This circuit is mainly composed of power supply circuit, infrared transmitting circuit, infrared receiving circuit, logic processing circuit and alarm circuit. The circuit principle diagram of this infrared anti-theft alarm experimental model is shown in the following figure.
VT7, VT8 and related components form a multivibrator whose oscillation frequency is determined by the values of R14, R15, C8 and C9. The oscillating signal enters the base of VT6 from the collector of VT7 through R17, and is amplified by VT6 to drive the infrared transmitting tube to transmit the signal to the outside world. When there is no object between the transmitting tube and the receiving tube, the transmitted infrared signal is received by D7, amplified by VT1 and VT2, from the VT1 collector through C4 coupling into the voltage multiplier rectifier circuit, forming a DC control voltage, so that VT5 is saturated and on, IC1 pin 8 and 9 input low level, after “not” logic processing, pin 10 output off level. Pin 3 of IC1 outputs a high level.
This high level pulls the 1-3 pin level of IC1 up through R8 in one way to maintain the high level output of the 3 pin, and in the other way to keep the VT3 off and the alarm circuit does not work.
When there is an object between the transmitting tube and the receiving tube, the emitted infrared signal is blocked, D7 receives no signal, at this time the signal voltage output of the voltage multiplier rectifier circuit is very low, VT5 is cut off, the entire circuit state changes, the 12 pin of IC1 becomes low, at this time the 3 pin output low level. This low level signal is passed through R8 to make pin 13 of IC1 low. At this time, even if the 12-pin level becomes high, as long as one input is low in the relationship with the non-gate, the output will be high, so the output state is locked and the 3-pin output low level will be maintained. At the same time, the VT3 is saturated, the alarm circuit works, and the alarm sound is issued in the horn.
Here the alarm signal generation circuit uses a special music integrated circuit, which generates an alarm audio signal after power-on, and drives the speaker to pronounce after VT4 power amplification. In order to cancel the alarm, two conditions must be met at the same time: one is to receive the infrared signal normally, and the other is that the 13 pin of IC1 must be forced to input a high level signal. The reset button in the circuit is set to force a high level signal to pin 13.
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First, circuit production
As long as the producer is correctly installed according to the logo in the circuit schematic, the entire production can be completed. Some of these components need to be noted in the installation of the following points:
1. Components are installed strictly according to the mark on the circuit board. For polar components, be careful not to install reverse.
2. When the alarm sound music integrated circuit IC3 is installed, its oscillation resistance R22 is directly installed on the IC3; Then the cut resistance pin is welded out from lC3 and connected to the circuit board.
3. When the infrared transmitting tube and receiving tube are installed, the pins should be left with sufficient length and bent after welding, so that the two pipes are placed horizontally with the circuit board.
4, the production of the power supply can be used power is not less than 2W, voltage is 9 ~ 12V transformer. In some places with DC regulated power supply, 9 ~ 12V DC power supply can be directly used for power supply.
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Second, function debugging
1. After all components are installed, connect the power supply, light up the power indicator, and measure the voltage at both ends of C1 with a multimeter. The normal voltage should be about 5V. If it is not normal, you should carefully check whether IC2 is inverted and whether the four rectifier diodes are inverted.
2, alarm circuit debugging: use a wire to short-connect the 8, 9 pins of IC1 to the ground, connect the power supply, and the alarm circuit should not work at this time. If the C and E of the VT3 are very short, the alarm sound can be heard in the horn at this time, if there is no sound, you should carefully check whether the music circuit is installed incorrectly, and whether the horn is connected correctly.
3, transmitter debugging: After all components are installed, use DC 5V power supply for debugging, use a multimeter to measure VT7 or VT8 base voltage to ground, if there is negative pressure, it means that the circuit has started vibration, the transmitter circuit works normally.
4, infrared receiving circuit debugging: 8, 9 pin to the ground do not take off the short wiring, connect the transmitter power, align the infrared tube, the distance can be closer, turn on the power to measure the voltage at both ends of C7, normal when the infrared is not blocked, the voltage is greater than 0.6V; When infrared rays are blocked, the voltage is less than 0.5V. If it complies with this law, it means that the infrared receiving part of the circuit works normally, otherwise it is necessary to carefully check whether this part of the circuit components are installed, and whether there is virtual welding or tin when welding.
5, restore all circuits, and then power on, if the alarm, press the reset key, alarm stop, gradually open the distance of the infrared beam tube, pay attention to be aligned. In order to facilitate debugging, the connection line here is 50cm, and then block the infrared ray, the alarm will be raised. Remove the object, the alarm will still be raised, and the alarm will be lifted after pressing the reset button. If the function is normal, the debugging is complete.
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Post time: Dec-13-2024