Complete tutorial: https://www.musiconerd.com/single-post/Build-this-MIDI-controller-Fliper-Dj

The Fliper DJ is a MIDI controller which is based in the Arduino platform. It contains 16 arcade buttons, 7 rotary potentiometers and 3 slider potentiometers. One of the potentiometers allows you to change the midi channel of the buttons, making it possible to have four banks of buttons, 16x4. The Fliper DJ is a USB-Midi class compliant device, no drivers or converters needed!