SmartArt - AD405 - Drew Browning


Passive InfraRed Sensors (PIR)

(aka pyroelectric sensors)


A PIR is a motion detector that detects changes in the level of IR light with a wavelength corresponding to body heat. It senses movement, not presence (as with emitter/detector pairs). A person may not be detected with a PIR if standing still long enough.


Parallax, Inc. PIR Sensor (#555-28027)

Also available from Radio Shack: Catalog #: 276-033.


This particular PIR is especially useful for installations since it very small and operates on lower power at logic levels.





More info:


Control the angle of sensitivity:


Shorter recovery time hack:


Drew’s version of the recovery time hack. (reduces recovery time from 2 seconds to .5 second):

You will need to solder a 47K resistor in parallel with the 200K surface mount resistor (actually labeled 204).




Using an X-acto type utility knife, first scrape away the solder mask (green coating) over the trace going to pin 3 of the integrated circuit.



Bend the leads of the resistor so the body of the resistor is on opposite side of the board.




The bent leads should hold resistor in place while you solder one lead to the foil trace and the other lead to the right side of the 200k resistor.




Use a small tip pencil type soldering iron and just enough heat to melt the solder. This is precision work. Be very careful not to overheat the solder joints. Take your time and use a vise or “helping hands” device to hold the circuit board.




How PIR sensors work


Focusing PIR sensors




Return to Sensing Movement page.