Hi,
I've been working on a rotating filament sensor (with a magnet + hal effect sensor).
I've gotten to the point where it seems to be working well and reliable (3 weeks now, on a printer running marlin).
I'm using rubber X-seals to ensure good contact with the filament without adding too much resistance.
Do any of you think it's an interesting device to have ?
It detects both when the filament spool is empty and when the print head is clogged.
I do "a lot" of 3d printing and these 2 cases seem to account for +90% of my failed prints (I often print flame resistant abs and this can clog at times)
I've made a small video, https://youtu.be/DCe-7jBzin0
I posted this on the reprap forum last week but there was zero response 
thx
Bram