I recently had to build an infrared close proximity sensor ... at D8 of the Arduino Uno (TP2). See a couple of random oscillograms below. Thus, the infrared emitter transmits bursts of 38kHz infrared ...

The larger versions of this trick pretty much all use ... sensor. This has neither. The black PCB seen to the right of the robot is an IR reflectance sensor. It shines an IR led at the floor ...