5540f901de
Re-ran the spike on the dedicated SPI3 wiring (CLK 14 / MOSI 15) with the same clean mount + atomic round-trip result. Flip the docs from "pending a re-run" to verified.
4.4 KiB
Hardware — parts and rationale
Part choices for the bench build, moved here from the README. The display medium decision (e-ink over LCD / memory LCD / OLED) is ADR-003; power is ADR-008; keyboard transport is ADR-009.
| 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: ~13 lines, ~79 cols at the editor's 10px font. 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 v0.8 | 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 typewriter body — hardware/case/ |
v1.0 concern. |
Why the strip aspect
The ~2.9:1 long-narrow shape biases the UX toward "current line + recent context" rather than "full page" — the writing posture we want. The renderer stays resolution-agnostic so a 10.3" e-ink upgrade (v1.x) is a swap, not a rewrite.
Bench status
The board is on the bench and bring-up is largely done — per-spike results
live in spikes.md and
v0.1-mvp-technical.md,
with failure write-ups in postmortems/. Notable: the
keyboard runs bus-powered on the S3's native USB port, and the SD/FAT stack is
verified on a 32 GB card on its own SPI3 host (2026-07-11, ADR-012)
(postmortem).