Filament Sensor / Tube Holder for Monoprice Ultimate / Wanhao Duplicator 6

Filament sensor and tube holder for the Monoprice Ultimate / Wanhao Duplicator 6. Fits into the slot on the rear of the printer. Uses an inexpensive [optical endstop](http://www.ebay.com/itm/321996984829), attached with two M3 screws. A [plugin for Octoprint](http://plugins.octoprint.org/plugins/filament_sensor_reloaded/) pauses printing when the sensor detects that filament has run out.