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Still rather crude, but it works pretty good.
Two encoders, one measures actual filament movement, the other movement of hob drive roller.
Arduino compares two and sounds buzzer if slip is detected or out of filament.
Displays amounts moved and % of "slip"
That is all it does currently. Plan on adding ability for it to stop/pause machine.
Could also measure actual filament movement for calibration purposes or even "auto" adjusting machine speed, etc. on the fly.
Plan on adding sd card to log data from entire print for further analysis.
Should also add a force sensor in bowden tube to measure "back-pressure"... that may be insightful for tuning best print temperature for each filament.
I also built this to test the many different hob designs I have.

You could also build yourself a hall-effect sensor that could be used to measure the filament diameter in real-time, but you'd have to modify the firmware to take advantage of that.

g.

geneb wrote:You could also build yourself a hall-effect sensor that could be used to measure the filament diameter in real-time, but you'd have to modify the firmware to take advantage of that.

g.

I like that idea, the more data the better.
How would a hall sensor measure filament diameter?

The arduino that is measuring movement could also gather diameter data to calculate speed or flow tweaks as printing! Hmmmm I like that.

If you want a completepy plug and play solution,

You could disconnect the motor from the origi al printer and read the values of the 4 wires with your setup. Then drive the motor according to demand but compensated for filament thickness.

In an ideal setup you would also measure the length of the bowden tube and move motor according to the diameter of the filament which has reached the nozzle using a controller such as a smith predictor. Ofcourse you would also want to measure the filament in 2 axes if you were really a perfectionist.

You'd build yourself a diy hall-effect sensor along the lines of this: http://www.simpits.org/geneb/?p=299

You'll then use light spring force to pinch the filament between two small bearings. One fixed in place and one on the end of an arm that is attached to the input shaft of the hall effect sensor. When you first set it up, you can "calibrate" it by using a 2mm machined gauge to find out what value the analog in provides at that position. (The hall effect sensor will provide a 0..5v output as the magnetic field from a neodymium magnet rotates around it. If you get the data sheet for the part I list in the article, you'll see how it works.) That will give you your "max" read on the input. Then allow the two bearings to touch, and that'll be your zero reading. use the map() function to translate that range to a 0..2mm dimension. Note that you'll have to make the firmware smart enough to know that the sample position is x mm away from the nozzle and only adjust when that point is due to actually be extruded through the nozzle. THAT is the tricky part.

g.

or your could just buy a cheap micrometer that has a serial out and use it to tell you the diameter.

http://www.soliforum.com/topic/3256/fil ... ng-device/

bubbasnow wrote:or your could just buy a cheap micrometer that has a serial out and use it to tell you the diameter.

http://www.soliforum.com/topic/3256/fil ... ng-device/

That is another cool solution that I like a lot!