Each row of controls consists of two buttons and two potentiometers. First button toggles recording on and off, second one clears the loop, first potentiometer controls the loop volume, and second one controls feedback. Each loop is 8 seconds long with independent volume and feedback controls.
Audio processing part is written in ChucK (C-like language for audio), interface (buttons, potentiometers and LCD) in node.js.
This project is available as open source: https://github.com/szymonkaliski/LoopPI
In 2016 LoopPI was updated with recent Raspberry PI and Wolfson audio card for better sound quality: https://github.com/szymonkaliski/LoopPI2