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Atreus Keyboard

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The Atreus is a mechanical keyboard designed primarily to match the shape of human hands and to be as portable as possible. The case measures 26x12cm and lacks even a number row, relying heavily upon the fn key. There is a circuit board for this design, but it’s also possible to manually wire the matrix.

I’ve seen a number of existing DIY 40% keyboard designs, but most of them stagger the rows, which I find very annoying now that I’ve gotten used to the columnar layout of the Ergodox. In addition, many of the designs I’ve seen waste a lot of room on the space bar, failing to take into account the fact that the thumb is the strongest and most versatile of the fingers. This design avoids both these problems while taking a more couch-friendly single-piece approach.


See the changelog for the various revisions made to the design since its initial release.


You can buy Atreus kits that have all the parts you need along with detailed assembly instructions from If you’d rather round up all the parts yourself, that’s possible too since the design is completely open source; see the bill of materials below.


Only a handful of punctuation marks (and no digits) are available unshifted, and all the modifiers are on the bottom row:

   q     w     e     r     t       ||       y     u     i     o    p
   a     s     d     f     g       ||       h     j     k     l    ;
   z     x     c     v     b       ||       n     m     ,     .    /
  esc   tab  super shift bksp ctrl || alt space  fn     -     '  enter

The numbers and most of the punctuation are on the fn layer with a numpad-style arrangement under the right hand:

   !    @     up     {    }        ||     pgup    7     8     9    *
   #  left   down  right  $        ||     pgdn    4     5     6    +
   [    ]      (     )    &        ||       `     1     2     3    \
  L2  insert super shift bksp ctrl || alt space   fn    .     0    =

The L2 key switches it to the function layer, and tapping L0 here brings it back to the first layer.

 insert home    ↑    end  pgup     ||       ↑     F7    F8    F9   F10
   del   ←      ↓     →   pgdn     ||       ↓     F4    F5    F6   F11
                          reset    ||             F1    F2    F3   F12
             super shift bksp ctrl || alt space   L0             

The firmware includes a number of other options, including colemak and dvorak. Customizing your layout is easy to do with the QMK configurator interface.



This layout has five modifiers and 37 non-modifiers.

I strongly prefer the feel and sound of tactile Matias Clicky switches for typing. However, I like having Matias Linear switches switches on the modifier keys (ctrl, alt, super, shift, and fn) because the tactile effect has no benefit for keys that are held down, and giving a different response helps you learn the layout more quickly.

For users that need to operate in sound-sensitive environments like open offices or libraries, Matias Quiet Click switches are a popular choice since they still offer tactility without the noise. Other users prefer switches in the Cherry MX family, which use different keycaps and switch plates but still work fine.


In order to avoid ghosting, each switch needs a diode. The 1N4148 is a readily-available choice, but nearly any signal diode would work.


The circuit board design uses a Pololu A-star micro. Hand-wired boards can also use a Arduino Pro Micro.

Be sure to get a microcontroller without headers so it will fit in between the bottom layer and the plate. USB micro is preferred over USB mini for this reason as well.


Caps for Matias switches are included in the official kits. Sculpted caps are also available from Matias or by harvesting from old Alps keyboards. It’s recommended that you use unlabeled keys, because due to the different sizes and orientations of certain keys (backspace, shift, enter, etc) many of the labels will be incorrect if present.

Cherry switches have more options. This DSA-shaped base set (spherical indentations on the key, same profile for each row) from Signature Plastics has 52 1x keys plus a few extras we won’t use. There are two “deep dish” keys in that set which you can place under your index fingers on the home row to help guide your hands to the right spot without looking. However, you only get a single 1.5x keycap, and the middle two thumb keys both use them, so you might want to pick up an extra.

Circuit Board

The atreus.rkt program calculates switch and diode positions based on row/column counts, spacing, and rotation factors, and emits a atreus.kicad_pcb file. The board outline and traces are done by hand and are stored in the header.rktd and traces.rktd files respectively. The atreus.kicad_pcb file can be imported into Kicad which can export Gerber files suitable for fabrication. A copy of the Kicad PCB file is included in the repository if you don’t want to recompile it using Racket. Recompiling is only required if you want to make changes to the procedurally-generated portions of the board.

Unfortunately most PCB fabricators require a minimum order of 10 or so, making this impractical for one-offs. The PCB is not required, so for one-off boards it’s usually more sensible to stick with a hand-wired build instead.


Layered laser-cut wood or acrylic. The mark II case (EPS files in the case/ directory) features 8 screw holes and a kind of “stair step” design around the top and bottom of the key clusters; mark I has straight lines.

The files alps-top-plate-3mm.eps, alps-switch-plate-3mm.eps, and bottom-plate-3mm.eps are to be cut in 3mm acrylic or wood. The spacer.eps file can be cut on something thicker; between 4.5mm and 6mm is recommended. Alternatively you can cut it in 3mm twice. The spacer needs to be at least as thick as the connector of the USB cable you’re using. If you are using Cherry switches, you should use cherry-3mm.eps for the top, switch, and bottom plates instead, but the spacer is the same.

There is also a programmatically-implemented version of the case written in OpenSCAD; it is more flexible (you can tweak the number of rows/cols, etc and recompile) but it doesn’t match the canonical case exactly; in particular the screw holes are placed differently.

The original case (case-mk-i.svg) design is also included; it is slightly less wide and has a minor asymmetry with the screws on the bottom side.

On a 100W Epilog laser, the 3mm layers cut in about a minute and a half. I did a run with 6mm acrylic of the other layers which took nearly 6 minutes.

Wood cases should be finished with sandpaper and lacquer, shellac, or polyurethane.


The QMK firmware is recommended. Standard layouts are available precompiled, or you can design your own in the configurator.

There is also the older atreus-firmware custom codebase which works but has fewer features. It is recommended mostly for learning purposes since the code is much simpler and easier to understand than QMK. Previously TMK was the recommended choice for firmware, but QMK has much better documentation and ease of use and is now recommended.

Bill of Materials

If you don’t want to get the kit you can source parts yourself. (You can also order a partial kit if you want to customize some of the parts.) Using Cherry switches is cheapest unless you can find cheap Alps-mount keycaps:

  • 50 Matias or Cherry switches from
  • 50 diodes from radio shack, ebay, or whatever
  • 40 1x, 2 1.5x Keycaps from OR full keycap set from
  • A-star micro from
  • Case materials from various sources
  • Case laser cutting: 7.5 minutes on a 100W Epilog laser; varies by source
  • USB micro cable, get anywhere

Recommended but optional:

  • 5 linear Matias or Cherry switches

The base keycap set from Signature Plastics only has one 1.5x key, which is used for the inner thumb keys. You can use a 1x key for one of them, but it looks kind of tacky, so I recommend getting a second 1.5x keycap separately.

Other Tools

You’ll need a soldering iron, solder, and a wire cutter. A multimeter can come in handy for testing the connections but is optional. You’ll also need eight M3 machine screws with nuts; the length of the screws depends on the thickness of the acrylic you use. You can add rubber feet to the bottom to prevent the board from sliding around when placed on a desk. You’ll also need sandpaper and lacquer for the wooden case.

If you are building a hand-wired board you will also need a glue gun, hookup wire, and wire strippers.


See the assembly instructions PDF.

Hand-wired boards will want the previous edition of the assembly instructions.

The LaTeX source to the assembly instructions is in the assembly directory.


These fine projects all provided inspiration for various aspects of the Atreus, as well as the folks on the #geekhack freenode channel.


If you’ve built an Atreus, please add your name to the build logs wiki.

There’s also a mailing list for people who have built or ordered an Atreus or are interested in doing so.


An experimental build uses the Teensy 3 microcontroller and ARM Forth-based firmware, but this is not really suitable for general-purpose use; it’s more of a curiosity.


Copyright © 2014-2018 Phil Hagelberg and contributors

Released under the GNU GPL version 3