* all open source and hardware,
* cost < £100 excluding projector and computer,
* detects can's nozzle pressure and distance from the screen,
* models paint dripping if you move too slowly!
* this instructable is quite high level, but please let me know if I've missed something important,
* the computing setup is for Linux. If you get it working on other systems, please post your instructions!
Skills you'll need
* wood working to make the wooden rear projection screen,
* electronic circuits and programming Atmel AVR micro controllers (or arduino),
* be able to install some libraries on your computer to allow processing to talk to the wiimote.
Step 1: How it works
* The wiimote sends the X and Y co-ordinates of the can to the computer via a bluetooth radio link.
* The computer is running a simple painting program that uses a projector to "paint" the lines as you draw with the can. It also takes care of mapping the wiimote camera to the screen using a 4 point calibration system.
* The spray can also detect its distance from the screen and the nozzle pressure: the further you are away the bigger the dot drawn, the harder you press the nozzle, the more opaque the paint dot becomes.