Filament runout sensor for reverse bowden

This is a filament run-out sensor designed to be inserted on a reverse bowden setup (on the feed-in tube to the extruder).

I designed it for my Muldex 3D printer.
Details about the printer: https://github.com/3dprintingworld/MULDEX

Edit: The “standard” body is designed for 2mm inner diameter tubing. I added a variant for 3mm ones. The outer diameter should be 4mm in both cases.

Edit 18/12/2021: I got a few false triggering events on the “3mm” body version, so I moved the sensor placement 0.2mm up in the body.

Other hardware I used:

• a Panasonic AV38523 switch
• 2 PC4-M10 pneumatic fittings