NEW VERSION WITH NEOPIXELS July 17, 2019 – https://www.thingiverse.com/thing:3750704
In this project, the Trellis triggers samples on an Adafruit Audio FX soundboard. The Pro Trinket interfaces between the two over serial and i2c and ties the samples to the buttons.
It's a really slick way to make a compact, all-in-one sound board. This version of the Audio FX Soundboard features a built in amp so you can wire speakers up to terminals or directly on the board.
Whenever a Trellis key is pressed, there's a loop in the arduino sketch that listens for button presses and plays back a sample from a list.