EE people - how good are circuit simulator programs?

[fuzzybabybunny]

I've basically been binge watching YouTube vids on beginner electronic engineering for the past week.

The more I watch, the more it seems that modern circuit design has a lot to do with taking pre-made ICs and/or tried and true circuit diagrams and getting them to work together to create the final device.

It also occurred to me that all of this seems like it should be accomplished easily in software, right? The software already has a massive and constantly updating library of parts and ICs. Instead of a breadboard you just assemble the circuit in software and can easily run simulations with a virtual multimeter, oscilloscope, etc based on certain inputs that you give it and watch for the desired outputs.

Does it kind of work like this? Am I better off just getting a good circuit simulator, designing and testing my circuits in the simulator, and when I feel like it, make it in real life with the expectation that it'll work right away because all the testing has been done in software?

 

[slugg]

They're perfect. Computers don't lie. That would be illogical. QED.

 

[John Connor]

Before Nvidia releases a new GPU they simulate the chip for a year. So yeah, it can be done.

Even in radio communications they have what are called SDRs. Software Defined Radios. The military is a heavy user.

 

[videogames101]

Depends.

A lot of models for say 14nm are actually empirical or "curve-fit" models, aka they go take measurements of the transistors and then fit the data into a model, rather than using a physics based model, because we don't have good enough formulas.

For something like a breadboard/PCB, yeah pretty much near perfect simulation is possible. But it can be hard to model parasitics of a breadboard for example.

Most design work for all electronics is done in software then verified on test runs.

Also depends on the complexity, if talking multi-tens or hundreds of GHz analog work? Simulation gets a whole lot more like art than science.

SO the answer depends, how accurate do you really need?

 

[freeskier93]

I've basically been binge watching YouTube vids on beginner electronic engineering for the past week.

The more I watch, the more it seems that modern circuit design has a lot to do with taking pre-made ICs and/or tried and true circuit diagrams and getting them to work together to create the final device.

It also occurred to me that all of this seems like it should be accomplished easily in software, right? The software already has a massive and constantly updating library of parts and ICs. Instead of a breadboard you just assemble the circuit in software and can easily run simulations with a virtual multimeter, oscilloscope, etc based on certain inputs that you give it and watch for the desired outputs.

Does it kind of work like this? Am I better off just getting a good circuit simulator, designing and testing my circuits in the simulator, and when I feel like it, make it in real life with the expectation that it'll work right away because all the testing has been done in software?

Not in my experience. The dirty secret seems to be companies and engineers like to keep their libraries to themselves. I've spent the last couple semester designing a board from scratch using Altium. Some of the big manufactures, like Texas Instruments and Microchip, have part libraries you can get behind an Altium paywall, but all you're getting of value are the footprints. Ultimately I had to spend a lot of time creating my own component libraries.

Basically it's not as simple as you think. I wish there was some magic program that could simulate everything but there isn't. Something like Altium can simulate using SPICE for analog stuff and XSPICE for digital. You're still limited in capability though. For example simulating something like a microcontroller is extremely complicated. I was using PIC microcontrollers and even Microchip's own IDE is limited in what you can simulate/debug in software.

Plus there are always going to be variables you can't account for in simulation, or things you simply cannot simulate. The biggest issues I had in design, which required new revisions, was not reading data sheets well enough or reading errata. Like you said it's mostly just putting puzzle pieces together, which means a lot of reading data sheets and figuring out how parts work.

 

[Red Squirrel]

I imagine good software could simulate a lot but it probably would not be able to simulate any weird things like wire capacitance, inductance etc that is caused by the physical layout of the circuit. Though I might be underestimating modern circuit software. For example if making a SMPS the location of bypass capacitors or how the inductor or transformer is winded and stuff actually makes a difference in the operation.

I'm a newb myself though, been watching lot of videos myself too. I ordered a bunch of stuff off digikey the other day to accidentally blow up experiment with.

 

[John Connor]

You can practically simulate anything. Even resistance.

They simulate flight, tanks, maybe boats, trains and cars. Up to and including nukes.

One day perhaps they will simulate surgery.

 

[edro]

Yes, literally ALL corporate electronics engineers use simulation software.
The PCB layout and simulation software is often the same software package.

 

[Drako]

The PCB layout and simulation software is often the same software package.

Well, not really. :hmm:

 

[VashHT]

Simulation is pretty sketchy at best in my experience. It's hard to get correct pspice models for every component on your board, in my experience people only simulate small parts of a board at most. Usually, we just do a small prototype run and troubleshoot an actual board.

 

[CountZero]

Simulations are all about the quality of input, garbage in -> garbage out.

If you are running low speed and well within spec simulations will give you a pretty good idea.

In school we'd use pspice for a first order level of design but we'd also use pots in key locations to tune things up for a specific chip or to overcome breadboard parasitics.

For actual designs it gets trickier. I work in chip design, not board but was doing some debug work. We had a component that had a spec of +/- 1% on VDD which is very tight. We were trying to shmoo a failure of our own chip but any time we moved that rail 5% down we'd fail. The part we suspected was provided to us by our partner and they would not share any details about failure modes or better more detailed specs. So you can imagine that the model was probably pretty slim and any spice simulation with that component likely had little value (outside of maybe the parasitic load it represented).

For chips simulation is pretty accurate. We've run spice on individual gates and gotten pretty good correlation with silicon.

 

[Wonderful Pork]

As mentioned, simulation is possible, however it takes a lot of time (thus $$) to get good component models and keep them in a constantly updated central library, so generally I don't spend the effort to simulate non-critical circuits.

Critical items generally have a corresponding budget to support spending the up-front time to get it right, otherwise cut & jumper the prototype and move on.

This is also why having good fundamentals and being able to calculate stuff on paper is necessary skill. Don't bring your iPad Spicy Schematics experience to an interview, kids! (Yes, that app is pretty awesome and surprisingly powerful, but seriously, learn how to calculate by hand so you can at least validate the output)

 

[fuzzybabybunny]

I see. Well, since I'm a complete beginner, I was hoping that I could learn by just using simulator programs. I'm always, always traveling, and so carrying around boards and wires and a soldering iron and an array of parts just isn't feasible. So a circuit simulator for learning and building virtual circuits seems like it would be a good way to learn for someone traveling.

In the beginning it'll be stupid circuits like "weee, I got an LED to light up" but then I want to move up to more interesting things. Getting different ICs to play together. I was thinking about simulating/building a battery/device charger using the new Qualcomm QuickCharge 2.0 / 3.0 specs?

 

[Printer Bandit]

Spicy Schematics is dead:

http://www.ischematics.com

 

[Wonderful Pork]

Spicy Schematics is dead:

http://www.ischematics.com

oh, thats too bad! iCircuit is also pretty good, especially for $10 or whatever.