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Autonomous security device on infrared rays. 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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Autonomous security device with IR beams can be used as a security signal sensor in cars of various models. Its feature is a compact design and full autonomy of operation due to the combination of an IR emitter and a reflected signal receiver in one housing. Schematic diagram of the device is shown in Fig.1.

Autonomous security device on infrared rays
Fig.1 (click to enlarge)

After switching on, after 6 seconds, the device switches to armed mode. The security device is triggered when a moving object moves in the security zone (in the car). The device emits an audible alarm for 1,5 minutes, and then automatically switches to armed mode, which is signaled by the LED turning on.

The main technical characteristics of the device:

  • Time to switch to security mode, s.......6
  • Alarm sounding time, min.......1,5
  • Type of radiation ....... IR rays
  • Modulation frequency, kHz ....... 10
  • Operating mode ....... pulse
  • Frequency of modulated packets, Hz.......2
  • Current consumption, mA.......100
  • Overall dimensions, mm......140x37x95

In the circuit on the elements DD1.1 and DD1.2, a rectangular pulse generator with a repetition rate of 2 Hz is assembled. On the elements DD5.3 and DD1.4, a controlled pulse generator with a repetition rate of 10 kHz is assembled, which begins to generate oscillations only when a positive signal is applied to pin 8 of the DD1.3 element. The signal from terminal 11 of the generator is fed to a current amplifier on transistors VT2 and VT6, in the collector circuit of which an infrared LED VD3 of the AL156 type is included. Thus, the infrared LED operates in a pulsed mode (it emits bursts of pulses with a frequency of 10 kHz with a repetition period of 2 Hz). The pulse mode of operation is selected in order to save battery power. The photodetector is assembled on a DD2 microcircuit. Reception of infrared oscillations is carried out by a VD2 photodiode of the FD320 type.

To power the DD2 microcircuit with a voltage of + 5V, a parametric voltage regulator is assembled on the elements VD1 and R2. A filter is assembled on the elements R1 and C1, which eliminates the passage of interference through the power circuits of the DD2 microcircuit. Capacitors C2, C3, C4 set the operating mode of the DD2 chip. The received signal from the emitter follower on the transistor VT1 is fed to the comparator, which is made on the element DD3.3. If the signals at its inputs 8 and 9 are equal in frequency and phase, a log is formed at terminal 10 of the DD3.3 element. "0", and with a difference in frequencies or phase of the signal, a chaotic change in the levels of the log is observed. "0" and "1".

When an extraneous moving object appears in the car interior, the reflected signal received by the receiver will differ from the transmitted one in frequency and (or) phase, which will cause the appearance of chaotic pulses at the output of the comparator (phase detector). The integrating circuit R10, C7 serves to eliminate false positives, which increases the noise immunity of the security system as a whole. The pulses from the integrator are fed to the input C of the trigger DD4.1. The first pulse switches the flip-flop DD4.1 to a state in which a log level is present at its output 1. "1", and on output 2 - log. "0". Transistor VT3 opens. The zero level from the collector of the transistor VT3 is fed to the input R of the trigger DD4.2, thereby allowing its operation. Pulses with a frequency of 2 Hz entering the input From the trigger DD4.2 are divided by 2, and from the output of the trigger (pin 13) are fed to the key on transistors VT7, VT8. which activates the car horn relay.

An audible alarm sounds with a repetition period of 5 s. At the same time, to prevent the system from looping, the transmitter of IR pulses (transistors VT7, VT2) is blocked through the VD6 diode for the duration of the alarm signal. log level. "1" from the direct output of the trigger DD4.1 through the resistor R13 begins to charge the capacitor C9. When the voltage on the capacitor C9 reaches more than half of the supply voltage, the trigger DD4.1 at the input R is reset. Transistor VT4 opens and the HL1 LED turns on, indicating the transition of the system to the armed mode.

Transistor VT3 closes at the same time, a single level from its collector unlocks the IR transmitter and blocks trigger DD4.2 at input R, which leads to turning off the sound signal. When the power is turned on, the delay in arming is carried out by applying a positive pulse through the diode VD5 to the input R of the trigger DD4.1. The pulse is formed when the capacitor C8 is charged through the resistor R11.

The printed circuit board of the device and the placement of parts on it are shown in Fig.2.

Autonomous security device on infrared rays

The board is made of double-sided foil fiberglass.

See other articles Section Automobile. Security devices and alarms.

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