A photo interrupter, also known as an optical switch, is a sensor that detects the presence or absence of an object passing between an infrared (IR) LED and a phototransistor. When an object blocks the light path, the phototransistor stops conducting, which can be interpreted as a signal change by a digital input. This allows for non-contact detection in various applications such as counting, position sensing, and speed measurement. A common implementation involves connecting the phototransistor to a microcontroller’s digital input pin. The microcontroller then monitors the pin’s state to determine if the light beam is blocked.
The ability to perform precise, non-contact detection makes this method valuable in industrial automation, robotics, and consumer electronics. It offers advantages such as immunity to electrical noise and wear, which are often present in mechanical switches. Historically, this type of sensing technology evolved from early optical detection methods, gaining wider adoption with the miniaturization and cost reduction of electronic components.
