Security device on the subscriber loudspeaker. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Security device on the subscriber loudspeaker. Encyclopedia of radio electronics and electrical engineering

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

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The radio broadcasting network can be used as a power source for a security device that is triggered when the security loop is broken (a thin wire encircling the protected object).

After listening to the radio, you must move the switch SA1 (any two positions and four directions) to the "Protection" position. In this case, the transistor VT1 is closed, since its emitter and base are short-circuited by a Shl cable.

Security device on the subscriber loudspeaker

The current from the radio network in standby mode is practically not consumed.

After the loop breaks, the Shl transistor VT1 opens with a base current through the resistor R2 from the voltage received from the radio network using a rectifier (diodes VD1 ... VD4) and capacitor C1. The rectified and smoothed voltage from the radio network through the transistor VT1 is fed to an asymmetric multivibrator on the elements VT2, T1, R3, R4, C2. The multivibrator uses positive feedback through the transformer T1 of the subscriber loudspeaker. After the manufacture of the device, in the absence of self-excitation, it is necessary to swap the ends of one of the windings of the transformer T1. The frequency of the audible alarm signal is determined mainly by the capacitance of the capacitor C2. In alarm mode, the device from the 30 V radio network consumes no more current than when listening to radio broadcasts.

In the absence of a radio network (for example, when using the device in a country house), it is necessary to connect a power source with a voltage of 1 ... 5 V (of any polarity) to the XP14 plug. In standby mode, the device consumes a current of about 9 μA at a supply voltage of 40 V, and about 2 mA in alarm mode.

If the device will not be used to listen to the radio, then RP1 and SA1 can be omitted from the circuit by replacing the normally closed contacts of SA1 with wires (in the diagram, the SA1 switch is shown in the "Security" position).

Transistors (for example, type KT315V) must be with a maximum allowable emitter-collector voltage of at least 30 V. Capacitors and diodes - also with an allowable voltage of at least 30 V.

Authors: V. Rozhin, A. Peplov, Kazan; Publication: N. Bolshakov, rf.atnn.ru

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