Electronic versions of the classic Etch-a-Sketch aren't particularly unusual, but so far this is the first time we've seen Arduino-controlled knobs with physical resistance and a proper shake-to-clear integrated into such a project. The Hack-a-Sketch takes a Lenovo ThinkPad laptop and adds the usual two Etch-a-Sketch rotary knobs; this time, though, they're hooked up to two potentiometers which control the onscreen drawing.
Video demo after the cut
Built into the knob board is a mercury switch used to trigger the screen-clear action. As with the original toy, shaking the laptop harder clears the screen faster and more completely; of course, in the original there was less chance of hard-drive damage after particularly vigorous shaking.
Project builder Michael has released the source code for the Arduino, and so if you're tempted you could build one yourself. Using a Tablet PC or an old UMPC would mean you could create something that looked more like a proper Etch-a-Sketch, too.