I made sound-reactive LED eyeballs for the band Total Unicorn's new masks. Total Unicorn is one of my favorite bands and the members are all friends of mine, so they know I am an electronics nerd. When they had new unicorn heads made, they asked me to make the eyballs for them. The previous masks' eyes were bicycle lights that just cyled through colors randomly, but they wanted the new ones to be sound-reactive. For the new eyes, I used 30mm RGB LEDs from Adafruit. The size and shape fits the new masks perfectly.
Total Unicorn also features a dancer whose mobility cannot be limited by extra electronics and wires. For her mask, I used two 10mm RGB automatic color cycling LEDs from SparkFun. A two AAA battery holder is mounted inside the mask, and does not add too much weight. The LEDs are mounted inside ping-pong balls which are mounted in the mask's eyes. The look is very similar to the sound reactive eyes.
The LED controller, consisting of the power supply and sound-reactive circuitry, is housed in an enclosure that clips onto the wearer's belt. The round thing on the front is a microphone. On the top there is a power switch and a sensitivity knob. The ribon cable runs up the wearer's back and inside the mask to the the eyes.
The unit is powered by a 9V (rechargable) battery. The LEDs need 12 volts, and are notciably dimmer at 9. A TC1044 charge pump is use to double the battery voltage, and an LM7812 regulates that down to 12V. The brain of the controller is a PIC12F1822 microcontroller. I had experimented with various circuits, including band-pass filtering the sound, but the best result was acheived by a simple voltage follower. The output of the voltage follower is a voltage that represents the volume of the ambiant sound. That voltage is read by an ADC input on the PIC. The brightness of the LED eyes is controlled by the volume. When the volume peaks, the color changes. The sensitivity knob controls the gain of the microphone preamp. So you can control what volume level causes a color change. The effect is really nice and follows the beat of the music extremely well.