Communicating between uCs on DC power?

Experts,

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.

Thanks!

holesflow: 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.

OK, so just how many wires do you have to start with?

2 wires, utp, same as cat6, starting with solid core, but ok moving to stranded. I have to wrestle with gauge, as from 30' need to power tiny uC and as many rgb leds as it will handle. I am already resigned to not powering the led(s) via uC pins.

The tiny uC is so i don't need to run more lines for rgb control. The remote led directs that, as told to by master. 1-way.

I've seen threads on this forum talking about theory, and am curious if anyone has done so in practice.

OK, so just how many wires do you have to start with?

I haven't. But digital model railway is one example where it's used.

You will need to show what wires go where between the 2 MCU's. To read a signal modulated on a power line will require a spare I/O pin on the reading MCU and the sending MCU will need an I/O pin to supply & modulate the signal being sent. A potential (though cumbersome) option might be to re-task the reset pin (PB5) of the sending MCU as a data pin but you then lose the ability to easily re-program the chip unless you have a high voltage programming rig.

holesflow: Experts,

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.

Thanks!

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 are prohibitive.