Quoted: Arduino is an open-source electronics prototyping platform based on flexible, easy-to-use hardware and software. It's intended for artists, designers, hobbyists, and anyone interested in creating interactive objects or environments.

I just met Josh who is teaching this series of micro-controller hacking classes at 911 Media Arts Center. He'll be using the Arduino micro-controller and scavenged parts from ink jet printers!

This seems pretty clever - controlling N*(N-1) LED's from just N available output pins from a micro-controller (as opposed to N led's for direct drive, or (N-A)*A for row/column addressing).

However, with a decoder, seems like you can get exponentially higher than this: 2^N is possible for a clocked circuit which can latch the LED address (but the chip count goes up).

So for 5 pins:
Direct: 5 LED's
Row/Column: 6 LED's
CharilePlexing: 20 LED's
Decoder: 32 LED's

Finally, you can can an "infinite" number of LED's driven through a serial interface. So - with "1 pin" you should be able to drive a clocked shift register to control a very large number of LED's (e.g., with 1 100 element shift register, full the registered rapidly in burst mode, and then pause to let a capacitor charge next to each LED).

I wonder if you can buy 3-wire modular LED's with built-in shift register and capacitors so you can hook these up like fully controllable "Christmas tree" lights.