Interfacing real b737 Yaw demper switch.

[Ethanoost]

Any advice please. I'm interfacing a real Boeing yaw demper switch in the overhead. It's an on (hold) off type of toggle switch held in place by some kind of mechanism. When a small current is supplied, the switch hold mechanism release and the switch flick back to off. Interfacing it with prosim via a relay is easy.
Here is the issue... there are only two terminals on the switch. The switch uses the same two terminals for the switch and release.. so when the switch is on, the terminals are connected (like any switch). Power should now be supplied through the same terminals for the release to off to occur. See pictures.

How do I interface both a power through a relay and an input signal through the same wires without frying my input card?

Any ideas would be appreciated.

Ethan

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[mickc]

Short answer, you can't.  That switch is a switch / circuit breaker combo.  the only way to trip it off is to exceed the current rating of 750mA.

The proper YD switches use a magnetic solenoid, which energized to hold the switch in the on position, otherwise it springs back to off.

[mickc]

Well actually you could do it by using 2 relays, one to switch on when the Y/D switch is on, which you connect to your I/O card, and one to apply a fake load to the load side of the breaker, triggered by the Prosim function.

This will isolate your IO card from any spikes from overloading the breaker, and you should be able to get say a 1.5A load by using some resisitors.

Its a dirty way to do it, and there will be a delay in the switch tripping as those breakers have built-in trip delays. These were custom built and the part numbers dont match up with the standard ratings in the datasheet (attached)

[Ethanoost]

Thanks for the quick reply. Two relays will work. I just need to figure out how to get a small enough load so the switch can trigger the relay without tripping the switch. And then a high load to trip the switch.

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[mickc]

Most small 12v relays have a coil current under 100mA so the relay should not cause the switch to trip.

For the "tripping" load, an ideal load would be one of those resistors they use for when you change to LED indicator bulbs on a car.  They provide a 21W load so the flasher operates at the correct speed.  That would work out to a 1.75A load at 12v.

like this one http://www.supercheapauto.com.au/Product/NARVA-LED-Load-Resistor-12-Volt-21-Watt/287170

[Ethanoost]

Gee thanks. I'll let you know how it goes..

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