Pyroelectric infrared sensor is a kind of sensor which can detect infrared and output electrical signal emitted by human or animal. As early as 1938, it was proposed to use pyroelectric effect to detect infrared radiation, but it was not paid attention to until the 1960s, with the rapid development of laser and infrared technology, it also promoted the study of pyroelectric effect and the application of pyroelectric crystals. Pyroelectric crystals have been widely used in infrared spectrometers, infrared remote sensing and thermal radiation detectors, and can be used as an ideal detector for infrared laser. It is intended to be widely used in various automatic control devices. In addition to the application of the corridor automatic switch and anti-theft alarm that we are familiar with, the application prospect is promising in more fields. For example: in the room when no one will automatically stop the air conditioner, water dispenser. A device that automatically turns off when no one is watching or when the viewer has gone to bed. Open the app on the monitor or automatic doorbell. Combine video or digital cameras to automatically record animal or human activities... . You can according to their own whimsy, combined with other circuits to develop more excellent new products. Or automated control devices.

Basic knowledge of pyroelectric sensors

Similar to the piezoelectric effect, pyroelectric effect refers to the phenomenon that the crystal surface is charged due to the change of temperature. Pyroelectric sensors are temperature-sensitive sensors. It is composed of ceramic oxide or piezoelectric crystal elements, made of electrodes on two surfaces of the element, in the sensor monitoring range of temperature change ΔT, pyroelectric effect will produce charge ΔQ on the two electrodes, that is, produce a weak voltage ΔV between the two electrodes. Because of its extremely high output impedance, there is a field effect tube in the sensor for impedance transformation. The charge ΔQ generated by the pyroelectric effect will be combined with ions in the air and disappear, that is, when the ambient temperature is stable and constant, ΔT=0, the sensor has no output. When the human body enters the detection area, due to the difference between the human body temperature and the ambient temperature, ΔT is generated, and there is ΔT output; If the human body does not move after entering the detection area, the temperature does not change, and the sensor has no output. So this sensor detects the movement of a person or an animal. Experiments have proved that the sensor without optical lens (also known as Fresnel lens), its detection distance is less than 2m, and with optical lens, its detection distance can be greater than 7m.

The following points should be noted in use:

First, the DC working voltage must meet our requirements, too high and too low will affect the module performance, and the power supply must be well regulated filter, such as computer USB power supply, mobile phone charger power supply, the older 9V stacked battery can not meet the module working requirements, It is recommended that customers use the power supply of the transformer and pass the voltage regulation of the three-end voltage regulator chip, and then supply power through the 220UF and 0.1UF capacitor filter.

Second, debug the human body as far away from the induction area as possible, sometimes although the human body is not in front of the module, but the body is too close to the module module can also sense the resulting has been output, and debugging the human body do not touch the circuit part will also affect the module work, the more scientific way is to connect the output end to an LED or multimeter, the module covered with newspaper, Leave the room and wait 2 minutes to see if the module still has output.

Third, the module can work normally when the load is not connected, and the work disorder after the load is connected. One reason is that the power supply capacity is very small, the load consumes more power, and the voltage fluctuation caused by the load work leads to the module's misoperation. The other reason is that the load will cause interference when the power work, such as the inductive load such as relays or electromagnets will produce reverse electromotive force. When the 315M launching board works, electromagnetic radiation will affect the module. The solution is as follows: A, the power supply part with inductive filtering. B, the load and the module use different voltage methods, such as: the load uses 24V working voltage, the module uses 12V working voltage, and the three-end regulator is isolated between them. C: Use a larger capacity power supply. Fourth, the human body sensor module can only work indoors and the working environment should avoid direct exposure to sunlight and strong lights, if the working environment has strong RF interference, shielding measures can be used. In case of strong turbulence, close doors and Windows or prevent convection. The induction area should avoid facing heating appliances and objects as well as debris and clothing that are easily blown by the wind.

Fifth, the human body sensor module is recommended to be installed in a sealed box, otherwise there may always be an output signal.

Sixth, if the detection Angle of the human body sensor module is required to be less than 90 degrees, you can use opaque tape to block the lens or cut the lens to achieve.

Seventh, the human body sensor module uses dual probes, the direction of the human body's hands and feet and head movement is closely related to the sensitivity of the sensor, and the characteristics of the infrared module determine that the induction distance cannot be accurately controlled.

Eighth, the probe (PIR) in the module can be installed on the other side of the circuit board. The probe can also be extended with a double-core shielded wire, and the length should be within 20 cm.