Autonomous security device on infrared rays. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Security devices and object signaling
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This device can be used to protect an object or as a signal sensor in automation devices for various purposes. 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.
After switching on, the device switches to standby mode after 6 seconds. When triggered by the presence of a foreign object, it emits an audible signal for 1,5 minutes, and then automatically switches to standby mode, which is indicated by the LED turning on. The sound signal can be interrupted manually with the "Reset" button, after 6 seconds. The device will return to standby mode.
Schematic diagram of the device is shown in Fig.1.
(click to enlarge)
Technical specifications
- Type of radiation ....... infrared rays with frequency modulation 10 kHz
- Operating mode ...... pulse with a frequency of 2 Hz
- Distance to the object to be determined......0,5 m
- Alarm duration......1,5 minutes
- Current consumption......100 mA
- Supply voltage ...... 7,5-12 V
- Overall dimensions......140x37x95 mm
On the elements DD1.1 and DDI.2, a generator of rectangular pulses with a frequency of 2 Hz is assembled. On the elements DD1.3 and DD1.4, a controlled pulse generator with a frequency of 10 kHz is made, which begins to generate oscillations only when a positive logical "1" signal is applied to pin 8 DDI.3.
The signal from the generators goes to the composite transistor VT6 and VT7, in the collector circuit of which the infrared LED VD3 is included. Thus, the LED operates in a pulse mode with a switching frequency of 2 Hz. The pulse mode of operation is selected in order to save battery power.
The photodetector is assembled on a DD2 chip. Reception of infrared vibrations is carried out on the photodiode VD2.
Since the DD2 chip is powered by a voltage of + 5V, a parametric converter for + 1V from + 2V is assembled on the elements VD5 and R9. To prevent the penetration of interference through the power circuits, a power filter for the DD2 microcircuit is used on the elements R1 and C1. Capacitors C2 and C3, C4 are elements that set the operating mode of the DD2 chip.
Next, the signal is fed to the comparator, which is made on the element DD3.3. If the signals at its inputs are equal in frequency and phase, a logical "3.3" is formed at the output of DD10 (pin 0), with a difference in frequencies at the output of DD3.3, a chaotic change in the levels "0" and "1" is observed. Therefore, when "spurious" signals hit the photodetector, the comparator generates an error signal. This ensures reliable, error-free operation of the device.
On elements C8 and R11, a circuit is assembled for delaying the transition of the device to standby mode after pressing the "Reset" button or after turning on the device. This is necessary so that a person can leave the security zone after turning on the device.
The transmitter and photodetector boards are shown in fig. 2,3 and 4,5 respectively.
The device uses K176 series microcircuits. They can be replaced by the same type from the K561, K564 series without changing the board design.
Capacitors K50-35 can be replaced with K50-I6, the rest of the K10-7V series can be replaced with KD. KT315B transistors can be replaced with KT315 with any letter, KTZ102A, B, KT816B - with KT602B, KT814B. Photodiode FD320 - on FD263. LED AL156 - on two series-connected AL107B, AL307 - on AL102B. Resistors - type MLT-0,125, MLT-0,25, Zener diode KT147A is replaced by KS156A. Diode KD522B - on KD521 with any letter.
Dynamic head - DEMSH.
Author: K.Afanasiev
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