Back in college I occasionally did DJ gigs. It was a lot of fun and I did some pretty neat things to make it easier. I had a remote control for my WinTV card and I remapped the buttons to control WinAmp, so I could control the music while I was dancing on the floor. Another thing I did was build some lights for inside my computer case.
When I originally built it, the lights were controlled by the internal serial port, and I wrote some software to advance the lights. I was even able to integrate the sound volume into it and had some rudimentary beat detection going so that the lights would change on the beat. Unfortunately, the system slowly degraded over time. The first problem was that the beat detection didn’t work when I upgraded from Windows ME to Windows XP. The next problem was that the external power supply died. Finally, I switched to Linux, so the software I had written to control it wouldn’t work.
In January 2007 I cleaned things up quite a bit. First, I connected the power to the computer’s power supply, thus removing the dependence on an external plug. Next, I set it up with a 555 timer chip and inserted a potentiometer to vary the speed of the flashing. I had to replace a light bulb, but the refurbishing took only a few hours. Now it seems to be working fairly well. See the pics and the video. There are 5 lights throughout the case, and they flash in order.
The circuitry is very simple. I have a decade counter which increments every time it gets a pulse. Each time it increments it turns on a different transistor, which powers a different light. On pin 6 it goes to the reset pin so that the decade counter only counts 1-5 over and over again. The 555 timer provides the pulse to the decade counter. If you want more details about the circuitry, contact me.
Video of the computer lights show in action (Windows Media Video (WMV) format, no audio)