The circuit diagram of cost effective metal detector has been published here. This circuit and an old pocket radio constitute a simple metal detector device. This circuit is a Colpits oscillator circuit is operating at medium frequency band. The radio and the circuit are placed close to each other. Radio is tuned to the same frequency of the circuit. At this condition there will be no sound from radio since their frequencies are matched and cancel each other. This is the final arrangement of metal detector.
If a metal object is placed near this circuit, the inductance of the coil changes. By the effect of this, frequency of oscillation of oscillator changes and a mismatch in frequency occurs between the circuit and radio. This change inductance is utilized here to detect metals. When mismatch occurs, radio produces hissing sound and metal is detected.
- To make L1 make 60 turns of 36SWG enameled Copper wire on a 1 cm PVC tube.
- Powering the circuit using an adapter rather than a battery induces noise. It is better to use battery for powering radio projects since it reduces noise.
- Radio for metal detector can be an old pocket radio.