Circuit Simulator
A virtual breadboard with real circuit math. Wire up batteries, bulbs, resistors and switches, watch the current actually flow — and try not to trip the short-circuit alarm.
What is the Circuit Simulator?
This is a free electric circuit builder that behaves like the real thing. You place components on a breadboard grid — a 9-volt battery, 15-ohm bulbs, resistors, switches, and plain wire — and every time the board changes, the simulator rebuilds the circuit's equations and solves them exactly, using modified nodal analysis, the same technique professional tools like SPICE are built on. The moving dots you see are the solved current; the bulb brightness is the solved power; the probe readings are the solved voltages. Nothing is faked.
That honesty is the point. Circuit diagrams in textbooks are static, and it is genuinely hard to develop an instinct for what electricity does from arrows on paper. Here you can close a switch and watch the current split at a junction, add a second bulb and see both dim, or connect the battery to itself and set off the short-circuit alarm — each mistake is instant, visible, and free, which is precisely what a classroom breadboard offers, minus the burnt fingertips.
How to Use It
The Components
Everything on the palette, and the numbers the solver uses for each:
| Component | Value | What it does |
|---|---|---|
| 🔋 Battery | 9 V | Pushes current around the loop. Tap to flip which end is +. |
| 💡 Bulb | 15 Ω | Glows with the power it dissipates — brightness is the solved wattage. |
| ⧟ Resistor | 10 / 25 / 50 Ω | Limits current without glowing. Tap to cycle its value. |
| ⏻ Switch | open / closed | Breaks or completes the loop. Tap to flip. |
| 〰 Wire | 0.1 Ω | Connects things with almost no resistance — which is why wire-only loops short. |
How Circuits Actually Work
Ohm's law is the whole engine. Current equals voltage divided by resistance: I = V ÷ R. Put the 9-volt battery across a single 15-ohm bulb and about 0.6 amperes flow, delivering about 5.4 watts — a bright bulb. Everything else in the simulator is this one law applied around loops and junctions.
Series shares, parallel copies. Two bulbs in one loop (series) share the 9 volts, so each gets half the push and the current drops to about 0.3 A — both bulbs glow dimly at about a quarter of the single-bulb power, roughly 1.3 W each. Two bulbs on separate branches (parallel) each get the full 9 volts and burn at full brightness — but the battery now supplies double the current, which is why parallel strings drain batteries faster. Load both presets and probe the bulbs; the numbers tell the story instantly.
A short circuit is Ohm's law with nothing in the way. Connect the battery's terminals through nothing but wire — the tightest loop this board allows is three wire segments, 0.3 Ω — and I = 9 ÷ 0.3 = 30 amperes, a wildly unsafe current for a small battery. Build it and the probe reads exactly that. The simulator trips its alarm above 6 A. In your house the same physics is why a frayed cable can trip a breaker: the breaker is doing exactly what this alarm does.
Things to Try
What the challenges secretly teach:
First light
Make any bulb glow. This needs the one idea everything else builds on: a complete loop from + to −. A bulb on a dead-end branch never lights, because current cannot flow into a cul-de-sac — it needs a way home.
Two in a row, then split the flow
Light two bulbs in series, then rebuild them in parallel. Series: same current through both, voltage shared, both dim. Parallel: full voltage across both, current doubled at the battery, both bright. This single comparison is most of a first electronics lesson.
Make a dimmer
Put a resistor in series with one bulb and leave another on a free branch. The resistor eats part of the 9 volts, so its bulb runs at a fraction of the power — get one bulb to four times the power of the other. Congratulations: you have invented the volume knob.
Build a master switch
Place one switch so that opening it kills at least two lit bulbs at once. It only works if the switch sits on the shared part of the loop, before the current splits — which is exactly where your house's breaker panel sits, and why one breaker can darken a whole room.
Honest Limits
The solver is real, but the world is simplified: this is a DC simulator with ideal components. Wire here has a fixed 0.1-ohm resistance, the battery never runs down or sags under load, bulbs have constant resistance instead of heating up, and there are no capacitors, inductors or AC — so no filters or oscillators. Those simplifications are deliberate: they keep every reading explainable with I = V ÷ R, which is the level this tool teaches. When a reading surprises you, the explanation is always Ohm's law, never a hidden model.
FAQ
Is the Circuit Simulator free?
Yes — the simulator is completely free and runs instantly in your browser. There is no download, no sign-up, and nothing to install.
Is the electricity real or just an animation?
The numbers are real. Every time you change the board, the simulator rebuilds the circuit's equations (modified nodal analysis — the same method professional tools like SPICE use) and solves them exactly. Bulb brightness, the multimeter readings and the moving current dots all come from that solution, not from a canned animation.
Why does the short-circuit alarm go off?
If you connect the two ends of the battery with only wire, almost nothing resists the current, so it spikes — in this simulator anything over 6 amperes trips the alarm. A real 9-volt battery shorted this way gets hot fast, which is exactly why fuses exist. Add a bulb or resistor to the loop and the alarm clears.
What do the components do?
The battery pushes 9 volts across the circuit (tap it again to flip its polarity). The bulb is a 15-ohm resistor that glows with the power it dissipates. The resistor cycles through 10, 25 and 50 ohms each time you tap it. The switch opens and closes the loop, and wire connects everything with almost no resistance.
Is my progress saved?
Your completed challenges are saved in your browser's local storage on this device, so the badges stay earned between visits. The board itself resets when you leave — rebuilding a circuit is half the learning.