Wayne Parham Messages: 18786 Registered: January 2001
Illuminati (33rd Degree)
What I'm suggesting is to have a separate 5V supply to run the processor that's always on. It will only draw a few milliamps.
The power actually can be anything between 5v and 6v (not a strict 5v TTL thing), so the processor supply can be a rechargable 6v battery, like (4) AA cells.
The point is, I would probably make provisions to keep the processor powered up, even if the rest of the circuit is powered down. The processor cannot sense the "power on" command if it isn't up and running.