I was wondering if it would be possible to power a little 3.3V microcontroller, by harvesting an electromagnetic field around an in-wall insulated 240V 50Hz AC power cable.
Something like contactless inductive charging, like in an electric toothbrush.
Efficiency would be poor, but for a low power device may be an alternative to batteries.
Does the EM field only exist when there is a load on the wire or is it always there, regardless if there is any device connected?
A limitation would be the power harvesting device would need to attach to an existing straight AC wiring without cutting the insulation. No coil on the "transmitter" side.
Is 50Hz way too low to be useful?
I came up with the idea after using a stud finder which has a little red LED that illuminates in the presence of live wires with a few cm range.