Saki Tomine's Compact Keyboard Uses a Clever Slit, Split, Truly Flexible PCB
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Saki Tomine's Compact Keyboard Uses a Clever Slit, Split, Truly Flexible PCB

Aug 05, 2023

Maker Saki Tomine, also known as Murasaki (むらさき), has designed a split dished ortholinear keyboard tailored for smaller hands — using a flexible PCB with clever cuts to conform to the keyboard's unusual layout.

"It seems that if you pursue a keyboard that is suitable for the structure of the human body, it will become a three-dimensional shape," Tomine explains, in translation, in a Fabcross post brought to our attention by Adafruit.

"There is a curved keyboard that follows the range of motion of the fingers. I'm curious if it's really easy to use, and above all, it's simply cool, so I'd like to use it. However, when I actually touched it, it just didn't fit my hand. Many of them are made by foreign men, so they are too big for Japanese women's hands."

The solution was, of course, to design a custom keyboard better-suited to smaller hands, but a desire for a dished layout brings a challenge: how to wire up the switches. The most obvious approach is to literally connect them with flying wires, a simple enough approach but undeniably awkward — and ill-suited to a compact case.

Tomine decided on a different approach: using a PCB printed on a flexible plastic substrate. Given the shape of the keyboard, though, even this wouldn't be flexible enough — so Tomine added cuts between each switch to allow the entire PCB to split apart, flex, and stretch. "By curving the wiring part that connects the switch and making a notch," Tomine explains, "we were able to create a free shape."

"I don't usually put scissors in the board, so I cut it while being nervous," Tomine continues. "It's as hard as paper and can be easily cut. Be careful not to cut the wiring with too much force. Cut off all the runner parts and pull. Oh! Stretch! It stretches both horizontally and vertically! Just as I imagined! It's a lot of fun."

The flexible slit PCB was initially added to an acrylic housing heated and bent into shape, with the hope that it could be adjusted again at a later date. "When you bend it, [however], it interferes with the acrylic bending machine," Tomine found, "so it seems impossible to bend it again later and make fine adjustments." The solution: a 3D-printed case, split in two for each half of the keyboard.

The finished keyboard, powered by an Arduino Pro Micro-compatible microcontroller with a tip-ring-ring-sleeve (TRRS) connector between the two halves, proved successful. "It's so different from the keyboard I'm using now that I've just started using it and now typing is as slow as a toddling penguin," Tomine admits. "But once you get used to it, you should be as fast as a penguin swimming underwater!"

Tomine's full write-up is available on Fabcross, in Japanese; an English version is available through Google Translate.