@brunofporto I had seen they had made something similar, though I also saw earlier in the post that it was susceptible to dust, and I presumed this was to do with the sensor. Surely monitoring voltage output by a motor would be simpler? I have no clue whether there is any way of reading a dc voltage input however. I simply had this idea because I was looking at anemometers for the raspberry pi, and saw one that worked in this same way. As far as I can recall, a motor's rpm has a linear relationship with voltage put in. Presumably the inverse is true for the voltage output, with the rpm put in.

Just ordered my duet this morning for an idex printer build. Definitely interested in a filament laser sensor, if there are spots for any more beta testers in the future. I would also like to put forward a design for a different type of filament sensor, using not lasers, nor ultra sound, but an electric motor. Would it be possible to mount a very small electric motor, and a wheel to rub up against the filament, and then read the voltage output? Surely if this was done correctly, it would allow you to read everything necessary, with no calibration required. Again, I'm just thinking, and haven't done any testing, but in principle, a zero voltage reading would indicate either a jam or that the printer has run out of filament, a sudden dip in the voltage would indicate grinding, and the overall voltage could be used to monitor the flow rate. It does occur to me for better accuracy, more than one motor would be ideal, but I don't see why this would be such a problem. The only other issue I can identify is that this sensor would be very large compared laser sensors, and therefore harder to install in a printer.