Black Light Unicorn are fans of the Adafruit Feather M4 Express microcontroller for its speed, good mix of features, and easy programming with Arduino tools. They thought: “Should we make a guitar pedal with it? Of course we should make a guitar pedal with it.” And they did.

The Teensy Audio Adaptor Board, with its SGTL5000 chip was the basis for sound. To make all the necessary connections for the Feather to control the SGTL5000, They mostly used I2S. They had some software issues with the I2C clock signals and submitted a pull request to get those fixed in the Adafruit’s ZeroI2S library.

All we needed now was a guitar effect. Some of the Audio library examples worked for us, but we wanted to start from scratch and make some effects from the ground up. So, we thought, what’s the simplest guitar effect? We figured tremolo is about as simple as it gets: just use an LFO to turn the volume up and down.

You can check out the code in the GitHub repo. Very briefly, here are the most interesting parts: tremolo.ino is where we connect up the I2S audio input, the tremolo effect, and the I2S output (using a mixer to make a depth control), and set up the volume, and the depth and speed of the tremolo.

See it in action and more in the post here.