ANET A8 optical z probe (BLtouch like with servo)

My big inductive probe suddenly died (led always ON) after only 6 months of good services... I ordered a new one on ebay from China, but as I woudd have to wait 4 weeks or so I decided to build an optical one which to my big surprize seems being really very accurate.

The idea is to make it as minimal as possible with just a flag attached to a metal pin moving between the fork of an optical IR sensor. The design makes the pin fully free to move under gravity and a cheap RC servo motor will park and release the probe .

After few days operational, I will for sure keep the optical one which gives several advantages:
- lighter (the inductive weights 80g)
- closer to the nozzle
- less intrusive, once retracted the pin is nearly at the level of the bottom of the heatblock which gives the opportunity to clean the nozzle easily
- very accurate
- it senses the top of the glass and not under the glass as inductive probes do
- it is cheap : you can get it for less than 3€ ...

I wanted to get the probe as close as possible to the hot end and succeeded to hide it on the back left corner just behind the left fan.

It is working very well, here is a repeatability test performed under MARLIN with M48 GCODE::
12:18:09.925 : M48 Z-Probe Repeatability Test
12:18:44.120 : Finished!
12:18:44.120 : Mean: -0.140000 Min: -0.141 Max: -0.137 Range: 0.005
12:18:44.120 : Standard Deviation: 0.001483

As you can see the range is 5 µm, and a standard deviation < 2µm which is better than the accuracy of the other parts of the printer ;-)

see it running here :https://youtu.be/GwbwwtUL2Po

EDIT : for those who like a cover, there is one !

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