A browser app for the Precision Clock Mk IV by mitxela. It drives a real clock over Web Serial — display modes, text and countdowns, brightness curves, satellite views, timing analysis — and with no clock attached it is one: the on-screen clock is the actual clock4 firmware compiled to WebAssembly, not an imitation of it.
Note
Independent, community-built. Not affiliated with mitxela.
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The C source that flashes to the physical clock is compiled to WASM at build time (from the clock4 submodule) and runs in the page — real NMEA parsing, real PPS discipline, real display latching. The build is v0.0.5: mitxela's released 0.0.4 plus five draft PRs — #5 $PMTXTS timing telemetry, #6 astro display modes, #7 hardening fixes, #8 sidereal & solar time, #9 self-learning temperature compensation. Draft firmware: it runs happily on my own clock, but it isn't upstream yet.
It's verified rather than assumed: 4,511 display checks against independently computed astronomical truth, plus a replay anchor against a physical Mk IV on real GPS data. The DEVICE → UPDATES panel shows the exact commit the running WASM was built from and can check it against GitHub.
- Standby — no clock, no simulation: the face shows your system time and the telemetry stays empty.
- Simulation — opt-in and labelled: a virtual GPS (with real satellite positions from live TLEs) feeds the firmware's own reception path, so lock, discipline and holdover all happen in real firmware code.
- Connected — a real Mk IV over Web Serial. Its NMEA drives the same firmware renderer and every chart; simulated data is never mixed in.
- FACE — every display mode (including live sidereal and apparent-solar time), text with marquee scrolling, countdowns, brightness / gamma / DAC curve editing, colon animations, the significance-fade precision display, observer location, and a timezone engine using the clock's own IANA rules database. Edit and apply
config.txtthrough the firmware's real parser. - SKY — polar az/el plot with signal heatmap, horizon mask and age-faded trails; a flat world map and an orthographic globe with satellites at their true sub-points and a day/night terminator; C/N₀ and position/DOP analysis; a GPS fix panel. Sky history persists across reloads and exports as CSV / JSON / GPX / NMEA, including a per-satellite history CSV.
- TIMING — with the draft firmware streaming
$PMTXTS: PPS phase with robust (median/MAD) jitter stats, the oscillator drift staircase, and a temperature-compensation fit that emits the firmware's owntc_*warm-start config block. - DEVICE — Web Serial connect, config editing, REST data sources that poll and push values onto the date row, recorded-data downloads, firmware provenance and update check, and a raw NMEA serial monitor.
- Hosted: https://peterlewis.github.io/pcc/ — Chromium browser (Chrome / Edge / Arc / Brave) over HTTPS. Safari and Firefox can look around (no Web Serial, so no hardware connection).
- Local dev — live source, no build step:
git clone https://github.com/peterlewis/pcc.git cd pcc && bash web/serve.sh # http://localhost:8765
- Build the static site (what CI deploys; needs emscripten to compile the firmware from source):
cd web && npm install && node build.mjs # → ../docs/
| Path | What |
|---|---|
web/ |
The app — source. Built to docs/ by CI and served on Pages. See web/README.md. |
web/emu/ |
The firmware emulator: clock4 submodule, emscripten shim, and the conformance suite. |
.github/workflows/pages.yml |
Compiles the firmware WASM + builds web/, deploys to GitHub Pages on every push to main. |
main is web-only. The original native macOS menu-bar app is paused and preserved on the macos-app branch:
git fetch && git switch macos-app
cd macos && swift build && swift run PCC- Precision Clock Mk IV — official documentation
- clock4 — hardware design & firmware source (mitxela)
- Forum thread — discussion on the mitxela forum
MIT — see LICENSE. Bundled third-party assets (fonts, map data, libraries) keep their own licenses; see THIRD_PARTY.md.