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 t