Intermediate Electronics Project #8 - METAL DETECTOR

The RLC circuit formed by R1, L1 and C1 is the metal detection part. The inductor L1 is an air cored one. So when a metal piece is brought near the coil, it acts as a core for L1 which results in an increase in the inductance of the coil. With this sudden increase in inductance of the coil, the overall reactance or impedance of the RLC circuit changes.
When there is no metal piece, the signal fed to the speaker causes some audible sound and with the reactance change around the RLC circuit, the signal sent to the speaker will be different then the first one.

Видео Intermediate Electronics Project #8 - METAL DETECTOR канала All About RC