Maximum Wire Length for PIR Sensor

Dear All,

I am trying to run a PIR Sensor over 25ft of solid core wire to my Arduino but I seem to be getting a lot of signal interference. I read somewhere that the maximum distance from the Arduino the PIR Sensor can be is 1-2 meters. Is this true?

I have tried connecting the PIR Sensor to the board and it worked. In addition, with only a 6 inch wire, the PIR Sensor works as well. It's just when the longer cable is connected. Is there a maximum PIR distance from the board, or do I need to do something to shield the wire or something to lower the "noise".

Thanks a lot, Lane

Most PIRs use an open collector output that is pulled low when the PIR is triggered.
Perhaps all you need is a stronger pullup (i.e. lower resistance) so the signal is held high more until the PIR pulls it low.


Thanks, sounds like you know what you are talking about. Unfortunately, I don't!

How can I accomplish lowering the resistance on the wire?

You add a pullup resistor to the end of the wire at the arduino end. Say a 1Kohm resistor from the signal pin to +5.

I will give this a try tomorrow morning, it's 12:30 am here. Just out of curiosity, what exactly does adding this resistor do? I sort of understand the idea of resistors, but am curious as to how exactly this would fix my problem.

Thanks for all your help!!

12:30AM here as well. The resistor makes it harder for random noise to change the signal level at the input pin.With 1K, the PIR needs to sink 5mA of current to change the signal from High to Low. Random noise is not going to do that. You can try different resistor sizes, see what provides good results. 10K, 4.7K, 1K.

Thanks makes a lot of sense...thanks!

Does using a longer wire "encourage" or "allow" more random noise? My real question is why does this only occur at longer distances?

You're the best.

"My real question is why does this only occur at longer distances?" Yes.

"My real question is why does this only occur at longer distances?" The longer wire acts like an antenna with more pickup area.

You might also benefit from putting some extra capacitance across the power/gnd pins at the PIR end. 0.1uF and 1uF in parallel to help with power droop as current is drawn for inceased activity, & noise filtering.