Hello All,
I was wondering if it is possible to power a relay momentarily when using the electro-coupler output on a ERR board (like a mini commander 2, or a cruise lite)?
If it is possible, what parts would be needed?
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Not only is it possible, I've actually done it. I used a 12VDC latching relay and this circuit to turn the cab lights on and off in my BEEP. I didn't have electrocouplers, so I figured I might as well use those outputs. 
If you just wanted a momentary closure, a simple 12V coil relay on one of them would do it. I wanted to have an on/off control.
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Neat!
Thanks GRJ. If I understand your diagram correctly, I would need a coil relay (instead of latching), a diode, and a capacitor?
diode makes the output look DC instead of AC correct? Cap helps the coil from bouncing?
I used a 12V DC relay, so I needed the diode and the small cap just keeps it from chattering. Small AC relays in this voltage range typically are much more expensive and usually much larger as well.
Obviously, for a momentary pulse on the relay, a single coil relay will do, you get about 1/4 sec of power when you fire the coupler, it's full-wave track power.
