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I am doing a school project where I intend to measure the cafeteria line with motion sensors and the send that information with a WiFi module to a server. This is my first time using Arduino and I am not sure how many motion sensors does it support.

  • for both simple and good, use one per GPIO you have that supports interrupts. for simple and not as good, use one per GPIO. you can eventually add more with port expanders, charlie plexing, even shift registers. – dandavis Jan 20 at 5:04
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Most PIR sensors provide a simple relay output. That means they are nothing more than a switch as far as the Arduino is concerned.

You can connect hundreds of switches to an Arduino. With judicious use of diodes and a matrix arrangement you can hundreds with not many IO pins. For example an 8x8 matrix of switches gives you 64 PIR sensors with just 16 IO pins. For n pins you can have (n/2)² switches with a balanced (n/2 by n/2) matrix.

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