The tread gauge is cheaper, but more complicated to modify. The hardest part to this style is keeping the bearings perfectly aligned, because if one is slightly crooked the measurement will change if the filament moves sideways. The pcb in the picture has an ATtiny on it to read the caliper signal and output width and length. I'm still trying to decide if I want to keep the ATtiny so it is a standalone device that outputs a measurement, or pass the raw data through and have the winder controller interpret it.
This is the circuit I use for the level shifting- http://www.instructables.com/id/Reading … and-Power/ . I have a zener diode to drop the 5v from the arduino to 3.3v. There is a hall sensor at the edge of the board above a 2mm magnet stuck to the lower bearing for counting rotations. How are you measuring the filament length on yours?
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