In 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.

       Therimon

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.

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.

Specifications

• Size: 2 bumps by 4 bumps.  Height is one and one third bricks.  (one brick plus one flat plate)
• Size:  1.25 x 0.625 x 0.575 inch.
• Mindstorms electric plate connector on bottom.
• Mindstorms value.  (Distance to 8 x 10 inch white paper rectangle)

  RCX	NXT	NXTraw
  0	0	1018	No object detected
  10	0	951	Object is 21 to 24 inches away
  25	8	854	Object is 15 to 21 inches away
  41	32	756	Object is 11 to 15 inches away
  56	55	659	Object is 8 to 11 inches away
  72	79	561	Object is 4 to 8 inches away
  88	88	457	Object is 0 to 4 inches away
  100	100	356	Interference from another IR signal

• Power required:  8.2 volts,  6 mA.     (Minimum Mindstorms battery voltage is 8.2)

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.

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Technical Description

The IRRD sensor  uses the same technology found in a TV remote control device.  The detector sends out modulated infra-red light, and looks for reflected light coming back.  When enough light is received back to trigger the detector circuit, the circuit changes binary state.  Light from the LED is a continuous string of bursts of modulated square waves.  The carrier frequency is 38 KHz..   A microprocessor generates the bursts, and sets the output voltage.  Hysteresis is created by the firmware.

The relationship of Mindstorms Value to distance is reasonably linear.  Here is a graph of a typical IRRD sensor, showing distance to a standard 8.5 x 11 inch sheet of white paper.


 

The amount of infrared light reflected depends on the distance, size, and “color” of the object.  Distances shown above are for a white wall.  The distances are less for objects that are smaller, or reflect less infrared light.
The darkest object observed was a textured brown plastic wastebasket, first detected at 10 inches.

Maximum range for different colors:

• 24 inches  -  White wall
• 24 inches  -  Red paper.
• 20 inches  -  Black paper.
• 19 inches  -  Dark wood door
• 10 inches  -  Textured brown plastic.


Maximum range for different size white paper object.

• 24 inches  -  2 x 3 foot rectangle.
• 21 inches  -  8.5 x 11 inch rectangle
• 17 inches  -  6 x 6 inch square
• 13 inches  -  3 x 3 inch square
•   7 inches  -  1 x 1 inch square


Values and distances may vary slightly between sensors, due to manufacturing tolerance.