We put up lights each year for the holidays, and while I don’t mind having the house decorated, I do not like having to put them up. Despite this, I feel mounting pressure each year to Do Better, which by default means more lights and decorations, which in turn mean even more work.

The year before last I had the idea that if I worked smarter I might avoid working harder, and that one of those musically synchronized setups would be pretty sweet. Problem is I came to this conclusion in October of 2008, and that didn’t leave enough time to properly procrastinate before throwing something together at the last minute, so I was forced to postpone. This past year though I was able to spend a solid 11 months procrastinating, which still left a couple short weeks to hurriedly throw something together.

So long story short, I did it, I put together a controller that sets christmas lights to music. And, providing that you weren’t privy to all of the nasty hacks and ugly short-cuts, it was actually kind of neat of to watch. Obviously though, I’m not entirely happy with the results, so I’m considering this year a practice run, and hope that with this as a basis to build upon, next year it will be pretty sweet. So treat the rest of this post as more of a rough brain-dump than a recipe or step-by-step, and hopefully it will prove interesting for comparison purposes next year.


Normally this is where I’d expound on some of my research, the options I investigated, costs, ease of use, etc. That’s not going to happen because with all of the procrastination this project required, I simply didn’t have the time. Instead I went straight for a pre-assembled parallel port relay board, and I took a page out of this guys book and mounted it in a plastic tool box.

I used some cheap extension cords, fixed to the ends of the toolbox with cable connectors, and wired it all together inside. The relay board needs a power supply, so there is an outlet inside for that.

A cord that exits the rear of the toolbox gets plugged into the mains to supply power to the whole thing, but since we’re combining electricity and the great outdoors, a GFI is a must.

I scored this parallel cable in an old pile of hardware. It worked great once I got the zip drive that was attached to it off and in the trash.

Finally, I made use of an old PIII notebook.

Christmas light controll

I know, it’s not much to look at. Sue me.


There are 8 pins on a parallel port that are (were) used to send character data to printers, and it’s these 8 pins that are used for outputs. That means controlling the outputs is as simple as writing to that byte. The pyparallel library makes this even easier, so for example, I was able to use something like the following, ran from a cronjob to start and stop the lights each day.

python -c 'import parallel; parallel.Parallel().setData(0)'

I wired everything up to the normally closed contacts of the relay board so the lights would fail-safe. In other words, you have to turn the relay on, in order to turn the corresponding lights off. The setData(0) above switches on all of the lights by turning the relays off, killing the lights is as easy as changing that to setData(255).

Initially I had the idea that I’d whip up something to analyze an audio track; that the light show would essentially be a visualization of the waveform. That, as it turns out isn’t the panacea that it would seem. Sure, the lights will flash in a way that seems vaguely in response to the music, but the results are just not as coordinated, or ordered, as the samples you see on the Internet.

So I then moved on to the idea of creating a time-series of output states that could be “played” along with the audio, but I was naive to believe that I could hand-craft this data file, so before all was said and done, I’d also written a PyGame application for keying in the outputs as the music played, and visualizing it during playback.

Finally, only after getting everything working I found out that the way “professionals” do this is actually pretty similar to what I came up with, only using MIDI, so I will definitely be looking into that before next year.