| name | circuit-simulator |
| description | Use when modeling, validating, drawing, simulating, or extending the /lab/circuit-sim circuit simulator — adding component types, MNA/transient/AC/nonlinear solver work, terminals and symbol drawing, probes, the oscilloscope/Bode views, or YAML/samples/share links. |
Circuit Simulator
Reference for the /lab/circuit-sim simulator: a device-stamp MNA engine (DC, transient, AC, nonlinear Newton-Raphson) with a Canvas instrument front-end. Drawing/terminal/symbol detail lives in drawing-rules.md (read it for any rendering work).
Architecture — three layers
lib/lab/circuit-sim/ ← HEADLESS engine (no React/DOM/canvas; vitest node env)
types.ts → ComponentType, CircuitComponent, Probe, ScopeSettings, AnalysisMode,
Waveform, componentNodes() ← single source of a component's node list
devices.ts → per-device STAMP registry (DC_STAMPS / TRANSIENT_STAMPS), StampContext, SolveEnv
mna.ts → assembleMNA(): builds the real MNA system by dispatching stamps
solver.ts → solveCircuit() (linear OR Newton-Raphson), solveDC(), LU (luDecompose/luSolve)
operating-point.ts → solveOperatingPoint(): DC node V + per-device branch I/power for the live overlay
transient.ts → transientStep(): trapezoidal companion step (delegates to solveCircuit)
complex-solver.ts → cluSolve(): complex LU (interleaved re/im) for AC
ac.ts → acSweep(): complex MNA per log-spaced freq → Bode (mag dB + phase deg)
sources.ts → evalSource()/sourceValue(): waveform value at time t
results.ts → nodeVoltage/componentVoltage/componentCurrent (probe values)
measure.ts → measureTrace(): Vpp/min/max/mean/RMS/freq over a ring buffer
validator.ts → validateCircuit() diagnostics + CircuitBuilder + assertDC/assertTransient
verifier.ts → verifyCircuit(): structural + KCL/KVL/power sanity (powers sample tests)
laws.ts → checkKCL/KVL/power, fuzzing helpers
draw.ts → getAllTerminals/terminalForNode/getTerminalPositions, gridSnap, symbol drawing
wiring.ts → generateWires() (hub-star Manhattan) + computeManhattanPath
placement.ts → renderCircuit()/validatePlacement() (headless geometry validation)
yaml.ts → serialize/deserialize round-trip
storage.ts → encodeCircuit/decodeShareYaml (base64url share links) + localStorage library
samples.ts → SAMPLES + groupedSamples() (6 categories, with "look for" notes)
components/lab/circuit-sim/ ← React/Canvas layer
instrument.ts → INSTRUMENT palette (theme-independent dark) + voltageColor() heat ramp
circuit-canvas.tsx → Pointer-Events canvas: place/drag/wire/pan/pinch-zoom/click-probe + draw;
DC-overlay annotations (node V chips + branch I), HTML5 drop-to-place, ResizeObserver
inspector.tsx → selected-component editor: value, waveform editor, switch toggle, probe buttons (onEndEdit closes undo coalesce)
scope-canvas.tsx → oscilloscope (trigger, volts/div, freeze, per-channel measurements) + draggable Δt/ΔV cursors
bode-canvas.tsx → magnitude(dB) + phase(deg) vs log-frequency
analysis-panel.tsx → tabs: Transient (scope) | AC (Bode)
scope-panel.tsx → drawFlowParticles() (animated current on wires)
circuit-studio.tsx → fullscreen "Studio" popout (createPortal): IDE layout — top run/transport bar, left palette,
canvas, right inspector + probe-manager, bottom analysis dock, status bar; resizable docks
(pointer-capture splitters, localStorage), keyboard shortcuts, Fullscreen API
probe-manager.tsx → editable channel list: rename / recolour / show-hide / remove probes
studio-tour.tsx → dismissable spotlight coach-mark walkthrough (data-tour anchors in circuit-studio); auto-opens
once per browser (localStorage cs.studio.tourSeen), replayable via the studio header "?" button
react-bits.tsx → StarBorder + ShinyText (reactbits.dev-style) for the "Open Studio" CTA (keyframes in globals.css: cs-star-*, cs-shine)
component-palette.tsx (draggable + Duplicate), toolbar.tsx, gallery-dialog.tsx
app/lab/circuit-sim/ ← Next route: page.tsx (metadata) + circuit-sim-page.tsx (wires it up, ?c= hydration,
"Pop out to Studio" toggle — embedded view + studio SHARE one useCircuitEditor)
Iron rule: the engine (lib/lab/circuit-sim/) is headless — never import React/JSX/DOM/canvas there. Placement validation, the solver, and all tests run without a browser.
Editor hook (use-circuit-editor.ts) — the single source of UI state
One useCircuitEditor() instance drives BOTH the embedded widget and the fullscreen studio (passed as editor). Beyond placement/wiring/probing it owns: undo/redo (past/future circuit snapshots, coalesced per gesture via a historyCoalesce key — drags/typing collapse to one step; endInteraction() closes the window), duplicateComponent, pause/resume/step + simSpeed (Run resumes a paused sweep unless the topology changed; runFrame is a pure stepper — it deep-copies companion {vPrev,iPrev} so it never mutates the caller), DC overlay (showDcOverlay → derived dcOp recomputed off the live circuit when not running), and probe edits (rename/recolour/visibility/clear).
Studio (circuit-studio.tsx)
Fullscreen overlay portalled to document.body (z-100). Esc is owned by the canvas only when it has something to cancel (placing/wiring/selection) — it stopPropagations then, else bubbles to the studio's window listener which closes it. Number keys 1–9 place components, Space run/pause, S step, ⌘Z/⌘⇧Z undo/redo, ⌘D duplicate, O dc-overlay, F fullscreen.
Data model (types.ts)
ComponentType = 'R'|'L'|'C'|'V'|'I'|'D'|'SW'|'OP'|'GND'.
CircuitComponent: id, type, value, nodeA, nodeB, x, y, rotation + optionals:
nodeC? — op-amp output node (nodeA = in+, nodeB = in−).waveform? — { kind: 'dc'|'sine'|'pulse'|'square', amplitude, offset, freq, phase, duty } (V/I sources).acMag? — AC stimulus magnitude.closed? — switch state.
componentNodes(comp) returns the node list: 1 (GND), 3 (OP), 2 (everything else). ALWAYS enumerate nodes through it — assembleMNA, validator adjacency, wiring, placement all do. Reaching for nodeA/nodeB directly is the classic op-amp bug (3rd terminal dropped).
Probe: { id, kind: 'nodeV'|'compI'|'compV', ref: nodeId|compId, label, color, visible, unit: 'V'|'A', samples (ring buffer), writeIdx, count }.
Solver — device-stamp MNA
Each device contributes to the MNA matrix via a stamp (comp, ctx: StampContext, env: SolveEnv) => void. ctx exposes row(node)→matrix row|null(ground), vsRow() (allocate branch row), addG(r,c,v), addZ(r,v), branchRows. env carries mode, dt, time, state (companion), prev (NR guess), nrState/nrFlags (NR limiting). assembleMNA() loops components dispatching DC_STAMPS or TRANSIENT_STAMPS.
Branch rows: V always; L only at DC (0V source); OP always (nullor output current). C/L use the trapezoidal companion in transient (conductance + current source, no branch row).
Four solve paths:
- DC op-point —
solveDC → solveCircuit(makeDCEnv()).
- Transient —
transientStep → solveCircuit(...), then companion vPrev/iPrev update post-solve.
- Nonlinear (diode) —
solveCircuit auto-detects any 'D' and runs Newton-Raphson (else one LU). Re-stamps each iteration around env.prev; converges when max node-voltage delta < NR_TOL (1e-7) AND no junction was voltage-limited this iteration (nrFlags.limited); ≤ MAX_NR_ITERS (100).
- AC —
acSweep() assembles a complex MNA per log-spaced frequency (R→G, C→jωC, L→1/jωL, V/I→stimulus), solves with cluSolve, returns Bode magnitude(dB)/phase(deg) per probe.
Device behavior
| Type | Term. | DC | Transient | AC |
|---|
| R | 2 | conductance 1/R | same | G = 1/R |
| C | 2 | open (no stamp) | companion gEq=2C/dt, iEq=gEq·vPrev+iPrev | jωC |
| L | 2 | 0V source (branch row) | companion gEq=dt/2L, iEq=iPrev+gEq·vPrev | 1/(jωL) |
| V | 2 | branch row, value = sourceValue (waveform bias or value) | value = evalSource(t) | unit stimulus / 0 |
| I | 2 | current injection | evalSource(t) | current stimulus / 0 |
| D | 2 | Is(e^(Vd/nVt)−1)+Gmin·Vd, NR-linearized | same | small-signal Geq at DC op-point |
| SW | 2 | conductance SW_ON=1e3 (closed) / SW_OFF=1e-9 (open) | same | same |
| OP | 3 | ideal nullor (linear): v(in+)−v(in−)=0, free output current → nodeC | same | same |
| GND | 1 | reference (node 0) | — | — |
Diode constants: Is=1e-14, n=1, Vt=0.025852, Gmin=1e-12. AC stimulus = first source with acMag, else first V, else first I; all other independent sources AC-grounded.
Validation (validateCircuit)
Ten diagnostic codes (severity: error|warning|info): EMPTY, NO_GROUND (err), INVALID_VALUE (err), ZERO_VOLTAGE (warn), FLOATING_NODE (err), OPEN_LOOP (err), PARALLEL_VS (warn), SINGULAR (err), DEAD_END (info), READY (info). Same function powers the UI sidebar and vitest assertions.
Logic that bites if you forget it:
INVALID_VALUE is passive-only (R/L/C value ≤ 0). Sources (V/I) may legitimately be 0; diode/switch/op-amp/GND have no meaningful value.ZERO_VOLTAGE only fires for a DC V source (value===0 && !waveform).- Adjacency (
buildAdjacency) cliques all of a component's componentNodes (so the op-amp output is "driven", not floating) and includes capacitors for connectivity.
verifier.ts exempts reactive- or AC-waveform-driven circuits from the "resistors have DC current" / "distinct voltages" checks (a pure sine biases to 0V at DC).
Programmatic test API: assertDC(circuit,{node:V},tol), assertTransient(...), circuit().v(5,1,0).r(1000,1,2).gnd().build().
Probing, scope & Bode
- Probe kinds:
nodeV (click any wire), compI (current through), compV (V across). results.ts computes values per kind; measure.ts derives Vpp/RMS/freq.
scope-canvas: shared time base, trigger (edge + level + source), auto-fit or volts/div, freeze (snapshots probes so the sim runs on), per-channel legend with live measurements.bode-canvas + analysis-panel: AC mode auto-recomputes the sweep on circuit/probe/option change.
Persistence & samples
yaml.ts flattens optional fields: wkind/wamp/woff/wfreq/wphase/wduty, acmag, closed, nodeC.storage.ts: encodeCircuit→?c= base64url share links (UTF-8 safe), decodeShareYaml hydrates on mount; localStorage library via pure upsertSaved/removeSaved helpers.samples.ts: groupedSamples() → 6 categories (Basics/RC/RLC/Filters/Bridges/Active); metadata (category, lookFor) keyed by name in SAMPLE_META. Don't hardcode a sample count anywhere (the old skill said "7" and rotted).
Field-tested gotchas
- Companion current sign — inject
+iEq INTO node a, −iEq from b (stampCurrent). Reversed → oscillating voltages.
- Diode NR convergence — seed
pnjlim's vold at 0 (not the raw vd), and only declare convergence when no junction is still limited (nrFlags.limited). Otherwise geq stays tiny while pnjlim ramps, node deltas look small, and it "converges" with the diode off (output ≈ 0).
- Diode companion —
Geq=Is/nVt·e^(Vd/nVt)+Gmin, Ieq=Id−Geq·Vd, stamp as conductance + stampCurrent(ai,bi,−Ieq).
- Op-amp is LINEAR (nullor) — no Newton needed. It needs a branch row (output current), the input constraint row
v(in+)−v(in−)=0, current into nodeC, and componentNodes updated everywhere for the 3rd terminal.
completeWire must set fromCompId/toCompId; both endpoints become the merged node keep. The renderer resolves the actual terminal via terminalForNode, not endpoint indices.- GND emits ONE terminal via
getAllTerminals (the old 2-duplicate form is gone). Tests that assumed "2 terminals/component" must sum componentNodes(c).length.
- Stale dev server — after engine edits, hard-reload; HMR can serve stale stamps. Symptom: a source value stays constant instead of following its waveform.
- Pinch-zoom — lock the two pointer ids in
pinchRef and re-seed when dropping to 2 pointers, or lifting a 3rd finger swaps the tracked pair and the zoom jumps.
- Inspector NumberField — skip the value→buffer resync while the field is focused, else live-commit reformats in-progress text ("0.5"→"500m").
Testing
vitest node env; the suite covers solver/transient/devices/mna/ac/complex-solver/results/measure/operating-point/diode-switch/opamp/validator/placement/wiring/yaml/storage/laws/verifier. placement.test.ts validates every sample (zero error-severity issues — no diagonal wires; grid-aligned terminals). Run: npx vitest run lib/lab/circuit-sim/.
E2E (e2e/circuit-sim*.spec.ts, incl. circuit-sim-studio.spec.ts for the popout): Playwright. Specs use const BASE = process.env.CS_BASE ?? '' — default (relative URLs) runs against the static export that playwright.config serves at :4321 (so npm run build first), or set CS_BASE=http://localhost:3000 to run against a live next dev. Studio assertions key off data-testid="circuit-studio" / studio-run and the status-bar text; the scope-channel signal is the legend rms readout (NOT a "Probes"/"CH1" label — those rotted once already).
References
Litovski "Modified Nodal Analysis" · Najm "Circuit Simulation" (companion/Newton stamps, pnjlim) · Vladimirescu "The SPICE Book" · Nagel "SPICE2" · IEC 60617 / IEEE 315 (graphical symbols).
