Simple Metal Detector Circuit Using Transistor

This is the design of simple circuit diagram of a low cost metal detector using a single transistor circuit and an old pocket radio. This is nothing but a Colpitts oscillator working in the medium band frequency and a radio tuned to the same frequency. This is the figure of the circuit.


Description of the circuit is following. First the radio and the circuit are placed close. Then the radio is tuned so that there is no sound from radio. In this condition the radio and the circuit will be in same frequency and same frequencies beat off to produce no sound. This is the set up. When the metal detector circuit is placed near to a metal object the inductance of its coil changes, and so do the frequency of oscillations. Now the two frequency is will be different, there will be no canceling and radio produces a hissing sound. The metal is detected. To make L1 make 60 turns of 36SWG enameled Copper wire on a 1 cm PVC tube. Powering the circuit using a adapter rather than a battery induces noise. It is always good to power radio projects from battery.