I want to measure an isolated voltage (by isolated I mean the ground of the circuit I want to measure is not connected to the micro ground), just like a voltmeter does (like a cross a resistor of an external circuit). What would be the best way to do this?
I thought about connecting and ADC pin to one node and the AREF to the other. Would this work, or does AREF have to be connected to GND? How do voltmeters do it?