Is there a way I can track how much filament is left on a roll?
Either an add-on sensor I can build or software that will track how much is used vs how much is supposed to be on the roll?
Have a Prusa Mk4 and it’s working ok so far but been having trouble with very long prints so trying to figure out if my rolls have enough left
Not really.
You can weigh it, and the slicer gives you an estimate of how much volume/mass is needed.
But it’s not too difficult to pause a print. Unload what little you have left and reload a new roll then resume the print.
That’s assuming you have another roll of the exact type/color filament you are using ready to go.
You could weigh it, but you’d have to know the specific spool weight. Some spools have a scale on the side giving a rough estimation on how much is left in grams, but you could only do this yourself if you knew how much was on it to begin with (calculating the volume left and printing a scale for example). Other than that… No. Have a new spool ready and wait until the old one is empty.