If you wanted to build a robot that chased light, you might start thinking about Raspberry Pis, cameras, and off-the-shelf computer vision systems. [Ed] of [Death and the Penguin] demonstrates this ably with a simple robot that finds the light the old-fashioned way. The basic circuit relies on a pair of light-dependent resistors (LDR), which are wrapped in cardboard tubes to effectively make their response highly directional. It then crudely steers the robot towards the brighter light between turning one motor hard on or the other, operating in a skid-steer style arrangement. It’s set up to enable PWM-like control, allowing one motor to run at a lower speed than the other depending on the ratio between the light sensors.