electronic whistle control

[tmackinator]

Since there seems to be no shortage of information here maybe someone can help. I'm looking for information (schematics) on building an electronic horn relay that will activate using the conventional transformer whistle control.
Thanks -TM

[lionelsoni]

To activate a motor-driven whistle or a dry-cell-powered horn, or something else less traditional?

[tmackinator]

I'm going to use either a dry cell horn or an electronic horn that I have built allredy. Most likely the dry cell horn as I wasn't happy with the performance of the electronic horn. Thanks TM

[lionelsoni]

I haven't tried this; but here is the train (so to speak) of thought that I would pursue:

I would try to use a PNP transistor (I believe the whistle-voltage is negative) in a common-emitter circuit, with the locomotive frame as the common and the horn connected to the collector and returned to the negative dry-cell voltage. I would make a low-pass T filter for the base circuit from two equal series resistors and a shunt capacitor. If necessary to make the threshold higher than the base-emitter voltage, I would add a base-emitter resistor.

Obviously, the resistor and capacitor values need to be worked out to fit the DC holding voltage from the transformer, the horn current, the transistor gain, and the 60-hz power frequency. I am hoping that you can figure all that out, if you can build an electronic horn.

[tmackinator]

Thanks Bob, I think you gave me too much credit for my electrical abilities. I usually rely on available schematics to build my circuits. I had found a couple of good sites with some useful circuits that I was able to build and get functional but I never saw anything to take the place of the old horn relay. That is what I was hoping to find. I'm going to research the info you gave me and see what I can come up with but it is probably beyond my scope. Thanks for the reply!-TM

[lionelsoni]

I might give this a shot next week, Tom, when I get back from a business trip.