PIR (Passive InfraRed) sensor for VEX
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Limited stock.       VPIR    Passive InfraRed sensor for VEX     $39.00 

The PIR sensor detects motion of people and animals..

The Passive InfraRed sensor (PIR) is a sensor for the VEX ™  Robotic System.  The PIR senses motion of a warm object, like a person or animal.  This is the same type of sensor used in motion activated lights, and in some burglar alarms.  The sensor detects changes in infrared light.  Infrared is like normal light, except you can not see it with you eye.  Infrared is also called Radiant Heat.  There will be no visible indication when the sensor is operating.

The infrared technology used in this sensor is different than TV remote control technology.  This sensor will not detect or interfere with other Techno-stuff sensors..

Motion detector for Mindstorms   PIR sensor


The sensor is programmed like a VEX switch or Bump sensor. The sensor has a binary output. Either it “sees” motion, or it does not. While it is seeing motion, the output will be zero. When it is not seeing motion, the output will be one. Note: When the sensor is first powered up it will read “zero” for about 30 seconds while the electronics stabilize. After that it will operate properly.


Technical Description

Infrared light coming into the sensor is focused on two identical detector elements by a fresnel lens.  The detector elements are connected to oppose each other, so only the difference is output.  When everything is stationary, the two detectors are equal, and the output is zero.  When the IR light is moving, the detectors are unbalanced, and produce a small output.  The small output of the detector is amplified, and used to trigger a one-shot timer.  This timer stretches the output pulse so it is long enough for the VEX to detect.