Line follower robots were one of the earliest automatic guided robots. They are able to follow a line marked on a contrasting background, usually a black line on a white surface or a white line on a black surface. Usually the line follower robot works on a closed loop feedback algorithm where the feedback from the line sensor is used by the controller for correcting the path of the robot. The sensors are usually LED/LDR, LED/Photodiode or LED/Phototransistor pairs and the controller is an electronic circuit which executes the desired feedback algorithm. Gear motors are used for driving the robotic wheels.