Filament Width Sensor Prototype Version 4

### What is it?
This is a prototype for an optical sensor that measures the width of plastic filament in real time as it goes into a filament extruder or 3D printer. It is prototype #4 (other 3 are on Thingiverse as well ).

For filament extruders, the measured width can be used as feedback in the extrusion process. Industrial sensors that do this are very expensive, even used. So this is a lower cost do it yourself option.

For 3D Printers, the idea is that with a real-time width measurement the 3D printer could compensate the extruded flow for changes in filament width. Also if there is variation between spools of filament, there is no need to calibrate for that when slicing. The g-code becomes independent of the specific filament diameter. These days, commercial filament is manufactured to very high tolerance. However if you make your own filament, it might be useful.

Its called a prototype, because it's something you may need to tinker with to get integrated with your so