The problem with "circuit simulators" on the web
Most browser-based circuit tools either fake it (animate current flow without real math) or wrap an existing SPICE engine. I wanted to actually implement the math myself — a Modified Nodal Analysis (MNA) solver, the same technique real SPICE tools use under the hood — and then give it a 3D interface instead of the usual flat 2D schematic.
The result is CircuitForge: place components on a 3D breadboard, wire them up, and get real computed node voltages and branch currents — not an animation.
The actual solver
MNA builds a matrix from Kirchhoff's Current Law at every node, plus extra equations for voltage sources, then solves it. Stripped down, the core loop looks roughly like this:
const g = 1 / resistance;
matrix[nodeA][nodeA] += g;
matrix[nodeB][nodeB] += g;
matrix[nodeA][nodeB] -= g;
matrix[nodeB][nodeA] -= g;
Solve Ax = z for the node voltage vector, and you get exact values — not an approximation. I validated it against hand-calculated results on a few real circuits (simple divider, diode network, a series-parallel KCL cross-check) before trusting it in production. Full writeup with the actual worked numbers is here: luvaai.in/learn/circuit-simulator-accuracy-validation.
Then the fun part: making it 3D
Three.js handles the scene, camera, and raycasting for placing/wiring components. The tricky bit wasn't rendering — it was making wire connections feel physical: snapping to component pins, detecting valid connection points, and keeping the 3D positions in sync with the underlying circuit graph the solver actually operates on. Two completely separate data models (3D scene graph vs. circuit netlist) that have to stay perfectly consistent.
What it can't do (yet)
Being upfront: this is DC operating-point analysis only right now — no transient simulation, no AC frequency sweeps. If you need to see a capacitor charge curve over time, this isn't there yet. It's on the roadmap, but I'd rather ship an honestly-scoped DC solver than fake a transient one.
Try it
Live at luvaai.in — no signup needed, just start placing components. If you've built anything with raycasting-based node/wire editors, or have thoughts on extending MNA to transient analysis, I'd love to hear it in the comments.