I have 2 microcontrollers, ATTinys at the moment, and between them is power for the "remote" one. I can't add more wires between them for communication.
Have any of you sent commands 1-way (2-way not needed) from a "local" to remote uC? It would be nice if serial, as sending text would be easier than creating a new command language.
Use a diode and smoothing capacitor on the remote one. Switch the power using a pFET or PNP transistor
directly from the serial pin in question. Make sure the resting state of the serial line corresponds to power
being on, which may need external inverter.
The remote serial in needs to sample the raw power before smoothing (make that diode a schottky so
the voltage difference isn't too high, and add a series resistor to limit the current while the smoothing
cap charges up.
You can think of this as high power serial!
Note that for long cable runs it simply isn't practical to power low voltage remote nodes - the IR losses