So, I’ve always been interested in those houses at christmas time that have a sign out front saying “tune to channel 105.9″ and they’re broadcasting christmas music and have their christmas lights flashing in time with the tunes. There was a guy in Raymond, NH that had this setup that I’ve been out to see a few times over the years. He also had a website that told the “basics” of how he did it. Never did he completely divulge the details.. but I did notice that along the bottom of his page he had a little graphic that said “powered by Light-o-Rama.” Upon further research, I found out that they [Light-o-rama] do have pre-built boxes that you purchase (for several hundred dollars) to do the light flashing from a PC.
Not wanting to spend hundreds of dollars yet not knowing how to turn on and off AC power from a PC (and with me being me), I set out to find an I’ll-build-one-myself alternative. This is the first entry of many to come that catalogues my learning process and my progress.
The first question I had to answer was “since a PC only has 12V and 5V DC power, how do i flick 110VAC power on and off?” The answer is: “There are a few ways.. optocouplers tied to triacs and solid state relays, being the most common.” So I turned to google and found many sites like this one and this one that offered up a million leads and a few million more questions. But at least now I knew how to get from DC to AC.
The next problem was that PC parallel ports only have 8 data lines.. and I want to individually control (the world!) many more light strands than 8. My friend at work suggested I look at an i/o expanding chip such as an MCP23009. That uses an I2C (eye-squared-see) interface to program the output pin states. I didn’t quite understand the I2C protocol when I read up on it, so the hunt continued. I eventually found a site by a guy who was using 74HC595 shift register chips and could handle MANY channels of output. I was so elated to have found a chip whose logic and control I understood and whose function would serve my purpose, that I bought 10 immediately. They’re very cheap, btw.. $0.52 per chip!
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=MM74HC595N-ND
Lesson learned, I should have kept researching before buying. Yes, those would work.. but better solutions exist and I have explored some of those already. I’ll talk more about those soon.