Low cost PCB mount motion sensor

Hello,
I am looking for a low cost PCB mount motion sensor. I don't have a lot of experience with sensors but have seen a lot of information
pointing to PIR sensors. Is this the way to go?
I'm looking for something that can interface with a digital I/O pin on a microcontroller and can detect basic movement in a decent sized office or small room.
Any thoughts?
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teaks wrote:

PIR typically involves a unit with a special lens producing "fingers" of coverage in the area. It is movement across the finger boundaries that produces the step changes that is often used to sense movement. Often the unit counts these step changes and requires several in a set period of time before triggering - to avoid a single noise pulse causing a false trigger. All this may be a little tricky to put on a pcb. However, if you would consider using a cheap external unit, wired to the pcb, this could be an excellent solution.
One alternative to consider is a simple microphone. Analogue or digital filtering can be added to give pretty impressive results for some situations. Using the infra-sonic part of the spectrum can be worth investigating. In your case, you can presumably use the microcontroller to reduce the false alarm rate.
--
Sue


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