User:Jstapko/personal/PIR

PIR Sensors
Several years ago, I cut apart and scrapped the motion detectors pulled from my grandparent's house when the building was demolished. The circuit boards had mysterious parts on them, with were only labeled with the letters "PIR." They turned out to be Passive Infrared Sensors, or heat sensing elements, typically used in motion detectors. This page is to collect information I have gathered on them. I eventually plan to salvage the circuit board for a different project.

Web Sites

 * 1) Wikipedia: Passive Infrared Sensor Main wikipedia page on these devices
 * 2) Wikipedia:Pyroelectricity Principle on which at least one type of PIR sensor is based
 * 3) Very advanced discussion of mathematics, physics, and chemistry behind PIR's Of particular note is a graphic explaining canceling out of piezoelectric effects by using 2 crystals (Is this why there are 2 "balanced" crystals in a typical sensor?)
 * 4) homemadecircuitsandschematics.blogspot.com page on PIRs Includes pinout with photo of a typical device, which includes my examples, and some example circuits.
 * 5) Instructables page on PIR "Retriggering" What is retriggering?
 * 6) Datasheet for a Holtek HT7611A "PIR Controller" I found one of these connected to both sensors on the example circuit board. The chip's pinout also helped me to identify the leads of the sensor.  Chip includes op amps, comparators, and light sensor connection.  Datasheet includes logic diagrams, pinouts, function descriptions, and example circuits.
 * 7) Datasheets for LM2904D, a single supply dual op amp I found on the PIR circuit board: Texas InstrumentsPhillipsSTMicro
 * 8) jeelabs.net discussion of PIR problems I didn't find this useful, but someone else might.

Images

 * 1) Doitpoms.ac.uk graphic of compensating for piezoelectric effect This may be why the sensors have 2 "balanced" sensing elements inside. Also shows an animation of how interference of waves received from a source and reflected from the mirrors interfere to produce alternating heat/cold to make the sensor produce a stream of pulses, instead of just one.
 * 2) Wiki Commons photo of pyroelectric sensor with case removed Is this the same as a PIR?
 * 3) homemadecircuitsandschematics.blogspot.com's image of the PIR pinout

Next Steps

 * 1) photos of my PIR boards
 * 2) arduino PIR sites
 * 3) application ideas for PIR's
 * 4) *shut down power transistors if they start to overload/thermal runaway
 * 5) *laser light sensor
 * 6) *theramin