Building a Split Keyboard for myself

I have only ever used a laptop. To sit with a laptop at a desk is to sit hunched over. Fine for a time, but ideally you’d want to sit up, with your back straight and look straight ahead.

This is a solved problem. Get a monitor or laptop stand and an external mouse and keyboard.

As you see I already had the monitor setup, but not the keyboard. Since I would use this keyboard all the time, it better be a great one. I chose my laptop, a Thinkpad, for that exact reason: it probably has the best laptop keyboard around. For my external keyboard I also wanted one of the best around.

This article tells the story of how I built an ergonomic split keyboard for myself. How I configured it and got good enough with it to be able to actually use it on a daily basis.

Let’s start with what makes a great external keyboard.

Great keyboard design #

Classic keyboards layouts emulate the typewriter through a sideways stagger that misaligns the keys. This stagger was necessary in typewriters their metal hammers would not get stuck. A constraint modern computers don’t share. 🙂

With the removal of the stagger most finger movement become vertical rather than diagonal, finger paths are more consistent and strain is reduced.

To have the keyboard as one glued-together brick means that your arms are not aligned with your shoulders, but point inward.

The ideal hand position is also not flat on the desk, but inclined to the side. Split keyboards make it possible to incline both hands independently of each other and in opposing directions, which is not possible if the keyboard is one large brick.

Finger are not the same length so a horizontal stagger can add comfort.

The best keyboard out there goes even further than that, but also comes with a much higher price point, less portability and a significant learning curve. I think the split keyboard will be the sweet spot for most people who want to have a great external keyboard.

Building process #

What is not for most people, though, is soldering together their keyboard themselves. More on that later. Let’s first choose a split keyboard design.

Picking a design #

The keyboard design should fit your needs.

The first thing to wrap your head around is how a keyboard can even be as small as this:

You can and have to program these keyboards. The Ferris can function because while you hold one of the arrow keys (in the bottom right) with your thumb, the rest of the keyboard get redefined, the keys now output something arbitrary you defined. This is called a layer. If you don’t have a number row, you can add a number layer. For example: usually you press E and get E, but if you hold the arrow key and press E, you can now get 3.

Layering is powerful and really can’t (and shouldn’t) be avoided when building a split keyboard. There are also combos, mod-tap and more. The fewer physical keys you have on the keyboard, the more reliant are you on these techniques. I knew, that as a beginner, I wanted a number row and many thumb keys. That already significantly reduced my options, which is a good thing.¹

I chose the Sofle design. It has amount of keys I wanted, a comfortable stagger, plenty of thumb keys and two encoders.

I chose splitkb.com as an EU-based vendor. There I could buy everything I needed at once with guaranteed compatibility, a guided part-picker, great documentation and no excessive shipping costs or import tax.

The Sofle kit requires me to solder the board myself. If you don’t want to solder:

• Splitkb also offers already soldered kits that you can just plug together.
  You still get all of the choice (switches, keycaps, display, encoder, trackpad), but without the manual labor. The price difference to self-soldering is a no-brainer if you consider the labor and tools.
• Other vendors sell completely assembled keyboards at higher prices. You get the working product, but none of the fun or choice of building.
• If you want to go dirt cheap you can go with AliExpress. Search for your design and get a preassembled keyboard or hunt down all the the parts you need.

Now to get my hands dirty.

Soldering and assembly #

The orientation guide helped me understand what all the parts were that I was looking at and how they would play together to (hopefully) become a functioning keyboard.

Choose the firmware #

Before anything gets soldered, test that the microcontrollers work by flashing their firmware.² My options were:

1. QMK: a text-based configuration language
2. Vial: a GUI where you don’t need to mess with key-codes

As much as I like configuring stuff, QMK looked like overkill. Vial was very easy to get into and is feature-complete for a beginners needs.

Soldering #

My soldering experience was limited to one 2h session, years ago. I was basically a beginner. Great that the first task is to solder some tiny SMD diodes. A task not recommended for beginners, but I knew it was gonna be fine and went fine. Sure, the first 30 looked terrible, but I got better. The second PCB went really smoothly (4x faster than first one.)

Next were the resistors.³ These were even smaller than the diodes. 🙂

With that I was done for day one after ~3h of soldering.

For 8€ one can add hotswap switch sockets. Without them you’d solder the switches directly onto the board. I chose what felt like the safer way, so that if I make a mistake or any switch breaks I don’t have to do a big desoldering effort. Which would be terrible (forshadowing.)

Through-out the first half of the first board I’m thinking “Why is this so hard to solder??? I thought I was good now!?”. By the second board it had become routine.

As the last job for the day I wanted to do the rotary encoders:

At the end of a 5h session I fuck up by soldering then encoder onto the wrong side of the board. Ouch. It only take one moment of inattention to mess up terribly.

I tried to desolder the encoder but it was not possible with my current tool. So, I went to the store and bought a new 30W iron. That also did not work. (Afterwards I found out that I needed the soldering iron with >30W that was marked as “unsafe for PCBs.” It is safe if you know what you are doing, which I wasn’t — so maybe it’s for the best. 😄)
Either way. I found a place in Berlin that does walk-in soldering work. After a two-hour train ride and 5-minute visit my board was fixed.

I put everything together, fixed some connections and tested the keys through Vials “Matrix Tester”. Everything worked, except for one row of keys.
I checked my soldering, redid connections, but … nothing. At some point I switch the microcontrollers and the dead row switches with along with it. A microcontroller problem it is.

After the newly ordered microcontroller arrived, was soldered up and put in, everything finally worked!

From initial research to completion the build took around 20 days and ca. 13h of soldering and hardware debugging.

Cost overview #

Here’s what I paid for my kit, plus the unexpected costs:

• Aurora Sofle Kit, switches, keycaps, microcontrollers, case, encoders and more: 226€
• 2m USB-C cable: 5€
• Reordered a microcontroller: 31€
• Bought a new soldering iron, which turned out to be only marginally better than old one: 43€
• Had a professional fix the encoder soldering mistake of mine: 20€

Total: 325€ plus ~13 hours of my time.

Configuration #

My keyboard is smaller than a full-keyboard. Some of the standard keys are missing for lack of space. Through configuration they will be made available.

For Vial configuration is done through the local app.⁴ Vial needs the devices /dev/hidraw* to be writable. This can be done with:

ls -tc /dev/hidraw* | head -n3 | tr "\n" " " | xargs sudo chmod a+rw

I run this through an udev rule on device connect that calls this script.

Thumb keys for modifiers #

First up are the ten thumb keys. The requirement for my keyboard (configuration) was that it works well with Emacs. There is a lot of holding down Control in Emacs. Since the thumb is our strongest finger I wanted have it hold down that (and other) modifiers.

With one on each hand (2/10):

• 2x Control

Then I have (4/10):

• Super: window management
• Hyper⁵: Emacs bindings

Emacs also has bindings with two modifiers plus shift (control+meta+shift+something), so I needed a shift outside of the thumb keys. The other goes shift goes onto the thumbs (5/10):

• Shift

With usage I quickly realized that the outermost keys were very hard to hit consistently and that the travel between the innermost to the outmost was slowing me down. I basically don’t use them now (7/10).

I only have 3 spaces left now and it needs to be these three (10/10):

• Alt
• Spacebar
• Layer change: see next section

I tried enter on a thumb key, but multiple Emacs org-mode bindings use two modifiers (two thumbs) plus enter.

Layer it on! #

A layer allows you to transform all keys on the keyboard. Here is what I get when I go into layer one:

You can see that I make keys accessible that are missing (#, *, ß, etc.) or so common that I want them more easily available (", ?, (), etc.)

Other people make much heavier use of layers than me. They have layers for numbers, special characters, movement, media, etc. I chose a keyboard with a number row, so I wouldn’t need to do this. After trying more layers I decided against it.

Knobs (Encoders) #

Those rotary encoders are actually quite flexible. For their functions I have settled on volume control and left/right (for video control.) And on press down it runs the sequence C-x 1 – Emacs’ delete-other-windows – which is very convenient.

I experimented with them as page up/down for webpage and document scroll, but I did not use it much. What I did use was Emacs’ other-window in the direction that I was turning the knob. That was quite cool and I used it plenty, but to have the volume and forward/backward available outside of a layer was more important.

Adjustment period #

To get back to your usual typing speed and muscle memory on a new keyword will take time and conscious effort. For me these were the points where I felt the pain:

1. Orthogonal⁶ key placement and related bad habits.
2. Special characters in new places.
3. Keyboard shortcuts are completely different.

The orthogonal layout meant that keys were in slightly different places (e.g. straight up from the home row, instead of up and sideways.) Though this was the least of my trouble. My touch typing mistakes were much worse.

On a staggered keyboard B is equally close to both index fingers on the home row and I used them interchangeably. On a split orthogonal keyboard B is on the left hand. For me that meant that my right index finger needed to unlearn that it could hit a B by going down and left.

Many special characters moved to layers as I already said. This too, took some getting used to. And while most letter keys were in the same place, the few that weren’t (the German ä & ß) threw off my writing speed.

But the hardest part were the keyboard shortcut that I had deeply etched into my muscle memory. Modifiers were now in different places. Key combinations used a different set of fingers. I had to look up some binding again and again because I just did not know them. They had been committed to muscle memory years ago and I had long forgotten what keys I needed to press.

Typing practice #

Typing tests are a great way to reduce typing friction and improve speed through deliberate practice. I used the full-featured website monkeytype.⁷

On my laptop keyboard I was at a comfortable 60wpm in English. I started out at an abysmal 10wpm on the new keyboard. I practiced regularly and added multiple increases in difficulty. I switched to German (more capitalization, harder combined words and ö, ä, ü, ß), added numbers and punctuation. It took me about 14h of deliberate practice to get up to 60wpm on the new keyboard too.

I saw the best progress when I drilled the “missed words” after a test, focused on accuracy over speed and stopped for the day when I hit a plateau.

Conclusions #

With that we have arrived in the present. A lot of work went into this project in building, configuring and adjusting to this new keyboard. I am left with a nicer computer setup for years to come. To me that was time well invested. And I enjoyed myself in the process.

I hope you feel inspired to do something like this for yourself (if you’re into this kind of thing.) 🙂

Much love,
Jonathan

References #

• Consistent keybindings across macOS and linux (same copy-paste and more.) This is especially useful with a shared external keyboard.
• The ultimate keyboard still awaits: the Svalboard. 3d printing and building this is someday project for me.
• List of EU vendors for keyboards and keyboard components
• Video: How to solder keyboards