Here's how it typically works:

Optoelectronic Sensor: The RPR220 module contains an infrared (IR) emitter and a phototransistor (light-sensitive transistor). The IR emitter emits an infrared light beam, and the phototransistor detects the reflection of that light.

Reflective Detection: The sensor is typically positioned in a way that the emitted IR light beam is directed towards a surface or object. When this beam of light encounters a reflective object, some of the light is reflected back toward the phototransistor.

Output Signal: The amount of reflected light received by the phototransistor changes based on the presence or absence of a reflective object. This change in light intensity is converted into an electrical signal.

Threshold Detection: The sensor has a threshold level that can be adjusted. When the reflected light exceeds or falls below this threshold level, the sensor's output state changes.

Digital Output: The sensor typically provides a digital output, which can be in the form of a logic high or low signal, depending on whether the threshold is met or not.