Tevo Little Monster Filament Detector

A simple filament detector that pauses the printer and waits patiently to be fed more filament.

The instructions I've provided are for a Duet-powered Tevo Little Monster. Perhaps someone can comment on how to work with the stock Smoothie. Here's a head start: http://smoothieware.org/switch#pause-when-out-of-filament
and
https://www.thingiverse.com/thing:2939019

**Tevo LM Filament Guide v4 - Detector.stl** - Trimmed .5mm off the diameter and fillet the front so it should be easier to sna