Short-circuit detection method with signalling a Raspberry (or Cubieboard in my case) over GPIO.
I have a peripheral device that signals its host in one particular case by shorting out its power supply. This is how the host detects that signal (and starts a wake up process). Not the usual approach but sometimes you just can't have that extra wire to use for signalling.
Tested on a Cubieboard + breadboard - works fine.
|11||PULSE(0 3 200u 0u 0u 400u 1m)||V2||2P-5.0||1|