The ultrasound idea from Markdnd is interesting, but isn't it so that ultrasound transducers have problems with linear movement? They detect rotation (not possible in this scenario) and radial movement, but an object passing by in a straight line is not so good.

I might be wrong, but believe that an ultrasound solution would require a mechanism to "wobble" the filament on its way past the transducer. If that is accomplished, then a disc type transducer might work. These are used in many applications, e.g. string music instruments, and are available in diameters down to about 10mm. They are also very thin and cheap.

Why do we want/need a filament sensor?

Me personally, to stop the print if the flow of filament stops for any reason, e.g. due to a clocked nozzle.

If the sensor can measure the exact length of filament extruded, that would be totally cool and open the door for dynamically maxing out the feeder speed for any filament. That would be a dream come true…

But, how about making that a requirement for filament sensor v2?

For starters, detection of that blocked nozzle can probably be accomplished with less fancy measures, and likely cover the immediate needs of most users. How about adding a timer? If no movement is detected within 1-2 seconds of the stepper engaging, then something might be wrong. This should greatly reduce the sensitivity requirement for any type of sensor. Due to the normal pressure between extruder and nozzle, a short period of time should have no significant impact on the ongoing print, as filament will still be flowing.

I was thinking about installing these for the X,Y motors: https://www.ebay.de/itm/172980421084?var=471745181900

The diodes will "eat" at least 0.5V, but that can be compensated.

Any thoughts?

I'm wondering if detection can be improved by adding a reflector on one or both sides of the filament channel?

You surely do not want the laser to reflect on itself, but the beam is hitting a curvature (round filament) and that means reflection to the sides. Maybe it would help to pick up those reflections and send them back. Thin stripes of aluminum foil might do.

Quick pencil drawing…

Not sure why the image doesn't load, but the link works also

Hi, I'm new here

I have a Duet Ethernet and accessories ready to be installed, but am still working on a new printer in which to use it, so no actual experience yet with this no doubt amazing controller.

I will definitely want to install a filament monitor, and the laser option seems like a very elegant approach. I already have a simple switch installed at the far end of the tube, to set off an alarm in case the filament runs out, and another closer to the extruder that stops the print if no new filament has been loaded. However, stop of movement due to a blocked nozzle is a bigger concern.

My reason for this post is a question related to complexity of the filament monitor; What is the added value of monitoring retraction and re-priming?

Both are fast-moving actions and unlikely to cause a blockage. If there is a stop of movement, I believe it would have happened already during normal feeding of the filament. I find it highly unlikely that retract/re-prime will trigger an alarm before normal movement and, even if it does, normal movement alarm will immediately follow. Am I overlooking something?

Another question; I would like to keep my simple switch as it is easier for me to resupply filament before it hits the extruder. Can a simple switch work in parallel with the filament monitor on a single end-stop port?

Thank you for all of your hard work. It is not the cheapest solution, but one that is extremely well supported and that makes all the difference.

Michael