Hey - has anyone built a filament sensor?  I searched,

Hey - has anyone built a filament sensor? I searched, but all I can find is instructions to build one that sets off a buzzer if the spool runs low, or one that verifies the filament diameter and prints it on an LCD.

What I was thinking was a pair of solid aluminum rollers with metal bearings being pulled together with a spring or two. These rollers would be wired (through the bearings) to the arduino board. The board would send current through the circuit and if it detects the switch closing (meaning the filament is out) it automatically pauses the print.

Not sure if this all makes sense?

actually, to simplify it, two rollers for the filament to go through with an end-stop type switch that gets pushed if the rollers come together.

Like this? http://tunell.us/

Yes, although that seems overly complicated for what I’m thinking. It seems like a simple normally open switch would do the trick with the programming added. I might play with this, thanks for the pointer.

If I were going for dead simple, I’d go with a loose tunnel of low-friction plastic and a normally-open microswitch with a roller tip. Is there a wavelength that all/most filament is opaque enough to?

Calculate the linear density of your filament based on the average diameter of it and the mass. Then every time you do a print, substract the amount used (as shown in the slicer) and substract it to the spool. I think that is how xyz does it