The part list consists of one Arduino, two resistors, and one IR emitter. That’s right, an emitter. When an LED (IR or otherwise) is reverse biased it can act as a light sensor.

Photoelectric sensors detect objects and surface changes using variations in optical properties. Each sensor includes a light emitter and a receiver, with most relying on infrared light. In optical ...

After uploading the IR receive demo included in the library, the Arduino spit out hex codes of what the IR receiver was seeing. [firestorm] wrote these down, and was able to program his Arduino to ...