Ender 3 Filament Runout Sensor Microswitch Holder

I needed a filament runout sensor that was as small as possible to fit between my filament guide and extruder. The microswitch I am using is https://www.amazon.com/dp/B00MFRMFS6/ref=cm_sw_em_r_mt_dp_U_7ySfEbZ968ZSQ

I followed this guide for setting it up:
https://www.youtube.com/watch?v=gwHpXaj_6xE&t=231s

You can also wire it to OctoPrint (see the one I remixed for good instructions).

I would suggest turning off any auto filament eject past a few mm as it can jam against the roller.