This is an easy metal detector circuit based on IC CS209A from the Cherry Semiconductors. A 100uH coil is employed to sense the presence of metal. The IC CS209A has a built in oscillator circuit and also the coil L1 forms a part of its external LC circuit that determines the frequency of oscillation. The inductance of the coil change in the presence of metals and the resultant change in oscillation is demodulated to make an alarm. The LED offers a visual indication too. This circuit can sense metals up to a distance of few inches.
