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Electronic Circuit Simulator in the Browser (falstad.com)
534 points by okket 20 days ago | hide | past | web | favorite | 134 comments

While we're on the subject, allow me to plug Electrical Age: https://electrical-age.net/

It's a minecraft mod, yes. It's also a fully functional DC electrical simulation, with realism as a primary focus. Any inaccuracies are either strictly required (= it runs at 20Hz for most purposes), or allowances for decent gameplay.

(Or bugs. Those are probably my fault.)

Minecraft is an amazing learning tool even for adults! I used Minecraft as a "build along" tool for fully understanding logic gates while reading "Code: The Hidden Language of Computer Hardware and Software" (which I highly recommend - great book!). I used a mod called "red power" to make laying out the circuits much easier (the color coded, bundled cables alone were worth using it). Perhaps I will have to fire up Minecraft and take Electrical Age for a spin - it looks REALLY cool!

People don't realize how much crazy stuff originates from minecraft.

For instance, battle royale (e.g. fortnite, pubg, realm royale, etc). That came from a minecraft mod based on hunger games before Arma+dayZ implemented it on their end. https://en.wikipedia.org/wiki/Battle_royale_game

But there's way more cooler stuff than that coming out of minecraft.

We have people building full blown computers in minecraft too.

Example: https://www.youtube.com/watch?v=SPaI5BJxs5M

You can even livestream yourself on a TV screen that you make on minecraft. Example: https://youtu.be/IdlZRhKmWJY?t=327

The full blown computers running in Minecraft has made me hope for more games that make computation an integrated part of game mechanics.

Like what if parts of the game code where represented as the environment. So that you can build your own game. Perhaps you can mod the game from inside the game. Or perhaps something more controlled, like modifying the level generation by interacting with the level itself.

>The full blown computers running in Minecraft has made me hope for more games that make computation an integrated part of game mechanics.

You know, speaking of which, I actually learned FORTH from Minecraft.

Years ago, there was a now-defunct mod, Redpower 2, that massively expanded on the game's existing redstone mechanics. Redstone wires that could be run on walls and ceilings, insulated wires, bundled cables that carried 16 signals in parallel, a plethora of single-block logic gates, and a huge array of added features like the motorized "frames" that let you move huge constructions all at once, or the sophisticated pneumatic-tube networks for moving, routing, and sorting items. It was hugely popular; many features it introduced worked themselves so deeply into the modded community that clones copying many of its mechanics would remain popular to this day.

And one of the things it added, in one update, was a computer - specifically, an emulated custom 6502 variant (the 65EL02) with 8K of RAM (expandable to 64K), and a boot disk for a FORTH-based operating system to run on it. (Some dedicated users did code up other operating systems; someone ported BASIC to the thing, although it took up an awful lot of that limited memory)

Nobody had ever seen anything like it in the modded community, and a lot of children (including me) made at least a nominal effort to learn some basic FORTH so we could build things like password-locked doors, or pilot frame-based flying machines to do useful things like quarry out half the world and deliver it to our doorstep. Lots of more advanced stuff got built, too - 3D printers, computer-controlled automatic crafting systems, teleporters with selectable destinations.

The Redpower computers ended up not terribly popular, in the end - FORTH, being a language from 1970 that nobody had heard of before and which didn't look much like anything else most Minecraft players had ever used, proved a pretty intimidating barrier to entry; and shortly after Redpower introduced their feature someone else made their own mod that added Lua-based computers with a much less barebones OS and friendlier ways of interacting with useful functionality. This had a much easier time taking off.

In my opinion, at this extreme, it becomes more like work, not fun. Might as well use the brain cells for building a "real" game.

I'm honestly curious: where do you think the boundary between work and play occurs here? It seems to me that many of those that make those mods do it mostly as a recreation, don't you think?

> where do you think the boundary between work and play occurs here?

a) complexity

b) failure rate

c) consequences

Exactly! And that's the beauty of designing such a game in the right way. There's an opportunity to narrow down the freedoms in just the right way to limit failure rates.

I don't think complexity alone is a game stopping issue. There are plenty of highly complex games that people find fun and addictive. But complexity in combination with high failure rates (a lot of trial and error) will kill the fun.

But I think that high complexity with low error rates is perhaps exactly what makes a game fun. If you can express yourself freely and roam around while expecting most of your actions to produce an interesting result the game will be very interesting.

It's a very nice mod. I love designing systems in modded Minecraft, it's very fun and relaxing.

A colleague of mine wrote a mod for controlling an IBM WebSphere app server via a virtual control panel in MC.

Don't discount your mod because it's made for Minecraft, this looks like a lot of fun!

ho wo use that lol to leasrn circuits ?

I'll throw my hat into the ring as well. I have also recently been building a small signal AC analysis circuit simulator [1]. The main idea behind it is to convert a closed source tool that has been around for years within the LIGO scientific collaboration to one that is open source and implemented in Python. It's almost functionally complete, can simulate transfer functions and (accurate) noise from op-amps, resistors, capacitors and inductors in circuits with current or voltage sources. There is a library of popular op-amps for which we've measured the noise, open loop gain and various other parameters, available to be simulated with.

[1] https://git.ligo.org/sean-leavey/circuit

Is there some fundamental differences between this and the more established simulators like (ng)spice and QUCS? Trying to understand the rationale of building your own

When LISO (the tool my project is based on) was first made, SPICE simulators couldn't properly handle "realistic" op-amp parameters, like finite open loop gain, strange phase shifts due to output impedance especially of FET-based op-amps, realistic noise, stability of circuits containing feedback loops, etc. Furthermore, SPICE models provided by manufacturers typically don't represent the real behaviour of their op-amps, especially when it comes to noise, so the idea was to build a tool to which you can give arbitrary, perhaps measured, noise spectra.

LISO also contains a brilliant fitting routine which can take a measured transfer function or noise spectrum and fit circuit parameters (e.g. op-amp noise, resistor values, etc.) to the data. It first uses some standard fitting algorithm (e.g. Nelder-Mead) to get close to the possible minimum, then uses a custom optimisation in log space to get the global minimum. If I remember correctly the author published a paper on this, and I can try to find it if someone is interested.

Looks pretty cool but the input is pretty esoteric to a newbie like me: https://git.ligo.org/sean-leavey/circuit/blob/master/example...

Same thing about the output format: https://git.ligo.org/sean-leavey/circuit/blob/master/example...

Is this a custom file format or a well known one?

Also, the references to LISO are all behind a user/password wall, which makes it hard to learn: https://wiki.projekt.uni-hannover.de/aei-geo-q/start/softwar...

Thanks for taking a look!

> the input is pretty esoteric to a newbie like me

Yeah, those input and output files are what LISO uses. This was developed between around 1995 and 2010, and was built mostly to solve specific problems the original author was having with circuits and not as a generic tool, hence the syntax. You can avoid using this syntax at all as everything gets parsed into Python objects - see e.g. [1].

> Is this a custom file format or a well known one?

Custom. It's similar to a SPICE input file, but not identical. The author told me that he didn't know about parsing algorithms like Lex/Yacc when he wrote it, otherwise it might have been nicer.

> the references to LISO are all behind a user/password wall

Sorry about that. As I said, this was a tool used internally within the collaboration for many years. I am working on getting at least the manual made publicly available, but there are some proprietary libraries with unclear licences preventing public release of the binary and source code. Ideally, eventually my Python project will replicate all of the features of LISO and we won't even need the old binary any more.

EDIT: if you like, I can send you the manual and binary for LISO to the email in your profile - let me know.

[1] https://git.ligo.org/sean-leavey/circuit/blob/master/example...

It has a familiar Fortran/Academia/FEM solver vibe. This is very, very likely a format inherited from a Fortran code.

Ah, that might be the inspiration. The author used FORTRAN for other projects.

Paul Falstad did (and does) all the heavy lifting for this project, but the co-host of the JS version at lushprojects.com is my site and I did the original port from a Java applet to a GWT application that complies to JS.

Glad to know so many people find it useful. I always thought it was a great visualisation tool which I why I wanted to put the effort in to do the port.

Off to bed now, but if people have questions I'll take a look at the discussion again in the morning.

This app really helped me through my degree, especially the internals of the 555 timer. Very intuitive and simple to use, but as soon as I found it, I knew it had a lifespan running as a Java plugin. Rejoiced profusely when I learned it was ported to JS! Thanks for the effort!

Where do I learn to write simulations like this? I'm doing numerical models this summer, and it feels like a lot of the notation is inconsistent, unlike programming.

What's your background? I ask because if you need to learn the physics behind how circuits behave then that's going to be a lot more difficult to self-teach than just learning how to solve differential equations computationally.

I've done a little bit of arduino nothing too impressive, and I've had basic physics. I'm still having issues understanding how graphs(the data structure) come into play and how to count the resistance in those situations. I've read several books on basic electricity. As for calculus I've only had calc 1. What should be my path to learn more about these simulations?

Glad to see other people still using GWT in the wild.

I remember when this was still a Java applet - nice to see that it has been since rewritten in JS.

I credit this app for being able to pass the first half of my sophomore year at University - just months before I failed four courses(the allowance was two) and was given a chance by the dean to redeem myself.

I was really happy to see it got rewritten in JS as well, because Java applets are a pain (or just plain impossible). Sadly, the JS version is also a lot slower, I don't know how that could have gotten prevented

Webassembly tends to help by a good margin.

Same here. This was a very useful tool to help build intuition around the theoretical homework problems from the intro circuits classes.

I'm currently teaching an electronics class and have used this site heavily for in-class demonstrations. Some of the concepts (like a Push-Pull amplifier) are much easier to understand when you can see a visualization of how it works.

I teach an occasional "electronics without math (except ohms law)" class at the local makerspace - I've been using falstad ever since they showed up (many thanks!)

SAME!! I don't know how I taught these subjects before I found Falstad. <3

It's funny to see this here—I've been a MEGA FAN of Falstad for many years now, and I use this and many of his other tools in every single one of my classes. If y'all don't know about this site, he's made SO MANY incredibly excellent and informative tools it boggles the mind.

Seriously people, this guy is a freaking genius. I want to meet him just so I can shake his hand, thank him, and buy him about a million beers.

Don't forget to do Options->European resistors!

This is a favorite among collegues. I believe at http://lushprojects.com/circuitjs/circuitjs.html already this is already marked.

Nice! I've been using this tool on an occasional basis for years (since long before it was converted from a Java applet to JS) and I noticed that the source code was available for download, but I had no idea it had switched to a fully open-source development model.

This tool is the lowest-barrier-to-entry to get into circuit design -- used the applet after trying commercial/trial tools (including "cloud-based" ones), and all failed me.

While we are at this subject, here's an electron wrapper of this I made for using in school environments: https://github.com/Immortalin/Simulacra

This is a fantastic tool! When I was younger, it was great to be able to experiment without needing any hardware and while having more visibility into what was happening. Especially cool that it lets you play with memristors.

That's very nice. I've used LTSpice extensively, but this was very helpful for understanding phase-locked loops. Seeing the current flow in the wires helps.

I used and enjoyed circuitlab.io until it went for-pay only. Nice to have an easy to use free alternative for very casual hobbyists like me.

That would be https://www.circuitlab.com/ -- I built it :)

Edit: if anyone wants, reply with your CircuitLab username and I'll give you a free membership upgrade when I get home this evening.

Been using iCircuit for iOS for a very long time, which is a C# port of falstad's engine. Only recently have I tried the demo of circuitlab; It would be much appreciated to give it a more comprehensive try... Username: up-n-atom


Username: yuhe

Thanks, that's very generous! I registered a while ago and I'd definitely pay for something like this if I was using it professionally, but I'm barely a hobbyist...

Username: snowdem0n

Very generous of you. I've loved using it to answer stackexchange answers but don't have enough use myself to justify the membership.

Just signed up, username: DavidGould.

I'm just getting started, so not sure what tools I'll end up using most, but it great to get to try this.

Thanks for building that. Awesome piece of software. Helped me a lot when I was dabbling in hardware coming from software.

Thank you, I'm just at the stage where I'm learning schematics and this looks like a fantastic tool!

Username: fluxsauce

Username is hn50

Many thanks.

I remember running Spice on an 8086... The day I bought an 8087 coprocessor...it was SOOOOO much faster!

I've been starting out with electronics tinkering, and this looks awesome! My username is jmgao.

Cool, just signed up as kstenerud. Never knew something like this existed!

Cool - my username is "seandss" - much appreciated, thank you!

If that's also true for brand-new users, the username is the same!

username: domsl

Hey I just signed up, it looks pretty cool. I still remember struggling with spice at school (almost 10 years ago) – I think this makes easier access to electronic simultion :)

Just signed up, username ulmas.

Thanks so much, Mike, so generous of you!

Username: tpdc

Thank you for the offer, even if you don’t get to me.

This looks amazing, thank you! username: dujoducom

Hey that's cool. Username is efosmark.

Nice! This looks really cool :)

Username: RandomException

Thanks, great site! My username is TKems

Username: k_samson Thanks. Great job!

Many thanks: Username: braintoaster

Yes please. username: pkaye

Thanks! I'm quentinv

Thanks! I'm sprawl2

Thanks username: asusta

Username: nikolay

Yes please: chromebin

Username: illuminati1911

Thank you! :)

Thanks! I'm wrs.

A big fan since 2012!

My username is magnetik

Thank you!

Thanks for the generosity:


Awesome - thanks!

Username: kburkitt

Thanks from kqr2!

username: iceychris Thank you very much :)

mine would be: lonewolf72. Thanks heaps

just signed up , username : Kagerjay

if not too late, nullmeme Thanks!

username: bxtel

Thanks! Looking forward to using this!

ade2 if it's not too late!

Username: ivd0


I want!

username: blarg1

username: michaa Thanks :)

Thank you!


user: kpatrick Thank You

username: Raft Thanks!

thanks, mine is rkasturi


Thanks so much for the upgrade!

username: CharlesInCharge

Thank you!

username: vkhurana

Thanks man! :)

ussername: shesto

thanks man ! :)

username: rogier






Thanks Mike!


Thanks Mike!

username: cristoper


username: Raft Thanks!

If you don't mind using a desktop app, there are still many great tools for hobbyists and for teaching.

Recently I've used: Qucs: https://sourceforge.net/projects/qucs/

Circuitmod: https://sourceforge.net/projects/circuitmod

These were also in my bookmarks of tools I've explored: CEDAR Logic Simulator: https://sourceforge.net/projects/cedarlogic

Logisim: https://sourceforge.net/projects/circuit/

For teaching LogicWorks is still my favorite.

KiCAD 5 was recently released (congrats team!) and it got ngspice integration which sounds neat. Haven't yet had time to try it out, but what I've seen so far looks promising. Of course with SPICE (and really any simulator) the problem is creating/finding good models for your parts or even generic ones.

I designed an actual board with this. Would have been SOL without it.

Same here. It never hit production, but this simulator was fully-featured enough to replace SPICE and accompany breadboard prototypes before I ordered a PCB run.

haha, production in my case was sending $3k to China for 100 units ;)

When I made this 3-phase source, the voltages were out of whack until I reset the simulation. Perhaps the phase offsets are relative to the time of placement, instead of some absolute reference?


Nice site!

That example circuit is called a resonant circuit and the oscillation that is seen after the power supply is removed happens because both the capacitor (C) and the inductor (or coil, L) store energy—in electric and magnetic fields, respectively—and start feeding each other.

FYI try this:

set the 100 ohm resistor to 1 ohm

set the 15uF cap to 15pF

close the switch, open it again - check out the spark (or rather the stupidly high voltage)

I built a simple keyboard matrix with a "scanner": http://tinyurl.com/yanykyws

That LED represents a something (probably firmware on the keyboard) reacting to the switch being pressed by a user.

Edit: I used a decade counter with a 5 col matrix for simplicity. I was using a 4 bit binary counter, but the browser started really bogging down with a bunch of components.

I wanted to build this from source to use offline, but so far I can't figure out how; the source is in Java, compiled to JS with GWT, and I haven't figured out how to install GWT yet. I've really enjoyed using it online.

Has anyone done a validation study comparing this simulator to a known-good simulator like Berkeley SPICE?

You can download a jar version, though perhaps it's older code. Still works fine:


Cool! I've installed it and it seems to work plausibly, though it's an old enough version that its "export URL" function is no longer compatible with the site. And the site has more features.

The validation question is interesting to me because I'd like to do things that go beyond just academic exercises, so I'd like to know how much confidence to have that the physical devices behave as modeled.

Wow, this would have been a game changer when I was taking EE courses. So much better than a half-working SPICE port on Mac OS X 10.2.

Awesome site. I've been using Circuit Jam for Android for years. https://play.google.com/store/apps/details?id=com.circuitjam...

I love that I can now play with this while on my computer and with monitors..

Used SPICE (PSpice) simulation tool a lot during college some 12 years back... but this is pretty nice and much easier

A variation on this that has 3D graphics, visual effects etc. is https://www.electricVLab.com

I used this to better visualize the circuits in my undergrad physics courses. I remember searching for a good animated representation of a curtain type of circuit with the expectation of finding some decent gifs/videos, but I stumbled upon this web app instead. :)

Falstad saved me during my university year. If just all field's had this type of material ...

Falstad ruined me during my university years, but i think we are talking about two different Falstads

555 internals looks beautiful. I wish I had this when studying 555 for the first time.

That's great, but we really need something like this that can allow us to simulate microcontrollers / raspberry pi. Development would become really simple for us software guys then !

Yes! I've wanted something like this since I was 12 and could never understand why it didn't exist. How else was I to learn circuitry at that age? Thanks!

I have 8 bookmarks in my browser and this has been one of them for the past two years. It's incredibly useful for EE stuff and fun to just mess around in.

Is there a way to use this without an internet connection?

Yes, you can install the java version on your local machine. http://www.falstad.com/circuit-java/

I've done this in the past and it works just fine.

on the topic of circuit analysis, read about https://en.wikipedia.org/wiki/Nodal_analysis and https://en.wikipedia.org/wiki/Topology_(electrical_circuits)

lots of interesting bits

I found this thing years ago and still occasionally go to it to play around with different circuit concepts. Very cool!

pretty neat, ive used http://www.partsim.com/ before - nice to see more simulations in the browser

Woah, I learned so much about electronics using the old java applet!

How do I get the scope output for circuits that I build?

You can add scope plots by right-clicking on any component and selecting "View in scope".

Always wanted to make one of these. Nice job!

i think i watched this before ony guy whos is korean student somewhere in USA, teches via YT very cool stuff...

glad this is here.

Thanks circuit lab username:asusta

What a wonderful site.

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