Hey I like that idea. I suppose one switch would short the input to ground and the other would short it to +5VDC. And it's probably unreliable to leave the input floating, so a resistor would have to go in parallel with each switch.

The other day I connected the circuit to my 300SL to read codes from the top controller. It was nice to be able to short an input, walk away, and return several minutes later to find all the codes read. In this case it found 11, 20, and two others above 20. It was nice to be relieved of the tedium of counting all of those pulses. And of course erasing them all was equally simple -- short two inputs and walk away. That's when I concluded this circuit was worth building and offering to the forum.