As I understand it, a non-contact voltage tester works by creating a capacitive connection from a power line to ground, via the detection circuit and the operator's hand/body. This connection passes a tiny amount of current which the detection circuit can pick up.
I'd like to use my Arduino to detect the presence of mains voltage (120v) in a wire without actually connecting to the conductor (for safety and isolation reasons). Because there may not be any current in the wire, current transformers/hall effect sensors would not work.
Is it possible to use a similar approach to the non-contact voltage testers to detect the voltage? I couldn't find any schematics online for commercial testers to see and understand how they work.
Best Answer
I ended up going with a circuit based on the design here. With my modifications, it seems to work well, and does not pick up other RF emissions as false positives.
simulate this circuit – Schematic created using CircuitLab
The antenna is a 4-inch length of solid 22 gauge wire. Out is high until voltage is detected. D2/C1/R1 filter out the 60Hz pulses from the 4011 output, so that the output stays constant.