Long Distance 90 Degree Electrical Automatic Room Light Control Using Pir Sensor Ceiling Mounted Pir Sensor
Pyroelectric sensor basic knowledge
The pyroelectric effect is similar to the piezoelectric effect and refers to the phenomenon that the surface of the crystal is charged due to changes in temperature. Pyroelectric sensors are temperature sensitive sensors. It consists of ceramic oxide or piezoelectric crystal elements. When the electrodes are formed on both surfaces of the element, the pyroelectric effect will produce a charge ΔQ on the two electrodes when the temperature of the sensor is within the range of ΔT. A weak voltage ΔV is generated between the two electrodes. Due to its extremely high output impedance, there is a FET in the sensor for impedance transformation. The charge ΔQ generated by the pyroelectric effect is lost by the combination of ions in the air, that is, when the ambient temperature is stable, ΔT=0, the sensor has no output. When the human body enters the detection area, because the human body temperature and the ambient temperature are different, 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 does not output. Therefore, this sensor detects the motion sensing of a human or animal. It is proved by experiments that the sensor does not have an optical lens (also called a Fresnel lens), and its detection distance is less than 2 m, and after adding an optical lens, the detection distance can be greater than 7 m.
Pay attention to the following points during use:
First, the DC working voltage must meet the values we require. Too high and too low will affect the module performance, and the power supply must pass good voltage regulation filtering, such as computer USB power supply, mobile phone charger power supply, old 9V laminated battery Can not meet the module work requirements, it is recommended that customers use the power supply of the transformer and after three-terminal regulator chip voltage regulation and then through 220UF and 0.1UF capacitor filter power supply.
Second, when debugging, the human body should try to stay away from the sensing area. Sometimes the human body is not in front of the module, but when the human body is too close to the module, the module can sense the output, and the human body should not touch the circuit part during debugging. The more scientific method is to connect the output to an LED or a multimeter, cover the module with a newspaper, and leave the room. After 2 minutes, see if the module still has output.
Third, the module can work normally when the load is not connected, and the work is disordered after the load is connected. One reason is that the power supply capacity is small, the load is relatively power-consuming, the voltage fluctuation caused by the load operation causes the module to malfunction, and the other reason is the load. When the power is working, interference will occur. For example, an inductive load such as a relay or an electromagnet will generate a back electromotive force, and electromagnetic radiation such as a 315M transmitting plate will affect the module. The solution is as follows: A, the power supply part is added with inductive filtering. B. The method of using different voltages for the load and the module, for example, the load uses 24V working voltage, the module uses 12V working voltage, and is isolated by a three-terminal regulator. C: Use a larger capacity power supply.
Fourth, the human body sensing module can only work indoors and the working environment should avoid direct sunlight and strong light. If the working environment has strong radio frequency interference, shielding measures can be adopted. If there is strong airflow interference, close the doors and windows or prevent convection. The sensing area should try to avoid facing the heating appliances and objects and the debris and clothing that are easily blown by the wind.
5. The human body sensing module is recommended to be installed in a sealed box, otherwise there may be an output signal.
6. If the detection angle of the human body sensing module is less than 90 degrees, it can be realized by opaque adhesive tape blocking the lens or cutting the lens.
7. The human body sensing module adopts a dual-element probe. The movement direction of the human hand, foot and head is closely related to the sensing sensitivity, and the characteristics of the infrared module determine that the sensing distance cannot be accurately controlled.
8. The probe (PIR) in the module can be soldered to the other side of the board. It is also possible to extend the probe with a double-core shielded wire and the length should be within 20 cm.