Security device for the car. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Security device for the car. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Automobile. Security devices and alarms

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Security devices are very common, which allow you to turn on sound signals in case an intruder enters the car interior. In some cases, it is convenient to protect a car or motorcycle with a two-wire security loop made of a thin wire, bare and inconspicuously laid around the vehicle, or attached to it. Touching such a loop or a break in one of its wires causes the alarm to go off.

Car security device

The figure shows a diagram of such a device. It consists of a measuring bridge on resistors R1 ... R4, a diode bridge V1 ... V4, a transistor V5, the load of which is the relay winding K1. Resistor R1 is connected to the end of the security loop. When the loop is closed when the wires are broken, the measuring bridge is unbalanced and voltage appears between points A and B. Thanks to the diode bridge, this voltage is always supplied to the base of the transistor V5 with a negative polarity, while the transistor V5 opens, relay K1 is activated and closes the alarm circuit with its contacts.

The device is powered by two sources: element E1 in the diagonal of the bridge with a voltage of 1,5 V and battery B1 with a voltage of 9 ... 12 V. To balance the measuring bridge, resistor R2 is used, the resistance of which should be approximately 1,2 ... 1,5 times higher than the resistance of resistors R1, R3, R4. For these resistors, the resistance spread should not exceed 10%, and their value is selected within 3 ... 10 kOhm. The resistance of the resistor R5 is equal to the resistance of the measuring bridge resistors. The device can use the relay RES-6 (passport RFO.452.116 or RFO 452. 136), RES-9 (passport RS4.542.202), RES-10 (passport RS4.524.303 or RS4.524.308), RES-15 (passport RS4 591.002 or RS4.591.003), R9S-34 (passport RS4.524.373 or RS4.524.378), etc.

In standby mode, the device consumes a very small current (0,2 ... 0,5 mA), which ensures continuous use of voltage sources such as "Mars", "Saturn" for a long time (tens of days).

Author: V. Alekseev

See other articles Section Automobile. Security devices and alarms.

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