┌─────────────────────────────────────────────────┐
  │                                                 │
  │                   C  O  D  A                    │
  │                                                 │
  │          22 keys. The distilled form.           │
  │                                                 │
  └─────────────────────────────────────────────────┘

---

Coda (n.): the concluding passage — a concentrated, essential statement that brings everything together.

Coda is a 22-key split keyboard layout and the minimal sibling of Cadenza. It removes the pinky column and inner column entirely — not as a constraint, but as a deliberate ergonomic choice. The result is a layout with zero pinky load, zero lateral index stretch, and an estimated SFB rate of ~0.90% — lower than Colemak-DH.

22 keys. The distilled form.

---

✦ The Coda family

Cadenza   36 keys   Full layout — Vial/QMK, all 13 layers, daily driver
Coda      22 keys   Distilled form — QMK keymap.c, concept stage

Coda shares Cadenza's design DNA: Colemak-DH base, Home Row Mods via Tap Dance, frequency-ranked symbol placement, dedicated CLI and International layers, and bilateral access for critical functions. What changes is the physical constraint: 3 fingers per side instead of 5, 2 thumbs per side instead of 3.

---

✦ Physical layout

 Left              Right
 ┌───┬───┬───┐    ┌───┬───┬───┐
 │ D │ G │ L │    │ H │ F │ C │   ← top row
 ├───┼───┼───┤    ├───┼───┼───┤
 │ T │ S │ R │    │ N │ E │ I │   ← home row  ← fingers rest here
 ├───┼───┼───┤    ├───┼───┼───┤
 │ M │ W │ B │    │ Z │ K │ U │   ← bottom row
 └───┴───┴───┘    └───┴───┴───┘
         ┌───┬───┐    ┌───┬───┐
         │ A │Spc│    │ O │Ent│   ← thumbs
         └───┴───┘    └───┴───┘

  Fingers: Index · Middle · Ring  (no Pinky, no Inner column)

22 positions total. The Colemak-DH inner home row — T S R / N E I — is preserved unchanged. A (7.4%) and O (5.0%) move from pinky keys to thumbs, solving the frequency gap created by removing the outer column.

---

✦ Why remove the pinky?

The pinky finger is responsible for the highest incidence of repetitive strain injury in keyboard users. It is simultaneously the weakest finger and — on a standard layout — one of the most heavily loaded:

Layout	Pinky load	Lateral stretch
QWERTZ	~14%	Very high
Dvorak	~7%	Moderate
Colemak-DH	~6%	Low
Coda	0%	Zero

---

✦ Key metrics

Metric	QWERTZ	Dvorak	Colemak-DH	Coda
SFB rate	6.31%	2.62%	1.28%	~0.90%
Home row usage	34%	71%	68%	64%
Pinky load	14%	7%	6%	0%
Lateral index stretch	Very high	Moderate	Low	Zero
German CH bigram	Same-finger	Cross-hand	Cross-hand	Inward roll
German IG bigram	Same-hand	Varies	Varies	Cross-hand

SFB = Same-Finger Bigrams. QWERTZ, Dvorak, Colemak-DH values documented (carpalx / Patrick Steele corpus). Coda estimated from column analysis. German + English combined corpus.

---

✦ Layer overview

Layer	Access	Purpose
L0 Base	Always active	20 letters · Tap Dance HRM
L-Nav	Hold A	Arrows · Word nav · Modifiers
L-Sym	Hold Space	Symbols · Punctuation · Brackets
L-Num	Hold O	Numpad 1–9 · Operators
L-Code	Hold Ent	Shell operators · Path nav · Code macros
L-WM	Hold G or H	Workspaces 1–10 · Focus · Window movement
L-Fn	Hold O + Ent	F1–F12 · Media
L-Mouse	Hold A + Space	Pointer · Scroll · Buttons
L-Overflow	Hold A + Ent	P V Y J X Q · ß €

Access key design

Layer access follows Frequency × Ergonomic Quality:

• A thumb → Navigation (most-used directional layer)
• Space thumb → Symbols (second most-used)
• O thumb → Numbers (third)
• Ent thumb → Code/CLI (fourth)
• G / H holds → WM (bilateral — hold right hand, left free for numpad)

---

✦ Highlights

• Zero pinky load — physically impossible on this hardware
• Zero lateral stretch — no inner column exists
• Colemak-DH home row preserved — T·S·R / N·E·I identical to Cadenza
• A and O on thumbs — the two highest-frequency non-home letters on the strongest fingers
• CH as inward roll — German's most common digraph (2.4%) is a fast right-hand roll
• IG cross-hand — German -ig endings (richtig, wenig) never cause same-finger bigrams
• Bilateral WM + Meta — G/H for WM · L/F for Meta · left hand free for numpad
• Nav combos — all 4 arrows on home row: N=← E=↓ I=→ N+E=↑
• Pre-encoded WM shortcuts — tap=⊞+N · hold=⊞+⇧+N, no manual Meta hold needed
• QMK keymap.c — unlimited macros, layer-specific combos, full C programmability

---

✦ Honest limitations

• ⚠ Concept only — no commercial 22-key PCB with this exact layout exists yet
• Steep learning curve — new hardware paradigm + layers + combos
• Backspace is a combo — Space + Ent simultaneously
• Symbols require layer hold — every comma and period needs a thumb hold
• P, V on overflow — ~1.5% of characters are one step deeper
• Meta + Alt conflict — L (Meta) and R (Alt) share the left ring finger

---

✦ Hardware

Coda requires a custom 22-key split PCB. Closest commercial options:

Board	Keys	Gap
Ferris Sweep	34	Has pinkies + inner column
Ferris Sweep Bling	34	Same
Absolem	46	Too many keys
Custom PCB	22	Target hardware

The Coda PCB would be a Corne Choc variant with the outer (pinky) column physically absent.

---

✦ Firmware

Coda targets QMK keymap.c — not Vial. Reasons:

• Layer-specific combos require COMBO_ONLY_FROM_LAYER — not available in Vial
• 34 Tap Dance definitions exceed Vial's ergonomic management threshold
• Unlimited macros in C vs. 16 in Vial
• Full git history of every key decision

// config.h
#define TAP_DANCE_ENTRIES 34
#define COMBO_COUNT 9
#define COMBO_ONLY_FROM_LAYER  // layer-specific combos for Nav ↑ and PgUp

---

✦ Documentation

File	Contents
docs/index.html	Complete design documentation in a nice HTML file which can be downloaded, showing all layers, tap dances, macros, combos
docs/DOCUMENTATION.md	Complete design documentation — principles, metrics, all layers, TD/macro/combo reference
docs/coda_compare.png	Ergonomic comparison — radar chart + metrics vs QWERTZ/Dvorak/Colemak-DH

---

✦ Relationship to Cadenza

Coda emerged from Cadenza v1.0.0 as a design exercise: what if we removed everything non-essential? The core home row, the HRM model, the CLI layer, the International layer, and the WM layer all carry over. What Coda adds is the radical physical constraint that forces every design decision to be justified.

Cadenza is the daily driver. Coda is the thought experiment that sharpens it.

---

✦ License

Designed by one7two99 · MIT · 2026

Sibling of Cadenza · Based on Colemak-DH by stevep99