I worked designing, building and programming test equipment for electronic production lines but I am now retired and doing electronics as a hobby. In these forums I have seen many examples of using simulation to test out circuit design. I have never used any such system but I think it is about time I did.
Which, preferably free, programme would be best for my usage and with a reasonably gentle learning curve?

 

hi AH,
I find that LTSpice will do most circuit simulation, it's not an easy learning curve, but there are many users on AAC who could help.

This is the LTS user group, it has many examples, etc

https://groups.yahoo.com/neo/groups/LTspice/info

E

 

I second that recommendation. As a hobbyist, I don't use circuit design and simulation software every day. One measure I have of software is how easy it is to come back to it after several months. I probably use LTSpice only a few times a year and re-familiarization goes easily.

John

 

I third the recommendation. LTS comes with a set of models, and libraries of third-party models are available for free from the Yahoo group and elsewhere. The LTS 'Help' is comprehensive, albeit somewhat terse, and the FAQ is worth a read.

 

trivia
http://ltwiki.org/?title=Main_Page
http://ltwiki.org/?title=Undocumented_LTspice

/!\ however depending on your field and needs - as i see it - the LT Spice is a descriptive illustration tool to get cool plot diagrams - other words - →everything can be done← in "LT" but it took me some years to get to that←←

if you need precisely model some specific area of electronics - i suggest comparing the - paid software prices and reviews and examples and related problems and sample problems
- because there may be stuff that does everything nearby only not that what you exactly require
- usually commercial programs have demo versions

- so we have a round full - wasting 2y to find exact software you need×afford or wasting 2y to learn the spice

 

Thanks all - it seems to be a unanimous decision. I have downloaded LTspice and will now begin learning...

 

Have a look in the LTspice/examples/educational folder for starters.

 

Which, preferably free, programme would be best for my usage and with a reasonably gentle learning curve?

As others have suggested, LTSpice is certainly the way to go. It's a fully-functional version of SPICE, it's free, and the learning curve is not too bad. You'll encounter some frustration and do a fair amount of head-scratching in the beginning, but after a couple of weeks you should be pretty comfortable with it. It certainly won't take you years to learn.

 

A lot of functions can be done with a right click in the schematic window area or on the parts so get familiar with that.
Running some of the examples, as Alec_t pointed out, is good.

 

Right, done my first useful circuit - simple op-amp circuit using an LT ic.
Now to work out where to find and how to use a model for the amp I want to use.
I may be some time...

 

Right, done my first useful circuit - simple op-amp circuit using an LT ic.
Now to work out where to find and how to use a model for the amp I want to use.
I may be some time...

Depending on your circuit sometimes it is easier to use a similar LT op amp than find the exact one you want to use.
But having said that there is a LTspice users group on Yahoo and a lot of models on LT wiki. You can also ask here. There are quite a few users so someone may have your model.

 

I suspect that the simulation with the LT one will do, but I want to do the model bit as an exercise 'cos I'm going to need to do that sometime.
Still learning.

 

My circuit simulation now uses an OPA342 though the results are indistinguishable from the LT1677.
Onwards and upwards

 

My circuit simulation now uses an OPA342 though the results are indistinguishable from the LT1677.

That isn't surprising. Most circuit designs employing op amps aim to work equally well with a variety of chips, and simulations using one op amp model versus another will show results that differ very little.

The exceptions to this occur mainly when a design relies heavily on some specific characteristic of a particular op amp such as very high gain-bandwidth product, high slew rate, ultra-low input bias current, rail-to-rail I/O capability, and so forth. In those cases, using an inappropriate op amp simulation model can yield results that are way off the mark.

But for most work, my experience has been that it rarely pays to be too finicky about choosing op amp simulation models, other than in the exceptional cases I noted above; most of them will serve equally well in telling you whether a design is likely to work the way you intended to, or is likely to fall short in some major way, or contains some unforeseen "oops!" that will prevent it from working at all.

If you don't have a SPICE model for the particular op amp you plan on using, in most cases it's quite sufficient to simply substitute a model for another op amp with similar characteristics. (The same applies, by the way, to other semiconductor devices such as BJTs, MOSFETs, diodes and so forth.) And if you do encounter a situation in which the fidelity of a SPICE model to the characteristics of the actual part seems to be really important, you need to be mindful of the reality that SPICE does not give exact results or the gospel truth, and can even serve up the most outlandish BS from time to time.

SPICE is a supremely useful design tool, but its results should always be taken with at least a grain of salt.

 

Just remember one thing which you're probably aware of but many who are starting out forget, it is that you can push tera amps through an 1N4148 and the program will just be like okey dokey then. So to iterate what OBW said you got to take it with a grain of salt and just use your experience as a guide.

Edit: Unit spelling converted from Icelandic to English.

 

Which, preferably free, programme would be best for my usage and with a reasonably gentle learning curve?

it will depend on your needs.

For analog work, I use mostly LTSpice (for speed and convenience), and then OrCAD. You may also try Multisim, Tina (there is a free version from TI), and MicroCap, and I'm sure countless others.

For digital / mixed signal, I use Proteus mostly, sometimes LTSpice, or Tina.

For RF, Genesys.

The key to using simulation is to understand its limitations. Knowing what your simulation tells and what it cannot tells you are critical.

 

Just remember one thing which you're probably aware of but many who are starting out forget, it is that you can push Terra amps through an 1N4148 and the program will just be like okey dokey then.

You can also create utterly impossible, but thoroughly legitimate, components for special simulation purposes.

Want to test out some aspect of circuit operation by forcing a node to a particular DC voltage, while leaving it unmolested for AC or transient purposes? Easy: connect it to a voltage source through a 1 gigaHenry inductor. Likewise, you can allow a node to assume whatever DC bias voltage the circuit dictates, while preventing any AC or transient voltage from being imposed on it: just shunt it to ground through a 1 gigaFarad capacitor. Want to put a capacitor someplace in a circuit, but temporarily get it out of the way when simulating something? Don't delete it, just change its value to 1 femtoFarad or 1 attoFarad.

Tricks, tricks, tricks...

 

You can also create utterly impossible, but thoroughly legitimate, components for special simulation purposes.

True, the possibilities it holds is what makes it so great. I've been using it on/off for a year and a half, still I've only scratched the surface...