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94  Silicon Chip In the January 1992 issue of SILICON CHIP, you described a “Baby Room Monitor and FM Transmitter” based on a BA1404 IC, made by the Rohm Corporation, Japan. I have been unable to find any information on this IC, or the address of the Australian agent. Could you please help me with the following questions? Would you have a data sheet available for this IC? If not, could you please advise me as to where I can obtain one, or give me the address of the Australian agent? Could you also tell me if it is possible to crystal-lock the IC at radio frequencies? If so, how can it be done? (W. W., Beresfield, NSW). • The Australian distributors for Rohm Co Ltd are: Fairmont Marketing, 57 St. Hellier Street, Heidelberg Heights, Vic 3081. Phone (03) 457 7300 or fax (03) 457 7339. They can supply data on the BA1404 although we published most of the relevant data in the October 1989 issue (no longer available but we can supply photo­ copies at the standard $6 fee). The circuit could be crystal locked but there is very little point since the D2 D1 In my model railway control system I am using a number of NE555 timer ICs as switches. Also incorporated is the Traffic Lights Simulator (again using NE555) and the Points Controller published in the February 1993 issue. Separately, they work fine; together, the Points Controller triggers all others, while the Traffic Lights Simulator triggers the NE555 switches. I already have 0.1µF capacitors as suppressors on all DC plus AC power inputs of the modules. Can you suggest a cure please? (M. W., Surfers Paradise, Qld). • When ever there is a problem of false triggering in 555 circuits, the standard cure is to install a 0.1µF capacitor in the positive supply line to the chip and, more importantly, con­ nect a 0.1µF or larger capacitor from pin 5 of each 555 to the 0V line. This capacitor is already present in the traffic light circuit. Notes & errata Woofer Stopper, May 1993: unfortunately, the uncorrected wiring diagram (Fig.2) found its way into the article. This contains several errors: (1) Q2 is shown upside down; (2) the 100kΩ resistor to the right of IC5 should be deleted; and (3) the 100kΩ resistor below D2 should be 220Ω. The correct overlay pattern is shown below as Fig.1. The published PC pattern is correct. SC 22k 22k 0.1 220  1000uF IC1 4060 Q2 IC5 4013 Q6 Q7 1 10M Q8 33pF  1 Q4 Q1 D3 100k 10uF 0.1 Q5 100k 78L05 IC2 4518 100k 1 33pF Q3 IC4 4024 IC3 4020 1 1k Fig.1: corrected parts overlay pattern for the Woofer Stopper. Mutual interference in model railway circuits 1k 1k I have built the Digital Capacitance Meter as published in the May 1990 of SILICON CHIP. It functions reasonably well, except that it has the annoying habit of stepping back and forth around the actual readout; that is, with the standard 0.1µF capacitor supplied, the nF scale reads back and forth from 97 to 102. I have replaced all the ICs one by one but still the trou­ble persists. I would Questions on the BA1404 transmitter is very stable, provided that the specified NPO capacitors are used. X1 Fixing jitter in the capacitance meter appreciate your assistance to help me fix this trouble. I enjoy your magazine and think it is very good value. (D. M., North Balwyn, Vic). • The reason for jitter in the display is possibly caused by the transformer not being correctly earthed. Check for continuity between the transformer metalwork and ground. You may need to scrape away the coating on the mounting feet of the transformer for a reliable earth contact. 2.2k trimpot (20kΩ) but it doesn’t seem to make much, if any, difference. I use a fairly new Jaycar model QM-1400 digital multimeter to take readings which should be fairly accurate. In point of fact, I would like to be able to bring the cut-off battery voltage nearer to 1V per cell, which seems to be a popular figure. The batteries I use are Optronics OP-3S 6V for a Sony AU-230 video camera. The unit as a whole is very satisfactory and easily trans­ported on a trip but I would like to be able to reduce the dis­charge battery voltage a little lower if possible. (J. L., Big­ genden, Qld) • We are concerned about your difficulty in getting a suffi­ ciently low end-point voltage and while we hesitate to suggest it, wonder about the accuracy of your digital multimeter. Check the voltage across the LM3362.5 reference. The tolerance range is 2.39-2.59V and the range of adjustment with the trimpot is ±70mV. The range of adjustment can be increased to ±120mV by omitting diodes D1 and D2 and connecting the trimpot directly across the LM336. If your multimeter gives a reading outside the tolerance range for the LM336-2.5, we would be inclined to doubt its accu­racy and, by extension, the accuracy of all your voltage read­ ings. If you want to reduce the endpoint voltage of the circuit to 1V per cell, you will have to recalculate the voltage divider string across switch S1. Note that you can also reduce the end-point voltage of the circuit simply by omitting protection diode D4. However, this will mean that you have no reverse polarity protection for the circuit and the reduction in end-point voltage will be propor­tionately greater for 12V batteries. 1 22k D6 D4 D5