Filament runout sensor for Ender3

This is yet another filament runout sensor

It is my remix of this [design](https://www.thingiverse.com/thing:3035553) for my Ender3 and keeps a clear view of the filament.

It is merged with this [sensormount](https://www.thingiverse.com/thing:3674501) which provides a solid fixation.

Instead of an optical sensor I use a small magnet on the lever and a reed contact - e.g. this kind of [door switch](https://www.amazon.com/xin-sheng-MC-38B-Embedded-magnetic-Security/dp/B077SFDTJF/ref=sr_1_2?dchild=1&keywords=Magnetic+Gap+Switch&qid=1604240006&sr=8-2)
Filament runout is simply detected when the lever with magnet falls down and activates the the reed switch.
Two small pieces of PTFE tube (6mm outside diameter) ensure smooth guiding of the filament.
Disabling the sensor - for e.g. filament change - can be done easely by flipping the lever backwards.
The hole in the middle of the lever allows 4mm retraction of the filament before turning off the power of the printer.

The reed