KOOP Instruments' Melodicade MX Packs Six-Plus Octaves Into a Velocity-Sensitive Cherry MX Keyboard

Michael, of KOOP Instruments, is a fan of electronic music-making devices — his latest design of which packs most of the range of an 88-key keyboard into a compact device built using Cherry MX keyboard switches backed by bottom-out switches for velocity sensing.

Based on the earlier Melodicade, which used arcade buttons, the 3D-printed Melodicade MX uses Cherry MX mechanical keyboard switches with custom-printed key caps. While that would usually be enough for an input device, Michael sought to make the Melodicade MX more usable for musical projects by giving each switch the ability to sense velocity — by popping tactile switches under the mechanical switches.

"With this specific keyswitch and tact switch pairing," Michael writes, "there's about a 1500 microsecond travel on hard hits, 6000µs on medium hits, and above 30000µs, I just assume a light key press and send it. Since the key sometimes doesn't completely bottom out on light hits, it's better than just dropping a note. Dynamic range isn't what a store bought piano would offer, but there's definitely a noticeable difference between light and hard hits."

Interestingly, the Melodicade MX doesn't rely on a custom PCB: Instead, everything is held in the 3D_printed chassis and wired directly. "I think this is past the point where a sensible person would have designed and sent away for a PCB," Michael admits, "but I rather like the idea of keeping things unrefined enough that a dummy like myself can assemble by hand with the help of a 3D printer and some off-the-shelf parts."

The finished Melodicade MX covers over six octaves — almost a full 88-key keyboard's worth — but takes up a surprisingly small amount of desk space thanks to the Wicki-Hayden layout normally associated with hexagonal keys on concertinas and bandoneons, created by Kaspar Wicki in the 1890s then refined by Brian Hayden in the 1980s.

The full build guide, which Michael estimates would cost around $180 in materials when ignoring minimum order quantities on some parts, is available on the KOOP Instruments website; Arduino source code for the driving Teensy 4.1 board is available on GitHub under the reciprocal GNU General Public License 3, and the 3D print files on Thingiverse under the Creative Commons Attribution-NonCommercial-ShareAlike license.