DIY Kits Human body sensing IR pyroelectric infrared sensor anti-theft alarm
The anti-theft circuit of pyroelectric infrared sensor is composed of pyroelectric infrared sensor PIR, integrated operational amplifier LM358, voltage comparator LM393, 110 alarm circuit and power-on delay circuit. This circuit can be used as home anti-theft. When the family leaves the room, the switch K1 is closed and the circuit starts to work. As long as someone enters the room for a period of time, an alarm will sound.
 
1. After the circuit is energized, when the pyroelectric infrared sensor PIR detects the infrared signal radiated by the human body in front, a weak electrical signal is output from the PIR "2" pin, which is amplified by the transistor VT1, and then input to the operational amplifier IC2A through C2. The 3" pin performs high-gain low-noise amplification, and then the signal is output from the "1" pin of IC2A.
 
2. IC2B acts as a voltage comparator in the circuit. Its "5" pin is provided with reference voltage by R10 and VD1. When the signal output from IC2A's "1" pin reaches IC2B's "6" pin, "5" and "6" The voltage input from the "pin" is compared. If the voltage of pin "6" is higher than that of pin "5" at this time, pin "7" of IC2B changes from the original high level to low level. At this time, C6 discharges through VD2, so that IC3's "2" pin becomes low level. If the voltage of "2" pin is lower than the reference voltage provided by the resistors R14 and R15 at pin "3", then IC3's "1" The "pin" changes to a high level, the transistor VT2 is turned on, and the music chip IC4 obtains the voltage. The audio signal output by the "2" pin is amplified by the transistor VT4 and drives the buzzer BELL to sound 110.
 
3. When a person leaves the detection area, the "7" pin of IC2B becomes high level, VD2 is turned off, and C6 has a charging time (30 seconds), which makes the buzzer delay alarm for 30 seconds.
4. VT3, R20 and C7 form a start-up delay circuit, which takes about 2 minutes (should be greater than the delay alarm time) to prevent immediate alarm when starting up, allowing people to have time to leave the scene, and also to prevent errors caused by power outages. action.
 

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On 12-Mar-21 at 06:11:12 GMT, seller added the following information:

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