Sensor information can be used by your robot to navigate and interact with its environment. Sensors report on the world around them; measuring light, distance, sound, movement, direction, temperature, pressure, or location. This chapter describes how common sensors used with two wheeled and four wheeled platforms work.
The first half of this chapter covers the primary sensors used in the chapters that follow: IR reflective sensors and SONAR distance sensors. These are used to determine if an object is near the robot. Reflective sensors detect nearby objects and are used for line following and edge detection (determining if the robot is near the edge of the surface it is moving on, such as the edge of a table). Distance sensors are used to determine the distance to objects up to ten feet away from the robot. The second half of the chapter covers other types of sensors you can add to enable the robot to respond to distance, sound, movement, or other stimuli. You should also have a look at Appendix D which describes a very useful aspect to sense, the robot's battery voltage.
Two are used for edge detection, but a third is required for line following. Additional sensors are available from many internet shops that stock robot parts, or direct from the manufacturer: http://www.pololu.com/catalog/product/958/
One is used to measure the distance to obstacles (Maker Shed product ...