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Sensitive metal detector with your own hands

The presented circuit of the metal detector has a very high sensitivity, since here the frequency divergence is monitored - an exemplary generator operating at a frequency of 0.5 ... 1 MHz and 5 ... 10 harmonics of the search oscillator. The detuning of the latter, for example, only at 10 Hz, leads to a change in the frequency of the difference oscillations by 50 ... 100 Hz.

The model generator of the metal detector is made on the elements DD2.1, DD2.2, ZQ1, etc., where ZQ1 is a quartz resonator at frequency f0 = 0.5.1.1 MHz, which ensures its high stability.

The tunable oscillator circuit (L1, C2, C3, VD1) must be tuned to one of the frequencies fc = k · f0, where kO {1/10, 1/9, 1/8, 1/7, 1/6, 1 / 5}. It is selected by the capacitor C2 (the engine of the resistor R2 - the element of fine tuning of the generator - should be in the middle position).

The mixer of the device is made on the element DD1.4. Elements DD1.3 and DD2.3 are buffer.

The frame of search coil L1 is a ring with a diameter of 250 mm, bent from a viniplast tube having an outer diameter of 15 and an inner diameter of 10 mm. The coil is wound with a wire PELSHO 0.27. It has 100 turns. For convenience of winding, the viniplast tube may have a longitudinal section. After laying coils of the coil, the tube is wound with an aluminum foil tape, which is needed here as an electrostatic screen. In this screen, a rupture must necessarily be made, otherwise it will become a shunt L1 shunt loop. To protect the searchcoil from mechanical damage, it is wrapped with two-three layers of PVC tape. In Fig. 125 shows the appearance of the coil thus manufactured. The socket on it is designed for an extension rod, which can greatly facilitate some work, for example, scanning the surface of the earth.

Elements of the device are placed on a board, which is placed in a metal box-screen. Extension, if it is, and should be metal. It can be made, for example, from a duralumin ski poles.

The power source of the metal detector can be a battery like Korund, a Nika battery, etc. To control the difference frequency, the author used headphones TON-2.

Date of publication on 21.11.2003.

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