Circuit design of thermal release human body infrared module temperature acquisition system

The human body infrared sensing module circuit is mainly composed of human body infrared sensor, Fresnel lens and special chip BISS0001. When someone appears in its detection area, the sensor can detect the signal and transmit the signal to the microcontroller. The microcontroller will then turn on the device or put the electrical equipment in the room in an openable state according to the actual situation. In addition, regarding the lighting situation in corridors and hand washing, when someone passes by at night, the human body's infrared sensor detects the person and turns on the corridor lights or bathroom lights. The thermal release human body infrared module circuit is shown in Figure 2.

Figure 2 Pyroelectric human body infrared circuit diagram

The pyro-infrared special chip BISS0001 is used in the circuit. It is a digital-analog hybrid special-purpose integrated circuit composed of an operational amplifier, a voltage comparator, a state control, a delay time timer and a blocking time timer. The internal circuit is shown in Figure 3 . When the infrared rays radiated by the human body are focused on the detection element of the pyroelectric infrared sensor through the Fresnel lens, the sensor in the circuit will output a voltage signal, and then the signal first passes through a band-pass filter, the upper limit of the filter The cut-off frequency is 16 Hz, and the lower limit cut-off frequency is 0.16 Hz.

Figure 3 BISS0001 chip internal circuit diagram

Since the detection signal voltage output by the pyroelectric infrared sensor is very weak (usually only about 1 mV), and it is a changing signal, at the same time, the function of the Fresnel lens makes the output signal voltage appear in the form of pulses (the pulse voltage is 0.1~ (about 10 Hz), so the voltage signal output by the pyroelectric infrared sensor should be amplified twice through operational amplifiers OP1 and OP2. After being processed by the bidirectional amplitude detector composed of voltage comparators COP1 and COP2, the effective trigger signal Vs is detected to start the delay timer.

The output signal Vo is connected to the microcontroller for detection. When there is someone, it outputs a high level of 5 V. When the person leaves, it is reset to 0 V after a delay for a period of time to facilitate the control of the main control circuit. The circuit design puts the chip in a re-triggerable state to suit actual classroom conditions. The working process of repeated triggering: In the repeatable triggering working mode, when Vc = "1" and A = "1", Vs can repeatedly trigger Vo to be in the effective state, and can cause Vo to remain in the effective state during the Tx cycle. During the Tx time, as long as Vs jumps upward, % will continue to extend - one Tx cycle from the moment when Vs jumps upward; if Vs remains in the "1" state, Vo will always remain in the valid state; if Vs remains in the " 0" state, Vo returns to the invalid state after the end of the Tx cycle, and also within the blocking time Ti, any change in Vs cannot trigger Vo to become the valid state.