Automotive security device. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Automotive security device. 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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The proposed security device, in contrast to the one discussed above, does not have a secret switch outside the car. Its role is performed by the SA2 reed switch with normally open contacts, for example, the KEM1 type. You can install the reed switch on the inside of the windshield, somewhere near its very edge. If a permanent magnet is brought to the reed switch from the outside of the glass, its contacts close, the transistor VT1 (Fig. 1) of the KTS15 type closes and de-energizes the vehicle signaling device VA, the sound signals will stop.

car security device
Ris.1

The security device, the scheme of which is shown in Fig. 1, allows you to connect an almost unlimited number of sensors, which expands the functionality of the device in question. The SA1 switch, located in a convenient hidden place in the car, turns on the guard in the armed mode.

Turning on the device is as follows. They bring the magnet to the reed switch, supply power with the SA1 switch, close the car doors and then remove the permanent magnet from the reed switch - the security device goes into armed mode. If after that you try to open at least one of the doors of the car or rock the body, the contacts of the rocking sensor SB1 will close and an audible alarm will sound (the standard alarm device of the car itself is used). An audible signal will be heard until the reed switch contacts close and the VT1 transistor de-energizes the vehicle signaling device.

This device works as follows. When the SA1 switch is turned on, the on-board network voltage is supplied to the device and the circuits of the K1 electromagnetic relay, VS1 thyristor and VT1 transistor are prepared for operation. When any interior door, hood or trunk lid is opened, the contacts of the switches SB2 - SBn will close and the relay K1 of the RES10 type (passport RS4.524.302) will operate, which, with its contacts K1.1, will connect the control electrode of the thyristor VS1 through the resistor R1 to the positive wire of the power source, which will open the thyristor. If you shake the car, then the contacts of the sensor SB1 will close and the supply voltage through the resistor R1 will also go to the thyristor. The current flowing through the resistors R1 and R2 creates a positive voltage on the control electrode of the thyristor VS1, which opens it.

Resistors R3, R4 provide a positive bias based on the transistor VT1, in the initial state it is open. The current flowing through the open thyristor VS1 and transistor VT1 excites the winding of the signaling device VA. An alarm sounds, which can be interrupted by the switch SA1, de-energizing the security device or closing the contacts of the reed switch SA2 using a permanent magnet. When the contacts of the reed switch are closed on the basis of the transistor VT1, a zero potential appears, the transistor closes and interrupts the power circuit of the signaling device VA, while the thyristor VS1 turns off.

In some vehicle models, the BA alarm device is powered through the horn relay. This allows you to significantly simplify the circuit diagram of the car guard (Fig. 2).

car security device
Ris.2

This device works similarly to the one discussed above. Its distinctive feature is that the thyristor VS1 connects the signaling device VA through the standard relay of audio signals K2. At the same time, a small current flows through the thyristor VS1 and the winding of the relay K2, which allows turning off the thyristor VS1 by removing the positive voltage on its control electrode. This function is performed by reed switch SA2 with normally closed contacts, for example type KEM1. If you bring a permanent magnet to the reed switch, its contacts will open, the thyristor VS1 will close and de-energize the coil of relay K2. The current through the load must be significantly less than the control current.

Both of the security devices discussed above are simple and accessible for repetition in amateur conditions. However, they have two drawbacks. This is the formation of a continuous sound signal after the security device is triggered and the need for direct intervention by the car owner to turn off the sound signal. To eliminate these shortcomings in the circuit, it is necessary to use a multivibrator and a time relay. Then the sound signal will periodically turn on and off depending on the duty cycle of the pulses generated by the multivibrator. The time relay allows you to set the time interval during which, after an alarm is triggered, an audible alarm will sound.

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