Music and Lights on a Bicycle II – The lights!

So in the previous post I explained how I set up the audio amplifier for the speakers. Next thing to take care of is the lights. I want the lights to pulse to the music with different color LEDs showing the bass and treble levels. For this purpose, I bought an RGB LED strip so I can easily control a large number of leds and have all the colors in the world! Also this is my first time working with led strips, so I am very excited to try them out.

There are many types of LED strips you can buy, and I went with the TM1809 because it was the cheapest I could find at the time ($30/meter). Also with this strip you can address the LEDs individually with just one data pin, which is really handy.

In a previous project I made a light organ, which had three frequency channels, one for the bass (~ 224 Hz), one for the treble (~ 3 kHz) and one for mid range frequencies (~ 1 kHz). It uses Multiple Feedback Active Band-pass Filters (MFAB) to select the frequencies. Unlike passive filters made from resistors, capacitors and inductors, MFAB filters have a very narrow bandwidth.

So my idea is to send the audio signal through three MFAB  filters, read the output values of the three channels from a microcontroller, and drive the LED strip with red, green and blue levels representing the frequency channel values. So the first step is to create the filters (see schematic below).

Schematic of the triple channel audio spectrum analyzer. The three filters separate the bass, treble and mid range frequencies.

After building the three filters on my breadboard, it is time to program a microcontroller to read the output voltages. I will explain this in my next post.