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owl [soylentnews.org] writes:

I recently got some cheap RCWL-0516 microwave motion sensors, mostly because I was wondering how China managed to make a radar for under a dollar:

Getting one working was quite easy, I just connected the VIN pin to 5 volts, GND to ground, and added a 1 uF decoupling capacitor on the 3V3 pin. When someone moves within ~5 meters, the OUT pin goes up to 3 volts for 3 seconds.

So it works, but how?

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