A pair of high resolution stepper motors in an enclosure designed to fit over the lower portion of an Etch-A-Sketch so that the two knobs can be controlled by the motors. Brackets at either end of the device would fold down to clasp on to the EAS.
Software (probably on a P.C., but possibly on the
device itself) would accept an image as input, convert it to grey scale or line art (as appropriate) and print it on the Etch-A-Sketch.
I'll leave I/O to the reader, since I don't think it really matters. Cheaper is probably better, since we're talking novelty here.
As a completely mechanical device, the EAS would be the slowest part of the whole operation. Still, I think an image could be printed in a reasonable amount of time. Since greyscale images will require more "pixels" they'll have to be down-scaled and will probably look fuzzy up close.
Imagine the market for "WORM" Etch-A-Sketches!
{Note: I posted this idea a few days ago and someone pronounced it Baked and provided a link. I opened the link and a cursory examination caused me to agree. However in the intervening time I've revisited the link and understand the item being discussed to be only half of what I'm proposing (an EAS plotter). In fact, my device is independent of the EAS altogether. The other, more important, part of my idea is essentially a printer driver. This allows you to render any content, not just what's input through a joystick or vector plotting program. Does this make the idea Baked? Am I protesting too much how good my idea is? I'll leave that up to you.}
{I can't remember who posted the link originally, but I wanted to let everyone know I wasn't trying to pull a fast one}