Snowflakes

This was my second display, built in 1983, but has been changed twice since then.   About 100 lights are wired in a series-parallel arrangement in the shape of a hexagonal snowflake.  The original configuration used 1 watt incandescent light bulbs.  I had two lights on each snowflake "arm" wired in series, so I used 7 volt bulbs with a 15 volt transformer.  There were 6 transformers, two for each of the 3 snowflakes.  As a result, there was lots of current going through the system so the transformers were pretty big.  The interface between the computer and the lights was a 48-channel digital triac board.  Having learned from my first triac board design, I was able to squeeze 48 channels onto a 9" by 11" printed circuit board.

Over the years I would "spiff" it up a bit with tinsel and better bulbs to make it look not so plain.  In 1997 I redesigned the wood supports so they looked more like what a snowflake was expected to look like.  I used clip-art from Corel Draw as my model.  I replaced all the 1 watt bulbs which were series-connected and put in premium 5 watt bulbs instead, and wired them in parallel.  Since they were 110 volt lights, I was able to get rid of the transformers and cut the current demands down drastically.  I used the same 48 channel triac interface board.  The triacs ran cooler than they did before when I had the lower voltage, but higher current. 

Since the snowflakes, which are 4 feet in diameter, were outside and the control was inside, I made a small simulator out of 150 neon bulbs that mimic the patterns on the lights outside.  This makes it easier to troubleshoot and program.

I used a 6809 development kit for the computer.  I wrote the code in assembly language, burned an EPROM  that resides in the development board memory space, and writes off the board to an interface board that I built.  This board has 3 PIAs and bus line-drivers on it that drives the triac board.

Different patterns show on the display.  The cycle repeats about every 5 minutes.  

This is my oldest display but it is the most popular.  Block Diagram  (pdf )