Closed Loop Filament Sensor

This is my version of a filament sensor for 1.75mm filament. If it is supported by the printers software, it can be used for building a closed loop monitoring system. This means, the printer calculates the amount of filament which should be used and it gets feedback how much has been really used. This way, the sensor can not only detect a simple out of filament condition, but also most kinds of filament jams or clogged nozzles.

Be aware, that this is still a work in progress! So far I've tested it only on my desk, not in the printer. Next, I have to find out how to modify Marlin for doing the job...
I will update this description as soon as it has been tested in the printer.

If you like to give it a try you need these parts:

- 1x optical endstop: https://www.aliexpress.com/item/Free-Shipping-Optical-Endstop-Light-Control-Limit-Optical-Switch-for-3D-Printers-RAMPS-1-4/32246136817.html
- 3x 686ZZ ball bearings.
- 1x small Lego Tire 14 x 6 mm, Part Color Code: 4246901, Item No