Filament Width Sensor - Prototype 2

Note: Prototype 3 is available: http://www.thingiverse.com/thing:454584

Also, I am selling a limited number of pc board kits for prototype 3 at:
http://owi.storenvy.com/

This is a prototype for an optical sensor that measures the width of plastic filament in real time as it goes into a 3D printing extruder. It is prototype #2. The idea is that with a real-time width measurement the 3D printer could compensate the extruded flow for changes in filament width. This version includes a custom designed pc board as well as a housing. A version of Marlin is modified to use the sensor data.
I added some pictures of the sensor in operation. The sensor outputs a voltage in milimeters (3v=3mm) that is shown on the voltmeter. There is also a video at http://www.youtube.com/watch?v=HHjDG1jdv5o.
I made some changes to Marlin to read the filament diameter real-time and compensate the extrusion rate. Picture added.
Latest update: I made some refinements to the case design to improve the screw holes and fit of the PC board (try 3.3.stl)
This prototype sensor is now part of the design of the latest Lyman extruder. I worked with Hugh on building the controller and incorporating the sensor into the system.
http://www.thingiverse.com/thing:380987
I added the files for the Seeedstudio order. I also updated the schematic to reduce the parts (MCU uses internal oscilator, no external xtal required). The Codewarrior Eclipse project is also included.
8/2/14 - I added a photo of a sample print showing control on and then shut off mid-print. The filament has a variation of at least .5mm roughly every inch. This is using some new Marlin code I am working on that implements a delay to the sensor readings to handle the transit delay caused by the filament sensor being a fixed distance upstream from the extruder nozzle.