The detector, a schematic diagram of which is shown in Fig.1, assembled all on a single chip CLP. One of its elements (DD1.1) used in the model generator, the other (DD1.2) is tunable. Oscillatory circuit model of the generator consists of a coil L1 and capacitors C1, C2, and tunable from the search coil L2 and capacitor C4; the first rebuild variable capacitor C1, the second is the selection of the capacitance of the capacitor C4.
On the element DD1.3 is a mixer oscillation model and variable frequencies. With the load of the node of the variable resistor R5, the difference frequency signal is input to the element DD1.4, and the amplified voltage of audio frequency - PA head phones BF1. The device can be detected half dollar coin (pre-perestroika currency) up to a depth of 60 mm. And a sewer pit cover - up to a depth of 0.6 m.
Publication: N. Bolshakov, rf.atnn.ru