Your robot can now move around, but you'll want to be able to sense a barrier or a target. One of the ways to do this is with an IR sensor. First, a tutorial on IR sensors is required. An IR sensor has both a transmitter and a sensor. The transmitter sends out a narrow beam of light, and the sensor receives this beam of light.

The difference in transit ends up as an angle measurement in the sensor, as shown in the following figure:

The different angles give you an indication of the distance from the object. The sensor turns these angle measurements into a voltage that you can sense to determine the distance. Unfortunately, the relationship between the output of the sensor and the distance is not linear, so you'll need to do some calibration in order to predict the actual distance and its relationship to the output of the sensor.