One of the my challenges was to build a bot that could effectively avoid obstacles before it hit them.  My first attempt was to use the Lego Light sensor and the RCX to do this. The RCX would send out IR pulses and the Light Sensor would be used to read them and, based on how long they took to get back to the Light Sensor, could determine proximity. This worked realively well, with the exception that it was difficult to “tell” which side the robot should “look out” for… I came across a Dual Infra-Red Proximity Detector (DIRPD) that is currently being made and sold by Peter Sevcik. Once I received the unit, I went fast to work.  My plan was to build a robot in time for Christmas to deliver a set of diamond earnings to my fiance as well as test the abilities of this new sensor.  The bot depicted is a paired down version of the actual one that was used, but it still functions in the same way.

The sensor was set as a Light Sensor SetSensorType(SENSOR_2, SENSOR_TYPE_LIGHT); The code was straight forward.  The bot would drive forward until SENSOR_2 returned one of the following values:
0 Object in front.
22 Object on left
48 Object on right.
75 No object detected -continue
Based on those values, a decision would be made to turn in a specific direction.  I also added in some randomizing for when the bot met an object head on.

The sensor worked exceptionally well.  Reaction distance was predictable at approximately 16 to 24 inches.  I only stumbled across one minor issue.  The bot would have difficulties when approaching a standard doorway (i.e. bedroom) from the center.  Both left and right would trigger and the bot would get stuck trying to decide what to do.  This is easily fixed by building a routine that could detect this, make the assumption that it was a doorway, stop detecting, go through for x amount of time, and proceed with detection.  This is also proof that the sensor is doing exactly what it was designed to to.

The quality of the product both in workmanship and function is top notch.  It is obvious that Peter takes time and know-how when creating each one of these. The visual quality of the sensor may make you think that this one came from Lego themselves if it wern’t for the TechnoStuff logo on the side…

If you are looking for an effective, easy-to-use sensor for proximity detection, the DIRPD is it.  It is easy to mount, program, fairly priced and looks good too boot! Good work Peter.

Have a sensor or add-on that you want reviewed? Drop me a line.