Cool project from Nat Friedman, he writes…

Last month while he was visiting, my friend Rony and I built a picture frame that can display three images on a single piece of paper.  Two of the images are mapped to the red and blue channels and linearly combined, and the third image (the word MARCH in the video above) is projected onto the paper from behind using a stencil.
The stencil under construction.
A microcontroller controls a set of red, blue, and white LEDs that light the picture, selecting each image in sequence by turning on one set of LEDs at a time.  Rony built the frame itself out of the black foam-core that architects use to make models, and it is really gorgeous.

This was my first project using an Arduino and I was completely blown away by the platform. The Arduino is an Italian-made open-source electronics prototyping platform. Ours was a very simple Arduino project, just fading in and out some LEDs (you can get the code here), but the platform can do a lot more. We used a Duemilanove (”2009″) board (pictured below) which has many digital input/output and analog input pins.

The board comes with a very simple IDE based on Java, Processing, and avr-gcc. You code for the device in C and a single click reprograms the onboard Atmel microcontroller over a USB cable. The documentation is excellent and the platform is extremely easy to code for; it only took us about 15 minutes to get the basic functionality working for this project. There’s a great serial interface you can use for printf-style debugging; just use Serial.println to send some output to your PC while your code is running. And Arduinos are extensible via a series of pluggable shields that can provide additional functionality like GPS, WiFi, and touch-screen support.

It really is the perfect starter platform for hardware hacking, and if you have any interest in this sort of thing at all, I strongly urge you to go buy the Arduino starter pack from adafruit industries right now.