The Edison robot can detect whether the surface is black or white with its line tracking sensor. It is possible to write a program that follows a black line. https://t.co/R3SbqT4ESE pic.twitter.com/JEQKSP7bUr

— Yoshiyuki Nakai (@yoshiyukinakai) January 30, 2019

The red LED shines light on the surface, and the light sensor measures the amount of light reflected. There is more light reflected from a white surface than a black surface. See also https://t.co/M40SdP3NdT pic.twitter.com/0IUBEjH5cW

— Yoshiyuki Nakai (@yoshiyukinakai) January 31, 2019

Found similar line tracking sensors on the underside of the toy train. pic.twitter.com/EtXlwfgtYp

— Yoshiyuki Nakai (@yoshiyukinakai) January 31, 2019

This was all I needed to do for making the Edison robot follow a black line using EdBlocks, the icon-based programming tool. https://t.co/CO4eb0fUKE pic.twitter.com/fhJH2CJ0fY

— Yoshiyuki Nakai (@yoshiyukinakai) January 31, 2019