Compact metal detector on the K175LE5 chip. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Compact metal detector on the K175LE5 chip. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / metal detectors

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The metal detector is designed to search for metal objects in the ground. It can also be used in determining the location of fittings and hidden wiring during construction work in the house.

Schematic diagram

A diagram of a compact metal detector based on a K175JIE5 chip is shown in fig. 2.1, a. It contains two generators (reference and search). The search generator is assembled on elements DD1.1, DD1.2, and the reference generator is assembled on elements DD1.3 and DD1.4.

Compact metal detector on the K175LE5 chip

Rice. 2.1. Compact metal detector on the K175LE5 chip: a - schematic diagram; b - printed circuit board; in - placement of elements; d - general view of the device

The frequency of the search generator, made on the elements DD1.1 and DD1.2, depends on:

from the capacitance of the capacitor C1;
from the total resistance of the tuning and variable resistors R1 and R2.

Variable resistor R2 smoothly change the frequency of the search generator in the frequency range set by the tuned resistor R1. The frequency of the generator on the elements DD1.3 and DD1.4 depends on the parameters of the oscillatory circuit L1, C2.

The signals from both generators are fed through the capacitors C3 and C4 to the detector, made according to the voltage doubling circuit on the diodes VD1 and VD2.

The load of the detector is the headphones BF1, on which the difference signal is allocated in the form of a low-frequency component, which is converted by the headphones into sound.

Parallel to the headphones, a capacitor C5 is connected, which shunts them at a high frequency. When the search coil L1 approaches a metal object, the frequency of the generator on the elements DD1.3, DD1.4 changes, as a result, the tone of the sound in the headphones changes. On this basis, it is determined whether there is a metal object in the search area.

Applied parts and replacement options

Trimmer resistor R1 type SP5-2, variable resistor R2 - SPOO,5. It is permissible to use other types of resistors in the circuit, preferably small ones.

Electrolytic capacitor C6 type K50-12 - for a voltage of at least 10 V. The rest are constant capacitors of the KM-6 type. Coil L1 is placed in a ring with a diameter of 200 mm, bent from a copper or aluminum tube with an internal diameter of 8 mm. There should be a small insulated gap between the ends of the tube so that there is no short-circuited loop. The coil is wound with PELSHO 0,5 wire.

It is necessary to stretch the maximum number of turns through the tube in any way: the more, the better. Headphones TON-1, TON-1 can be used as BF2 headphones. To power the metal detector, a Krona-type battery or other types of 9 V batteries are used. In the metal detector circuit, the K176LE5 microcircuit can be replaced with K176LA7, K176PU1, K176PU2, K561LA7, K564LA7, K561LN2 microcircuits.

Device mounting

The details of the device, except for the inductor, power supply and headphones, can be placed on a printed circuit board cut out of 1 mm thick foil fiberglass (Fig. 2.1, b). It is possible to use another type of printed circuit board.

The L-shaped form of the board is chosen so that it can be placed in the housing of the ShR type connector.

A handle made of a metal tube is attached to one end of the connector, and a metal ring with an L1 coil is attached to its other end using an adapter made of insulating material.

The general view of the device is shown in fig. 2.1, d, and the placement of the device elements - in fig. 2.1, c.

Setting

Before setting up the metal detector, the adjusted and variable resistors must be placed in the middle position and the contacts SB1 must be closed. By moving the slider of the tuned resistor R1, achieve the lowest tone in the headphones.

In the absence of sound, the capacitance of the capacitor C2 should be selected. If a malfunction occurs in the operation of the metal detector, a capacitor with a capacity of 7-14 uF should be soldered between terminals 1 and 0,01 of the DD0,1 microcircuit.

Author: Yavorsky V.

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