Photointerrupter is an optoelectronic sensor consisting of an LED and a photodetector (usually a phototransistor or photodiode), arranged in a U-shaped housing. The object to be detected passes through the gap, interrupting the light beam.

Key Components:

• IR LED: Emits infrared light across the slot.
• Phototransistor/Detector: Detects the presence or absence of light.

Working Principle:

When no object is present, light from the LED reaches the detector, keeping it ON. When an object passes through the slot, it blocks the light, causing the output to switch states.

Applications:

• Object detection
• Speed sensing (e.g., encoder wheels)
• Position sensing
• Printer paper detection
• Slot-type switches

Common Types:

• Transmissive (slot-type)
• Open-frame vs. shielded
• Analog vs. digital output variants

Circuit Tips:

Use a current-limiting resistor for the LED (typically 100Ω–1kΩ). Add a pull-up resistor on the output if using an open-collector phototransistor.