typewriter

A distraction-free, hackable, DIY writing machine. ESP32-S3 + e-ink + a real mechanical keyboard. You write Markdown, you commit, you push. Nothing else runs on it.

Status: pre-MVP. Hardware not yet on bench. Bring-up in progress.

---

Vision

A single-purpose appliance that boots into a text editor with a Vim keymap, edits Markdown files, and (optionally) pushes them to a git remote (GitHub first) over Wi-Fi. No browser, no notifications, no apps. Open lid → write → push (or don't) → close lid.

Two file scopes coexist on the SD card:

• Tracked — lives in the git working copy, gets committed and pushed.
• Local — never leaves the device. Drafts, journal entries, scratch, things that aren't ready or aren't anyone else's business.

Same editor, same keymap; the difference is just whether Ctrl-G (commit & push) is offered.

---

Hardware

Part	Choice	Why
MCU	ESP32-S3-N16R8 (16 MB flash, 8 MB octal PSRAM)	USB OTG host (for the keyboard), Wi-Fi, BLE, dual core @ 240 MHz, plenty of PSRAM for git pack data and screen buffer. Best-supported Rust target in the ESP family.
Display	GDEY0579T93 + DESPI-c579 breakout (5.79", 792×272, 1-bit)	Good Display panel matched with its own FPC breakout. Strip aspect (~2.9:1) — Freewrite-coded: ~12 lines of edit area, ~95 cols. Tiny framebuffer (~27 KB) leaves PSRAM headroom. The DESPI-c579 is a passive level-shifter / FPC-to-header board, not an active controller — driven over plain SPI like any other epd.
Keyboard	Nuphy Air60/Halo65 wired USB-C	ESP32-S3 acts as USB host via TinyUSB. BLE-HID is a fallback but contends with Wi-Fi for radio time during push.
Storage	microSD over SPI	Holds both the git working copy (/sd/repo/) and the local-only scratch space (/sd/local/). Internal flash is for firmware + config only.
Power	USB-C wall power for MVP, 18650 + IP5306 in Phase 3	Measure power profile on real hardware before sizing the battery. E-ink + sleep should give multi-day battery life but battery introduces charging, safety, and BMS complexity we don't need on day one.
Enclosure	3D-printed, hinged lid	Phase 4 concern.

Why the 5.79" strip aspect: less screen than a 7.5" page-shaped panel, but the long-narrow shape biases toward "current line + recent context" — the writing posture we actually want. The smaller framebuffer is cheap on RAM, and SPI panels keep the GPIO budget open for SD + future peripherals. A larger panel (10.3" via IT8951) stays on the table for v1.x once UX is proven.

---

Software stack

Language: Rust on esp-idf-rs (std). Decision is load-bearing — see the rejected alternatives below.

Layer	Crate / Component	Notes
HAL / runtime	esp-idf-svc, esp-idf-hal	std build, gives us heap, threads, VFS, mbedtls, Wi-Fi stack.
Display	embedded-graphics + epd-waveshare (or custom driver)	Pixel framebuffer with partial-refresh regions. We track dirty rects ourselves. The GDEY0579T93 uses an SSD1683-class controller; if it's not already in epd-waveshare, we write a small driver against embedded-hal SPI — ~300 LoC, low risk.
Editor core	Custom, in-tree	Rope buffer (ropey), mode state machine, Vim keymap table.
TUI-style layout	Custom thin layer (~500 LoC)	API inspired by Ratatui (Layout, Block, Paragraph) but renders directly to embedded-graphics. See below.
USB host	esp-idf TinyUSB bindings	Boot-protocol HID is enough for the keyboard.
Git	gitoxide (gix)	Pure-Rust, modular. We only need add / commit / push (smart HTTP). No libgit2, no mbedtls glue beyond what esp-idf already gives us.
TLS	mbedtls via esp-idf	Used for GitHub HTTPS. ~120 KB heap during handshake — fits in PSRAM.
Auth	GitHub Personal Access Token in encrypted NVS	SSH on embedded is painful; HTTPS+PAT is the pragmatic path.
Filesystem	FAT on SD (esp_vfs_fat)	Working copy lives here. Internal LittleFS holds config.

Why not Ratatui

Ratatui assumes a character-grid terminal with an ANSI backend. E-ink is a pixel framebuffer with partial-refresh windows. The right primitive for e-ink is dirty-rectangle tracking aligned to the panel's refresh regions — Ratatui's per-cell diff model fights this. We can borrow its widget API shape (it's a good one) without dragging in the terminal abstraction. Net saving: probably 200 KB of binary and a lot of pretending the screen is a VT100.

Why not Gleam + Shore

BEAM doesn't run on ESP32. AtomVM does, but: memory budget is tight, Gleam-on- AtomVM is bleeding-edge, and there are no bindings for USB host / e-ink / SD / TLS / git in that ecosystem. Shore is also terminal-oriented, so the same impedance mismatch as Ratatui applies. Building this on Gleam would be a research project stacked on a research project. Revisit in 2-3 years.

Why not C / Arduino

Workable, well-trodden, fastest path to a blinking screen. But this is a project I want to keep evolving — Rust's refactoring leverage and type safety pay off the moment we start adding modes, palette, search, etc.

---

UX boundaries set by the medium

E-ink is a brutal honesty filter on UI choices. Hard constraints we design around, not against:

• No cursor blink. Kills the panel and the battery.
• Typing latency target: ≤ 200 ms from keypress to glyph on screen, using partial refresh on the affected line only.
• Full refresh every ~20 partials to clear ghosting. User-visible flash — schedule it on pauses (>1 s of no input).
• No smooth scrolling. Page-style jumps only.
• No animations. Anywhere.
• Render only changed lines, not the viewport.

---

Roadmap

Frequent releases. Each version is a usable artifact, not a checkpoint.

v0.1 — MVP: "it writes, it pushes" — [ ]

The minimum thing that justifies the hardware existing. Full design: product · technical.

• ESP32-S3 boots, e-ink shows splash + boot log
• USB host enumerates the Nuphy, key events reach the editor
• One hard-coded file (/sd/repo/notes.md) opens on boot
• Insert-only editing (no modes yet), backspace, enter, arrow keys
• Line wrap, no line numbers yet
• Save on Ctrl-S → SD
• Wi-Fi credentials via captive portal on first boot, stored in NVS
• Ctrl-G runs: git add notes.md && git commit -m "wip" && git push to a pre-configured remote, using a PAT entered during setup
• Partial refresh on edits; full refresh on save

Out of scope: Vim, palette, multiple files, branches, conflict handling.

v0.2 — Vim navigation — [ ]

• Mode state machine (Normal / Insert), mode indicator in status line
• Movement: h j k l, w b e, 0 $, gg G, Ctrl-d Ctrl-u
• i a o O A to enter Insert
• Esc returns to Normal
• Line numbers (absolute) in the left gutter

v0.3 — Vim editing — [ ]

• x dd yy p P, dw dd d$, repeat with .
• Undo / redo (u, Ctrl-r) — bounded history in PSRAM
• Numeric prefixes (3dd, 5j)

v0.4 — Visual mode + ex commands — [ ]

• Visual char (v) and line (V) modes, y d c on selections
• : command line: :w :q :wq :e <path>
• Status line shows file path, dirty flag, mode

v0.5 — File palette + multi-file — [ ]

• Ctrl-P opens fuzzy file palette over both /sd/repo/ and /sd/local/, with a scope marker (e.g. [git] / [local]) per result
• Open, switch, close buffers (keep ≤ 3 in memory)
• :e and palette share the same recent-files list
• :enew creates a new file — prompts for scope (tracked vs local)
• Ctrl-G is disabled / hidden when the current buffer is local-scope

v0.6 — Markdown affordances — [ ]

• Heading lines bolded in render
• List continuation on Enter inside - / 1.
• Soft-wrap at word boundaries
• Optional column ruler at 80

v0.7 — Search + better git — [ ]

• / forward search, n N
• :Gpull (fetch + fast-forward only; refuse on conflict and surface it)
• :Gbranch to switch branches; refuse with dirty tree
• Commit message prompt instead of hard-coded "wip"

v0.8 — Power: battery + sleep — [ ]

• Measure idle / typing / push current draw on bench
• 18650 + IP5306 charge board, soft power switch
• Light sleep on idle > 30 s (keyboard interrupt wakes)
• Deep sleep on lid close (reed switch); restore cursor + buffer
• Battery indicator in status line

v0.9 — Robustness — [ ]

• Crash-safe writes (write to .tmp, fsync, rename)
• Recover from interrupted push (re-attempt on next save)
• SD card removal / reinsert handling
• Wi-Fi reconnect with backoff
• Settings screen: SSID, PAT rotation, default remote, commit author

v1.0 — Polish — [ ]

• Boot time ≤ 3 s to usable cursor
• Font selection (at least one serif + one mono)
• Enclosure design files in hardware/
• User guide

v1.x — Stretch / nice-to-have

• 10.3" panel upgrade via IT8951
• Multiple remotes / repos
• Spell-check (dictionary in flash, naive)
• Stats: words today, streak
• Theme: light / dark (inverted e-ink)
• BLE-HID fallback for wireless keyboards

---

Repo layout (planned)

/firmware       Rust crate, esp-idf-rs target
                (SD card mounted at runtime contains /repo and /local)
  /src
    editor/     rope buffer, modes, keymap
    render/     embedded-graphics + dirty rects
    git/        gitoxide wrapper, auth
    usb/        TinyUSB host glue
    fs/         SD + NVS
  build.rs
  sdkconfig.defaults
/hardware       BOM, schematic, enclosure (later)
/docs           ADRs, power measurements

---

Open questions / risks (tracked, not yet resolved)

• gix-clone + gix-pack smart-HTTP push working on esp-idf-rs with mbedtls — needs an early spike before locking the stack.
• TinyUSB host stability with arbitrary HID descriptors (Nuphy reports consumer-control keys we may need to ignore).
• Heap fragmentation over a long writing session with PSRAM allocator.
• Real-world e-ink ghosting with current partial-refresh cadence.

These get resolved by writing code, not by deciding harder.