MIDI Muppet - Another DIY Arduino based 2 button MIDI controller for the Helix HX Stomp - Helix - Line 6 Community
Build a Programmable USB Midi Controller - FADR-4 - YouTube
Amazon.com: Vangoa MIDI Keyboard Controller 25 Keys, Worlde Panda MINI USB Midi Keyboard with Drum Pads, Beat Maker Machine Pad, Black : Everything Else