i am looking for an off the shelf sensor that can sense a wire buried 100mm underground (my soldering and custom circuit days are long behind me). my initial thought is to sense frequency signal strength. wire is carrying 230v, 50hz, 50mA although current can be upped if required. ideally sensor should have a digital output with sensitivity/threshold trip value adjustable for calibration.
im looking at eddy current sensors - too expensive, hall effect sensors, inductive proximity sensors but cant see the wood for the trees.
any ideas, inspiration or thoughts gratefully received.