Optical Bedlevel sensor for K8200/3Drag

There are several types of bedlevel sensors around. With the K8200 or 3Drag you are constantly running out of I/O-Ports and so some of those sensors are a real challenge (e.g. those with servos).

Furthermore I did not want to install more wires and thought, the three available should be sufficient.

So, here is a optical bedlevel sensor, based on IR reflection. It includes a microcontroller to make the measurements based on IR pulses and eliminate environmental IR (e.g. the heated heatbed).