I recently had to build an infrared close proximity sensor that could tell if something was dropped in a parcel delivery drop box. After some searching, I ...

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.

The sensor is intended as an alternative to pyroelectric sensors or PIR detectors in home automation, building automation, healthcare, security and industrial applications. Typically human presence ...