Around 2003 I came across the MIDI Gadget by Paul Everett which I thought was just the coolest. As an amateurish pianist, I was fascinated by the idea of a two-dimensional keyboard, and the Wicki-Hayden layout seemed to make a lot of sense. I cannibalized the keys from an old keyboard from my junk box, wired them up in a diode matrix, added a PIC microcontroller, and made a MIDI Gadget of my own. Paul had modeled his after the concertina, to be played with the hands facing each other. Mine was intended to be played with the palms down, but, like Paul's, it gave each hand its own keyboard.
Several versions followed and it evolved further and further away from the original MIDI Gadget, so at some point I decided to give it its own name, the gadgetina. It started out as a MIDI controller that needed to be connected to an external MIDI sound generator, but I added a MIDI synthesizer chip to make it a standalone instrument.
The final design gives each hand 42 notes in 7 rows, along with octave shift keys and preset buttons. Each half has its own MIDI channel, program change, and velocity, all settable via the preset buttons. There's an alphanumeric display and two rotary encoders for editing parameters. Inside, a Parallax P8X32A "Propeller" microcontroller runs the show. The case is made from sheet PVC cut on a CNC mill.
Each of the gadgetina's keyboards has six keys per row. This is a minimal subset of Wicki-Hayden that covers all the notes without duplicates. I decided on this minimal subset because I didn't want the gadgetina to get much wider, and also because I didn't really understand the value of duplicate notes.
Unfortunately, the lack of duplicate notes severely reduces the gadgetina's usefulness as a Wicki-Hayden instrument and probably makes real W-H enthusiasts shake their heads. You see, the Wicki-Hayden layout is isomorphic, meaning that chord and scale shapes are the same no matter what note you start on. This is one of its touted advantages over the piano keyboard. But isomorphism breaks at the edges of the keyboard, and on the gadgetina, unfortunately, the side edges are only six keys apart. It's a little too common to run out of keys while playing and have to figure out where to wrap around to the other side. It's not such a problem for me because I learn pieces from sheet music; if I were improvising or playing by ear, I might be more frustrated.
As the gadgetina's keys (Cherry keyswitches, btw) are not velocity-sensitive, the pieces I play on it come from the harpsichord and organ repertoire, since those instruments are similarly velocity-insensitive. Some videos of the gadgetina in action are below. Be warned: I rely on the novelty of the keyboard and non-traditional sonorities to distract from the inadequacies of my playing!