This DIY cardboard piano syncs with your favorite MIDI music apps | Engadget
Amazon.com: Vangoa MIDI Keyboard Controller 25 Keys, Worlde Panda MINI USB Midi Keyboard with Drum Pads, Beat Maker Machine Pad, Black : Everything Else
Add MIDI Port to Keyboard : 15 Steps (with Pictures) - Instructables
How a MIDI keyboard works | Open Music Labs | Midi keyboard, Keyboard, Diy instruments