Spinning Sign

I wrote an article about how to build a “spinning sign”, you can read it at the Seattle Robotics Society. I fiddled around with the idea until I managed to make the clocks in the above picture. In brief, the image is created by spinning a wand of 8 LEDs at 20 RPS. That way I can make the 8 LEDs do the work of 1200 (150 columns). The signs are really serial terminals. The actual clock connects to the spinning sign (through the shaft) and emits a new message five times a second. The ideas in the article pretty much just worked, although I have learned a few more things:

1. I can get reliable communications at 9600 baud, as long as the sign is very well balanced.
2. The clock box emits a message five times a second, so that glitched messages disappear quickly. I should have also used a checksum to avoid displaying the glitches in the first place.
3. The design in the article uses an elaborate mechanism involving an optoisolator to detect the timing signal and an RC network to reject glitches. A much better approach is to sense when the timing signal is pulled to ground (protected with a diode), and do glitch rejection in software.

I used three-color LEDs (from superbrightleds.com) to build a full color sign. It displays the 8 basic colors well, but my attempts at greyscale just flickered. I haven’t figured out a creative use for it yet. In the picture below, note the balance weights (screws and washers) on the bumps on the square.