Confusing choice of circuit simulators. Is Multisim good?

[hurricanehenry]

Hello. I've got Multisim Touch on my iPad. It seemed the most affordable to me at the moment (I think only a few dollars).

But I'm confused by the vast array of simulator choices out there, some with PCB layout options, etc.

Can anyone give me some guidance?

I think this will be sort of like all the other software packages in the world, where once you start on one track, you are generally locked into that vendor's software suite (Adobe, Microsoft, etc).

I know SPICE is probably the underlying program for everything, but the graphical simulators make things clearer and easier for a beginner like me.

I have seen mentions of EAGLE, and the FRITZING, etc. all very confusing and overwhelming.

[T3sl4co1l]

(At least as of a few years ago, being that Multisim v10 is the last I used.)

It's a basic SPICE environment, so you get analog stuff, XSPICE elements (but they suck, and go largely unused), digital (via event-driven simulation, using some proprietary code -- everyone makes their own flavor, because XSPICE sucks at digital), interactive elements, and emulation elements (I think there's 8051 and PIC something in there?).

Event-driven digital is fundamentally different from analog simulation.  Whereas analog sim calculates the next timestep based on numerical tolerances, events are scheduled by the timing constraints written into the digital models.  So, if an analog input voltage rises past a logic threshold, that's converted into an event.  The logic outputs then have to be updated: another event is scheduled, using the propagation delay.

Just beware of what it is: analog and digital are two different domains, and events can be missed.  I have a lovely screenshot of a simple "74HC04" inverter that received an input voltage, and didn't produce (and propagate) events to the digital model.  Which is fun, because that logic output was driving a gate driver, so the switching circuit was shorted out for a few microseconds there, through no fault of my modeling...

Talking about digital models is relevant because a lot of manufacturers write models just for one or a few environments, and that's it.  Most models are approximations of the real thing (both for speed and IP-hiding reasons).  The models that aren't, are large (50k+?) and encrypted (usually HSPICE), and require additional licensing to use (e.g., to enable the BSIM3 plugin for someone's transistor-as-in-monolithic-chip-level models).  Anyway, PSPICE has its own (incompatible) digital primitives, LTSpice has another, Altium uses SimCode, Multisim uses some other kind of code, etc.  Models using these elements simply aren't compatible, and will require between "some" and "a lot" of work to convert.

Anyway, as SPICE goes, I would rank Multisim above LTSpice and Altium, and probably most free or budget packages (which I haven't seen or used, so I don't know for sure).  PSPICE is probably better, and OrCAD (the schematic capture end of it, which is now integrated with PSPICE IIRC) I don't think is any worse.

The schematic capture is kind of weird (I mean, everyone uses their own shortcut keys, and concepts of objects and how to connect and move and edit them, so it's not like this is unusual..), and keeping a complex design in sync with the PCB (Ultiboard, or via netlist output to others) can be tiring.

Again, assuming the free/budget versions are comparable to the old one, of course.

Tim

[Lukas]

Don't underestimate LTSpice: despite being free and having a rather simple/oldschool (but very efficient) user interface, it's a really good SPICE. Certainly good enough for >90% of every EEs SPICE needs. Heck, LT uses it to design their analog ICs, so it can't be that bad...
Mike Engelhardt is happy to explain why LTspice is better than every other SPICE out there: http://cds.linear.com/docs/en/lt-journal/LTJournal-V24N4-01-df-SPICEDifferentiation-MikeEngelhardt.pdf
Relevant as well: http://www.theamphour.com/196-an-interview-with-mike-englehardt-spice-simulator-synteresis/

Just don't expect to get junk like clunky virtual oscilloscopes, blinking LEDs, etc.

[sanman]

I use Multisim 14 and it is pretty good. If you are a student there are several places that sell Multisim at an educational discount.

You are required to have an annual Support Subscription in order to get updates. Make sure to read about the differences between versions and make sure it meets your requirements.

Being able to design complex circuits and use a virtual Scope, Spectrum Analyzer, Logic Analyzer, etc. and put voltage and current probes anywhere in a circuit is pretty fantastic for learning and prototyping.

Cheers!

[ebclr]

Take a look on Proteus, for beginners is a nice shot

[r0nius]

Proteus (I'm assuming you're talking about ISIS) is my favorite, however it's VERY expensive and contains a lot of features beginners don't need (imo). Also I personally don't have a license for it so I don't get to use it much, which may be a factor in why I prefer it. Perhaps I'm bored of others? 

When I first started my EE degree we were using OrCAD Capture CIS Lite a lot. Easy to install, comes with plenty of libraries and just the right amount of functionality to actually learn with. Two years later and we're still using it, though not nearly as frequently.

Bottom line, if you're beginning and want a free and reliable SPICE, I would suggest OrCAD. I should mention I've never used Multisim before, but I'm not the biggest NI fan right now after being forced to use LabVIEW for 18 weeks straight in three separate classes.

[T3sl4co1l]

Speaking of libraries, Multisim's library is EXTENSIVE, including real parts (symbol, footprint and simulation).  Maybe dated, but since as I explained, you can't generally expect to use new models and parts, so one would assume most of your simulations will use classic components, anyway.  So that's fine.

LTSpice has almost nothing built-in, but the user-made libraries are vast.

Altium has pretty good diversity on libraries (these days, available through their "vault" system), but almost exactly zero simulation models.  Anyway, the footprints (and almost all the symbols) suck anyway, so power users never touch them.  (Multisim's symbols and footprints are a mixed bag, and worth improving upon, but they're largely tolerable, especially with the out-of-the-box functionality.)

There are quirks in LTSpice's proprietary engine additions that I don't like.  But, I don't have any specific examples offhand to complain with... 

Tim

[ebclr]

Where i can get Orcad for free ?

[Assafl]

OrCAD was never free. In the late 80's early 90's OrCAD capture was indeed a wonderful, small app capture (and eventually simulate and PCB) - but I think it was acquired by Cadence and the latest iterations (the ones I've seen) are humongous.

There is a free functional "lite" unlimited duration demo (limited by design size) at: http://www.orcad.com/buy/try-orcad-for-free
 

[hurricanehenry]

Wow. Thanks for all the responses.

This area looks like a real headache!

I can understand how all these incompatibilities make things troublesome, and especially the lack of "tolerance" for event-driven simulations.

What a mess.

At least now I have a better idea of what is going on with these simulators.

I guess most people who are not hobbyists pick the simulator that works best with the particular chip/IC architecture(s) they are dealing with on a day to day basis for their jobs.

[T3sl4co1l]

The most important thing to remember is, a simulator is simply a numerically computed environment.  It is only as representative of reality, as the models you use, and the circuit you build.  If you ignore parasitic components that happen to be significant to behavior, that's your problem -- no simulator can anticipate such things!*

*A full PCB level EM simulation can be done (e.g. Ansys, in the five to six digit tier), which computes the parasitics directly, but you're still subject to the quality of component models.  (You might further be concerned about thermal performance, which such simulators can model, too (if you want to pay for it..), where again you'll need to make still more assumptions to realize a realistic model.)

Tim

[b_force]

Multisim and LTSpice are both fine to use.
For most things, I highly prefer Multisim, but it has some weird bugs when simulating certain things.
Also they don't use the standard SPICE format, so you need to rebuild SPICE files you find around the web.
It is absolutely great for frequency response simulations for filters circuits etc

LTSpice is good for all the other things, only very slow, tedious and clumsy in my opinion (especially the user interface), but you get results.

Keep in mind, simulations are only good to get a rough idea how circuits work.
See it as a good starting point.

[rstofer]

Considering that when I graduated EE school, the HP35 had just been introduced and I had a plug-in 4 function calculator, these new gadgets are pretty nice.

I'm using LTspice and, for my limited needs, it works well.  On Yahoo Groups there is a very active LTspice group with some VERY knowledgeable people.  True masters in that environment!

One cool thing you can do with LTspice is model op amp integrators and build up an analog computer.  It is even easier in Matlab with Simulink.

[hurricanehenry]

With not much budget (as a non-professional hobbyist) for simulators, I guess it is looking more and more like I should be focusing my efforts to learning LTSpice as a simulator for starting theory, and then going straight to building the circuits (or parts thereof) to measure effects.

I gather that LTSpice is freeware?

[b_force]

With not much budget (as a non-professional hobbyist) for simulators, I guess it is looking more and more like I should be focusing my efforts to learning LTSpice as a simulator for starting theory, and then going straight to building the circuits (or parts thereof) to measure effects.

I gather that LTSpice is freeware?

No, you have to see it to use it on the side, together with your building blocks

[hurricanehenry]

With not much budget (as a non-professional hobbyist) for simulators, I guess it is looking more and more like I should be focusing my efforts to learning LTSpice as a simulator for starting theory, and then going straight to building the circuits (or parts thereof) to measure effects.

I gather that LTSpice is freeware?

No, you have to see it to use it on the side, together with your building blocks

Sorry not quite understanding what you just wrote?

Thanks.

[b_force]

That a practical circuit and some measurement tools are still needed.

[mikem1017]

I prefer TI TINA.  I've now tried multisim, pspice, and ltspice and none are as easy and functional as TI tina - not to mention that TI tina is FREE.  Just my 2 cents

[hurricanehenry]

Ok thanks, will check it out now

[VEGETA]

Try PartSim: http://www.partsim.com/

totally free and online... also supports Digikey. Do you need anything bigger?