The original plan was to use a mouse sensor like we saw here: http://moddersandrockers.com.
We tried this and destroyed three mice but to no avail. Finally we settled for just using the mouse's scroll wheel to slide the fiddlestick over. We then used three buttons and combinations thereof to choose a tone. By sliding over the wheel the violin produces sound.
Using Pure Data we channeled the serial read from the Arduino to Midi-notes in Ableton Live. There we coupled the incoming midi-notes to sounds.
The violin body was build using a laser cutter, for the top and bottom, and mill for the thickness.
You can download all required files here: http://jorgoscoenen.be/arduino-violin.zip