The screen itself consists of eight identical modules with 8x8 RGB LEDs each, resulting in a full-color (24 bit per piel) screen with 32x16 pixels (almost HD :P). The PCBs are homemade and soldering them took me quite a while... but I guess it was worth it :)
Every module is controlled by an Atmel ATmega48 with three 8-bit PWM channels - one for each color. Therefore massive multiplexing is needed to drive all 64 LEDs. At first I had doubts if this setup would be bright enough, but as you can see, brightness is ok (although today I would choose an controller with more PWM channels but this thing is actually three years old and I didn't find a good one back then).
The controller is clocked with 8 MHz, per pixel 256 clock cycles are needed for PWM and some more for switching the active pixel. Nevertheless this results in a refresh rate of round about 400 Hz, making it absolutely flicker free.
All eight modules are connected to an SPI Bus, which is responsible for transferring the image data. Since a standard PC hasn't a SPI interface I took an USB to serial converter and used another microcontroller as serial to SPI converter. The serial port runs at 460kbaud resulting in a maximum frame rate of 37.5fps. This is ok but today I would take an Controller with built-in USB... :)
On the PC a small programm generates the video data for the screen. On the images you can see an audio spectrum. I have a few other visualizations (scolling text, a simple pong game, even videos are possible but scaled to 32x16 pixels most videos loose their details ;) ) but the audio spectrum is my favourite.
Here's a video showing it in action: