PIR sensor teardown

This is a tear-down of an interesting PIR (passive infra red) sensor found from some unknown light system believed to be powered from 230V AC.

The chips used seem to be ST LM2904 low power opamp and TFK U2100 timer control chip. The sensors are PIR sensor and LDR.

The most interesting part is that most of the “circuit board” is not made of traditional circuit board material, but instead pieced of metal put inside plastic material.



This can be bent open quite easily to reveal all that is packed in there.



What was revealed was relay, adjustment potentiometers, over voltage protection VDR and transformerless power supply components.


  1. Tomi Engdahl says:

    How PIR modules work and using them to control LED strings.

    Thanks to the wonders of the Arduino, there are a load of useful electronic modules available on ebay at ridiculously low prices. You don’t need an Arduino to use many of these devices, so here’s how you can add a buffer transistor to a PIR module to let it switch strings of battery operated LED lights.
    The typical quiescent current of these PIR modules is just 50uA (50 micro Amps) so they will run a VERY long time on a set of rechargeable cells before they need recharged. The time they last depends on how often the lights are triggered.
    This allows the possibility of an outdoor Xmas tree in the middle of nowhere that turns on whenever anyone walks near it and then turns off when they leave. Add a solar panel to top up the batteries and you could have a very low maintenance decorative effect.

    As mentioned in the video, the modules may have a movable link that can switch between two modes. retriggerable and non-retriggerable. In non-retriggerable mode the lights will turn on for a fixed time and then turn off again even if there is continuous movement, but then re-trigger again for another time cycle. In retriggerable mode the timer keeps being reset every time movement is detected, meaning the lights will simply stay on while someone is in the vicinity. the retriggerable mode is the best in this application, and is set by default on many of the modules.

  2. Tomi Engdahl says:

    Arduino Controlling Multiple P.I.R Sensor on Same Bord

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