Simple Reliable Universal Filament Runout Sensor

There are lots of filament runout sensors out there, but they either don't work with all filaments (optical ones), or tend not to be reliable (mechanical switch ones), or are complicated (multi-part ones), or some of all of the above.

This is a minimalist sensor design that requires only one print and 3 additional parts. Firstly, you'll need a [URBESTAC 250V 5A SPDT 1NO 1NC Momentary Hinge Roller Lever Micro Switches 3 Pins](https://www.amazon.com/gp/product/B00MFRMFS6). You want exactly this switch as the design is perfectly tailored for it so that 1.75mm filament will reliably trigger it.

You'll also need 2 self-tapping M2 12mm screws to fasten the switch in place. Use the two pilot holes and the switch will be perfectly positioned.

Wire up the 3 contacts to your Raspberry Pi GPIO board (pwr, ground and an input line), and you'll never outprint your filament again!