Filament Watch

This is part of filament_watch, which pauses or stops OctoPrint if the filament jams or runs out during a 3D print. Code and setup instructions at https://github.com/rllynch/filament_watch.

These STLs hold a "Signswise 600p/r Incremental Rotary Encoder" from [Amazon](http://www.amazon.com/gp/product/B00UTIFCVA?psc=1&redirect=true&ref_=oh_aui_detailpage_o09_s00). The encoder measures the filament being consumed by the printer. If the actual filament consumed is significantly less than the f