Build and Solve Circuits Online: Circuit Builder and Resistor Network Games
Two new interactive circuit simulators on SciFunLab: a drag-and-drop circuit builder with Kirchhoff's law solver, and a resistor network puzzle game with 8 levels including Wheatstone bridges.
Circuit analysis is one of those topics where the theory makes sense but the practice trips people up. Kirchhoff's laws aren't hard to state — KCL says currents at a node sum to zero, KVL says voltages around a loop sum to zero — but applying them to an actual circuit with multiple branches takes practice.
Two new simulations on SciFunLab are designed for exactly this: Circuit Builder and Resistor Network.
Circuit Builder: Draw, Wire, Solve
The Circuit Builder is a drag-and-drop sandbox where you place components and draw wires to connect them. Components include voltage sources, resistors, capacitors, bulbs (visual current indicators), and switches.
Once wired, the simulator applies Kirchhoff's laws using a nodal conductance matrix. It finds the voltage at every node, then calculates current through each branch. Bulbs glow proportionally to current — so you can immediately see which branches are carrying power.
Presets to start with:
- Series resistors — Three resistors in a line. Total resistance = R₁ + R₂ + R₃
- Parallel bulbs — Two bulbs side by side. Each sees the full voltage; combined resistance is R/2
- Mixed circuit — Series and parallel combined. See how two bulbs and a resistor interact
- Switch demo — Open = infinite resistance = zero current everywhere. Close it and current flows.
Resistor Network: 8-Level Puzzle Game
While Circuit Builder is a sandbox, Resistor Network is structured as a puzzle game. Eight levels with increasing complexity:
- Single resistor — establishes the interface
- Series circuit — R₁ + R₂ + R₃
- Parallel circuit — 1/R = 1/R₁ + 1/R₂ + 1/R₃
- Series-parallel combo — two-step reduction
- Wheatstone bridge — requires nodal analysis, not reducible by simple rules
- Delta-to-Y transform — triangle of resistors converted to Y configuration
- Resistor ladder — repeating H pattern (appears in DACs and transmission lines)
- Free-build Pi network — build your own topology
Each level includes adjustable resistor values (randomize for a fresh challenge), a step-through solution panel, and a hint system (costs maximum stars). Scoring: 1 attempt = 3 stars, 2 = 2 stars, 3+ = 1 star.
What These Teach
The most common misconception in introductory circuits is treating parallel resistors like series — adding them directly instead of adding reciprocals. Circuit Builder makes this visible immediately.
The Wheatstone bridge in level 5 is where most students hit their first real wall. A diamond of four resistors with a bridge resistor in the middle doesn't reduce to simple series/parallel. The step-through explanation walks through nodal analysis — the general method that works for any network.
Both games are free and run in your browser: Circuit Builder and Resistor Network.