A photointerrupter is basically a photosensor that combines the transmitting and receiving parts in a single package. An infrared emitter is usually used as the transmitting element while an infrared detector is employed as the receiving element. The detector element is usually shielded to ensure that it only detects the beam from the coupled source. The two elements are arranged in such a way that the detector is capable of detecting when an object gets between it and the source.

Gallium Arsenide Infrared LEDs are the most common light sources used in photointerrupters. Shielded NPN silicon phototransistors are the commonly used detection elements. In order to operate as on/off switchers and to detect obstacles, most photointerrupters employ the transmissive technology. The design specifications of photointerrupters differ from one make to another mainly depending on the intended applications. Some have optical encoding capability that enables them to detect direction and speed. Application specific photointerrupters have special features that are added to suit the needs of an application.

Photointerrupters have diverse uses in various industries. They are employed in various applications including pellet dispensing systems, office automation equipment, ATMs, optical limit switches, and general object detection to name a few. Their applications have been growing exponentially with growth in industrial automation.