Motion Sensor for NXT
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Limited Stock   Nmotion    NXT Motion Sensor    $39.00       

The Motion Sensor detects motion of people and animals..

The sensor is a Passive InfraRed sensor (PIR) for the Lego Mindstorms NXT system.  It 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 withTV remote controls, other Techno-stuff sensors, or with the RCX infrared communications port.

  Motion Sensor with vertical mounting 

The easiest way to program the motion sensor is to download and import the sensor block from the techno-stuff website.

The example below shows the sensor block (yellow) in a burgler alarm. When someone enter the room the lamp goes on and a sound file is played.

Air pressure sensor program in Lego RIS 1.0

The motion sensor electronics must stabalize (warm up) before it will give a valid result. This usually takes about 30 seconds. Before warm-up is complete, the sensor will indicate motion even when there is none. You can download the "Motion Warmup" myblock which will cause your program to wait until the sensor has stabalized.

You can download the "Burglar Alarm" program shown above if you would like to try it.

The sensor may be programmed in other languages.  Program it as a RCX Light* sensor.  The output will be zero for no motion, and around 83 when motion is detected.


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 NXT to detect.