Robotics Infra-red sensors
Infra-red sensors work in the same way as light sensors 20210524205224 but they operate in a frequency band that is not visible for the human eye. They are very commonly used in robotics because the modulation of the light is very easy to achieve, and because the are less prone to interference.
Infra red sensors are used in a break-beam mechanism with motors to keep track of the rotation of this one.
Modulation
Modulation of light is achieved by rapidly turning on and off the light, transforming the frequency to a particular one that can be used to code information.
Notes References
20210514183815 INDEX - Robotics
20210523205724 Robotics Simple Sensors - Basics
20210524205224 Robotics Light sensors