This is a project inspired by Hack-a-Day's networked graffiti wall, which they call the large low resolution display. It runs from their business card server. I built a mini version of this project, which is 4x4, uses white LEDs, and runs from my computer's parallel port. It gets its power from it, as well as the signals.
How it works: The parallel port has 8 outputs. These can be pulled either high or low from Microsoft Quick Basic. The LLRD has 16 LEDs in a grid pattern; that is, if you apply power to 3 on bottom and 1 on the side, then LED (3,1) will light up. The parallel port supplies the LEDs with all the power they need. I wrote a program in qbasic that simply selects the right outputs to turn on the right LEDs to make the picture I want. Anyway, enough chit-chat, here is a video and pictures:
The control board:
The back, showing the grid-like wiring:
Close-up of an LED box:
Zoomed-out view (Sorry for the blurry pic, my hands are a bit shaky.
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If you have any additional questions, please ask them. I'd be happy to tell you more on how it works, and details on the control board. Please comment!
