If you guys will give me the name of a company that actually stocks in the UK, I can find the part.
John S, I see your modification, but have a question.
the unmodified circuit makes the final transistor conduct when you want a chuff, and it pulls the "sensor in line" to ground, since the emitter is connected to ground (although some sound circuits might want a pullup on the sensor in)
But your modification causes the transistor to basically connect the source voltage when it conducts but the conduction path seems backwards, since the source voltage is positive, i.e. I don't see that your modification does anything to change the sensor in from floating to positive.
Wouldn't you need to change Q8 to a PNP transistor?
My idea would be to drive the opto from the sensor in pin, and then use the opto's output to switch your chuff input on the bachmann sound board. May not need any resistors or anything else other than the optoisolator.... (would like to know the current draw that the Bachmann sound system demands "through" the "original" chuff contacts. I would guess it's in the low 10's of milliamps.
Greg
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