Infrared alarm pure hardware circuit
The alarm can detect infrared rays emitted from the human body, when people
Enter alarm within the surveillance area can sound an alarm, suitable for homes, offices, warehouses, laboratories and other important occasions burglar alarm. Means circuit schematic shown in Figure 1. By an infrared sensor, a signal amplifying circuit, a voltage comparator, a delay circuit and sound an alarm circuit. An infrared detecting sensor detects the human body IC1 infrared signal radiated forward by the output pin of IC1 ② weak signal, the transistor VT1 and the like constituting the first stage amplification circuit, and then input to the operational amplifier IC2 via the high-gain C2 , low noise amplification, this time by a signal output pin IC2① been strong enough. IC3 for the voltage comparator, its first reference voltage is provided by a pin ⑤ R10, VD1, when the signal reaches the output voltage IC2① ⑥ foot pin of IC3, the voltage of the two inputs are compared, this time from the original ⑦ feet IC3 high to low. Alarm delay circuit IC4, R14 and C6 form a delay circuit for about 1 minute. ⑦ When the pin IC3 goes low, C6 discharges through VD2, ② case IC4 pin goes low, it is compared with the reference voltage pin ③ of IC4, when it is lower than the reference voltage, the IC4 ① pin goes high, VT2 conduction, Xiangqi BL power alarm. After the disappearance of the body's infrared signal, IC3's ⑦ feet high output resumed, this time VD2 end. Since the voltage across C6 is not mutant, it is slowly charged through R14 to C6, when the voltage across C6 is higher than the reference voltage, IC4 pin ① only goes low, about 1 minute, 1 minute alarm i.e. .
