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Here's a thought;
Slicers estimate the actual LENGTH of filament needed for each print, typically in mm.
It isn't REALLY DIFFICULT to estimate what is left on the reel and decide whether it is a good or bad idea to start a print with what is left.
Given the cost of a kilo or a pound of filament, the last few feet of filament is probably worth pennies - so,

WHY ?

This could work and also help to adjust flow rate based on filament diameter.

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

If the computer is controlling it, seems the computer would be "surprised" by the printer going into pause. I don't know how the software would handle it.

If it's printing from the SD card, does a G-code pause work? If so that would be excellent.

Did some first tests on capturing the messages sent by repetier host to the printer and back and i think it should be doable.
When I have time I will try to hook up a teensy in between the computer and the rambo. But first I'm busy with my upgrades (e3d v6, enclosure and building a filament extruder for making my own filament)
I don't know if this would also work if you are printing via sd card.

Also I found this:
http://www.thingiverse.com/thing:454584

I would take a filament thickness sensor over a simple "out of filament" alarm any day. I know there is some minor work being done to make firmware adjust flow rate based on reported filament thickness. Would be great for dimensional accuracy. AND, it would work as an "out-of-filament" alarm, too!

The issue you'll have trying to do this with an extra device is that repetier needs to see a largish number of segments ahead in order to be able to motion plan, so at the point you decide to pause it will already likely have 16 additional moves in memory, and it will continue to run through them until it runs out.
The firmware change probably isn't very complicated, there is already a pause function in the firmware.

Has there been any movement on this? I'm surprised I haven't seen anything but old threads.

You may be interested in the Duet3D filament monitor that is currently in beta. It measures movement of the filament - both forwards and reverse - and transmits that to the controller electronics. Then the main firmware compares the measured filament movement with the amount commanded, and triggers a message and a pause if the difference exceeds the configured tolerance. So it not only detects filament runout, it also detects the extruder drive not pushing enough filament through, which can be caused by too much back pressure from the nozzle, or the hobbed shaft jammed with plastic.

More info at https://duet3d.com/wiki/Duet3d_Filament_Monitor. There are currently some free filament monitor kits available for users who design mounting pieces to for them on particular printers. See the forum at duet3d.com for details.

I was hoping there would be something specific to the Rostock Max. I'm capable of firmware work, but would need to port the patch for each upgrade. In addition, I'd need to dig into the internals to find an available pin, and so forth. Maybe its not as difficult as I'm imagining, but if it were easy, I'd assume someone would have already implemented it.