Telegraph Relay Controller

A bit of old-school hacking today. 🙂

I picked up an old J.H. Bunnell telegraph relay, which from what I’ve been able to deduce is a mainline type 2-3 relay made sometime in the late 1800’s. It was missing a few parts, but a binding post from the junk box and a spring from an old floppy drive soon fixed that. I hooked it up to the power supply and hey, whaddya know, it still works!

J.H. Bunnell Relay

Manually turning the relay on and off is fun, but I figured I could do better. So, I programmed an AVR micro controller to tap out some morse code on the relay. The relay draws a little over half an amp at 12 volts, so there’s no way the AVR was going to drive it directly; instead the AVR controls a simple transistor switch that trips the relay. The result? Pure awesomeness:

Now to maybe find some practical use for it. I’m thinking some sort of early-warning system is in order.

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3 Responses to Telegraph Relay Controller

  1. Irfan says:


    Are you an amateur radio op? I am and love CW so this kind of toy is appealing. In fact, I own a similar railroad sounder with a straight-key mounted on the same wood base.

    • Craig says:

      I am, but I haven’t been on the air in a long time. It’s something I want to get back into but it keeps taking a back seat to all the other projects I have going on. 🙂

      • Irfan says:

        Understood. I have the same problem with projects. I was off the air for about 15 years. Got back into it and try and keep at least one antenna up and a simple rig around so that when the mood strikes me I can play. vy 73!

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