knucklehead

👊 Knucklehead

Knucklehead[^1] is a mnemonic, macOS-optimized ergonomic columnar layout for corne-style 42 key split keyboards, designed[^2] to ease the transition from Apple ANSI keyboards.

Drawn with @caksoylar’s Keymap Drawer

Legend

Symbol	Key Name	Symbol	Key Name
🆆	Smart 🆆ord behavior	🆇	E🆇it smart 🆆ord behavior
⌃	Control	⇥	Tab
⌥	Option	␣	Space
⌘	Command	⇡	Page Up
▲	Meh (⌃ + ⌥ + ⇧)	⇣	Page Down
✦	Hyper (⌃ + ⌥ + ⌘ + ⇧)	⛭	Brightness Up
⇧	Shift	⛯	Brightness Down
⇪	Caps Lock	⟲	Firmware reset (hold: bootloader mode)
⌫	Backspace
⌦	Delete	L1	Layer 1
⏎	Return	L2	Layer 2
⏻	Power	Fn	Function Layer

Features

Mnemonic Affordances

Key	Cue	Mnemonic Affordance(s)
⇥ (Tab)	␣ (Space)	Tab as a space multiplier; proximity.
` ~	H, ⇥ (Tab)	~ a.k.a. “Home” directory on 'nix systems; proximity. Same position, opposite hand as ⇥ (Tab), typically adjacent on Apple keyboards.
- _	N + L	Negative, Low; adjacent to = +
= +	E + U	Equals, Up (+); adjacent to - _
[ {	N + H	Proximity; used to define a New Hash table/map on many programming languages; adjacent to ] }
] }	E + ,	Proximity; used to End hash tables/maps on many programming languages; , is also typically used to delimit items within hash tables/maps; adjacent to [ {
-_ =+ [{ ]} |\	Apple ANSI position	This key cluster retains their order/position relative to each other as on Apple keyboards, but moved to vertical combos more easily accessible to stronger fingers.
/ ?	Y + I or | \	Shape similarity, proximity, symmetry; same column as | \; “why?”; interrogation symbol.
| \	I + . or / ?	Shape similarity, proximity, symmetry; logical OR — same position, opposite hand as & (logical AND); same column as / ?.
&	R + X	Shape similarity; logical AND — same position, opposite hand as | (logical OR)
*	S + C	Star, wild Card
⇪ (Caps Lock)	⇧ (Shift)	Same position as ⇧ (shift), but on Fn layer
! @ # $ % ^ & * ( )	1 2 3 4 5 6 7 8 9 0	Symbols maintain their standard ANSI association with numbers as laid-out on L2, replicated as combos on L1 and L2
Fn	Apple ANSI position	Fn keys retains their familiar lower left corner position, mirrored on the right.

Other Associative Affordances

Keys are repositioned in clusters to either “familiar” relative positions, or otherwise logical ones, using ANSI Apple keyboards as a reference, e.g.:

• Arrow keys are placed on Layer 2 in traditional VIM + QWERTY positions.
• ;: is positioned next to , < and . >, as a natural punctuation cluster.
• 1–5 numbers retain their familiar “left, upper-row” position on Layer 2, while 6–0 are positioned in the next row below. This not only feels natural for single handed numeric typing, but also moves the most used symbols [for programming] to more accessible positions.
• Fn keys are aligned with their corresponding numeric positions on Layer 2.
• Bluetooth profile selector combos on the Fn layer are aligned with their corresponding numeric positions.
• Media keys retain almost their relative position, except they’re re-arranged a bit so:
  • volume up / down align with + / - and Up / Down arrows, and U (“up”) and L (“low”) keys.
  • back / forward align with Left / Right arrows.

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Static, Associative Key Placement

This layout aims to keep keys (and combos) in the same place across layers, and to strike a balance between comfort and intuitiveness. Layers may enhance that key’s functionality, or replace it with another key, but that key itself won’t move to a different location.

When a key is replaced on upper layers, an associative mnemonic is used to make it easier to orientate yourself in the new layer (e.g. Fn keys are placed in the same positions as their corresponding numbers on Layer 2).

On upper layers unused keys are “transparent”, so events flow down to (and are activated on) the base layer, and thus the base layer’s key placement is preserved.

Together with the single base layer and upper layer swapping, these principles of static, associative key placement aim to make the modal nature of layers more intuitive and predictable, enabling faster development of muscle memory.

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Timer-less Home Row Mods

By using @urob’s Timer-less Home Row Mods, modifier keys (⌃, ⌥, ⌘, ▲) can be activated by holding keys in the “home row”, consistently across layers, without interfering with normal typing (i.e. without the need to tap a key within a certain time window).

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Smart 🆆ord Behaviors

A smart word behavior is one where, to perform an action for which you would normally hold a key, you’re only required to tap it at the beginning of a sequence to “enter” that special mode, and you remain in that mode until you press a key not in the defined “continue-list” (a “break-word” key, like ␣ [space]), or until you explicitly “exit” that mode.

The most common example of this type of behavior is ZMK’s &caps_word (or QMK’s).

This layout uses 2 smart word behaviors (marked with the 🆆 symbol):

Smart Shift

The right hand middle thumb ⇧ (shift) key will act as follows:

Action	Effect
hold	Normal “shift” behavior.
tap	Sticky “shift” behavior (i.e. will apply a “shift” modification to the next key pressed within 1s). Useful when capitalizing words at the beginning of sentences without holding the key (for example).
double-tap	&caps_word, i.e. retains “shift” behavior until a character not in the “continue-list” is pressed. Useful for ALL_CAPS word sequences, like conventional constant names on some programming languages.
Fn + tap	⇪ (CAPS LOCK).

Smart L2 Layer

Both inner thumbs (marked as L2 on L1) will act as follows:

Action	Effect
hold	Normal &mo “momentary layer” behavior.
tap	Sticky layer behavior, i.e. will switch to L2 until the next key pressed (within 1s), and immediately exit back to L1. Useful when entering a single number, single arrow movements, single media key actions, etc.
double-tap	Stays on L2 while numbers, arrows, , . / - _ + = *, ⌫ or ⌦ are pressed. Useful when entering longer numeric sequences, math operations, repetitive arrow navigation, etc.

E🆇iting Smart 🆆ord Behaviors

Sometimes you may enter a smart behavior by accident, or may need to cancel it to accommodate special use cases. For these situations there are special “cancel” keys, marked with an 🆇:

On L1 the right-most 🆇 key (top row, right hand) — and since on L2 that key position is “transparent”, it’s essentially the same key on that layer — will cancel any smart word behavior (i.e. it will exit &caps_word, and/or exit L2’s smart layer behavior and bump you back to L1). It’s positioned to mirror the traditional ESC key since it’s another type of “escape”.

On L2 the same thumb keys you use to summon it will act as follows:

Action	Effect
tap	Will exit the smart layer behavior and bump you back to L1. (It will also cancel &caps_word, so it can be used for that as well; from L1 this would technically be a triple-tap, so the top-right 🆇 key is more convenient)
hold	Will also exit the smart layer behavior, but will immediately enter the normal &mo “momentary layer” behavior as well and remain on L2, so as long as you keep holding it you shouldn’t see a difference, but as soon as you let go you’ll be bumped back to L1. I implemented this to account for accidental “muscle memory” hold actions, making it more forgiving and less confusing.

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Non-Stacking Upper Layers

One of ZMK’s great features is its stacking layers model. It works great for features like multiple “active” base layers, while sharing a common set of “momentary” upper layers (e.g. to switch alpha base layout at runtime, like from Colemak to QWERTY, while maintaining common upper layers for num, nav, fn, etc.).

However, unless you really understand this behavior and adapt your mental model to it, it may feel confusing and unintuitive at first, and get you lost in a layer maze.

Since the primary aims of this keymap are ease of use and intuitiveness, this behavior is purposefully avoided in a few ways:

Single Base Layer

L1 is the one true base layer. There is no way to permanently activate any other layer - only momentary (&mo), sticky (&sl), and smart layer behaviors are used.

To use a different base layer/layout, you’ll need to switch it at compile time. See: Using layouts other than Colemak-DH.

Upper Layer Swapping (vs. Stacking)

To prevent even momentary layer stacking, a “cancel” (🆇) event is triggered in some circumstances prior to switching to a layer, so that you’re first bumped back down to L1 before switching to the desired layer. This all happens transparently without delay, so from your perspective you just “swapped” upper layers, instead of stacking them. This ensures any transparent keys in that upper layer will fall through to L1, and sticky timeouts will bump you back to L1 immediately, as you would expect. These special cases are marked with the same 🆇 symbol.

Without this behavior it might’ve been confusing if you pressed the Fn key while on L2’s smart layer mode, and pressed a transparent key expecting an L1 keycode when instead you get an L2 one.

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Using layouts other than Colemak-DH

In order to use layouts other than the default Colemak-DH layout, you’ll need to comment-out the #include "L1_colemak-dh.dtsi" statement in ./knucklehead/base.dtsi, and uncomment the corresponding layout file you wish to use. E.g.:

# ./knucklehead/base.dtsi

-#include "L1_colemak-dh.dtsi"
+// #include "L1_colemak-dh.dtsi"
// #include "L1_colemak.dtsi"
// #include "L1_dvorak.dtsi"
-// #include "L1_qwerty.dtsi"
+#include "L1_qwerty.dtsi"

Feel free to submit PRs with additional layouts.

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Drawing the Keymap

This project uses @caksoylar’s Keymap Drawer to generate the keymap SVG displayed at the top of this document. It can be re-generated by running the Draw keymap, or locally through the Zsh script:

./scripts/draw.zsh

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Resources

• ZMK Firmware GitHub
• ZMK Documentation
• ZMK Discord Server
• @caksoylar’s Keymap Drawer, ZMK config and Display improvements for Corne-ish Zen
• @urob’s ZMK config
• Colemak-DH and the Effort Grid
• Darryl’s beautiful Corne-ish Zen

[^1]: Name inspired by the Knuckle mnemonic.

[^2]: “Designed” is perhaps too strong a word. “Haphazardly and painfully iterated over dozens of permutations, gradually removing annoyances and disruptions to my flow” is too long, though.