This metal detector was found in a French magazine Radio Plans from 1977. The phone can be a piezoelectric transducer and the L1 scanning coil can be formed by about 20 turns of wire 28 in a plastic form of 20 to 30 cm in diameter. The null point adjustment is made in L1 which is a coil with about 50 turns of wire 28 in a tube that can slide over a ferrite core. The power can be done by battery since the consumption of the detector is very low.
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