Claude Code wrote a smartwatch firmware from scratch in three days — the full workflow
cyberdinn · reddit · 2026-10-24
A developer used Claude Code (Opus 5.5) to write Kronograf, an open-source (MIT) firmware for the LilyGO T-Watch 2020 (ESP32, 240×240 screen) in three days: 3 watch faces, 13 apps, iPhone notifications over Bluetooth (ANCS), a network toolbox, and a macOS simulator. Prebuilt binaries are available.
What worked:
- A structured brief first (north star, hardware, stages 0–9), then one stage at a time: build, flash, test on the wrist before moving on
- A simulator compiling the same UI so Claude could render headless screenshots (--shot) and check its own UI work
- Two repo logs: DECISIONS.md (56 decisions, each with a reason) and BLOCKERS.md (what broke, what was tried)
- Plain C for data parts, tested on host: ANCS notification protocol, a streamed protobuf parser for a 1 MB transit feed, time zones verified across 12 zones over two years
What still needed a human: anything physical (flaky micro-USB connector → OTA updates and resumable block flashing), battery-only bugs (watchdog left armed plus an interrupt storm, tracked via serial logs), and wrist-level judgement calls like raise-to-wake thresholds.
Project: github.com/storagebits/kronograf
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