Bi-Directional Filament Sensor

thingiverse

This sensor reads filament bi-directionally instead of just one way. You don't have to pull a lever to load or unload when the printer detects a filament runout, and it can also push back the filament through this sensor during unloading. There are two versions: ball type and flat type. If you have an 8mm metal ball bearing, you can use either one. The ball end is included, but in my testing, it had friction when the filament pushed against the printed ball end. The flat type has a smooth path since it's designed for printing small parts.