Begin by assembling the LED matrix and “backpack” board as described in the Adafruit LED Backpacks tutorial.

If using the LED matrix for the first time, we very strongly recommend working through that full tutorial first. This will let you test and confirm that the Matrix is properly assembled before moving on to this more advanced project.

If working with a breadboard as shown below, solder row headers on to the microphone breakout and LED matrix backpack boards (three pins on the former, four on the latter). You can optionally use 90 degree headers if you’d like either component to be positioned standing up.

Thanks to the “smarts” of the LED matrix backpack, this whole project requires fewer than a dozen connections total:

• Connect the Arduino’s 3.3V pin both to the mic amp VCC pin and the Arduino’s AREF pin. We use one of the power rails on the breadboard to route 3.3 Volts to both locations. The AREF connection is very important — don’t overlook this!
• Connect the Arduino 5V pin to the LED matrix + pin.
• Connect Arduino GND pin to both the mic amp GND pin and the LED matrix – pin. You can use a breadboard power rail, or the Arduino has multiple GND pins available.
• Connect Arduino analog pin 0 to the mic amp OUT pin.
• Connect Arduino pins SDA and SCL to the matrix backpack D (data) and C (clock) pins, respectively. Earlier Arduino boards don’t include SDA and SCL pins — instead, use analog pins 4 (for SDA) and 5 (SCL).

For a current “R3” Arduino board (such as the Arduino Leonardo or more recent Arduino Uno and Mega boards), the wiring should resemble this:

If using a “classic” Arduino board — an Arduino Uno version R1 or R2, Arduino Duemilanove or Diecimila (with 328P chip), the matrix data and clock lines should be connected to analog pins 4 and 5:

Note: the project only works with 8-bit AVR boards. It relies on a library that’s written in assembly language, and won’t compile on newer 32-bit boards like Arduino Zero or Adafruit Metro Express.

Piece of cake!

You can power the Arduino from the USB connection or using a battery or power supply connected to the DC jack. The LED matrix draws a couple hundred milliamps at most, so we can safely power it through the Arduino.