I live in America, so the electricity coming out of the wall is 120 VAC. Let’s say that I have a light fixture connected to a standard-issue three-way circuit. Power from the main circuit box feeds into a switch via L, N wires plus a ground wire. That switch is then connected via L, N, traveller, and ground wires to a second switch box. The second switch then feeds into the light itself.
So let’s say I want to convert this to a smart switch. Can I install something like a Sonoff Touch with into the switch location fed by mains and then use the traveller wire and the AC ground to use a GPIO pin and the AC ground to connect a switch in the second location (with the L and N wires in the second switch box just connected to bypass the switch entirely)?
Basically, can I do this:
(Use an AC circuit’s ground wire as the ground in a low-current 3.3VDC circuit?)