Ever try signing your name with a mouse or a trackball? Not so easy. You could buy a graphics tablet with a pen. [Rahul Ramakrishnan] has a different approach. He took two 10-turn pots, and attached some strings and a washer. A pencil goes through the washer, and a BeagleBone Black reads the pots to determine what it is drawing on the paper. A couple of retractable badge lanyards keep tension on the string.
This ingenious design would be easy enough to replicate with any microcontroller that can read the two pots. The only awkward part is the need to press a button down when you want the device to treat the pencil as down (see the video below). It would probably be easy to rig up some switch on the pencil to make operation a little smoother.
On the computer side, [Rahul] includes HTML code that uses the Processing.js and BoneScript libraries to capture the input drawing. Real tablets, of course, don’t work this way, but it is a very simple way to obtain X and Y coordinates of the pencil. We’ve seen BeagleBones at the heart of logic analyzers and even in a redesign of the Super NES, and the board is known for having a lot of horsepower while still having capable real-world I/O.