Hi Michael,

Yes, it looks as though you would be a good person to ask about this one, and I appreciate your having gone to considerable lengths to help here.

Hmm...I'm wondering if it wouldn't be possible to simplify the circuit, and to get away with just a single inverter gate?:



Unfortunately, I think this produces a +10V spike on the circuit output whenever the inverter's output returns to the high level. Maybe this is a problem for my microcontroller's interrupt input, so I wonder whether I should be concerned about clamping the signal with a 5.1V zenner diode?

Better still, how about we omit the power hungry inverter, and replace it with an n-channel mosfet. I think this eliminates the +10V spike at the circuit output, as the ground terminal of the timing capacitor is never driven to the +5V level. From my modest understanding, it appears that this may get me down to within the single uA overall power consumption realm in the inactive state(?).



Am I making much sense here?

I like the MOSFET idea as I can get one tomorrow. Getting hold of a 1G inverter gate might take a little more doing.

Regards,
M.