Actual version is running very well, but it is hard to replicate, because of the calibration : 

this part of the build is not documented, because I don't really know how to replicate the calibration process (the visual tool I used back in the days is overly innacurate. It worked for me once but I could not release it)...

So I decided to build a new version of the device, with no need for calibration.

Still bluetooth, still battery-powered, but without the usb-related fonctions (joystick, serial output).

The new device will only have a 9-dof IMU, a microcontroller, a bluetooth transponder, a status LED and a 1000mah lipo and charging circuit (providing +20h running time). Using a custom, real PCB, and a 3d printed enclosure built to fit every headphones on the market (using rubber bands of course :D ).

Parts are currently on their way, please wait 3-4 weeks for them to get home, and me to build a beta-version (alpha is working already)