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Security signal 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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This autoguard, in comparison with similar devices published in the Radio magazine earlier, does not have any fundamental novelty. However, it is interesting in that it is assembled on only three microcircuits and four transistors and at the same time has a good set of performance qualities.

When developing the guard, the author sought to make it as simple and reliable as possible and not contain expensive and scarce parts. On the other hand, he should not have been inferior in terms of security functions to the well-known watchmen of his class.

The watchman immediately sounds an intermittent audible alarm if an unauthorized attempt is made to open the hood or trunk lid of the vehicle. When opening the passenger compartment door, this happens with some time delay. The device also reacts to body shocks and vibrations, for example, when trying to remove a wheel or other parts. In this case, the alarm signal will also be somewhat delayed.

The watchdog uses an analog method of forming time intervals. This simplifies the circuit, as it allows you to set the required values ​​of time intervals without additional hardware costs. The well-known temperature instability of time delays, inherent in the chosen method of their formation, is not of great importance for the operation of the security signal device.

The control LED in the device is two-color. By the color of its glow, one can judge the mode of operation of the security device at the current moment.

The circuit diagram of the watchman is shown in fig. 1. The main node of the device is an RS-trigger on the elements DD1.2, DD1:3. Sensors SF1-SF4 are door switches for interior lighting of the car, SF5. SF6 - trunk and engine compartment lighting switches, although, in addition to them, additional switches can be installed and connected in parallel. The description of the vibration sensor and its operation is described in detail in [1]. The basis of the sensor is a piezoelectric element from the ZP-2 sound emitter. The signal from the piezoelectric element is fed to the amplifier-shaper, made on the operational amplifier DA1 (Fig. 2). The sensitivity is set with a trimmer resistor R16. If a vibration and shock sensor is not needed, the piezoelectric element and the amplifier-shaper are excluded.

Security signal device

When the device is turned off, all capacitors are discharged. After it is turned on by the toggle switch SA1, the capacitor C3 begins to charge through the resistors R1, R2. During this time, the output of the elements DD1.2, DD2.2 will be a high level voltage, and the output of the element DD1.3 will be low.

Security signal device

At the same time, the capacitor C2 is rapidly charged through the diode \/D6. The VTZ transistor is open, and the HL1 LED shines red, indicating that the time delay for the device to switch to standby mode is in progress. During this time, the driver must leave the passenger compartment and close his door. Other doors, the hood and trunk must also be closed.

The exposure time is set by a tuning resistor R1.

In order for the watchman to switch to standby mode, capacitor C3 must be charged to the switching threshold of elements DD1.1, DD1.2, DD2.2. At this moment, the generator is started, assembled on the elements DD2.1, DD2.2. transistor VT2 begins to periodically open with low-level pulses and green is added to the constant red glow of the LED HL1, flashing at a frequency of 1 ... 2 Hz. Simultaneous illumination of the red and green LEDs gives a color reminiscent of orange. The device can be in standby mode for an arbitrarily long time.

Transistor VT1 of the main unit (see Fig. 1) operates in switching mode. When the contacts of any of the switches SF1-SF4 are closed, the transistor VT1 opens, a high-level voltage appears at the lower input of the DD1.1 element, the trigger DD1.2, DD1.3 switches and a low-level voltage appears at the output of the DD1.2 element. Capacitor C6 through resistors R9, R10 will start to discharge to the switching threshold of the element DD1.4. This time (it is set by resistor R10) is necessary to disarm the object without turning on the alarm, to open the salon door and turn off the power with the SA1 toggle switch.

After switching at the output of the DD1.4 element, the low level will change to a high one, allowing the generator to work on the elements DD23, DD2.4. The pulses of the generator, operating at a frequency of 0,8 Hz, periodically open a powerful transistor VT4, due to which the signal relay K1 of the car is triggered at the same frequency.

When the doors are opened, the convergence LED will change from alternating red-orange to green immediately, i.e. before the alarm sounds. This will remind the driver that before the end of the time delay, you need to turn off the watchman with the SA1 toggle switch.

If you close the contacts of the switch SF5, SF6, a low level will go to the input of the DD1,4 element, which is lower according to the circuit, while at the output of this element the low voltage level will change to a high one and allow the generator to work on the elements DD2.3, DD2.4, as in the mentioned above case, only now the alarm will sound immediately.

The voltage drop from the output of the element DD1.4 through the diode VD3 passes to the lower input of the element DD1.1 according to the circuit. The trigger will switch and record an attempt to enter the trunk or under the hood of the car. Transistor VT2 will be open, and VT3 will be closed, the color of the NI LED will be green.

If a single LED (red glow) is sufficient, ALC331A should be replaced with AL307B, and the R7VTZ circuit should be excluded.

With the ratings indicated on the diagram, the transition time to the standby mode can be changed within 5 ... 18 s, and the delay time for signaling - 5 ... 10 s.

The alarm sounds until the watchman is turned off by the SA1 toggle switch. This is convenient when the owner of the car is constantly nearby, i.e. within hearing of the car signal. Otherwise, the device will have to be supplemented with some kind of timer and a blocking unit for the ignition circuits of the car, which of course will complicate the watchman.

Almost all parts of the guard are mounted on a printed circuit board made of one-sided foil fiberglass 1,5 mm thick. The drawing of the board is shown in fig. 3. The board with parts is fixed in the casing from the relay-voltage regulator PP365-B1; any suitable sturdy plastic box will do. Resistors R1 and R10 are placed on the front wall of the box.

Security signal device
(click to enlarge)

The device uses fixed MLT resistors and KM capacitors. Oxide capacitors C3 and C6 should be selected, if possible, with a low leakage current from types K52-1, K50-35. Trimmer resistors R1, R10 - SP4-1. Transistors KT361A can be replaced with KT361B. KT361G, and KT972A - on KT972B or KT829 with any letter index. Chips K561LA7 can be replaced by K176LA7, 564LA7. Instead of the ZP-2 piezoelectric element, ZP-5 is suitable.

The HL1 LED is installed in the car interior so that its glow is clearly visible from the outside, and the device itself is in a place that is hard to reach for an intruder. Where the SA 1 toggle switch is mounted should only be known to the driver.

Connect the device to the on-board network according to the diagram in Fig. 1 flexible conductors through the seven-pin connector X1. For those car models where there is no horn relay, it must be installed. Relay winding resistance should not be less than 240m. Parallel to the relay winding, a diode D226 (VD5) with any letter index is necessarily included, the cathode to the positive power wire.

The adjustment device does not require, and with serviceable parts and correctly performed installation, it starts working immediately. It is only necessary to set the desired delay in the transition to standby mode with the resistor R1, and then with the resistor R10 - the signal delay.


  1. Vinogradov Yu. Vibration sensor for a security device. - Radio. 1994, no. 12, p. 38,39.
  2. Rozanov N. A simple security device for a car. - Radio, 1994, No. 9, p. 32,33.

Author: V.Pryamushko, Togliatti

See other articles Section Automobile. Security devices and alarms.

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