the act of imitating the behavior of some situation or some process by means of something suitably analogous

Do you know who Paul Falstad is?  If not, you really need to get to know him, or at least, his web site.  He’s a Geocacher, a Java programmer, and a Math nerd.  [Editor’s Note:  I don’t know Paul, I just read his web site.]  The easiest book mark I can access in my web browser is a link to one of Falstad’s applets:  A Circuit Simulation written in Java.  A very functional simulator, at that.

Want a non-Java solution and using OS X or iOS? Check out iCircuit.

When it comes to simulating circuits in electronics, for a long time, engineers relied solely on pSPICE.  This meant you would generally build a netlist in a text file or generate one through a schematic capture program.  You would then define some parameters like a sweep of frequencies, run the simulator, wait for the results.  While the information was useful, it could take forever to just get everything right.

Falstad’s circuit simulator as simple as:  draw a circuit and watch the feedback instantly.  Just look at the default circuit when the simulator loads:

simulator screen shot

A simple circuit that allows you to charge up the inductive and capacitive elements, by clicking on the SPST switch.  (Clicking on the SPST switch in the schematic will open and close it.)  The built-in scope allows you to monitor voltage and current through a node, wire, or component.  You can also get other instantaneous parameters as well.

Creating your own circuit is really straight forward.  The key is in the Right-Click Context Menu.  As you get to using the simulator, you’ll learn some of the keyboard shortcuts.  Select an element.  Something to note, it isn’t obvious at first how to create components.  You have to “click-drag” to draw a component on the screen.  Click once to start drawing it, and then drag.  Release to stop drawing.

Next time you want to simulate a filter or are curious about what a voltage divider will do, check out this very cool engineering resource.  It is one of the fastest and easiest ways to simulate electronic circuits.


Fan of making things beep, blink and fly. Created AddOhms. Stream on Twitch. Video Host on element14 Presents and writing for Hackster.IO. Call sign KN6FGY.


  1. Matteo Pascoli Reply

    Hi James! I am struggling to make a sram with discrete cmos. No matter how long I search the net, I can’t find anyone who did that.
    Anyway, I have modeled a latch with falstad simulator. My problem is, it works fine if I uncheck “show bulk”; but if I enable it again, the output just follows the input, ignoring the “enable” signal. I must say that I am a newbie with electronics, and I don’t understand why this happens. And most importantly, whether the circuit should work if I build it.
    I could send you the text to import the circuit I made, how can I do it?

    • Sorry, I do not think this is something I can help you with. I’ve never built a digital circuit in falsted, so I’m not sure what the issues would be.

  2. ​I mirrored his fantastically easy to understand simulator, because he makes it available at GitHub and I wanted to showcase many of my circuits all in one place whose development his simulator has made possible. Yeah, I’ve used LTSpice on occasion and Micro Cap, v.11, but either they’re more rigid in disallowing surges or else they don’t allow surge oriented circuits at all, respectively. So, I prefer to use Paul’s.

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