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Pulse power in train controllers A few months ago, I purchased “14 Model Railway Projects” which is a most interesting publication. The kit my son is assem­bling is from the final article, the “Diesel Sound Simulator”. We have controllers of both the “pulse” and “fully rectified wave­form” types. What are the effects of running an engine with the “pulse” circuit or a “rectified wave form” type? I have found the waveform type produces better results than the pulse type. The pulse type is a Hornby R921 putting out 12V DC at 4VA and the waveform type is a Bachmann 6607A putting out 17DC at 0.6 amps (7VA, although I don’t know how that maths works. 17 x 0.6 = 10.2). Is amperage the key? It seems from your articles that 3A is a good value. This figure contrasts signifi­ cantly with the 0.6A maximum used by a local model railway at­ traction (Mike Scott’s Trainworld). noise. It could be any one of a number of faults such as loose laminations, shorted turns, anti-phase primary connections or who knows what. Please, please, give it all up as a bad job before you kill yourself or someone else. By the way, your letter had no address on it but was post­marked “Darwin Mail Centre”. Normally we do not feature letters in SILICON CHIP where no address is supplied but in your case we have made an exception. We hope you get a chance to read this! Millivoltmeter drive modification I am interested in constructing your AC Millivoltmeter as described in the August & September 1988 issues. I have a SIFAM meter movement from an old hybrid AC millivoltmeter which has its scale calibrated precisely as in your design. Because this is a very high quality movement I would like to incorporate it into your 1988 design. The question is, can the circuit be 94  Silicon Chip He seems to be able to happi­ ly double-head a very long train (two Lima class 31s). (J. H., Auckland, NZ). • We are not sure about the question you are asking. As de­scribed in the article, the Diesel Sound Simulator circuit can be made to work with both pulse or rectified (waveform) controllers. However, once set up to work with a particular controller, it will not necessarily work well with other controllers. As far as pulse and waveform controllers are concerned, most so-called “pulse” controllers do not use the same system of pulse width modulation at about 200Hz as used in the SILICON CHIP controller design. As such, they do not perform as well as our design and generally not as well or as reliably as simpler recti­fied waveform designs. Most locos with can motors draw currents of less than 1A but others require a lot more and if smoke and lighting circuits are added, plus double-heading, then a much higher current is re­quired. of IC7b. The accompanying circuit shows the general scheme and you will prob­ably need to increase the 6.2kΩ resistor at pin 3 of IC7b to provide the appropriate zero offset to the meter. We must emphasise that we have not tried either of these ideas but one or the other should be workable. A 300V range can be included by using a 12-position switch and by splitting the 1.1Ω resistor at the bottom of the existing input voltage divider. The two new resistors would be 0.75Ω and 0.35Ω. More on battery capacity meters I have a suggestion in reply to the request in “Ask SILICON CHIP” July 1996 for a battery capacity meter. I too am a regular RC model aircraft flier and have been using the following method to determine nicad battery capacity for several years with suc­ cess. If your nicad battery discharger has a LED to indicate that discharge is taking place, it is a simple matter to connect a single-cell crystal clock in parallel with the LED. If you set the hands on 12.00, the clock will begin ticking when the dis­charge button is pressed and stop ticking when the LED goes out. It is then just a simple calculation to work out the battery capacity. For example, if the discharge rate is 200mA and the clock reads 2.00 (two hours), then the capacity = 2 x 200 = 400mA.h. (R. H., Kingston, Tas). Notes & Errata modified to accommodate a 5mA meter instead of the 100µA movement specified and if so how? I had thought that a simple transistor current amplifier would do the trick, perhaps even a PNP/NPN push-pull pair but I have not been able to find any data on such an idea. I would also like to include a 300V range. (J. L., Yate, UK). • As far as we can tell, the circuit should be able to drive a 6mA meter movement without problems although the calibration trimpot VR4 will need to be reduced to 200Ω or 250Ω. If you find that the LM833 cannot do the job, you will need an emitter follower to boost the output current Stereo Simulator, June 1996: pin 7 of the M65830P (IC2) is shown connected to both +5V and GND on the circuit diagram on page 16; it should only be connected to +5V. The PC board overlay diagram on page 19 is correct. 16V 15A Power Supply, Circuit Notebook, July 1996: there are number of mistakes and omissions in the circuit on page 17. First, the 56kΩ resistor from the collector of Q4 should go to the +25V line instead of to the base of Q1. Second, D4 should be a LED. The designer has also suggested that the 100µF capacitor across the output terminals be increased to 220µF and a 1kΩ resistor be connected across the 10kΩ potentiometer VR3 (Voltage SC Max).