IR Proximity Detector
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This sensor is out of stock and being withdrawn.

Withdrawn   Proximity Detector lets you know when you are getting near a wall or large object.
This sensor is replaced by the Infrared Relative Distance sensor, IRRD.

Building a robot that moves around is easy.  Making one that does not self-destruct is more difficult.  Lego sells a mechanical switch that can be used to detect when your robot hits a wall.  Unforturnatly, when you hit the wall, it is sometimes too late.  Fast moving robots usually can not stop in time to prevent the robot from breaking apart.  The Proximity Detector provides warning BEFORE you hit the wall.  This gives your robot time to reverse, or turn away from the wall.  The detector trigger point can be adjusted from a few inches to a foot.  With good lighting conditions, the range can be increased up to 3 feet.

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.

IRPD    IR Proximity Detector    $24.00

         IR Proximity Detector..

       Bill-bot       Robot billiard ball using two IR Proximity Detectors.

Placed on a pool table, the robot will bounce around like a ball in motion.  Two Infra-Red Proximity Detectors cause the robot to turn before it hits the table edge.  When an IRPD detects the table edge, it turns off the motor on the opposite wheel.  When the edge is no longer seen, the motor is turned back on.

A variation on this is the table-top robot.  It runs around on top of a table without falling off.

You program the detector just like the Lego light sensor.  Use the Light Sensor block in the Mindstorms program environment to cause program branches.  In the example below, Motor A will run until the IR Proxmimity Detector sees a wall, then it will turn off.  In a simple, one-motor robot, the robot would run up to the wall, then stop before hitting the wall.

 The trigger distance is set by a 3 position range switch on the detector.  The distance can be fine-tuned to some extent by changing the sensor threshold in the program.  Distance can also be changed  by using a hinged lego piece to change the amount of light reaching the detector.

See the technical description below for details on how the IR Proximity Detector works, and how to adjust the trigger distance.