A regulated supply feeds a single trunk trace to a junction node, which fans out into seven parallel component loads (LED bank, MCU core, sensor, motor driver, RF module, memory chip, power LED array) — the same PCB the 3D "Circuit Board City" stylizes as a skyline. Every trace segment's resistance comes from real copper geometry:
ρ(T) = ρ₀·(1 + α·(T − 20°C)) ρ₀ = 1.68×10⁻⁸ Ω·m, α = 0.00393/°C
R_trace = ρ(T) · length / (width · thickness) thickness = oz · 34.8 µm
I_total = V / (R_trunk + R_parallel), R_parallel = 1 / Σ(1/R_branch_i)
V_junction = V − I_total · R_trunk (Kirchhoff's voltage law)
I_i = V_junction / (R_trace_i + R_component_i) (Kirchhoff's current law: ΣI_i = I_total)
P_i = I_i² · R_i (Joule heating per segment)
Thinning the trace or raising board temperature increases every trace's resistance (copper's positive temperature coefficient), pulling more of the supply voltage across the copper itself instead of the components — visible directly as the trunk's color shifting from cool green toward hot red and the junction voltage sagging below the supply.
- Trace color — power-dissipation heatmap (P=I²R), normalized per-frame so the relatively hottest run always reads red.
- Pulses — travel proportional to that branch's actual current; the motor driver (lowest resistance) always carries the most current.
- Peak J density — worst-case current density (A/mm²) across all traces; above ~30 A/mm² a trace this size is outside safe external-layer ratings and the readout turns red.