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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Hidden wiring indicator. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Indicators, detectors

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Option 1

One of the simplest devices is the hidden wiring detector shown in fig. 1.

Hidden wiring indicator
Ris.1

Resistor R1 is needed to protect the K561LA7 chip from an increased voltage of static electricity, but, as practice has shown, it can not be installed. The antenna is a piece of ordinary copper wire of any thickness. The main thing is that it does not bend under its own weight, i.e. was tough enough.

The length of the antenna determines the sensitivity of the device. The most optimal value is 5 ... 15 cm. When the antenna approaches the electrical wiring, the detector emits a characteristic crack.

With such a device it is very convenient to determine the location of a burnt-out lamp in a Christmas tree garland - the crackling stops near it. The ZP-3 type piezo emitter is connected in a bridge circuit, which provides an increased "cod" volume.

Option 2

Figure 2 shows a more complex detector, which has, in addition to sound. also a light indicator. The resistance of the resistor R1 must be at least 50 MΩ.

Hidden wiring indicator

There is no current-limiting resistor in the VD1 LED circuit. since the DD1 chip (K561LA7) copes well with this function itself. If the input currents of the element D1.1 allow, then by removing the resistor R1 from the circuit shown in Fig. 2, we will get a device that responds to a change in the static potential in the surrounding space. To do this, the WA1 antenna is made 50 ... 100 cm long using any wire. Now the device will respond to the movement of the human body.

Putting such a device in a bag, we get an autonomous security device that gives out light and sound signals if any manipulations occur with or near the bag.

See other articles Section Indicators, detectors.

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