Reverselay Toolhead Runout Sensor

This design only works when using an MMU as a synced extruder follower to a direct extruder toolhead.

Please read this page to understand the concept of an extruder follower and how this sensor works:

https://github.com/Annex-Engineering/Belay

Here is a toolhead runout / filament detection switch compatible with all direct extruders that have a collet / ECAS at their entry point for MMU systems.  This switch is inspired by annex belay, and it adds just a spring to the original design to make it work.  The sensor can be placed anywhere in the reverse bowden path.  The idea is that when the filament fed by an MMU hits the top of the gears on the direct extruder, Reverselay (the name of the design) has a small amount of space for the filament to expand pressing the switch to its ON position.  

Depending on the length of the reverse Bowden tube you can experiment with using one, two or three springs stacked (I am using two springs) to make sure consistent clicking of the switch ONLY when the filament bottoms out on the top of the gears of the direct toolhead extruder.

Additionally, having pressure on the filament as it is fed to the direct toolhead extruder may help keep dual direct gears loaded, which may translate into better layer stacking.

The additional pressure also helps increase flowrate to the extruder (as it is being assisted by the follower extruder).

Please read the method of operation of this sensor in the original Annex Belay GitHub page (linked here).

The only addition to the original BOM is one or more springs (nestled together), the longer the reverse Bowden tube, the more springs that will have to be ganged to make the design work reliably:
 

https://www.amazon.com/gp/product/B076LRMLLL