Thursday, December 14, 2006

Christmas Sign...must be a sign of Christmas

Years ago, around 1990-1991, I wanted to have the fanciest Christmas ornament on the block. I must've have gotten that idea after watching Chevy Chase's Christmas vacation. Anyway, I designed a sign made up of probably 250 to 300 leds. Power consumption between 11 and 27 watts.

It writes 'Merry Christmas' out by starting on the left and continuing to the right. When the last LED is lit, the whole thing resets itself, all the LEDs go out and the pattern is repeated, ad nauseum. There are some different patterns available though, twinkle, blocks of LEDs switch on and off, as well as different speeds can be had.

I'm afraid I was responsible for the entire design, including the clock and all other circuitry. I guess I always did like tinkering with resistors, diodes and the like. "Ummers and puffers" as we used to call them. The heart of the clock circuit is the ubiquitous 555 timer, the devices that light up the LEDs are 74LS164N 8 bit shift registers. You can think of it as a bucket brigade. The LEDs are the cheapest kind available.

The overall size is about 1 meter by .25 meters. After designing the circuit boards, I had them printed in a silk screening place, where they normally do logos on T shirts, so this was quite a different job for them. Then I etched them at home myself and then drilled the holes for all the components using a drill stand and a portable electric drill. This was tricky, as the holes are very small and the bits break easily.

The case was made out of plexiglass (or Lexan) .


We have had this in and around our house during the Christmas season for the last fifteen years or so. However, this year when I got it out, it didn't work! Having totally forgotten how this thing even worked, I had to tinker with it to get it to go. A cold solder joint was the problem. Found it by pure luck. I did manage to blow 2 power supplies though, while testing. Luckily, I had a third, which was a DC one, so I had to bypass my original AC design.

Now I'm confident it will likely work for another fifteen years.....

Sorry about the crappy GIF, but I do have a life.

1 comment:

Ronny said...

what a crappy GIF ome kees hahah..