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GRIN Quern

Policium announced his GRIN Quern – an ergonomic keyboard with GRIN/Sagittarius layout and center trackpad.
Published October 6, 2022

The GRIN Quern is Policium's entry for the Seeed Keyboard Competition. (Only five days left!)

It features a Seeed XIAO RP2040 controller, and a Cirque trackpad with encoder ring put in the middle of a physical layout similar to that of the Sagittarius.

And if you know what a quern-stone is, the name doesn't need much explanation.

I thought that when I was turning the rotary encoder in the center, it looked like I was turning a millstone – Policium.


While the layout is heavily reminiscent of the Sagittarius by Gondolindrim and Tom, and also of the author's own GRIN layout, the motivation was to realize a layout that @KeebTaro, a streamer friend of Policium wanted to do:


  • 58 keys
  • GRIN/Sagittarius layout
  • trackpad + rotary encoder
  • OLED display
  • Seeed XIAO RP2040 controller
  • IO expander

It seems keyboards with a space in the center are now popular in Japan and elsewhere. Examples are Ergotonic49, cocot46, Ambi, etc.

My friend calls the center space "Buddha space". It seems to be a place to display something important. Other designs include a numeric keypad, encoder, trackball, and many others – Policium.

We are talking about an MX-compatible high-pro project, so the knob and trackpad would be lower than the keys around them, making them less convenient to use. The solution was to create a 3D-printed base.

The trackpad is a Cirque TM040040, and since the QMK already includes a driver for the Cirque Pinnacle 1CA027, it can be used simply by connecting it via I2C or SPI.


As Policium points out, the XIAO controller has 11 usable GPIO pins. Two of those pins are used as I2C for display, two for rotary encoder, and one for serial communication for RGBLED control. There are only 6 pins left!

With a normal switch matrix, the limit would be 3*3=9 keys. In a round-robin matrix, up to 30 keys are possible. (Thanks for the reference to and the exotic matrices series! :))

However, the author used an IO expander this time: the TCA9555, which is a lower-voltage version of the PCA9555a. (QMK includes a driver for the PCA9555.)


Published on Thu 6th Oct 2022. Featured in KBD #98 (source).

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