4. Uses a 1024 point Fast Fourier Transform (or FFT)
to divide the audio spectrum into eight musically related
5. Allows user specified control of the density of
LEDs used per band.
6. Special dynamics mode periodically reassigns the
LEDs for each band which, in effect, changes the
physical layout of the LEDs.
7. Uses the Teensy 3.1 microcontroller (uC) and
software written in the Arduino environment.
In a nutshell, this color organ digitizes audio from
either a microphone or from line level inputs, sends it
through the automatic volume control (if enabled), and
then feeds it to a 1024 point FFT. The FFT (described a
little later) breaks down the complex digitized audio into
frequency bins and subsequent processing transforms
the bins into eight frequency bands which are used to
drive a string of WS2812B RGB LEDs.
The hardware for the color organ consists of the
major parts described in Table 1.
Figure 1 shows the schematic diagram of the color
organ. I built my color organ using point-to-point wiring.
Figures 2 and 3 show the front and back of the circuit
board. The Teensy 3.1 is connected to the audio adapter
with header pins that extend from the adapter through
the Teensy’s PCB (printed circuit board), then through
March 2017 25
Teensy Audio Adapter
This part handles the digitization
of audio coming from either a
microphone interface or stereo
line inputs. It has a small
number of analog components
necessary to bias the off-board
condenser microphone. It also
provides a microSD card
interface supporting a FAT type
Touchscreen LCD Display
All user interaction with the
color organ (with the exception
of turning the color organ’s
power off and on) is done via a
touchscreen LCD display.
Teensy 3.1 Microcontroller
All of the color organ’s
functionality is provided by
software running in this ARM
based microcontroller. The 32-bit
Teensy 3.1 has 262,144 bytes of
Flash memory for program/data
storage and 65,536 bytes of
WS2812B (NeoPixel) RGB
The display aspect of the color
organ is provided by a string of
120 RGB LEDs. Each LED is
individually addressable and
each provides its own Pulse
Width Modulation (PWM)
controller for varying color and
brightness. These LEDs are
capable of a wide range of
colors and extreme brightness.
■ FIGURE 1.
1. Connections between the audio adapter and Teensy 3.1 are made when the adapter is soldered onto the top of the Teensy.
2. Only one section of the 74AHCT125 is used.
3. Power cord, power switch, power supply, and RCA line input jacks are mounted to the case and wired onto the circuit board.
4. A program pushbutton was added because the audio adapter hides the button on the Teensy.