NumitronTop

Numitron Clock

Top-board schematic and PCB layout for the four-tube clock described in the Obsidian note electronics/Numitron Clock/Numitron Clock.md, read on 2026-09-18. The detailed top-board decisions in that note supersede its older, general power and interconnect descriptions.

Open NumitronTop.kicad_pro in KiCad. The design was captured and checked with KiCad 10.0.5. All schematic symbols are included in the project-local library and embedded in the sheets.

Review this revision

• Power and inter-board interface
• Control and light sensor
• Four tube drivers
• Connector and firmware contract
• Electrical design notes
• Preliminary BOM
• Socket drawing and dimensions
• Provisional socket footprint
• Top layout, underside layout and dimensions / review notes
• Bring-up and ordering checks
• Archived component datasheets
• ERC result and exported-netlist audit

The top board is placed and routed on a 110 × 40 mm working outline with all 55 schematic parts, four M2.5 mounting positions, local power distribution and ground copper on both faces. The extra depth provides a separate underside strip for the wide SOIC drivers. The layout notes explain component placement, the perpendicular underside connector orientation and review process.

The GZC9-A socket footprint remains provisional, as explicitly authorized on 2026-09-25: 18 mm assumed tail circle, 0.5 mm estimated terminal thickness, 2.5 mm plated holes and 3.8 mm copper lands. Verify physical fit before ordering. Enclosure/cable fit, exact capacitor order codes and hardware measurements also remain assembly/release checks. WWVB versus GPS belongs to the bottom board.

The owner confirms the actual tubes are marked DR2000 and have prefix decimal points. The archived RCA table assigns that feature to DR2010 instead. The design preserves the requested HH.MM display and routes the eighth channel to pin 1; verify that decimal connection on the actual tubes before enabling it.

Development

ES100 time-source test firmware

The reusable async ES100 driver and Pico 2 breadboard program live in firmware/. Build and check them with the pinned firmware toolchain (Rust/Cargo, Pico 2 target, flip-link and picotool are supplied by Nix):

nix develop .#firmware --command bash scripts/check_firmware.sh

The generated UF2 is firmware/target/pico2-es100.uf2. See the firmware guide for wiring, BOOTSEL flashing, USB logs and the hardware test handoff. Physical reception has not been validated; this does not decide WWVB versus GPS.

Hardware tooling

Use the pinned Nix flake; no global package installation is required. KiCad is supplied by the existing local application installation on macOS. The flake pins the supporting Python, Poppler, SVG-rendering and local Freerouting tools, not that external KiCad application.

nix develop
bash scripts/review.sh

The review command runs KiCad ERC, audits the saved schematic's netlist and provisional socket footprint, exports schematic and footprint SVGs, and renders inspection PNGs under ignored tmp/render/. It does not regenerate or overwrite the schematic or footprint. Source PDFs and the socket drawing are archived in Git with their provenance and hashes.

scripts/build_schematic.py --write records the initial schematic capture and is deliberately opt-in: it overwrites the native KiCad files. After editing in KiCad, preserve those edits; reconcile the generator before using it again.

hardware/top-board/socket-footprint.json records the socket assumptions. scripts/build_socket_footprint.py --write captures them into the project-local Numitron.pretty library; reconcile manual footprint edits before regenerating. The schematic assigns Numitron:GZC9-A_B9A_Provisional to V1-V4.

nix develop --command bash scripts/review_placement.sh checks the saved PCB against the netlist, runs DRC with schematic parity and generates the top/bottom review drawings. It does not regenerate placement or routing. board-drc.json and placement-checks.txt retain the results.

build_placement.py --write is a one-time placement capture using KiCad's bundled Python; it refuses to discard routing without an explicit override. placement.json is the initial coordinate record, while the saved native board is authoritative. The power routing, local-router exchange and ground-fill helpers likewise require care around later CAD edits; do not run capture scripts just to review the design.

The repository covers the future whole clock. Its hardware design currently contains only the top board; the Pico 2 firmware is a separate time-receiver experiment. The bottom board will supply protected 5 V, regulated 3.3 V, the control interface and I2C pull-ups. Its schematic and layout remain future work.