Car alarm Signal-003. Encyclopedia of radio electronics and electrical engineering

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

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The proposed device is intended for signaling when trying to open the doors, hood or trunk of a car. The development took into account the failures of some imported security systems during operation in Russian conditions. The signaling scheme is shown in Fig.1. The system is armed using a magnetic key fob. Switching on is confirmed by a short acoustic signal and a flashing LED.

Rice. 1. Schematic diagram of a car alarm

An acoustic signal when the guard is triggered gives a HA1 piezo siren of any type with a frequency of 24 s - a signal, 24 s - a pause. At the same time, the HL1 lamp (21 ... 55 W) installed in the cabin emits a light signal with a frequency of 1 s.

The supply voltage from the vehicle's on-board network is constantly supplied through the FU1 fuse to the R14-VD8-C7-C8 stabilizer and the DD1 microcircuit. When a magnetic key fob acts on the K4.1 reed switch, a high-level voltage pulse is fed to input C (pin 11) of the DD1.2 element, on which the chatter suppression circuit is assembled. From its output, the signal passes to the counting trigger DD1.1 and puts it in a single state. A high level from pin 1 of DD1.1 is supplied to the bases VT3 and VT4. Through VT4, the blinking LED VD9 turns on, signaling that the system is armed.

A line of sensors SB3...SB1 is connected to the VT7 emitter. All sensors are contact type, and when triggered, they close to ground. In this case, VT3 opens, and relay K1 is activated. Its contacts K1.1 are closed, and the +9 V supply voltage is applied to DD2. Two multivibrators are assembled on the DD2 chip. The multivibrator on DD2.1, DD2.2 provides a pulse mode for turning on the signal lamp HL1 through VT1 and a short circuit relay. The second generator on DD2.3, DD2.4 determines the frequency of switching on the sound signal HA1 through VT2 and relay K2. The duration of the signal is determined by the elements C5, R9, and the pauses - C4, R7.

The pulse generator for the signal "Peak" (arming) is assembled on DD3.1 and DD3.2. The supply voltage DD3 is supplied from the contacts of the reed switch. The signal duration is about 0,5 s.

Rice. 2. Car alarm circuit board

The device is assembled on a printed circuit board, the drawing of which is shown in Fig.2. The current consumption of the device in the "standby" mode is determined by the stabilizer and the DD1 chip and is approximately equal to 14 mA.

Door sensors SB1 ... SB4 - standard, contact type; hood and trunk sensors SB5, SB6 - special, also contact type. Tilt sensor SB7 - self-made. It provides an alarm in case of unauthorized tilting of the car in any plane (jacking).

Rice. 3. Scheme of the swing sensor of the first type

Let us consider two types of rocking sensors used in such systems. One (Fig. 3) consists of two ring anisotropic magnets, in the magnetic field of which a coil containing 12000 ... 15000 turns of wire 00,01 mm is placed. The lower magnet is rigidly fixed on the base, the upper one can move on the rod. The changing magnetic field when the top magnet is tilted changes the magnitude of the signal in the coil. The captured signal, usually through a comparator and a shaper, is fed into the siren's switching circuit. The measuring head used by some motorists as a swing sensor from magnetoelectric devices, firstly, is oriented only in one plane, determined by the axis of rotation of the frame, and secondly, the head itself is not designed for operation in conditions of shock and vibration, and even with a weighted arrow.

Another type of sensor (Fig. 4) is with a mercury contact. The sensor consists of a slightly curved metal tube 1, closed on both sides with screw plastic plugs 2 sealed with epoxy compound. Metal electrodes-contacts 3 are passed through the plugs. One end of the signal circuit is connected to the tube, the other one connects both contacts. The tube contains a small ball of mercury 4 from a medical thermometer (about 0,5 g). With a slight inclination (less than 10°), the ball, rolling, closes one of the contact electrodes, giving a signal to the system. The sensor is installed diagonally relative to the longitudinal axis of the vehicle.

Rice. 4. Scheme of the swing sensor of the second type

This device uses one signal lamp (21 ... 55 W) installed inside the cabin. The effect of the signaling is the same, but the parking light lamp filaments are saved, for which the pulsed switching mode drastically reduces the service life.

Rice. 5. Scheme of the third type of swing sensor

I do not advise you to introduce ignition blocking circuits, for some reason they fail in the first place and in the most inconvenient place.

Rice. 6. Schematic diagram of a single-stage matching amplifier

For lovers of car "clucking" for every reason, whether it's a cat on the hood or a fallen twig, I suggest a shock (shock) sensor. The design of the sensor is shown in Fig.5. The sensing element is a round plate coated on one side with a piezo-sensitive layer. You can use the piezoelectric element ZP with the protective case removed. The plate is fixed on the stand with one edge, and a spring is attached to the diametrically opposite edge. The wires are soldered to the stand and the middle of the record. When the spring vibrates, the microdeformation of the piezoelectric layer occurs, and an EMF appears on its surface. The captured signal is fed through a diode limiter and a single-stage matching amplifier (Fig. 6) on a transistor VT1 (h_21э>4.1) to the input of a controlled RC generator on a Schmitt trigger. From the output of the generator, rectangular pulses pass into the audio signal control circuit. The keychain is made of a small anisotropic magnet sewn into a soft leather case or a souvenir toy. Reed switch K1 (Fig. XNUMX) with soldered conductors can be placed in a plastic tube and fixed at the bottom of the windshield, masked with a sticker.

Literature

1. Andrianov V.I. Sokolov A.V. Automobile security systems. - St. Petersburg, 2000.
2. Bannikov V. Diodes in generators and shapers on microcircuits. - Radio amateur, 2001, N4, S.20.
3. Chip & Dip. Electronic components and devices: Catalogue. - 2000, p. 100.

Author: I.Semenov, Dubna, Moscow region; Publication: radioradar.net

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