Our wiring diagrams illustrated this project with a half-size breadboard, but for a smaller package the parts can also fit on an Arduino breakout shield:

Depending how you choose to orient the LED matrix, the matrix.setRotation() function can be used to keep the graph upright.

Just a concept — this is not functional — but it’s interesting to note that an Arduino Micro, the LED matrix and the microphone amplifier are almost perfectly matched to the dimensions of a 9 Volt battery:

If you do attempt an extra-compact build like this, please keep in mind that the Arduino Micro includes a 5 Volt regulator, allowing it to be powered from a 9 Volt battery. Most small form-factor Arduino-compatible boards do not include a regulator, and will be damaged if you attempt to power them directly from 9 Volts! For such boards, either add your own regulator to the circuit, or use an appropriate battery pack: three alkaline AA or AAA cells in series, or four rechargeable NiMH cells.

Additionally, the code may need adjustments for some “alternative” Arduino boards…most likely the analog channel number, which may be mapped to different pin numbers on different boards.

Finally, because ADC registers are accessed directly, specific interrupts are used, and the FFT code is in AVR assembly language, this software will not run on upscale boards like the ESP32, Pico RP2040 or Teensy 3.0. It is strictly for “classic” Arduinos.