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I am looking for a free circuit simulator for educational purposes. My requirements are:

  1. Visual ("draw a circuit diagram, click simulate")
  2. It should contain light bulbs as circuit components such that

    2.1. They become (visually) brighter if you apply more power

    2.2. You can change the manufacturer specs for example "3.5V,0,2A"

  3. It should contain swiches, npn-transistors, diodes and LEDs as well (the LEDs should react to interactive changes in the simulation)

Any recommodations for this? It would be nice if the simulator runs under Linux, but that's not a strict requirement.

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We're looking for long answers that provide some explanation and context. Don't just give a one-line answer; explain why your answer is right, ideally with citations. Answers that don't include explanations may be removed.

Wasn't there a nearly identical question a few weeks ago? –  Olin Lathrop Jan 5 '12 at 14:26
@OlinLathrop: you could vote to close it. –  sybreon Jan 5 '12 at 15:01
@sybreon: I could, but then I'd have to do a search and find the question this is a dup of. –  Olin Lathrop Jan 5 '12 at 15:25
@OlinLathrop - I thought there was, and I did the search, but I can't seem to find it. –  Kevin Vermeer Jan 5 '12 at 17:21
Please, am I just being terrible, but I can't see a lightbulb anywhere. –  Solver Feb 15 at 20:13

9 Answers 9

up vote 17 down vote accepted

I often use the falstad simulator: http://www.falstad.com/circuit

It's a Java applet, so will work on pretty much any operating system. The interface does take a bit of getting used to, and there are problems saving in Linux (it gives you a link to copy and paste, and copy and paste in Java doesn't work too well in Linux).

Other than that it ticks all your boxes. It also has some good sample circuits.

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Thanks, that's nice. Do you know how is the format called, the program generates if one clicks on export? –  student Jan 5 '12 at 13:09
Hm, yes, copy and paste doesn't work for me... –  student Jan 5 '12 at 13:16
@user406686 It encodes the schematic into a URL –  W5VO Jan 5 '12 at 14:50
@W5VO Yes this is the case if you click on export link. I mean the qource code you get if you click on export. –  student Jan 5 '12 at 16:09
It's what gets encoded in the export link option. It's a custom format specific to this program. It contains a list of the coordinates, components, parameters, etc. You might be able to work out what is what by making small changes and exporting and looking for differences. –  Majenko Jan 5 '12 at 16:19

CircuitLab is a beautiful in-browser circuit simulator that was launched a few days ago by a pair of MIT students. I think electronics.SE is going to love it! It does full mixed-signal analysis and appears quite capable. I look forward to seeing where it goes!

Here's a screenshot:

CircuitLab screenshot

You can share circuits via convenient short URL's. For instance, here is the circuit shown in the schematic: http://circuitlab.com/circuit/fq7c97

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Not tried yet, but seems very neat! And seems that also Olin could "accept" it :) –  clabacchio Feb 29 '12 at 10:13
Update: I've tried net labeling to replace wires, it works! Seems very nice!!! And it has a Spice-like simulation feature...now remains to try if it's possible to share simulations, even if I think that for something Falstad remains more immediate, like the visual representation of current and voltage –  clabacchio Feb 29 '12 at 10:17
I just give it a quick try, too. Sharing seems VERY possible. I opened one of the quick-start circuits, hit "open in editor" and the circuit will open in the browser without the need of java/flash plugins. IMO, its just plain html. And one can run the simulation in the browser ... I think I am gonna love this one. falstad is nice, but the need to install java just for that plugin had always bugged me. The lack of animated current flow is negligible, imo. –  PetPaulsen Feb 29 '12 at 10:42
You have to register to share circuits ... –  PetPaulsen Feb 29 '12 at 10:45
@PetPaulsen surely it's negligible for "engineering" use, but to explain the basic of some devices can help more than a lot of words and numbers, I think –  clabacchio Feb 29 '12 at 17:16

I like LTSpice you can find it here: http://www.linear.com/designtools/software/ It does jsut about everything.

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LTSpice is great: it's friendly and free and works well. It's natively for Windows, but it works fine in Linux under WINE. However, it doesn't have the feature requested that "bulbs will glow more brightly when the voltage increases". That's something more likely found in toy programs, I think. –  nibot Jan 11 '12 at 12:39
I would not say it is a friendly software but once you learn it you will have a very powerful tool. Plus it comes with all the Spice goodness - lots of libraries. –  Szymon Bęczkowski May 4 '13 at 13:13

I tried www.DoCircuits.com and found it quite easy to use, machine independent - works on the cloud, has real looking components and devices and is free :-) However, its an early version so I think many more features will get added - but I guess the direction is interesting.

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The 'free' version is very limited - max 10 components etc. –  UpTheCreek Dec 10 '14 at 11:09

PartSim is a free and easy to use circuit simulator that runs in your web browser. It includes a full SPICE simulation engine, web-based schematic capture tool, and a graphical waveform viewer. It also includes an integrated Bill-Of-Materials manager that lets you assign Digi-Key Part Numbers to your models. To test it, visit http://partsim.com/

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I downloaded Yenka few days ago. Didn't get the chance to really try it out, but from the looks of it, it seems quite easy to learn and use. It is also free for none commercial use. This is from their website:

"Yenka Electronics lets you design and simulate circuits using over 150 types of component, testing and refining your design as you work."

Check it out here: http://www.yenka.com/en/Yenka_Electronics/

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Never tried it, but I've seen some posted schematics and they seem really ugly. But I don't know how it works. –  clabacchio Mar 1 '12 at 10:08

Take a look at both Qucs (slightly harder to use) and LTSpice. Both satisfy 1, 2.2, and 3. Qucs is linux, LTSpice is under windows. Neither satisfy requirement 2.1, unless you are okay with looking at graphs as analogs of brightness.

Edit: I've been using Multisim lately, and it is far superior to Qucs and LTSpice in terms of ease of use. Its pricey, though.

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You can get QUCS for windows too. –  Joe Frazier Mar 1 '12 at 1:22

I cannot vouch for its complexity, accuracy, or capability, but "EveryCircuit" for Android is free (for very small simulations; $10 for full version) and does change the intensity of brightness for light emitting diodes. It's kind of a fun mobile app.

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Another options would be ngspice it is an opensource program for circuit simulation. It looks fairly new, and I can't tell you how well it works. People are updating the software, so future improvements I imagine are expected.

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