SparkFun SEN-09299 Photo Interrupter GP1A57HRJ00F
This sensor is composed of an infrared emitter on one upright and a shielded infrared detector on the other. By emitting a beam of infrared light from one upright to the other, the sensor can detect when an object passes between the uprights, breaking the beam. Used for many applications including optical limit switches, pellet dispensing, general object detection, etc. Gap width = 10mm
Want this in a kit with a 3 pin header, 220 Ohm resistor and a breakout board? get it here.
Get the breakout board here