When I was a teenager, I created my first lightshow by connecting some small incandescent light bulbs in parallel with my speakers. Then, I pushed the bulbs through small holes in the center of aluminum pie plates which acted as reflectors. I put the needle of my turntable on the first track of my Grand Funk Railroad record and basked in the glory of my igenuity.

Let's fast forward 35 years (that was quick). Vinyl is dead. The CD may soon be an object of curiosity. Music is digital and if you're like me, you listen to most of it on an iPod.

With this project, you can create a portable light show for your iPod or any other MP3 player.

Using nothing but analog devices, this circuit breaks the audio spectrum into three octaves: octave a, octave b=2*a, and octave c=2*b=4*a. Since the audio spectrum runs from 20 to 20Khz then a+b+c = 20Khz. Or, a+2a+4a = 7a = 20Khz.

So, a = 20Kz/7 = 2857Hz, the b octave runs from a to 3a or 2857Hz to 8571Kz and the c octave covers 8571Khz to 20Khz.

To design the filters, I downloaded Filterpro 2.0 from the T.I. website and selected 2nd order butterworth implementations.

The plot below shows how the Low Pass, Bandpass, and High Pass filter responses overlap each other: