Passenger's night watchman. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Security devices and object signaling

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Unfortunately, we are familiar with the concern for the safety of personal belongings and luggage during long journeys. The electronic device described here is a kind of specialized security system, which, we believe, can greatly facilitate the life of a passenger.

Ris.1

A schematic diagram of a simple security device that generates an alarm sound signal when a loop sensor breaks is shown in fig. 1. On the logic elements DD1.1 and DD1.2 of the K561LA7 (DD1) microcircuit, a generator of rectangular pulses is assembled, following at a frequency of 2 ... 3 Hz (fk = 1 / 2R4C2), which switch the tone generator, made on the elements DD1.3. and DD1.4 of the same chip. The tone generator frequency is about 1 kHz (fT=1/2R6C3). Piezoceramic emitter HA1 converts the generator signal into sound. The power source of the GB1 device is a lithium battery "2BLIK-1".

Ris.2

The design of the "watchman" (in disassembled form) is shown in fig. 2. The printed circuit board of the device (Fig. 3) is made of double-sided foil fiberglass with a thickness of 1 mm.

Ris.3

The foil on the side of the parts is used only as a common (negative) wire of the power source. To skip the conclusions of parts or connecting conductors, samples are made in it - circles with a diameter of 1,5 ... 2 mm. Places of soldering to this foil side of the board are indicated by small squares (with empty circles inside - for wire jumpers connecting one or another section of printed wiring to it). Examples of mounting a resistor and an oxide capacitor on such a board are shown in fig. four.

Ris.4

All resistors - MLT-0,125. Capacitors C1-C3 - KM6, C4 - oxide K50-35.

Restrictions in the choice of parts are only overall - the height of the parts installed on the board should not exceed 10 mm.

Before mounting the sound emitter HA1 and capacitor C4, it is necessary to assess the state of their insulation. With a power supply voltage of 6 V, the leakage current in them should not exceed 1 μA.

The mounting board, the sound emitter and the battery are placed in a case measuring 48x32x17 mm, glued from high-impact polystyrene 1,5 ... 2 mm thick. When soldering conductors to the sound emitter and the battery, it is better to use low-temperature solder and a good flux - overheating is undesirable here.

Ris.5

The loop sensor is a PEV-2 or PEV-3 winding wire folded in half with a diameter of 0,07 ... 0,1 mm of the desired length with a two-pin connector at the end. It is stored wound on a shuttle-reel (Fig. 5). The connector can be from a calculator. The mating part of the daisy-chain connector can be mounted directly on the "watchman" case, but it is better to take it out on a mechanically strong two-wire cord (a shielded wire covered with plastic is convenient), which will allow you to shorten the cable accordingly.

A broken cable is usually not repaired (in road conditions anyway), so when you go on a trip, you need to have several fully assembled cable sensors with you.

Assembled without errors, the "watchman" does not require adjustment. You just need to make sure that in standby mode, that is, with a whole loop, the current consumed by it does not exceed a few microamperes, and the sound signal that occurs when the loop is turned off is powerful enough. You can increase the power of the sound signal by appropriate selection of the resistor R6: the radiation reaches its maximum when the frequency of the tone generator coincides with the frequency of the mechanical resonance of the piezoelectric element of the sound emitter used. The current consumed by the watchman in the alarm mode is -0.5...1 mA.

The power source of the "watchman" is any battery with a voltage of up to 12 V. But with an increase in voltage, the standby current (Inotp = Upit / R1 + 1 ... 2 μA) and the current Iconsumed by the device in alarm mode will increase accordingly (see table). True, the volume of the alarm signal will also increase.

"Watchman" with a loop sensor, which is used to stitch or tie protected things, reliably protects them from an intruder.

Author: Yu. Vinogradov, Moscow; Publication: N. Bolshakov, rf.atnn.ru

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