This Line Following Robot sensor or surface scanner for robots is a very simple, stamp-sized, short range (5-10mm) Infrared proximity detector wired around a standard reflective opto-sensor CNY70(IC1). In some disciplines, a line following robot or an electronic toy vehicle go along a pre drawn black line on a white surface. In such devices, a surface scanner, pointed at the surface is used to align the right track. IC1 contains an infrared LED and a photo transistor. The LED emit invisible infrared light on the track and the photo transistor works as a receiver. Usually, black colored surface reflects less light than white surface and more current will flow through the photo transistor when it is above a white surface. When a reflection is detected (IR light falls on the photo transistor) a current flows through R2 to ground which generates a voltage drop at the base of T1 to make it conduct. As a result, transistor T2 start conducting and the visual indicator LED(D1) lights up. Cap...