What is the human induction switch?
Human body sensing usually uses PIR modules directly.
PIR module is a digital intelligent automatic control product based on passive human infrared technology, with high sensitivity and reliability.
Its main components are shell, filter, pyroelectric element (induction sensitive element), FET, capacitance and so on. Wherein, the filter is arranged at the window, forming the window through which the infrared ray passes. The short wavelength of sunlight and fluorescent light (about 5um) can be well filtered by the filter. Pyroelectric element (induction sensitive element) The induction element converts the weak changes of infrared signal between 8-12um into electrical signals. In order to be sensitive only to the infrared radiation of the human body, the radiation surface of the induction element is usually covered with special Fresnel lens, so that the interference of the environment is significantly suppressed.
PIR module can detect infrared radiation emitted by humans or some animals and convert it into electrical signal output. Its triggering mode is generally divided into non-repeatable triggering mode and repeatable triggering mode.
Non-repeatable trigger mode: after the induction output high level, the output will automatically change from high level to low level once the delay time is over.
Repeatable trigger mode: That is, after the induction output high level, during the delay period, if there is a human body active within the induction range, the output will remain high level, and the high level will be changed into low level after the human leaves. (The induction module will automatically extend a delay period after detecting every activity of the human body, and the time of the last activity is the starting point of the delay time.)
Based on actual user requirements, most of the smart mirror lamps choose PIR module with repeatable trigger mode. As long as MCU detects the effective level output of PIR module, the corresponding LED of the mirror lamp will start to work.
Advantages and disadvantages of the PIR module
Advantages: PIR module itself does not emit any type of radiation, device power consumption is small, good concealment. The price is low.
Disadvantages: easy to be interfered by various heat sources and light sources; Passive infrared penetration is poor, the infrared radiation of the human body is easy to be blocked, not easy to be received by the probe. Susceptible to radio frequency radiation interference. When the ambient temperature is close to the human body temperature, the detection and sensitivity decrease obviously, sometimes causing short-term failure.
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