Visualize Your Tunes with an ATtiny85 Audio Spectrum

Music is always more interesting when you have visual feedback to go along with it, and this ATtiny85-based device lets you inject a VU meter into your audio input in (quite small) style. The unit takes in a signal via an audio jack, and after some filtering, sends it to an ADC pin on the ATtiny85 chip.

Once received on the ATtiny, the fix_fft library is employed to break the signal down into its frequency components for output. To deal with the MCU’s limited amount of RAM, the 128x32 pixel SSD1306 OLED screen used for visualization is populated in 32x32 chunks with this ssd1306 library. The ATtiny85’s internal oscillator calibration register (OSCCAL) is set to 240 for a frequency of around 30MHz, and input values are mapped and pre-scaled, giving a sampling frequency that works out to roughly 2MHz.

The device is housed in a 3D-printed enclosure, and in addition to the ATtiny85 input, the unmodified sound signal is passed along to another audio jack for your listening enjoyment! A short demo of the spectrum is seen in the video below with animated lines pulsing to the music. Code, print files, and a circuit diagram for the build are available on GitHub.