TCRT5000 Reflective Infrared Optical Sensor Module
Easily experiement and prototype with the TCRT5000 Reflective Infrared Optical Sensor Module from PMD Way.
They are useful for detecting a change of color, which is ideal for line-following robots or if the sensor is close to or then away from something.
An infra-red LED transmits a beam of light which is reflected back to the receiver on the module. Your device/microcontroller etc can then work with the signal from the receiver to determine what is happening.
Using the module, you can connect to the analog output from the sensor, or use the potentiometer to create a set digital on/off point - ideal for line-following robots where you need a binary result of yes/no.
For more information, download the datasheet (pdf).