I am having trouble wrapping my head around an issue with a 5 and 12 volt concurrent system. I have a breadboard with 5v and ground on one side and 12v and ground to the other. I have the Uno controlling the 8 relay module with the 12 volt powering 4 separate motors on 4 of the relays. No problems there. However, I am trying to make this as easy as possible for people to use. I am looking for a way to sense (5v analog pin?) if the compressor plugs are actually connected to the relay that will power the motors. I don't know if I have to attach another set of wires to the voltage plug and then back to the analog pin to see if there is voltage. If I do it with a 5v regulator to step down the voltage to the analog pin it fries the wires back to the relay.
Any ideas are greatly appreciated,