Thanks Tony, I'm taking it off and looking at it now.

Okay so the mount broke, it's too thin, in the area of the ring that attaches it to the Nimble under the drive cable. So I have added a spar to see if it helps and will try it again. Will post it if it works.

Okay so i gave it test, reached in and undid the idler. After around 3-4 seconds it went to pause and displayed:

I re-tensioned the idler and hit resume and maybe missed around 1/4 of a layer of infil on a 20x20 cube, so quite recoverable.

It does work.

The filament monitor uses a relatively simple protocol to send the angle to the Duet every 50ms or so. I have not written up the documentation for the protocol yet, once I do then you could use a MCU to interface any encoder to the Duet using this protocol.

moved to the filament monitor forum. More to follow about the beta tests.