How to Build & Simulate Circuits Online — A Beginner's Guide

Why Simulate Circuits?

Building physical circuits is expensive and error-prone for beginners. One wrong connection and you've blown a component. Our free Circuit Builder lets you experiment risk-free — place components, wire them up, and watch current flow in real time.

Getting Started

Head to Circuit Builder and you'll see a blank canvas.

1. Place Components

Drag components from the sidebar:

• Resistors — limit current flow (measured in Ohms)
• Capacitors — store and release charge
• LEDs — light up when current flows through them
• Batteries — provide voltage to drive your circuit
• Switches — toggle current flow on and off

2. Wire Them Up

Click on component terminals to create wires between them.

3. Watch Current Flow

Hit Simulate and watch electrons move through your circuit. The tool calculates real voltage drops and current values using Kirchhoff's laws.

Your First Circuit: LED + Resistor

1. Place a 9V battery
2. Connect a 330Ω resistor to the positive terminal
3. Connect an LED from the resistor to the battery's negative terminal
4. Hit simulate — the LED lights up!

Why the resistor? Without it, too much current flows through the LED and it burns out. This is Ohm's Law: I = V/R = 9/330 ≈ 27mA.

Series vs. Parallel Circuits

Series (components in a line): current is the same everywhere, voltage divides. If one LED burns out, the whole circuit stops.

Parallel (components side by side): voltage is the same everywhere, current divides. If one LED burns out, the others keep working.

This is why your house uses parallel circuits!

What's Next?

Try building a voltage divider, an RC circuit, or experiment with complex networks — all free at firstprincipleslearningg.com/physics/circuit-builder.