Ultrasonic Range Finder

Today I thought I’d write a quick post introducing Sparki’s ultrasonic range finder.

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Lots and lots of robots and robot kits use an ultrasonic range finder, especially the cheaper ones, as it is possibly the cheapest way of measuring distances in the direction the sensor is pointing.

It works by sending out a sonar sound wave from one side and the other side receives this once it has rebounded from the nearest surface. Using the time this takes, a judgement about the distance of the object can be made.

Image from Arcbotics: http://arcbotics.com/products/sparki/parts/ultrasonic-range-finder/

Understanding how this hardware works is key to being able to use it successfully, as often the robot will be slightly off centre when it detects the object and it is up to the programmer to be aware of this margin of error and correct it before the robot can approach and pick up an object.

Although ultrasonic range finders are used a lot they do have disadvantages:

  • the sonar is sent out in a cone, anything outside the cone will not be detected

  • soft surfaces absorb a lot of the sonar so that can alter the readings and the robot will be less able to detect a soft object
  • there can be reading errors and anomalies

In more expensive robots a laser range finder is often used, as well as simply a camera or vision sensor as these are more precise and accurate than ultrasonic range finders, in general.

Tomorrow I will be adding a new program which relies on the ultrasonic range finder to work.

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