Rudimentary Filament Runout Sensor

This sensor uses a tiny (20mm) Omron (D2FC_7) microswitch and precision print enclosure to detect filament runout at very low cost. As the filament presses on the microswitch actuator directly, it's basically friction detection subject to wear but should last years as the microswitch chosen is used in my Logitech Mouse (and many other quality devices), it has performed thousands of press/release cycles over many years without issue.

That being said, friction over time does result in wear, so allow for swapping out the microswitch in time. I'm looking into using a lever version which should last longer but have also a friction-less version (optical) is in development...