given a new set. And he refused to have anything more to do with Radio Rentals. So, whoever it was he spoke to at Samsung sooled him on to me as being the next nearest service centre (you’ll keep mate)! Thus it was that he turned up on my doorstep. He started off by complaining to me about the lousy service he had received from Radio Rentals. Well, I wasn’t going to become involved in that kind of argument, even by default. I suggested he calm down and stop making wild accusations. And I added that it was most unlikely that the present fault was in any way due to Radio Rentals’ work but was almost certainly a different problem. In any case, I needed time to look at the set before making a pronouncement of any kind and suggested he go off and do some shopping for an hour or so while I checked things out. So off he went, muttering witch’s curses (at least, that’s what they sound­ed like). With the back off the set I went straight to the modifica­tion site. As I fully expected, Radio Rentals had carried out the modifications exactly according to the modification sheet, neatly and professionally; there was no way that the job could be criticised, or that they could be blamed for the present problem. When the customer returned, I confirmed that the problem was nothing to do with the Radio Rentals modification, that it was a quite separate problem, that it would be fixed under war­ranty, but that it might take a couple of days to sort it out. Well, he wasn’t happy at this but then, I doubt that he has ever been happy about anything. That said, he had little option but to accept the situation and so he went off in high dudgeon. Rolling picture His description of the fault was quite accurate; the pic­ture was rolling slowly downwards and, more importantly, adjust­ ing the vertical hold control in the chip. Anyway, I tried increasing the value of R306 by adding another 22kΩ. That done, the system looked good. I let it run for a couple of days, which it did without so much as a blink, then phoned the customer and told him it was ready. So he duly picked it up. I reminded him that the set was still under warranty and that, if it gave any further trouble, he should contact me imme­diately. He didn’t say much, choosing instead to maintain a rather surly silence – if that makes sense. Anyway, I hoped I had seen the last of both him and the set. The phone explodes (VR301), had only a marginal ef­fect. In any case, it was insufficient to correct the problem. The vertical hold control is a 250kΩ pot, wired as a vari­ a ble resistor, which connects to pin 29 of jungle chip IC501 (TA7698P) via a 39kΩ resistor (R305). The other end of VR301 connects to the 12V rail via a 240kΩ resistor (R306). The only other component in this circuit is C352, a 0.22µF electrolytic capacitor. So it is all very simple without, seemingly, very much to go wrong. I checked the 12V rail, which was correct, as was R305 and R306. VR301 was then checked and the value of resistance in circuit seemed to make sense for the setting of the shaft. That left only C352 which, being an electrolytic, was a suspect. I pulled it out and checked it, and it measured OK. But I replaced it any- way; no point in taking chances with these devic­es. Unfortunately, this had no effect. So I had checked and cleared all the external components and found nothing wrong. That left only the chip as the main suspect. I don’t like changing chips without good reason but it seemed the only thing left. And I had one on hand, so I made the swap. And that seemed to be the answer. The picture immediately locked up quite firmly with the vertical control in its existing setting and this seemed about right, although it was somewhat towards one end. I let the set run for a few hours and it re­ mained rock steady. But I was a little concerned that the control was not as well centred as I thought it should be, although I couldn’t think of any reason for this apart from possible tolerance spread I thought I had too, because several weeks went by and I had almost forgotten about it. Then one morning the phone rang and when I picked it up it exploded – verbally, that is. Yes, it was Moaning Mick and he really turned it on; the so-and-so set had broken down again, it was no so-and-so good, I was no so-and-so good, I was dishonest, everyone else was dishonest, and on it went. I let him rave until he paused for breath, then quietly asked him what was wrong. That didn’t go down too well because apparently I was supposed to know. But, between splutters, I gathered that it was the same fault as before. So I simply said, “Bring it in and I’ll check it again. And it won’t cost you anything”. He muttered something which I took to be an acknowledgement and hung up. And so the set finished up back on my bench. Naturally, I wasn’t any happier than the customer, After all, I had to find the fault; all he had to do was complain. More to the point, I realised I had a tricky problem on my hands. Every likely compon­ent had been either checked or changed, yet the fault persisted. It is a truism that when this situation occurs, the most likely explanation is that something hasn’t been checked proper­ ly. We think we’ve checked it, but we’ve overlooked something. So what was it? Thinking about it like that, I realised there could only be one likely answer – VR301, the 250kΩ vertical hold control itself. Yes, I’d measured its resistance in circuit but had more or less simply March 1994  51 The vertical hold control circuit in the Samsung CB-515 TV set comes off pin 29 of IC501 & connects to the 12V rail (bottom of diagram). Changing the IC was not the answer. accepted the reading as being “rea­ sonable”. And that wasn’t good enough in this case. So I pulled the pot out and measured the resistance between the wiper and each of the outer contacts in turn, while rotating the wiper through its full range. And this told a very different story; different, and quite strange. The range of resistance from the moving arm to either terminal was only about 50kΩ. But as strange as this was, it did provide an immediate explanation for the fault. There was simply not enough resistance range to cope with all the variables in the circuit, including the tolerances in the IC chip. And it was now clear that it must have been just such a tolerance that tricked me into believing that changing the IC had cured the fault. As to why this provided a temporary “cure” which didn’t last – well, more on that later. Right then I was in no mood to speculate on any of the finer details. I had found the fault, the pot was crook, and I needed to fit a new one. Unfortunately, I had nothing in stock which would suit (at least, physically) and a new one had to be ordered from Sam­sung. This arrived in a couple of days, 52  Silicon Chip I fitted it, removed the extra 22kΩ I had added previously, and put the set through its paces. It worked perfectly but I ran it for a couple of days before calling the customer to tell him it was ready. He called a couple of days later, still grumbling and threatening everybody concerned with the most dire consequences if anything further went wrong. And that’s one of the most difficult aspects of this job – to remain civil in the face of such rude­ness and ignorance. I did my best to explain to him that everyone concerned had acted in good faith but it didn’t seem to work. Anyway, he went on his way and that was the end of the matter. It all happened several months ago and I have not heard from him since. And I doubt whether I will now – I hope! It comes in twos But that is not the end of the faulty pot story. A couple of weeks ago, one of my regular lady customers brought in an Akai model CT-K115, and it was rolling in exactly the same manner as the previously mentioned Samsung. More to the point, this model Akai uses the same chassis as the Sam­sung. Naturally, I went straight to the vertical hold pot, pulled it out, and made the same measurements as before. Sure enough, it was the same fault. It was not quite as bad as in the previous case but was still obviously bad enough to cause problems. At this point, I made a rather fortuitous decision. In the normal course of events I would have simply discarded the pot and fitted a new one. But I didn’t have one in stock and the customer had asked whether I could possibly get the set back to her in time to see a special program that night. And I had said I would do my best to oblige. The upshot was that I decided, for a couple of reasons, to pull the pot apart. One reason was an attempt to satisfy my curiosity as to why it was faulty; resistors do not normally go low, although rare cases have been reported. The other reason was a faint hope that, if I could find the reason, I might be able to do something about it and avoid the delay in obtaining a replacement. Granted, it was a long shot but what did I have to loose? The pot is in two parts, held together with five little clips, which were easily prised back, releasing the punched bakelite plate carrying the carbon element and the three termi­nals. And this was most revealing. From the three terminals there are three short, parallel, carbon tracks; two outer ones to the ends of the resistor ele­ment, and a centre one to a circular carbon pad which makes contact with the wiper mechanism. Mechanically, it was all per­ fectly conventional. What wasn’t so conventional was a strip of reddish-brown paint that had been applied across these three parallel tracks. Or at least it looked like paint; its real composition, or its purpose, remains a mystery. But its location aroused my suspi­cions immediately; if it had developed any kind of leakage bet­ween the carbon tracks, it would have produced exactly the be­haviour I was observing. More to the point, if this was the case and I could remove this coating, I would have achieved both my aims; proved the cause of the fault and salvaged the pot for immediate use. I decided to try to scrape away the paint – or whatever it was – from be- 12 MONTHS WARRANTY ON PARTS & LABOUR THAT MAKE LIFE EASIER PRODUCTS YOU NEED AUSTRALIAN MADE TEST EQUIPMENT SHORTED TURNS TESTER Built-in meter to check EHT transformers, in­ clud­­­ing split diode type, yokes and drive trans­ formers. $95.00 + $3.00 p&p DEGAUSSING WAND Great for comput er mon­­­i t­o rs. 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 HIGH VOLTAGE PROBE tween the tracks using a sharp needle. It was a fiddling job, due to the small dimensions involved, but it came away fairly easily. And my suspicions were justified; the pot values immediate­ly returned to normal. I lost no time in fitting it back into the set, confirmed that the fault had been cured, let it run for a couple of hours, and had it ready for the lady in time for her evening program. So that’s the saga of the dicey pots. I know it poses as many questions as it answers but at least one can now be on the alert for similar situations. One thing seems obvious; the paint apparently deteriorates slowly over time so that, initially, the fault could be corrected by readjustment of the control. Thus, in some cases, service help would only be sought when the adjustment ran out. And this is also the possible explanation for the second failure of the Samsung set after the first apparent cure. But what is the paint and what is its purpose? I have no idea but it is significant that it is not common to all these pots. All those that I have encountered with the paint – and there have been some since – have been in original equipment, while the replacement units appear to be free of it. So your guess is as good as mine. And yes, “if only” I had taken more care with that initial pot measurement. Something different And now, from my colleague J. L., south of Bass Strait, something a little different. This is how he tells it. The dear old lady arrived at my door bearing her much-loved radio cassette player. Her problem was that it had blown up after the power supply authority crossed its wires and put 6kV on one of the local phases! Her neighbours had lost refrigerators, TV sets, microwave ovens, video recorders, and washing machines but, as far as she could tell, the only thing she had lost was her radio. However, after six months of trying to get compensation from the authori­ty, she decided to see if it could be repaired at a price she could afford. I had to tell her that I didn’t like her chances. The set was a Sanyo AM/FM stereo cassette player, about 10 or 12 years old. Although nominally a portable battery-operated unit, it was fitted with an internal AC powerpack to make it a generally more versatile model. And as is so often the case, the owner had never had a set of batteries in it – it had always been used in the kitchen as an AC-powered radio. Built-in meter reads positive or negative 0-50kV. For checking EHT & focus as well as many other high tension voltages. $120.00 + $5.00 p&p REMOTE CONTROL TESTER Designed to test infrared or ultrasonic remote con­ trol hand­pieces; eg, for TVs, VCRs, house alarms and car alarms. Supplied with extension infrared detector lead. Output is via a LED and piezo speaker. $97.00 + $4.00 p&p. SILICON CHIP COLOUR TV PATTERN GENERATOR Built-up kit comes with power plugpack, RF lead. $250.00 + $9.00 p&p. TV & VCR (new) tuners – $47.00 each VCR converters – $49.00 each TV, VCR TUNER REPAIRS FROM $22 REPAIR OR EXCHANGE Phone for free product list 216 Canterbury Rd, Revesby, NSW 2212, Australia. Phone (02) 774 1154 Fax (02) 774 1154 Cheque, Money Order, Visa, Bankcard or Mastercard March 1994  53 My first test was to check the continuity of the AC lead and the primary of the internal power transformer. It was no surprise to find the lead OK but the transformer open circuit. Next, I fitted a set of seven C cells and tried the radio switch on the front panel. The volume control had been left full on and I was nearly deafened by the roar of one of the local rock stations. Given the history of the defect, I would have wagered nothing on the survival of the internal electronics, yet it seemed that the transformer primary was the only casualty. As is usual with so many of these types of jobs, the prob­lem was not so much replacing the transformer but in knowing what value of transformer to replace it with. The battery voltage (10.5V) gives some clue as to what the transformer voltage might be but one can never be sure. One way is to fit a transformer with, say, a 25V secondary and then activate it slowly with a Variac. As the secondary voltage comes up the set will come to life and the art is decid­ing when it seems to be operating normally. At that point, the secondary of the substitute transformer should be delivering around the correct output for that particular set. Having decided what voltage is needed, the next problem is to check if the best available transformer will actually fit into the space vacated by the defunct unit. However, when I opened the cabinet, I was faced with a transformer the likes of which I have never seen before. It was a very thin, flat package, rather like an ordinary transformer after an attack by a steamroller. There was no way that I could get a transformer of conventional con­ 54  Silicon Chip struction to fit in the space available. It was quite obvious that I was going to have to get an original replacement if the set was ever going to be restored. So I enquired of my local Sanyo agent to see if the transformer was still available and what the price might be. It was a case of good news and bad news. Yes, the trans­former is still in stock but it was going to cost me $40. With freight and a small retail margin added, plus my labour charges, the total cost was going to be more than the old radio was worth. Then I had the bright idea of using an AC plugpack to replace the internal transformer. The low voltage AC could then be fed into the set through the existing AC socket. It would need to be modified in some way to avoid the risk that someone might try to inject 240V but that didn’t look like an insurmountable problem. The more immediate worry was to find out what value of low-voltage AC was needed to operate the set. So I asked my friendly Sanyo agent if I could look at his service manual for this model. In fact, we took a photocopy of the circuit so I had all the information I might need to get the radio working again. It was while I was pondering over the diagram, trying to work out what the AC input to the power block might be, that I noticed the words “Ext DC in”. As it turned out, all my worrying had been for nought. The set had provision for 3-way power – 240V AC, internal batteries, or an external 9-10.5V DC supply. The external supply was via a conventional DC socket so all I had to do was to get a 9V DC plugpack and the DOL’s set was going again, without any need to cut, drill or modify! As it happened, I had a suitable old plugpack in stock and was able to press that into service, at minimal cost to the customer. If only I had looked more closely at the set when I first fitted the batteries, I would have seen the DC socket and could have saved myself an hour or more of angst. I need not have even taken the back off. That’s what comes of spending so much time inside TV sets and VCRs. All jobs look like big ones until you find out that they aren’t! Thanks J. L. Yes, “if only” – I know SC how you feel. 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 Voice activated audio switch for FM wireless microphones This VOX circuit is intended for use with FM wireless microphone circuits & will provide audio muting of the transmit­ter section. It uses just one CMOS IC & a handful of transistors. By DARREN YATES There are two common applications for a voice-operated switch or VOX as it is commonly called. The first is to stop and start a tape recorder so that it runs only when a voice or sounds are present to be recorded. Second, a VOX is commonly used to take the place of the press-to-talk switch on transmitters as used for amateur radio communications or in hands-free cellular phones in cars. 56  Silicon Chip The VOX presented here differs slightly in that it doesn’t switch a relay but it switches the audio output on and off. When you speak, a CMOS switch closes and stays closed until about 1.5 seconds after you stop speaking. As such it could be teamed with the FM Wireless Microphone project described in the October 1993 issue of SILICON CHIP. This would have the advantage of more professional opera- tion as the wireless microphone would not pick up noise when you were not speaking. In effect, the VOX circuit provides audio muting for the transmitter. This should not be confused with the muting feature commonly incorporated into FM tuners so let’s explain the princi­ple a little further. Most FM tuners such as those used in hifi systems have muting. This has two effects. It prevents the tuner from produc­ing copious hiss when being tuned between stations and it also mutes the audio when the received signal strength drops below a set level which is usually around 10 microvolts or thereabouts. On the other hand, when you are using an FM wireless micro­ phone, you usually would disable the muting feature on the tuner. If not, you could have the annoyance of the audio being muted on and off as the speaker moves D3 1N4004 2.2k 10k 10 10 10k Q2 BC558 B 100k 0.1 Q1 BC548 B 100k C C 220k E 180k MIC 4.7k E 0.1 10k 470pF Q3 BC548 B 0.1 Q4 BC548 2x1N914 D2 1M B C D1 2.2 1M 390  330  IC1b 14 C 4 5 3 IC1a 4066 E E 100k 6-15V REG. 100 16VW 100k 6.8k 13 2 1 47k 7 47k 2.2 100k OUTPUT 2.2k B E C VIEWED FROM BELOW 10 16VW 10 VOICE ACTIVATED AUDIO SWITCH Fig.1: the electret microphone picks up the audio signal & feeds it to a preamplifier stage consisting of Q1 & Q2. From here, the signal is fed via two paths: (1) to Q3 & (2) to CMOS switch IC1a. Q3 drives a voltage doubler circuit based on D1 & D2. When a signal is present, Q4 turns on & drives CMOS switch IC1b which in turn closes IC1a to switch the audio signal through to the output. around and causes the FM signal to fluctuate. So with the receiver (read: tuner) wide open all the time, it will reproduce all noises picked up by the microphone whether or not the speaker is talking. Now it’s no good having a VOX circuit to turn the FM wireless microphone transmitter on and off. If the transmitter is turned off, the tuner will immediately produce hiss; lots of it. Hence the transmitter must run continu­ously to keep the tuner quieted (ie, not producing hiss) but the audio preamplifier must be muted. That is the purpose of the VOX circuit presented here. Circuit diagram Looking at the circuit diagram in Fig.1, the electret microphone insert picks up the audio signal which is then fed to the preamplifier consisting of transistors Q1, Q2 and their associated components. The gain of this preamplifier is set to 33 by the 10kΩ negative feedback resistor and the 330Ω resistor con­nected to the emitter to Q1. To make sure that the amplifier doesn’t amplify RF signals, a 470pF capacitor across the 10kΩ feedback resistor limits the upper frequency response (-3dB down) to 33kHz. The output of the preamplifier is taken from the 2.2kΩ collector resistor of Q2. From here, the signal takes two paths. First, it is amplified by Q3 which has a gain of about 12. Its output drives a diode voltage doubler using diodes D1 and D2, as well as the 0.1µF and 2.2µF capacitors. PARTS LIST 1 PC board, code 01203941, 118 x 51mm 1 electret mic insert 4 PC pins Semiconductors 1 4066 CMOS quad analog switch (IC1) 3 BC548 NPN transistors (Q1,Q3,Q4) 1 BC558 PNP transistor (Q2) 2 1N914 signal diodes (D1,D2) 1 1N4004 rectifier diode (D3) Capacitors 1 100µF 16VW electrolytic 4 10µF 16VW electrolytic 2 2.2µF 63VW electrolytic 3 0.1µF MKT polyester 1 470pF 63VW MKT polyester Resistors (0.25W, 1%) 2 1MΩ 3 10kΩ 1 220kΩ 1 6.8kΩ 1 180kΩ 1 4.7kΩ 5 100kΩ 2 2.2kΩ 2 47kΩ 1 390Ω Miscellaneous Tinned copper wire (for link), plastic case, solder What we end up with across the 2.2µF capacitor is a DC voltage of around 8-9V whenever a signal of sufficient loud­ness is picked up by the microphone. This voltage is used to turn on transistor Q4 which in turn drives IC1b which is one-quarter of a 4066 CMOS analog switch. Finally, the voltage from pin 4 of IC1b is used as the control signal for IC1a and this switches the audio signal from the collector of Q2 through the to the output. To make sure that no clicks or plops occur when switching, two 47kΩ resistors and a 10µF capacitor equalise the DC on both sides of the switch. The 10µF capacitor shunts AC signals to ground which would otherwise be fed through the 47kΩ resistors to the output. Power supply Just about any power source from 6-15VDC can be used. If you intend using the circuit in conjunction with the FM Wireless Microphone you can use the same 9V battery supply. Diode D1 provides reverse polarity protection while the 100µF capacitor provides supply bypassing. Construction All of the components for the Voice-operated Audio Switch are installed on a PC board measuring 118 x 51mm and coded 01203941. Before you begin any soldering, check the board carefully for any shorts or breaks in the copper tracks by comparing it with the published artwork. Once you’re satisfied that everything looks correct, start by March 1994  57 220k 2.2k 10k 10uF 1M D2 1M 390  100k 10uF IC1 4066 Q4 D3 330  180k Q1 0.1 47k 47k 100k 4.7k 100k Q3 1 470pF MIC 0.1 Q2 0.1 10k 6.8k 100k 10k 2.2k 10uF D1 2.2uF 10uF 100k O/P 100uF GND 6-15V 2.2uF installing the single wire link and then continue with the resistors. If you are unable to distinguish the colour bands on the resistors (which is quite possible with some brands of 1% resistors), use a multimeter to check the resistance values. Now solder in the three diodes, followed by the transistors and the IC. Take care with the transistors since Q2 is a PNP type, while Q1, Q3 & Q4 are all NPN types. Make sure that you install them correctly, otherwise the circuit will not work, or worse, the transistor may be damaged. Lastly, solder in the capacitors, Fig.2: make sure that all polarised parts are correctly oriented during the PC board assembly. Note also that Q2 is a PNP type while the remaining transistors are all NPN types. the microphone insert and the four PC stakes. When you have finished installing the compon­ents, check for any solder splashes on the underside of the PC board which could cause shorts between the tracks. If you find any, clean them off with your soldering iron. Testing Now for the smoke test. Connect up your power supply in series with your multimeter on a low milliamps range – around 100-200mA is ideal. When you switch the power on, you should get a current consumption of around Fig.3: this is the full-size etching pattern for the PC board 10mA. Any more than this, and you should switch off and check the board carefully against the overlay wiring diagram. You may have a component installed in the wrong place or in the wrong way around. If it passes the smoke test, take your multimeter and measure the voltage at pin 13 of IC1a. You may find it easier to go back to the 100kΩ resistor connected to pin 4 of IC1b. If when you speak at normal volume, the voltage quickly rises up to somewhere near the supply voltage, then all is OK. When all is quiet (and it may need to be fairly quiet), the voltage should drop to 0V after about two or three seconds. Lastly, to check that the audio signal is being switched, connect the audio output to a signal amplifier (the CHAMP low-power amplifier published back in the February 1994 issue is ideal), then speak and listen for the audio to switch in and out. If this appears to be OK, then you should be right. Connecting up If you are building this project for use with the FM Wireless Microphone published in the October 1993 issue of SILI­CON CHIP, you will need to make several minor modifications. These involve omitting the electret, transistor Q1 and their associated components from the wireless microphone circuit and then coupling the output signal from the VOX circuit into the 8.2kΩ input resistor for Q3. If you need to adjust the audio gain, this can be reduced by decreasing the 10kΩ feedback resistor from Q2 on the SC VOX board. RESISTOR COLOUR CODES ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ No. 2 1 1 5 2 3 1 1 2 1 58  Silicon Chip Value 1MΩ 220kΩ 180kΩ 100kΩ 47kΩ 10kΩ 6.8kΩ 4.7kΩ 2.2kΩ 390Ω 4-Band Code (1%) brown black green brown red red yellow brown brown grey yellow brown brown black yellow brown yellow violet orange brown brown black orange brown blue grey red brown yellow violet red brown red red red brown orange white brown brown 5-Band Code (1%) brown black black yellow brown red red black orange brown brown grey black orange brown brown black black orange brown yellow violet black red brown brown black black red brown blue grey black brown brown yellow violet black brown brown red red black brown brown orange white black black brown SILICON CHIP BOOK SHOP Newnes Guide to Satellite TV 336 pages, in paperback at $49.95. Installation, Recept­ion & Repair. By Derek J. Stephen­son. First published 1991, reprinted 1994 (3rd edition). This is a practical guide on the installation and servicing of satellite television equipment. The coverage of the subject is extensive, without excessive theory or mathematics. 371 pages, in hard cover at $55.95. Servicing Personal Computers By Michael Tooley. First pub­ lished 1985. 4th edition 1994. Computers are prone to failure from a number of common causes & some that are not so common. This book sets out the principles & practice of computer servicing (including disc drives, printers & monitors), describes some of the latest software diagnostic routines & includes program listings. 387 pages in hard cover at $59.95. The Art of Linear Electronics By John Linsley Hood. Pub­lished 1993. This is a practical handbook from one of the world’s most prolific audio designers, with many of his designs having been published in English technical magazines over the years. A great many practical circuits are featured – a must for anyone inter­ested in audio design. Optoelectronics: An Introduction By J. C. A. Chaimowicz. First published 1989, reprinted 1992. This particular field is about to explode and it is most important for engineers and technicians to bring themselves up to date. The subject is comprehensively covered, starting with optics and then moving into all aspects of fibre optic communications. 361 pages, in paperback at $55.95. Digital Audio & Compact Disc Technology Produced by the Sony Service Centre (Europe). 3rd edition, pub­ lished 1995. Prepared by Sony’s technical staff, this is the best book on compact disc technology that we have ever come across. It covers digital audio in depth, including PCM adapters, the Video8 PCM format and R-DAT. If you want to understand digital audio, you need this reference book. 305 pages, in paperback at $55.95. Power Electronics Handbook Components, Circuits & Applica­ tions, by F. F. Mazda. Published 1990. Previously a neglected field, power electronics has come into its own, particularly in the areas of traction and electric vehicles. F. F. Mazda is an acknowledged authority on the subject and he writes mainly on the many uses of thyristors & Triacs in single and three phase circuits. 417 pages, in soft cover at $59.95. Surface Mount Technology By Rudolph Strauss. First pub­ lish-ed 1994. This book will provide informative reading for anyone considering the assembly of PC boards with surface mounted devices. Includes chapters on wave soldering, reflow­ soldering, component placement, cleaning & quality control. 361 pages, in hard cover at $99.00. Electronics Engineer’s Reference Book Edited by F. F. Mazda. First pub­ lished 1989. 6th edition 1994. This just has to be the best reference book available for electronics engineers. Provides expert coverage of all aspects of electronics in five parts: techniques, physical phenomena, material & components, electronic design, and applications. The sixth edition has been expanded to include chapters on surface mount technology, hardware & software design, Your Name__________________________________________________ PLEASE PRINT Address____________________________________________________ _____________________________________Postcode_____________ Daytime Phone No.______________________Total Price $A _________ ❏ Cheque/Money Order ❏ Bankcard ❏ Visa Card ❏ MasterCard Card No. Signature_________________________ Card expiry date_____/______ Return to: Silicon Chip Publications, PO Box 139, Collaroy NSW, Australia 2097. Or call (02) 9979 5644 & quote your credit card details; or fax to (02) 9979 6503. semicustom electronics & data communications. 63 chapters, in paperback at $140.00. Radio Frequency Transistors Principles & Practical Appli­ cations. By Norm Dye & Helge Granberg. Published 1993. This timely book strips away the mysteries of RF circuit design. Written by two Motorola engineers, it looks at RF transistor fundamentals before moving on to specific design examples; eg, amplifiers, oscillators and pulsed power systems. Also included are chapters on filtering techniques, impedance matching & CAD. 235 pages, in hard cover at $85.00. Newnes Guide to TV & Video Technology By Eugene Trundle. First pub­ lish-ed 1988, reprinted 1990, 1992. Eugene Trundle has written for many years in Television magazine and his latest book is right up date on TV and video technology. 432 pages, in paperback, at $39.95.  Title Price  Newnes Guide to Satellite TV  Servicing Personal Computers  The Art Of Linear Electronics  Optoelectronics: An Introduction  Digital Audio & Compact Disc Technology  Power Electronics Handbook  Surface Mount Technology  Electronic Engineer’s Reference Book  Radio Frequency Transistors  Newnes Guide to TV & Video Technology $55.95 $59.95 $49.95 $55.95 $55.95 $59.95 $99.00 $140.00 $85.00 $39.95 Postage: add $5.00 per book. Orders over $100 are post free within Australia. NZ & PNG add $10.00 per book, elsewhere add $15 per book. TOTAL $A March 1994  59 AMATEUR RADIO BY GARRY CRATT, VK2YBX Lowe’s HF-150 general coverage shortwave receiver Lowe’s new general purpose receiver, the HF150, costs less than the flagship HF-225 model yet offers more bells & whistles with the option of computer control & more memories for oftused frequencies. Exactly one year ago, we reviewed the HF-225, a shortwave receiver designed and built in England. Offering superb perfor­ m ance, the receiver also carried quite a hefty price tag, exclud­ing it from the budget of many shortwave enthusiasts. Now, Lowe Electronics has responded to market demands for a lower priced receiver and offer their latest model, the HF-150. Technically similar in many ways to the HF-225, the HF-150 has been designed as an easy to use “little brother” receiver. The unit is best described as a dual conversion super­het receiver, having an inbuilt synchronous AM detector to allow reception of CW, AM and SSB signals. It is amazingly small, having front panel dimensions of 185 x 80mm, and weighs only 1.3kg. A 5-digit LCD shows the receiver frequency, mode and memory number, when the appropriate buttons are pushed. Frequency coverage is continuous from 30kHz to 30MHz. The unit boasts twice the memory capacity of the HF-225, offering 60 user programmable EEPROM memory channels, which Lowe state will retain data for more than 10 years! Little brother to the HF-255, Lowe’s new HF-150 receiver covers the CW, AM, SSB & FM bands over the frequency range from 30kHz to 30MHz. A large LCD indicates the frequency & mode, & there are 60 user-programmable memories. 60  Silicon Chip The unit can be powered from an external DC supply, has external speaker and record outputs, can accept either 50Ω or 600Ω antenna inputs, and offers respectable sensitivity and selectivity figures, almost identical to the HF-225. Identical intermediate frequencies of 45MHz and 455kHz have also been used, together with a combination of IF filters offer­ing bandwidths of 7kHz in the wide mode and 2.4kHz in narrow mode. Receiver tuning is achieved in exactly the same manner as the HF-225; ie, by varying the frequency of both the local and heterodyne oscillators. The local oscillator is a PLL circuit, whilst all other oscillators are crystal derived. A numerical offset is calculated by the controlling microprocessor, so that the display reads correctly, even when the intermediate frequency is offset. Tuning The HF-225 has a series of five pushbuttons to control tuning and memory selections, and a rotary switch to enable the user to select CW, USB, LSB, AM, AMS (synchronous AM) or FM. The HF-150 design has simplified user operations somewhat, so that memories, frequency tuning and receiver mode are selected using only three pushbuttons, operating in conjunction with the liquid crystal dis­play. In addition, the tone control has been deleted. The end result is a clean, uncluttered front panel layout of miniature proportions. In fact the entire unit can be easily held in one hand. The dedicated FM mode has been deleted from the previous design but it is possible to resolve FM using the “slope detec­tion” technique, by tuning the receiver 3kHz above or below the FM carrier frequency. However, some other very convenient features have been added, increasing the versatility of the receiver. Unlike the HF-150, the older HF225 design does not incorporate an RF amplifier stage. This is fine for those of us equipped with long wire or dedicated frequency antennas, but a disadvantage for travellers wishing to use the receiver. To overcome this problem, the HF150 has an inbuilt single stage JFET preamplifier, which is selected by a slide switch on the rear panel. Appropriately marked “whip”, this position is suitable either for the whip antenna supplied in the AK-150 accessory kit for the receiver, or for just a few metres of hook-up wire, often used as a temporary HF receiving antenna by many shortwave enthu­siasts. Another convenient feature not present on the HF-225 is the addition of two battery holders, each carrying 4 “AA” cells. The user manual for the receiver advises that nicad cells will power the receiver for 3-4 hours and can be recharged, whilst remaining in the receiver, in about 16 hours. Alkaline cells can also be used, although they should be removed if the receiver is operated from an external DC source. Remote keypad The HF-225 utilised a combination of pushbuttons for coarse frequency selection and a conventional rotary dial for fine tuning. The HF-150 also offers this method of frequency selec­ tion. However, a far more convenient method is to use the optional remote keypad control. This connects to the rear panel of the receiver, and allows discrete frequencies to be entered directly. This is very useful for quickly checking stations at known frequencies, or for setting the frequency in a particular band of interest and then searching for signals with the main tuning control. The 12-button keypad can be conveniently positioned next to the receiver for ease of operation. Frequencies are entered in kilohertz, by entering the appropriate series of digits and then the “#” key. Because frequencies entered via the keypad are accurate only to the nearest kilohertz, the receiver must be retuned slightly to correctly resolve SSB signals. Computer interface For computer biased amateurs or shortwave enthusiasts, the optional IF-150 RS-232 computer interface allows an HF-150 receiver to be connected to the serial port of any IBM compatible computer or terminal, and provides control of the reception mode and frequen­cy. The RS-232 interface simply plugs into the remote keypad socket on the rear panel of the receiver. Commands to the interface use simple mnemonic instructions and free format numbers, so its operation is straight­forward. Alter­natively, the interface and receiver can be driven from a dedi­cated program, provided this uses the correct protocol. An example program suitable for IBM computers is supplied with the inter­ face on a 3.5-inch 1.44Mb diskette. Control facilities allow remote tuning of the receiver in 8Hz steps, selection of any one of the eight possible reception modes, and recall of the receiver memory contents. Memory down­loading is possible on HF-150 receivers with firmware revision 1.3 or later. A 32-page user’s manual provides details of the various commands used to control the receiver, gives examples of the com­mands used for memory store and recall, and shows how to set the operating mode and frequency. One very pleasing aspect of both the HF-225 and HF-150 is the abundance of technical information supplied with the receiv­er. The user manual include five pages of circuits, while the optional HF-150 Technical Manual gives 38 pages of circuit descriptions, PC board layout diagrams, alignment details, a parts list, disassembly instructions, and enlarged copies of circuit diagrams for the receiver, keypad unit and RS-232 interface unit. The HF-150 has a recommended retail price of $995, which is about 30% less than for the HF-225. The IF150 RS-232 interface is available for $135 (includes the software), while the Technical Manual is available for $49. For further information, contact Emona Electronics Pty Ltd, 92-94 Went­ worth Avenue, Sydney, NSW SC 2000. Phone (02) 211 0988. March 1994  61 Here’s a project to really catch your eye! It uses 10 light emitting diodes (LEDs) & flashes them around in a clockwise direction. By DARREN YATES I F YOU’RE new to electronics then you’re probably looking for a sim ple but eye-catching project to build that won’t cost the earth. This LED chaser uses 10 LEDs which flash in rotation around the outer edge of the board. It’s ideal for shop front ‘attention-grabbing’ displays or if you just want to learn more about digital electronics and have some fun along the way. Light chasers have been around for a long time. Originally they used a motor-driven rotary switch and incandescent lamps but these days you can do it quite simply with an IC or two and some light emitting diodes (or LEDs). Light chasers can have a variety of different ways in which the patterns of light chase around a loop. In this design, we have two lights chasing around a loop of 10 LEDs. The rate at which they run can be varied simply by adjusting a trimpot. How it works The circuit shown in Fig.1 has two ICs, five transistors and 10 LEDs. IC1 is a 555 timer connected up as an astable mul­tivibrator or oscillator. Its frequency is controlled by the 100kΩ trimmer potentiometer (or ‘trimpot’ for short), the 22kΩ and 2.2kΩ resistors and the 2.2µF capacitor. The frequency of this oscillator is worked out from the following formula: Frequency = 1.44/[(R1 + (2 x R2))C1] where R1 = the value of the trimpot + 2.2kΩ; R2 = 22kΩ; and C3 = 2.2µF. The output of the 555 is taken from pin 3 and this pulse waveform is con- BUILD THIS SIMPLE LED CHASER 62  Silicon Chip A 100 16VW 2.2k A A  A  A    6V LED1-10 100k VR1 4 7 22k 3 IC1 555 6 2  16 8 14 CLK 0 0.1 1 15 1 IC2 4017 10k RST 2 470 B 3 Q2 BC547 B C Q3 BC547 10k 7 470 C E 5 K Q1 BC547 10k 4 B C E K 4 CLK EN 13 10k 10  K 470 470 E B A 2 B  K C E 2.2 25VW E C VIEWED FROM BELOW 3 10k  K 470 5 1  K Fig.1: the circuit uses 555 timer IC1 to clock IC2, a 4017 decade counter. Its outputs each go high in turn & control LED driver transistors Q1-Q5. When output ‘5’ goes high, the counter is reset & so the sequence is continually repeated. Q4 BC547 B C E 8 Q5 BC547 SIMPLE LED CHASER nected to the clock input at pin 14 of IC2. This is a CMOS (Complementary Metal-Oxide Silicon) 4017 Johnson decade counter. This IC has 10 outputs, each of which go high in turn. While these 10 outputs are available to drive LEDs, we’ve used only the first five outputs; ie, those labelled ‘0’ to ‘4’. Reset pin Most Johnson counters also come with a RESET pin. In normal operation, this pin is held low but when it is taken high, it resets the counter to its initial condition with the ‘0’ output high and all of the others low. In our circuit, you’ll see that we’ve connected the ‘5’ output back to the RESET input. What happens now is that each output will cycle through from ‘0’ to ‘4’ but when the next rising edge appears at pin 14, the ‘5’ output goes high and this goes straight to the RESET input. The counter resets itself and sends the ‘0’ output high and the counter cycles around again. Even though there is a small delay while the ‘5’ output resets the circuit, it happens so quickly that it is not notice­able. This same principle works with the other outputs as well. If you connect output ‘7’ to the RESET input, the output cycle would be 0-1-2-3-4-5-60-1-2 and so on. Each of the five outputs we’ve used is connected via a 10kΩ current limiting resistor to the base of a BC547 NPN transistor. When one of the outputs goes high, it turns on its associated transistor which in turn switches on the two LEDs connected in series with its collector. This continues for each output and its associated transistor. By mounting the two LEDs connected to each transistor diagonally opposite each other, we can make it look as though there are 10 separate PARTS LIST 1 PC board, code 08103941, 133 x 82mm 4 stick-on rubber feet 1 100kΩ trimpot 1 6V lantern battery, Eveready 509 or equivalent Semiconductors 1 NE555 timer (IC1) 1 4017 Johnson counter (IC2) 5 BC547 NPN transistors (Q1-Q5) 10 5mm red LEDs (LED1-10) Capacitors 1 100µF 16VW electrolytic 1 2.2µF 25VW electrolytic 1 0.1µF 63VW MKT polyester Resistors (1%, 0.25W) 1 22kΩ 1 2.2kΩ 5 10kΩ 5 470Ω Miscellaneous Tinned copper wire, solder, battery clips. outputs with the two LEDs diagonally op­posite chasing each other. If you take a quick look at the overlay diagram, you’ll see that the LEDs are set around the PC board in an oval shape. If you run the chaser in a dark room, you will see the oval shape appear as the LEDs chase each other. Power is supplied by a 6V battery and we suggest you use a lantern battery; eg, Eveready 509 or equivalent. They are rela­tively cheap and can last for years when used at low currents. Construction All of the components for the LED chaser are installed on a PC board measuring 133 x 82mm and coded 08103941. Before you begin construction, check the copper side of the board for any shorts or breaks between tracks. If you find any, they should be repaired before you proceed further. Start off by installing the wire links. Make sure that you make them as straight as possible. Use the overlay wiring diagram of Fig.2 to make sure that they go in the correct position. After the wire links, you can continue by installing the resistors and the trimpot. Again, make sure that you install them in the correct location. Next up, you can solder in the ICs, transistors and the capacitors, followed by the PC pins. Be careful not to apply too much heat to the ICs and transistors or you may damage them. The last job is to install the LEDs. It’s important that they go in the March 1994  63 LED2 LED9 A 100uF K A LED4 A K K BATTERY 2.2k IC1 555 Testing 1 Q1 Q2 Q3 Q4 470  22k 470  K 470  A 470  A LED6 VR1 470  LED7 0.1 correct way around. Use the overlay diagram and the pictorial diagram of the LEDs on the circuit to check which way they go. Lastly, make up a set of clip leads for the supply to the 6V battery. Make the negative lead from black wire and the posi­tive lead from red wire. K Q5 2.2uF 10k 10k 10k 10k 10k LED5 LED8 Now that you’ve finished the construction, A K A K IC2 switch your multi­ meter 4017 to a low current range (say 1 200mA) and connect it in series between the battery LED3 LED1 LED10 and the circuit. A A A K K K As soon as you make a complete connection, you should see the LEDs jump into life, with opposite LEDs lighting up in turn. The current consumption should be less than 10mA. If the LEDs fail to light, disconnect the battery and check your board thor­ oughly against the overlay diagram for any possible errors. In particular, make sure that the ICs, transistors & LEDs are correctly oriented. Note that if you inadvertently connect the battery around the wrong way, there is unlikely to be any damage since it’s only 6V. If you find that the circuit appears to be working but two LEDs opposite Fig.2 (top): install the parts as shown here, taking care to ensure correct polarity of the ICs each other fail to light, & LEDs. Trimpot VR1 adjusts the chaser speed. Fig.3 above shows the full-size PC pattern. check to make sure that they are both correctly installed. You may find that one of them pot VR1. If you want the LEDs to go a board in a box or simply put some is installed the wrong way around. lot faster, reduce the 2.2µF capacitor rubber feet at the corners as we have done and amaze your friends with your Note that you can change the speed to 1µF. SC of the chasing LEDs by adjusting trimTo finish off, you can install the PC new-found knowledge. RESISTOR COLOUR CODES ❏ ❏ ❏ ❏ ❏ No. 1 5 1 5 64  Silicon Chip Value 22kΩ 10kΩ 2.2kΩ 470Ω 4-Band Code (1%) red red orange brown brown black orange brown red red red brown yellow violet brown brown 5-Band Code (1%) red red black red brown brown black black red brown red red black brown brown yellow violet black black brown ELECTRONIC KEY KIT EA July 1992 * An IC on a small PCB which is shaped like a key (no battery!) which, when connected against two terminals that are wired to a decoder kit, can be used to activate door strikers, car alarms, central locking, etc. * Over 1/2 million codes * The most secure key ever * ON SPECIAL AT $50 for two keys and one decoder kit. FM TRANSMITTER KIT – MKII SC November 1993. This low-cost FM transmitter features pre-emphasis, high audio sensitivity (can easily pick up normal conversation in a large room), a range of well over 100 metres, and excellent frequency stability. Specifications: tuning range 88108MHz; supply voltage 6-12V; current consumption (<at> 9V) 3.5mA; pre-emphasis 75u*s; frequency response 40Hz to greater than 15KHz; S/N ratio greater than 60dB; sensitivity for full deviation 20mV; frequency stability with extreme antenna move­ m ents 0.03%; PCB dimensions 1 x 1.7-inches. The double sided, solder masked and screened PCB also makes for easy construction and no coil winding is necessary. The kit includes a PCB and all the on-board components, plus an electret microphone and a 9V battery clip. $11 Ea. or 3 for $30. ELECTRIC FENCE KIT SC April 1993. A complete kit for an electric fence con­ troller mounted on one PCB. Even the high voltage flyback trans­former is mounted on the PCB. Can be powered by a 12V battery which is charged by our SOLAR CHARGER KIT, or a small plugpack, etc. Draws an average current of 15mA or 25mA, depending on the mode selected: Low power - up to 1km; High power - up to a few kilometres. Delivers a healthy kick of 2.3KV into an open circuit and 1.8KV into 500 ohms and conforms to AS3129. $40 If you buy the combination of SOLAR CHARGER and the ELECTRIC FENCE kits the total price is $80 PASSIVE TANK SET We have a limited number of matching “tank sets” which are based on passive XX1080 tubes. With the lens supplied, these will reduce passive vision in sub-moonlight illumination. The sets include a low light lens, tube, eyepiece and a power supply kit. $200 ATTENTION ALL MOTOROLA MICROPROCESSOR PROGRAMMERS We have advanced information about two new STATE OF THE ART microprocessors to be released by Motorola: 68C705K1 and 68HC705J1. The chips are fully functional micros containing EPROM/OTPROM and RAM. Some of the features of these new LOW COST chips include: * 16-pin DIL for the 68HC705K1 chip * 20-pin DIL for the 68HC705J1 chip * 10 fully programmable bi-directional I/O lines * EPROM and RAM on chip * fully static operation with over 4MHz operating speed. These two chips should become very popular. We have put together a SPECIAL PACKAGE that includes a number of components that enable “playing” with the abovementioned new chips and also some of the older chips. IN THIS PACKAGE YOU WILL GET: * One very large (330 x 220mm) PCB for the Computer/ Trainer published in EA Sept. 1993, one 16x2 LCD character display to suit, and one adaptor PCB to suit the 68HC705C8. * One small adaptor PCB that mates the programmer in EA March 1993 to the “J” chip, plus circuit. * One standalone programmer PCB for programming the “K” chip plus the circuit and a special transformer to suit. THE ABOVE PACKAGE IS ON SPECIAL AT A RIDICULOUS PRICE OF: $99 Note that the four PCBs supplied are all silk screened and solder masked, and have plated-through holes. Their value alone would be in excess of $200!! A demonstration disc for the COMPUT­ ER/TRAINER is available for $10. No additional software is cur­rently available. Previous purchasers of the COMPUTER/TRAINER PCB can get a special credit towards the purchase of the rest of the above package. HARD DISC DRIVES These are BRAND NEW 10Mb IBM-compatible HARD DISC DRIVES. Originally made by Seagate Technology. Sure their capacity is not up to modern standards but look at the price! Overall dimensions: 148 x 85 x 208mm. Limited quantity. $39 40kHz ULTRASONC PARTS The difficult parts needed for making a good quality crystal controlled ultrasonic movement detector (eg, EA April 1990; SC July 1989) are a pair of good quality 40kHz transducers (Murata) plus a 40kHz crystal. We can offer this set of three parts at a giveaway price of: $6 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 of mains? LIMITED STOCKS. $15 TUNING FORK PCB CLEARANCE Each one of these identical PCB filter assemblies contains six 3-terminal tuning fork filters (IN - GND - OUT) at different frequencies in the audio range: 1.8-3.1kHz. These high quality dual tuning fork filters have very narrow bandwidths and could be used in selective call systems, oscillators, etc. Each PCB also contains two high current GAS ARRESTORS which sell for about $20Ea! Clearance: $10 for a pair of identical PCB assemblies. 400 x 128 LCD DISPLAY MODULE - HITACHI These are silver grey Hitachi LM215XB dot matrix displays. They are installed in an attractive housing and a connector is provided. Data for the display is provided. BRAND NEW units at a low: $40 LASER OPTICS The collimating lens set is used to improve the beam (focus) divergence. The 1/4-wave plate and the beam splitter are used in holography and experimentation. All are priced at a fraction of their real value: 1/4-wave plate (633nm)............... $20 Collimating lens sets................... $45 Polarizing cube beam splitters$65 MAINS FILTER BARGAIN A complete mains filter employing two inductors and three capacitors fitted in a shielded metal IEC socket. We include a 40 joule varistor with each filter. $6 Note that we also have some IEC extension leads that are two metres long at $4 ea. STEPPER MOTORS These are brand new units - main body has a diameter of 58mm and a height of 25mm. Will operate from 5V, has 7.5-degree steps, coil resistance of 6.6 ohms, and it is a two-phase type - six wires. ONLY: $12 We also have available a suitable driver IC for these mo­tors: UCN­ 5804B <at> $10. Information included. COMPUTER KEYBOARDS New 54-key TI keyboards. Unencoded matrix type with edge connector (15 connections). All switches are SPST momentary with the exception of the “Alpha lock” key (latching). Features cursor control keys, a function key, enter & shift keys, and a control key. Very LIMITED QUANTITY: $14 FIBRE OPTIC CABLE High-quality twin-core fibre optic cable. Inner core diamet­er 150u*m; cladding 500u*m; outer protection jacket diameter 3mm. Bargain at: $10 for 6 metres OATLEY ELECTRONICS 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. PLEASE ALSO SEE OUR ADVERT ON PAGE 3 March 1994  65 COMPUTER BITS BY DARREN YATES A binary clock of the software kind Binary notation is the essence of programming whether you do it in assembler or BASIC. This month, we present one of our past projects in software form – a binary clock. SILICON CHIP BINARY CLOCK This is the on-screen display generated by the Binary Clock software. For those unaccustomed to binary readouts, the display also shows the time in hours, minutes & seconds. Programming Tip If you’re always losing your DOS prompt amongst the other information on screen, add these lines to your AUTOEXEC.BAT file. The prompt becomes yellow type on a red background while normal screen printing remains as white on black for normal DOS opera­tion. The current time and date are also displayed. PROMPT $e[1;33;41m Time:$t$_ Date:$d$_ $P$G $e[0;37;40m PROMPT Time:$t$_Date:$d$_$e[1;33;41m$p$g$e[0;37;40m Note: You must have the ANSI.SYS device driver installed in your CONFIG. SYS file. If not, add the following line: DEVICE = C:\DOS\ANSI.SYS 66  Silicon Chip Talking in ones and zeros in something that we humans do not undertake easily yet they are the only real language our faithful computing companions can understand. So the programming languages flourish (BASIC, Pascal, C, Lisp, ADA, Prolog and Cobol), everyone trying to make their own to suit their own application: BASIC for beginners, Cobol for economists who know little about computer language, and C for programmers who know little about the English language (just kidding). However, the one thing they all have in common is the translation of what the programmer understands into something the computer understands. And to this end, a knowledge of binary notation is vital. Back in the October 1993 issue, we presented a project which used programmable array logic or PALs to produce a clock which used a series of LEDs to display the time in binary format. Then, late last year, we received a letter from a reader, Eric Hughes of Tasmania, who had developed a program on the Atari ST which performed the same task. Based on his ideas, we generated our own version for the PC. It runs under QBASIC or most of the Quick­BASIC compliers, at least those from versions 3.0 and up. The program listing is published here and requires a VGA card and monitor. The program briefly is divided up into two sections – the main module and the screen display routine called DISPLAY. The main module sets up the output screen, placing the various ‘8 4 2 1’ sequences. It also draws and captures the “lights” that indicate which bits are on or off. This is done by the GET statement. The main operation of the program is inside the WHILE..WEND loop in the main module. This continuously updates the time and calls the DISPLAY subroutine each second to update the display. The DISPLAY subroutine does a number of things. First, it takes the time from the TIME$ command and sections it off into hours, minutes and seconds and places these values into appro­ priately named strings. These values are then placed into a three level array, ‘D’. Inside the FOR V..NEXT V loop, these values are turned into a binary string array H$ containing 1s and 0s. Array H$(0) now contains a binary string which represents the hours, H$(1) the minutes, and H$(2) the seconds. The final FOR W..NEXT W loop checks each character in the string array H$ and then places either the “off light” if its a 0 or the “lit light” if it’s a 1. This continues indefinitely until the Q key is pressed. This program can be easily adapted to suit CGA screens by switching to screen 2 and scaling all of the coordinates from a 640 x 480 grid down to a 320 x 200 grid; similarly for EGA, by switching to SCREEN 9 and scaling the coordinates from 640 x 480 to 640 x 350. You may also like to try to shrink the code a little further. This program is by no means the definitive version and there are several ways in which it could be improved, but it could form the basis of a useful learning tool. The WHILE D(V)<>0 loop in the DISPLAY subroutine is where the decimal number is converted to binary. It uses a simple form of successive approximation, as used by many up-market analog-to-digital converters (ADCs). It first checks the most significant bit to see if it is set. If so, it adds a 1 to the appropriate H$ array. This is done by dividing the original section of time, say minutes for example, by 2 and then taking the integer of that value. You then subtract twice this integer from the original number, which is stored in variable F. If the remainder is 1 then that bit is set, otherwise it is 0. For those of you who don’t wish to type in the whole pro­gram, we can supply BINARY.BAS plus an executable version, BI­NARY.EXE, on disc for $7 plus $3 for postage. Please specify the disc format required. You can phone in your order along with your SC credit card details. Binary Clock Program Listing REM Binary Clock for PCs REM Written By DARREN YATES B.Sc. – requires VGA screen & card DIM SHARED B(200), c(200) DECLARE SUB DISPLAY (B, c, A$) SCREEN 12, 1 LINE (0, 0)-(639, 479), 2, B LOCATE 2, 28: PRINT “ SILICON CHIP Binary Clock” LOCATE 10, 38: PRINT “HOURS” LOCATE 22, 15: PRINT “MINUTES” LOCATE 22, 60: PRINT “SECONDS” BIN$ = “32 16 8 4 2 1” LOCATE 28, 7: PRINT BIN$ LOCATE 16, 29: PRINT BIN$ LOCATE 28, 51: PRINT BIN$ SCREEN 12, 1 CIRCLE (20, 20), 15, 15 GET (4, 4)-(36, 36), B PAINT (19, 20), 4, 15 GET (4, 4)-(36, 36), c PUT (4, 4), c WHILE QUIT$ <> “Q” AND QUIT$ <> “q” FOR G = 1 TO 3 H$(G) = “” NEXT G A$ = TIME$ IF A$ <> OLDA$ THEN CALL DISPLAY(B, c, A$) OLDA$ = A$ QUIT$ = INKEY$ WEND SUB DISPLAY (B, c, A$) DIM D(3), H$(3) hour$ = MID$(A$, 1, 2) minute$ = MID$(A$, 4, 2) second$ = MID$(A$, 7, 2) hour = VAL(hour$) minute = VAL(minute$) second = VAL(second$) D(1) = hour D(2) = minute D(3) = second LOCATE 7, 39: PRINT D(1) LOCATE 20, 17: PRINT D(2) LOCATE 20, 62: PRINT D(3) FOR v = 1 TO 3 WHILE D(v) <> 0 f = D(v) D(v) = INT(f / 2) r = f - (2 * D(v)) IF r = 0 THEN H$(v) = “0” + H$(v) IF r = 1 THEN H$(v) = “1” + H$(v) WEND IF LEN(H$(v)) < 6 THEN FOR G = 1 TO 6 - LEN(H$(v)) H$(v) = “0” + H$(v) NEXT G END IF NEXT v FOR w = 1 TO LEN(H$(1)) bit$ = MID$(H$(1), (LEN(H$(1)) - (w - 1)), 1) IF bit$ = “1” THEN PUT (425 - (w * 35), 190), c, PSET IF bit$ = “0” THEN PUT (425 - (w * 35), 190), B, PSET NEXT w FOR w = 1 TO LEN(H$(2)) bit$ = MID$(H$(2), (LEN(H$(2)) - (w - 1)), 1) IF bit$ = “1” THEN PUT (250 - (w * 35), 380), c, PSET IF bit$ = “0” THEN PUT (250 - (w * 35), 380), B, PSET NEXT w FOR w = 1 TO LEN(H$(3)) bit$ = MID$(H$(3), (LEN(H$(3)) - (w - 1)), 1) IF bit$ = “1” THEN PUT (600 - (w * 35), 380), c, PSET IF bit$ = “0” THEN PUT (600 - (w * 35), 380), B, PSET NEXT w END SUB March 1994  67 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 BOOKSHELF Circuit analysis using a computer PC-Assisted Linear Circuit Analysis & Drawing, by Ian Sin­clair. Published 1993 by Butterworth-Heinemann Ltd (Newnes), Oxford, England. 279 pages, soft covers, 190 x 246mm. ISBN 0 7506 1662 8. Price $49.95. With all the circuit analysis programs now available for computers, it is not surprising that books relating to the topic are now being produced. This one is written to complement a circuit analysis program called “Aciran” which has been created by the author and which is available only from him. While that may seem to be a drawback, it appears that the functions of Aciran as a program are quite similar to a number of analysis programs such as Spice. This means that the book can be read in the general sense and the author makes it clear in the text where there are particular circuits which have performance which cannot be fully analysed by the Aciran software. Perhaps the most useful application of the text will be to the novice who is trying to decide whether or not to purchase circuit analysis software. Some design engineers do not like circuit analysis programs and are inclined to the view that such analysis will give rise to a “blinkered” approach to design, with the result that less innovation will occur. On the other hand, many circuit designs do call for a systematic analysis to be made in order to guarantee that they will perform as intended. Such analyses can be tedious and very time-consuming although some engineers have streamlined the process for their particular work by storing all the formulas in a programmable calculator or have transferred the formulas to a program written in Basic or C. In effect, they have written their own programs to do the job so that a painful and often boring job becomes a matter of routine. That still leaves wide applications for circuit analysis programs and it is up to the designer or engineer to decide whether to adopt a specialist one-off approach or take the gener­al approach with circuit analysis software. In practice, it seems that some designers love analysis programs and others hate ‘em. So be it. Either way, this text features lots of sample gain vs frequency and phase plots for many circuits and these will be of great use to novice designers in showing what this sort of software can do. We should point out that the book does assume that the reader has a good knowledge of AC circuit theory, as well as active circuitry design procedures involving transistors, FETs and op amps. Such know­ledge will be necessary in order to fully understand the gain and phase plots. As far as the contents are concerned, the book begins with a few pages on the principles of circuit analysis and then talks about computer basics, backing up, copying files and so on. Chapter 2 is entitled “Aciran In Action” and talks about the specific analysis program listed above, with respect to passive circuits. However, it is quite general in nature and applicable to most circuit analysis software. Chapter 3 continues with passive circuits while Chapter 4 moves on to active circuits and features transistors and FETs. Aciran handles these active components in a similar way to other analysis software except that it does not have a library of common transistors – the user has to tell the program the specific parameters before circuit analysis can proceed. Chapter 5 moves on to operational amplifier ICs and here the Aciran program comes with a library that encompasses a number of “bog standard” op amps (read: old and outmoded ones that nobody wants to use any more), such as 5532, 5534, TL084 and 741 but misses out on more modern, desirable and capable op amps. In the latter cases, the user is expected to provide the following parameters: input impedance, output impedance, open loop gain, gain bandwidth product and open loop gain tolerance (%). Surpris­ingly, slew rate is ignored and the author makes the comment that “the slew rate limitations of operational amplifiers should be remembered if you are concerned with high frequency waveforms at the higher amplitude levels.” I should think so too! Chapter 6 is entitled “Last Lap” and deals with resonant lines, open and shorted lines and imperfect components. It also has notes on PSPICE, the acknowledged standard amongst circuit analysis software. Chapters 7, 9 & 10 then deal with Autosketch, a more or less standard circuit drafting software. The treatment is fairly thorough but I am not sure that it is appropriate in this text since it appears to be majoring on circuit analysis – even the title and the cover design emphasises this. In conclusion, this text is well written and generally on target. However it would appear to have a fairly limited appeal, especially if you don’t intend purchasing the author’s software. If you wish to purchase the book, it is available from Butterworth-Heine­ mann, 271-273 Lane Cove Rd, North Ryde, NSW 2113. Phone (02) 335 4444. SC (L.D.S.) March 1994  71 REMOTE CONTROL BY BOB YOUNG How to service servos & winches This month, we will look at the problems encountered in servicing servos & winches. Normally, these are very reliable but like any electromechanical device they eventually wear & give trouble. The modern servo is indeed a marvel of electronic engineer­ing; compact, powerful, accurate, robust and above all, reliable. They are a far cry from the rubber driven escapements that I cut my teeth on back in 1955. They are even a far cry from the first servos that I built for the Silvertone Mark I proportional system in 1966. I am still amazed when I look back at the progress made in those eleven years. My first proportional servo was fitted with a discrete amplifier consisting of about fifty components, of which eleven were transistors, all jammed into a relatively large Orbit PS-2 servo. The next servo, the PS-3, was much smaller and we just managed to shoehorn the same electronics into a two-deck assem­bly. It was grumble, grumble all around. Assembly hated assem­ bling them and servicing disliked servicing them. They were however, very accurate and a good seller because of their size. We had hardly put that servo to bed when I received a phone call from the Orbit representative asking me to meet him at the airport as he had something very interesting to show me. I can still remember the stunned feeling when I saw what he had to offer – a new servo, half the size of the PS-3. How was I going to fit an amplifier into that? Luckily, in the other hand he had the answer – an in-house IC they had commissioned especially for this servo. There was nothing on the market like it at the time and I was doubly stunned. We had no sooner put the PS-4 into production than the big IC shortage caused by the arrival of the calculator hit us. The IC-maker could not deliver those ICs for two years. I had just set up a new, larger premises and employed new staff to accommodate the increased production called for due to the popularity of the new servo. There was no other alternative than to fit a dis­crete amplifier. It looked impossible and it almost was. They were difficult to produce and cost me dearly. I learned bitter lessons about single source supply from that exercise. However to return to the modern servo and the servicing thereof. The modern servo in concept varies little from our old PS-2. The housing contains a servo motor and gear train, which in turn is coupled to a potentiometer and an amplifier. Error amplifier This photo shows a servo made by Silvertone Electronics. Note the double-deck PC board with the parts crammed in to save space for the motor & feedback pot. 72  Silicon Chip The amplifier is in essence an error cancelling system which will always seek to find the null. If the control stick on the transmitter is moved, then the servo will move until the error is cancelled and the servo is in null once again. The only difference between a servo on the throttle which is position­ able and the steering servo which selfneutralises is that it is hooked into a channel which does not have spring return on the control stick. In the good old days of tuned reeds, we had two Fig.2: the circuit diagram of a typical FM receiver. Note the provision of a tuning point to aid the alignment process. separate types of servo, positionable and self neutralising. From a statistical point of view, mechanical damage is by far the most significant issue, with electronic failures few and far between. Jammed or overloaded servos probably account for the bulk of the electronic problems but we cannot judge this accu­rately as mostly the model no longer exists or the servos have been removed for servicing. Servicing equipment in a model is a real pain as the equipment is usually jammed into all sorts of difficult to get at places or sealed into a waterproof housing. I really discourage people leaving the radio in the model partly because I do not want to run the risk of damaging some of those beautifully built and finished models. Whilst on the subject of jammed or overloaded servos, one problem area is the throttle linkage Bowden cable. Fuel seeps down this fine tube and with time the castor oil solidifies and creates considerable friction between the cable and the outer casing. It pays to remove the cable from time to time and clean it and the inside of the tube. I have seen throttle servos stall because of this problem. Another potentially serious area in regard to the throttle installation is the problem of over-travel jamming the throttle servo up against the carburettor stops. This means that the servo is stalled on and so its current drain zooms up to around 600mA. Batteries do not last long under these conditions. Servo motors and amplifiers do not take to kindly to this sort of treatment either. Modern transmitters have a very elaborate servo endpoint adjustment routine for this reason. Make sure you use it and use it carefully. If your transmitter is not fitted with this facility, then use some sort of mechanical over-travel device. These consist of a clutch or some sort of spring arrangement which will absorb the over-travel without stalling the servo. Here again the compres­sion of the springs will increase the servo current, depending on the spring tension. The best method is to use an adjustable servo arm and a lot of care. Likewise, all flying controls should move freely without friction. Any friction in this area will tend to degrade the servo centring accuracy and again push up servo current. I have had Fig.1: this exploded diagram shows all the parts used in a typical servo control. The key elements include the decoder PC board (21), the motor (17), a servo feedback pot (18, 19), various gears & the output wheel or arm (2, 3). Modern servos are built around dedicated IC servo chips (eg, the NE544 from Signetics) & are very compact & reliable. March 1994  73 REMOTE CONTROL – Servicing the servos instances where aging batteries and slowly increasing servo current, due to degradation of the control linkages, have come together to such an extent that flyers who routinely flew eight 15 minute flights used up the receiver battery on their seventh, or last, flight. And it really was their last flight, with that model at least. Visual inspection I usually begin the servo servicing with a visual inspec­tion of the gear train, looking for broken gears, dirt ingress, etc. One important point to watch for in some servos is that control surface flutter in flight can cause enormous stress on the servo gears and in some cases excessively wear the teeth or, in extreme cases, actually melt them. I also check that the output gear over-travel stops are not bent or broken and that the holes in the servo case which locate the gear axles are not worn oversize. Check the outside of the case for broken mounting lugs or cracked case sections and if available check the output arm for cracks or splits around the drive ferrule. The twisting forces and down very slightly. The feedback potentiometer is particularly prone to damage from engine vibration. This applies particularly to the throttle and rudder servos, which tend to sit in the same position for the entire flight. The vibration on the pot wiper eventually drills a little hole clean through the pot track into the substrate. At this point the servo tends to sit chattering to itself and chewing up servo current. Replace the pot if this happens. For this reason, it is a good idea to routinely move the servos around the various locations. This spreads the pot wear over the full arc. The flying controls are not as prone to vibra­tion damage, because they are moving constantly into new sectors on the arc. However, they do wear the track in time and pot inspection is most important during routine maintenance. Horizontally mounting the engine in the airframe is the best method to minimise vibration damage. Vertical mounting, either upright or inverted, tends to resonate the wing skins and in­creases the overall level of vibration in the model. The pot wipers “Another potentially serious area is the problem of jamming the throttle servo up against the carburettor stops. This means the servo is stalled on and its current drain zooms up to around 600mA”. in a crash often split the drive ferrule or strip the output gears. Next, check the amplifier lead and the connector for nicks or broken wires. This is a most common occurrence in a crash. Clean the connector with a toothbrush and CRC-226 and check for loose wires or connections. During servo servicing, always be on the lookout for damage caused by engine vibration. Servos are often screwed down so tightly on the grommets that engine vibration can destroy compon­ents under severe conditions. The correct method of mounting is to screw down the mounting screw until it just touches the top of the grommet and then back it off about half a turn. The servo should then move freely up 74  Silicon Chip also tend to resonate with this form of vibration. Horizontal mounting absorbs the vibration into the length of the wing spar and dampens the level considerably. The pot wipers in the fuselage are usually at right angles to this form of vibration, hence there is less wear on the pot track. Any care which is applied to the engine mounting in regards to vibration will pay dividends in longer radio life and reduced noise levels. The modern sealed pot used in most of the Japanese servos these days seems to be much better in this regard than the old removable pot in the earlier sets. If you do have a problem with the sealed pot there is little that can be done other than to replace it with a new one. If you have one of the older replaceable elements, mark the location of the pot in the housing so that it goes back into much the same location. Carefully loosen the two screws holding the element in place and completely remove one of them. The other can stay in place, for the element will now lift clear of the housing. Keep the servo inverted while removing the pot element, because there is often a little carbon brush on the tip of the pot wiper which falls out when you remove the element. If you lose this, you are up for a new wiper assem­bly. Once the element is clear of the housing, clean the track with a cloth and inspect for holes or worn sections in the tracks. The pot wipers tend to wear a track through the resist and this shows up quite clearly under a magnifying glass. Once satisfied that the track is clean and in good condition, wipe a very light smear of Vaseline over it. Clean and re-tension the wiper and reinstall the pot element into the hous­ing. Make sure the marks on the element and the housing line up. If you have made a mistake here the servo may slam up against the end stops and strip the gears. Nip up the two screws so that the element can be moved. Now making sure that nothing is shorting to the servo amplifier, switch on the radio with the servo plug in and check the neutral. If it is out, move the pot element until the servo is in neutral and tighten the two screws. Some servos are fitted with a screwdriver adjustment for the pot, which is located at the bottom of the output arm locat­ing screw hole. If this is the case, then nip up both pot housing screws firmly and using a fine jewellers screwdriver, insert it into the hole in the output gear and adjust the neutral, again with the radio switched on. Inspect the amplifier for broken com­ponents and frayed wires. Often, wires get pinched between components during assembly and engine vibration can wear through the insulation in time. Spray CRC-226 onto the front and rear bearings of the servo motor and let them run free, out of the gear train, to allow the CRC to seep into the bearings. That’s it as far as the mech­anicals are concerned. Next month, we’ll deal SC with servicing the electricals. 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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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 VINTAGE RADIO By JOHN HILL Refurbishing a Trio 9R-59D communications receiver One of my more interesting jobs recently has been the refurbishment of an old valve Trio communications receiver which I obtained for just $100. Despite its age, the old Trio performs quite well. Some time ago, I bought a Trio 9R-59D communications re­ceiver from well known vintage radio collector, Peter Hughes. It’s good to buy things from people you know because, in this in­stance, a service manual had been passed on down the line from the original owner to Peter and then to me some eight months after I purchased the set. You generally don’t get that sort of service from your local junk shop or antique dealer. My radio collection consists entirely of domestic radio receivers with two exceptions: the Trio communications receiver and a military transmitter/ receiver, the latter an A510 wireless station of 1956 vintage. The army outfit doesn’t turn me on at all and will probably go to the first person who makes a reason­able offer. The communications receiver, on the other hand, is of much greater interest. The Trio is of Japanese manufac- The Trio 9R-59D communications receiver. This partic­ular unit is about 24 years old & although it looked a little unloved when first acquired, the set cleaned up rather well. 76  Silicon Chip ture, is approximately 24 years old, has eight valves and gives continuous frequency cover­age from 550kHz to 30MHz. Such a set can receive quite a wide range of transmissions. A few domestic receivers can also cover this frequency spectrum but they cannot handle SSB (single sideband) transmis­sions. To make sense out of these “Donald Duck” like sounds, a receiver needs a BFO (Beat Frequency Oscillator) and that is one essential refinement a communications receiver is equipp­ed with. Now anyone who knows anything about communications receivers will know that the set I bought is generally considered a budget outfit. The Trio was built to a price and there is no way it can be compared with some of the more up-market equipment of either today or 20 years ago. It is not, never was, never will be, and was never intended to be the pinnacle of technological develop­ment. However, at the time they were made, they were reasonably priced and the sets sold quite well. In fact, it reached a stage where there were enough of these receivers in use to warrant space in amateur radio magazines regarding various modifications that would help improve their performance. One such modification (the addition of a voltage regulator valve) had already been done to my outfit before I bought it. I have photocopies of other suggested improvements but I will leave things as they are. There are a few grey areas regard­ing the Trio’s circuitry and to tinker with things that one knows nothing about is inviting disaster. These so called “grey areas” are items such as the mechanical IF filters and the product or “pro” detector which aids clear SSB reception. The alignment aspect of the receiver is also a bit humbling as there are nine coil slugs, eight trimmers and a padder. One really needs to know what to do otherwise the whole set can be easily detuned. But more about alignment later on. A top view of the chassis layout. Note that most of the valve cir­cuitry is built onto two printed circuit boards. Main features If one has never owned a communications receiver before, the Trio doesn’t seem a bad outfit. When there is nothing else to compare it with, the Trio is an impressive box of tricks that has many features not found on domestic receivers. These extras include: two volume controls (RF gain and AF gain), an S meter to indicate signal strength, an aerial trimmer, a band spread tuning capacitor, and the previously mentioned BFO. In addition, there is a band selector and a function switch, plus a headphone jack for personal listening. Now that’s a lot more knobs and gadgets to play around with than most The bandspread tuning capacitor takes the worry out of fine tuning. receivers have to offer! At the back of the receiver there is a control to zero the S meter needle, aerial and earth connections, and three terminals for a loudspeaker connec- tion (either 4-ohm or 8-ohm). I did a little modification of my own here and fitted a 3.5mm mono socket so as to accommodate the plug on my wall speaker lead. March 1994  77 This under-chassis view shows the various alignment components – no less than nine slugs, eight trimmers & a padder. The fac­tory alignment instructions (in the manual) are essential for aligning the receiver correctly. There is another of my modifications on the back panel. The sound reproduction was so harsh I fitted a “top-cut” switch to make the set a little more listenable. It’s just a small capaci­tor across the primary of the output transformer and this reduces the high-frequency response enough to remove the original harsh­ness. Repairs The Trio was fairly dusty when I bought it and had the appearance of being unloved for quite some time. This was soon remedied by a good clean up and all the painted surfaces were given the treatment with automo- tive cut and polish compound. The set came up looking like new. Very little was needed in the way of repairs. The Trio is a relatively modern set and is built mainly on PC boards using small modern components. The usual “replace all the paper capaci­ tors” routine seemed unnecessary even though there were a couple of paper capacitors underneath the chassis. The high voltage electro­ lytics checked out OK and were left in place too. Even the valves tested OK with the exception of the 6AQ5 output valve. This is not surprising because most used 6AQ5s test poorly and they seem to have a relatively short life compared to many other valves. A near new 6AQ5 was installed so as to keep the valve complement up to scratch. Incidentally, there is no rectifier valve in this particular radio receiver. The silicon power diodes used in the high tension supply are original equipment. One part of the set that did need attention was the dial stringing. The Trio has two dials and two tuning controls. One is for general tuning, while the other is for bandspread tuning. Both dial cords were quite tatty looking and were replaced. The band­spread dial cord is driven by a very small diameter shaft which seems to fray the cord much faster than a larger diameter shaft. Alignment At this stage, it was tryout time and I must confess that I was a little disappointed with the set’s performance. It could only be described as “mediocre” and gave the impression that the set was out of alignment. An 8-valve set should perform much better! However, at that stage I had no alignment instructions and that formidable array of coil slugs and trimmers was a frighten­ing sight. Unless one is really familiar with the set, these controls are best left alone. It’s not hard to completely detune a receiver when you don’t know what you are doing. One thing that was noticeable was a slight double peak on the S meter. The meter, which is connected into the IF circuit, showed two peaks when Many of the parts in the old Trio are mounted on one of two PC boards. Not many valve receivers were built as neatly as this one. 78  Silicon Chip A “top-cut” control was added to reduce harshness in the audio output. It uses a switch to connect a capacitor across the prim­ary of the output transformer. This small variable capacitor adjusts the BFO so that CW (Morse code) & SSB transmissions can be properly received. The rear panel carries output screw terminals for 4-ohm & 8-ohm loud­ speakers. The 3.5mm mono socket below these terminals allows the use of a plug-in wall-mounted speaker. This close-up view shows the tuning controls. The large knob in the centre provides the main tuning, while the smaller concen­tric knob provides bandspread tuning. The control shafts are connected to their respective tuning capacitors by dial cords. tuning across a station. This is a fair indication of misalignment problems and a thorough tune-up was definitely in order. Fortunately, the instruction manual sent by Peter Hughes arrived just at the right time. It contained full details on how to align the receiver using a radio frequency generator – just the information I was seeking. The alignment procedures were quite detailed and involved no less than 16 individual steps. These steps need to be complet­ed carefully if the alignment is to be accurate. When injecting the generator signal into the set via the aerial and earth termi­nals, a 400Ω resistor is bridged across the terminals. In order to obtain really accurate frequencies, a small modern receiver with a digital readout dial was used to calibrate the RF generator. Although my Heathkit RF generator is reasonably accurate, using a digital receiver to check the various alignment frequencies helped to keep the Trio’s dial calibrations spot on. This is often not the case with mechanical dials, particularly with an out-of-alignment receiver. Naturally, aligning the receiver in the correct manner made a big difference to the set’s performance and the improvement was quite noticeable. As a result of this, the old Trio is about as good as it is ever likely to be. After comparing the Trio with a couple of other communica­tions receivers (one old, one new), it seems to be a reasonable job for the price – especially the price that I paid for it. When connected to a good aerial and earth, it performs quite well and, no doubt, will keep me occupied for many hours in the future. One particular use I put the Trio to is listening to the regular Sunday night chat by a number of Historical Radio Society members who have amateur radio licenses. This radio net comes on air around 8.30pm EST on or around 3.575MHz. An interesting aspect of this Sunday evening session is that it was originally started by Peter Hughes (VK2­ MLG) and Phil Ireland (VK2GJF). It therefore seems appropriate that I listen in on one of Peter’s old receivers. Anyway, until I buy myself a modern communications receiver, the old Trio will SC have to do. March 1994  79 IC DATA Manufacturer’s data on the LM3876 audio amplifier IC Used in the 50W power module described elsewhere in this issue, the LM3876 is a high performance audio power amplifier with very low noise and distortion. It features SPiKeTM pro­tection circuitry and 100 watts peak output capability. By LEO SIMPSON The LM3876 is described as having an 11-pin TO-220 package although it does not look very similar to the familiar 3-lead TO-220 package as used for 3-terminal regulators. The LM3876 package is 20mm wide and has 11 leads which are cranked to in­crease their spacing. The metal tab is not isolated and connects to the negative supply rail for the IC. Fig.1 shows the package details. Maximum power dissipation is 125 watts. The LM3876 is capable of delivering 100W peak power into an 8-ohm load. In normal use, it will deliver around 50W into 4Ω or 8Ω loads. Some of the main features of the LM3876 IC include: • S/N ratio: 114dB A-weighted, with respect to 40W • • • • • • THD <0.06%, 20Hz to 20kHz <at> 40W IMD (SMPTE) <0.004% 84V maximum supply rail Input mute function Supply under-voltage protection Short circuit and over-voltage protection • 30mA quiescent current • Open loop gain typically 120dB • 120dB power supply rejection ratio National Semiconductor rate the LM3876 to deliver 40W into 8Ω but it delivers quite a bit more in practice. Hence, we have rated the amplifier module featured elsewhere in this issue at 50 watts. The LM3876 is one of a family of monolithic power amplifi­ ers from National Semiconductor. Others in the range are the LM3875 which is virtually identical to the LM3876, except that it lacks the audio mute Fig.1: physical dimensions & package outline of the LM3876T audio power amplifier. 80  Silicon Chip facility, and the LM2876 which can be regard­ed as a de-rated version of the LM3876. Fig.2: a typical audio power amplifier application circuit (dual supply rails). Single or dual supply? Although it is possible to run the device on a single supply rail, it does require extra circuitry compared with the dual supply circuit. The single supply circuit also has the input and output AC-coupled and is likely to produce a solid turn-on thump as the output coupling capacitor is charged. The LM3876 was really designed to be a dual rail amplifier and that is how we recommend its use. Fig.2 shows National Semiconductor’s suggested dual voltage amplifier circuit and this is very similar to the 50W audio module published elsewhere in this issue. Fig.3 shows the equivalent schematic of the LM3876, exclud­ing the active protection circuitry. This shows a more or less conventional power op amp circuit with quasi complementary output stage (ie, all NPN transistors). Note that there is no facility for adjusting the quiescent current as this is taken care of during the IC manufacture. Mute operation As noted above, the LM3876 has an inbuilt mute feature and as can be seen from Fig.3 this entails an NPN transistor with its base grounded and its emitter connected to pin 8 (the Mute pin) via two diodes and a 1kΩ resistor. For normal operation, pin 8 must be pulled to the negative supply rail and a minimum of 0.5mA must flow for the transistor to be correctly biased. In turn, the transistor controls the operation of a PNP differential pair which mutes the output when no current flows through pin 8. Fig.4 shows the relationship between the mute input current and the output reduction. The important thing to note is that the current through pin 8 needs to be at least 0.5mA to ensure that there is no attenuation in the output signal. This only becomes critical if supply rails are reduced from the normal ±35V down to, say, ±20V pass filter at 400Hz, we measured the total harmonic distortion at 1kHz to be 0.002% at 40W RMS output. SPiKeTM protection “SPiKe” stands for “Self Peak Instantaneous Temperature” (in degrees Kelvin) and is National Semi- conductor’s name for the protection system in the LM3876. In effect, the chip continually monitors its internal temperature and sets its safe area of operation accordingly. It can be likened to the mechanism whereby a 3-terminal regulator will reduce its output current delivery if its internal THD vs. output power Fig.5 shows the THD + noise vs output power for the device operating at 1kHz into an 8-ohm load. As you can see, from 0.5W and up, the THD+N is about 0.01%. This is measured with a band­width of 80kHz. Using a high Fig.3: equivalent schematic of the LM3876 audio power amplifier, excluding the active protection circuitry. March 1994  81 connections to the output stage transistors and protects against shorting the output to ground (0V) or the supply lines. The output current is initially limited to about 6A peak until the thermal protec­tion cuts in. Thermal protection Fig.4: mute current (mA) vs. output muting (dB). Fig.5: total harmonic distortion plus noise (THD + N) vs. output power. The THD + N is generally around .01%. temperature becomes excessive. However, SPiKeTM is more comprehensive than that. Fig.6 shows a simplified schematic of the LM3876 with the SPiKeTM features de­picted. It incorporates current limiting and over voltage protec­tion. The current limiting works via second emitter Not depicted in the schematic of Fig.6, the LM3876’s ther­mal protection shuts down the device when the temperature on the die reaches 165°C. When the die temperature drops below 155°C, the device starts operating again but if the temperature again rises, shutdown will occur at 165°C. Therefore the device will heat up rapidly if a short circuit occurs and then will cycle on and off until the fault is removed. As far as we can determine from the literature supplied on these devices, the thermal protection limit of 165°C applies only when heavy currents are being delivered. SPiKeTM protection, on the other hand, works to a temperature limit of 250°C which is 100°C higher than the nominal maximum junction operating temperature for this device or for any plastic encapsulated semiconductor. Conventional monolithic power amplifier ICs provide their SOA (safe operating area) protection by monitoring the voltage and current conditions in the output stage and limiting the signal drive before the SOA conditions are exceeded. This pro­tects the device but it often severely limits the power which can be delivered and no account is taken of the device’s operating temperature. The SPiKeTM protection circuit, by contrast, senses the temperature of the output transistors and operates as the temper­ature reaches 250°C. Depending on the transistor tempera­ture, the safe operating area is reduced for all pulse widths as the case temperature rises. The graphs of Figs. 7, 8 & 9 show the progressive reduction of SOA for case temperatures of 25°C, 75°C and 125°C. Hence, by dynamically varying the SOA, the LM3876 is able to deliver a peak power output of as much as 100 watts – not bad for a device with a maximum power dissipation of 125 watts. Importantly, to get the maximum power out of the LM3876, you must not skimp on the heatsink. If you use a skimpy heatsink, you’ll get skimpy power output. Over voltage protection The over voltage protection circuitry protects the LM3876 against voltage spikes which can be developed at the output when driving inductive loads. These spikes can far exceed the voltage ratings unless they are clamped. In conventional amplifiers, this is done by clamping diodes to the supply rails from the output but in the LM3876 this function is Fig.6: equivalent schematic diagram of the LM3876 amplifier with simplified SPiKeTM protection circuitry. 82  Silicon Chip FIG.7 FIG.8 FIG.9 These graphs show the progressive reduction of SOA for case temperatures of 25°C, 75°C & 125°C. By dynamically varying the SOA, the LM3876 is able to deliver a peak power output of as much as 100 watts. performed by the output transistors themselves, these being turned on to limit the voltage. In this mode, they can sink 6A peak. Under voltage protection Also depicted on the diagram of Fig.6 is under voltage protection although we regard this as a misnomer. It should be called “under voltage shutdown”. The device is not actually protected against low voltages (nor could they damage it) but the output stages are biased off for supply voltages of less than ±9V. This prevents any turn on or turn off thumps for the speakers which are usually the result of a power amplifier losing control of the output stage when the supply voltage is very low. This under voltage protection feature should not be confused with the pin 8 muting feature described above. For best results, the external muting is operated with a capacitor at pin 8 and this adds to the internal muting effect. PC board layout is critical to achieve the very good per­formance available from the LM3876. Keeping the output and input ground returns separated is essential and the use of “star earth­ing” SC is strongly advised. March 1994  83 Silicon Chip lator; Service Tips For Your VCR; Speed­ing Up Your PC; Phone Patch For Radio Amateurs; Active Antenna Kit; Speed Controller For Ceiling Fans; Designing UHF Transmitter Stages. 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. 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. 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). 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. 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. 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. 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. 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. 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. January 1990: High Quality Sine/Square Oscil- October 1990: Low-Cost Siren For Burglar 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. 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. 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 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. 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. 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. 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. 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. 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. 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 Volt- age 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. 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. March 1994  85 PRODUCT SHOWCASE VGA to PAL converter for education There are many applications in busi­ ness and educational presentations when a large screen display is invalu­able but there is a limit to the size of VGA screens and their cost rises exponentially as size increases. However, large PAL monitors are relatively cheap and available and if they can be pressed into service to enable a large number of people to watch a compu­ter screen, so much the better. This device from Avico makes it happen. Basically, the Videomaster PV-640 is a small plastic box powered by a plugpack DC power supply (not included) with VGA and S-VHS inputs and with composite video, PAL and VGA outputs. Essentially, you plug in the VGA cable from your computer and your existing VGA monitor then plugs into the VGA converter output. Then you either use the composite video output or the PAL modulated RF Bass loudspeakers for cars Kenwood has announced four woofers ranging from 152mm (6-inch) to 304mm (12-inch) and with power handling capacity from 150W to 450W peak. The new woofers employ heavy-duty strontium ferrite magnets, large voice coils and triple spiders made of polyamide elastomer. All four have moulded polypropylene cones with concave centre caps. All models have gold plated ter­ minals which can accept banana plugs or large gauge speaker ca­bles. The ratings are as follows: KFC-W1600, 152mm, 150W peak from 30Hz to 7kHz; KFC-W2001, 203mm, 300W peak from 20Hz to 6kHz; KFC-W2500, 254mm, 360W peak from 18Hz to 3.5kHz; and 86  Silicon Chip KFC-W3000, 304mm, 450W peak from 18Hz to 4kHz. The new line-up is covered by a 12-month parts and labour warranty and is available at selected Kenwood car audio dealers. For further information on your near­est car audio dealer, phone Ken­wood on (008) 066 190. signal to connect to your large screen monitor. This allows you to use your VGA monitor and the large screen display simultaneously. Systems supported include Notebook PCs with 640 x 480 pixels in 256 colours, 640 x 480 pixels in 16 col­ours and 320 x 200 pixels in 256 col­ours (most games). One other very useful facility provided by the Videomaster converter, by virtue of its composite PAL video output, is that it enables computer displays to be taped via your video recorder. The unit is supplied with a VGA cable, S-VHS video cables, an RCA to RCA cable for composite video or modulator signals and a disc of utility software. Voted the Byte magazine "Best of Taipei Computer Show – June 1992", this is a very useful accessory which is bound to find wide applications. For further information on price and availability, contact the Australian distributor, Avico Electronics Pty Ltd, Unit 4/163 Prospect Highway, Seven Hills 2147 Phone (02) 624 7977. New scanner from AOR AOR Ltd of Japan has released an updated version of their most popular scanner, designated the AR-3000A. It offers reception over the enormous range of 100kHz to 2036MHz, with no gaps. Listening modes available over the whole range are NFM & WFM (narrow & wideband FM), SSB upper & lower sidebands, AM and CW Tuning rates are selectable from an ultra-fine 50Hz per step for SSB and CW reception up to 999.95kHz for the TV & VHF broadcast bands. Up and down tuning can be via the up and down buttons or via the rotary tuning knob, the latter being most conven­ient for resolving SSB transmissions. Good selectivity is ensured by the use of 15 bandpass filters before the GaAsFET RF amplifiers. An RS-232C port is provided for computer control of parameters such as frequency, receiver mode, frequency steps, writing to and from memory, signal strength, RF attenuator and memory bank changeover. A rear panel switch changes control from the keypad to the RS-232C port. 400 memory channels are provided, in four banks of 100. Each memory channel will store the mode, frequency, RF attenuator setting and lockout status. Scanning and search rate is very high at 50 channels/second and 50 steps/second respectively. The large backlit liquid crystal dis­ p lay gives a large amount of informa­tion such as frequency, signal strength, memory channel and so on. All func­tions are under the control of a micro­processor which has a lithium backup battery. For further information con­tact Emona Electronics, 92-94 Went­worth Ave, Sydney 2000. Phone (02) 211 0988. Stereo hifi VCR has "intelligent" HQ Most VHS VCRs these days have at least some feature of the HQ video enhancement system but this new stereo hifi machine from Akai fea­tures "intelligent" HQ. Designated the Akai VS-G60 Virtuoso, the machine takes about 15 seconds to optimise recording and playback from an in­serted tape and then it remains with that setting until the tape is ejected. Another feature of the VS-G60 is on-screen programming in up to nine languages via a menu system. A convenient shuttle ring on the remote control offers such features as high speed reverse review, still, slow, play, cue and high speed cue – in fact a total of 13 speeds in both SP (standard play) and LP (long play) modes. Pic­ ture flicker is minimal due to Akai's dual mode digital tracking system. The VS-G60 has a recommended retail price of $799 and is covered by a 12-month parts and labour warranty. For further information and the name of your nearest dealer, contact Akai on (02) 763 6300. March 1994  87 Test set for radio communications AWA Distribution has released a compact but highly specified test transceiver made by Schmonandl of Germany. The MES1000 is a menu-driven test set suitable for all types of radio communication equipment. Measurements such as adjacent channel power and har­ monics are possible, together with simultaneous frequency and power measurement at run-in, decay and at channel changes of the equip­ment under test. AM, FM and call­ing systems such as a sub audio, double tone and sel-call are all sup­ported. All basic parameters of the sig­nal generator such as type of modulation, modulation source and out­put level can be stored in non­volatile memory. Numerous meas­ urements can be performed such as distortion, SINAD and signal-to­-noise ratio. Tunable filters are in­cluded and the audio signals can be displayed via a built-in digital scope on the front panel, regardless of whether they are external or demodulated. Optional Centron­ ics and GPIB interfaces are avail­able. For further information contact AWA Distribution, 112-118 Talavera Rd, North Ryde, 2113. Phone (02) 888 9000. New cassettes from TDK TDK has introduced a new Normal Position audio cassette tape line-up, which comprises D (Dynamic), AD (Acoustic Dynamic) and AR (Acoustic Response). All are available in various playing times and the cassette mechanisms have been improved. The new D range has improved MOL (Maximum Output Level) by 3.5dB and has a lower bias noise (-55dB) than previous D formulations. The new AD has improved MOL of +5.5dB in the low frequency range (315Hz) and +4.5dB in the higher frequencies (10kHz). 88  Silicon Chip Finally, the new AR's MOL is +6.5dB (ref 315Hz), putting it on a par with metal tapes. For your nearest TDK dealer, ring (02) 437 5100. Low cost scope card The Compuscope Lite is a high speed data acquisition card for the PC-XT/AT for capture and storage of analog data. Two channels are provided at 8 bits resolution, capable of 40 megasamples/second on channel A or 20 megasamples/second with both channels in use, with 7MHz bandwidth. Trigger source can be via channel A or B, external or from keyboard with capability for post, mid or pre-triggering on positive or negative slopes. A test square wave output sig­nal of 900mV at around 100kHz is also provided. The supplied software can deliver the data to printer or disc, in binary or ASCII format, with communication possible via modem, Ethernet, token ring or other networks. Software modules are available for mathematical analysis of data and driver software is available for most popular compilers. For more information on the Compuscope Lite, contact Boston Technology Pty Ltd, PO Box 1750, North Syd­ney 2059. Adjustable zener consumes just 35µA The Zetex ZR341 is an adjustable zener diode with a low current consumption of 35µA (typical). This product can serve as a regulator, a voltage monitor or a voltage protection de­ vice. Two external divider resistors enable programming of the output voltage over the range from 2.5V to 20V The low power consumption makes it suitable for battery powered computers and telecommunications equipment. The ZR431 is available in surface mount SOT-223 or TO-92 packages. Operating temperature range is from -40°C to +85°C and temperature stability is 50ppm/°C. For further information about Zetex products, contact GEC Electronics Division, Unit 1, 38 South St, Rydalmere 2116. Phone (02) 638 1798. Encapsulant for electrical protection Safety, ease and speed of use are among the features claimed for an Australian-made electrical repair kit called Epirez 324A. The epoxy-based maintenance system enables encapsulation and protection of electric motor coils and windings. as high as 150°C. Dielectric strength is 315kV/cm while volume resistivity is 1016Wcm. Since it is solventless, Epirez 324A is not unpleasant or hazardous to han­ dle. Marked measuring cups, included in the kit, make the material almost foolproof to use and it is easy to apply. Work time is 30 minutes at 25°C. No baking is needed to effect curing after application which makes for fast turnaround of work. Epirez 324A comes in a 2kg kit and an 18kg bulk pack, with full instructions on its use. More information on the product is available from Epirez Construction Products, 2 Seville St, Villawood 2163. Phone (02) 726 8899. It also provides a dependable moisture seal for splicing or blocking plastic encapsulated cables. When cured, typically within 24 hours at 25°C, the product displays excellent electrical properties at temperatures Stepper motors for experimenters Those who are interested in the ar­ticle "Control Stepper Motors with your PC", as featured in the January 1994 issue, may be wondering where they can obtain suitable stepper motors. Wonder no more. Oatley Elec­tronics have two suitable models which can get you up and running. Model number one is a 2-phase type having six wires, a diameter of 58mm and 7.5° steps. Model number two has four wires, a diameter of 56mm and 1.8° steps. Model number one is $12 while model number two is $20. These are good prices. You can purchase them from Oatley Electronics, 5 Lansdowne Parade, Oatley 2223. Phone (02) 579 4985 or fax (02) 570 7910. T-Tech Quick Circuit for PCB prototypes Designers who frequently require PC board prototypes will be interested in this new computer driven milling and drilling machine. About the size of an average plotter, this machine actually func­tions like a plotter except that in­stead of carrying a pen in the move­able head, it carries a high speed mill or drilling head. To use it, you place a sheet of copper laminate on the bed, locating it precisely with steel pins. The machine then proceeds to mill out the circuit pattern on the board so that in under an hour for a typi­cal PC board you have a prototype. In essence, the process is as fol­lows. First you design your PC art­ work using any current CAD pack­age. The Gerber or Excellon plot is then converted to create the drill­ing and milling data. In effect, the Quick Circuit milling table has to mill around each track of the art­work so that it is isolated from the surrounding copper. Once the conversion data has been prepared and the copper lami­nated pinned on the bed, the machine first does all the drilling and then the milling. Finally, the board is routed to size and any complex shape can be produced. The major difference between the resulting prototype and a con­ ventional etched PC board is that most of the copper remains on the laminate. Naturally, the process can be applied to any single or double layer PC board, using conventional or surface mount com­ponents. The Quick Circuit can also be used for engraving nameplates and signs and as an NC drilling ma­chine. For further information, contact the Australian distributor, Satcam, Unit 13a, Woodbury Industrial Es­tate, 274-316 Victoria Rd, Rydal­mere 2116. Phone (02) 684 1877. March 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. Frequency counter display problem I recently purchased a kit for the 1GHz frequency counter described in November & December 1987 and January 1988 issues of SILICON CHIP. On switching on, the display lights up as expected, however the test LED does not light up (I checked for correct mounting of the LED) and does not respond to any adjust­ment of VR1. The display shows 000kHz as expected, however the first digit is not completely lit up – (it appears as a letter “L” in reverse). As the unit counts this error is carried on through the whole range of digits, showing it is not a faulty connection on an individual display. I suspect a faulty IC and would welcome your advice to allow me to finish this project. I have also just had given to me a frequency generator and I wonder if you can help me to operate it. The details are: Signal Corps, Frequency Meter, BC-221-AH, 125 to 20.000 Kilocycles. Nicad discharger gets tired I have a problem with my nicad discharger built to the design in your July 1992 issue. It works well on all but the 6V range where it gets “tired”. While toggle voltages on all other ranges are exactly to spec, on the 6V range the discharger will not switch cleanly to indicate end of discharge. At considerably less than 5.5V, the “discharge” LED gradually fades out and the “complete” LED barely lights. On increasing the voltage again, on a power supply, even as high as 12V, the IC will not reset as it does on all other ranges. I have noticed that (at 5.5V) touching pin 1 of IC1 does trigger the circuit and a second touch resets it. I am satisfied that everything is 90  Silicon Chip 3082:CZR 34542 Phia.43. It is beautifully made and appears to be complete although without a power supply. Evidently it originally plugged into another unit. If I can get it operational it will be invaluable to me in my home-brewing. (E. Cook, 13 McLachlan Drive, Bunda­berg, Qld). • The test LED in your frequency counter may not be lighting up since the voltage at the output of your particular ECL Schmitt trigger (IC2a) does not always go low enough to turn on a LED. Try a few other LEDs to see if these work. Some red LEDs require up to 1.9V across them in order to light while others only need 1.5V. If you have a multimeter which has a diode test and can light LEDs, you can select the lowest turn-on voltage LED. As an alternative, you can dispense with the LED and use your multimet­er to check the change in output voltage of this Schmitt trigger. The low voltage should be about 3.4V while the high voltage should be about 4.3V. Note that you will need to use a as per design and the 2.5V reference remains constant. Have you had any similar problems reported to you or do you have any ideas. What have I missed? I have tried three different ICs with no joy. My main use of the unit is with camcorder batteries and the 6V range is the most important, therefore help! (N. D., Burnie, Tas). • It is true that the discharger switches less cleanly at 6V. However, we have not heard of anyone finding that the circuit does not reset back if the voltage is increased. To eliminate the overlap between the “Complete” and “Discharge” LEDs, disconnect pin 5 of IC1 from pin 3 and connect it instead to pin 1 (ie, pin 5 now goes to pin 1). To improve the resetting, try increasing the 820kΩ resistor to 1.2MΩ. short lead 100kΩ resistor connected to the end of your multimeter probe to prevent the Schmitt trigger oscillating. This is outlined in the trou­bleshooting panel on page 53 of the January 1988 issue. Concerning the backward “L” on the first digit of the display, while the 7216A IC may be faulty, we suggest you investigate all other avenues first before replacing it. Firstly, if the IC is in a socket, solder it directly into the board. Secondly, ensure that pins 13, 18 and 24 are connected to the 5V supply and that pins 27, 1 and 8 are at ground. The frequency generator that you have just acquired is a classic from the past but we don’t have any information on it. Possibly one of our readers may be able to help you with a circuit. Solid state message recorder Congratulations! I have just finished building the simple solid state message recorder described in SILICON CHIP, July 1993. It works perfectly and the reproduction quality is far better than any of your previous designs, despite the simplicity. However, I’d very much like to take it a bit further. In the accompanying text you refer to the chip’s message addressing facility but frustratingly only show a whole row of intriguing looking address lines going nowhere. My curiosity is aroused! I wonder if you would consider publishing some “add-ons” to demonstrate what else this wonderful chip can do. Failing that, perhaps you could just list the functions of A0 - A7 and how they may be accessed. Or maybe you could publish the manufacturer’s data sheets on the ISD1016AP? Or maybe, if it’s not asking too much, all of the above. (S. H., Werribee, Vic). • The ISD1016AP chip is quite a versatile unit when it comes to solid-state recording. However, making use of the extra features re­quires quite a bit more circuitry. The address pins are only inputs, not outputs, which means that you cannot digitally detect whereabouts in the EPROM the device is up to. Putting it briefly, the ISD1016’s EPROM is divided up into 160 sections, each 0.1 seconds long. By setting the 8-bit address pins, you can start recording or playback from any one of these 160 locations. But it isn’t possible to go from one location to another – you can only start from a location and then continue on. When you stop recording, the 1016 inserts an end-of-message (EOM) bit and this signifies when the device should stop. Unfor­tunately, it would take a complete issue of the magazine to publish the data sheets on this device, but you can contact R & D Electronics on (03) 558 0444 for more details. Radfax decoder not functioning I recently had the Radfax kit (featured in the November 1989 issue of SILICON CHIP) constructed and hooked it up to my computer, with the matching software, but no fax maps have been printed. My SSB shortwave receiver seems to pick up a good signal but the red LED light on the decoder does not come on, suggesting that the signal from the radio is not being processed. I have followed the instructions in the reference manual with regards to the different settings, but there is no dif­ference. On the screen, all I obtain is a blank or wavey lines. Disconnecting the output from the decoder makes no difference. The line from the receiver to the decoder is a coax lead about 40cm long, with 3.5mm plugs and connections (the manual advises 6.5mm). Could you advise me on possible solutions? (K. M., Cowra, NSW). • There are several points to watch in getting the Radfax decoder up and running. First, keep the shortwave receiver well away from your computer. It radiates a lot of noise which can desensitise the receiver. Second, the fact that the red LED is on does not indicate that you are getting a reliable signal. You still need to adjust the BFO for optimum reception and then experiment with the settings until a picture is received. Note also that the fax transmissions Running a lure at variable speed Have you ever considered a construction project along simi­lar lines to the “Jumbo Clock” in the November 1993 issue but a “Jumbo Digital Stop Watch”? I know that you can pick up a hand­held stop watch from Tandy or Dick Smith for around $10 or so, but there must be numerous instances where a large scale stop watch using 70mm displays would be useful to a large number of sporting clubs. Maybe you might consider a project along these lines please? I have left the best until last. What are the problems associated with having a variable speed AC motor of approximately 1½ horsepower? Let me explain how I wish to use this motor so that you may better understand my problem. The motor is to be used by a dog club as a means of running a lure which the dogs chase (this lure is something similar to the “bunny” at a greyhound track, except that the load on the motor is not the bunny pulled by a steel cable, but a piece of plastic or fur. This is pulled around an irregular course by means of approximately 500 metres of nylon string and fixed pulleys which are “nailed” into the ground and act as corners for the course). As some breeds of dogs are are not continuous and you need to wait for the start of each transmission. Finally, it is generally futile trying to receive your first transmissions during the day – the best reception is at night. Confusion on the Jumbo Clock The Jumbo Clock in the November 1993 issue of SILICON CHIP appeals to me but before purchasing a kit, I like to familiarise myself with the theory of operation. And here is my problem. I seem to have missed out somewhere as I eventually come to a blank wall when going through the explanation of the circuit diagram. I’m OK as far as the operation of capable of obtaining speeds of up to 55km/h, the need for a variable speed motor is essential. This is because the lure has to be at a certain distance from the dogs at all times and because all dogs don’t run at the same speed. I would probably be looking at a 1-1½ horsepower single phase motor. Could you please advise what options are available to our club. (G. W., Wishart, Qld) • We are not sure that there would be much interest in a large readout stopwatch but will see what readers think. With regard to your question on speed control, it is not possible to control the speed of an induction motor over a wide range unless you use a variable frequency AC supply. For a motor rated at 1.5 horsepow­ er, this would be very expensive. However, universal AC motors (brush type), as used in most appliances and power tools, can be controlled over a wide range and we would suggest you look at the Drill Speed Controller published in the September 1992 (amended November 1992) issue of SILICON CHIP. This project is available in kit form from Altron­ics, Jaycar and Dick Smith Electronics and could be used to control motors up to about 1 horsepower rating. With suitable pulleys or gearing, you should be able to find a motor to suit your purpose. IC5 & IC6 is concerned. My trouble is with IC7 & IC8a. The last sentence on page 17 of the article states “finally, the CO output from counter 3 clocks a latch when the count of 10 hours is reached”. Discussing this point in more detail on page 19, the last paragraph states that “IC8a is clocked by the CO output of IC7. When IC7 reaches a count of 10 its CO output goes high and Q-bar of IC8a goes low thus turning on Q2 and ..” Now here is my problem. “Two out” or pin 14 of IC7, accord­ing to SILICON CHIP and data books, is high for all counts except for count 2. This is applied to R of IC8a which overrides the clocked input. Under these circumstances I can’t see that Q of IC8a goes high and Q-bar goes low. (This point March 1994  91 Boosting the SLA battery charger Is it possible to specify alterations to your August 1992 SLA battery charger to permit efficient charging of 6V 140 amp-hour batteries. I am planning to use a bank of eight of these batteries as the core of a remote area power supply. (R. S., Albert Park, Vic). • In June 1990, on page 101, we published two higher powered versions of the of the previous SLA battery charger, as featured in of the R input overriding the clocked pulses is admitted in paragraph 2 on page 20 of the article). In passing, my data book says CO of IC7 is high for counts 0 to 4 and low for counts 5 to 9. Pin 14 is low for the dura­tion of count 2 and high for all other counts. I do hope you will put me right as I do want this clock, due to my eyesight being so poor at night. (R. C., Beech­ boro, WA). • You are to be commended on your circuit theory! You are quite right. There is an error on the circuit diagram. The RESET input at pin 4 of IC8a should have been connected to the RESET input on pin 15 of IC7, not pin 14. As you point out, the circuit can’t possibly work the way it has been drawn – you were the first to spot it. The PC board is correct, as is the overlay wiring diagram. With pin 4 of IC8a connected to pin 15 of IC7 and the Q output at pin 1 of IC9a, the RESET input at pin 4 of IC8a is low most of the time, and only goes high when the rising edge appears at the 2OUT output at pin 14. This only occurs when a ‘2’ is displayed via IC7 and Q-bar (pin 2 of IC8a) is low; ie, the 10-hours display shows a ‘1’. This Q-bar output is also connected to the RESET input at pin 4 of IC9a. If the time is ‘2:59’, Q-bar at pin 4 of IC8a is high, which pulls the RESET input at pin 4 of IC9a high, prevent­ing it from being clocked. The reason for this is that otherwise, we would go from ‘2:59’ back to ‘1:00’. However, if the time is 12:59, the Q-bar at pin 2 of IC8a is low and so too is the RESET at pin 4 of IC9a which 92  Silicon Chip means that IC9a can now be clocked when it receives the next rising edge from pin 14 of IC7. When IC9a is clocked, the Q output at pin 1 goes high, pulling up pin 15 of IC7 and pin 4 of IC8a. This switches off the 10-hours display and the remaining circuitry works to change the hours through from ‘12’ to ‘0’ and then ‘1’ as in the time change from ‘12:59’ to ‘1:00’. We hope that this clears up the confusion. produce a range of special cables for these requirements. However, the idea of a one Farad capacitor to help the battery along is a bit far-fetched in our opinion. First of all, we cannot imagine any electrolytic capacitor having a lower impedance than the average car battery; in fact, the impedance of the battery connecting cables will usually be higher than the battery itself which will be measured in milliohms. Second, all high-power amplifiers use inverters to step up the battery supply to, say, ±50V DC or more. So ultimately, it is the impedance of the inverters that determines the supply impedance to the amplifiers and this is likely to be substantial­ly higher than the impedance of the battery supply, including the cables. Third, the impedance of the supply lines to a power ampli­fier rarely has much bearing on the overall performance of the amplifier, including its transient performance, except when the signals are such that the amplifier is being pushed close to or beyond clipping. So you should forget about big capacitors and spend your money on good cabling and perhaps a second battery. Monster capacitor for cars Cockroft-Walton voltage multipliers I’ve seen some literature recently that suggests you can improve the reproduction of high-power car sound systems by fitting a “Monster Cap” (a one Farad capacitor) across the battery supply to the power amplifiers. The idea is that the car’s bat­tery cannot supply the instantaneous surges demanded by the car amplifiers and the Monster Cap has a very low impedance and can therefore deliver the wanted “herbs”. Is there anything in this idea or is it all based on marketing hype? (A. J., Ingleside, NSW). • We have seen the product literature you refer to and it is available from the same people who distribute Monster Cable in Australia, Convoy International Pty Ltd, phone (02) 698 7300. Big sound systems do place quite a lot of demand on the car’s elec­trical system and in some cases it is necessary to upgrade the alternator as well as install a second battery. Heavy duty cables for both the battery supply lines and speaker connections are desirable for best performance and Monster Cable How do I determine the necessary values and voltage ratings of capacitors in a Cockroft-Walton voltage multiplier circuit? I intend to alter a “bug zapper” design so that I can use the voltage multiplier in place of a 2.5kV (or 5kV) <at> 20mA high voltage transformer. The multiplier circuit would be cheaper than the transformer. It is also my desired preference. Does the capacitor voltage rating have to only be greater than the input voltage (240V AC); eg, can I use 350V or 630V polyester capacitors? It surely can’t be close to peak output voltage. What is the minimum voltage rating acceptable? How do I control the amount of energy discharged? This must be linked to the capacitor values (as E(Joules) = 0.5CV2) but which ones? Is it only the first capacitor at the AC input, or all of them? Or do I have to put a 5kV capacitor (expensive!) across the output. And why do they use 1nF-10nF in most circuits? Are there any safety considerations with this setup? March 1990. These boosted circuits would be valid with the circuit published in August 1992 but charging 140 amp-hour bat­teries is a “big ask”. For optimum charging time, you need to charge them at around 30 amps and therefore eight to 10 power transistors, mounted on a large heatsink, would be required. If you wanted to charge eight of these batteries in paral­lel you would need a supply capable of 200A or more, which is really not practical for this circuit. Fig.1: a typical CockroftWalton voltage multiplier. Cn out polycarbonates. Thus, the minimum capacitors that are really practical are probably 0.01µF at 1kV. Any high voltage power supply must be regarded as lethal and one that runs directly from the mains carries a double wham­my. 2Vm 2Vm Cn-1 Cn-2 Cn-3 RL Tone controls for guitar amplifier C4 2Vm RS v s = VmS I N  t C1 C3 C2 2Vm Vm Incidentally, I am using 1N4007 diodes (PIV 1kV) for the rest of the circuit. (A. E., Preston, Vic). • As shown in the accompanying circuit, in a Cockroft-Walton multiplier, all capacitors with the exception of the input ca­pacitor should have voltage rating equal to twice the peak input voltage. If you were using 240VAC as the input, the capaci­tors would need a voltage rating in excess of 680V. The effective output capacitance of the circuit can be regarded as the capacitor value of each stage, divided by half the number of stages. For example, for a voltage quadrupler using 1µF capacitors, the output capacitance is equal to 0.5µF. The size of the capacitors used is related to the output regulation, the input frequency, the ripple amplitude, the input current limiting impedance and the surge current rating of the diodes. For a discharge application such as the one you are contemplating, the capacitors should also have adequate peak discharge current capability. We would caution against using a Cockroft-Walton multiplier running directly from the 240VAC mains supply unless you have quite a high input current limiting resistor of at least 10kΩ and with a voltage rating of 1kV AC or more. We would not use poly­ester capacitors at all for this job as their voltage and dis­charge current ratings are inadequate. You should either use polycarbonate or ceramic capacitors and since the required vol­tage rating for the capacitors is in excess of 680V, that rules I play the electric guitar and want to build an amplifier to suit my needs as commercial models just cost too much. After considering the many designs that are currently around, I purchased a kit for a 4-channel guitar mixer/preamplifier, as featured in January 1992, from Jaycar Electronics. After completing the project and mounting it in a 19-inch rack cabinet, I was more than pleased with the results. The unit turned out to be very quiet and sensitive, produc­ing good clean sound. However, I wonder if you can help me. The tone controls work very well with good adjustments with the bass and midrange controls but the treble control seems to have very little boost and cut; not enough for my liking. There is enough when you’re using the keyboard but not enough when you want that top edge sound to a guitar. Could you please tell me how to boost up the treble control to get a lot more out of it and whether the boost could be at 8kHz instead of 10kHz? Which components would I have to change and what value? I am also building my own speaker box to house the power amplifier and four 10-inch speakers to produce the sound. Could you please tell me what size the enclosure should be and whether it should be open-backed or fully closed. I intend to carpet it and fit speaker grilles over each speaker. Is the Jaycar 10-inch speaker (Cat CG-2376) a good choice? This speaker is rated at 65W RMS which would give me a total of 260 watts power handling, making it suitable for many of the high-powered amplifier designs around at the moment (fR = 68Hz; QMS = 2.56; QES = 1.00 and VAS = 37.72 litres). In the near future, have you any plans for a high power amplifier, with an average power output of around 200W into 8Ω loads that I could team up to your new 4-channel guitar amplifier mixer? Are Mosfets still available for power amplifier designs and if so where can I purchase them from? (K. S., Sellicks Beach, SA). • With regard to the 4-channel mixer, you can increase the amount of treble boost and cut by reducing the 6.8kW resistors on either side of the treble pot to 4.7kW. We caution against reduc­ing the values below 4.7kΩ, however. You can also change the crossover frequency of the treble control by increasing the .0015mF at the wiper to .0022mF, although there will then be increased interac­tion with the midrange control. We hesitate to recommend the use of four loudspeakers in an enclosure because of the dilemma concerning their connection since they are of 8Ω impedance. As far as the amplifier is con­cerned, you could connect them in a series parallel configuration to provide an 8Ω load but this is not ideal since each speaker is then in series with its neighbour. This means it will not “see” the low impedance of the amplifier and so its response will be undamped. Quite likely, it will be boomy. For overall performance, you would probably be better off considering the 12-inch 200W model CG-2381 from Jaycar. This will give a lighter and more compact enclosure and comparable power handling. Better still, go for two 12-inch 100W drivers in paral­lel to give a 4Ω load. This will give the best efficiency. Hitachi TO-3 Mosfets are still available from suppliers such as Jaycar Electronics and Altronics now has a line of TO-3 equivalents. We have had a Mosfet amplifier under development, using eight plastic Mosfets in TO-3P packages to deliver a genuine 200 watts into 8Ω or 300 watts into 4Ω. We have tried several types, including the new Hitachi 2SK1058 and 2SJ162 plastic Mosfets. With these latter types we have found an intractable problem with instability at frequencies around 90MHz. Apparently, this is caused by having the Mosfet source connected to the metal tab. Other complementary types, with the drain connected to the tab, do not have the instability problems but require quiescent cur­rent stabilis­ation and are expensive. When we have a satisfactory solution, you will see it SC in the magazine. March 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 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. 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. HP4263A LCR (BRIDGE) METER $3500.00. Brand new. Won in competi­ tion, never used (list price $5954 plus sales tax). Inspection welcome (079) 42 1950. 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. 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 MAC 2Mb SI & LC 4Mb P’Book CO-PROCESSORS 387SX to 25 387DX to 33 $63 $68 $278 $275 $545 $985 $105 $105 Protect your valuable issues Silicon Chip Binders LASER PRINTER HP with 4Mb $260 TOSHIBA T3200SX T44/6400 T5200 4Mb 4Mb 2Mb $360 $340 $160 SUN SPARC 10/20 16Mb $1140 $150 $265 $265 1Mb V2 BAT SRAM 2Mb V2 BAT SRAM 1Mb V2 FLSH SRAM 2Mb V2 FLSH SRAM $120 $310 $230 $380 $230 $380 Sales tax 21%. Overnight delivery. Credit cards welcome. Ring for Latest Prices 1st Floor, 100 Yarrara Rd, PO Box 382, Pennant Hills, 2120. Tel: (02) 980 6988 Fax: (02) 980 6991 PELHAM 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. 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. 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 ➦ RADIO/ELECTRONIC PARTS: 30 years of collecting up for grabs. Valves, magazines, germanium and silicon semis, ICs, RF connec­tors, all types of components. For a huge list 20 A4 pages long send two 45c stamps to Radio Parts Sale, PO Box 516, Mowbray 7248. MEMORY & DRIVES PRICES AT JANUARY 27TH, 1994 Enclosed is my cheque/money order for $________ or please debit my ❏ Bankcard   ❏ Visa   ❏ Mastercard Card No: ______________________________ Card Expiry Date ____/____ Signature ________________________ Name ___________________________ Address__________________________ __________________ P/code_______ March 1994  95 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 SECONTRONICS COMPONENTS, COMPUTERS, ELECTRON TUBES S/H TEST EQUIPMENT, COMPUTER REPAIRS All prices include sales tax. 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. Phone (02) 554 3114; Fax (02) 554 9374. After hours only bulletin board on (02) 554 3114 (Ringback). Let the modem ring twice, hang-up, redial the BBS number, modem answers on second call. Software & Parts PO Box 92, Bexley North, NSW 2207. UNUSUAL BOOKS: Electronic Devices, Fireworks, Locksmithing, Radar Invisibility, Surveillance, Self-Protection, Unusual Chem­istry and more. For a complete catalog, send 95 cents in stamps to Vector Press, Dept S, PO Box 434, Brighton, SA 5048. 68705 MICRO EMULATOR!!!: Yes! A fair dinkum 68705 hardware ICE for $285 (B&T $330). Run programs in RAM, builtin disassembler, single step, break points, the works! It even emulates 2716, 2732 and 2764 EPROMs. Can be used with a PC, MAC etc. Optional 687053/U/R PC Voice Recorder V1.2 PC Talking Voltmeter V1.1 Serious Guide to Building Kits Altronics ................................ 68-70 Antique Radio Restorations.........94 A-One Electronics........................37 Av-Comm.....................................21 David Reid Electronics ..............87 Dick Smith Electronics........... 10-13 Emona Instruments.....................83 Emtronics.....................................35 Harbuch Electronics....................87 Instant PCBs................................95 Jaycar .........................................55 Kalex............................................15 $12 $17 $12 Macservice..................................75 Oatley Electronics.....................3,65 PC Computers.............................95 $14 All orders plus $3 p&p Darren Yates, PO Box 134, French's Forest 2086. ($115) and C4/C8 ($95) programmers for direct connec­tion to 68705 emulator. Kits and further information from Graham Blowes, Mantis Micro Products, 38 Garnet St, Niddrie 3042. Phone (03) 337 1917(ah), (03) 575 3349(bh), fax (03) 575 3369. 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 (see page 25 for ordering details) Silicon Chip Publications, PO Box 139, Collaroy 2097. 96  Silicon Chip All Electronic Components..........61 JV Tuners.....................................53 5.25" or 3.5" disc for IBM PC LM3876T 50W Amplifier IC Advertising Index Pelham........................................95 Peter C. Lacey Services..............50 RCS Radio ..................................94 Rod Irving Electronics .......... 26-30 Secontronics................................96 Silicon Chip Back Issues....... 84-85 Silicon Chip Binders....................95 Silicon Chip Book Club................59 Silicon Chip Software..................25 Silicon Supply & Manufact...........96 Tektronix..................................OBC Transformer Rewinds...................95 _________________________________ 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.