2 wire PIR

Hi all,

I’m trying to make an alarm system with SE-10 PIR motion sensors for my home. Unfortunately when I build my home I only put 2 wires for the motion sensors ( at that time I was thinking to use wireless PIR sensors).
As a startup I was thinking to power the motion sensor from a INPUT pin(almost like a push button) and when the pir detects movement to pull down this supply. The micro controller would sense the supply go down and trigger the alarm.
Here’s what i come up till now:

But as you guess this don’t work and it’s seems that I got stuck.

Thank you for any help.


Kind of like sawing off the tree branch you’re sat on to do the sawing… I can’t see a way you can do this with two wires, the PIR needs power to switch its own power supply off as soon as it does it, it will allow the power back on, it may not even be detectable depending on the exact behaviour of the PIR during a brown out.

R and C value depends on detector current consuming.



I modified everything according to your schematic but still no luck. Can you please tell me what means for you pin 1,2,3 at microcontroler side and also at the pir side.


-resistor at microcontroler side is 330
-zener is 4.7V
-capacitor 1microfarat
-transistor is BC328

Pin 2 on left side goes to digital input (2 - 13 on Uno board), and connected to output of the sensor on the right side of diagram.
When alarm triggered - signal set to LOW. Software should check on it status.

330 Ohm - should be o’k, if sensor drain current no more than ~ 3 mA, so you can afford
drop down voltage ~ 1 V. Decrease proportionaly on higher current ( 5 ma - 200 OHm, 10 mA - 100 OHm etc).
Diod - any rectifier, 100 mA - 1 A forward current, NOT zener.
Capacitor - the bigger, the better. More than 50 microF. prefereble.
Transistor BC328 is good.


Sorry, I also have a similar problem where I have a 2-wire PIR I would like to wire up to my Ardunio, but dont understand how I transfer power to the PIR and detect movement.

I am a beginner, used to writing software for a PC, this will be my first project using Arduino so any assistance would be appriciated.

From what I understand looking at the diagrams the power is transmitted to the PIR and the resitance is measured on its return, is that correct?

Thank you

Tony Cross