I want to add a third switch to a room with two existing switches. This third switch will be simulated by a 4 relays and a raspberry pi.
Image source: wikipedia, Multiway_switching
So 1 have one relay which connects the LT(left top) wire with the RT(right top) wire.
1 relay which connects LB(left bottom) with RB(right bottom).
1 relay which connects LT with RB.
1 relay which connects LB with RT.
If I receive an internet command to turn on the light, I'll switch the fist two relays from on to off or reverse. And change the last two relays from off to on or reverse.
This way I believe I can switch the light status, but I'll never know if it was on or off before switching the status.
Is their a way to check if current if flowing in a 220v connection and output the result to a raspberry pi?