Occasionally, I’ll find myself trying to describe how a circuit works, and pencil and paper just won’t cut it. I need to show them not just how the circuit diagram looks, but how the voltage and current flows through the various components. Rather than take the time to build up a complicated SPICE simulation, there’s one tool that is perfect for quick circuit modeling: Paul Falstad’s Circuit Simulator Applet.
To place a component or wire, just click on the “Draw” menu, and select the part. Then click and drag to place the circuit component. The component values can be edited by double-clicking them, and sliders in the sidebar can control parts like potentiometers and voltage sources. You can also adjust the speed of the simulation and the speed at which the current (shown as dots flowing along wires and components) travel through the circuit. Circuits can even be saved as local text files to be opened again later, or exported as links to share them with other people.
If you’re just getting started in electronics, or looking to refresh your knowledge on how some common circuits and components work, the site features a large library of pre-built example circuits in the simulator. Examples include everything from the humble voltage divider, all the way up to sequential logic, phase-locked loops, and a spark gap Tesla coil. Strangely enough, there are even some memristor circuit examples!
Paul Falstad’s Circuit Simulator Applet is a great learning resource, and I highly recommend playing around with it. It’s definitely a site worthy of a place in your bookmarks.