Things you should know about LTSpice

[andy_c]

Originally Posted by deandob

Is there any way to adjust a component value (eg. potentiometer) while the simulation is running and see it automatically update the sim results?

That's what .step does. There's no way to "tune" a value in real time though, at least not with LTspice.

[keantoken]

There is no real-time capabilities in LTSpice AFAIK.

- keantoken

[deandob]

Ah - you can use .step to change the value over a timeline I gather. Not as useful as dynamic but still helpful.

Is there an alternative sim package (freeware) that does real time run updates?

[andy_c]

Originally Posted by deandob

Ah - you can use .step to change the value over a timeline I gather. Not as useful as dynamic but still helpful.

Is there an alternative sim package (freeware) that does real time run updates?

Not sure what you mean by "over a timeline"? If you use .step for a single parameter with N values, N simulations will be performed, and N curves will be shown on the output graph. Tuning is only useful IMO when the time duration of a simulation is very short, like AC analysis. Transient can take a while, which makes tuning clumsy. I worked as a developer on a simulation tool that had tuning, so I'm familiar with its uses. I'm not aware of any freeware that has it.

[deandob]

Might be easier if I explain what I'm doing. I have an opamp constant current source that is varied by the voltage on its non-inverting input. I want to model the current through the load output by varying a potentiometer on the non-inverting input. I started out varying the value of the resistive elements of the pot and plotting on a paper graph the load current but was thinking there must be an easier way to do this with such a basic circuit / simulation.

The step does work as it gives me various curves, except its difficult to work out what curves (flat DC current lines actually) relate to what values.

Sorry for the noob questions, I guess I got to spend more time playing, reading and learning....

[andy_c]

Try "select steps" from the right-click menu on the graphs. I believe there's a better way of doing this, but I'll have to do some searching in the Yahoo group.

[andy_c]

Okay, here is the trick from the Yahoo LTspice group (thanks to the moderator, Helmut Sennewald). He's talking about the up/down arrow keys below.

Make the waveform window active.

Click on the label you are interested. It's the text near the top
of the waveform window, e.g. V(out).

Now you have a cursor attached to the curve.

You can step up/down with the cursor keys.

Move the cursor near the cross hair. When you see the "1" then
click the right mouse button. A small status window appear.

Cursor Step Information
Cursor 1: Val=2 (Run: 3/5)


There is also a selection in the Plot settings menu.
Plot Settings -> Select Steps

Best regards,
Helmut

[deandob]

Thanks Andy for the headstart - a number of your tips over the last few posts have helped a lot.

Now back to the simulations & circuit tweaking....

[andy_c]

You're welcome! I'm glad to have found that old post of Helmut again, as I'd completely forgotten that useful trick.

[keantoken]

I will add these things to the first post when I can, but I am not yet able to edit my first post.

I will ask a mod.

- keantoken