Demo board

emcvisual

Working title. The name lives only in branding.config.json and can be changed with a script, see docs/RENAMING.md.

Try it in the browser: https://tombueng.github.io/emcvisual/

You cannot see the electromagnetic fields of a circuit board. This tool computes them from a board file and turns them into a 3D world you can look at and listen to: where does it glow, where does it hum, and what happens when the edge gets slower or the input capacitor moves closer to the switching regulator?

It also checks about 30 known EMC layout mistakes, says what to do first, explains every finding with its calculation and fix, and each time says why the statement could be wrong here. It is built on a catalogue of mistakes with sources (docs/research/EMC-MISTAKES-CATALOGUE.md), a technical review (docs/review/TECHNICAL-REVIEW-2026-10.md), generated boards with each mistake as a test bench, and a comparison with a full-wave simulation.

Everything runs in the browser. The board file does not leave your computer. The user interface speaks English and German.

What it reads

Boards from IPC-2581 and ODB++ exports give the same board and the same results as the KiCad original (checked on real boards). Eagle stores only the outlines of copper pours; the app pours them itself, the way Eagle does. Details, export settings and limits: docs/IMPORT.md.

What it does

Stage 1 (M0–M6), working: quasi-static simulation of the magnetic near field (Biot–Savart with image currents in the reference planes), and with it:

• import of KiCad, IPC-2581, ODB++ and Eagle boards; reference planes are detected, sources suggested from net names and parts
• sources: clock and data lines (also across series resistors), differential pairs, current loops of switching regulators (pads also picked in 3D), storage inductors
• the field as a glowing volume, isosurfaces, a slice plane, field lines of the selected source, ant view
• speech bubbles in 3D: the findings numbered at their place on the board (with their effect on the far field), sources with near field and distance to the limit, hotspots on request
• a virtual near-field probe with a spectrum analyser, a far-field estimate against selectable standards (CISPR 32, CISPR 11, CISPR 14-1, FCC Part 15) with an explanation of each standard
• sound: every source has a voice, loud where its field is strong
• diagnostics: interrupted return paths (also plane splits and narrow slots), reference changes at vias, missing stitching vias, unterminated lines with a resonance in the measured range, lines at the plane edge, signal layers without an adjacent plane, lines without a reference plane, hot loops and switch nodes of regulators, common mode with cables and crosstalk into cable lines (worst-case estimates), the regulators' switching current on the supply cable, filters bypassed by overlapping copper, filters and shields at connectors, ESD protection at USB/HDMI connectors, decoupling, crystals at the edge or a connector. All rules with threshold, origin and test board: docs/RULES.md. The findings are ordered by their share of the computed far field; the number on a bubble says what fixing only this spot changes in the model. Every finding has a priority (red, yellow, green), an explanation with the calculation, the fix, things to avoid, and the reasons why the statement could be wrong here
• real 3D part models: from your model folder or a GitHub repository (STEP, WRL, GLB, STL, found by file name), standard parts from KiCad's library, or from KiCad's GLB export
• scenarios as JSON, PNG and CSV export, an EMC report as HTML (printable as PDF)

Plan, acceptance criteria and notes: docs/stage-1/PLAN.md.

Stage 2 (in progress): return currents detour around slots in the plane and jump through the nearest stitching via or capacitor at a layer change (the detours are shown in 3D); electric field from line and node charges; stray field of open and shielded storage inductors. Details: docs/future/STAGE-2-PLANE-CURRENTS.md.

Stage 3 (in progress): full wave with openEMS. The app exports a job, tools/openems/run_job.py computes it locally, and the result can be loaded next to the fast model as a second field source: volume, probe, scan and far field. In the quasi-static range both agree to about 1 dB; on a validation board the fast far field agrees with openEMS within 1 dB between 30 and 350 MHz. Details: tools/openems/README.md, docs/future/STAGE-3-FULL-WAVE.md.

Field check for CI: the same calculation as a Node script. It reports near field, far-field margin and layout findings per source and fails when a pull request makes something worse. The script is at https://tombueng.github.io/emcvisual/cli/field-check.mjs, instructions in docs/CI-FIELD-CHECK.md.

Stage 4 (in progress): the "Measure" tab: a 3D printer moves a near-field probe over the board, a receiver measures a spectrum at each point, and the result appears as a slice at the measuring height and as a difference to the simulation. A virtual rig measures the simulation and shows the whole chain without hardware; the drivers for OctoPrint, G-code over USB and the tinySA are written but not yet tried on a device. Details: docs/future/STAGE-4-SCANNER.md.

What comes later (plane solver, phase and waves, hand probe, VR): docs/ROADMAP.md.

Getting started

npm install
npm run dev

Then choose "Load demo board" in the browser, or drop your own board on the window (.kicad_pcb, IPC-2581 .xml, ODB++ .tgz/.zip or Eagle .brd). In Chrome and Edge the app follows the opened file: every save in the CAD program reloads the board, and sources and view stay (badge "live" next to the file name). The step-by-step guide to every panel is docs/USER-GUIDE.md.

Real part models (right, under "Real 3D part models"): a KiCad board names only the path of each part's model, such as ${KIPRJMOD}/3d/Relay.step or ${KICAD10_3DMODEL_DIR}/Package_SO.3dshapes/SOIC-8_3.9x4.9mm_P1.27mm.step. The app looks for the file by its name:

• in a folder on your computer ("Choose a folder with models …", with subfolders; the files stay in the browser),
• in a GitHub repository (https://github.com/<owner>/<repo> or a subfolder …/tree/<branch>/<path>),
• in the project folder of a board opened by link (${KIPRJMOD}/… sits next to the .kicad_pcb),
• in KiCad's standard library (from gitlab.com, STEP; can be switched off).

If a model exists several times, the same library folder wins, then STEP before GLB, WRL and STL. STEP is triangulated in the browser with OpenCascade (WebAssembly, in the background), with the colours from the file. Parts without a model found are listed.

Alternatively KiCad's own export: "File → Export → glTF/GLB" (without the board body) or kicad-cli pcb export glb --no-board-body --subst-models board.kicad_pcb, then drop the .glb on the window as well. The parts are matched by their reference; the GLB takes precedence over the libraries. Boards from other CAD tools carry no model references; their parts are shown as boxes.

Example boards to try

Public boards in every format the app reads, loaded straight from GitHub (also under "Examples …" in the app, grouped by format):

The boards belong to their projects and are under their licences; they are not in this repository.

Boards can also be opened by link: ?demo loads the demo, ?board=<URL> a board file (any of the formats above) from a server that allows cross-origin reads (e.g. raw.githubusercontent.com), optionally with &models=<URL> for a GLB. Example: Glasgow revC3.

What the simulation can and cannot do

It shows where current loops create magnetic fields and how changes to loop area, return path and edges affect those fields, and it finds the known layout mistakes (checked on generated boards with each mistake, tools/emc-cases). It does not predict whether a device passes an EMC test: tests mostly fail on common-mode currents on cables, which the app estimates only roughly for the worst case; there are no resonances and no enclosure. Every explanation says why its number could be wrong here. Assumptions and limits are in docs/stage-1/PHYSICS.md, the known kinds of mistakes in docs/research/EMC-MISTAKES-CATALOGUE.md, the technical review in docs/review/TECHNICAL-REVIEW-2026-10.md.

Documentation

• docs/USER-GUIDE.md: how to use the app, panel by panel, with a FAQ and a glossary
• docs/IMPORT.md: boards from other CAD tools (IPC-2581, ODB++, Eagle)
• docs/RULES.md: every finding with threshold, origin, confidence and test board
• docs/research/EMC-MISTAKES-CATALOGUE.md: 40 layout mistakes with mechanism, lab symptom, detection rule, fix and sources
• docs/stage-1/PHYSICS.md: model, formulas, validity, literature, comparison with full wave
• docs/stage-1/ARCHITECTURE.md: structure of the app
• docs/stage-1/PLAN.md: goals, milestones, acceptance criteria
• docs/review/TECHNICAL-REVIEW-2026-10.md: review of the physical and normative statements
• docs/DECISIONS.md: decisions with their reasons
• docs/ROADMAP.md: stages and dependencies
• docs/future/: stages 2 to 5 and cross-cutting topics
• docs/CI-FIELD-CHECK.md: the field check in CI
• docs/AI-PARTS-MANUAL.md: how an AI agent can fill in the source parameters of a board

Licence

0BSD (Zero-Clause BSD): anyone may use, change and share the code for any purpose, also commercially, without attribution. openEMS (stage 3) is under GPL-3.0 and installed separately; it is not part of this repository. To read STEP models the app loads occt-import-js (OpenCascade as WebAssembly, LGPL-2.1) unchanged as its own worker with its own .wasm file; its licence applies to it.