Line detection sensor that is used in line follower robot is usually based on the principle of light reflection to distinguish the color line with the background. In the dark color of light absorption is greater than that of white light reflected to the sensor becomes smaller.
The position sensor to track the trajectory and the example
Light used for the introduction of the line is usually visible light and infra-red. Sensors for visible light commonly used are LDR (Light Depending Resistance), while for the infrared light is a transistor and photo diode (photodiode). Sensors placed at the bottom of the frame to hang the robot, so that its position can be located just above the track that will be read.