LED Colour Organ circuit

Nearly all the existing designs I found used direct switching of the lights (with no software control in between) and contained manual potentiometers for light sensitivity and overall gain setting. Furthermore, I couldn`t find many references to the frequency filter circuitry explaining the frequencies the circuit was designed to detect and why (it seems most published designs are based on other published designs leading
LED Colour Organ circuit - schematic

to fairly `sloppy` audio-stage circuitry). So it was time to brush up on op-amp filter design and build something myself. At the local hardware store I found some strings of LED lights (for Christmas decorations) and thought that wiring up a Christmas tree as a colour organ would be a pretty fun thing to do. From that T. O. M. T. E. was born (Tone Operated Microprocessor Tree Enhancement), details of which you can find below along with detailed construction notes. (for the non-Swedish reader, Jultomte is Swedish for Santa Claus, hence the funky abbreviation!) The sound processing circuitry for TOMTE is probably a little over-the-top for the application it is used for here, however it represents a good quality sound-to-light interface design which is probably useful for a number of other light/audio projects I can think of, so even if you don`t intend to build the Xmas decoration I designed, the circuitry is still useful. The microphone is connected to a pre-amplifier (because microphones produce so little electricity) and then on to an amplifier (which has automatic gain control from the microcontroller), the signal is then split into 3 frequency ranges (low, mid, high). Finally the sound is passed through peak-detectors (actually these add a little gain and convert the AC audio signal into DC) which is then measured using the ADC of a PIC18F. The PIC MCU then controls the available lights and the gain of the amplification...

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