Reverse Bowden + Filament Sensor Combo with UBBI. For Neptune 4s using LS FanMod.

I've been using SilencedFrost's “Reverse Bowden Addon…”, which features his ingenious UBBI connector.   I don't care for Eligoo's filament sensor after having some issues with it interfering with filament travel.  And I like having the filament runout sensor near to the extruder, wastes less filament.  So this is a simple combo of clogged_nozzl3's Small UBBI sensor and Frost's Bowden adaptor.  It uses a Kailh Black GM 8.0 mechanical microswitch and a 4mm ball bearing to push between filament and the microswitch.

This arrangement should work with Neptune4, N4Pro, N4+, or N4Max.  The "LS Fanmod" is a reduced weight, better cooling (and better looking) printable alternative to the existing Eligoo plastic housing.  The wiring relative to the existing sensor connector is shown in the photos. Splice the wires from that to run down to the microswitch.  The switch is wired to the outer two contacts (so that the contacts close when there is no filament in the path).  The added wire can be strapped to the bowden tube; I also strapped the cable from my Cartographer probe in the bundle.

This has been tested and works well.  But should you need to adjust it for variance in the activation positions of the switch or from printing inaccuracies, you can adjust:

• Should the microswitch not stay open when filament is running through it, you can file the printed surface where the screw holds down the microswitch to push the little button of the switch further against the ball.
   
• Should the microswitch not reliably close when filament leaves the sensor, use a thin razor knife or small file to slightly increase the opening that the metal ball sits in.

You can buy the Kailh Black GM 8.0 microswitch on eBay or Alie, or better, just check that box of old broken computer mice that you pretend you'll fix someday – many of them use this switch inside.  I salvaged one from an intermittent logitech M325.  I got the 4mm steel ball from a skateboard/fidgetspinner bearing.  The screw can be m3 or 4-40 -- use a washer if the head is small.

See the instructions on SilencedFrost's or clogged_nozzl3's model for parts needed and about printing and assembly of the sensor body.  You will need to have supports enabled for my remix.

(I printed with tree supports, automatically applied).