Hidden wiring finder on a logic chip. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Indicators, detectors
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Many devices that allow you to detect the location and damage of hidden electrical wiring consist of an antenna sensor that receives an alternating electric field, an amplifier, and sound or arrow indicators. For efficient operation of a capacitive antenna, the amplifier must have a large input impedance, which is often achieved by switching on a field-effect transistor source follower at the input [1-3].
In the described device, it is proposed to use a high input impedance of a CMOS microcircuit, which is transferred to a linear mode to amplify analog signals [4]. Figure 1 shows a diagram of a finder that allows you to locate and damage hidden electrical wiring, a radio network, a wire break in an unshielded cable, a malfunction in an electric garland.
Sensor-antenna W1 is a ring with a diameter of 2 cm from an insulated mounting wire, which is connected with a shielded wire to the input of the device. The screen of the wire near the sensor is isolated, and in the device it is connected to a common wire. The unshielded part of the wire must be the minimum length. The sensor signal is applied to pins 8 and 9 of the DD1 chip. Element DD1.1 of the microcircuit is transferred to a linear mode by means of negative feedback through resistors R1, R2. Capacitor C2 and variable resistor R2 allow you to adjust the depth of negative feedback by changing the input resistance, and hence the sensitivity of the device. Capacitor C1 eliminates self-excitation of the amplifier. The output of the element DD1.1 is connected directly to the inputs of the elements DD1.2...DD1.4, as a result of which the linear mode of these elements is set automatically. The signal amplified by the DD1 microcircuit is fed through the capacitor C3 to the X1 connector, to which high-impedance telephones (TON-1, TON-2) or a subscriber loudspeaker are connected.
Figure 2 shows the circuit of the seeker, in which the sensitivity is regulated by a variable capacitor C1, and the piezoelectric radiator HA1 serves as a sound emitter.
To increase the sound volume, the piezo emitter is connected in a bridge circuit. Capacitor C1 (Fig. 3) is made of printed circuit board conductors (Fig. 4). The dielectric gasket of the capacitor is cut out from the photographic film from which the emulsion layer has been removed. The spring can be taken from a ballpoint pen.
The device is powered by a Krona battery or a 7D-0,125D battery. Instead of the K176LA7 chip, you can use K176LE5. The use of K561 series microcircuits gave slightly worse results. Variable resistor R2 (Fig. 1) - any type with a resistance of 10 ... 100 kOhm. As a capacitor C1 (Fig. 2), you can use one of the sections of the KPI radio receiver.
To set the necessary limits for capacitance change, a capacitor with a capacity of 100 ... 200 pF is connected in series with the KPI. The dimensions and shape of the sensor-antenna are chosen depending on the required sensitivity and ease of use of the device. It is possible to manufacture several interchangeable sensors of different sizes and shapes.
The method of working with the finder has no peculiarities and is similar to that described in [2,3].
Literature
- Gordeev V. Transistor seeker//Radio. -1981. -#4. -p.54.
- Pavlov L. Seeker with IC//Radio. -1981. -#4. -p.55.
- Borisov A. Hidden wiring seeker// Radio. -1991. -№8 -S.76.
- Voskoboynikov M. Digital microcircuits in low-frequency devices//Radio. -1981. -№7-8 -С.37
Author: L.D. Bogoslavets, Cherkasy region
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