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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Autoguard. 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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When an attempt is made to rob a car, the watchdog device will warn the owner with a short, intermittent sound signal.

After turning on the autoguard, the car owner has six seconds to get out of the car and close the door. If after that, for some reason, the car body sways, the device will work and after 6 seconds. will give an intermittent sound signal with a repetition rate of 3 Hz and a duration of 12 ... 15 seconds.

So that the signal is not a surprise for the owner, the device gives a short (0,1 sec) warning signal at the time of operation.

The electrical circuit diagram is shown in Fig.1.


Fig.1 (click to enlarge)

The displacement sensor consists of a coil L1 and a magnet suspended above it on a soft spring. To reduce the decay time of the pendulum oscillations, it is necessary to tie a thread 3-4 cm long to the magnet.

The ratio of the resistances R1 and R2 is chosen so that the voltage at pin 1 of the DD1 chip corresponds to the log "0" level.

The filter on the elements VD1, R5, R6 passes to the input 1, DD1 pulses with a duration of more than 50 ms.

When the device is turned on, capacitors C4 and C67 are discharged. At the output of element 10 DD1.3 there is a high level that charges C4. After 6 sec. C4 will charge, allowing the trigger DD1.1, DD1.2 to work. If a pulse is received at input 1 of element DD1.1, the trigger will work and a low-level signal will appear at the output of element 3 DD1.1, which will go through C5 to input 13 DD1.4 and the device will give a short beep. In this case, a high-level signal from pin 4 DD1.2 after 6 seconds. will charge the capacitor C6, allowing the operation of the 3 Hz frequency generator.

The ratio of the values ​​​​of resistors R10 and R9 is chosen so that the running generator discharges C4, then a low level appears at the output 4 of the trigger, which discharges C6 and stops the generator. After a while, C4 will charge again and the device will go into standby mode.

To establish the device, it is necessary to disconnect the control electrode of the thyristor and apply 12 V power to the circuit. The voltage at pin 6 of the DA1 microcircuit should not differ from the voltage at point A by more than 0,5 V. Otherwise, you will have to choose DA1 with more accurate balancing.

Most operational amplifiers for 140UD1408 work stably in this circuit with a significant change in external temperature and supply voltage. But if it is still not possible to achieve good balancing, a capacitor with a capacity of at least 100 microfarads should be placed in the gap at point A. If the voltage at terminal 6 is greater than at point A, then the positive terminal of the capacitor is connected to resistor R3. Beli less, then vice versa.

The duration of the sound signal depends on the value of the resistor R9, it can be 12 ... 15 seconds.

The flexibility and shape of the spring is selected with the oscillation frequency of the magnet - about 5 Hz. And the thickness of the damping thread is chosen so that the vibrations completely stop after a few seconds. After that, by changing the distance between the magnet and the coil, the required sensitivity of the sensor is set.

The device is connected according to the scheme in Fig.2.

auto guard
Ris.2

The connection is made with just two wires, parallel to the horn button.

At the same time, it must be remembered that the autoguard only works with a car signal (with a breaker on the membrane).

Author: A.Koynov

See other articles Section Automobile. Security devices and alarms.

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