Commercial Circuit Simulator Goes Free

If you are looking for simulation software, you are probably thinking LTSpice or one of the open-source simulators like Ngspice (which drives Oregano and QUCs-S), or GNUCap. However, there is a new free option after the closing of Spectrum Software last year: Micro-Cap 12. You may be thinking: why use another closed-source simulator? Well, all the simulators have particular strengths, but Micro-Cap does have very nice features and used to retail for about $4,500.

The simulator boasts a multipage schematic editor, native robust digital simulation, Monte Carlo analysis, 33,000 parts in its library, worst-case and smoke analysis, Smith charts, and it can even incorporate spreadsheets. There’s a built-in designer for active and passive filters. Have a look at the brochure and you will see this is a pretty serious piece of software. And now it’s at least free as in beer.


The number of models supported for active devices is impressive and includes some very recent MOSFET models, not just the old standard models. It can also read just about any regular Spice or IBIS model. It can also export Spice files if you want to use another engine or share designs with other Spice users. There are also quite a few examples provided. There are also over 2,000 standard digital parts including all the usual 7400 families, CD4000 CMOS, and even ECL.

As a bonus, we tried it under Wine and it worked well — at least the 32-bit version. The 64-bit one would probably work with a little effort. On a big monitor, you might want to use Winecfg to set a higher DPI setting, although the toolbar icons are fixed in size which is a little inconvenient. You can, however, select “large toolbar” on the Options | Preference menu, which will help.


One nice touch is that you can view a simulation and interactively change component values and watch the results update right away.

We frequently use Spice when we are too lazy to do the math required to pick an optimal set of values. With this software, you can set ranges for various circuit components, tell the program what you want to optimize, and it will compute the best values for you.

The smoke analysis is somewhat unique. The idea is to run a transient analysis and the program determines if any circuit values exceed the maximum value for a component. You get a nice colored graph that tells you how close you are to smoke or, if you have some red bars, what parts will smoke.

Another neat feature is that you can create very cool 3D plots. This is especially useful if you are stepping parameters or measuring the effect on parameter variation like temperature.

One other feature we liked is that the program can output a netlist for printed circuit board programs including Protel, Accel, Orcad, and PADS. Over 18,000 components in the library have packages available and there is a package editor. We wish it would work with KiCAD, although we are pretty sure you could figure out some conversion path from one of the formats available.

Why Free?

The software was under development since 1982. We don’t know the circumstances of Spectrum’s closing but we hope it was to move on to something great. However, we appreciate the free release of this powerful simulator that can give LTSpice a run for its money. True, we expect there won’t be future development, but the package seems very complete and with the ability to import models, it will be very useful for a long time to come.


If you are trying to learn the program, there are some starting instructions for an older version that should get you the basics. You can also find the user’s manual and a reference manual on the site.

We went looking for tutorials and found that [Kiss Analog] just started a set of video tutorials. There’s only one complete, so far (see below), but we are sure there will be more on the way.

If you’d rather do LTSpice, we have a tutorial. Then again, for just playing around, the Falstad simulator is pretty nice and requires no installation.

118 thoughts on “Commercial Circuit Simulator Goes Free

      1. It means “very good”
        Blender is for 3d animation and modeling, is open source and free, and is in the top of the class for that type of software, rivaling some pretty expensive commercial software. Used by professionals too.

        If you go to youtube and search “blender”, just look at the thumbnails, and perhaps read the snippit of description, you’ll get an idea. (If you aren’t into 3d animation there’s no real need to watch any of the videos)

      2. Blender is a great, industry standard 3D modeling and animation software. And video editor. And 2D graphics and animation tool. And much more than that. It can’t replace LibreOffice or GIMP, yet. But it will probably be added in one of future releases…

          1. I used piers to hammer nails since I was young. It was the right size feel and weight. I don’t do a lot of hammering. I finally bought one a few years ago at a dollar store for flattening home made PCB vias and the price was right.

            I don’t use any of the 3 packages either, but I do use spice,

      3. Typically it would mean really good and powerful, professional quality, and free. ..along with a UI thats completely borked and has a massive learning curve to get used to doing things with different inputs than any other software. Not sure if that applies here, but thats what blender is.

    1. Not exactly. Blender came to the masses because a guy who worked at the company that developed it took over the source code so that development could continue after the commercial effort ended. That is not yet the case here.

  1. Not quite. Blender was closed source and one of the developers offered to buy it from the company. The company gave him a number, and he raised the money to pay for it, with donations, in order to make it open source. In this case it’s basically abandonware. If you invest your time into learning it, then you will be stuck without any new features etc.

      1. Yeah well that’s an example of a winner writing it’s own history. Some of us where around when it happened, plus it’s recorded elsewhere on the web what happened as well.

    1. Yes, it was originally a closed-source, in-house tool, but free for anyone to use if you had the hardware/OS to run it. ( Your last two sentences, though, sharply veer off into left field and abandon reality where Blender is not just constantly being worked on, but major companies are heavily investing in it. ( Please make a practice of doing fact-checking before posting to avoid looking foolish in the future.

          1. He didn’t say Blender is abandonware. First he describes what happened to Blender, then says “In this case”, and switches to what’s happened with Microcap.

    1. For papers it seems like the two most common options are Microsoft Visio and LaTeX using the circuitikz package. I am personally not a fan of Visio but it does get the job done with minimal learning curve. LaTeX gives excellent results but the learning curve is pretty steep.

      If you just want nice looking schematics (not necessarily for publication) I would suggest getting comfortable with your EDA software of preference (I like Kicad)

      1. I used Visio at one place I worked because it was closest thing to a CAD that I can use without the hassle of getting approval for req. as it was classified as general office software.

        I wrote a converter program to convert our CAD footprint and component models into it and used that a lot for placement plannng. Being able to export Auto CAD DXF for our mech people, window metafile for word was very handy.

      1. But also, releasing source code may have a cost. I seem to recall reading that when Netscape went open source, the company spent time and money preparing the code. I can’t remember details, but the code couodn’t be released as is. Maybe it needed to be cleaned up.

        When the mail/newsreader PINE was let go from the University of Washington, the license was changed and some work was needed. Maybe it was one last update, but I vaguely recall more work was required.

        1. They’re not allowed to open source software components that they bought from someone else. The program code very likely includes packages that they don’t own the rights to.

        2. Spice software quite often contain trade secrets. i.e. encryption that protect chip vendors IP, so that they would release a more accurate representation of what’s inside. Spice models are serious business for simulation as it is only as good as the models.

          Also there are some serious legal consequences if the software vendor rectroactively open sourced the code.

        3. When LucasArts closed, Raven released the source code from the Jedi Knight games they’d worked on.

          They quickly took it back down, because the code contained a lot of proprietary stuff from Microsoft and Bink that they didn’t have the rights to publish. It was a couple days before the source was sanitized enough for publishing again.

          Releasing the source for a product can be a lot more complicated than uploading the code.

      1. I can confirm the 32 bit CD version works with the playonlinux 4.3.4 package

        open playonlinux
        click install a program
        click install a nonlisted-program
        install a program in a new virtual drive
        name it microcap12
        select use another version of wine
        choose wine 4.21
        choose 32 bit Windows installation
        browse the microcap12 extracted CDROM files path
        choose “setup.exe”
        do not run microcap program on install completion

        Click playonlinux Configure
        select microcap12 virtual drive
        Click make a new shortcut from this virtual drive
        select mc12.exe
        exit wizard
        exit Configure
        click mc12 on playonlinux list menu

        I was running the windows 7 OS signature with playonlinux’s 32bit wine 4.21 during this process
        Note, installing wine 4.21 can be done though playonlinux Configure menus

          1. The logical falacies abound, confirmation bias, ancedotal evidence, false equalvilances…

            The fact is that there is no way to say how many people who talk like that actually contribute to the projects as there is no statistical analysis of people who talk like that.

            That being said, it is very presumptious to think that your personal experiences of people who talk like that stand for a representation of the general public of FOSS projects.

            Then it is also illogical to chalk people who talk like that specifically to be greedy but that person could just be anti authoritarian.

            I dont often contribute specifically to FOSS projects, I write detailed bug reports when i run into them but i dont contribute code except for one or two projects. Does this mean i am greedy because i run several different packages but i only contribute to one or two? Does that mean that i am only allowed to run the packages that i contribute to?

            In my opinion, closed source software is greedy and open source is cheap. the original retort of greedy is wrong, they should have said cheap ass. Im neither of those posters but yes i am a cheap ass and i use FOSS because i dont have to pay some large conglomerate for their shitty software that is just as buggy as any other piece of software. The fact is that the more people who use FOSS encourage even more people to use FOSS creating a network effect that benifits the group more than the individual, so championing for FOSS even without code contribution is still a contribution and thus not really greedy.

          2. I can’t reply to Mike for some reason, so I’ll reply here.

            “The logical falacies abound, confirmation bias, ancedotal evidence, false equalvilances… ” You just throw it out there, as if you had any hard data that contradicts the views.

            Open source projects can be successful, but only if they reach a large size and financial support. To claim otherwise shows a lack of experience.

            Other projects rely heavily on the code originator, or someone who took over. Most of the contributions end up being fixes.
            For anything larger you need a lot of organization to integrate the submissions and ensure a certain quality. Almost nobody can do that on the side, unpayed.

            “The fact is that there is no way to say how many people who talk like that actually contribute to the projects as there is no statistical analysis of people who talk like that. ”
            Oh please! Attitude says a lot about what to expect from people. Asking kindly or saying code or GTFO is not the same.
            Asking for statistical data for everything is just a cheap way to disagree. Let alone you can’t evaluate everything statistically, because categorizing it is yet again a subjective faulty process.

            Maybe you should try Bayesian statistics to understand how people are able to act with incomplete information.

            “In my opinion, closed source software is greedy and open source is cheap.”
            The rest of your post is just based on your wishes, and shows that the prediction was right. You think network effects just make it happen magically. You added no statistics of your own, either.

            You simply hate against individual software developers who make a living from software, and compare them to big conglomerates. You are really brave, I admire you.

            A little tip: the most successful open source software is actually financed by big congolmerates, such as Google, Oracle, MS, IBM etc. Yes, especially Linux, who would have thought…

            “Then it is also illogical to chalk people who talk like that specifically to be greedy but that person could just be anti authoritarian. ”
            “GTFO” is not anti authoritarian, it’s plain rude and respectless for the work someone has done.
            People have to understand that you can’t treat single developers and big corporations the same way. Yes, those are also single people you insult, actually the lifetime of their work.

            Ever thought of that?

      1. To that I have to relate this story. I volunteer at a small rural county museum, where the coordinator relies on her son. as her computer tech advisor. He is someone who is big on FOSS concept. My response was I like the concept, but it has a butt loade of hard core rigid unmoving attitude. Problem being one can never know if the whiners are the doers, or the freeloaders, who never donate financial support to the projects they use on a daily basis. e My opinion is that the whiners are the free loaders, not doers, because that how it is in the real world

        1. Agreed. I have made freeware and open source software.

          After open sourcing what I see most of the time is the same type of whiny comments. If the project isn’t huge, most of the work is done by one person or a handful.

          The more rude in demanding they were, the less they contribute.

    1. Opening former closed source products is much harder than it seems, as their source code may contain 3rd parties closed parts that they have no rights to release. Sorting out and ditching these parts would cost money, and swapping them with FOSS code to make a product that works again would cost a fortune. Releasing the source code as-is would expose them to nasty lawsuits. It’s not always about greed.

  2. I’ve noticed that after installing the CD version, that there were updates that could be downloaded.

    I imagine the website will not be maintained indefinitely, so ideally some way needs to be found to update the CD installer files with the latest files that can be downloaded in the update.

    And of course ideally, the whole thing needs to be be made open source and put somewhere the community can continue the development.

  3. Wow, this gave me a huge flashback. My final year college project in Electronic Engineering in University College Dublin in 1990 involved a comparison of Microcap vs PSpice!

    At the time, IIRC, Microcap won hands-down for usability but PSpice won on accuracy, compared to the real (albeit very simple) circuits we built as references.

    I just had to download the latest version to have a look. Yup, it’s come on a long way in 30 years :-D

  4. Meh.

    I don’t mean to be negative. It’s very generous that the developer will let us use it for free.


    Eventually we all die.

    I don’t think I want to spend to many of my living moments learning a tool that will never again see an update. If the source were released so that it could be forked and live on then that would be different.

    1. Excuses, excuses.

      > Released in June 1980, this product was the first integrated circuit editor and logic simulation system available for personal computers. Its primary goal was to provide a “circuit creation and simulation” environment for digital simulation.

      You are looking at code that had been maintained for almost 40 years! It is older than some people here. The code should be more than mature that it should be relatively bug free for general use anyways.

    2. Yes totally agree, I want long term corporate support like I get for my symbian phone, err, my microsoft Windows Phone that replaced it, err my Google+ account, sorry I meant my Sonos……

      No one-man-band 40 year fly-by-nighters for me!

  5. This was not a product endorsement/ recommendation, simply news. Thank you Al for making many of us aware of, an option we otherwise wouldn’t be aware of. The only downside could be, in time, the only user support will be available from a user community, if that’s a downside.

  6. This is some top notch software and you’d be a fool not to get it and learn it because it’s very powerful …. I’ve been using it since the days it ran on DOS 6.x and to get the full features you needed a 486 DX computer that had the math co-processor …. The Windows 95 version pretty much set the tone and standard for everything that came after it including LT Spice

  7. This program’s father was SPICE, the FIRST circuit analysis program written in Fortran in the 60’s. Then came PSPICE and then bought or cloned by MicroSim, and I assume improved by Spectrum. My guess/opinion is that it is the BEST. I used and taught it for many years. Bo W4GHV since ’54

    1. In general, simulators model finished circuits. I don’t know if µCap has any solver functions, but I’d be surprised if it did. You can probably use it to brute-force a solution by having it iterate on values, but unless you really don’t know how to solve something, this is not the way to do things.

      1. Not true. Teaching a college lab for a complex amplifier design I tinkered with PSPICE while the students sweated. I did a rough design myself, swept component values, etc. I finished before the students and used it as a great learning tool. BTW I caught bitching by the older professors for teaching calculator use. They remained in the stone age.

      2. It has an excellent optimizer that works well even on rather complex circuits. I use it to fit lumped parameter RLC circuits you’d be hard pressed to match by hand. You can basically import (freq, mag, phase) into a Laplace Table driven LTVofI device and then it will have for instance the same admittance as that table. From there you can built up a lumped circuit with the appropriate elements to produce the same admittance and let er rip. It helps if you manually bang things in by hand, but getting things fit down to under 1% error it does splendidly so long as you gave it enuf elements, with enuf range to pull it off.

  8. I run this on my MacBook Pro with Parallels installed so that I can run Windows based programs. Works great – and fast! I personally think the GUI is as intuitive and pleasing to the eye as any I’ve used. Cheers!

  9. Getting an error No such file or directory ‘C:\Users\username\downloads\mc12\standard.cmp’ Anyone have a solution? Doing this with both the x86 and 64 bit executable.

  10. Is there a kind of MicroCap Forum where you could ask your questions in case of problems? I dont see much like this on the web… If there is no support at all or kind of forum i dont see much future for MicroCap.

    1. MicroCap is very mature and thus is very powerful. It is also very intuitive and has a huge library of both parts and sample circuits to get going, so I think it will be around for a long time. I can help answer questions on my YouTube channel and you can get help here.

  11. I do not know whether the Spectrum site was gone at the end of March, but today it was there and accessible. I just downloaded Micro-Cap 12 directly (and checked the files in Virus Total and they were all green).

    Full disclosure: I haven’t attempted to install it.

  12. I don’t know if the Spectrum software website was gone at the end of March, but it was up and accessible today. A few minutes ago I downloaded Micro-Cap 12. I checked all the .zip and .pdf fles with VirusTotal and they were all green.

    Full disclosure: I have not attempted to install yet.

    1. MicroCap is very mature and thus is very powerful. It is also very intuitive and has a huge library of both parts and sample circuits to get going, so I think it will be around for a long time. I can help answer questions on my YouTube channel and you can get help here.

  13. No wonder, if you charge 4500$ for something, make sure you hired artists to do some graphics and GUI design professionally. You wont sell your product if the GUI looks like a terrible marriage of MS Excel ’97 and Amiga OS! I hear people talking about blender, well, they are doing alot better these days, half the reason is because the UI actually is comfortable. The same things can be said about programs like FL Studio, Qt Creator, etc. — don’t cheap out on the graphics unless you want your investment to go belly up in the wake of the competition that will surely come to fulfill that need.

    1. The GUI for MicroCap is very nice and intuitive. It is arguably one of the best and is now free. They owner retired and instead of selling the company he gave back to the community and offers the program for free and keeps the website up for us to download it for free. Pretty amazing man!

  14. Micro-Cap 12 won’t let me put a conditional statement in its capacitance parameter to vary its capacitance per conditions. I’m using this capacitor as a throttle which I name: ‘tcap’ …

    .define tcap {100f + STOP}

    .define STOP if(I(IndLoad) > 300, 30p, 0)

    The intention is to raise the capacitance of tcap to 30pF (or, more) if its current should rise to a minimum of 300 amperes. Its default capacitance is 100 femto Farads.

    What do I do?

    1. Correction…

      I meant to say that …

      The intention is to raise the capacitance of tcap to 30pF (or, more) if the current of IndLoad should rise to a minimum of 300 amperes. The default capacitance of tcap is 100 femto Farads.

  15. This is immensely powerful software, from the built in iterative optimizers on thru rich parametric stepping, Monte-Carlo analysis it has so much to offer. I’ve been using it since I was in high school circa mid 1990’s and honestly I’d be lost without MicroCap. It was such a gift for them to make it freeware. That said the support, while reasonably good can be a bit cryptic when trying to access some of the more obscure functionality. I’ve made inroads with the optimizer, Laplace Tables etc.

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