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Can I use an outdoor mains PIR with a Pi?

Posted: Fri Nov 01, 2019 4:38 pm
by phluxm
Hello!

I'm a coder with only a little electronics knowledge and I've got a project that requires an outdoor weatherproof PIR sensor but that needs to interface with the Pis GPIO.

I have 2 PIRs:
https://www.amazon.co.uk/Infrared-Detec ... p_p_img_12
https://www.amazon.co.uk/gp/product/B00 ... le_o02_s00

and a couple of questions for using them...
  • Both PIRs have 3 wires but one is blue, brown, black the other blue, brown, red. I am correct to think I supply 5v on the brown wire, attach blue to GND and then the red/black one goes to the Pi's input pin?
  • Will these PIRs (presumably designed for 220v mains power) work on a 5v supply from the Pi? Will a lower voltage affect the PIRs range or sensitivity etc? I've got one of the PIRs giving me fluctuations in voltage but I need to almost have my hand over it to get big jumps in the readings
  • Do use these voltage fluctuations on the red/black wire to trigger the pi? If so how do I read this with the Pi? I'm using Python's Python (RPi.GPIO) API and used the code GPIO.setup(17, GPIO.IN) but the voltage change is pretty small and the Pi seems to only read the input voltage as a 1 or a 0. Am I doing something wrong? Is it right that Pis pins do not take analog readings? (I could set a value as a response threshold if they did)
Thanks for your help!
Ben

Re: Can I use an outdoor mains PIR with a Pi?

Posted: Fri Nov 01, 2019 5:24 pm
by rpdom
I doubt either of those PIRs will work with a Pi without some serious modification. They are, as you say, designed for mains use, not 5V or 3.3V. They will probably have a PSU inside to drop the voltage down to 5V and a relay circuit to switch the output. Neither of those would be needed for the PI.

But, you could possibly use them to drive a mains relay or something to safely switch the GPIO inputs on the Pi.

Re: Can I use an outdoor mains PIR with a Pi?

Posted: Fri Nov 01, 2019 6:30 pm
by blimpyway
Search for Arduino mini PIR sensor modules. These should work from 2.7 to 12.0 volts, so they-re ok with Pi's 3.3V gpio

Re: Can I use an outdoor mains PIR with a Pi?

Posted: Fri Nov 01, 2019 8:04 pm
by rpdom
blimpyway wrote:
Fri Nov 01, 2019 6:30 pm
Search for Arduino mini PIR sensor modules. These should work from 2.7 to 12.0 volts, so they-re ok with Pi's 3.3V gpio
Are they rated for outdoor weatherproof use as required?

Re: Can I use an outdoor mains PIR with a Pi?

Posted: Fri Nov 01, 2019 8:26 pm
by blimpyway
most likely not these modules are just the sensor with its circuit.
The rating is given by the case and gaskets/glue/silicone used to close it air/dust/water tight.

If you need an official weatherproof rating is one problem, if you need just to weatherproof the sensor is a different one.


PS if one follows a "LED from mains circuit" they can replace LED with an optocoupler to detect mains 220V AC presence with a GPIO pin.

https://www.google.com/search?q=led+fro ... 81&bih=477

Re: Can I use an outdoor mains PIR with a Pi?

Posted: Sat Nov 09, 2019 12:27 pm
by phluxm
Thanks everyone! I ended up just using a 5v PIR and enclosing it in a weatherproof junction box then sealing it in with silicone sealant in the end.