A simple anti-theft device. Encyclopedia of radio electronics and electrical engineering

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

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A simple diagram of an anti-theft device installed inside the car and providing an audible signal when an intruder enters the car is shown in the figure.

The device works as follows: before leaving the car, the driver turns on the S1 toggle switch installed in a secret place. In this case, the capacitor C1 with a capacity of 100 ... 220 μF and an operating voltage of at least 16 V is charged through a resistor R2 with a resistance of 5 .... 10 MΩ. During the charge of the capacitor C1 (5 ... 10 s), the driver must get out of the car and close the door. After about 10 s, the capacitor is charged to a voltage at which the field-effect transistor V1 of the KP103 or KP201 type opens and a negative polarity voltage is applied to the drain of transistor V2 (of the same type as V1), close in magnitude to the battery voltage. The gate of the transistor V2 through a resistor R1 with a resistance of 10 kOhm is connected to the terminal of any ceiling lamp, connected to the push-button switches and to a storage capacitor C2 with a capacity of 50 ... 100 microfarads with an operating voltage of at least 16 V.

When any car door is opened, the interior lighting is turned on and a voltage is supplied from the terminal of the lighting ceiling through the resistor R1 to the gate of the transistor V2, which ensures the opening of the transistor V2. Capacitor C2 at the same time quickly charges and keeps transistor V1 in the open state for 2 ... 2 minutes, even if the passenger compartment door is closed after opening. The current of the transistor V2 through the resistor R6 charges the capacitor C3 and after 5 ... 10 s the voltage across the capacitor reaches 4 V. If the toggle switch S1 is not turned off during this time, then the multivibrator on transistors V3, V4 will switch from the inhibited state to self-oscillating mode. In this case, the transistor V5 will periodically open, in the emitter of which relay K1 is turned on. The contacts of this relay periodically turn on the sound alarm. The sounding time of the sound alarm after closing the car doors can be adjusted by selecting the value of the capacitor C2. The duration of the signal messages and the pause between them are determined by the values ​​of the capacitors C4 and C5. For the ratings of these capacitors indicated on the diagram, the duration of the alarm sound and pause are 0,5 and 1,5 s, respectively.

When opening the hood or trunk lid, the microtoggle switches B6 and B7 are turned on, which should be installed under the hood and trunk lids. In this case, the capacitor C3 is quickly charged to the battery voltage, which will immediately cause the car's sound alarm to sound. The decoupling silicon point diode V6 of type D223, D101, D102, DYUZ serves to ensure that the sound alarm is turned on both after opening the hood or trunk lid, and when they are subsequently closed. All electrolytic capacitors in the circuit must be with low leakage currents. These requirements are met by tantalum capacitors of the type ET, IT, K52 and K53 with various additional indices. It is allowed to replace transistors P213 with P201, P203, P214, P216 with any letter indices.

When mounting the circuit, you should use a grounded soldering iron, otherwise its electrostatic potential can damage the field-effect transistors. To impart moisture-resistant characteristics to the mounted circuit, it should be varnished (for example, with nail polish). The performance of the scheme is checked step by step. First, the current consumption of the circuit in standby mode is measured. This current must not exceed 15 mA. When the circuit is turned on, the voltage across the resistor R4 should rise within 1,5 ... 2 minutes. This rise time is controlled by selecting the value of the capacitor C1.

Then, by measuring the voltage across the resistor R5 with the doors closed and then opening one of them, make sure that this voltage varies from 9 ... 10 V to 4 V for 2 .. 3 minutes. This time characterizes the sounding time of the alarm. Increasing or decreasing the value of the capacitance of the capacitor C2, respectively, increase or decrease the sounding time of the alarm. The voltage on the capacitor C3 should reach the level of 4 V for 5..10 s after opening the car doors. This time is necessary for the driver of the car to turn off the alarm with toggle switch S1 before it is triggered. By changing the capacitance of the capacitor C3, the delay time for the alarm after opening the car doors is adjusted.

The threshold voltage at which the multivibrator is triggered on transistors V8, V3 depends on the value of the resistor R4. If the transition to the self-oscillating mode occurs when the voltage on C3 is less than 4 V, then the value of the resistor R8 should be increased. It should be noted that the contacts of relay K1 are rated for current up to 2 A. Therefore, in cars that are not equipped with a relay for turning on car signals, it is necessary to install an additional relay of the RS-527 type for turning on the headlights of a VAZ-2103 car or a starter relay RS-507B or RS502 from GAZ cars -24 and "Zaporozhets". The winding of such a relay must be connected in series with contacts K1.

The disadvantage of the security device is that it uses electromagnetic relays that reduce the reliability of the circuit. This drawback can be eliminated by using a trinistor of the KU202N type, not shown in the diagram, instead of the relay. The trinistor cathode is connected to the -12 V terminal, and the anode through the audio signal winding to the +12 V terminal. The trigger voltage is applied to the control electrode of the trinistor from a matching stage made on transistor V5. The emitter of this transistor must be connected to the positive bus of the battery, and the collector - through two resistors connected in series with resistances of 100 ohms each with a negative bus. The control electrode of the trinistor is connected to a common connection point of these resistors. The base of transistor V5 is connected through a 100 ohm resistor to the collector of transistor V3.

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