I have a circuit with two power connectors, J1 and J2. I would like to be able to detect which one the power is coming from. The trick is that the connectors need to provide power to each other. See concept drawing below. I can't think of any way other than putting in a series impedance and then using a diff amp to detect current direction. Can anyone think of a simpler way? Currently I'm using a jumper on the board to tell the circuit which one is providing the power.
The voltage is 24Vdc. Current range is 20mA to 800mA. Induced voltage drop can be around 1Vdc.
The reason is to have the circuit under power behave differently (master/slave) ie. Master is powered via J1, and the slave is powered by J2.