Very simple metal detector circuit is given here, it uses Inductive proximity sensor. It has the range of metal detection in few mm to cm, output signal from the sensor is fed into the base of switching transistor SL100.
The Buzzer element is connected across the switching transistor as a output device. When there is no metal across the sensor then buzzer keeps silence otherwise it produces beep sound. (Here this circuit given for hobby purpose only)
|1.||Inductive proximity sensor||1|
|2.||Transistor – SL100||1|