Circuit design of temperature acquisition system for pyroelectric human infrared module

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The human body infrared sensing module circuit is mainly composed of a human body infrared sensor, a Fresnel lens and a special chip BISS0001. When someone appears in its detection zone, the sensor can detect the signal and transmit the signal to the microcontroller. The microcontroller then turns on the device or allows the electrical equipment in the room to be turned on according to the actual situation. In addition, regarding the corridor and the hand-washing lamp, when someone passes by at night, the human body infra-red senses the person to turn on the corridor lamp or the bathroom lamp. The pyroelectric body infrared module circuit is shown in Figure 2.

Figure 2 Thermal release human body infrared circuit diagram

The circuit uses a pyroelectric infrared dedicated chip BISS0001. It is a digital-analog hybrid ASIC consisting of an operational amplifier, a voltage comparator, a state control, a delay time timer, and a lock-up timer. The internal circuit is shown in Figure 3. . When the infrared radiation radiated by the human body is focused on the detector element of the pyroelectric infrared sensor through the Fresnel lens, the sensor in the circuit will output a voltage signal, and then the signal is first passed through a band pass filter, the upper limit of the filter The cutoff frequency is 16 Hz and the lower cutoff frequency is 0.16 Hz.

Figure 3 BISS0001 chip internal circuit diagram

Because the pyroelectric infrared sensor output detection signal voltage is very weak (usually only about 1 mV), and is a changing signal, and the Fresnel lens makes the output signal voltage pulsed (pulse voltage is 0.1~) The voltage signal output from the pyroelectric infrared sensor should be amplified by the operational amplifiers OP1 and OP2 for secondary amplification. After processing by the two-way amplitude detector formed by the voltage comparators COP1 and COP2, the valid trigger signal Vs is detected to start the delay time timer.

The output signal Vo is connected to the single-chip microcomputer for detection. When there is a person, it outputs a high level of 5 V. When the person leaves, after a delay, it is reset to 0 V for the control of the main control circuit. The circuit design puts the chip in a repeatable trigger state to suit the actual situation in the classroom. Repeatedly triggering its working process: In the repeatable trigger mode, when Vc=“1” and A=“1”, Vs can repeatedly trigger Vo to be in an active state, and can cause Vo to remain valid for a period of Tx. During the Tx time, as long as Vs jumps up, the % will continue to extend from the time of the Vs transition to a Tx period; if Vs remains in the "1" state, then Vo remains active; if Vs remains " In the 0" state, Vo returns to the inactive state after the end of the Tx period, and also during the blocking time Ti, any change in Vs cannot trigger Vo to be in an active state.