IR Relative Distance sensor
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Limited Stock    IRRD-T    Infra-Red Relative Distance sensor    $39.00               

This sensor has been tested with NXT using the Lego NXT conversion cable (W770323).

The IRRD sensor shows how close you are to an object.

The Infrared Relative Distance sensor (IRRD) is a sensor for the Lego Mindstorms™  Robotic Invention System.
The IRRD senses when it is close to an object, and gives you an indication of how the distance is changing.  Your program can use this information to avoid a collisions, find an object, or make decisions on how far away the object is.

The IRRD show relative distance, up to two feet.  It works by measuring reflected infra red light.  Objects that are close reflect a lot of light.  The amout of light reflected also depends on the size of the object and it's color.  Thus the distance measured is relative, not absolute.
The IRRD can be used as a simple proximity detector (IRPD), with trigger distance set by software.  Advanced programs can have multiple responses dependent on the distance.

The sensor uses TV remote control technology.  It works by sending out infrared light, and looking for IR light reflected back.  Infrared is like normal light, except you can not see it with you eye.  There will be no visible indication when the sensor is operating.

NOTE:  This product uses the same Infra-red technology that the RCX uses to communicate with your PC.  When the IR Proximity Detector is in operation, it may interfere with communication between the RCX and PC.

IR distance sensor for Mindstorms

Infrared distance sensor for Mindstorms

Distance sensor on RCX


With just the RCX, IRRD sensor, and a simple program, you can build a musical insturment that plays musical notes depending on the position of your hand.  This type of insturment is called a Therimon.

You program the detector just like the Lego light sensor.  Use the Light Sensor block in the Mindstorms program environment to cause program branches.  The IRRD returns eight different values depending on what it sees.  In the example below, the RCX will produce four different tones depending on the distance to your hand.  This example could be expanded to six tones.

Music program using distance sensor

The IRRD sensor can detect walls, or the floor.  Here is a picture of a table top robot, that runs around  on the table, without falling off.

The IRRD sensor can also b used as a scanner, as in this robot by Volga Aksoy.



Adjusting the Sensitivity

The maximum range of the IRRD sensor is adjustable with a small screwdriver. When the maximum distance detected (RCX value = 10) is changed, the distances for other RCX values change in proportion.

RCX value CCW Center CW
10 175 40 26
25 145 36 23
41 104 25 18
56 79 18 11
72 61 11 9
89 30 9 4