Fullscreen HTML5Med Res (??MB)HTML4

Build A TENs Unit For Pain Relief SILICON CHIP AUGUST 1997 $5.50* NZ $6.50 INCL GST C I M A N Y D 'S A I L AUSTRA E N I Z A G A M S C ELECTRONI 500W audio amplifier PRINT POST APPROVED - PP255003/01272 SERVICING - VINTAGE RADIO - COMPUTERS - SATELLITE TV - PROJECTS TO BUILD Bass Barrel ISSN 1030-2662 A low-cost, easy-to-build subwoofer 08 August 1997  1 9 771030 266001 SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings.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 Contents Vol.10, No.8; August 1997 FEATURES  3 How Holden’s Electronic Control Unit Works; Pt.2 Learn how the Commodore’s automatic transmission is electronically controlled – by Julian Edgar 22  Computer Bits: The Ins & Outs Of Sound Cards A brief look at sound card basics and what to do when the sound isn’t forthcoming – by Jason Cole PROJECTS TO BUILD 12  The Bass Barrel Subwoofer At last – a high-performance subwoofer that’s compact, cheap and easy to build. You can use it at home or in the car – by Julian Edgar The Bass Barrel Subwoofer – Page 12 24  A 500 Watt Audio Power Amplifier Module This rugged power amplifier module delivers 500W RMS into a 4-ohm load and 278W RMS into an 8-ohm load – by Leo Simpson & Bob Flynn 36  Build A TENs Unit For Pain Relief TENS stands for Transcutaneous Electrical Neural Stimulation. Our unit has all the necessary features and is easy to build – by John Clarke 54  PC Card For Stepper Motor Control This addressable card plugs into your PC’s parallel port and lets you drive a stepper motor under software control – by Rick Walters 500 Watt Audio Power Amplifier Module – Page 24 66  Remote Controlled Gates For Your Home It’s based on windscreen wiper motors and a pair of scissor jacks. We show you how to build the drive mechanism and the control circuit – by Phung Mai SPECIAL COLUMNS 53  Satellite Watch Changes to BMAC services from Optus B3 – by Garry Cratt 60  Serviceman’s Log Just give it a flamin’ good thump – by the TV Serviceman 76  Radio Control Easy-To-Build TENs Unit For Pain Relief – Page 36 The philosophy of R/C transmitter programming – by Bob Young 84  Vintage Radio New life for an old Kriesler – by John Hill DEPARTMENTS   2  Publisher’s Letter 20  Circuit Notebook 33  Order Form 72  Product Showcase 90  Ask Silicon Chip 92  Notes & Errata 94  Market Centre 96  Advertising Index Addressable PC Card For Stepper Motor Control – Page 54 August 1997  1 Publisher & Editor-in-Chief Leo Simpson, B.Bus., FAICD Editor Greg Swain, B.Sc.(Hons.) Technical Staff John Clarke, B.E.(Elec.) Robert Flynn Rick Walters Reader Services Ann Jenkinson Advertising Manager Brendon Sheridan Phone (03) 9720 9198 Mobile 0416 009 217 Regular Contributors Brendan Akhurst Garry Cratt, VK2YBX Julian Edgar, Dip.T.(Sec.), B.Ed John Hill Mike Sheriff, B.Sc, VK2YFK Ross Tester Philip Watson, MIREE, VK2ZPW Bob Young 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: $54 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) 9979 5644. Fax (02) 9979 6503. ISSN 1030-2662 PUBLISHER'S LETTER Australia can make those greenhouse reductions Hands up all those people who have not been impressed by Prime Minister John Howard’s attempt to get different targets for Australia’s greenhouse emissions. Mr Howard maintains that Aus­tralia should be a special case, essentially because of our mining and metal refining industries. This didn’t cut much ice with most other countries because they all reckon that Australia is part of the same planet – an argument that’s difficult to disagree with. In fact, Australia does not have an unusually energy-intensive economy in comparison with other OECD countries. We might be mining-intensive but we are not exactly overloaded with heavy industry. The OECD as a whole has reduced energy use per unit of economic output by more than 20% over the last 20 years while Australia has improved by only about 5%. By not agreeing to a 15% reduction in greenhouse emissions (below 1992 levels) by the year 2010, we are ensuring that there will be little or no change to our wasteful ways. It would be better to aim for the target, even if we failed trying. In fact, our government is taking a completely wrong ap­proach. Rather than thinking in terms of reductions in greenhouse emissions and how much it might cost, the correct approach is to see how much money might be saved. Just recently, a Sydney fast food chain has shown it can reduce its energy bill by 22%, while making a 33% return on the investment in energy efficiency. That is a very good return on investment in anybody’s language. Other fast food chains are following suit and taking meas­ures to reduce the cost of lighting, air conditioning and cook­ing. This is all pretty easy stuff which leads to the question: why weren’t they making these savings years ago? The same ques­tions should be asked of virtually every company and public body in Australia. At present, the answers are pathetic. In truth, Australian companies and public organisations are poor performers by comparison with the world’s best, not only in terms of energy efficiency but in terms of return on sales, return on investment, return on equity and virtually any other measure you might care to think of. Consider how good greenhouse reductions (read energy savings) can be from a typical company point of view. They make an investment which is subject to the normal depreciation allow­ances (ie, they get tax deductions) and then any savings they make are straight profit. Many companies then go on to claim the good publicity by claiming that they are “environmentally green and clean” and all that rot. But the real reason to make the investment is to make (or save) money. They don’t have to “care” about the environment at all. Let’s face it, a reduction of say 20% over a period of 12 years is only 1.5% per annum which is pretty tiny really. Many companies could make the 20% reduction in just one year. Can’t we as a country manage the target? Australia is supposed to be the “clever country”, isn’t it? Leo Simpson 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 How Holden’s electronic control unit works; Pt.2 In last month’s issue we showed how the software con­trolling the Holden engine management system works. This time we examine how the Commodore’s automatic transmission is electroni­cally controlled. By JULIAN EDGAR I N BOTH THE VR and VS model  Commodores, an electronic con­ trol unit dubbed a Powertrain Control Module (PCM) is used to control both the engine management and the transmission. The PCM is a physically larger package than the Electronic Control Module used in previous Holdens but it is closely related, with similar software and hardware used in both packages. As with last issue’s story, this article draws heavily on computer programmer Ken Young’s DynoCal (now known as Kalmaker) software program. The program allows the man­ ipulation of all the variables within the Holden PCM program. It also allows the down-loading of the PCM’s EPROM program, meaning that actual data maps can be seen. The VR V6 Commodore of Awesome Automotive in Ade­ laide was used in conjunction with the Kalmaker Late-model Holdens use a Powertrain Control Module which inte­grates automatic transmission control with engine management. software package to gain much of the information shown here. The automatic transmission used in both the VR and VS Com­modores is the GM Hydra-Matic 4L60-E trans- mission. It is basical­ly a hydraulically-controlled transmission with some added elec­tronic control, as signified by the ‘E’ suffix. The items electronically controlled August 1997  3 Transmission Controls OPERATING CONDITIONS SENSED SYSTEMS CONTROLLED VOLTAGE •   BATTERY COOLANT TEMPERATURE •  ENGINE SPEED (RPM) •  ENGINE POSITION (TP SENSOR) •  THROTTLE FLUID TEMPERATURE (TFT) •  TRANSMISSION GEAR POSITION •  TRANSMISSION • VEHICLE SPEED SENSOR (VSS) POWERTRAIN CONTROL MODULE (PCM) SOLENOIDS •   SHIFT CONTROL SOLENOID •  PRESSURE SOLENOID – “ON” – “OFF” •  TCC SOLENOID – “PWM” •  TCC • 3-2 CONTROL SOLENOID Fig.1: this diagram shows the parameters sensed (left) & the systems controlled (right). PRESSURE CONTROL SOLENOID AUTOMATIC TRANSMISSION OUTPUT SPEED SENSOR (OR VEHICLE SPEED SENSOR) TORQUE CONVERTER CLUTCH “ON-OFF” SOLENOID TORQUE CONVERTER CLUTCH PWM SOLENOID 1-2 SHIFT SOLENOID “A” 2-3 SHIFT SOLENOID “B” 3-2 CONTROL SOLENOID TRANSMISSION FLUID PRESSURE SWITCH ASSEMBLY Fig.2: all the automatic transmission components under the electronic control system are shown here in the transmission are: •  line pressure control solenoid; •  1-2 and 2-3 shift solenoids •  3-2 control solenoid; •  torque converter clutch on/off solenoid; •  torque converter clutch pulse width modulated solenoid. The operating conditions sensed by 4  Silicon Chip the Powertrain Control Module are: •  battery voltage; •  engine coolant temperature; •  engine speed (rpm); •  throttle position; •  transmission fluid temperature; •  transmission gear position; •  vehicle speed. A further input comes from the driver-controlled Power/Economy switch mounted on the centre console. Fig.1 shows the operating conditions sensed, the PCM and the items controlled. The physical shape and location of the transmission components relating to the electronic control system are shown in Fig.2. Functions of controlled systems The line pressure control solenoid (PCS) takes the place of the throttle valve used in the hydraulically-controlled version of this transmission. The PCM varies line pressure via this sole­noid, which is controlled by the current flow through it. Line pressure is increased during times of high engine load which is sensed from various input sensors, including throttle position, speed and engine intake air temperature. Controlling line pres­sure with the PCM means that the pressure can be better correlat­ed with the engine’s torque curve, as shown by Fig.3. The 1-2 and 2-3 shift solenoids control the movements of the 1-2 and 2-3 hydraulic shift valves. These solenoids are normally-open exhaust valves that work in four combinations to shift the transmission into different gears. However, only in ‘D’ can these solenoids control shifts; in the manual positions ‘3’, ‘2’ and ‘1’ the transmission shifts under hydraulic control. The shift sole­noids are either fully open or fully closed. The 3-2 control solenoid is a pulse width modulated sole­ noid used to improve the 3-2 downshift. It controls hydraulic pressure so that the release of the 3-4 clutch and the applica­tion of the 2-4 band are smooth. The duty cycle of this valve is determined by the throttle position, vehicle speed and the gear demanded. The torque converter clutch solen­ oids are used to lock up the torque converter, giving very low slippage. The torque con­verter on/off solenoid has priority in applying and releasing the clutch. It is a normally-open exhaust valve which when earthed, causes converter feed pressure to increase and shift the torque converter clutch valve into the ‘apply’ position. The pulse width modulated torque converter solenoid is used to provide smooth engagement of the clutch. The apply rate of the torque converter clutch is determined by the duty cycle fed to the PWM solenoid. Matching Line Pressure with Engine Torque Adaptive Controls SHIFT DURATION ACTUAL SHIFT DURATION Engine Torque Hydraulically-controlled line pressure Electronically-controlled line pressure ENGINE SPEED (RPM) Fig.3: electronically controlling the line pressure in the trans­mission means that the pressure can be better correlated with engine torque output than in a conventional automatic transmis­sion. Critical to transmission control is the sensing of input and output speeds. While engine rpm gives the input speed to the torque converter, it does not give the input speed of the trans­mission, because of slippage in the torque converter. The input shaft speed of the transmission is calculated from the vehicle speed sensor data and the gear ratio that the transmission is currently in. The torque converter slip is calculated by subtracting the transmission input speed from the engine rpm. Note that the transmission slip can be either positive or negative. The torque converter slip is used in the pressure control logic, shift logic and torque converter clutch diagnostics. As an example of the latter, the PCM can determine whether or not the torque converter clutch is stuck in the engaged posi­tion due to a mechanical fault. It does this by monitoring slip when the clutch is commanded to be off. No slip means that the clutch is still engaged. The control of the torque converter lock-up clutch is de­pendent on a number of variables. The clutch will not lock up if a downshift or upshift is in progress, there is a change occur­ring 2 3 CONSECUTIVE SHIFTS 4 AS LINE PRESSURE INCREASES, SHIFT DURATION (ABOVE) DECREASES FLUID LINE PRESSURE HYDRAULIC CONTROLS ARE LESS PRECISE IN MATCHING LINE PRESSURE TO ENGINE TORQUE DESIRED RANGE FOR SHIFT DURATION 1 LINE PRESSURE (kPa) TORQUE (Nm) ELECTRONIC CONTROLS ALLOW LINE PRESSURE TO MATCH ENGINE TORQUE 1 2 3 4 CONSECUTIVE SHIFTS Fig.4: self-learning controls the shift times. Line pressure can be varied over a range so that shift times remain consistent, even as the transmission wears. Fig.5: several maps are used to control the operation of the torque converter lock-up clutch. This map is for fourth gear when in Power mode. The highlighted bar shows that the clutch will lock-up at 75 mph (121km/h) when the car is being driven with a 50% throttle opening. in the throttle position or the gear selector is in a manual range. Furthermore, the temperature of the engine coolant must be above 50°C (examples are from the VR Commodore V6), the transmission fluid temperature must be over 0°C and the transmission slip must be below August 1997  5 Fig.6: the transmission constantly monitors the 1-2 shift time, counting over-long shifts as errors. This chart shows the error count at different throttle openings. At 25% throttle, 253 errors have occurred – a substantial number! Fig.7: in response to the shift errors in Fig.6, the line pressure has been increased by 4.3 psi to shorten the shift. The transmis­sion constantly chases optimal shift times in this manner. 25 rpm. There is also a delay period before the clutch will engage, even when all the required conditions are being met. When the clutch is (finally!) being engaged, the duty cycle applied to the PWM torque converter solenoid is a calculated value. Should the 6  Silicon Chip transmission fluid temperature rise excessively, the torque converter clutch is applied in gears 2, 3 and 4. This reduces transmission slip and so also reduces the likelihood of further temperature increases. Fig.5 shows one of the two-dimensional charts controlling the torque converter lock-up clutch operation. This chart is for fourth gear, Power mode. The cursor is pointing to the bar show­ing that at a 50% throttle opening lock-up occurs at 75 mph (all units within the American derived program are Imperial). The change to a higher gear is termed an upshift. Upshift logic is performed if the current gear is 1, 2 or 3. Three tests are performed in quick succession for an upshift. If the result of any test is positive the remaining tests are skipped. The three tests are: •  A fixed upshift where the speed is greater than a preset threshold, which depends on the gear lever range and the set mode (power or economy). •  A full throttle upshift where there is a wide throttle opening (normally over 90%), speed is greater than the specified upshift speed and engine speed is greater than the specified upshift engine speed. These variables are dependent on gear, coolant temperature and barometric pressure. •  A part throttle upshift where there is less than full throt­tle, the upshift speed and/or rpm is greater than that shown by two 2-dimensional maps based on speed, throttle position and the position of the power/economy switch. If none of the upshift tests command an upshift or if the car is already in fourth, downshift logic is performed. The downshift logic again comprises the fixed downshift, full throt­tle downshift and part throttle downshift approach. The level of the hydraulic line pressure helps to determine clamping pressures of clutches and bands and the harshness of the changes. The program calculates a desired pressure based on the temperature of the transmission fluid, throttle position and road speed. This is converted to solenoid current. The PCM then meas­ures the amount of current flowing through the line pressure control solenoid and compares this with the calculated current. If the difference is greater than a calibrated value, a trouble code is set. The PCM controls the time taken for each gear change, with the desired shift times for the 1-2 and 2-3 gear changes included in the program. The times taken for the shifts are measured and compared with the desired or reference times. If the times are incorrect, the shift time is altered by changing the line pres­sure via its control solenoid. Fig.4 shows the approach taken. Incorrect shift times can be caused by transmission wear (although there is compensation for wear) and fluid temperature variations. In practice, the transmission seems to spend a lot of time chasing its programmed shift times. Corrections to the shift time are held in an adaptive memo­ry. Dubbed the Pressure Adapt Modifier (PAM), the values are arranged in an array of 17 learning cells, which are referred to according to throttle position. The values in this table are modified on the basis of the correction factor needed to cause shifts to occur within the desired times but only when certain conditions of throttle position and change in road speed are being met. The PAM is very similar to the Long Term Fuel Trim memory used to correct engine air/fuel mixtures and is held in non-volatile memory. Fig.6 shows an actual logged PAM chart. At a throttle posi­tion of 25% (horizontal axis), 253 shift errors have been counted, indicating that the 1-2 change at 25% throttle openings is frequently taking too long. To correct this, hydrau­ lic pressure has been increased, as Fig.7 shows. At a 25% throttle opening, line pressure has been increased by 4.3 psi. At other throttle positions, the opposite is occurring – the shifts are too quick and so pressure is being dropped (at 50% throttle, for example). These charts are constantly changing as the program chases optimal shift times. When regulating a 3-2 downshift, the duty cycle for the 3-2 downshift valve is a function of throttle position and road speed. However, its duty cycle is also corrected if the air conditioning is on, if the range selector is in D1 or D2 and for transmission fluid temperature. The final figure is then checked against the programmed maximum and minimum duty cycles permitted for this solenoid. Conclusion In the same way in which the Holden V6 and V8 engines are relatively simple mechanical designs made competitive by very advanced engine management, the old-fashioned hydraulically controlled Hydra-Matic has been effectively updated by the addi­tion of sophisticated electronics. It’s possible to sit in a moving car Transmission Data Log Record The Kalmaker software allows the logging of transmission factors in real time. While the system logs at 10Hz, the accompa­nying graph has been simplified, with data shown at 0.5s intervals. The graph shows the behaviour of engine rpm, torque converter slip, throttle opening, vehicle speed and Pressure Control Solenoid current for a 16.5s period. During this time the Awesome Automotive Commodore V6 was accelerated from a standstill to a speed of 108km/h. The throttle was then closed and the car gradually slowed to a speed of 54km/h. The car was left in ‘Drive’ during this manoeuvre. The pink line shows the car’s speed and the black line shows throttle position, both being referenced against the right-hand axis. Engine revs are shown by the yellow line, while torque converter slip is shown by the aqua line. It can be seen that when the car is stationary, engine speed and torque converter slip are of a similar magnitude. This is because at an idle speed of 700 rpm, the slip must be 700 rpm if the car is not moving! With a throttle opening of 100% the car accelerates rapidly with the amount of slip decreasing. The first-second gear change occurs at and see on a plugged-in laptop PC the continual monitoring of shift-times, the result­ing changes in PCS current and the locking and unlocking of the torque converter clutch. Watching the live screen really brings home the complexity of the calculations 13 on the Y-axis and with the newly-applied load, the slip within the torque converter rises. It slips by up to 1700 rpm before the value drops back to about 300 rpm after about 1.5 seconds. In second gear, Leon Vincenzi has kept his foot flat to the floor until the engine speed reaches 4750 rpm, upon which he has lifted his foot entirely (23 on the horizontal axis). The trans­mission immediately changes from second to third to fourth, with this transition taking only 0.2 seconds. Again there is a major increase in slip through the torque converter, which then goes into negative numbers as the engine brakes the car. During these processes the Pressure Control Solenoid is being varied in its duty cycle, controlled by the current flow through it (shown by the blue line). A high current flow results in a low fluid pressure, while a low current flow increases fluid pressure and thus clamping forces. With the application of full throttle the current rapidly reduces, staying at 156mA for the 1-2 full throttle gear change. It rises to 1074mA as the throttle is lifted, responding to the reduced torque load on the transmis­ sion. Even when engine braking, the PCS keeps pressures low. continually occurring in the silver box behind the kick-panel! Contacts (1) KAL Software (Brad Host) 0412 266 758; (2) Awesome Automotive SC (08) 8277 3927 August 1997  7 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.dse.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.dse.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.dse.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.dse.com.au A high-performance subwoofer that’s compact, cheap & easy to build By JULIAN EDGAR Photos: GEORGINA COBBIN The 300mm stormwater pipe which forms the main body of the subwoofer enclosure can be cut with an electric jigsaw. 12  Silicon Chip I F YOU’RE TIRED of subwoofer designs that have internal volumes the size of a road tanker or stand as tall as a refrig­erator, this one’s for you. The Bass Barrel has an effective volume of only 20 litres and uses two 6.5-inch woofers. But it can still produce room-shaking bass, especially in smaller houses. In fact, the Bass Barrel would be ideal for use in a flat or unit in company with two small satellite speakers. The design is also well-suited to in-car duties where the small air volume inside the car’s cabin improves the bass re­sponse even further. It can easily be accommodated in the boot or the rear hatch area of a compact car. While we aren’t going to claim that the Bass Barrel will transport you to an actual rock concert, it delivers impressive performance for such a small package. The enclosure was designed using the brilliant Bass Box computer program, with literally hundreds of designs modelled on the screen before this one was selected. This approach bears no comparison with past design methods which relied on tables, graphs, rule-of-thumb and build-it-and-listen techniques. Now you can adopt an intelligent approach to subwoofer design and to designing other types of loudspeaker systems as well. The subwoofer was designed with several aims in mind. It had to: (1) use a compact, easy-to-build enclosure; (2) have reasonably high efficiency; Fig.1: the internal layout of the Bass Barrel. It is built inside a short length of 300mm plastic stormwater pipe. Note that the 63mm ID vent exits through one end panel, while the 55mm ID vent exits through the other. and (3) have a good bass response. The design is based on two Altronics C3086 6.5-inch Redback woofers. These are mounted face-to-face in what is called a compound isobaric configuration – see Fig.1. Mounting the drivers in this manner reduces non-linear distortion and, more im­ portant­ly, reduces the required enclosure volume to just half that required for a single driver! The down­side is that the sensitivi­ty of the compound The three internal baffles (left) are cut from 20mm Medium Density Fibreboard. This is the central baffle, which has holes for the two vent tubes and the speakers. The tuned-length ports (above) are made from 55mm ID and 63mm ID plastic pipe. Both ports are 270mm long. August 1997  13 The baffles, ports and speakers are arranged inside the main 300mm tube as shown here. The smaller 55mm ID vent tube is in the foreground. The three baffles are glued one-by-one inside such as Liquid Nails. pair is reduced by 3dB compared to a single speaker design (with a 1W input) but this can be compensated for by careful box design. Note that the two 8Ω drivers are mounted in parallel, which means that the design has a nominal impedance of 4Ω. So what sort of box design have we used? It’s called a 6th Order (A) Bandpass Double Vent design or more precisely, with the speakers mounted tune the chambers. While there are numerous types of bandpass boxes, the 6th order (A) design de­scribed here vents both chambers to the outside but has no con­necting port between the chambers. So why use a bandpass design rather than a conventional bass reflex or sealed enclosure? The answer is that a bandpass design is especially suited to subwoofer applications because both as in Fig.1, a Compound Isobaric 6th Order (A) Bandpass Double Vent design. Now even if you never make it, you can still impress others with your new-found knowledge! A bandpass enclosure basically has two separate chambers, so that each side of the driver works into a separate air volume. The bass frequencies produced result from air movement in the vent or vents that are used to Fig.2 (left): the central baffle requires holes for the paired drivers, the small vent and the large vent. The exact positions of the holes is not critical; just arrange them as shown here. Fig.3: the drivers are wired out of phase so that their cones travel in the same direction. When one cone move forwards, the other moves backwards and vice versa. 14  Silicon Chip the main cylinder using a building adhesive the upper and lower frequency rolloff points can be con­trolled, meaning that it can be used without a cross­over (although we don’t recommend this). The enclosure can also be designed to give a very good low frequency response and the distortion is low. On the list of negatives, a band­pass design has a narrow bandwidth and is generally more complex to build than a conventional enclosure but we reckon we’ve solved that last problem. What’s more, a sub­woofer should only have a narrow response, so lack of bandwidth is not really a problem at all. Fig.1 shows the layout of the Bass Barrel enclosure. A 15-litre volume is used on one side of the drivers and a 5-litre volume on the other side. The larger of the two volumes is tuned to 38Hz via a 55mm-diameter vent which is 270mm long, while the smaller volume is tuned to 75Hz by a 63mm diameter vent, also 270mm long. The ports are cunningly arranged so that they are entire­ly within the enclosure. This is harder to arrange than it sounds, given that each port is longer than the longest dimension of the volume it is venting! The trick is to vent the front chamber through the rear panel and the rear chamber through the front panel. Comparing the predicted performance with both bass reflex and sealed enclosure designs shows the This photo shows the partially completed unit with the first end baffle and the smaller vent tube in place. Quilt wad­ding is used on all exposed surfac­es. The middle baffle must be positioned exactly 250mm down from the end of the main tube. advantage of using a bandpass approach. The predicted -3dB point is 36Hz for the Bass Barrel design, 60Hz for the best ported box design, and 100Hz for the best sealed box. And importantly, that’s with the same input signal level – a point sometimes overlooked when comparing dif­ferent box designs that vary in sensitivity. Incidentally, in a car the Bass Barrel has a predicted -3dB point of 29Hz. Fig.4 shows the normal and in-car predicted response curves. Subsequent testing has shown that the completed subwoofer lives up to its modelling predictions. Gathering the parts The main body of the enclosure is made from 300mm plastic stormwater pipe, while the baffle and end pieces are cut from 20mm medium density August 1997  15 specified ac­cording to its inside dia­ meter (ID), because that’s what’s im­ portant to the design. The 63mm ID pipe is used for waste­water plumbing under sinks, etc, while the 55mm ID variety is pressure water pipe. The 20mm-thick medium-density fibreboard (MDF) is also commonly available from hardware stores, while the quilt wadding is available from cloth supply shops like Spotlight. We covered the Bass Barrel in a stretch automotive carpet called Meltrim® which is available from auto trimmers. Cutting the materials Seal around the edge of the speaker connector before turning over the last baffle and pushing it into place. fibreboard. The vents are made from PVC pipe. Plastic stormwater pipe was chosen for the main housing instead of an all-MDF design because of the difficulty that many home con­structors have cutting straight lines through sheets of fibreboard. However, if you would prefer to build an all-MDF enclosure, see the breakout box. The enclosure was lined with acoustic material in the form of quilt wadding. The 300mm PVC stormwater pipe used is a thick-walled design. It is available from major plumbing supply businesses but although less than half a metre is needed for the enclosure, the minimum that will be available is almost certain to be a metre. Be warned though that some businesses will ask that you buy a full length of six metres and that’s not really a viable proposi­tion! If you do find it impossible to buy the pipe in short lengths, talk to plumbers at major industrial building sites and see if you can scrounge an off-cut. The plastic pipe used for the two vents is commonly avail­ able from hardware stores. Note that it has been Begin the construction by cutting the main 300mm-diameter tube to a length of 370mm, making sure that the ends are square. This done, carefully measure the inside diameter of the tube and use this measurement to mark out the three MDF discs. The three MDF discs can then be cut out using an electric jigsaw. The next step is to cut a hole for the speakers plus holes for each of the two vents in one of the discs – see Fig.2. This disc becomes the central baffle. You will also have to drill a small hole for the speaker leads to pass through. Next, using the centre disc as a template, mark the loca­ tion of the large port on one of the end discs and the location of the small port on the other (ie, each end disc should have only one hole). Cut these holes using a jigsaw and carefully sand them so that the port tubes are a good fit. The two port tubes can then each be cut to a length of 270mm. Final assembly Eight countersunk MDF screws are used to hold each of the internal baffles securely in place. These should be evenly spaced around the circumference of the main tube. 16  Silicon Chip The first step in the assembly is to fit the end baffle with the small hole to one end of the main cylinder. Use Liquid Nails® (or some other similar building adhesive) to bond the disc into place, then fit eight evenly-spaced MDF screws around the outside of the cylinder to further secure the baffle. Countersink the holes so that the screw heads sit flush with the surface of the tube. Next, fit the 55mm ID vent tube into place and seal the gap between the tube and the baffle using Silastic® or a similar sealant material. Note that this sealant should also be applied when ever a vent tube goes through a baffle. You should also glue quilt wadding (or Innerbond material) to all exposed interior surfaces as you The Bass Barrel takes up almost no space at all. A CD is resting on top of the unit to give an idea of the scale. assemble each stage of the Bass Barrel. The next step is to mount the speakers on the centre disc. Unlike conventional speakers which are slipped through the mount­ing hole from the front, the Bass Barrel speakers are mounted face against the baffle. Mark out the mounting holes on one side of the baffle, then drill the holes and bolt the speakers togeth­er from either side of the baffle. Wire the speakers together as shown in Fig.3. Note that the positive terminal on each speaker joins to the negative terminal of the other speaker. When you have finished the wiring, connect a 1.5V battery across the main speaker lead and check that the Fig.4: the predicated free-air and in-car response curves for the Bass Barrel. The blue line shows the in-car response. The design was produced using the Bass Box loudspeaker program. August 1997  17 PARTS LIST 2 Altronics Redback 6.5-inch woofers, Cat. C3086 1 370mm length of 30mm-dia. plastic stormwater pipe 1 600 x 700mm piece of 20mmthick Medium Density Fibreboard (MDF) 1 270mm length of 55mm ID plastic pipe 1 270mm length of 63mm ID plastic pipe 1 930 x 300mm piece of thin quilt wadding 1 1-metre length of heavy-duty figure-8 hook-up wire 32 MDF screws, 20mm long 4 3mm x 40mm-long bolts plus nuts and washers 1 loudspeaker terminal block Miscellaneous Liquid Nails® or similar building adhesive; Silastic® or similar silicone sealant; Meltrim® auto­motive carpet; mesh grilles. speaker cones both move in the same direction. If they head in opposite directions, reverse the connections to one of the speakers. Don’t forget to seal the speaker wire hole through the baffle with Silastic®. Once the speakers are in position, slide the centre baffle down the main We used a cutdown speaker grille and a shortened plastic stormwater fitting to form a grille for each of the ports. Howev­er, there is some port noise with this arrangement, so you may care to leave the grilles off. cylinder and over the small vent tube. Position it so that its upper surface is exactly 250mm down from the top of the tube, then use Liquid Nails® and screws to hold the baffle in place. The large vent can now be installed. Push it down into the central baffle until its end is flush with the end of the main cylinder, then seal the baffle holes. This done, cover the inside of the cylinder with quilt wadding and do the same to the inside of the remaining end baffle. Finally, mount the terminal block on the end baffle, wire it to the speakers and then glue and screw the baffle Special Offer On Subwoofers The Redback 6.5-inch woofers used in this project are available only from Altronics. We have negotiated a special deal with Altron­ics, so that instead of paying $90 for the two speakers you’ll pay only $69 plus $5.50 freight. Phone 1800 999 007 to place your order, or fill in and post or fax the coupon below. Please send me two Redback 6.5-inch woofers (Cat. C3086) at the special price of $69.00 + $5.50 p&p. Enclosed is my cheque/money order for $­74.50 or please debit my: ❏ Bankcard   ❏  Visa Card   ❏ MasterCard Card No. Signature­­­­­­­­­­­­_______________________________  Card expiry date______/______ Name Street __________________________________________________________ PLEASE PRINT __________________________________________________________ Suburb/town_____________________________________ Postcode_________ Send coupon to Altronics, PO Box 8350, Perth Business Cen­tre, WA 6849; or fax (08) 9328 3487 18  Silicon Chip into place. The end of the large vent should sit flush with the outer surface of the end baffle when it is in place. As before, seal the gap between the vent and the baffle. Testing Let the glues and sealants dry properly before trying it out – pre­ferably overnight! To test it, connect the Bass Barrel to an amplifier and a music source but don’t connect any other speakers to the system at this stage. You should not be able to hear very high frequencies (treble), while the bass should be a tight thump, thump. If there are any loud buzzes or whistles, you’ve got air leakage problems and the gaps will have to be tracked down and sealed. As with all subwoofers, the best sound will come if the Bass Barrel is driven by a dedicated amplifier working with a crosso­ver circuit. A suitable “Subwoofer Controller” was described in the December 1995 issue of SILICON CHIP and is available from Altronics as a kit of parts. This design features adjustable cutoff frequency and level controls and even includes automatic power switching for the subwoofer power amplifier. We don’t recommend connecting the Bass Barrel across one of your existing speakers without a crossover network, as this could unduly load the output circuit of the amplifier. Our Bass Barrel was covered in Meltrim®, a stretch automotive carpet. To tidy the ends of the cylinder, Building An All-MDF Enclosure Fig.5: if you don’t want to use 300mm plastic stormwater pipe (or can’t get hold of it), the same basic design can be made entirely from MDF, with 10mm-thick material recommended. This diagram gives the dimensions. Make sure that all the joints are well sealed. we covered the carpet joins with a rubber moulding which is readily available from specialist rubber shops. Alternatively, the countersunk screw holes can be suitably filled, the enclosure sanded smooth (use only very fine sandpaper on the plastic of the main cylinder) and the unit paint­ed. Mesh grilles We used mesh grilles (cut down from a larger grille) over the ports, with the surrounds made from suitably shortened plas­tic stormwater fittings which were painted black. Note, however, that the mesh grilles cause some port noise to occur, so leave these out if very clean bass is required (the noise is only very minor). So there you have it – a compact subwoofer that delivers superb bass, costs very little and is easy to build. It sure changes perceptions that bigger is always better when it comes to a SC subwoofer. Fig.6: the impedance curve for the Bass Barrel subwoofer. The minimum impedance is just under 4Ω which means that the Bass Barrel represents a safe load at all frequencies of interest. August 1997  19 CIRCUIT NOTEBOOK Interesting circuit ideas which we have checked but not built and tested. Contributions from readers are welcome and will be paid for at standard rates. Timer with 240VAC switching This circuit is 240VAC mains powered without using a transform­er so the critical 0.47µF 250VAC X-class capacitor must not be substituted for a capacitor with inferior ratings. X-class ca­ pacitors are designed to go open-circuit in case of malfunction. The momentary pushbutton switch S1 and the relay must also be mains-rated and the circuit must be built so that it is fully isolated. The timer is started by pushing the momentary pushbutton to feed power to the bridge rectifier via the 0.47µF capacitor. This capacitor’s reactance limits the voltage to the bridge rectifier and the remainder of the power supply while the zener diode limits the resulting DC supply to 15V. The 15V supply powers a 555 timer connected as a monostable multi­ vibrator. As soon as power is applied via switch S1, pin 3 of IC1 goes high to turn on relay RLY1. One pair of the relay’s contacts (RLY1a) then close to continue feeding power to the bridge rectifier after switch S1 is released. Pin 3 stays high for the time period 1.1RC, with R and C being the components at pins 6 & 7. With the 10MΩ resistor and 330µF capacitor specified the time will be about one hour although the actual period will depend largely on the tolerance and leakage current of the ca­pacitor. The second pair of relay of contacts (RLY1b) will connect the load to the 240VAC mains supply. After the mono­stable times out, pin 3 of IC1 will go low, the relay will be de-energised and both relay contacts will open to disconnect the mains supply from the circuit and the load. The suggested relay has 10A contacts and a 500Ω coil. M. Frankowski, Warszawa, Poland. ($35) WARNING! This entire circuit floats at 240VAC and is potentially lethal. Do not build it unless you know exactly what you are doing. Pistol target frame timer This target frame controller has been designed to make the target turn away for seven seconds then face the shooter for three seconds; this cycle repeating five times. The target then faces away until the circuit is reset manually. IC9 is used as a start latch, such that when the start button is pressed, pin 1 of IC9 goes from low to high and stays high (unless reset), enabling pin 1 of AND gate IC2a. Transistor Q1 is bias­ed on when power is applied to the circuit (target facing) by virtue of 20  Silicon Chip exclusive-OR gate IC10a and inverter IC11a. Q1 turns off when the start button is pressed, starting the first 7-second off period. At the same time as the start button is pressed, the high on pin 1 of AND gate IC2a allows 1-second pulses from IC3 to clock divide-by-10 counter IC7. IC7 counts to seven and is then stopped by AND gates IC8b & IC8c. The high at pin 4 of IC8b does several things: it clocks IC12 to its first cycle count of five; it causes Q1 and relay RLY1 to turn on; and it enables pin 11 of IC2d to send clock pulses to divide-by-3 counter IC5. Pin 4 of IC2c goes high at the count of 3 and causes pin 3 of IC8a to go high. This has several outcomes: IC5 is reset via pin 4 of IC11c; Q3 & Q2 turn on to reset IC7 back to zero; and pin 5 of IC7 goes low, which turns off Q1 and relay RLY1, thus turning the target away. This cycle repeats five times; ie, six off periods each seven seconds long and five on periods each three seconds long. IC12 counts the number of off periods such that when it counts to 6, pin 5 goes high. This takes the clock inhibit input (pin 13) high which inhibits further counting and disables pin 8 of IC2b, preventing pulses from IC3 from clocking the rest of the timer. IC6 & IC4 convert the BCD outputs of counters IC5 & IC7 to drive the com- mon cathode displays (LTS­5303­AR, etc). These indicate the progress of the counters. The relay switches +12V to the target solenoid which con­trols an air valve to rotate the target frame to the shooter. P. Howarth, Gunnedah, NSW. ($50) August 1997  21 COMPUTER BITS BY JASON COLE The ins & outs of sound cards Sound cards have been around for quite some time and have improved from the mono 8-bit sound card up to the stereo 64bit sound card with 3D enhancement. Sound cards can also handle MIDI (Musical Instrument Direct Input). With the increased use of sound on the Web and better quality sound effects in games, sound cards have become more important than before and, at the same time, more complex. A sound card also lets you listen to CDs and audio files and allows you to record sound signals fed in via the line input socket or via a microphone connected to the microphone input. Most sound cards come with five The Line Out socket delivers audio signals at line output voltages. Any sound produced by the sound card is made available at this connector and is in the order of 1V, which is generally the standard for line outputs. I say generally because some units provide signal outputs of 1.5V or even 2V. The Line Out connector can be connected to a set of amplified speakers or to your home stereo for It is important that the resources allocated to the sound card do not conflict with other devices. If conflicts do occur, there are a number of ways of changing the current setup, depending on the type of card you have. sockets on their backplane bracket. These sockets are: Mic In, Line In, Line Out, Speaker Out and Midi/ Joystick. The Mic In socket accepts low level input signals from the microphone and these are typically only a few milli­ volts. The Line In is for line voltage signals and these are typically around 1V. These voltages are generally found on the line level outputs of VCRs and most audio equipment. 22  Silicon Chip even greater volume output. The Speaker Out socket (stereo) delivers an amplified Line Out signal and is connected directly to a pair of speakers. People sometimes mistakenly connect amplified speakers to this socket, which results in massive distortion due to signal overload. If you find that you get massive distortion and a lot of sound output at low volume settings, check your connections to the sound card. Amplified speakers must be connected to the Line Out socket. The Midi/Joystick connector is a dual-purpose connector that can either be used for Midi input or to accept a joystick, the latter being the most popular. Midi is used primarily by musicians and only rarely for home use, which is why this socket doubles as a joystick connector. Joysticks are great to use in some games but be warned: a cheap joystick is just that . . . cheap. If you want a joystick that really works, you will have to pay a bit more than $30. Owners of cheap joysticks will under­stand this statement. Sound card hassles Sound cards, although great to have and often a necessity, have traditionally been a common source of problems. Fortunately, most modern sound cards are exceptionally well made and with the advent of Plug and Play are now also easy to set up. It is imperative that the sound card be set up correctly, whether it be for Windows 3.x or Win95 or DOS. You need to know the sound card’s IRQ (interrupt request) number, port setting and the DMA channel. Stereo cards often require two DMA channels, while the Midi section also requires a port setting. In Windows 95, this information is usually found automatical­ly during the Plug and Play installation routine. Conversely, in Windows 3.x you have to feed in all the necessary information yourself. You glean this information when you install the card (most sound cards now come with software that tells you the current setup). It is important that the resources You can check the resources assigned to the sound card via the System Properties dialog box (Windows 95). This is brought up by double-clicking the System icon in Control Panel, clicking the Device Manager tab, selecting the device, clicking Properties and then selecting the Resources tab. the data could be transmitted, thereby allowing stereo sound to be produced. Sound card technology has since advanced even further, giving higher sampling rates and better quality sound. The 32-bit sound card is now the card of choice for sound enthusiasts and music professionals. Of course, a 32-bit card costs more than its 16bit cousin. A 16-bit card such as the Sound Blaster Vibra16, for example, costs $150-200, whereas the 32-bit Sound Blaster AWE32 costs around $500. But wait – the 64-bit sound card has now made its appearance which means that prices for 32-bit sound cards are on the way down. Sound cards & network cards allocated to the sound card do not conflict with other devices. If conflicts do occur, there are a number of ways of changing the current setup, depending on the type of card you have: (1) Pre Plug and Play cards – in the old days, hardware jumpers on the board determined the setup. To change these jumpers, you had to open the computer, remove the sound card and reposition the jumpers in accordance with the instructions in the manual. The card then had to be replaced and tested again. (2) Almost Plug and Play cards – Plug and Play may be new but there have been Plug and Play “wannabes”. These were the cards that used software to alter the settings for you. This meant that you did not need to open the case when there were problems; instead, you could quickly reconfigure the card using software. However, you still had to select the settings yourself and the software could not detect possible conflicts. This meant that settings were generally chosen on a trial and error basis. (3) Plug and Play – with Plug and Play, the cards became smarter and we moved into a new era of computing that allowed almost anyone to add hardware. Plug and Play does what we have been asking for, for a long time: it asks the card what resources it wants and checks whether they conflict with those used by other devices. If they don’t, those resources are allocated to the new device. If they do, the system automatically makes changes to avoid such conflicts. All this is done by the system BIOS during the boot-up sequence. When you want to change the settings, you can quite often do it on the fly; ie, you can change the settings without resetting the computer or restarting Windows 95. The important thing about Plug and Play is that it works without asking us any questions. Port conflicts Although IRQ conflicts are generally the cause of sound card problems, port conflicts can be a problem too. When you have a conflict, always check the port settings as well. DMA settings can also cause problems, so make sure these are correctly allo­ cated. As a general rule, you can allocate DMA channels 1 and 5 to a sound card. Early sound cards were 8-bit designs that gave reasonably good sound, although a relatively low sampling rate meant mono sound output only. The later 16-bit cards effectively doubled the rate at which Network cards and sound cards sometimes do not work well together. If you use a network card in a business environment and are experiencing troubles, try removing the sound card. Quite often that fixes the problem. If so, try changing the settings for the network card and try again. Of course, it is not necessarily the sound card that is at fault in these circumstances but it can get in the way by compet­ing with the network card for resources. If necessary, leave the sound card out altogether. After all, sound is not that important on a business computer when you’re trying to make money. If you must have both types of card, try changing the sound card. The better sound cards have more options when it comes to configuring them, which means that you should be able to avoid potential conflicts. Cheaper sound cards can also conflict with the BIOS settings of some SCSI cards. Personal preferences From a personal standpoint, I’ve always found that Crea­tive’s Sound Blaster range works extremely well. These sound cards come with excellent manuals and they are now all Plug and Play which makes them very easy to install. Best of all, the Plug and Play feature actually works, provided of course that you have a Plug and Play BIOS and are using Windows 95. Another reason for choosing the Sound Blaster range is that Creative continually upgrades the software and makes it readily available via SC the Internet. August 1997  23 This amplifier is capable of delivering over 500 watts into 4Ω or around 280 watts into an 8Ω load. The large heatsink is mandatory and needs to be fancooled if it is to withstand the rigours of operating under maximum dissipation conditions. We envisage it as being used in high-end stereo systems and for musical instrument and PA work. 500W of audio power 24  Silicon Chip W N Pt.1: By LEO SIMPSON & BOB FLYNN O MATTER WHICH WAY you look at it, this is a big power amplifier. It’s physically big, it needs a big power supply and a big fan-cooled heatsink and it delivers lots of power. A pair of these amplifiers would be the basis of a magnificent stereo system for the home, especially if you have a large listening room. Perhaps you might think that a 500 watt per channel stereo system would be too much. The answer to that depends on what sort of music you like listening to and how efficient your loudspeak­ers are. If you like rock music with its fairly limited dynamic range (ie, loud all the time), then a 1000 watt system would be going over the top. But if you listen to a lot of classical piano music and your speakers are of only average efficiency, then 500 watts per channel might not be enough! One of the authors of this article has a large piano in his (large) loungeroom and often has the opportunity (every day) to compare the real piano with CDs played through the Studio 200 power amplifier published in the February 1988 issue of SILICON CHIP. That amplifier has a music power output of 120 watts per channel into 8Ω and 190 watts per channel into 4Ω. In a straight comparison for absolute loudness and dynamic range, the real live piano, played by an accomplished pianist, wins every time. We’re not talking about ridiculously loud music here – just a piano competently played. What is not commonly realised is that the piano is probably the most difficult musical instrument to accurately Do you want a big power amplifier for musical instrument or PA use? Something with real grunt? Well here it is, the big­gest power amplifier ever described in an Australian magazine and probably the biggest published anywhere in recent years. It delivers 500 watts RMS into a 4Ω load and 278 watts into an 8Ω load. August 1997  25 26  Silicon Chip Fig.1: the circuit uses 12 output transistors in a complementary symmetry arrangement, driven by an MJL21193/4 pair; ie, the same as the output transistors. Short circuit current limiting is provided by Q24 & Q25. The supply rails are ±80V so we have had to specify high voltage transistors for the input differen­tial pair, Q1 & Q2. record and reproduce because of its huge dynamic range – even when it’s not being played particularly loudly, most amplifiers and loudspeakers are not up to the task. But a pair of these new power amplifiers and large loudspeakers to match would certainly cope with any CD of classical piano! Without getting too much ahead of ourselves, this new amplifier design produces only about 5dB more power than the 1988 design so the difference in absolute loudness won’t be huge. On the other hand, it will be noticeably louder and will be far less likely to be over-driven than the older design. Background to the design It’s been a long time coming, this amplifier. It was first mooted more than 12 months ago in 1996 and we have made several false starts since, only to come to a stop as component availability or suitability stopped us from proceeding further. Also along the way we produced a full bridge design, effec­tively two power amplifiers on the one PC board which drive the single loudspeaker in anti-phase. The driving voltages from the two amplifiers add and so the power delivered is the sum of the power outputs from the two amplifiers. The advantage of the bridge design is that the amplifier supply voltages can be sub­stantially less than the equivalent large single-ended amplifier. The lower supply voltages mean that the electrolytic ca­pacitors in the power supply are less expensive and the transis­tors used throughout the amplifier can have a lower voltage rating. In practice, it was the rarity of suitable high voltage high current driver transistors that pushed us along this line of development. However, the resulting bridge amplifier proved to be not as efficient as a single-ended design and with the heatsink avail­able to us at the time, Fig.2: these are the load lines for 4Ω and 8Ω operation. The straight lines are for resistive loads while the arched lines are for reactive 4Ω (2.83Ω + j2.83Ω) and 8Ω (5.6Ω + j5.6Ω) loads. The concave lines show the 1200W power hyperbola (dotted) and the one-second SOAR curve for six MJL21193/4 power transistors. As you can see, the reactive 4Ω load comes quite close to the one-second SOAR curve. That is why a total of 12 output power tran­sistors is required. it proved impossible to cool it effec­ tively, even with two fans! After running up that blind alley, we went back to the drawing board. This time we were successful, with a bigger heat­sink, fan cooling and a thermal cutout. And instead of using conventional driver transistors, we used power output transistors in the driver stages. The power transistors specified have the advantage of being much more rugged and with a minimum gain-bandwidth product of 4MHz, their high frequency performance is just as good as many driver transistors such as the commonly used Motorola MJE340/350 pairs. The result of all the development Specifications Output power....................................278 watts into 8Ω; 500 watts into 4Ω Music power.....................................315 watts into 8Ω; 590 watts into 4Ω Frequency response ........................-0.3dB at 20Hz and 20kHz (see Fig.8) Input sensitivity.................................1.43V RMS (for full power into 8Ω) Harmonic distortion..........................typically less than .01% Signal-to-noise ratio............................... 117dB unweighted (20Hz - 20kHz); 122dB A-weighted Damping factor.................................>170 at 100Hz & 1kHz; >75 at 10kHz Stability.............................................unconditional August 1997  27 AUDIO PRECISION SCTHD-W THD+N(%) vs measured 10 LEVEL(W) 19 JUN 97 22:07:52 1 0.1 0.010 0.001 10 100 800 Fig.3: THD (total harmonic distortion plus residual noise) versus power at 1kHz into a 4Ω load. AUDIO PRECISION SCTHD-W THD+N(%) vs measured 10 LEVEL(W) 19 JUN 97 22:09:02 1 0.1 0.010 0.001 10 100 800 Fig.4: THD (total harmonic distortion plus residual noise) versus power at 1kHz into an 8Ω load. work is an amplifier capable of delivering 500 watts into a 4Ω load at .04% harmonic distortion and 278 watts into an 8Ω load at less than .009% harmonic distortion. Using the IF Music Power test conditions, the power output is 590 watts into 4Ω and 314 watts into 8Ω. Big power like this does not come in small packages. The amplifier uses 28  Silicon Chip 14 power transistors in all, from the Motorola MEL21193/94 series. These plastic power transistors are rated at 250 volts, 16 amps (30 amps peak) and 200 watts and have been featured in previous amplifier designs in the April 1996 and March 1997 issues of SILICON CHIP. As indicated above, two of the power transistors are used as drivers while the other twelve are used in the output stage. All are mounted on a large single sided heatsink. The PC board meas­ures 362 x 99mm. This month we are presenting just the PC board module itself but because of its sheer size and power output we strongly recommend that readers do not “do their own thing” and install the module with just any old power supply components and in just any old chassis. So next month we will present the full details of mounting the PC module in a chassis with a big power supply, fan cooling, the overload protection module presented in April 1997 and so on. By the way, we will be presenting it as a rack mounting mono amplifier only; if you want that magnificent stereo setup mentioned above, you would need two of these mono amplifi­ers. Performance The main performance parameters are summarised in the accompanying specifications panel and also demonstrated in a number of graphs. These indicate that just because a power amplifier deliv­ers a lot of power it does not mean that it cannot deliver high performance as well. This amplifier is very quiet (-122dB A-weighted with respect to full power into 8Ω) and has low distor­tion, typically around .01% or less. In fact, the amplifier is quieter than any CD player on the market. Note that there is not a lot of difference between the music power output and the continuous power output of this ampli­fier; ie, 500W continuous versus 590W music power. This amounts to a “dynamic headroom” figure of 0.7dB for 4Ω loads. This is a reflection of the fact that the power supply is very well regu­lated – a consequence of using an 800VA transformer and a filter capacitor bank of 80,000µF in total. While this may seem extravag­ant, cutting back on the power supply parameters does prejudice the performance. Note also that our power figures are quoted for a mains supply voltage of 240VAC. Typically, the mains supply is higher than this and so the maximum “unclipped” power output will be somewhat higher again. Bipolars vs. Mosfets In line with our philosophy of generally not using Mosfets in audio amplifiers, we have used bipolar tran- sistors in the output stages. Bipolar transistors have the advantage of requir­ing a lower quiescent current (to avoid crossover distortion) and for a given supply voltage they deliver more power than an equiv­alent design using Mosfets. Bipolars are also generally cheaper than equivalent complementary Mosfets (ie, N-channel and P-chan­nel pairs). Furthermore, as a result of our recent testing of this amplifier under conditions of maximum power dissipation, we are convinced that a Mosfet amplifier of this power rating would require considerably larger fan-cooled heatsinks if it was to be able to deliver its rated power on a continuous basis. Mosfet amplifiers are reputed to be almost “unburstable” because if they become overheated, they tend to shut down. While this is an advantage under overload conditions, this characteristic is a drawback when you want the amplifier to deliver lots of power on a continuous basis. As a Mosfet amplifier gets hotter, it deliv­ers less power. If it gets very hot, it throttles right back. By contrast, if a bipolar design becomes very hot, it still keeps on delivering the goods and the heatsink must prevent the output transistors from becoming overheated otherwise they will be destroyed. Overall though, a bipolar design is more efficient and requires less heatsinking. AUDIO PRECISION SCTHD-HZ THD+N(%) vs FREQ(Hz) 5 19 JUN 97 22:46:21 1 0.1 0.010 0.001 20 100 1k 10k 20k Fig.5: THD versus frequency at 250W RMS into a 4Ω load. AUDIO PRECISION SCTHD-HZ THD+N(%) vs FREQ(Hz) 5 19 JUN 97 22:44:35 1 0.1 Circuit details The full circuit diagram is shown in Fig.1. Aside from the large number of output transistors, the circuit is almost identi­cal in configuration to the lower power designs featured in April 1996 and March 1997. It also incorporates the same short-circuit overload protection circuit as in the March 1997 design. For the benefit of those readers who have not seen the previous articles and for the sake of completeness we shall go through the circuit description in detail. Note that the supply rails are ±80V or a nominal 160V in total, under no signal conditions. This very high voltage has required us to specify more rugged transistors than have been required in the past. This is particularly the case for the driver transistors, as already mentioned, and for the input transistor pair, Q1 & Q2. In 0.010 0.001 20 100 1k 10k 20k Fig.6: THD versus frequency at 150W RMS into an 8Ω load. the latter case, we have specified two 2N5401s rather than the BC556s we have used in the past. The 2N5401s have a collector voltage rating of 150 volts versus 80 volts for the BC556. The input signal is coupled via a 2.2µF capacitor and 1.2kΩ resistor to the differential pair of transistors Q1 & Q2. Q3 is a constant current source which sets the current though the differ­ential pair. The current through Q3 is set by diodes D1 & D2 and this sets the voltage across Q3’s 120Ω emitter resistor to 0.85V. This sets the current though Q3 to 7mA and so this is shared by Q1 & Q2 at 3.5mA each. Q3 is included instead of a common emitter “tail” for Q1 & Q2 because it renders the amplifier less sensitive to variations in the power supply rails. This is known as PSRR (power supply rejection ratio) and all good amplifier August 1997  29 AUDIO PRECISION SCFRQRES AMPL(dBr) vs FREQ(Hz) 5.0000 19 JUN 97 22:40:55 4.0000 3.0000 2.0000 1.0000 0.0 -1.000 -2.000 -3.000 -4.000 -5.000 20 100 1k 10k 20k Fig.7. frequency response at 20W into a 4Ω load. AUDIO PRECISION SCFRQRES AMPL(dBr) vs FREQ(Hz) 5.0000 19 JUN 97 22:42:24 4.0000 3.0000 2.0000 1.0000 0.0 -1.000 -2.000 -3.000 -4.000 -5.000 20 100 1k 10k 20k Fig.8: frequency response at 10W into an 8Ω load. designs, including op amps, feature a very high PSRR. Current mirror The collector loads of Q1 & Q2 are provided by Q4 & Q5 which operate as a “current mirror”. While it is a little hard to visualise just how a “current mirror” works, it is easier if you think of Q5 acting as a sharp 30  Silicon Chip cutoff diode, providing a voltage at the base of Q4 which is equal to the base-emitter voltage drop of Q5 (about 0.6V) plus the voltage drop across its 220Ω emitter resistor. What happens is that if Q2 tends to draw more than its share of emitter current from Q3, the voltage at the base of Q4 tends to increase and so Q4’s collector current tends to rise also. This forces Q1 to pull a bit more current and stop Q2 from taking more that its fair share. We say that Q4 “mirrors” Q5 and so Q1 “sees” a collector load which is a higher impedance than would otherwise be the case. The result is increased gain and improved linearity from the differential input stage. As a matter of interest, current mirror stages are very commonly used in op amp ICs, partly because they are easy to design in and partly because of their enhanced performance. The signal from the collector of Q1 drives a cascode stage comprising transistors Q7 & Q8, together with the constant cur­rent load transistor Q6 (top of the circuit). The cascode stage is another circuit which is a little hard to visualise but if you break it into sections, it is easier. Note that Q8 has a 3.3V zener diode ZD1 to hold its base voltage constant and so Q8 acts like an emitter follower to provide a constant collector voltage to Q7. This eliminates any gain variations (non-linearities) which would otherwise occur if Q7’s collector voltage was free to vary. The varying current drawn by Q7 becomes the input signal to the emitter of Q8 which is effectively operating as a “grounded base” stage. Q8 converts the varying signal current at its emit­ter into a varying signal voltage at its collector. The combined effect of operating such a cascode stage is improved linearity and bandwidth compared with a single common emitter stage. A 100pF capacitor from the collector of Q8 to the base of Q7 rolls off the open loop gain of the amplifier to ensure a good margin of stability; ie, to eliminate the possibility of the ampli­fier oscillating supersonically. The output from the cascode stage is coupled to the driver transistors, Q10 & Q11. As mentioned previously, these are MJL21193/94 power transistors, the same as in the output stage. Note that the signals to the bases of Q10 & Q11 are identical, apart from the DC offset provided by Q9. Vbe multiplier In setting the DC offset between Q10 & Q11, Q9 is actually setting the quiescent current in the output stages. It provides a forward bias of about 2.3V or so between the bases of Q10 & Q11 so that they are always slight- ly turned on, regardless of whether signal is present or not; that is why it is referred to as “quiescent” current. Q9 acts as a “Vbe multiplier”, multiplying the voltage between its base and emitter by the ratio of total resistance between its collector and emitter to the resistance between its base and emitter. In practice, trimpot VR2 is adjusted not to give a particu­lar voltage between the collector and emitter of Q9 but to set the quiescent current through the output transistors. We’ll discuss how this is done in the setting up procedure. It is important that the bias voltage produced by Q9 tracks the temperature of the output stage transistors. As the output transistors become hotter, Q9’s collector-emitter voltage should drop, so that the quiescent current is reduced and the danger of thermal runaway is averted. Our prototype photo this month shows Q9 directly on top of Q12 but next month it will be shown above Q12. Output stage The output stage of the amplifier is effectively a comple­mentary symme- try emitter follower, comprising six NPN transistors and six PNP transistors. We need this many transistors to safely deliver the high peak currents involved (up to 17 amps peak) at high voltages. The load line curves of Fig.2 demonstrate that while 12 output transistors are adequate to cope with reactive 4Ω loads (typified by the 2.83Ω + j2.83Ω curve), there is not a lot of power capacity to spare when you look at the 1200W and SOAR hyperbola curves. In other words, while 12 big power transistors might look like a lot, every one of them is needed to safely deliver full power into typical 4Ω loudspeaker loads. Each output power transistor has a 0.47Ω emitter resistor and this more or less forces the output transistors to roughly share the load currents. If one of the power transistors tends to take more than its share of load current, the corresponding voltage drop across its emitter resistor will be proportionately higher and this tends to throttle the transistor back until its current comes back into line with the others. The emitter resistors also help to stabilise the quiescent current to a small degree and they slightly im- prove the frequency response of the output stage by providing current feedback. Gain setting Negative feedback is applied from the output stage back to the base of Q2 via an 18kΩ resistor. The amount of feedback is set by the 18kΩ resistor and the 560Ω resistor at the base Q2. These set the gain of the amplifier to 33. The low frequency rolloff is set mainly by the ratio of the 560Ω resistor to the impedance of the 100µF capacitor. This gives a -3dB point of about 2.8Hz. The 2.2µF input capacitor and 18kΩ bias resistor to Q1 have similar effect and give a -3dB point of 4Hz. The two time-constants combined give an overall rolloff of about 7Hz. At the high frequency end, the 820pF capacitor and 1.2kΩ resistor feeding the base of Q2 form a low pass filter which rolls off frequencies above 160kHz (-3dB). The overall amplifier frequency response is demonstrated in the curves of Fig.7 and Fig.8. An output RLC filter comprising a 5.7µH choke, a 6Ω resis­tor and a 0.15µF capacitor couples the signal to the loudspeaker. It isolates the am- SILICON CHIP This advertisment is now out of date. Please feel free to visit the advertiser’s website: www.emona.com.au August 1997  31 Parts List For 500W Amplifier Module 500 amplifier PC board 1 PC board, code 01208971, 362mm x 99mm 4 20mm fuse clips 2 5A or 7.5A 20mm fuses (see text) 1 coil former, 24mm OD x 13.7mm ID x 12.8mm long, (Philips 4322 021 30362) 1 2-metre length 1mm enamelled copper wire 1 200Ω trimpot (Bourns 3296W or similar) (VR2) 1 100Ω multi-turn horizontal mount trimpot (VR1) 7 PC stakes 2 TO126 heatsinks, Jaycar Cat. HH8504 or similar 1 single-sided heatsink, 400mm wide x 118mm high x 48mm deep, or two 200mm x 118mm x 48mm 14 TO-3P insulating washers 2 TO-126 insulating washers 17 3mm x 10mm screws 3 3mm nuts Semiconductors 2 2N5401 PNP transistors (Q1,Q2) 2 BC556 PNP transistors (Q3,Q25) 4 BC546 NPN transistors (Q4,Q5,Q7,Q24) 1 MJE350 PNP transistor (Q6) 2 MJE340 NPN transistors (Q8,Q9) 7 MJL21194 NPN power transistors (Q10,Q12-Q17) plifier from any large capacitive react­ ances in the load and thus ensures stability. Perhaps more importantly, the filter attenuates any RF signals picked up by the speaker leads and stops them being fed back to the amplifier’s input stage where they could cause audible breakthrough – no-one likes listening to radio stations when they are supposed to be hearing CDs. Overload protection & offset adjustment Two other circuit features need to be mentioned: DC offset adjustment and overload protection. Strictly speak­ing, the DC offset adjustment is not really necessary if the amplifier is not to be used with an output transformer, as 32  Silicon Chip 7 MJL21193 PNP power transistors (Q11,Q18-Q23) 4 1N914 small signal diodes (D1,D2,D3,D4) 2 1N4936 fast recovery diodes (D5, D6) 1 BZX55C3V3 3.3V 0.5W zener diode (ZD1) Capacitors 4 100µF 100VW electrolytic 1 100µF 16VW electrolytic 1 2.2µF 16VW electrolytic 1 0.15µF 275VAC (Philips MKP 2222 336 10154) 5 0.1µF 100VW MKT polyester 1 820pF MKT polyester or ceramic 1 100pF 500V ceramic (Philips 2222 655 03101) Resistors (0.25W, 1%) 4 22kΩ 1W 2 18kΩ 1 6.8kΩ 1W 1 1.2kΩ 1 560Ω 1 470Ω 2 390Ω 5W 10% 4 270Ω 2 220Ω 1 180Ω 1 120Ω 5 100Ω 2 30Ω 3 18Ω 1W 12 0.47Ω 5W 10% it would be if it was driving a 100V line transformer for PA work. However, because we envisage that some readers will want to use the amplifier for public address, we have included DC offset adjustment. This is provided by the 100Ω trim­ pot (VR1) between the emit­ters of the input pair, Q1 & Q2. VR1 is used to adjust the current bal­ance between the input pair and this, because it is a DC feedback circuit, causes the DC offset at the output to vary. The trimpot is adjusted to make the DC offset as close to 0V as possible; it should be possible to keep to less than ±5mV. Transistors Q24 & Q25 and diodes D3 & D4 provide the over­load protection feature. Q24 monitors the current flow through the emitter resistor of Q12, via a voltage divider consisting of a 300Ω resistor and a 270Ω resistor. Normally, Q24 & Q25 are off and play no part in the ampli­fier’s operation. However, if the current through the 0.47Ω resistor of Q12 exceeds about 3 amps, Q24 begins to turn on and shunts the base current from Q10, the associated driver transis­tor. This means that not only is Q12 throttled back, but so are the other five NPN output transistors, Q13-Q17, because they all must operate in an identical way. Hence the peak output current is prevented from exceeding about 18 amps. This means the amplifier can deliver full power into a 4Ω load but if a 2Ω load, for example, was connected, the power output would be heavily limited. The same process happens for Q25 which monitors the emitter current of Q18 (and thus Q19-Q23). The diodes D3 & D4 are included to prevent Q24 & Q25 from shunting the drive signal when they are reverse-biased; this happens for every half cycle of the signal to the driver transistors. Diodes D5 & D6 are included as part of the protection cir­cuitry and they absorb any large spikes which may be generated by the inductance of the loudspeaker when the current limiting circuit cuts the drive to the output transistors. D5 & D6 are fast recovery diodes, included to ensure their operation at high frequencies and high power. Thermal cutout Because the overload protection simply limits the current to the load, the output transistors and the fuses are protected from sudden death in the case of a momentary short circuit but if the overload (or short circuit) is maintained and the drive continues, the amplifier will very rapidly overheat and may still expire unless the fault condition is correctly quickly. To prevent failure of the output transistors, the circuit includes an 80°C thermal cutout. This is not shown on the circuit of Fig.1 but is a vital part nevertheless. It is part of the relay protection circuit to be presented next month. Next month, we’ll present the circuit of the power supply and for the relay protection circuit and give the construction details of the complete SC amplifier. 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  GIFT SUBSCRIPTION DETAILS RATES (please tick one) 2 years (24 issues) 1 year (12 issues) Australia (incl. GST)  $A135  $A69.50 Australia with binder(s) (incl. GST)**  $A159  $A83 New Zealand (airmail)  $A145  $A77 Overseas surface mail  $A160  $A85 Month to start__________________ Overseas airmail _____________________________  $A250  $A125 **1 binder with 1-year subscription; 2 binders with 2-year subscription YOUR DETAILS Your Name_________________________________________________ Message_____________________ _____________________________ Gift for: Name_________________________ (PLEASE PRINT) Address______________________ _____________________________ (PLEASE PRINT) Address___________________________________________________ State__________Postcode_______ ______________________________________Postcode_____________ Daytime Phone No.____________________Total Price $A __________ Signature  Cheque/Money Order   Bankcard   Visa Card   Master Card ______________________________ Card No. Card expiry date________/________ Phone (02) 9979 5644 9am-5pm Mon-Fri. Please have your credit card details ready OR Fax (02) 9979 6503 Fax the coupon with your credit card details 24 hours 7 days a week Mail order form to: OR Reply Paid 25 Silicon Chip Publications PO Box 139, Collaroy 2097 No postage stamp required in Australia August 1997  33 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.dse.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.dse.com.au Main Features •  Adjustable voltage •  Adjustable pulse width •  Adjustable pulse rate (frequency) •  Intermittent (pulsed) or continuous output •  Battery operation for safety Kill pain with: Transcutaneous Electrical Neural Stimulation Do away with analgesics and alleviate pain electronical­ly with a TENS Unit. This device produces pulses of current into elec­trodes placed on the skin adjacent the painful area and has a surprising success rate on most sufferers. The SILICON CHIP TENS unit provides all the necessary features and is considerably cheaper than commercially available units. By JOHN CLARKE 36  Silicon Chip T O BE IN CONSTANT and prolonged pain is a dreadful condi­tion and while analgesics can help, they cannot be used long-term without the risk of kidney and liver damage plus other side effects. The alternative method to pain relief is with the use of a TENS Unit. These are now regularly used to help pain victims with a good success rate. TENS is an acronym for Transcutaneous Electrical Neural Stimulation. This description can be simplified to a method which passes pulses of electrical current through the skin via elec­ trodes to stimulate the nerves below. This stimulation tends to prevent transmission across the nerve junctions and so the brain does not receive the pain sign­al. An alternative suggestion of why the TENS unit works in relieving pain is that the stimulation produces endorphins which are a natural pain killing substance. The effectiveness of TENS is to some extent dependent upon the willingness of the patient to believe that the treatment will work. It is widely used by physiotherapists and certainly has a high success rate on people who approach it as a “high technolo­gy” pain relief method. Fig.1: this scope waveform shows the continuous pulse train across the electrodes. The frequency is 221Hz. How it’s used The SILICON CHIP TENS Unit comprises a medium sized plastic case with several controls on the front panel. The controls adjust the output voltage, the pulse width and the pulse rate (frequency). Two electrodes connect the TENS Unit via a lead and these are placed on the skin adjacent to the painful area. The electrodes are readily available from most pharmacies. The TENS Unit produces high voltage pulses which pass the current between the electrodes via the skin and stimulate the underlying nerves. The controls are generally adjusted until the tingling is just a little too much for comfort. The sensation tends to decrease as time goes on and so the output voltage may need to be gradually increased over the period of one treatment, usually lasting 20 minutes or so. An intermittent control sets the TENS Unit to produce short bursts of voltage once every second rather than a continuously pulsed signal. This mode is useful for long treatment sessions and when the patient has become accustomed to the effect from Fig.2: this is the same pulse train as in Fig.1 but at a faster timebase setting, in this case 500µs/div. As you can see, the pulse amplitude is 80V peak and the width is 190µs. You can adjust the peak voltage down to 12V and the frequency to as low as 2Hz. The pulse width can be altered from 40-200µs. the continuous mode. The accompanying oscilloscope waveforms show the signals that are produced by the TENS Unit. Fig.1 shows the continuous pulse train across the electrodes. The frequency is 221Hz. Fig.2 shows the same wave- form at a faster timebase setting, in this case 500µs/div. As you can see, the pulse amplitude is 80V peak and the width is 190µs. You can adjust the peak voltage down to 12V and the frequency to as low as 2Hz. Pulse width can be al­tered from 40-200µs. August 1997  37 and the load current between Vout and the ground supply. We can maintain a constant Vout for a variety of loads by controlling the amount of time Q1 is switched on. Fig.6 shows the circuit configuration of the switching oscillator which modulates the output voltage of the step-up converter. Heart of the circuit is an IR2155 made by Internation­al Rectifier Corporation in the USA. It is described as a “high side self-oscillating power Mosfet/IGBT gate driver”. It is the ideal device where Mosfets or IGBTs need to be driven in a variety of configurations. Resistor R1 and capacitor C1 at pins 2 and 3 set the oscil­lator frequency and the result is that Mosfets Q1 and Q2 are turned on and off alternately, with a typical “dead time” of 1.2µs between one Mosfet turning off and the other turning on. Fig.3: this scope waveform shows the intermittent pulse output. In this case, the waveform consists of bursts of nine pulses every sec­ond. Fig.3 shows the intermittent mode. In this example, the waveform con­sists of bursts of nine pulses every second but this can be varied. Block diagram The block diagram for the TENS Unit is shown in Fig.4. The 6V supply from the battery is stepped up in the converter com­prising IC1 and T1. This provides a DC output adjustable from below 9V up to 80V, using VR1. The resulting DC voltage is con­verted to a pulsed signal using the switchmode oscillator. VR3 and VR4 set the fre- quency and pulse width respectively. An inter­mittent oscillator comprising IC4 is switched into circuit with S2 to gate the switching oscillator. This gives short bursts of the pulsed signal. Fig.5 shows how the basic step-up converter circuit oper­ ates. It comprises inductor L1 which is charged via transistor Q1 from the V+ supply. The charging current is shown as i1. When the transistor is switched off, the stored energy in L1 is dumped through diode D1 into capacitor C1. The actual voltage across C1 is dependent upon the amount of charge in L1 Diode pump Note that the voltage at the drain (D) of Q1 is greater than the supply voltage for the IR2155. For Q1 to fully turn on, its gate (G) must be raised above the source by several volts. This is achieved using a diode pump consisting of diode D2 and capacitor C2. Initially, the Vcc supply to the IC is set at about 15.6V due to an internal regulator and the current via R2 from Vsupply. In addition, Mosfet Q2 is switched on via a 15.6V signal at pin 5 driving its gate. Capacitor C2 now charges to the 15.6V supply via D2 and the switchedon Q2. When pin 5 goes low, Q2 is turned off and pin 7 is connected internally to pin 8 to switch on Q1. Q1 pulls pin 6 up to Vsupply and pin 8 is shifted to Vsupply plus the 15.6V across C2. So the circuit bootstraps itself up to whatever the Mosfet driving voltage needs to be. Pins 6, 7 and 8 of the IR2155 are floating outputs which can be shifted to 600 volts above the pin 4 ground. In our case we are only using the circuit to switch up to 80V. Circuit details Fig.4: this is the block diagram of the TENS circuit. The 6V supply from the battery is stepped up in the converter comprising IC1 and T1 to provide a DC output of up to 80V. The resulting DC voltage is converted to a pulsed signal using the switchmode oscillator. 38  Silicon Chip The full circuit for the TENS unit is shown in Fig.7. Power from the 6V battery is switched to the circuit via S1 and the 100µF capacitor decouples the supply. IC1 is the switchmode controller. It has a switching transistor at pin 1 and a feedback input at pin 5. The frequency of oscillation rate is Fig.5: this shows how the basic step-up converter circuit works. Inductor L1 is charged via transistor Q1 from the V+ supply. When the transistor is switched off, the stored energy in L1 is dumped through diode D1 into capacitor C1. set by the .001µF capacitor at pin 3 and the current flow through the primary of T1 is limited by the 0.22Ω resistor between pins 6 and 7. Current through T1’s primary is switched off when the voltage across this resistor exceeds about 300mV. Fig.6: this is switching oscillator which modulates the output voltage of the step-up converter. D2 and C2 constitute a diode pump to boost the supply voltage to correctly switch Q1. The voltage induced into T1’s secondary when the primary field collapses charges two 0.47µF capacitors via diode D1. Voltage feedback from VR1 and the 10kΩ resistor into pin 5 and trimpot VR2 sets the output voltage. VR2 is adjusted to give 80V when VR1 is at its maximum resistance. Transformer T1 is used instead of a single inductor, as depicted in Fig.5, for two reasons. Firstly, the maximum voltage allowed at pin 1 (the collector of the switching transistor within IC1) is 40V. Since we want 80V, the Fig.7: the TENS circuit uses IC1, T1 and diode D1 to step up the battery voltage to a maximum of 80V. This is modulated by the switchmode oscillator IC2 and Mosfets Q1 & Q2 to drive the skin electrodes. August 1997  39 Fig.8: the wiring details for the case and PC board. Take care to ensure that all polarised parts are correctly installed. 2.59:1 ratio between the primary and secondary of T1 will ensure that the pin 1 voltage will be only 30.9V. The second reason is so that the primary can provide a supply for the self-oscillating Mosfet gate driver, IC2. 40  Silicon Chip Diode D3 charges the associated 4.7µF capacitor and the voltage across it is limited to +39V by zener diode ZD1. This mechanism also limits the maximum voltage at pin 1 of IC1 to a diode drop above 39V due to D3; ie, +39.6V plus or minus the zener diode tolerance. IC2’s power is supplied via an LM334Z constant current source, IC3. The 68Ω resistor between the R and V- pins of IC3 sets the constant Capacitor Codes  Value IEC Code EIA Code  0.47µF   470n   474  0.33µF   330n   334  0.1µF   100n   104  .001µF   1n0   102 current to 1mA. IC3 has a maximum voltage rating of 30V so it might seem that a voltage of 39V from ZD1 could present a problem for this current source chip. However, an internal zener diode in IC2 regulates the supply voltage at its pin 1 to +15.6V and so the maximum voltage across IC3 will be 39V - 15.6V = 23.4V. Q1 and Q2 are 200V Mosfets which switch the voltage from the two 0.47µF capacitors to produce the requisite output pulses on the electrodes. Q1 & Q2 constitute a “totem pole” output stage with Q1 turning on to charge the 0.47µF output capacitor via the series 150Ω resistor and the load resistance (which in this case is the patient). Each time Q1 turns off, Q2 turn turns on to discharge the capacitor via the series 150Ω resistor. Putting it another way, Q1 can be regarded as controlling the pulse width of the output waveform while Q2 controls the pulse rate (ie, the frequency). In more detail, Q2 is switched on for the time set by the 0.33µF capacitor at pin 3 and the resistance between pins 3 and 2 (of IC2). VR3 adjusts this on-time between about 0.5s and 5ms, giving a pulse rate between 2Hz and 200Hz. Q1 is switched on for the time duration set by potentiome­ter VR4, the Inside the TENS unit is a battery-powered circuit which produces up to 80V DC. This is pulsed by a pair of Mosfets to drive the electrodes. Note the three screws which are used as pillars to keep the battery holder in place. series 12Ω resistor and diode D4. The pulse width ranges between 40µs and 200µs. Intermittent mode IC4 is a 7555 CMOS timer which provides the intermittent mode. It operates as a free running oscillator but in a rather unusual configuration. The normal output at pin 3 is used to charge the 10µF capacitor at pins 2 & 6 via the 47kΩ resistor and diode D5 and discharge it via the parallel 100kΩ resistor. This gives a pulse waveform at pin 3 with an uneven duty cycle; the pulses are high for 0.22s and low for 0.7 seconds. However, we don’t use the normal output at pin 3 to modulate IC2. Instead, we use the capacitor discharge pin (pin 7). The pin 7 output is a Mosfet which is open circuit when pin 3 is Resistor Colour Codes  No.   1   1   1   1   1   3   1   1   1   1 Value 100kΩ 47kΩ 18kΩ 10kΩ 2.2kΩ 1kΩ 180Ω 150Ω 68Ω 12Ω 4-Band Code (1%) brown black yellow brown yellow violet orange brown brown grey orange brown brown black orange brown red red red brown brown black red brown brown grey brown brown brown green brown brown blue grey black brown black red black brown 5-Band Code (1%) brown black black orange brown yellow violet black red brown brown grey black red brown brown black black red brown red red black brown brown brown black black brown brown brown grey black black brown brown green black black brown blue grey black gold brown black red black gold brown August 1997  41 PARTS LIST 1 PC board, code 04307971, 157 x 87mm 1 plastic case, 188 x 98 x 37mm 1 adhesive label, 95 x 185mm 1 TENS electrode set with lead (available from chemists) 1 EF25 ferrite transformer assembly with N27 (Siemens) or 3C80 (Philips) ungapped cores and horizontal mounting bobbin plus clasp and spring (Philips 2 x 4312 020 3402 4, 1 x 4312 021 2626 1 and 1 x 4312 021 2612 1 and 1 x 4312 021 2619 1 or equivalent) (T1) 1 4 AA cell holder (rectangular) 1 battery clip for holder 4 AA cells 1 3.5mm phono panel socket 1 100kΩ linear pot. (VR1) 1 2MΩ linear pot. (VR3) 1 500Ω linear pot. (VR4) 3 16mm OD knobs with pointer marks 2 SPDT toggle switches (S1,S2) 1 3mm green LED (LED1) 1 3mm LED bezel 15 PC stakes 3 small cable ties 4 self-tapping screws to secure PC board 3 3mm x 20mm screws and nuts 1 60mm length of 3mm ID tubing 1 200mm length yellow hookup wire 1 200mm length blue hookup wire 1 300mm length black hookup wire 1 200mm length green hookup wire 1 300mm length red hookup wire 1 150mm length of twin wire rainbow cable 1 3.5-metre length of 0.5mm diameter enamelled copper wire Semiconductors 1 MC34063 DC-DC converter (IC1) 1 IR2155 Mosfet driver (IC2) 1 LM334Z current source (IC3) 1 ICM7555CN, LMC555CN, TLC555CP CMOS 555 timer (IC4) 2 IRF610 N-channel Mosfets (or equiv 200V <at>>1A, TO-220) (Q1,Q2) 1 39V 1W zener diode (ZD1) 2 1N4936 500V fast recovery diodes (D1,D2) 3 1N914, 1N4148 diodes (D3-D5) Capacitors 1 100µF 16VW PC electrolytic 1 10µF 25VW PC electrolytic 2 10µF 16VW PC electrolytic 1 4.7µF 63VW PC electrolytic 3 0.47µF 100VW MKT polyester 1 0.33µF 63VW MKT polyester 1 0.1µF 63VW MKT polyester 1 .001µF 63VW MKT polyester Resistors (0.25W, 1%) 1 100kΩ 1 180Ω 1 47kΩ 1 150Ω 1 18kΩ 1 68Ω 1 10kΩ 1 12Ω 1 2.2kΩ 1 0.22Ω 5W 3 1kΩ Fig.9: winding details for the transformer. Both the primary and secondary are wound using 0.5mm-diameter enamelled copper wire. 42  Silicon Chip high and conducting when pin 3 is low. Each time pin 7 of IC4 pulls low, it discharges the 0.33µF capacitor at pin 3 of IC2 and this stops IC2 from oscillating. This prevents any output to the electrodes and is an effective method of modulation. Construction The SILICON CHIP TENS Unit is built onto a PC board which is coded 04307971 and measures 157 x 87mm. It is housed in a plastic case measuring 188 x 98 x 37mm. An adhesive plastic label measuring 95 x 185mm is fitted to the lid of the case. Begin construction by checking the PC board for any defects such as shorted tracks or hairline breaks in the copper pattern. Repair these before assembly. The full wiring details are shown in the diagram of Fig.8. Insert the 15 PC stakes first. These are positioned at all the wiring points. Next, insert and solder in all the resistors. You can use the accompanying resistor colour code table when selecting the resistors although it is also a good idea to check each value with a digital multimeter before it is installed. Next, install the five diodes, making sure that the 1N4936s are used for D1 and D2. Three of the ICs are 8-pin DIP devices so don’t mix them up when installing them. Make sure that the ICs and Mosfets are correctly orientated when they are installed. The capacitors come next and the accompanying table shows the codes which may be on the MKT style devices to indicate their values. The electrolytic types must be oriented as shown and with the correct voltage rating. Higher voltage rated capacitors can be used. The winding details for the transformer are shown in Fig.9. Start by stripping the end of the 0.5mm enam­ elled copper wire and solder it to pin 1 on the bobbin. Wind on 44 turns in the direction shown and terminate the end to pin 4. The secondary is wound by soldering a 0.5mm wire to pin 8 and winding on 17 turns in the direction shown. Finish on pin 5. You can then wrap the windings in a few layers of insulation tape. The transformer is assembled by sliding the cores into place in the bobbin and securing them with the supplied clips. If no clips are supplied then you can secure the cores togeth-er with a cable tie around the core’s An effective alternative to analgesics can be provided by TENS in many situations. TENS stands for Transcutaneous Elec­trical Neural Stimulation and is widely used by physiotherapists for treatment of sports injuries and back pain. The skin electrodes can be readily purchased from your local pharmacy. former is wound correctly. If the primary and secondary are out of phase, the correct voltage cannot be obtained. Check that the voltage at pin 1 of IC2 is around +15V DC. With the pulse width pot (VR4) set fully clockwise and continuous mode selected, you should measure about +40V DC at pin 6, indi­cating that switching is taking place. If you have access to an oscilloscope, the output pulses can be observed to verify that the pulse width and frequency are to specification. The output can also be tested with a multimeter set to read AC volts. Connect your multimeter leads to the output socket and measure the voltage. You should obtain about 7VAC with all pots set to maximum when the continuous mode is selected. Note that this is only an indication of the Warning! perimeter. Insert the transformer into the PC board with the orienta­tion shown in Fig.8. Pin 1 of the bobbin is adjacent to the 0.47µF capacitor furthest from diode D1. To secure the battery holder, we used three 25mm-long 3mm screws and nuts in the positions shown near the transformer. These locate the 4-AA cell holder at the end of the case. We used some plastic sleeving over the screw threads to prevent scratch­ing the holder. The front panel label can be affixed to the lid of the case (the half with the brass thread inserts in each corner) and the holes drilled for the two switches, the 3mm LED bezel and the three pots. Attach all these components to the lid. Note that some pots with long shafts may need to be cut to length before assembly. Drill a hole in one of the end panels for the output socket. Follow the diagram of Fig.8 to connect all the components on the lid to the PC board. The battery clip is se­ cured to the PC board with a cable tie to prevent the wires from breaking at the PC stakes. Cable ties are also used to secure the wiring into a neat loom. Testing Fit the batteries and connect a multimeter (set to the 200V DC range) •  This TENS Unit (or any other similar device) must not be used on a person with a Heart Pacemaker. •  Do not connect the electrodes to the body so that there can be a flow of current through the heart. •  Electrodes must not be placed on the neck, since this can stimulate nerves which control breathing and blood pressure. •  Do not use the TENS Unit for headaches or attach the elec­trodes to the head. •  Do not be tempted to use the TENS Unit from a mains adap­tor, plugpack or power supply. This could be dangerous if a breakdown occurs in the isolating transformer. If you want to reduce the cost of battery replacement, we suggest using re­chargeable nicad cells. between the (-) terminal of the battery and the metal tab (drain) of Q1. Switch on and check that LED1 lights and that there is voltage on Q1’s drain. Set the voltage pot VR1 fully clockwise and adjust trimpot VR2 for a reading of +80V. If you are not able to obtain the correct voltage, check that the trans­ output; some multi­meters may give different readings With intermittent mode selected, you should see the voltage changing from 0V to a higher reading. Using TENS Connect the electrodes to the TENS Specifications Output level .........................................................................................2-80V Output pulse width ........................................................................ 40-200µs Frequency ......................................................................................2-220Hz Intermittent rate ........................................................... 700ms off; 220ms on Supply Voltage ......................................................................................... 6V Current Consumption ...................................30mA <at> 80V out and 6V input (frequency and pulse width at mid setting) August 1997  43 OUTPUT CONTINUOUS OFF + + + POWER 4 5 INTERMITTENT 1 MAX 9 MIN PULSE RATE 4 MAX PULSE WIDTH 5 6 7 3 2 8 + 1 1010 8 + 1 9 MIN 7 2 8 + 6 3 7 3 2 5 4 6 9 0 10 LEVEL 10 10 Fig.10 (above): this is the actual size artwork for the PC board. Check your board carefully against this pattern before installing any of the parts. Fig.11 (right): actual the size artwork for the front panel. unit using the 2.5mm plug to 2 x 2mm probe lead as supplied with the electrodes. If you wish to make your own leads, the 2mm probes are available from Dick Smith Electronics (Cat. P-1750). The electrodes should be smeared with K-Y* jelly (*trade mark of John­son & Johnson Pacific) or salt water solution to provide a reliable skin contact. They can be attached to the skin using any of the variety of tapes used to secure wound dressings. Attach the electrodes in 44  Silicon Chip TENS (Transcutaneous Electrical Neural Stimulation) position on either side of the pain source. Before switching on the TENS Unit be sure that the voltage is turned down to the minimum. Wind the voltage up until sensa­tion can be felt and adjust the pulse rate and width for the desired effect. The voltage will need to be wound up during treatment to compensate for the body’s adaptation to the stimula­tion. The intermittent selection is used where the treatment period is long (normal treatment sessions are typically for 20 minutes) or where the user finds the continuous effect to be waning. Further details on the TENS treatment techniques can be obtained from your General Practitioner. NOTE: Electrodes may be difficult to locate. Two sources are as follows: Water Fuel, 18 Springfield Road, Springvale, Vic 3172, phone (03) 9574 0002; or, Masters Medical, 8 Palmer Street, Parramatta, NSW 2150, phone SC (02) 9890 1711. SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.jaycar.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.jaycar.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.jaycar.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.jaycar.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.jaycar.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.jaycar.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.jaycar.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.jaycar.com.au SATELLITE WATCH Compiled by GARRY CRATT* Changes to BMAC services from Optus B3 Optus B3: . June 10 saw several changes to BMAC services on this satel­lite, affecting viewers in the Northern Territory and South Aus­tralia. ABC South Australia, ABC Northern Territory and Imparja have all moved in frequency and viewers using non-frequency agile Plessey receivers will need to upgrade their channel allocation chip, in order to tune the new frequencies. Details of all chang­es are carried on the ABC’s Internet web site at: http://ww.abc.net.au/corp/translist/ howtune.htm. Asiasat 2: Recent additions to this satellite include the American government broadcaster “Worldnet” at IF 1270MHz, horizontal polarity, 6.6MHz audio. This service previously operated on Intelsat 511 at 180°E. That service has now been discontinued. Another new broad­ caster on this satellite is “Baztab” TV, an Iranian program, broadcast Monday to Thursday from 2.45-4am AEST. Previously located on Arabsat 2B, this service operates at IF 1470MHz, horizontal polarity. Also sharing the same frequency is “ Mahuga Hadeen TV”, another Iranian broadcaster, which operates Monday to Thursday from 4-5am AEST. Recent changes to the Star TV digital service on this satellite saw the un­ encrypted Sky News UK and Star Plus movie channel disappear, presumably now operating with conditional access. These services were operating at 1250MHz IF. The ESPN digital feeder channel at 1450MHz is still operating “open key”. Panamsat 2: Several new stations appeared during June on this satel­lite. WCETV at IF 1250MHz, vertical polarity, 6.2/6.8 audio, appears to be a Chinese gambling channel operating daily from 11pm-6am AEST. AB Asia, a similar channel operates at 1335MHz IF, vertical polarity. Broadcaster TVSN has added Chinese and Japanese audio chan­ n els to their transponder, on The test pattern from Space TV Systems in Taiwan. 5.55MHz and 5.75MHz respectively. five Chinese channels and two hardThe broadcaster has added similar ad- core XX rated “Exxxstacy” channels. ditional audio subcarriers to their sig- By July 1, the two XX rated channels had been dropped but the others con­ nals on both Asiasat 2 and Palapa C2. tinue testing. One strange appearance on Pas 2 Space TV systems say their subK-band late in June was a 4-channel mence in digital bouquet that included Northern scription service will com­ Territory broad­caster Imparja and ABC September. Although details of the type of digital receiver required are Central. Signals appeared at 1000MHz unknown at present, the signal is IF, horizontal polarity. viewable during the test phase using Nokia, Panasat 630 and Hyundai digi­ Intelsat 802: Intelsat 802 was successfully tal receivers. launch­ed by Ariane V96 on June 25. The satellite will be deployed at 174°E, Gorizont 30: Papua New Guinea broadcaster replacing Intel­ sat 701, which will EMTV has added a new radio broadreplace Intelsat 511 at 180°E. I701 is sched­uled to commence operations at caster to its analog transponder. Loer frequency 180°E in September. These changes cated at audio subcarri­ will effectively eliminate the inclined 7.4MHz, the radio station is called 93FM and broad­ casts a mixture of orbit tracking now re­quired to receive English and local languages. I511. SC Intelsat 702 (177°E): Space TV Systems (Taiwan) commenced trials of their digital service in late June. Early test channels included * Garry Cratt is Managing Director of AvComm Pty Ltd, suppliers of satellite TV reception systems. Phone (02) 9949 7417. http://www.avcomm.com.au August 1997  53 By RICK WALTERS Addressable card for driving a stepper motor This interface card allows you to drive a stepper motor using software control. It plugs into your PC’s parallel port and you can connect up to eight units in daisy-chain fashion. The interface card featured here is the first of two new cards that allow you to control stepper motors via the parallel port of a PC. It is capable of driving one stepper motor, while the second unit (to be described next 54  Silicon Chip month) is capable of driving two stepper mo­tors. In practice, you can connect up to eight cards (in daisy-chain fashion) to the printer port, so that you can control eight different motors. Each card is set with a unique address from 1-8, so that it can be individually selected. In addition, two or more cards can be coded with the same address in a master-slave setup, so that even more motors can be controlled. Of course, those cards that have the same address will identically control their motors. In operation, an address from 0-7 is placed on three pins of the PC port connector, then the strobe line is toggled. This latches the address in a decoder. If this address matches that selected by a jumper on the card, the logic levels present on the port’s normal data lines are latched (stored) and fed to the motor drivers. Fig.1 (right): the circuit is based on address decoder IC1 and 8-bit data latch IC1. When the correct address is fed to IC1, the data on the Port A lines is latched into IC1 and transferred to the Q outputs. These outputs then drive transistors Q1Q12 to control the stepper motor. August 1997  55 Note that the card is capable of driving the stepper motor in both the forward and reverse directions. When the motor is not stepping, the driver transistors are turned off to prevent the motor from overheating. Circuit details The circuit of the card is shown in Fig.1. It uses IC1, a one-of-eight active low decoder, as the address latch. Basically, this IC looks at the binary coded decimal (BCD) data on its A, B & C inputs and pulls the corresponding decimal output (Y0-Y7) low. In greater detail, this only occurs when the strobe line from inverter stage IC3b goes to a logic high (+5V). This momen­ tarily pulls the latch enable input (pin 4) of IC1 high via a .001µF capacitor. The decoded output then goes low (0V) to give a unique address. If this is the output selected by the address link, the decoded logic low is fed to pin 2 of IC3a. IC3d inverts the strobe signal and so pin 3 of IC3a will also be low. As a result, pin 1 of IC3a goes high and momentarily pulls the latch enable input (pin 11) of IC2 high via a second .001µF capacitor. IC2 is a 74HC573 8-bit data latch. When its LE input is taken high, the data present on its Data inputs (D0D7), as fed in from Port A of the parallel port, is latched and transferred to the Q outputs. The latch enable signal then goes low 47ms later (as set by the associated 47kΩ pull-down resistor), so that the data remains latched until the next strobe signal. Resistors (0.25W, 1%) 1 10MΩ 4 2.2kΩ 1 47kΩ 1 470Ω 9 10kΩ from the positive supply rail through Q1, coil MA and Q4 to ground. Conversely, when outputs Q1 & Q2 are high and Q0 & Q3 are low, transistors Q6, Q2 and Q3 are tuned on and the current flows through the coil in the opposite direction. Therefore, depending on the logic levels at the Q0-Q7 out­puts of IC2, we can control the direction of the current through the two coils and thus the stepping direction of the motor. If all outputs are low, all the transistors are off and no current flows through either coil (ie, the motor is stopped). To actually step the motor it is necessary to switch the current through the coils in a logical sequence. Table 3 lists the different modes for driving a stepper motor, along with the binary code required at IC2’s output which, of course, is identi­cal to that at CON1. The decimal value can be used in a Basic program to apply the correct bit pattern to the parallel port. Almost all motors can be powered from the 12V supply, in­cluding centre-tapped 5V motors (because we don’t use the CT). If you want more torque and a faster stepping speed, you can run the motor from a higher voltage, in which case a resistor must be added in series with each coil to keep the motor current within specification. It is the inductance of the motor windings which limits the current and hence the torque, so by applying a higher voltage we get a higher initial current. Miscellaneous Tinned copper wire for links Card selected indicator Parts List 1 PC board, code 07108971, 120 x 112mm 1 DB25 PC-mount male rightangle connector 1 stepper motor, Oatley Electronics M35 or equivalent 1 8-way x 2-pin header strip (2.54mm pitch) 1 jumper for header strip 1 3-way terminal block (5.08mm pitch) 1 4-way terminal block (5.08mm pitch) Semiconductors 1 74HC137 decoder (IC1) 1 74HC573 8-bit latch (IC2) 1 74HC02 quad nor gate (IC3) 4 BD682 PNP Darlington transistors (Q1,Q2,Q7,Q8) 4 BD679, BD681 NPN Darlington transistors (Q3,Q4,Q9,Q10) 4 BC548 NPN transistors (Q5,Q6,Q11,Q12) 1 1N914 small signal diode (D1) 1 5mm red LED (LED1) Capacitors 2 100µF 25VW PC electrolytic 2 0.1µF monolithic ceramic 1 0.1µF MKT polycarbonate 2 .001µF MKT polycarbonate The only circuit function yet to be described is the card selected indicator. This is based on D1 and IC3c and lights LED1 whenever a valid address is received. This feature provides a convenient way of checking which card has been selected at any given time in a multi-card system. The way in which this works is quite straightforward. As shown, pins Motor drivers Transistors Q1-Q6 and Q7-Q12 form two bridge circuits which drive the stepper motor coils. One circuit is controlled by the Q0-Q3 outputs of IC2, while the other is controlled by the Q4-Q7 outputs. Because these two bridge circuits are identical, we shall only describe the circuit based on transistors Q1-Q6. We’ll begin by considering what happens when outputs Q0 & Q3 of IC2 are high and Q1 & Q2 are low. In this case, transistors Q5, Q1 & Q4 will all be turned on and so current flows Table 1: Resistor Colour Codes ❏ No. ❏  1 ❏  1 ❏  9 ❏  4 ❏  1 56  Silicon Chip Value 10MΩ 47kΩ 10kΩ 2.2kΩ 470Ω 4-Band Code (1%) brown black blue brown yellow violet orange brown brown black orange brown red red red brown yellow violet brown brown 5-Band Code (1%) brown black black green brown yellow violet black red brown brown black black red brown red red black brown brown yellow violet black black brown TRANSFORMERS •  TOROIDAL •  CONVENTIONAL •  POWER •  OUTPUT •  CURRENT •  INVERTER •  PLUGPACKS •  CHOKES STOCK RANGE TOROIDALS BEST PRICES APPROVED TO AS 3108-1994 SPECIALS DESIGNED & MADE 15VA to 7.5kVA Tortech Pty Ltd 24/31 Wentworth St, Greenacre 2190 Phone (02) 642 6003 Fax (02) 642 6127 Fig.2: install the parts on the PC board as shown here. Don’t forget to fit a jumper to the pin header to select the address of the card and take care when mounting the power transistors as they don't all face in the same direction. 8 & 9 of IC3c are normally pulled high via a 10MΩ resistor and so pin 10 is low and LED1 is off. However, when a valid address is received, the decoded output from IC1 goes low and so pins 8 & 9 of IC3c are pulled low via D1. This in turn switches pin 10 of IC3c high and so LED1 lights to indicate that the card has been selected. Because a card can be selected and deselected very quickly, a 0.1µF timing capacitor is included between the inputs of IC3c and ground. This ensures that the LED stays lit for one second after the card has been de­ selected. Building the card The circuit is easy to build, with all the parts mounted on a PC board coded 07108971 (120 x 112mm). Fig.2 shows the parts layout on the board, while Fig.3 shows the full-size etching pattern. Begin by checking your etched board for defects by compar­ ing it with Fig.3. In particular, check for undrilled holes and shorts between tracks, especially around the IC pads. This done, install the wire links (11), followed by the resistors and diodes. Table 1 shows the resistor colour codes but it is also a good idea to check the values using a digital multimeter, just to make sure. The capacitors can be installed next, followed by LED1 and the transistors. Be careful when fitting the transistors as two different TO-220 types are used. Note also that the metal faces of Q3, Q4, Q9 & Q10 (all BD679) face towards CON1 (the DB25 connector), while the metal faces of Q1, Q2, Q7 & Q8 (all BD682) face towards CON3. Take care to ensure that the LED is correctly oriented. Its anode lead will be the longer of the two, while the cathode lead will be adjacent to a flat section on the bevel at the bottom of the plastic body. Finally, complete the assembly by fitting the 8-way pin header and the P.C.B. Makers ! If you need: •  P.C.B. High Speed Drill •  P.C.B. Guillotine •  P.C.B. Material – Negative or Positive acting •  Light Box – Single or Double Sided – Large or Small •  Etch Tank – Bubble or Circulating – Large or Small •  U.V. Sensitive film for Negatives •  Electronic Components and •  •  Equipment for TAFEs, Colleges and Schools FREE ADVICE ON ANY OF OUR PRODUCTS FROM DEDICATED PEOPLE WITH HANDS-ON EXPERIENCE Prompt and Economical Delivery KALEX 40 Wallis Ave E. Ivanhoe 3079 Ph (03) 9497 3422 FAX (03) 9499 2381 •  ALL MAJOR CREDIT CARDS ACCEPTED August 1997  57 Listing 1 10 REM Step motor clockwise 20 PORTA = &H378 ‘This is for LPT1 Enter &H278 for LPT2 30 PORTC = PORTA + 2 ‘and card 1 selected 40 DATA 153, 150, 102, 105, 102, 150, 153, 105 50 FOR A = 1 TO 4: READ ROTCW(A): NEXT ‘Read data for clockwise steps 60 FOR A = 1 TO 4: READ ROTCCW(A): NEXT ‘Read data for anti-clock steps 70 OUT PORTA,105: OUT PORTC,11 ‘Set motor to known position 80 FOR A = 1 TO 12 ‘Go forward 12 steps of 30 degrees 90 FOR B = 1 TO 4: OUT PORTA,ROTCW(B) ‘Four steps of 7.5 degrees 100 OUT PORTC,11: OUT PORTC,10 ‘Select card one, then take strobe low 110 FOR C = 1 TO 350: NEXT ‘Delay to allow motor to step 120 NEXT B: NEXT A 130 OUT PORTA,0: OUT PORTC,11: OUT PORTC,10 ‘De-energise motor coils 140 FOR A = 1 TO 20000: NEXT ‘Pause for a while 150 REM Now step motor anti-clockwise 160 FOR A = 1 TO 12 ‘Go backwards 12 steps of 30 degrees 170 FOR B = 1 TO 4: OUT PORTA,ROTCCW(B) ‘Four steps of 7.5 de­grees 180 OUT PORTC,11: OUT PORTC,10 ‘Select card one, then take strobe low 190 FOR C = 1 TO 350: NEXT ‘Delay to allow motor to step 200 NEXT B: NEXT A 210 OUT PORTA,0: OUT PORTC,11: OUT PORTC,10 ‘De-energise motor coils three connectors. Make sure that the DB25 connector is sitting flat against the board before soldering its pins. Testing To test the board you will need a 25-way “D” male-to-female cable (ie, a printer cable) and a power supply capable of supplying 5V at a few milliamps and 12V at up to 1A. If you are careful, you can pick up the 5V supply from the games port on the computer. The connec­ tions on the 9-pin “D” connector are pin 5 for the 5V line and pins 4, 5 and 12 for ground. The 12V rail can come from a suit­able plugpack supply. Alternatively, you can wait and build the power supply to be described in next month’s issue. Before applying power, connect the card to your computer’s parallel (printer) port LPT1 using the extender cable. You will also have to install a jumper on the pin header to set the ad­dress of the card. If you only have one controller card, you can choose any address you like although it’s probably best to fit the jumper to the C1 position. That way, you won’t have to alter the program shown in Listing 1 in order to address the card. Now load Basic and enter the program shown in Listing 1. You can omit the line numbers if you use Q-Basic. You can also omit the remarks (after the ‘) as they are only there to give you an idea of what the software is doing. When you run this program, the motor should rotate clock­ wise one revolution, stop and then step anticlockwise to its original position. A pencil mark on the gear will let you see what is happening. Check that LED1 on the card lights to confirm that the card has been addressed. If you use LP2 as the parallel port, you will have to change line 20 (ie, Table 2 Fig.3: check your board against this full-size artwork before installing the parts. 58  Silicon Chip Card No. Address Card 1 11 Card 2   9 Card 3 15 Card 4 13 Card 5   3 Card 6   1 Card 7   7 Card 8   5 change &H378 to &H278). The address value for each card from 1-8 is given in Table 2. The illogical sequence of the numbers is due to the fact that both C1 and C3 on PortC are inverted logic; ie, if they are programmed high in Basic (or any other language), they will actually go low. If the stepper motor you use is different to that specified in the parts list, your results may not be the same as ours. If the motor runs in the wrong direction, just swap the wires to pins 1 and 2 of CON3. The motor we used has 7.5° steps and if the one you use is different (eg, if it has 1.8° steps), you will have to change the number 12 in lines 80 & 160 to some other value to get a complete revolution. For example, you would have to change 12 to 50 for a motor with 1.8° steps. A close examination of the program shown in Listing 1 will reveal how it all works and you can experiment with your own values. The values we have used are for a single full step with both windings energised. You Up to eight cards can be connected to the printer port, so that you can control eight different motors. Each card is given a unique address by fitting a jumper to an 8-way pin header. may wish to load the “one winding energised” values into the program and compare the torque difference. Fault finding If it doesn’t work, the first thing to do is to check that you have the jumper or link set for card 1. If this is OK, check that LED1 lights when you run the program. If LED1 doesn’t light, connect pins 4 & 16 of IC1 together and run the program again. If the LED now lights, then the prob­lem probably involves IC3b or the components connected to pin 4 (LE) of IC1. The same technique can be used to test the circuitry that drives the latch enable input (pin 11) of IC2 (ie, connect pin 11 to pin 20). SC August 1997  59 SERVICEMAN'S LOG Just give it a flamin’ good thump Most jobs are fairly routine but these three jobs hardly fall into that category. Of course, the customer doesn’t always help and the one job that should have been straightforward was complicated by the customer’s rudeness and uncooperative attitude. A month ago, I was asked by Mrs Johnston to attend to her Sanyo TV. The problem didn’t sound like much in that most of the time the set worked perfectly. It was just that, every three days or so, it wouldn’t start although Mr Johnston could “fix” that by thumping the back. But it was an- 60  Silicon Chip noying and now it did it all the time. The set was a Sanyo CPP2601SV-00 employing an 84P-B26 chassis and is a large 63cm stereo remote control model. It all sounded so easy – just whip the back off, fix the obvious dry joint or loose plug, replace the back and Bob’s your uncle. A piece of cake really and what’s more, it should take no more than half an hour. I should have known better. I arrived at the appointed time full of optimism and had the back off, the soldering iron switched on and the meter ready before the tea arrived. The TV switched on perfectly and did so for the next 20 subsequent efforts. Mrs Johnston assured me that it always played up almost straight away but I know all about the contrariness of inanimate objects. I left it on while I finished my tea and then tried again. It still worked perfectly. I felt like Homer Simpson – TV goes on, TV goes off, TV goes on, etc. The time was slipping by, with no sign of a problem at the end of 30 minutes. It was time for a different approach. Using a strong flashlight, I examined every board very carefully but, as usual, access to the chassis was rather difficult. The leads to the front panel are far too short and the chassis could only be moved about 80mm out of the cabinet. Not only that, but there is a plastic support frame which obscures the main PC board. I decided to gently tap each board in turn but that made no difference. That was it – I couldn’t afford to waste any more time. I refitted the back, pushed the set back into its corner and switched it on for the last time. The set came on, to our mutual frustration. Mrs Johnston then had a go herself with the remote. She switched the set off and it wouldn’t come back on. How did she do that? I tried the remote and the main on/off switch – the set was completely dead. I was now too far committed to back away, so off came the back and we both tried switching the set on and off again. And would you believe it? – it now worked perfectly. I then replaced the back, carefully noting where it made contact with the chassis in case it was dislodging a plug or socket. This time, with the back on, Fig.1: the power supply circuit in the Sanyo CPP2601SV-00 63cm colour TV set. the set worked perfectly, no matter what either of us did. Three quarters of a hour had gone by now and we both had other things to do. Obviously, this was a job for the workshop and I advised the Johnstons accordingly. As it turned out, they were going on a fortnight’s holiday a few days later and so we organised for the set to be delivered to the workshop before they left. The fault appears Finally, the set was on the bench and the back came off yet again. Actually, the back wasn’t in very good condition. It is made of a very brittle hard plastic and had cracked in a few places where Mr Johnston had been hitting it. He must have been giving it a frightful whack on occasions! It took three days of continuous running before the fault finally appeared. And when it did, it didn’t take too much of a tap to make it work again for another three days. After about two weeks, I finally deduced that the problem was somewhere in the power supply although I still didn’t know the exact nature of the fault. The standby light could always be made to come on with the remote control, which meant that the +5V and +12V rails were fine from the Power Sub unit. And during one of the short periods while the set was not working, I measured approximately +325V on the collector of Q311 but found that there was no output at all on the five secondary power rails. Because it took so little vibration to make the set work again, all measurements had to be made with extreme delicacy. Eventually, I had precious multimeters and a CRO permanently hooked up all over the set, waiting for it to play up. This was a real nuis­ ance as it left me with only a limited amount of test equipment for fixing other things. My next step was to establish that the optocoupler (D311/TLP632) was working correctly. I found that there was +1V applied to pin 1 (on the LED side) when the set was off and 0V when the set was on. And there was 0V across the transistor on the secondary (hot side) of the optocoupler when the set was off and -20V across pins 4 & 5 when it was on. This implied that the optocoupler was working correctly. What’s more, leaving the meter connected between pins 4 & 5 of this device seemed to “correct” the fault because the set always started reliably while ever it remained connected. Obviously, the extra drain of the meter was having an effect on some part of the circuit. My two weeks were nearly up and something had to be done. I placed the set on its side for better access and shone a bright lamp onto the PC board. Freezing the various plug and socket contacts didn’t seem to make any difference and they all looked perfect. The components that did have a reaction to the freezer were the optocoupler (D311), chopper transistor Q331 and electro­lytic capacitors C327, C328 and C330. I changed them all and reworked the soldering on the entire board but, after three days, it played up again. Next, I replaced A301 (a JUO168 thick film IC which func­tioned as an error amplifier), along with resistors R306 and R307, the latter used to bias Q311. It made no difference and I was now only left with a few components that hadn’t been changed. I was fairly satisfied that it wasn’t a dry joint or a hairline fracture in the board and I was also fairly sure that the secondary (cold side) of the chopper transformer (T301) was OK. Of August 1997  61 Serviceman’s Log – continued course, I hadn’t checked the chopper transformer itself, mainly because I had regarded it as an unlikely culprit. However, as I was now running out of ideas, I removed it and carefully examined it, especially where the leads are wrapped around the posts. I could find nothing untoward, so I resoldered all the wire wraps and replaced the transformer. And that appears to have fixed the problem. Despite a further week of intensive testing, there was no sign of the fault and I can only conclude that one of the solder joints associated with the transformer must have been at fault, this despite the fact that they all appeared to be OK. The only other possible culprits are D332, D333 and C335 but none of these ever responded to tapping or freezing. I admit that it’s rather an unsatisfactory conclusion but I believe that the problem has either been permanently fixed or, at least, postponed for quite a while. Why can’t they make TV sets easier to service? Of course, the Johnstons will never 62  Silicon Chip appreciate how much effort I put in to overcome this obscure problem. But as Sanyo put it, that’s life! The crook VCR Mr Nasty brought his Samsung VCR in just after Christmas, complaining that it wouldn’t play. This was a VB-306 Winner mid-drive unit and when I removed the covers and inserted a cassette, it was pretty obvious where the fault lay. The loading arms wouldn’t move at all and it could only fast forward or rewind. Unfortunately, there is no access underneath the deck and the only way to get to the mechanism is to remove it, which is what I proceeded to do. This involves removing countless screws from the top and bottom, along with the front escutcheon, before the deck can be unplugged from the main PC board. Removing the loading motor assembly on the underside of the deck reveals a large rack gear which engages a master cam. And you didn’t need to be a genius to figure out what was wrong. The first tooth of the rack was missing and the teeth on the cam gear were all damaged. Obviously some force had been applied here to cause this. The gears were relatively cheap but, after adding in the freight and my labour to remove and replace them, the custom­er was looking at a bill of about $100. I may have thought that this was good value but not so Mr Nasty. Instead, he flatly contradicted me when I called him with the news and almost implied that I was being dishonest and at­tempting to overcharge him. I left the machine disassembled so that he could see the problem for himself when he called to pick it up. He was even more displeased with this and I received neither thanks for my diagnosis nor any payment for the time I had spent on the ma­chine. I was quite surprised at his rather disagreeable attitude and thought that that would be the end of it. I had more or less forgotten about the incident when suddenly, after about six months, his wife brought the machine in and asked for it to be repaired for the figure I had quoted. (Don’t you just love some of these guys? They back themselves into a corner by being obnox­ious and then hide behind their wives after they’ve thought better of it). Taken aback by this sudden about face, I carefully examined the parts to see if anyone else had had a go at the machine after it had left my shop. However, everything appeared to be as I’d left it and so I reluctantly agreed to take the job on. I don’t like dealing with customers who have been unreasonable in the past but I reasoned that it would be a straightforward job and I would be able to recoup my previous losses. Removing the old rack (or “slide main” as they call it) isn’t difficult but, when installing the new one, one has to align eight points simultaneously to ensure the correct timing. The two difficult ones are underneath near where it engages the gear cam drive (not shown in the service manual). The next point to watch for is the “Gear E/J Eject” drive which is loose and must be aligned so that slot #1 matches tooth #1 on the ejector rack at the top of the deck and tooth #1 on the gear master cam underneath. After that, it’s plain sailing and you simply reas­semble the parts in the reverse order that they were removed. Anyway, it all worked perfectly once it was all back together again. Obviously, the original gears had been damaged by someone forcing a tape in or out, though Mrs Nasty subsequently denied this when she called to pick up the unit. Instead, she was more interested in finding out what sort of guarantee I gave. I told her that I guaranteed the parts supplied and the work done for 90 days but only for the same fault and provided that the equipment was not abused, as was so obvious in this case. I don’t think that this advice sank in (or, more likely, she chose to ignore it) because she brought the machine back two weeks later, complaining that it didn’t work again. I stopped work, connected it up in front of her, inserted a tape and pressed play. There was sound but no picture; just snow. I ran a tape cleaner but it made no difference, so I removed the covers and gently wiped the heads using a lint-free cloth dipped in oil-free acetone. It left black marks on the cloth! I replayed the tape and the picture was now perfect. I reassembled it in front of Mrs Nasty and explained what had happened but, like her husband before her, she declined to pay for the work done to rectify their abuse of the machine and disappeared with it without so much as a word of thanks. I don’t need customers like that and I certainly won’t be doing any more work for them. A pig in a poke Steve runs a secondhand furniture shop not far away and one day he brought in this large Samsung stereo TV he’d bought at auction for $300. Of course, it wasn’t working and he wanted me to fix it for him. I know him well enough to tell him that he was mad to buy such a pig in a poke and gave him a quick rundown on some of the costs involved if certain parts like the picture tube were cactus (eg, anything up to $1000 for a large screen – and this was large). He didn’t turn a hair, being the eternal opti­mist he is, and agreed to pay to have it diagnosed and costed. When I removed the back and found a large plastic bag full of parts, I liked his chances even less. As I quickly discovered, this bag contained a number of parts that were missing from the deflection board. The flyback transformer had also been unsol­dered and was lying free inside the cabinet. Where was I to start? I removed the parts from the bag, sorted them out and found out where they had come from before performing some basic resistive checks with a multimeter. Most of the parts were either completely short or open circuit and had either come from the line output stage or the power supply. The line output transistor (2SC1880) was short circuit, as was chop­ per transistor Q801 (BUV48). Because the flyback transformer had been removed, I ini­tially suspected that it was also faulty. However, a few basic checks revealed that it was probably OK, so I replaced it. I also replaced the chopper transistor (Q801), the line output transistor (Q401) and any other parts that were faulty. Restoring the power supply was obviously the next objec­tive. A few checks revealed that fuse F801 and resistors R807 and R817 were all open circuit. The latter are designated on the circuit as 0.27W types but had been replaced with 0.22W 5W wire­ wound resistors. I quickly fixed that by fitting the correct fusible types. The power supply is a conventional switchmode type and is somewhat similar to the ones used in Akai and Nokia TVs. The difference is that it has two regulator circuits, with VR801 controlling the primary oscillator for +130V in the standby condition and VR802 controlling a secondary oscillator and feed­back circuit which ensures that the 130V rail remains constant in the power on condition. Both ICs in the power supply (IC801 and IC802) had pre­viously been replaced, along with a few other components. To be on the safe side, I replaced all the small capacitors (C817, C813, C814, C838 & C803) and then checked all the remaining diodes and transistors using a multimeter. I then removed both the deflection board and the small signal board from the August 1997  63 set to protect them from any further damage should something be badly amiss with the power supply voltages. Before applying power, I decided to take a few more precautions. First, I connected a dummy load consisting of a 100W 240V globe and a parallel voltmeter to the cathode of D814 (the +130V rail). Second, I shorted the base and emitter leads of the line output transistor to prevent the line output stage from firing up. And third, I connected the AC input via a Variac, with a 200W globe in series to limit the maximum current to a safe value. Now for the big test. I applied power and slowly advanced the Variac, all the time keeping my finger near the on/off switch. And at 130V AC, the oscillator fired up, the 100W dummy load began to glow and the meter on D814 read +130V. Delighted at this progress, I slowly wound the Variac up to the full 240V. Everything remained intact and so I switched off and removed the base-emitter short from the line output transis­tor after first confirming that there was 130V on its collector. Now for the acid test – would the line output stage fire up properly? I switched out the 200W globe and 64  Silicon Chip wound the Variac up again but nothing happened. The CRO revealed nothing on either the base or the collector of Q402 (the horizontal driver transistor), so I traced the circuit back from the collector through T401, R402 and D406, towards the +14V rail. According to the circuit I had, D406’s anode is connected directly to the +14V rail at the anode of D816. There is even a link position on the board, marked J109, to allow for this con­nection but there was no link in position. And, what’s more, this link had apparently never been fitted, so what was going on? In fact, it appears that the circuit is in error. In prac­tice, D406’s anode is linked via J430 and J813 to the emitter of Q805. And this transistor is controlled by Q803 which, in turn, is controlled by Q804. When Q804 turns on, Q803 also turns on and this does two things: first, it switches the +14V rail through to IC802 and second, it turns on Q805 which switches the +14V rail through to D406 and subsequently to the collector of Q402. So why wasn’t the +14V rail being switched through by tran­sistors Q803 and Q805. Answer – because unplugging the small-signal board had removed the base drive to Q804. This drive signal is normally supplied from the main board via pin 2 of connector CNP801. As a quick test, I switched my multimeter on the x1 ohms range and connected the red lead to the chassis and the black lead to the anode of D835 (in series with Q804’s base). The 2.4V across the test leads from the multimeter’s internal battery was more that enough to bias Q804 fully on and the EHT section burst into life. The meter on the 130V rail now showed that it was too high but readjusting VR802 soon corrected this. By now, I was optimis­tic that the set was a “goer” so I removed all the safety gear I had connected, reinstalled all the boards and switched on. Eure­ka! – up came the sound and we had a perfect picture. I rechecked and adjusted the two B+ pots before leaving the set to soak test. It was still going strong after about a week and I felt confident enough to ring Steve and tell him to collect it. So, in the end, Steve’s confidence was well founded and he had certainly got himself a bargain – this time! But I don’t generally advise people to acquire TV sets in this manner. SC BOSSMAN ELECTRONICS Soon we should be fully set up with this new company which is a subsidiary to OATLEY ELECTRONICS, for the purpose of giving TAX EXEMPT PRICES to entitled organisations. The product range that will be included on this list will increase rapidly. For enquiries call BOSSMAN ELECTRONICS on: 02 9584 3562. PIC IC PROGRAMMER Ready made, coming soon, Email or Fax for more information: $49 SOLID STATE PELTIER EFFECT DEVICES These can be used to make a solid state thermoelectric cooler/ heater. 12V/4.4A 40 x 40 x 4mm. Basic information to suit: $27, 12V DC fan to suit for $8. TO-3 TRANSISTORS IN 1kg BAGS Approx 1kg of semiconductors recovered from working equipment. All devices are in the TO-3 package. Approx 80 devices per kg wide variety of type numbers, some of which are common types of transistors, voltage regulators & Schottky diodes. These devices have been poorly stored & have bent pins, etc. $6. 650nm LASER POINTER SPECIAL Light weight (2XAAA) pen sized pointer with 5mW/650nM laser diode, 140mm long, 18mm diameter: $55. 650nm LASER MODULE Our new module is fitted with a 650nm laser diode! Very small, 35mm long, 10mm diameter, 3 to 4.5V operation: $50. DISCO LASER LIGHT SHOW PACK The above 5mW/650nm kit plus our AUTOMATIC LASER LIGHT SHOW: $99. NEW COMPUTER CONTROLLED STEPPER MOTOR KIT Coming soon. This kit functions similarly to our previous stepper motor kit but has improvements to the driver electronics that can allow larger motors to be driven more efficiently, with much reduced loading on the computers parallel port, together with 2.5kV opto isolation between the stepper driving circuit and the computer. Previous purchasers may contact us for a simple modification to greatly reduce the loading on the computer’s parallel port. PCB and all on board components kit plus software and information: $39, or $49 with two M35 motors included! DIGITAL BAR CODE WANDS New USA made wands fitted with 2.5m long curly cord terminated in a 5-pin 240 degree DIN plug, with optical sensor, visible red LED, a photo IC detector, & precision aspheric optics. Converts barcodes into a digital pulse train as it is manually swept across the barcode. Employs a sapphire tip, pot size is 0.19mm. Output is open collector TTL/CMOS compatible & the wand needs to be powered from 5V. $45. INFRARED TESTER USING CONVERTER TUBES Used high resolution US-made night vision tubes with some blemishes together with a high-voltage generator kit. Have either 25 or 40mm diameter, fibre-optically coupled input and output windows. Use to test infrared remote controls without lensing or as a cheap IR viewer with lensing. Produce a good image in low light, need IR illumination in dark places: $40. MAGNIFIERS/LOUPES Jewellers eyepiece: $3, Twin lens loupes: 50mm $8, 75mm $12, 110mm $15. The set of 4: $30. SUPER BRIGHT BLUE LEDS BY FAR THE BRIGHTEST BLUE EVER OFFERED, super bright at 400mCd: $1.50 each or 10 for $10. 5mm LEDS AT SUPER PRICES 1Cd red: 10 for $4. 300mCd green: $1.10 ea or 10 for $7 (make white light by mixing output of red green & blue). 3Cd red: $1.10 ea or 10 for $7. 3Cd yellow (small torch!) also available in 3mm: 10 for $9. Super bright flashing LEDs: $1.50 ea or 10 for $10. CENTRAL LOCKING This four-door central locking kit is a commercial product that includes 2 master and 2 slave actuators, wiring loom, control unit, necessary hardware and instructions: $60. The UHF REMOTE CONTROL KIT has a switched relay output for operating an alarm etc, an indicator output for driving a buzzer etc, and logic level outputs for operating the CENTRAL LOCKING KIT. Comes with a ready-made transmitter with two pushbuttons (lock, relay on - unlock, relay off), and a receiver PCB and all on-board components. 5 LEDs make for easy tuning and diagnostics: $35. SIREN KIT, includes speaker $12. 12V PANASONIC GEL BATTERY BARGAIN New 12V/2.3Ah Panasonic sealed lead-acid rechargeable video batteries at a fraction of their real value. 180(L) x 60(H) x 22(W)mm, 0.67kg, made in Japan. The contacts (which are easily solderable) are at one end of the battery. $10 each. Now that’s a bargain but what about two of these batteries plus one intelligent GEL/LEAD-ACID BATTERY CHARGER for a total of $25!! 12V/7Ah GEL BATTERY BARGAIN Fresh stock 7Ah battery (150 x 95 x 65mm, 2.7kg) plus one GEL/ LEAD-ACID BATTERY CHARGER for: $33. DC MOTOR SPEED CONTROL– EXPERIMENTERS PACK One 20A motor speed controller kit (similar to SC June 97) $18, plus two small new 12VDC motors (40mm dia. 40mm length) plus one used car windscreen wiper motor (which has internal gear reduction) for: $32. AMPLIFIER - PREAMPLIFIER AND MORE! A professional mostly SM PCB that contains a 5W amplifier based on a TDA1905 IC, and a separate audio preamplifier section. We also provide a prewired high quality unidirectional electret microphone that has a wind filter and a mounting clip. A small speaker and basic hook-up information is also included. Appears to have been designed for a communications system. Great for many applications including a two-way intercom (2 required) that does not require switching! Available at less than the cost of the electret microphone: $15 each, 2 for $24. HELIUM NEON LASER BARGAIN Large 2-3mW HeNe laser head plus a compact potted US made laser power supply. The head plugs into the supply, and two wires are connected to 240V mains. Needs 3-6V/5mA DC to enable. Bargain: $100. LASER ENGINE Brand new complete laser engine as used in laser printers. Includes a Polygon scanner motor with Xtal controlled driver PCB, 5mW/780nm laser diode in collimated housing mirrors/ mirrors lenses etc. Information on how to make the motor and laser operational included. Bargain at $35. SWITCHMODE POWER SUPPLIES Modern design compact (145 x 80 x 50mm), totally enclosed in a perforated metal case, 12VDC/2A & 5VDC/5A out: $17. The same power supply installed within a flat PC type white powder-coated metal box, 380(L) x 365(W) x 55(H)mm, is also available: $20. BARGAIN ARGON LASER HEADS The cheapest way to get a BLUE-GREEN LASER beam! These used Argons have around 30mW output (may require licensing!!) and are guaranteed for 6 months. A power supply for these is based on a transformer with 80V<at>2A and 3V<at>20A secondaries. Ring or email for more information. Head only: $250. MINI TV STATION Make your own mini TV station with this metal-cased, commercial transmitter with telescopic antenna. Dimensions 123 x 70 x 20mm, 12V operation. Includes power switch, indicator LED, RCA audio and video connectors, twin RCA-RCA lead. Our 32mm AUDIO PREAMPLIFIER kit ($8) (comes with an electret microphone), and a CCD camera will complete the station. Transmitter $30 or $20 when purchased with a CCD camera. REGULATED 10.4V-500mA PLUGPACK to power the whole system: $10. AUDIO - VIDEO MONITOR Compact high resolution 5" screen B/W audio and video monitor. Has two-way audio, built in microphone, audio amplifier, speaker and pushbutton “talk” switch. Needs a preamplifier and microphone for remote audio monitoring (our 32mm audio preamplifier is ideal). Has two camera inputs to allow manual or auto switching (adjustable speed) between each camera. Needs 12V DC 1A (our switched mode supply is ideal), size 160 x 190 x 150mm, has audio and video outputs for connecting to a VCR etc. Monitor and 6-way mini input connector only: $125. 650nm VISIBLE LASER POINTER KIT YES, NEW 650nm kit!!!: Very bright! Complete laser pointer that works from 3-4V DC. Includes 650nm/5mW laser diode, new handheld case 125 x 39 x 25mm, adjustable collimator lens, PCB battery holder: $35. learning remote control: $25 for PCB and all on-board components, used PIR to suit: $12. 32mm 10 LED IR ILLUMINATOR New IR (880nm) LEDs have an output about equal to our old 42 LED IR illuminator: $14. 32mm AUDIO PREAMPLIFIER An $8 kit that produces a “line level” signal from an electret microphone, connect the output to our: UHF VIDEO TRANSMITTER ($30) or $20 when bought with the camera for a complete Audio-Video link. 32mm AUDIO AMPLIFIER An LM386 based $9 audio power amplifier which can directly drive a speaker – needs the 32mm preamplifier. WHAT IS 32mm? All boards are 32mm, so you can house these kits in a plastic 32mm joiner: cheap plumbing part. VISIBLE LASER DIODE MODULE KIT – COMING SOON This kit has the same circuit as our “visible laser diode kit” but has a smaller circuit board allowing it to be fitted into a piece of tubing. Dimensions of the board are less than 25mm wide/50mm long. 650nm/5mW laser diode. 3V operation. $29. FAX POLLING Back by popular demand! POLL: 02 95707910 and 02 95794985. PC POCKET SAMPLER KIT Ref EA Aug. 96. Data logger/sampler, connects to PC parallel port, samples over a 0-2V or 0-20V range at intervals of one/hour to one/100µs. Monitor battery charging, make a 5kHz scope, etc! Kit includes on-board components, PCB, plastic box and software (3.5" disk): (K90) $30. WOOFER STOPPER Mk II Works on dogs and most animals, ref SC Feb 96. PCB and all onboard components, transformer, electret mic & horn piezo tweeter: (K77) $43, extra tweeters (drives 4): $7 each. Approved 13.8V/1A DC plugpack (PP6) $10. UHF REMOTE TRIGGER Single channel Rx and Tx: (K77T) $40. MASTHEAD AMPLIFIER KIT Our famous MAR-6 based masthead amplifier. 2-section PCB (so power supply section can be indoors) and components kit (KO3) $15. Suitable plugpack (PP2): $6. Weatherproof box: (HB4) $2.50. Box for power supply: (HB1) $2.50. Rabbit-ears antenna (RF2) $7. (MAR-6 available separately.) USED PIR MOVEMENT DETECTOR Commercial quality 10-15m range, used but tested and guaranteed, have open collector transistor (BD139) output and a tamper switch, 12V operation, circuit provided: $10. 12V - 2.5W SOLAR PANEL KIT US amorphous glass solar panels with backing glass terminating clips, etc – a solar panel kit. On SPECIAL: $20 each or 4 for $60. WIRELESS IR EXTENDER Converts the output of any IR remote control to UHF. Self-contained transmitter attaches to IR remote. Kit includes two PCBs, all components, 2 plastic boxes, Velcro strap: (K89) $39. (9V battery not included). Plugpack for Rx (PP10): $11. CHARACTER DISPLAYS Back in stock late this month! Standard 32 x 4 character displays using Hitachi ICs. ON SPECIAL: $18. NICAD CHARGER & DISCHARGER Professional, fully assembled and tested fast NICAD battery charger and discharger PCB assembly. Switchmode circuit, surfaced mounted on a double-sided PCB. Nominal unregulated input 13.7V DC, 900mA charge current. Appears to use voltage slope detection for charge terminating, also has a timer (4060) to terminate the charge. We supply a thermistor for temperature sensing. For fast-charging 7.2V AA nicads. Basic information provided. Incredible pricing: $9 each or 3 for $21. MOTOR AND PUMP New, compact plastic pump with a 240V AC 50Hz 0.8A 91W 2650 RPM induction motor attached. Probably a washing machine part. Very quiet operation, made in Japan, overall dimensions 160 x 90 x 90mm, weight 1.2kg, inlet 25mm diameter, outlet 20mm dia­meter. Other end of motor has 20mm-long 4mm dia. shaft. Motor can be rewound for lower AC voltage and or reduced power operation without disassembling the unit. We calculated 5.5 turns per volt: $19. CCD IMAGE SENSOR High quality “Thomson” brand, 576 x 550 pixels with antiblooming, with full data but no circuit suggestions available, usable response from 400-1100nm, 30dB S/N at 40 millilux, 2/3" optics compatible format: $35. BEST “VALUE FOR MONEY” CCD CAMERA The best “value for money” CCD camera on the market! Come and see us for a comparison to any cheaper models advertised! Tiny CCD camera, 0.1 lux, IR responsive, high resolution. This camera has a metal lens housing (not plastic) and performs better than many cheaper models. The pinhole lensed version of this camera is also available for the same price: $120. SALES TAX EXEMPT PRICE FOR EITHER OF THE ABOVE IS: $99. If you need different lenses, ring and ask!! COMING: A lower priced high-quality Standard or Pinhole CCD camera Quality product for under $100. Fax/ring or email for more info. SOLAR REGULATOR Ref: EA Nov/Dec 94 (intelligent battery charger). Efficiently charge 12-24V batteries from solar panels but can also be used with simple car battery chargers to prevent overcharging. Extremely high efficiency due to the very efficient MOSFET switch & Schottky isolation diode. We now offer a 7.5A or 15A kit: $26/$29 (K09). NEW SEMICONDUCTOR BARGAINS CA3140 MOSFET input op amp: 5 for $5. TL494 switchmode power supply IC: 5 for $5. NE555 timer IC: 10 for $5. ICL7106 LCD display driver: $5. ICL7107 LED display driver: $5. IRFZ44 MOSFETS: 60V, 0.028 ohm on resistance, 50A: 10 for $30. COLOUR CCD CAMERA - NEW This high-quality CCD camera is built over 3 boards which are joined with a flexible cable that can be folded into a very compact camera. Head board: 42 x 20.5mm, lens height: 24mm. Main board: 42 x 42 x 9mm. Power board 42 x 20.5 x 8.8mm. SPECIAL introductory price: $350 (less with ST exemption). PO Box 89, Oatley NSW 2223 Phone (02) 9584 3563 Fax (02) 9584 3561 480 x 128 LCDs Hitachi LM215 dot matrix LCD displays. Clearance: $15 each, 3 for $35. KITS FOR CCD CAMERA SECURITY New INTERFACE KIT FOR TIME LAPSE RECORDING: now has relay contact outputs! Can be directly connected to a VCR or via a OATLEY ELECTRONICS orders by e-mail: oatley<at>world.net WEB SITE: http://www.ozemail.com.au/~oatley major cards with phone and fax orders, P&P typically $6. August 1997  65 Remote controlled gates for your home Don’t you just love the idea of remotecontrolled gates? There is your stately mansion, secure behind heavy wrought iron gates. You roll up in your Lexus ES400 and the gates slowly swing open as if by magic. As you pass through, the gates swing shut again and you are secure inside your domain. By PHUNG MAI Well, OK you might not have a stately mansion nor a Lexus ES400 for that matter but the idea of remote controlled gates is still pretty attractive, isn’t it? Even if you just have ordinary gates, someone, probably you, has to open and close them each time you pass through. That’s not too pleasant on a cold, wet winter’s night. Now 66  Silicon Chip you can add remote control. Just think of the extra prestige automatic gates will add to your home. It’s quite common for people to have automatic garage doors but you can go one better with automatic gates. Of course, anyone can have automatic gates fitted to their home but surprise, surprise, they cost big dol- lars. The system presented here can be obtained at a fraction of the cost and you will end up with the added satisfaction of building it yourself. Mechanical concept The basic mechanical parts required to motorise your gates are a pair of 12V DC wiper motors from a car and a pair of scis­sor jacks, again from cars. You can pick these up very cheaply from car wreckers. You can buy them more cheaply at trash and treasure sales because these people think they’re selling junk! But you know better. The wiper motors and scissor jacks for the gates shown in the accompanying photos cost just $12.00. Cheap, huh? Fig.1 shows the concept. The wiper motor is attached to the moving gate while one section of the scissor jack is attached to the gate post. The wiper Fig.1: this diagram shows the general concept for the motorised gates. The wiper motor is attached to the moving gate while one section of the scissor jack is attached to the gate post. The wiper motor drives the threaded shaft of the jack to pull the gate open or shut. You need one wiper motor and one scissor jack mechanism for each gate. motor drives the threaded shaft of the jack to pull the gate open or shut. You need one wiper motor and one scissor jack mechanism for each gate. The photos illustrate the concept. The prototype gates are in front of a carport but the idea can be used anywhere, in inner-Sydney Paddington or on a country property out the back of Bourke. Since DC motors are used to motorise the gates, it is a simple matter to open or close them by changing the current direction through the motors. Beside the scissor jacks and automotive wiper motors alrea­ dy mentioned, you will need a couple of universal joints as found in standard 1/2-inch drive socket spanner sets and a few pieces of steel and bolts to clamp the jack sections to the gate posts. The scissor jacks should ideally have a 1/ -inch shank to match the universal 2 joint – it will make your job a little easier later. Making the drive system OK; you’ve got the wiper motors, universal joints, jacks and some steel. Despite the fact that the job is involved with metals, it is not a massive task. You will be impressed when you see your little toy pushing and pulling the gates. Fig.2 shows the drive system in cross-section. The steps you must follow are: (1) Disassemble the universal joint. (2) Centre punch into the universal joint at the male end. (3) Drill and tap the square shank of the universal to fit the threaded section of the motor shaft. These steps will align the motor shaft to the universal joint before they are welded togeth­er. (4) Disassemble the scissor jacks to obtain the wanted parts. Use a hacksaw or an angle grinder to cut away the unwanted sections. (5) After you have removed the threaded shafts from the jacks, you need to make one end of the shaft square to fit to the female end of the universal joints. As noted above, some jacks come with a square drive so they are the type to go for. Also make sure that the screwed shaft has good “square section” threads. Some jacks are very flimsy and have a very shallow thread­ ed portion; they should be avoided. (6) Measure the depth of the female end. Mark one side of the universal joint at about half of the depth. Drill at the marked point into the female end through the shaft to fit a suitable split pin. (7) Reassemble the universal joint. Drive system assembly The next task is to assemble the various parts to make a workable drive. One section of the jack is used to hold the threaded bearing for the shaft to wind through. This section is welded August 1997  67 MOTOR SHAFT AND UNIVERSAL JOINT MALE SIDE ARE WELDED TOGETHER AT DRILLED HOLE SUPPORTER MANUAL OVERRIDE THROUGH FEMALE SIDE WIPER MOTOR MOTOR SHAFT, THREADED SECTION SQUARE END THREADED SHAFT THREADED BEARING Fig.2: the drive system depends on universal joint to couple the wiper motor to the threaded drive shaft. to a clamp attached to the gate post. The method of at­tachment is up to you. You can either weld or drill holes and fit bolts, depending on whether you have wooden or metal gates. The distance between the pole to the threaded bearing is approximately two-thirds the length of the threaded shaft. You will have to allow for movement of the threaded bearing in the supporter slot, to allow for the change in the angle of the threaded shaft. The steps are as follows: (1) Thread the shaft into the tapped hole in the universal drive shank and then weld them together. (2) Bolt the base of the motor to the gate, as shown in the photos. The distance between the position of the motor on the gate to the hitch should be approximately half the threaded shaft length. (3) Wind the shaft through the threaded bearing about half of the length, then open the gate toward the shaft, place the shaft into the female end of the universal joint and then fit the split pin to connect them together. PARTS LIST 1 single channel UHF transmitter kit; available from Oatley Electronics. 1 single channel UHF receiver module (Oatley Electronics) 1 PC board, code 15108971, 122 x 99mm 4 SPDT 12V PC-mount relays 2 12V DC wiper motors 2 10A fuses 2 scissor jacks 1 universal joint and split pin (see text) Semiconductors 1 AX5328 decoder (IC5) (Oatley Electronics) 2 74HC00 quad 2-input NAND gates (IC1,IC2) 1 74HC20 dual 4-input NAND gate (IC3) 1 74HC107 dual JK flipflop (IC4) 68  Silicon Chip 1 7805 5V regulator (IC6) 4 BC337 NPN transistors (Q1,Q2,Q3,Q4) 5 1N4004 diodes (D1,D2,D3,D4,D5) 1 1N914, 1N4148 small signal diode (D6) Capacitors 1 1000µF 16VW electrolytic 4 2.2µF 25VW electrolytic 1 1µF 25VW electrolytic 1 0.47µF metallised polyester (greencap) 5 0.1µF monolithic Resistors (0.25W, 5%) 4 2.2kΩ 2 1kΩ 5-pin resistor arrays (RN1, RN2) 1 1kΩ 1 100Ω Besides making the connection, the split pin is a vital feature of the system. If it ever jams or fails due to loss of power or other cause, you will always be able to open the gates by removing the split pins. (4) To test the gate, connect the motor to a 12V car battery. Make the motor run forward and reverse a few times by changing the polarity, making sure that it is not jammed. Normally a wiper motor requires about 5A or so and you will have two motors drawing this current. To power them, you will need a 12V car battery on permanent trickle charge, say at around 100mA or so. By using a car battery you will not be shut out of your home if there is a blackout and there is little chance of the circuit ever locking up in the case of voltage spikes on the mains supply. Note that most wiper motors these days have two-speed operation. Choose the speed to give the smoothest operation of your gates. Circuit details The circuitry to control your gates is built around the single channel UHF remote control featured in the February 1996 issue of SILICON CHIP. This used an AX5326 encoder chip in a keyring transmitter and an AX5328 decoder on a small PC board populated with surface mount components. Both these items can be obtained from Oatley Electronics – phone (02) 9584 3563 or fax (02) 9584 3561. The AX5328 receiver board is mounted on a large PC board with a few logic chips and four relays to control the two wiper motors. The circuit of this board is shown in Fig.3. While we show the circuit powered from a transformer with two windings, the whole circuit can be powered from a 12V car battery, as noted above. To do this, delete the transformer and the bridge rectifiers and connect the battery to the points marked +12V and VM+. Note that the whole circuit could also be operated without the UHF remote control by pushbutton SW3. You will need to refer to the February 1996 article for the details of the UHF transmitter and receiver circuits. When the transmitter button is press­ ed, the output of IC5, the AX5328, will go high. In essence, the circuit consists of two JK flipflops in IC4 and four RS Fig.3: the circuit depends on a UHF receiver and decoder which drive several RS flipflops based on IC1 and IC2. These in turn control four relays which switch power to the motors to operate them in either one direction or the other. flipflops based on NAND gate packages IC1 & IC2. All these flipflops are reset when power is first applied. IC4b is used to debounce push­ button switch SW3. Assuming the cir­ cuit has been power reset, all flipflops will be cleared (ie, all Q outputs low) with SW1 and SW2 opened (gates closed). If a valid signal is detected by decoder IC5, pin 17 will go high and this is inverted by IC3a to trigger flipflop IC4b. This makes flipflop IC4a toggle; August 1997  69 from high to low and the RS flipflops based on IC1c/1d and IC2b/2c will be toggled via C11. Relays RLY2 and RLY4 will operate and the gate motors will be driven in the opposite direction until the flipflops are again reset by the limit switches SW1 & SW2. PC board assembly Fig.4: the parts layout for the PC board. Take care to ensure all polarised parts are installed correctly. ie, its outputs change state, with Q (pin 3) going high and pin 2 going low. This causes the two RS flipflops based on IC1a/1b & IC2a/2d to change state after being toggled by IC4a’s Q-bar signal via capacitor C12. As a result relays RLY1 and RLY3 will operate. Both motors now run until the above RS flipflops are reset by the limit switches SW1 and SW2. These switches are installed on the gates so they can reset the flipflops when the gates are com­pletely opened (or closed). With the flipflops reset, relays RLY1 and RLY3 are opened to stop the motors. The output of 4-input NAND IC3b gate also resets flipflop IC4b so that it can accept another input signal for closing the gates. When the transmit button is pressed again, pin 3 of IC4a will change state You will need a wiper motor, a universal joint and a threaded shaft from a scissor jack to make each drive system. 70  Silicon Chip In describing this project, we will assume that you have the February 1996 issue and therefore will have the construction information for the UHF transmitter and receiver module. The motor control part of the circuit, as shown on Fig.3, is accommo­dated on a PC board coded 15108971 and measuring 122 x 99mm. The component layout for the PC board is shown in Fig.4. This has the UHF receiver module mounted at one end and the four relays at the other. Check the board for any open circuit tracks or undrilled holes and fix any defects before inserting components. This done, fit all the wire links and the PC stakes for external connections. Next, fit the resistors, the two resistor arrays and the diodes. The next step is to fit the capacitors, noting that the electrolytics must have the correct polarity. The four transistors, the ICs and the relays can now be installed. Note that the UHF receiver module should be left out until after the PC board has been fully tested. Testing To test the unit, first connect a 20cm test wire to the edge GND pin on the board. This wire will be used to trigger or reset the flipflops being tested. This done, connect 12V DC to the AC input connector, then check to see that +5V is present at pin 14 of IC1, 2, 3 & 4 and pin 18 of IC5. If all is OK so far then try grounding the SW3 pin with the test wire. This simulates a valid input signal being received. Two of the relays should operate. Assuming relays RLY1 and RLY3 did, then reset them by grounding the SW1A and SW2A terminals. This simu­lates the operation of the limit switches. Now ground the SW3 pin again and relays RLY2 and RLY4 should operate. Again, you can reset them by grounding the SW1B and SW2B pins. If the above steps didn’t work, then you have to check the individual flipflops and you can check to see that the The motor attaches to the gate and drives the shaft to pull the gate open or closed. Note the split pin which enables the univer­sal joint to be uncoupled. We suggest that a metal guard be fitted over each drive shaft to prevent the possibility of accidental injury. The wiper motors are weatherproofed by metal boxes which give a tidy presentation (see photo on page 66). The drive shafts will need to be kept well greased. A sliding rubber boot inside a metal guard would provide good protection for the shafts. flipflop outputs are high or low with your multimeter. If the flipflops are all working correctly, you may have to check that the transistors are all switching on when they should and finally, that there are no open circuits in the relay connec­tions. Assuming that all checks are OK, you can now install the UHF receiver module on the PC board. Finally, test the whole circuit once again with your remote control. Electrical installation The control box should be located near the battery and indoors or under cover, to keep it out of the weather. It is suggested that all cables be run through plastic conduits and fuses must be included, as shown on the circuit. You will need flexible conduit at the gates themselves. The cables should be 4mm auto wire or thicker, to avoid unwanted voltage drops when the motors are running. You have a number of choices when it comes installing the limit switches SW1 and SW2. Perhaps the easiest is to use a pair of microswitches each for SW1 and SW2 and have them operated by the gates when they are fully opened and fully closed. When the whole circuit is wired up, check the gate opera­tion carefully using the manual switch SW3 and then the UHF remote control. Finally, fit metal guards over each drive shaft SC to prevent accidental injury. Fig.5: this is the full size etching pattern for the PC board. PLEASE NOTE: although we have produced a PC board pattern for this contributed design, the circuit has not actually been built or tested by Silicon Chip Publications. August 1997  71 PRODUCT SHOWCASE Onkyo AC-3 home theatre receiver Amber Technology has announced the Onkyo Integra TX-DS838 Home Theatre Receiver, with Dolby Digital (AC-3) Surround decod­ing, dual DSP processors and 12 surround modes. The discrete output circuitry of the TX-DS838 delivers 100W RMS per channel in stereo mode or 90W RMS to the front left, centre and right channels and 50W RMS to each of the rear chan­nels in surround mode. The non-NFB (negative feedback) power amplifiers feature dual inverted Darling­ ton circuitry. Heavy-duty power supplies feature an automatic cooling fan which switches on under heavy loads to prevent overheating. The TX-DS838 is equipped with dual 24-bit Motorola 56009 and 56004 DSP chips working in unison to provide improved DSP processing capability. There are twelve digital surround modes: Dolby Digital Surround AC-3, AC-3 Action, AC-3 Drama, AC-3 Musi­cal, Dolby Pro Logic, Pro Logic Action, Pro Logic Drama, Pro Logic Musical, Hall, Live, Arena and Stadium. The receiver features comprehensive video signal routing and switching, with four video and eight audio inputs. A front-panel input (Video 4) is provided for easy connection Laptop computer batteries Premier Batteries has introduced laptop computer batteries to their range of products. This new range is compatible with Toshiba, Com­ paq, IBM, NEC and Macintosh computers. The new batteries are fitted with the latest Nickel Metal Hydride cells, giving perfor­mance and run times said to be equal to or better than provided by the original batter­ies. All batteries are direct replacements for the original product and carry the comprehensive Premier warranty. For further information, contact 72  Silicon Chip and play­back from a Camcorder. A 3-page on-screen display offers easyto-follow adjustment of all operating par­ ameters. Intelligent Power Management automatically activates the entire AV system when the connected television is switched on. The Onkyo TX-DS838 measures 435 x 175 x 428mm, weighs 15kg, is finished in black brushed or burnished gold aluminium, and has a recommended retail price of $2999.00. For further information, contact Amber Technology, Unit B, 5 Skyline Place, Frenchs Forest, NSW 2086. Phone (02) 9975 1211; fax (02) 9975 1368. Visio Technical for schematic diagrams Premier Batteries Pty Ltd, 9/15 Childs Rd, Chipping Norton, NSW 2170. Phone (02) 9755 1845; fax (02) 9755 1354. Based on drag and drop technology, Visio Technical 4.5 allows users to quickly create 2-D drawings and technical sche­ matics, without the long learning curve normally associated with CAD software. The package comes with more than 2000 “Smart­ Shapes” (including electrical and electronic symbols), organised into 78 task-specific stencils. Drawings are created by dragging and dropping the symbols you want from the stencil library along the lefthand edge of the screen and onto the drawing area to the right. According to Visio, the SmartShape symbols resize without distorting. The technology also ensures that sections of shapes appear or remain hidden as needed and that text goes where it belongs. Naturally, you can also create your own SmartShapes using the inbuilt SmartShape Wizard. A powerful set of drawing tools is included for creating custom shapes and the program features automatic layout and intelligent line routing. This means that the program can automatically reposition shapes and connecting lines as required. AutoCAD compatibility is another feature and the program can both import and export AutoCAD file formats. In addition, there are import filters for files created in CorelDRAW, Corel­ FLOW, Micrografx Designer and ABC Flowcharter. Files can be imported and exported in a variety of formats, including BMP/DIB, CGM, EPS/AI, GIF, IGES, JPEG, PICT, PNG, TIFF and WMF. As might be expected these days, Visio Technical 4.5 sup­ports Internet publishing and you can save drawings as HTML files with linked image maps, or as GIF, JPEG or PNG graphics. There’s also support for TrueType and other Windows fonts, an inbuilt spelling checker and improved colour formatting with new gradient fills. Visio Technical 4.5 runs under Windows 95 and Windows NT. A 16-bit version of the program (Visio Technical 4.1) is also included in the package on a separate CD ROM for Windows 3.1x users. The recommended retail price is $499 or users can upgrade from previous versions for $249. For further information, contact Visio International Inc., Level 17, 275 Alfred St, North Sydney 2060. Phone 1800 551 976. Mitsubishi’s video projector A new projector from Mitsubishi Electric is now available. With a screen projection diagonal of up to 762cm (300 inches), the projector can create an image which is over 10 times larger AUDIO TRANSFORMERS Manufactured in Australia Comprehensive data available Harbuch Electronics Pty Ltd 9/40 Leighton Pl. HORNSBY 2077 Ph (02) 9476-5854 Fx (02) 9476-3231 than current 68cm TV sets. Mitsubishi’s Liquid Crystal Polymer Composite (LCPC) pro­jector has an extremely bright image because, unlike conventional projectors, it does not require a polariser and thus uses light more efficiently. The Mitsubishi projector can be connected to a TV, VCR, video camera, laser disc player, PC or (when it is released in the future) to a Digital Video Disc player. The projector is multi-system compatible (NTSC, PAL and SECAM) and can connect to a variety of computer platforms (eg VGA, Mac 13", NEC 98). Other features include a manual zoom, focus adjust­ment and volume control. The Mitsubishi LCPC Projector has THE “HIGH” THAT LASTS IS MADE IN THE U.S.A. Model KSN 1141 The new Powerline series of Motorola’s 2kHz Horn speakers incorporate protection circuitry which allows them to be used safely with amplifiers rated as high as 400 watts. This results in a product that is practically blowout proof. Based upon extensive testing, Motorola is offering a 36 month money back guarantee on this product should it burn out. Frequency Response: 1.8kHz - 30kHz Av. Sens: 92dB <at> 1m/2.83v (1 watt <at> 8Ω) Max. Power Handling Capacity: 400W Max. Temperature: 80°C Typ. Imp: appears as a 0.3µF capacitor Typical Frequency Response MOTOROLA PIEZO TWEETERS AVAILABLE FROM: DICK SMITH, JAYCAR, ALTRONICS AND OTHER GOOD AUDIO OUTLETS. IMPORTING DISTRIBUTOR: Freedman Electronics Pty Ltd, PO Box 3, Rydalmere NSW 2116. Phone: (02) 9638 6666. August 1997  73 a recommended retail price of $10,999 and is available from selected electrical re­ tailers. For more information, contact Mitsubishi Electric on 1 800 811 212. CAN interfaces for PCs National Instruments has announced the first available PCI-based and ISA-based Windows 95 Plug and Play-compatible interfaces to connect PCs to Controller Area Network (CAN) devices. The PCI-Can (for Windows NT/95 PCs) and AT-CAN (for Windows 95 PCs) meet the physical and electrical requirements for in-vehicle networks based on CAN. The AT-CAN includes full Windows 95 Plug and Play compa­tibility, giving users the benefits of automatic configuration for easier installation and maintenance. The PCI-CAN and AT-CAN include NI-CAN driver software, which provides a high-level application programming interface (API) for reading and writing data frames on the CAN bus. Both are compatible with LabVIEW and LabWindows/CVI, as well as other KITS-R-US RF Products FMTX1 Kit $49 Single transistor 2.5 Watt Tx free running 12v-24V DC. FM band 88-108MHz. 500mV RMS audio sensitivity. FMTX2A Kit $49 A digital stereo coder using discrete components. XTAL locked subcarrier. Compatible with all our transmitters. FMTX2B Kit $49 3 stage XTAL locked 100MHz FM band 30mW output. Aust pre-emphasis. Quality specs. Optional 50mW upgrade $5. FMTX5 Kit $98 Both a FMTX2A & FMTX2B on 1 PCB. Pwt & audio routed. FME500 Kit $499 Broadcast specs. PLL 0.5 to 1 watt output narrowcast TX kit. Frequency set with Dip Switch. 220 Linear Amp Kit $499 2-15 watt output linear amp for FM band 50mW input. Simple design uses hybrid. SG1 Kit $399 Broadcast quality FM stereo coder. Uses op amps with selectable pre-emphasis. Other linear amps and kits available for broadcasters. 74  Silicon Chip industry-standard programming languages. These products give users PCbased connectivity to communi­ cations networks that are becoming more commonplace in both test and industrial automation applications, including automotive testing and diagnostics, factory automation, and machine control. For more information, contact National Instruments Austra­lia, PO PO Box 314 Blackwood SA 5051 Ph 0414 323099  Fax 088 270 3175 AWA FM721 FM-Tx board $19 Modify them as a 1 watt op Narrowcast Tx. Lots of good RF bits on PCB. AWA FM721 FM-Rx board $10 The complementary receiver for the above Tx. Full circuits provided for Rx or Tx. Xtals have been disabled. MAX Kit for PCs $169 Talk to the real world from a PC. 7 relays, ADC, DAC 8 TTL inputs & stepper driver with sample basic programs. ETI 1623 kit for PCs $69 24 lines as inputs or outputs DS-PTH-PCB and all parts. Easy to build, low cost. ETI DIGI-200 Watt Amp Kit $39 200W/2 125W/4 70W/8 from ±33 volt supply. 27,000 built since 1987. Easy to build. ROLA Digital Audio Software Call for full information about our range of digital cart players & multitrack recorders. ALL POSTAGE $6.80 Per Order FREE Steam Boat For every order over $100 re­ceive FREE a PUTT-PUTT steam boat kit. Available separately for $19.95, this is one of the greatest educational toys ever sold. Box 466, Ringwood, Vic 3134. Phone (03) 9879 5166; fax (03) 9879 6277. Email info.australia<at>natinst.com or http://www.natinst.com/ C&K Electronics & Jesec Switches merge Australian electronic component suppliers C&K Electronics and Jesec Switches Plus are combining 44 years industry experience with Contactless angle sensors Philips has introduced the KM11OBH/2430 and KM11O­BH/2470 angular displacement sensors, which utilise the company’s magne­ toresistive sensor technology to produce a contactless device completely free from wear and micro-linearity errors. Mechanical wear and contact corrosion, which can lead to severely impaired performance, are the two most common problems encountered with p o t e n t i o m e t e r- b a s e d a n g l e s e n s o r s . T h e KM11OBH/2430 has a measurement range of 30° and the KM11OBH/2470 has a range of 70°. Both devices operate at temperatures between -40°C and +125°C, making them suitable for use in automotive applications such as engine management, safety and driver/passenger comfort systems. They are also small enough to be used in applications such as computer printers, medical equipment and instrumentation equipment, as well as in general industrial applications. Additional information can be obtained from Philips Components, 34 Waterloo Rd, North Ryde, NSW 2113 or from the Philips Internet Home Page at http://www.semicon­ductors.philips.com High density DC-DC converter Analog Devices’ new ADDC­02808­ PB high-density DC-DC convert­er is the first designed specifically for pulse applications such as solid state radar where transmit/receive (T/R) modules are used. When fast transient response, minimum output voltage devia­tions and saving space and weight are important, the ADDC­02808PB is the solution. The standard ADDC02808PB operates from a 28V input bus and provides up to 25A pulsed output current at 8V. Peak pulse power is 200W and peak pulse power density is more than 120W per cubic inch. For further information on this device, contact Hartec, 205A Middle­ borough Rd, Box Hill, Vic 3128. Phone SC 1 800 335 623. SILICON CHIP SOFTWARE Now available: the complete index to all SILICON CHIP articles since the first issue in November 1987. The Floppy Index comes with a handy file viewer that lets you look at the index line by line or page by page for quick browsing, or you can use the search function. All commands are listed on the screen, so you’ll always know what to do next. Notes & Errata also now available: this file lets you quickly check out the Notes & Errata (if any) for all articles published in SILICON CHIP. Not an index but a complete copy of all Notes & Errata text (diagrams not included). The file viewer is included in the price, so that you can quickly locate the item of interest. The Floppy Index and Notes & Errata files are supplied in ASCII format on a 3.5-inch or 5.25-inch floppy disc to suit PC-compatible computers. Note: the File Viewer requires MSDOS 3.3 or above. OR D ER FOR M PRICE ❏ Floppy Index (incl. file viewer): $A7 ❏ Notes & Errata (incl. file viewer): $A7 ❏ Alphanumeric LCD Demo Board Software (May 1993): $A7 ❏ Stepper Motor Controller Software (January 1994): $A7 ❏ Gamesbvm.bas /obj /exe (Nicad Battery Monitor, June 1994): $A7 ❏ Diskinfo.exe (Identifies IDE Hard Disc Parameters, August 1995): $A7 ❏ Computer Controlled Power Supply Software (Jan/Feb. 1997): $A7 ❏ Spacewri.exe & Spacewri.bas (for Spacewriter, May 1997): $A7 ❏ I/O Card (July 1997) + Stepper Motor Software (1997 series): $A7 POSTAGE & PACKING: Aust. & NZ add $A3 per order; elsewhere $A5 Disc size required:    ❏  3.5-inch disc   ❏ 5.25-inch disc TOTAL $A Enclosed is my cheque/money order for $­A__________ or please debit my ❏ Bankcard   ❏  Visa Card   ❏ MasterCard 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) 9979 6503; or ring (02) 9979 5644 and quote your credit card number (Bankcard, Visa Card or MasterCard). ✂ the announcement of their merger. The new compa­ny, to be known as C&K Components Plus, will have its head office and distribu­tion centre in Braeside, Victoria, with sales offices in Sydney and Adelaide and sales agents in Queensland and WA. C&K Components Plus plan to expand their present range of 15,000 stock items, including switches, connectors, enclosures, circuit protection devices, variable resistors, sound and visual components and general products. All items will be supported by comprehensive product catalogs and detailed up-to-date litera­ture. C&K Components Plus will also soon be announcing its Internet web presence on buynet at http://buy­net. com.au Further information about C&K Components Plus products can be obtained by calling Sydney (02) 9635 0799, Melbourne (03) 9587 4044 and Adelaide (08) 8363 4343. The email address is: ckplus<at>ca.com.au August 1997  75 RADIO CONTROL BY BOB YOUNG The philosophy of R/C transmitter programming This month we will look at some of the principles in­volved in the programming of the modern R/C transmitter. We discuss the use of memories and initial R/C model setup for best flying response. In the course of my radio service work I spend a lot of time listening to tales of woe from concerned or frustrated customers, so much so that, like doctors, you begin to feel that the only people (or R/C systems) in the world are those who are unwell. This can be depressing at times and it must be a real prob­lem for doctors. However, in my work as an R/C system designer, I find these tales very important because I can do something to help and I have used the information gathered to great effect in recent years. The work we did on third-order intermodulation came out of the endless murmurings and hand wringing that surfaced in the lead-up to the MAAA Frequency Subcommittee conference in Sun­bury, Vic. The very popular AM versus FM articles, which are now being picked up by overseas magazines, arose from a South Austra­lian reader’s letter. This poor fellow was under intense pressure from the technocrats in his club who were telling him to get rid of his “inferior” AM equipment and buy the new all-singing, all-dancing FM gear. The transmitter intermodulation articles came to light as a result of the uncertainties that triggered the reluctance of the clubs to accept the earlier issue Keyboards and my subsequent investigations to arrive at the 76  Silicon Chip truth of the matter. As a result, the new highly modified Issue 4 Keyboard has gained wide accept­ance amongst those previously reluctant clubs and is thus alle­viating the worries about transmitter intermodulation for clubs across Australia. Because I was prepared to listen to the worries, inves­tigate and report on what I saw as the truth, those SILICON CHIP articles have completely transformed the way things are being done in clubs all around Australia. There is renewed interest in 29MHz operation; AM no longer carries the stigma imposed by the FM sales hype; 3rd order intermodulation interference (3OI) is a thing of the past in most clubs and transmitter intermodulation is now well understood. However, in the words of one member of the trade, the transmitter intermodulation articles “created a storm” and there are now opposing points of view circulating in the R/C movement. Some members of the trade are not too happy about those articles because they have shifted the emphasis to dual-conver­sion receivers for operation on 36MHz and those in the trade not supplying dual-conversion 36MHz receivers are walking around with noses severely out of joint. At the top of the list of these trade members is Bob Young of Silvertone Electronics, who does not yet have a dual-conversion Rx in his range. This is interesting because it is being whispered in cer­tain quarters that Bob Young of SILICON CHIP fame is pushing the Tx intermodulation line to help Silvertone sales. Wearing two hats is a trying process at times. Programming Now let’s get onto the main theme of programming transmit­ters. There are a wide range of people engaged in R/C activities. Some just need a toy to play with for a few hours to take their mind off work or home pressures. Others, like the dedicated inter­national level contest modeller, need the very best that technolo­gy can provide for that competitive edge. In the middle is a vast array of wants and needs. Sadly, modern mass-production and marketing techniques tend to constrain development so that the needs of the many tend to be forced along lines dictated by the needs of the few. Such is the case in modern transmitter development and now the beginner and sports flier is faced with a choice of the computerised monster more suited for the international competitor or nothing. It was to bridge this gap that I designed the Mk.22 trans­mitter which we have covered in past columns. Unfortunately, whilst that transmitter fulfilled the necessary technical role, the high cost of manufacture in this country has lifted it out of the beginners’ price bracket. Having listened and established that there is much unhappi­ n ess regarding the programming of the Fig.1: servo error should be minimised by transmitting the maximum number of steps available and using the mechanical linkages to reduce the control surface travel. This also stiffens the linkage in regards to control flutter. Fig.2: An off-centre servo will give unequal throw about neutral and will call for less than ideal settings in the transmitter. modern computer radio, let us see what can be done to ease some of the burden. This month we will look at the fundamental principles of programming transmit­ters and some of the common complaints associated with this programming. As programming begins with the model design, we will start from the very beginning. Crook manuals The single most common complaint that I receive is that the instruction manuals are almost incomprehensible. Add this to the fact that the programs are now so complex and it’s not hard to understand why so many people are completely overwhelmed by the whole business. One customer told me that he had flattened the Tx battery three times just trying to program exponential control into his elevators. Another told me that she had locked out all functions except basic 4-channel operation. The poor quality of the factory manuals has driven several people to completely rewrite the manuals for some systems, so have a look at what is available in the model shops for your system. There is an excellent manual written in good English by Don Edberg for the Futaba Super-7 system, for example. Not only does it show how to program in easy logical steps but also gives the theoreti­cal and practical reasons for using each of the programming functions. There is no doubt that the computerised encoder is by far the best method of encoding and a virtual must for the serious competitive modeller. However, in trying to make the transmitter all things for all people, the manufacturers have completely lost the plot in regard to a simple transmitter for the beginner and sports flier. So let us look at some of the fundamentals in order to simplify programming for these two groups. Model memory One of the very interesting developments in the computer encoder is that of model memory. This allows each program to be stored in a separate memory so that the program may be recalled when needed. This has opened new avenues for the contest flier in that multiple configurations of a single model may be stored in sepa­rate memories and changed in flight. Thus, an F3B model may be configured for towline launch, cruise, en­durance, speed or landing (crow), all at the touch of a button or flick of a switch. This is pretty powerful stuff considering that six to eight servos may be involved with multiple point mixing on most of these servos. Programming such a model takes years of experience and requires an excellent knowledge of aerodynamics combined with a very sound grasp of the ramifications of swapping between programs. At the club level, a more mundane use of model memory is to be found. This is the process of storing the flight trims for each model so that when each model is flown that program is called up ready for use. This program may also store such infor­mation as direction of rotation of the servos, channel alloca­tion, servo travel length and mixing ratios. Now it is immediately apparent that there is great danger here for the absent-minded or the modeller who is less than fully aware of the value of preflight checking. What if the model is flown with the wrong program loaded? Controls may be reversed, mixed incorrectly or worse still, allocated to different channels. Anyone who has ever taken off with the ailerons reversed can attest to what happens next. I have done it in my early days but God alone would know how you would cope with a channel wrongly allocated. Horror stories abound in all clubs of models flown with the wrong programs in place and there is absolutely no excuse, for if the correct preflight checks had been carried out the error would have been found on the ground. I am not a great fan of model memory for this type of application. At the height of my contest flying career, long before model memories were invented, I flew aerobatic, helicopter and pylon models all from the one transmitter and on the same day. I even refused to use “dual rate” because I believed that flying was pure instinct and to learn to use two sets of control responses only complicated the learning process and diminished the final performance. I could also have used as many transmitters as I needed (after all I did manufacture the things) but again I wanted that one transmitter to be a part of me. I wanted no variations in stick angles, stick movement, spring pressures, switch placement or transmitter weight or feel. I wanted August 1997  77 Radio Control – continued every hour of practice to reinforce my familiarity with that one transmitter. And it worked. I won many a contest against some of Australia’s best fliers of those days. Setting up the model The secret of my success was all in the setting up of the model. Now there are certain fundamentals which are currently being ignored at club level due to the fact that computer trans­mitters permit sloppy practices which are not in the best inter­est of peak performance of any model. The techno-junkie will revel in the flexibility of the computer encoders. Rudder too sensitive? No problem; just dial in a 50% reduction in servo travel. Elevator operating in the re­ verse direction? No worries; just flip it with servo reverse. And that is how the program stays for the rest of the life of the model. The next model is set up just as casually with travel directions flipped, etc and the stage is set for a possible calam­ity. The astute modeller will look at the setting-up process from the design of the model onwards, with a view to maximising performance, reliability and safety from the very outset. This astute modeller will realise that dialling out 50% of the servo travel at the transmitter end will immediately double the ampli­fier minimum impulse and servo gear slop errors at the servo end, reducing control accuracy in flight and possibly exposing the model to control flutter. Our diligent modeller will instead aim at minimising servo error by employing the maximum number of steps available in the transmitter and using the mechanical linkages to reduce the control surface travel (see Fig.1). This also stiffens the link­age in regards to control flutter. What our thinking modeller will do is use the transmitter to quickly establish the correct control throws on the field by using the electronic adjustments and then, when he arrives home, transfer these adjustments into the mechanical linkages, paying particular attention to setting all transmitter trim controls to neutral, setting servo arms to 90° and reset­ting the transmitter for maximum data transfer. 78  Silicon Chip If your model flies with control surfaces and/or servos off centre, badly balanced controls and more control throw than is necessary, then it is not correctly trimmed and you will never be able to execute manoeuvres properly. An off-centre servo will give unequal throw about neutral (see Fig.2) and again call for less than ideal settings in the trans­mitter. Of course, this can be very useful for maintaining maximum resolution in the transmitter under certain conditions but to leave it because of laziness is wrong. Certainly small variations can be accommodated without loss of system integrity but the opera­tive word is “small”, if you care about top performance. Our thinking modeller will also realise that one day he or she is bound to make a mistake. Thus, he will always attempt to design each model so that servo reversing is not necessary, at least on all flying controls. Suddenly, our astute modeller realises that, in the event of the wrong program being loaded, he has sidestepped a potential accident as a result of attention to good practice and that perhaps he does not need model memory anyway. Thus, we have now greatly reduced the number of programming steps required to set up any one model. Certainly this is the case for most sports fliers and great care should be exercised in not allowing yourself to fall into the trap of the quick and dirty fix. Programming makes it very easy to slip into sloppy habits. Yes, it is more tedious and yes it appears to negate the major advantage of the computer radio but long term success is measured largely in the degree of fi­nesse that one applies to his trade. Allied to the foregoing is the problem of using dual rate to cut down on excessive control throw. Again, the end result is to increase the servo inaccuracy. The most impressive fliers that I have seen are those that let the aircraft fly itself, interfer­ing with the controls only when necessary. Dr Ralph Godkin showed me this back in the early 1960s with the most stunningly impres­sive display of low flying I have ever witnessed – and on reeds (not proportional) to boot. Most modellers tend to use far too much control throw with the result that the flight looks jerky and out of control. This particularly applies to beginners and makes learning just that much more difficult. Instead, the controls should be adjusted so that maximum throw is set to give the desired result. For example, we were required to complete three rolls in five seconds in our aerobatic schedule. In fact I found that I could get away with three rolls in six seconds without loss of points, so my maximum aileron throw was set to give this result. Likewise, full elevator gave the minimum loop diameter called for and so on. Sure, square corners in the manoeuvres complicated things a little but there are aerodynamic ways around this. As a result of this philosophy I extracted the maximum accuracy from the R/C system combined with the maximum rigidity of the control surfaces. Smooth flying Consequently people always remarked on how smooth my flying was and how crisp the exits from the manoeuvre were. The problem arose when other people wanted to fly my models. On several occasions, very experienced aerobatic pilots nearly crashed my models because the controls were so soft that they did not have enough control throw to complete the manoeuvre they had started. I refused to permit people to fly my models from that point on. Beginners need a little more control throw than this be­ cause very soft controls call for the pilot to be in absolute control of all situations. Too much control throw will make the aircraft twitchy and difficult to control and greatly increase learning times. Striking the correct balance is the important point and it is here that a good instructor is crucial. Thus the golden rule in programming your transmitter is to always look well ahead and plan every step with that one ultimate result fixed firmly in your mind – that is, to maximise every aspect of the model’s performance in order to make you the most competent, impressive to watch and safety conscious pilot in your club. Next month we will look at the step-by-step details of proSC gramming. SILICON CHIP This page is blank because it contained advertising which is now out of date and the page has been removed to prevent misunderstandings. SILICON CHIP This page is blank because it contained advertising which is now out of date and the page has been removed to prevent misunderstandings. SILICON CHIP This page is blank because it contained advertising which is now out of date and the page has been removed to prevent misunderstandings. SILICON CHIP This page is blank because it contained advertising which is now out of date and the page has been removed to prevent misunderstandings. SILICON CHIP This page is blank because it contained advertising which is now out of date and the page has been removed to prevent misunderstandings. VINTAGE RADIO By JOHN HILL New life for an old Kriesler A vintage radio receiver must be correctly aligned if it is to function correctly. However, many vintage radio enthusiasts neglect this important procedure. There are two types of vintage radio collectors - those who do not do their own repairs and those who do. Alf started out being one of the former but over a period of time has become one of the latter. He has read up on the subject, asked lots of questions and is now doing reasonable repairs. But Alf had a problem. He had restored a 5-valve Kriesler mantel receiver but it didn’t work very well at the high frequen­cy end of the dial, although it functioned reasonably well at the low frequency end. Receiver alignment was a particular problem for Alf. Desp­ite the fact that he had a very good signal generator and various alignment instructions to follow, he was unable to get on with the job because he didn’t really understand the instructions he had. I can sympathise with anyone in this situation because I have been there myself. My first receiver alignments were total disasters due to not having the right equipment on one hand and not knowing what to do on the other. The vague instructions I had at the time summed up align­ment by saying: “adjust the iron cores or slugs at the low fre­quency end of the dial and the trimmers at the high frequency end.” As the set being aligned didn’t have iron cores in the aerial or oscillator coils, that presented a problem. But there were slugs in the intermediate frequency (IF) transformers – and one slug is as good as another when an overconfident mug like me has absolutely no idea of what he is doing. So the IF transformer slugs were twiddled at one end of the dial and the trimmers twiddled the other. To make matters worse, these adjustments were made at the wrong ends of the dial. This dial error was possibly caused by my father who dab­bled in radio in his younger days. Dad always referred to the low frequency end as the “top” end of the dial – which it is if you happen to be thinking wavelengths in metres and not frequency in kHz. Whatever the cause, my early attempts at receiver alignment were not what could be described as good and I was guilty of totally misaligning a number of receivers; that is, until I learned how to do it correctly. My turn to instruct The Kriesler’s IF transformers were out of adjustment, to the extent that they were double peaking. IF alignment is an import­ant aspect of any receiver tune up to ensure that the set performs correctly. 84  Silicon Chip It’s all very well for those who have been properly trained to be critical but when it comes to alignment, it is difficult for novices to find understandable instructions for receivers that became obsolete half a century ago. I blindly blundered on until a kindly old bloke took pity on me and showed me how it was done. Being shown and being told are two different things and the former is much easier to comprehend. So it looked as though it was my turn to pass on the favour and show Alf how to align his Kriesler mantel set. One problem with receiver align- This Kriesler mantel model from the mid-1960s is a commonly encountered valve radio. Although this unit was fully restored, it lacked performance until it was correctly aligned. It also re­quired a valve replacement. ment is that it varies from set to set because the components themselves changed as radio developed over the years. Early superhets have air-cored aerial and oscillator coils and may also have a bandpass filter or a radio frequency stage. In addition, the IF transformers are tuned by adjusting the variable capacitors that are placed across each of the two transformer windings. If we go forward a little in time we find that receivers no longer have bandpass filters, while the IF transformers are adjusted with iron cores and tuned to higher frequencies. Howev­ er, the aerial and oscillator coils may still be air-cored. Other varieties have iron cores in the aerial and oscilla­tor coils or, in some instances, the oscillator coil only. There are also dual-wave receivers of various types to worry about. Confused? I know I was! Learning vintage radio repairs from scratch isn’t easy. primary and secondary windings and, instead of using a slug, the coil is tuned by sliding the winding along the rod. The oscillator coil is slug-tuned with an iron core, as are the two IF transformers. With the 5-valve Kriesler on the workbench, an aerial was connected to the set so that the problem could be assessed. It was as Alf claimed and performed poorly at the high frequency end of the tuning range. A few preliminaries had to be taken care of before commenc­ing the alignment. First, some frequency checks were made on Alf’s signal generator using a modern receiver with a digital readout. These checks indicated that the little “Palace” transis­torised signal generator was quite accurate and that it was well within the usual 2-3% Alf’s Kriesler Alf’s Kriesler was from the mid1960s and it had a built-in ferrite rod aerial. The coil consists of the usual The oscillator coil was adjusted at the low frequency end of the tuning range. In this instance, it needed little alteration. August 1997  85 This photo shows the ferrite rod antenna fitted to the old Kriesler. Moving the coil position can sometimes improve the reception but, in this case, it worked best in its original location. The 6N8 valve was extremely sick and was one of the reasons for the set’s poor performance. tolerance these instruments have. Next, an output meter was improvised by connecting a .047µF 630V capacitor in series with a multimeter lead. The meter was then set to AC volts and connected between chassis and the output valve plate. The capacitor blocks the DC plate voltage and passes only the audio signal, which is shown on the meter. An output meter has much greater sensitivity to level changes than the human ear. While reasonable alignments can be done without instruments (a signal generator and output meter), these accessories make the job so much easier. So if you are thinking of taking the plunge and doing your 86  Silicon Chip own alignments, now may be a good time to consider buying the necessary equipment. With everything in place, a modulated signal of 455kHz (the receiver’s IF) was fed into the control grid of the converter valve. If the IF transformers are correctly aligned, there will be a single peak which will be heard through the receiver’s loudspeaker and seen on the output meter when the signal genera­tor is swept slowly through 455kHz. In this case, there were two peaks which were quite some distance apart – not the ideal situa­tion! When adjusting the first IF transformer, it was noted that the iron slugs had been screwed well in and were touching each other. IF slugs will usually peak in two places: either screwed in or screwed out. The outer position is correct. The second IF transformer also had its slugs badly adjusted. (Editorial comment: many IF transformers, fitted with iron cores, could produce a false peak. When the cores were screwed in too far, the false peak resulted from unwanted coupling between the windings, rather than peaks in the winding inductance. It was a well known trap in the early days of iron-cored IFs.) After the transformers were correctly tuned, there was only a single peak when the generator was swept across the IF. So far so good! It was now time to align the aerial and oscillator cir­ cuits and so the signal generator leads were moved to the receiv­er’s aerial and earth connections. Most Melbourne radio stations line up very well on old dials, as their frequencies have changed little over the years. As the worst one is only 4kHz out, it is possible to do a reason­able alignment to station callsigns rather than to the frequency scale on the dial, if it has one. The Kriesler has no frequency scale to align to but the stations lined up quite well with their dial markings, even before the alignment was commenced. Apparent­ly, that part of the receiver had not been tampered with as had the IF transformers. There was a line on the dial marked PS (pointer start). With the tuning gang closed, the pointer came to rest on the mark. With the signal generator set to 621kHz (3AR) and the receiver tuned to that frequency, the oscillator coil slug was adjusted until the output meter indicated maximum deflection. Strictly speaking, both the oscillator and aerial coils should be peaked at this stage but the coil assembly on the ferrite rod was securely taped in place, indicating that it had never been moved. As a result, it seemed logical to leave it where it was and to simply adjust the oscillator circuit. This was done by rocking the dial setting across the generator signal and simultaneously adjusting the oscillator coil until maximum signal (on the output meter) was achieved. Actually, the original setting was not far out and these adjust­ ments put the pointer right on 3AR. Silicon Chip Binders REAL VALUE AT $11.95 PLUS P &P ★  Heavy board covers with 2-tone green vinyl covering ★  Each binder holds up to 14 issues ★ SILICON CHIP logo printed in gold-coloured lettering on spine & cover This “Palace” brand signal generator is a compact transistorised unit and is powered by a standard 9V battery. Frequen­cy checks proved the generator to be quite accurate. A frequency of 1422kHz (3XY) was then selected for the high frequency adjustments. Once again the dial pointer was spot on. If the pointer had not been accurately positioned it could have been corrected by adjusting the oscillator trimmer (this trimmer controls the dial pointer position at the high frequency end of the dial). All that remained to do at this stage was to adjust the aerial trimmer for maximum output meter deflection while tuned to 1422kHz. We found that the aerial coil trimmer was out of adjust­ment but not badly so. It’s still crook After disconnecting the generator leads and attaching an aerial, we found that the receiver still performed poorly at the high frequency end. There had been an improvement but not as much as had been hoped for. So in spite of all the previous adjustments and the ob­servation that the aerial coil had never been adjusted, it was felt that this was now worth checking, just to make sure. Unfor­ tunately, removing the tape and sliding the former back and forth around did nothing to boost the performance and so it was eventu­ally returned to its original position. It was time to check a few valves. Alf’s valve tester cannot test 9-pin valves because of a broken socket. On my tester, all the valves except one checked out OK, the exception being the 6N8 IF amplifier. This valve was very weak and the meter needle struggled to rise to the halfway position on the “bad” scale. Replacing the 6N8 made a noticeable difference to the set’s performance at the high frequency end of the dial. However, it still seemed to be lacking somewhat and the final solution was to connect an earth lead to the receiver. This increased the volume noticeably and considerably reduced interference hash from a 22,000V power line in the street outside. It should be noted that most valve receivers work better with an earth. It not only helps regarding reception but also eliminates or reduces a lot of interference. Most valve radios have an earth connection for good reason –they work better with one! Receiver alignment is an important aspect of restoring an old radio. There is not much point in replacing all those age-damaged components if the alignment is not restored as well. Only then will it perform as it SC should. Price: $A11.95 plus $3 p&p each (NZ $6 p&p). Just fill in & mail the handy order form in this issue; or fax (02) 9979 6503; or ring (02) 9979 5644 & quote your credit card number. Coming Next Month* Capacitor Discharge Ignition System Capacitor Discharge Ignition systems are particularly suitable for use with 2-stroke engines, older 4-stroke engines and some high-performance engines. This design operates from reluctor, points or Hall effect signals and features multiple spark output to improve fuel burning in the cylinders. Addressable Card For Driving Two Stepper Motors Continuing our series on stepper motor controllers, this latest card is similar to this month's design but is capable of controlling two stepper motors. We give the full circuit and construction details. On sale 27th August Australia-wide *Note: the preparation of these articles is well advanced but circumstances may change the final content. August 1997  87 Silicon Chip Back Issues September 1988: Hands-Free Speakerphone; Electronic Fish Bite Detector; High Performance AC Millivoltmeter, Pt.2; Build The Vader Voice. April 1989: Auxiliary Brake Light Flasher; What You Need to Know About Capacitors; 32-Band Graphic Equaliser, Pt.2; The Story Of Amtrak Passenger Services. May 1989: Build A Synthesised Tom-Tom; Biofeedback Monitor For Your PC; Simple Stub Filter For Suppressing TV Interference; The Burlington Northern Railroad. July 1989: Exhaust Gas Monitor; Experimental Mains Hum Sniffers; Compact Ultrasonic Car Alarm; The NSW 86 Class Electrics. September 1989: 2-Chip Portable AM Stereo Radio (Uses MC13024 and TX7376P) Pt.1; High Or Low Fluid Level Detector; Studio Series 20-Band Stereo Equaliser, Pt.2. June 1991: A Corner Reflector Antenna For UHF TV; 4-Channel Lighting Desk, Pt.1; 13.5V 25A Power Supply For Transceivers, Pt.2; Active Filter For CW Reception; Tuning In To Satellite TV. July 1991: 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; The Snowy Mountains Hydro Scheme. September 1991: Digital Altimeter For Gliders & Ultralights; Ultrasonic Switch For Mains Appliances; The Basics Of A/D & D/A Conversion; Plotting The Course Of Thunderstorms. 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. August 1990: High Stability UHF Remote Transmitter; Universal Safety Timer For Mains Appliances (9 Minutes); Horace The Electronic Cricket; Digital Sine/Square Generator, Pt.2. September 1990: Low-Cost 3-Digit Counter Module; Simple Shortwave Converter For The 2-Metre Band; the Bose Lifestyle Music System; The Care & Feeding Of Battery Packs; How To Make Dynamark Labels. October 1990: The Dangers of PCBs; Low-Cost Siren For Burglar Alarms; Dimming Controls For The Discolight; Surfsound Simulator; DC Offset For DMMs; NE602 Converter Circuits. October 1989: FM Radio Intercom For Motorbikes Pt.1; GaAsFet Preamplifier For Amateur TV; 2-Chip Portable AM Stereo Radio, Pt.2; A Look At Australian Monorails. November 1990: How To Connect Two TV Sets To One VCR; Build An Egg Timer; Low-Cost Model Train Controller; 1.5V To 9V DC Converter; Introduction To Digital Electronics; Build A Simple 6-Metre Amateur Band Transmitter. 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. December 1990: The CD Green Pen Controversy; 100W DC-DC Converter For Car Amplifiers; Wiper Pulser For Rear Windows; 4-Digit Combination Lock; 5W Power Amplifier For The 6-Metre Amateur Transmitter; Index To Volume 3. December 1989: Digital Voice Board; UHF Remote Switch; Balanced Input & Output Stages; Operating an R/C Transmitter; Index to Vol. 2. January 1991: Fast Charger For Nicad Batteries, Pt.1; Have Fun With The Fruit Machine; Two-Tone Alarm Module; LCD Readout For The Capacitance Meter; How Quartz Crystals Work; The Dangers of Servicing Microwave Ovens. January 1990: High Quality Sine/Square Oscillator; Service Tips For Your VCR; Phone Patch For Radio Amateurs; Active Antenna Kit; Designing UHF Transmitter Stages. February 1990: A 16-Channel Mixing Desk; Build A High Quality Audio Oscillator, Pt.2; The Incredible Hot Canaries; Random Wire Antenna Tuner For 6 Metres; Phone Patch For Radio Amateurs, Pt.2. March 1990: Delay Unit For Automatic Antennas; Workout Timer For Aerobics Classes; 16-Channel Mixing Desk, Pt.2; Using The UC3906 SLA Battery Charger IC; The Australian VFT Project. February 1991: Synthesised Stereo AM Tuner, Pt.1; Three Low-Cost Inverters For Fluorescent Lights; Low-Cost Sinewave Oscillator; Fast Charger For Nicad Batteries, Pt.2; How To Design Amplifier Output Stages. March 1991: Remote Controller For Garage Doors, Pt.1; Transistor Beta Tester Mk.2; A Synthesised AM Stereo Tuner, Pt.2; Multi-Purpose I/O Board For PC-Compatibles; Universal Wideband RF Preamplifier For Amateur Radio & TV. April 1990: Dual Tracking ±50V Power Supply; Voice-Operated Switch (VOX) With Delayed Audio; 16-Channel Mixing Desk, Pt.3; Active CW Filter; Servicing Your Microwave Oven. 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. June 1990: Multi-Sector Home Burglar Alarm; Build A Low-Noise Universal Stereo Preamplifier; Load Protector For Power Supplies; Speed Alarm For Your Car; Fitting A Fax Card To A Computer. 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. October 1991: Build A Talking Voltmeter For Your PC, Pt.1; SteamSound Simulator Mk.II; Magnetic Field Strength Meter; Digital Altimeter For Gliders, Pt.2; Military Applications Of R/C Aircraft. November 1991: Build A Colour TV Pattern Generator, Pt.1; A Junkbox 2-Valve Receiver; Flashing Alarm Light For Cars; Digital Altimeter For Gliders, Pt.3; Build A Talking Voltmeter For Your PC, Pt.2; Build a Turnstile Antenna For Weather Satellite Reception. December 1991: TV Transmitter For VCRs With UHF Modulators; Infrared Light Beam Relay; Colour TV Pattern Generator, Pt.2; Index To Volume 4. January 1992: 4-Channel Guitar Mixer; Adjustable 0-45V 8A Power Supply, Pt.1; Baby Room Monitor/FM Transmitter; Experiments For Your Games Card. March 1992: TV Transmitter For VHF VCRs; Thermostatic Switch For Car Radiator Fans; Telephone Call Timer; Coping With Damaged Computer Directories; Guide Valve Substitution In Vintage Radios. April 1992: IR Remote Control For Model Railroads; Differential Input Buffer For CROs; Understanding Computer Memory; Aligning Vintage Radio Receivers, Pt.1. May 1992: Build A Telephone Intercom; 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; IR Remote Control For Model Railroads, Pt.3; 15-Watt 12-240V Inverter; A Look At Hard Disc Drives. August 1992: An Automatic SLA Battery Charger; Miniature 1.5V To 9V DC Converter; 1kW Dummy Load Box For Audio Amplifiers; Troubleshooting Vintage Radio Receivers; MIDI Explained. October 1992: 2kW 24VDC - 240VAC Sinewave Inverter; Multi-Sector Home Burglar Alarm, Pt.2; Mini Amplifier For Personal Stereos; A Regulated Lead-Acid Battery Charger. January 1993: 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 Projects For Model Railroads; Low Fuel Indicator For Cars; Audio Level/VU Meter (LED Readout); An Electronic Cockroach; 2kW 24VDC To 240VAC Sinewave Inverter, Pt.5. ORDER FORM Please send me the following back issues: _____________________________________________________________________ _____________________________________________________________________________________________________________ _____________________________________________________________________________________________________________ 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 ___________ 88  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) 9979 5644 & quote your credit card details or fax the details to (02) 9979 6503.  Card No. March 1993: Solar Charger For 12V Batteries; Alarm-Triggered Security Camera; Reaction Trainer; Audio Mixer for Camcorders; A 24-Hour Sidereal Clock For Astronomers. April 1993: Solar-Powered Electric Fence; Audio Power Meter; Three-Function Home Weather Station; 12VDC To 70VDC Converter; Digital Clock With Battery Back-Up. May 1993: Nicad Cell Discharger; Build The Woofer Stopper; Alphanumeric LCD Demonstration Board; The Microsoft Windows Sound System; The Story of Aluminium. June 1993: AM Radio Trainer, Pt.1; Remote Control For The Woofer Stopper; Digital Voltmeter For Cars; A Windows-Based Logic Analyser. July 1993: Single Chip Message Recorder; Light Beam Relay Extender; AM Radio Trainer, Pt.2; Quiz Game Adjudicator; Windows-based Logic Analyser, Pt.2; Antenna Tuners – Why They Are Useful. August 1993: Low-Cost Colour Video Fader; 60-LED Brake Light Array; Microprocessor-Based Sidereal Clock; Southern Cross Z80-Based Computer; A Look At Satellites & Their Orbits. 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 Cockroach. October 1993: Courtesy Light Switch-Off Timer For Cars; Wireless Microphone For Musicians; Stereo Preamplifier With IR Remote Control, Pt.2; Electronic Engine Management, Pt.1. November 1993: Jumbo Digital Clock; High Efficiency Inverter For Fluorescent Tubes; Stereo Preamplifier With IR Remote Control, Pt.3; Siren Sound Generator; Engine Management, Pt.2; Experiments For Games Cards. December 1993: Remote Controller For Garage Doors; LED Stroboscope; 25W Amplifier Module; 1-Chip Melody Generator; 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; Engine Management, Pt.4. February 1994: Build A 90-Second Message Recorder; 12-240VAC 200W Inverter; 0.5W Audio Amplifier; 3A 40V Adjustable Power Supply; Engine Management, Pt.5; Airbags - How They Work. March 1994: Intelligent IR Remote Controller; 50W (LM3876) Audio Amplifier Module; Level Crossing Detector For Model Railways; Voice Activated Switch For FM Microphones; Simple LED Chaser; Engine Management, Pt.6. April 1994: Sound & Lights For Model Railway Level Crossings; Discrete Dual Supply Voltage Regulator; Universal Stereo Preamplifier; Digital Water Tank Gauge; Engine Management, Pt.7. May 1994: Fast Charger For Nicad Batteries; Induction Balance Metal Locator; Multi-Channel Infrared Remote Control; Dual Electronic Dice; Simple Servo Driver Circuits; Engine Management, Pt.8; Passive Rebroadcasting For TV Signals. June 1994: 200W/350W Mosfet Amplifier Module; A Coolant Level Alarm For Your Car; 80-Metre AM/CW Transmitter For Amateurs; Converting Phono Inputs To Line Inputs; PC-Based Nicad Battery Monitor; Engine Management, Pt.9. July 1994: Build A 4-Bay Bow-Tie UHF Antenna; PreChamp 2-Transistor Preamplifier; Steam Train Whistle & Diesel Horn Simulator; Portable 6V SLA Battery Charger; Electronic Engine Management, Pt.10. August 1994: High-Power Dimmer For Incandescent Lights; Microprocessor-Controlled Morse Keyer; Dual Diversity Tuner For FM Microphones, Pt.1; Nicad Zapper; Engine Management, Pt.11. September 1994: Automatic Discharger For Nicad Battery Packs; MiniVox Voice Operated Relay; Image Intensified Night Viewer; AM Radio For Weather Beacons; Dual Diversity Tuner For FM Microphones, Pt.2; Engine Management, Pt.12. October 1994: Dolby Surround Sound – How It Works; Dual Rail Variable Power Supply; Build A Talking Headlight Reminder; Electronic Ballast For Fluorescent Lights; Build A Temperature Controlled Soldering Station; Electronic Engine Management, Pt.13. November 1994: Dry Cell Battery Rejuvenator; Novel Alphanumeric Clock; 80-Metre DSB Amateur Transmitter; Twin-Cell Nicad Discharger (See May 1993); Anti-Lock Braking Systems; How To Plot Patterns Direct To PC Boards. December 1994: Dolby Pro-Logic Surround Sound Decoder, Pt.1; Easy-To-Build Car Burglar Alarm; Three-Spot Low Distortion Sinewave Oscillator; Clifford – A Pesky Electronic Cricket; Cruise Control – How It Works; Remote Control System for Models, Pt.1; Index to Vol.7. January 1995: Sun Tracker For Solar Panels; Battery Saver For Torches; Dolby Pro-Logic Surround Sound Decoder, Pt.2; Dual Channel UHF Remote Control; Stereo Microphone Pre­ amplifier;The Latest Trends In Car Sound; Pt.1. February 1995: 50-Watt/Channel Stereo Amplifier Module; Digital Effects Unit For Musicians; 6-Channel Thermometer With LCD Readout; Wide Range Electrostatic Loudspeakers, Pt.1; Oil Change Timer For Cars; The Latest Trends In Car Sound; Pt.2; Remote Control System For Models, Pt.2. March 1995: 50 Watt Per Channel Stereo Amplifier, Pt.1; Subcarrier Decoder For FM Receivers; Wide Range Electrostatic Loudspeakers, Pt.2; IR Illuminator For CCD Cameras; Remote Control System For Models, Pt.3; Simple CW Filter. April 1995: FM Radio Trainer, Pt.1; Photographic Timer For Dark­rooms; Balanced Microphone Preamp. & Line Filter; 50W/ Channel Stereo Amplifier, Pt.2; Wide Range Electrostatic Loudspeakers, Pt.3; 8-Channel Decoder For Radio Remote Control. May 1995: What To Do When the Battery On Your PC’s Mother­ board Goes Flat; Build A Guitar Headphone Amplifier; FM Radio Trainer, Pt.2; Transistor/Mosfet Tester For DMMs; A 16-Channel Decoder For Radio Remote Control; Introduction to Satellite TV. June 1995: Build A Satellite TV Receiver; Train Detector For Model Railways; 1W Audio Amplifier Trainer; Low-Cost Video Security System; Multi-Channel Radio Control Transmitter For Models, Pt.1; Build A $30 Digital Multimeter. July 1995: Electric Fence Controller; How To Run Two Trains On A Single Track (Incl. Lights & Sound); Setting Up A Satellite TV Ground Station; Door Minder; Adding RAM To A Computer. August 1995: Fuel Injector Monitor For Cars; Gain Controlled Microphone Preamp; Audio Lab PC Controlled Test Instrument, Pt.1; Mighty-Mite Powered Loudspeaker; How To Identify IDE Hard Disc Drive Parameters. September 1995: Keypad Combination Lock; The Incredible Vader Voice; Railpower Mk.2 Walkaround Throttle For Model Railways, Pt.1; Jacob’s Ladder Display; The Audio Lab PC Controlled Test Instrument, Pt.2. October 1995: Geiger Counter; 3-Way Bass Reflex Loudspeaker System; Railpower Mk.2 Walkaround Throttle For Model Railways, Pt.2; Fast Charger For Nicad Batteries; Digital Speedometer & Fuel Gauge For Cars, Pt.1. November 1995: Mixture Display For Fuel Injected Cars; CB Trans­verter For The 80M Amateur Band, Pt.1; PIR Movement Detector; Dolby Pro Logic Surround Sound Decoder Mk.2, Pt.1; Digital Speedometer & Fuel Gauge For Cars, Pt.2. December 1995: Engine Immobiliser; 5-Band Equaliser; CB Transverter For The 80M Amateur Band, Pt.2; Subwoofer Controller; Dolby Pro Logic Surround Sound Decoder Mk.2, Pt.2; Knock Sensing In Cars; Index To Volume 8. January 1996: Surround Sound Mixer & Decoder, Pt.1; Magnetic Card Reader; Build An Automatic Sprinkler Controller; IR Remote Control For The Railpower Mk.2; Recharging Nicad Batteries For Long Life. February 1996: Three Remote Controls To Build; Woofer Stopper Mk.2; 10-Minute Kill Switch For Smoke Detectors; Basic Logic Trainer; Surround Sound Mixer & Decoder, Pt.2; Use your PC As A Reaction Timer. March 1996: Programmable Electronic Ignition System; Zener Tester For DMMs; Automatic Level Control For PA Systems; 20ms Delay For Surround Sound Decoders; Multi-Channel Radio Control Transmitter; Pt.2; Cathode Ray Oscilloscopes, Pt.1. April 1996: Cheap Battery Refills For Mobile Telephones; 125W Power Amplifier Module; Knock Indicator For Leaded Petrol Engines; Multi-Channel Radio Control Transmitter; Pt.3; Cathode Ray Oscilloscopes, Pt.2. May 1996: Upgrading The CPU In Your PC; Build A High Voltage Insulation Tester; Knightrider Bi-Directional LED Chaser; Simple Duplex Intercom Using Fibre Optic Cable; Cathode Ray Oscilloscopes, Pt.3. June 1996: BassBox CAD Loudspeaker Software Reviewed; Stereo Simulator (uses delay chip); Rope Light Chaser; Low Ohms Tester For Your DMM; Automatic 10A Battery Charger. July 1996: Installing a Dual Boot Windows System On Your PC; Build A VGA Digital Oscilloscope, Pt.1; Remote Control Extender For VCRs; 2A SLA Battery Charger; 3-Band Parametric Equaliser; Single Channel 8-bit Data Logger. August 1996: Electronics on the Internet; Customising the Windows Desktop; Introduction to IGBTs; Electronic Starter For Fluores­c ent Lamps; VGA Oscilloscope, Pt.2; 350W Amplifier Module; Masthead Amplifier For TV & FM; Cathode Ray Oscilloscopes, Pt.4. September 1996: VGA Oscilloscope, Pt.3; Infrared Stereo Headphone Link, Pt.1; High Quality PA Loudspeaker; 3-Band HF Amateur Radio Receiver; Feedback On Pro­g rammable Ignition (see March 1996); Cathode Ray Oscilloscopes, Pt.5. October 1996: Send Video Signals Over Twisted Pair Cable; Power Control With A Light Dimmer; 600W DC-DC Converter For Car Hifi Systems, Pt.1; Infrared Stereo Headphone Link, Pt.2; Multi-Media Sound System, Pt.1; Multi-Channel Radio Control Transmitter, Pt.8. November 1996: Adding An Extra Parallel Port To Your Computer; 8-Channel Stereo Mixer, Pt.1; Low-Cost Fluorescent Light Inverter; How To Repair Domestic Light Dimmers; Build A Multi-Media Sound System, Pt.2; 600W DC-DC Converter For Car Hifi Systems, Pt.2. December 1996: CD Recorders –­ The Next Add-On For Your PC; Active Filter Cleans Up CW Reception; Fast Clock For Railway Modellers; Laser Pistol & Electronic Target; Build A Sound Level Meter; 8-Channel Stereo Mixer, Pt.2; Index To Volume 9. January 1997: How To Network Your PC; Using An Autotransformer To Save Light Bulbs; Control Panel For Multiple Smoke Alarms, Pt.1; Build A Pink Noise Source (for Sound Level Meter calibration); Computer Controlled Dual Power Supply, Pt.1; Digi-Temp Monitors Eight Temperatures. February 1997: Computer Problems: Sorting Out What’s At Fault; Cathode Ray Oscilloscopes, Pt.6; PC-Controlled Moving Message Display; Computer Controlled Dual Power Supply, Pt.2; Alert-A-Phone Loud Sounding Alarm; Control Panel For Multiple Smoke Alarms, Pt.2. March 1997: Driving A Computer By Remote Control; Plastic Power PA Amplifier (175W); Signalling & Lighting For Madel Railways; Build A Jumbo LED Clock; Audible Continuity Tester; Cathode Ray Oscilloscopes, Pt.7. April 1997: Avoiding Windows 95 Hassles With Motherboard Upgrades; A Low-Tech Timer With No ICs; Digital Voltmeter For Cars; Loudspeaker Protector For Stereo Amplifiers; Model Train Controller; Installing A PC-Compatible Floppy Drive In An Amiga 500; A Look At Signal Tracing; Pt.1; Cathode Ray Oscilloscopes, Pt.8. May 1997: Windows 95 – The Hardware Required; Teletext Decoder For PCs; Build An NTSC-PAL Converter; Neon Tube Modulator For Light Systems; Traffic Lights For A Model Intersection; The Spacewriter – It Writes Messages In Thin Air; A Look At Signal Tracing; Pt.2; Cathode Ray Oscilloscopes, Pt.9. June 1997: Tuning Up Your Hard Disc Drive; PC-Controlled Thermometer/Thermostat; Colour TV Pattern Generator, Pt.1; Build An Audio/RF Signal Tracer; High-Current Speed Controller For 12V/24V Motors; Manual Control Circuit For A Stepper Motor; Fail-Safe Module For The Throttle Servo; Cathode Ray Oscilloscopes, Pt.10. July 1997: Infrared Remote Volume Control; A Flexible Interface Card For PCs; Points Controller For Model Railways; Simple Square/Triangle Waveform Generator; Colour TV Pattern Generator, Pt.2; An In-Line Mixer For Radio Control Receivers; How Holden’s Electronic Control Unit works, Pt.1. PLEASE NOTE: November 1987 to August 1988, October 1988 to March 1989, June 1989, August 1989, May 1990, August 1991, February 1992, July 1992, September 1992, November 1992 and December 1992 are now sold out. All other issues are presently in stock. For readers wanting articles from sold-out issues, we can supply photostat copies (or tear sheets) at $7.00 per article (includes p&p). When supplying photostat articles or back copies, we automatically supply any relevant notes & errata at no extra charge. A complete index to all articles published to date is available on floppy disc at $10 including packing & postage. August 1997  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. High frequency track cleaner I have a real problem with dirt build-up on the wheels of my locos and rolling stock. All my rolling stock has metal wheels because I am using a carriage lighting system, similar to that described in the March 1997 issue of SILICON CHIP. I have been told that my dirt problems would be solved if I used a high frequency track cleaner. Apparently this senses the presence of dirt between the wheels and track and then zaps it off. Have you described such a system? (G. R., South Tacoma, NSW). • We have not described such a system. Nor are we sure that a high frequency high voltage system would do much to remove dirt and in fact, it might even lead to dirt build-up, in much the same way as dirt builds up on high voltage equipment due to static attraction. Nor are we confident that a high frequency track cleaning system could be used in conjunction Signal tracer appears to be unstable After completing the Signal Tracer featured in the June 1997 issue of SILICON CHIP, I found that the circuit just screeched, with no audio or RF sounds. I checked the circuit diagram against the PC board and found an error on the PC board. The input from switch S2b middle left (marked 2 on overlay) was going through a 0.1µF capacitor, then going to pin 2 of IC2 in­ stead of pin 3, while pin 3 of IC2 was tied to earth. After making modifications to the PC board the circuit seems to be working correctly with audio and RF sound but I have a fair amount of oscillation noise when the tracer is set on RF HIGH and not connected 90  Silicon Chip with you constant voltage lighting system – the two systems may interact. We’ll put it to our readers. Does anyone have experience with a high frequency track cleaning system and does it work? Electronic speedo is not the answer Like many other motor enthusiasts, I have changed my dif­ferential, which causes the speedo to be incorrect. How about a project to construct an electronic speedo? I have plenty of ideas on how this could be done but you guys should be able to sort out the mechanics. (L. Z., Ungarie, NSW). • We described an electronic speedo in the October & November 1995 issues but this would not solve the problem of your odometer and you could not use your existing speedometer either. If your speedo uses a Hall Effect pickup it may be possible to design a pulse multiplier to correct for the ratio of your new differen­tial to a test circuit. I connected a shielded cable to the probe and tied the shield to earth only at the PC board end and this has improved it a little. Could you advise if there is anything else that can be done to reduce the noise further? I live close to a major Sydney radio station and this may be the cause. (G. Moore, Seven Hills, Vic). • As indicated in the Notes & Errata on page 92, there is a discrepancy between the circuit and the PC board layout for this project although the unit would work either way. The reason it appears to take off is that it is so sensitive and it is mounted in an unshielded case. However, when the Signal Tracer is con­nected to a circuit it behaves normally. but we are unable to provide such a circuit from our files. However most speedos are still driven by a cable and so the only effective way is to change the gears in the speedo itself or possibly add a gear adapter at the back of the speedo. If the differential was a manufacturer’s option for your car, it should be possible to obtain the correct speedo or speedo gearbox. The people to approach in this field are any of the large auto instrument service companies. Soldering iron controller I want to regulate the temperature of a 230 watt soldering iron – approximately 10 amps AC. In September 1992 you published a 5A drill speed controller, however it will not handle the current. Do you have any other suggestions to assist in this prob­lem? (P. B., Villawood, NSW). • Unless your soldering iron employs a step-down transformer, there is no way it could draw 10 amps and if it is rated at 230 watts then it is unlikely to be driven at 23V. Therefore, we assume that your iron actually runs at 240VAC and only draws 0.95A to give it a rating of 230W. In this case, it can be com­fortably run by the 5A drill speed controller. However, we should point out that without some means of temperature feedback, no circuit can regulate the temperature of a soldering iron. The drill speed controller will certainly enable you to reduce the power fed to your iron but it will not provide any temperature regulation. Running a 16V pump in a 32V system I have a friend living on a property with a home electrici­ty supply. He has had the system in operation for about 17 years, mostly before commercial systems were available and his is decid­edly home-made. Amongst other voltages available in his system, he has a 32V DC supply from 16 lead acid accumulators and from this he runs an electric air pump to supply air to his tropical fish. He could not find a commercial pump to suit, so he has a home-made pump run by an aircraft electric motor which he runs from half the 32V battery supply; ie, at 16V. He then alternates the half bank manually until both halves need charging, as near as he can estimate. This pump runs 24 hours each day and 365 days each year and has done so for a few years now. It only stops when the rubber diaphragm tears and he switches to an identical stand­by pump until repairs are made. Would the Motor Speed Controller featured in the June 1997 issue work on the 32V supply and be able to provide the approx­imate 16V to the motor? It should be well able to supply the current because he thinks it only draws a few amperes but the higher voltage is the concern. (R. B., Seymour, Vic). • There should be no problem operating the Motor Speed Con­troller from 32V. There is no need to alter any components, although you should check the temperature of the voltage regula­tor tab (REG1), as it may possibly need a small heatsink at this higher voltage. If the motor only draws a couple of amperes then you will only need one Mosfet. Splitting the 4-channel lighting desk I constructed the 4-Channel Lighting Desk for one of our rock bands about two years ago and it has been working fine ever since. The band has asked if there is any possibility of rebuilding the unit to make the setup easier and reduce the number and length of the 240VAC extension leads. The possible solutions include mount­ ing all high-voltage components in separate housing as a Stage Box with a multi-core cable between the Lighting Desk and Stage Box. The multi-core cable would run the collector outputs of Q1, Q2, Q3 and Q4 to pin 1 of IC9, IC10, IC11 and IC12 respectively. There would be one earth cable for the 680Ω resistors and two cables from the AC output Needs a bigger smoke alarm panel I have purchased two kits of the Smoke Alarm Panel and 20 kits of the Smoke Detector interface published in the January & February 1997 issues of SILICON CHIP. My wife and I are hearing impaired and we have two young daughters with normal hearing. We live in a big two storey house which requires 10 smoke detectors and one control panel for the downstairs living area and another 10 smoke detectors and one control panel for upstairs. At some stage I will be connecting the wire from the siren output from the downstairs panel to the sound siren, a flashing light alarm and to a 9V relay. This will connect an alarm/lighting system for the deaf control panel in our house. This control panel will flash the of the power transformer to the main PC board. Could you please check my proposed alterations, as I’m not sure if the AC voltage will interfere with the signals control­ling the optocouplers. (J. K., St Marys, NSW). • Your method of splitting the unit at the optocoupler is valid but we would suggest that the Stage Box section of the circuit be separately powered with its own 12VAC transformer rather than feeding the AC down the multi-way cable. This will minimise any chance of interference. Replacing perished foam speaker surrounds I recently purchased a pair of secondhand “AR” brand speak­ers. The foam surround on the woofers has deteriorated. To have them professionally repaired would cost a lot of money and besides, I would like the satisfaction of repairing them myself. I found a couple of places in the USA that sell repair kits, however they don’t seem interested in responding to overseas customers. Do you know of any company in Australia that sells these kits? If so, per­haps you could do an article on speaker repairs. (G. lights in most rooms of the house to warn us of the following events: front/back doorbell, telephones, baby cries, security and smoke detectors. I would need to link between the two smoke alarm control panels to make all 20 smoke detector sirens sound when any one of the 20 detectors senses smoke in the house. What do I need to do to achieve this? (A. S., Glen Iris, Vic). • You will require two wires to interconnect the two Smoke Alarm Panels. One connection is run between the ground (GND) of one panel and the GND of the other. The second connection is to tie the pin 7 outputs of IC3 in both panels together. This will enable the alarm in both panels if the detectors sense smoke. You can remove the 10kΩ pullup resistor at pin 7 of IC3 from one of the panels. E., Armidale, NSW). • We do not know of any company that imports the repair kits you refer to. We would be wary of any repair job that simply replaced the foam surround on loudspeakers. Often, you will find that when the foam surround perishes, the cone is flexed in unusual modes and this causes creases and other signs of fatigue in the cone itself. In severe cases, where the foam is far gone, the cone itself may sag. In other words, if the surround is perished, the cone may have deteriorated as well. Even if you do manage to repair the foam surround it is most important that the cone is properly aligned, with the voice coil centred in the gap. To do that you must cut away the dust cap to gain access. You may also find that if the foam surround has perished you may have problems with corrosion as well. In practice, we believe that, depending on the age of the speakers, it may be more practical to refurbish the cabinets with new drivers where necessary and even with new crossover networks, although this is not a job for the amateur. One firm that does this work is Audiosound Laboratories, 148 Pitt Road, North Curl Curl, NSW 2099. Phone (02) 9938 2068. August 1997  91 How about a “valvesound” amplifier? I would like to suggest a singleended Mosfet transformer coupled amplifier as a project, with a power output of about 25 watts RMS. I’m sure the output transformers could be bifilar wound with a 1:1 ratio. In my opinion, solid state amplifiers that are capacitor coupled are a little clinical. I’m sure the above requested amplifiers will have a smooth warm sound, sound­ ing sweet and open like that of a valve, single-ended amplifier, but not requiring a massive un-affordable power supply as valve amplifiers do. (R. L., Somerville, Vic). • While such a project is feasible, we do not think that it would result in valve-like sound. There are several reasons why valve amplifiers sound the way they do and the first is their moreor-less gradual overload characteristic. The second is that their harmonic distortion is often more or less second harmonic which means that the distortion is musically related to the fundamental. This often leads people to state that such-and-such valve ampli- Big brother is definitely watching you With all the current media interest at present in hidden surveillance cameras, spy cameras, hidden audio devices, thermal cameras, infrared cameras and any other device that can be used for surveillance, I am wondering just what is out there and who are they keeping an eye on. I am hoping you would do a series of articles in your great magazine on what there is at present, what the future holds, how do we recognise it and if possible some projects on their detection. Another possible project I would like to see is a Digital Command Control for model railway locomotives that is very small in size and suitable for “N” scale. (S. F., Strathgordon, Tas). • An article on surveillance cameras would merely illustrate the fact that these devices are now very widespread. In many cases, they are quite 92  Silicon Chip fiers are “more musical”. Indeed, they are more musical but this is not the best high fidelity approach since amplifiers that produce significant harmonic distortion which may be masked also produce inter­ modula­tion which is definitely not pleasant. The third reason why valve amplifiers sound “less clinical” is that they usually have far less negative feedback. The high negative feedback in solid state amplifiers has two results. First, it greatly lowers the inherent distortion of the circuit, leading to a much cleaner (or clinical) sound. Second, it leads to a much lower output impedance and this results in more elec­trical damping on the loudspeaker. This leads to a tighter, less boomy bass. Most solid state amplifiers these days are direct coupled instead of capacitor coupled and this improves the loud­speaker damping factor even further. In effect, while a solid state amplifier can be designed to drive a transformer, it is still likely to have a very clean, high quality sound. The most recent example of this is the 175W transformer coupled design in the March 1997 issue. apparent; you only have to look for them. Most shopping malls have cameras for the main concourses, many large buildings have cameras throughout (including in the eleva­tors), as do factories, petrol service stations, parking sta­tions, toll booths on expressways, shops, banks and clubs. In banks, hotels and clubs the cameras are generally quite obvious while in shops they are usually concealed but there are notices to say that cameras are in use. Believe them. In most cases, the cameras may not be directly monitored but will feed video recorders which run 24 hours a day. In the event of a crime, the tapes are examined by the police and often lead to a conviction. There are also a number of TV programs which run along this theme, with “Real TV” being the main one. In the major cities, video cameras have been used to con­trol traffic flow for more than 20 years. Cameras are also often used in apartment complexes and even homeowners are now using them. We published a doit-yourself article on the subject in the June 1995 issue. The other point to recognise is that all these cameras are watching you, not just somebody else. If you are virtually anywhere in a public place, you could be on camera. On a more cheerful note, one of our contributors is working on a DCC design for model trains. Notes & Errata Audio/RF Signal Tracer, June 1997: users of this project will find that the unit produces a lot of noise and what may sound like “motor-boating” when it is switched to high gain and RF modes and with no connections to the input probe and earth clip. This is normal and is a function of its high gain. As soon as the unit is connected to a circuit the noise drops and the wanted signal will be heard. There is a discrepancy between the circuit on page 40 and the wiring diagram on page 43. The circuit shows the signal from switch S2b coupled to pin 3 of IC2 via a 0.1µF capacitor and pin 2 grounded. The PC board has this reversed, with pin 3 grounded and signal going to pin 2 via the 0.1µF capacitor. The PC board is correct. If the unit is to be used on valve amplifiers, there is the possibility that connecting the unit to a voltage above 100V may blow the LM318 IC’s input protection diodes. To prevent this, we suggest soldering two 1N914 diodes in inverse parallel across the 100kΩ bias resistor to pin 3. These diodes can be installed on the copper side of the PC board. 12V/24V Motor Speed Controller, June 1997: there is a mistake in the text on page 30, third paragraph down. The text states “Make sure that they (the diodes) are connected in the right direction across the motor; ie, anodes to the positive supply line.” The diode(s) should be connected with cathode to the positive supply line, as shown in the circuit and wiring diagrams. Flexible Interface Card for PCs, July 1997: the circuit on page 25 shows 4.7kΩ resistors to the LEDs of the 4N28 optocouplers but 1.5kΩ resistors on the wiring diagram on page 27. Either SC value will work. Silicon Chip Bookshop Guide to Satellite TV Installation, Recept­ion & Repair. By Derek J. Stephen­son. First published 1991, reprinted 1997 (4th 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. 383 pages, in hard cover at $55.00. Guide to TV & Video Technology By Eugene Trundle. First pub­lished 1988. Second edition 1996. Eugene Trundle has written for many years in Television magazine and his latest book is right up date on TV and video technology. 382 pages, in paperback, at $39.95. Servicing Personal Computers By Michael Tooley. First published 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 $75.00. 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. 336 pages, in paperback at $55.00. Digital Audio & Compact Disc Technology Produced by the Sony Service Centre (Europe). 3rd edition, published 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 $69.00. Power Electronics Handbook Components, Circuits & Applica­tions, 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 pub­lished 1994. This book will provide informative reading for anyone considering the assembly of PC boards with surface mounted devices. Includes chapters on wave soldering, reflow­soldering, component placement, cleaning & quality control. 361 pages, in hard cover at $99.00. Radio Frequency Transistors Principles & Practical Applications. By Norm Dye & Helge Granberg. Published 1993. This 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, impedance matching & CAD. 235 pages, in hard cover at $95.00. Electronics Engineer’s Reference Book Edited by F. F. Mazda. First published 1989. 6th edition. 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, semi­-custom electronics & data communications. 63 chapters, soft cover at $125.00. Audio Electronics By John Linsley Hood. Pub­lished 1995. This book is for anyone involved in designing, adapting and using analog and digital audio equipment. Covers 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. Prices valid until 31st March, 1998 tape recording, tuners & radio receivers, preamplifiers, voltage amplifiers, power amplifiers, the compact disc & digital audio, test & measurement, loudspeaker crossover systems and power supplies. 351 pages, in soft cover at $55.00. Understanding Telephone Electronics By Stephen J. Bigelow. Third edition published 1997 by Butterworth-Heinemann. This is a very useful text for anyone wanting to become familiar with the basics of telephone technology. The 10 chapters explore telephone fundamentals, speech signal processing, telephone line interfacing, tone and pulse generation, ringers, digital transmission techniques (modems & fax machines) and much more. Ideal for students. 367 pages, in soft cover at $49.95. Video Scrambling & Descrambling For Satellite & Cable TV By Rudolf F. Graf & William Sheets. First pub­lished 1987. This is an easy-to-understand book for those who want to scramble and unscramble video signals for their own use or just want to learn about the techniques involved. It begins with the basic techniques, then details the theory of video encryption and decryption. It also provides schematics and details for several encoder and decoder projects, has a chapter of relevant semiconductor data sheets, covers three relevant US patents on the subject of scrambling and concludes with a chapter of technical data. 246 pages, in soft cover at $50.00. ✓ Title o o o o o o o o o o Price Guide to Satellite TV $55.00 Servicing Personal Computers $90.00 Video Scrambling & Descrambling $50.00 The Ar t Of Linear Electronics $70.00 Digital Audio & Compact Disc Technology $90.00 Radio Frequency Transistors $95.00 Guide to TV & Video Technology $55.00 Electronic Engineer's Reference Book $160.00 Audio Electronics $75.00 Understanding Telephone Electronics $55.00 Postage: add $5.00 per book. Orders over $100 are post free within Australia. NZ add $10.00 per book; elsewhere add $15 per book. TOTAL $A August 1997  93 MARKET CENTRE Cash in your surplus gear. Advertise it here in Silicon Chip. CLASSIFIED ADVERTISING RATES FOR SALE 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): $25 per column centimetre (Max. 10cm). Closing date: five weeks prior to month of sale. C COMPILERS: Ever ything you need to develop C and ASM software for 68HC08, 6809, 68HC11, 68HC12, 68HC16, 8051/52, 8080/85, 8086 or 8096: $140.00 each. Macro Cross Assemblers for these CPUs + 6800/01/03/05 and 6502: $140.00 for the set. Debug monitors: $70 for 6 CPUs. All compilers inc ‘HC12, XASMs and monitors: $480. 8051/52 or 80C320 Simulator (fast): $70. Disassemblers for 12 CPUs only $75. Try the new C-FLEA Virtual Machine for small CPUs, build a “C-Stamp”. Demo disk: FREE. All prices + $5 p&p. GRAN­ TRONICS PTY LTD, PO Box 275, Wentworthville 2145. Ph/Fax (02) 9631 1236 or Internet: http://www.mpx. com.au/~lgrant. To run your classified ad, print it clearly on a separate sheet of paper, fill out the form below & 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) 9979 6503. _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________  Bankcard    Visa Card    Master Card Card No. ✂ Enclosed is my cheque/money order for $­__________ or please debit my Signature­­­­­­­­­­­­__________________________  Card expiry date______/______ Name ______________________________________________________ Street ______________________________________________________ Suburb/town ___________________________ Postcode______________ 94  Silicon Chip MICROCRAFT IS NOW ON THE WEB: Dunfield (DDS) products are now available ex-stock at a new low price; please ask for our catalogue. Micro C, the affordable “C” compiler for embedded applications. Versions for 8051/52, 8086, 8096, 68HC08, 6809, 68HC11 or 68HC16 $139.95 each + $3 p&h • EMILY52 is a PC based 8051/52 high speed simulator $69.95 + $3 p&h • DDS demo disks $7 + $3 p&h • VHS VIDEO from the USA (PAL) “CNC X-Y-Z using car alter­nators” (uses car alternators as cheap power stepper motors!) $49.95 + $6 p&h (includes diagrams) • Fixed price electronic design and PCB layout • Credit cards accepted • All goods sent registered mail • Call Bob for more de­ t ails. MICRO­CRAFT, PO Box 514, Concord NSW 2137. Phone (02) 9744 5440 or fax (02) 9744 9280. http://www.micro.com.au email sales<at>micro.com.au MicroZed new Web page address: http://www.microzed.com.au/~microzed GOLD COAST/TWEED Electronic Kit Assembly and Troubleshoot­ing Service. Ph Geoff (07) 5570 7435. HOMEMADE GENERATORS: how to instructions. Eight pages free text and colour photos on the Internet at: http://www.onekw.co.nz/ VIDEO CAMERAS & EQUIPMENT Now! $75 PCB VIDEO CAMERA MODULES with Board or Pinhole Lens - Now! $75 Cat No MOD-BW 506 This Month Only! INFRARED ILLUMINATORS & KITS Complete Lamp 240vac Auto on/off $149. PCB LED Kits: 52mm Round Lamp Tubular Hooded Enclosure 50 LED 3.5-10 Watt $50. Rectangular 10 x 10cm 88-210 LED 6-44 Watt $79-$149. PCB Video Camera Modules 420/460 Line 0.05 lux $144/$177. 28 x 28mm PCB Modules THE TINIEST! Robust Mini Cube Cameras $147. Dome Ceiling Cameras $197. C Mount Cam­eras - Only! $99. Colour Modules & Cameras $449. TINY 12 x 12 x 4mm PCB Audio Modules from $30. TV Video/Audio Transmitter Mod­ules $54. Baluns 100/75 Ohm Use UTP or Telephone Cable for Video Only! $19. Monitors 5.5, 7, 9, 12 Inch from $119. Quad Screen Processors from $410. Colour Quads 512 x 512 Only! $999. Wireless CCTV Video/Audio Sets TX Camera & Receiver from $373. 74mW Infra Red LEDs from 48 cents! 3200mcd SuperBright Red LEDs 50 cents. Flashing Red, Green, Yellow, Orange LEDs $1. BEFORE YOU BUY! Ask for our Detailed, Illustrated Price List & Application Notes. Also available CCTV Technical, Design, Reference Manuals & CD ROM. Prices include tax. Discounts available! Allthings Sales & Services 08 9349 9413 fax 08 9344 5905. DS1620 SOFTWARE (WIN) – Digital thermometer/thermostat/programmer ver 3.0 (-30C to 120C) $30, DS1620 $12, PH $5. Mr Softmark, PO Box 1609, Hornsby, NSW 2077. Phone/fax (02) 9482 1565. A SIMPLE PIC84 PROGRAMMER: LED model 6 lights $70, LCD model 16 x 1 char. $80, pp $5. Others available. EST Electronics (02) 9789 3616. Fax (02) 9718 4762. RAIN BRAIN AND DIGI-TEMP KITS: 8-station controller and 8-chan­ n el, RS232 digital thermometer uses the incredible DS1820 sensor. Call Mantis Micro Products, 38 Garnet St, Niddrie, 3042. P/F/A (03) 9337 1917. http://www.home.aone.net.au/mantismp MicroZed Computers BASIC STAMPS & PIC Tools With third party supporting products, all in stock. Easy to learn, easy to use sophisticated CPU based controllers. PO Box 634, ARMIDALE 2350 (296 Cook’s Rd) Ph (067) 72 2777 – may time out to Mobile 014 036775 Fax (067) 72 8987 http://www.microzed.com.au/~microzed Credit cards OK. Send two 45c stamps for info MEMORY * MEMORY * MEMORY SIMMS Parity/Standard 4Mb 30-pin 60ns $41 $30 4Mb 72-pin 60ns $42 $32 8Mb 72-pin 60ns $86 $54 16Mb 72-pin 60ns $126 $108 32Mb 72-pin 60ns $263 $208 EDO SIMMS 72pin 60ns 4Mb / 8Mb $36 / $56 16Mb / 32Mb $106 / $208 64Mb / 128Mb $708 / $1490 DIMMS 168-pin 60ns 8Mb / 16Mb $70 / $114 32Mb / 64Mb $207 / $458 SDRAM 168-pin 12ns 8Mb / 16Mb $84 / $132 32Mb / 64Mb $255 / $653 TOSHIBA 16Mb Tecra 500/650 Sat. $201 16Mb Tecra 700 > 740 $267 GATEWAY 2000 16Mb Solo 2100/2200 $215 16Mb P5 166XL/G6-200 $169 IBM 16Mb Thinkpad 760, 365 $182 32Mb Aptiva S P200 $209 DELL 16Mb Latitude 4100 MX, MC, LC $205 32Mb Dimension M -SDRAM $422 16Mb Optiplex GS $224 HEWLETT PACKARD 8Mb Laserjet 4,5,6P/MP $67 8Mb Laserjet 5L, 6L $138 16Mb Omnibook 800 $224 CAMERA CARDS 8Mb Compact Flash $170 12Mb Compact Flash $315 8Mb ATA Flash $180 12Mb ATA Flash $234 We carry over 600 different modules for all makes, including ACER, AST, CANON, APPLE, NEC, ZENITH, SUN & SILICON GRAPHICS Pricing as at 01/07/97. PHONE FOR LATEST EX TAX PRICING OVERNIGHT DELIVERY $8 LIFETIME WARRANTY!! SALES TAX – 22% CREDIT CARDS WELCOME 651 Forest Rd, Bexley 2207 PELHAM Pty Suite 6, 2 Hillcrest Rd, Ph: (02) 9980 6988 Pennant Hills, 2120. Fax: (02) 9980 6991 Ltd Email: pelham1<at>ozemail.com.au makes all the project PCBs published in SILICON CHIP and other Australian magazines Tel +61 2 9587 3491 Fax 9587 5385 E-mail rcsradio<at>cia.com.au MicroZed have 5V UPS. Uses 2 x AA nickel cadmium cells. els. 2 x 40, 4 x 20, 2 x 16 LED BL $36 ea. BASIC Stamp handbook Version 1.8. Covers Stamp I & II $38 incl. post from MicroZed. WANTED MicroZed have a range of LCD pan- VALVES WANTED to buy. New and used. All types required. Phone (047) 51 5620. POSITION VACANT Electronics Technical Writer Silicon Chip Publications Pty Ltd is a small but growing magazine publishing company, situated in the Warriewood Valley near Sydney’s northern beaches. As part of our ongoing expansion program, we require a full-time technical writer for Silicon Chip, our monthly electronics magazine. The job: you don’t need to be a design engineer, as practical electronics design is not part of the job. What you do need is a good understanding of electronic circuitry and, above all, the ability to write clearly and logically. Your everyday activities will include: writing feature articles, editing rough articles written by our design engineers, and writing articles that describe the design and construction of electronic equipment. Some know­ledge of computers and photography would be well-regarded but it’s your electronics knowledge and the ability to write well that will land you this position. You will also need a good eye for detail, be able to work well in a team environment, and be flexible and willing to learn. How to apply: applications close on 18th August, 1997 and must be made in writing to: The Publisher, Silicon Chip Publications Pty Ltd, PO Box 139, Collaroy, NSW 2097. August 1997  95 14 Model Railway Projects ALF Our stocks of this book are now limited. All we have left are newsagents’ returns which means that they may be slightly shop soiled or have minor cover blemishes. Otherwise, they're undamaged and in good condition. SPECIAL CLEARANCE PRICE: $3.95 + $3 P&P (Aust. & NZ) This book will not be reprinted Yes! Please send me _____ copies of 14 Model Railway Projects at the special price of $A3.95 + $A3 p&p (p&p outside Aust. & NZ $A6). Enclosed is my cheque/money order for $­A__________ or please debit my ❏ Bankcard   ❏  Visa Card   ❏ MasterCard Signature­­­­­­­­­­­­___________________________  Card expiry date______/______ ______________________________________________________ Street Emona.........................................31 Freedman Electronics..................73 Harbuch Electronics....................73 Instant PCBs................................95 Jaycar ............................IFC, 45-52 Kalex............................................57 Kits-R-US.....................................74 MicroZed Computers...................95 Model Railways Book..................96 Oatley Electronics........................65 Pelham.........................................95 Rod Irving Electronics .......... 79-83 Card No. Name Aust. Comms. Authority...............87 Dick Smith Elecronics.... 8-11,34,35 Shop soiled but H PRICE! Advertising Index PLEASE PRINT Silicon Chip Back Issues....... 88-89 Silicon Chip Bookshop.................93 ______________________________________________________ Silicon Chip Binders................OBC Suburb/town_________________________________ Postcode_________ Silicon Chip Software..................75 Send your order to: SILICON CHIP, PO Box 139, Collaroy, NSW 2097; or fax your order to (02) 9979 6503; or ring (02) 9979 5644 and quote your credit card number (Bankcard, Visa Card or MasterCard). Silicon Chip Wallchart..............OBC RCS Radio...................................95 Tortech.........................................57 Microprocessor For Digital Effects Unit This is the 68HC705-C8P pro­ gramm­ed micro­pro­cessor IC for the Digital Effects Unit (see Feb­. 1995). Price: $45 + $6 p+p Payment by cheque, money order or credit card to: Silicon Chip Pub­ lica­ tions, PO Box 139 Collaroy 2097. Phone (02) 9979 5644; Fax (02) 9979 6503. 96  Silicon Chip Circuit Ideas Wanted Do you have a good circuit idea. If so, why not sketch it out, write a brief description of its operation & send it to us. Provided your idea is workable & original, we’ll publish it in Circuit Notebook & you’ll make some money. We pay up to $60 for a good circuit but don’t make it too big please. Send your idea to: Silicon Chip Publications, PO Box 139, Collaroy, 2097. Zoom Magazine.........................IBC _____________________________ PC Boards Printed circuit boards for SILICON CHIP projects are made by: •  RCS Radio Pty Ltd, 651 Forest Rd, Bexley, NSW 2207. Phone (02) 9587 3491. •  Marday Services, PO Box 19-189, Avondale, Auckland, NZ. Phone (09) 828 5730.