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Infrared car guard. 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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This is a remote control system with frequency coding and long exposure to the photodetector. Of course, frequency coding is not the height of perfection, but nevertheless it works effectively. In order for the scanner frequency at a certain moment not to accidentally coincide with the autoguard frequency, a 2-second time delay is used, which almost completely eliminates random frequency selection.

The autoguard includes a remote control on infrared LEDs of the AL107B type, made according to a well-known scheme. Also included in the autoguard is a K176IE12 clock chip and a Q1 quartz resonator with a frequency of 32768 Hz to form time intervals.

The main technical characteristics of the device:

  • Time to switch to security mode, s.......20
  • Alarm duration, s.......40
  • Alarm interruption frequency, Hz.......1
  • Alarm delay time, s ......2
  • Current consumption in armed mode, no more than, mA.......10
  • PCB dimensions, mm ......60x65
  • Control panel dimensions, mm ......25x30

Schematic diagram of the remote control is shown in Fig.1.

Infrared car guard

The remote control includes a multivibrator on the elements DD1.1-DD1.3, an inverter DD1.4, a pulse key on transistors VT1, VT2 and infrared light-emitting diodes VD1, VD2. The multivibrator frequency is adjusted by selecting the resistance of the resistor R1. The printed circuit board of the control panel is shown in Fig.2.

Infrared car guard

To power the remote control, you can use the Krona battery, which will ensure its long-term use.

The schematic diagram of the autoguard is shown in fig. 3. Autowatch contains a counter-shaper of time intervals on the DD2 chip, two triggers on the elements DD1.3, DD1.4 and DD3.2, DD3.3, a receiving device on the DD4 chip with a VD6 photodiode and a key on transistors VT2, VT3.

Infrared car guard
Fig.3 (click to enlarge)

When the device is turned on with the SA1 toggle switch (before leaving the car), the capacitor C1 sets the counters of the DD2 microcircuit to the initial zero state with its charging current. At pin 10 of the DD2 chip at this time, the log. "0", which is input to the element DD3.4 and opens it. From pin 6 of the DD2 chip, pulses with a frequency of 2 Hz passing the DD3.4 element and arrive at the clock input C (pin 7) of the DD2.1 counter are the same time, the zero level at pin 10 of the DD2 chip, inverted by the DD3.1 element, blocks the trigger assembled on the elements DD3.2 and DD3.3, and prohibits the passage of the signal from the contact sensors SB1 -SBn, connected to the cathode of the diode VD3, through the transistor VT1 to the elements DD1.1, DD1.2. The guard is in this state until the counter DD2 counts 39 pulses with a frequency of 2 Hz. This time, equal to 20 s, gives the owner of the car the opportunity to exit the passenger compartment and close all doors. But after this time, a unit appears at the output 10 of the counter DD2, which closes the element DD3.4 and prohibits the receipt of counting pulses with a frequency of 2 Hz at the counting input C DD2. The same signal (log. "1"), acting on the inputs of the element DD3.1, unlocks the trigger on the elements DD3.3, DD3.2, and the circuit enters the car protection mode.

Car door switches can be used as contact sensors. The same push-button switches can be put on the hood l on the trunk lid. The cascade on the transistor VT1 serves as an inverter and at the same time protects the DD3 chip from failure when a positive voltage is applied to pin 1 while the power of the autoguard is turned off. When one of the contact sensors SB1 - SBn is triggered, the cathode of the diode VD3 closes to ground, the transistor VT1 closes and a positive potential is set on its collector, which switches the trigger on the elements DD3.3, DD3.2. At the same time, a log level is set at its output 4. "1". From the output of the inverter DD1.1 log. "0" goes to pin 1 of the element DD1.2 and opens it. From pin 4 of counter DD2, second pulses through element DD1.2 are fed to pin 7 of counter DD2 and the key on transistors VT2 and VT3, which turns on the horn relay Kf. Counter DD2 counts 39 pulses received at pin 7, and after 40 s is set to zero (at pin 10 - log. "0"). Then, according to the scenario described above, there is a 20 second delay (as when turning on the power), and the circuit goes into armed mode again.

To turn off the autoguard, a control panel is used that emits pulses in the IR range. The photodetector, consisting of a VD6 photodiode and a resonant amplifier on the elements DD4.1 DD4.3, receives a signal from the remote control panel. The frequency to which the device responds is set by the circuit elements L1, C9. Its resonant frequency should correspond to the frequency of the remote control multivibrator. From the resonant amplifier, the signal is fed to the constant voltage driver. If the frequencies of the circuit L1, C9 and the multivibrator of the control panel match, a log level appears at pin 10 of the DD4.5 element. "1". To prevent the auto-guard from triggering in case of an accidental coincidence of the frequencies of the device and the scanner, the circuit R19, C11 forms a time delay of 2 s.

After charging the capacitor C11, the signal is fed to pin 8 of the trigger on the elements DD1.3, DD1.4, which, at pin 11, generates a positive pulse that arrives at pins 5, 9 of the DD2 chip and resets the counter. The moment the device is turned off is indicated by the HL1 LED.

The printed circuit board of the autoguard is shown in Fig.4.

Infrared car guard

Coil L1 is wound on an SBR-23 core and contains, depending on the frequency, from 100 to 500 turns (from 16 kHz to 5 kHz, respectively) of PEV-1 wire 0,1 mm. To power the microcircuits in the circuit, a VD5 zener diode of the KS210 type with a stabilization voltage of 10V is used.

See other articles Section Automobile. Security devices and alarms.

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