Color sensing (as well as detecting empty spaces) settled on IR-based sensors commonly used in line-following robots. You can watch the clock in action in the video embedded below just under the ...

The sensor is really just an infrared photodiode inside of a tube. The diode is connected to an analog input pin on an Arduino. The sensor can be pointed at an object, and the Arduino can sense ...

(InfraRed detector) A sensing device that picks up radiation in the infrared band. Used extensively for still and video night vision cameras, cooled IR detectors can sense the makeup of nebulae ...