Marcus wrote in to tell us about his latest ping pong ball electronics project, the Gravitron. In half of a ping pong ball, he’s crammed 12 LEDs, an accelerometer, and an ATmega168 for a brain. If you pick it up and tilt it, it will light the highest LED. It’s sort of poetic.
If you’re as impressed as I am with his efficiency of space, check out Marcus’ other ping pong ball experiments on his blog.