How to detect a commercial motion sensor (pi4)

Hi there,

I’m working on a home alarm system.
I want to detect my Bosch motion sensors with my raspberry pi 4.
I power the sensors with 12V.
These sensors are normally closed.

My first thought was detecting them via something like Piface’s input, but I think there is no Piface for Rpi4.

What would be the best way detecting these sensors without frying my pi?

Hi Thomas,

Do you mean they are PIR sensors that operate a relay? You could use a simple resistor divider to drop it down to 3.3v to make it safe for interfacing with the 3.3V GPIO pins. Just make sure you use relatively high impedance resistors so you don’t exceed the 16mA limit on the Pi’s GPIO pins.

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