Placed

Andiron

ESP32-C6 heating controller for a UK wiring centre, built for Home Assistant and ESPHome. Board revision v1.0

Andiron is an isolated I/O board for a domestic heating system. It sits in the wiring centre, switches the zone valves and boiler demand through four volt-free changeover relays, and talks to the boiler over OpenTherm. All the logic (schedules, thermostats, weather compensation) lives in Home Assistant. The board was designed around an ESPHome firmware, which will be written and published once the first boards are in hand.

Mains voltage. The relay contacts can switch 230 V. Do not build or install it unless you are competent to work on mains wiring, and read the safety notes in docs/design.md first. Status: v1.0 passes ERC, DRC and the spacing checks, but no board has been built or tested yet.

Renders

Top	Bottom

The 3D views use stand-in models for the ESP32-C6 module (ESP32-S3-WROOM-1, same body) and the USB-C receptacle (GCT USB4105, same footprint).

Bill of materials

The full BOM with LCSC part numbers and cost estimates is in docs/BOM.md; the JLCPCB upload file is docs/bom/andiron-bom-jlc.csv. At LCSC prices from October 2026, components came to roughly $16 per board, or about $24 per board for a run of five once Extended-part loading fees are included. The four relays are $7.60 of that. PCB, assembly and shipping come on top, from the JLCPCB quote.

Getting started

Tools

Working on the board with Claude Code and Konnect

1. Install KiCad 10 and Konnect, and put konnect on your PATH (or point .mcp.json at it).
2. Open the repository in Claude Code and approve the Konnect server when asked. Claude can then read and edit the schematic and board, run ERC and DRC, and search JLCPCB parts.
3. Ask Konnect to download the JLCPCB parts database once (download_jlcpcb_database); tools/bom.py reads the same file for prices.
4. Start with docs/requirements.md and docs/design.md for what the board does and why.

The layout is generated, not drawn by hand: part positions live in tools/layout/place.py, shared dimensions (relay row, terminals, isolation zones, slots, antenna keep-out) in tools/layout/geometry.py, and hand-laid copper in tools/route/prep_board.py. Edit those and rerun the pipeline rather than moving tracks in the PCB editor.

Regenerating outputs

KPY=/Applications/KiCad/KiCad.app/Contents/Frameworks/Python.framework/Versions/Current/bin/python3
$KPY -I tools/sync_netlist.py "$PWD" tools/route/placed.kicad_pcb   # after a schematic change
$KPY -I tools/layout/place.py tools/route/placed.kicad_pcb          # after a placement change
tools/route/run_pipeline.sh "$PWD" 40    # route, pour, silkscreen, DRC, sanity (close the PCB editor first)
python3 tools/bom.py                     # docs/BOM.md and docs/bom/andiron-bom-jlc.csv
tools/render.sh                          # docs/images/

Repository layout

Open questions that must be answered before ordering are at the end of docs/design.md; the boiler model code is the main one.

License

Open hardware. The board design and documentation are licensed under the CERN Open Hardware Licence v2, Permissive, the hardware counterpart of MIT; the scripts in tools/ are under the MIT License. See LICENSE.