An anti-theft device that simulates an engine malfunction. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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An anti-theft device that simulates an engine malfunction. 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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Car thieves are becoming extremely resourceful in finding and damaging anti-theft devices. What if the engine starts and stops intermittently? If the car is equipped with equipment that simulates an engine malfunction, a potential thief will most likely not suspect the operation of an anti-theft device and will look for a new victim.

The new device provides a normal engine start, and after 12 seconds it opens the ignition coil circuit, causing the engine to stall. After 4 seconds, the circuit closes again, allowing the thief to restart the engine. The cycle repeats, and after another 12 seconds the engine stalls and does not start. By this time, the kidnapper may have driven a short distance from the parking lot.

(click to enlarge)

The thief may move away in a car equipped with this circuit, but he will soon give up his intentions after repeatedly stopping the engine. The timer IC periodically cuts off voltage from the ignition coil, simulating an engine failure.

In the scheme of the anti-theft device shown in fig. 1, uses 555 timer ICs and low current C/MOS ICs. Leaving the car, the driver activates the device with a disguised switch Si. Non-smoking drivers can well disguise the Si switch in a lighter, the wire of which is disconnected from the battery and connected to the circuit at point A. For additional protection, the ignition switch can be connected in series with the Si switch.

After the circuit is set to work by switch Si, when the ignition is turned on, trigger 1 is started, assembled on two NAND gates, as a result, 0,5 Hz pulses from the output of the timer 555 go to the shift register CD 4015. The CD 4015 IC contains two four-bit register, which in this case are connected in series. After 12 s (six pulses), the NAND gates open transistor Q2, which opens the normally closed relay contacts and thereby stops the engine. After the shift register receives two more timer pulses, the NAND gates close transistor Q2, allowing the motor to restart.

The cycle is restarted, but when the ignition is turned on for the third time, trigger 2 is turned on and engine start is blocked until the driver returns and opens switch Si. Timing diagrams are shown in detail in fig. 2.

(click to enlarge)

The start-stop periods of the anti-theft scheme are 12 and 4 s, respectively. After the engine is stopped for the third time, it cannot be started until the driver opens the switch Si concealed in the vehicle interior.

To make the device look less like an anti-theft device, it can be assembled on a small circuit board and housed in a housing resembling a pollution control device.

By connecting pins 5 and 12 of the shift register to an additional two-input NAND gate, an alarm can be generated after 60 seconds. The valve can control a relay that turns on the horn, headlights or siren, if necessary, to draw attention to the stolen car.

Chip analogs:

555 - KR1006VI1
CD4011 - 561LA7
CD4015 - 561IR2

Publication: N. Bolshakov, rf.atnn.ru

See other articles Section Automobile. Security devices and alarms.

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