Probing and waveform viewer

When moving a wire or a component its voltage/current get probed with the same click and drag action. It’s quite annoying as it messes up the waveforms that you have carefully set up in the waveform viewer. However, seems like this doesn’t happen all the time, especially with wires. I would suggest to use some keyboard key to enable probing (as you already need to use Alt to probe voltage between two nets).

Also, waveform viewer often assigns same color to several waveforms in the same window.

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You can disable editing(so that mouse syntax is exclusively for probing) by holding down the alt key.

Otherwise, I’m trying the keep the syntax sufficiently distinct so that no such mode is required. You and edit or probe without having some extra state latched.

That’s too bad. I think it’s just too worksome and slow to always setup the waveforms again after editing the circuit. Maybe there could be an option to adjust the probing behavior in the future?

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I thought you were asking for something else.

Of course you can save the plot settings. Press the little floppy disk icon. After you rerun the simulation, press the space bar to get back to the same settings but with the new data.

You can can different plot setting files under different names. I think you can drag the .pfg file into the waveform viewer and it will adopt the settings of that file.

Saving and loading plot settings just to circumvent the problem is too slow and complicated IMO. Even though you have to use function keys to modify the circuit in LTspice, it’s still much faster to work with because you don’t mess up the waveform viewer every time you move wires or components.

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I agree with Olli. One thing that can be done is to keep the zoom when the simulation is performed again. In the current version, if you zoom in and simulate again (even without changing the circuit), the waveforms are maintained, but the zoom is not.

(edited due to a typo)

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Hello everyone,

I was wondering if there is some kind of differential voltage probe implemented in QSPICE. If yes, how can I activate it?

Thank you in advance for answering!

While pressing the ALT key, press left mouse button at node #1, drag to node #2 while holding ALT and left mouse button, then release.


Hello Jope,

Thank you very much for your answer! I tried to apply your advice, unfortunately without success. Every time I move the cursor with the left mouse button pressed, regardless of whether I hold down the ALT key or not, the previously selected element / wire piece is moved.

Hello Jope,

I take back my statement. Your suggestion works, but only when the waveform viewer window is open, which makes sense. I had accidentally closed the window in the meantime, that’s why it didn’t work.

Hi Mike,

Please, could you consider adding an option to either:

  • Probing enabled only with some keyboard key pressed, or
  • Probing disabled with some keyboard key pressed.

I would prefer the former but the latter would work as well. This way it would be possible to move components in the schematic without making unwanted changes to the waveform viewer signals. It would speed up working with QSPICE and significantly decrease the amount of frustration. Please :slight_smile:

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My favourite solution would be two modes, one for editing, on for probing, implemented as two tabs in the main schematic window.
After a simulation run, a copy of the simulated schematic is made (e.g. as *.qschsim) and used as basis for the probing mode. The probing mode is then activated automatically. Now I can probe without extra buttons to press, without the fear of accidentally moving something. It would have its own probing specific context menu etc. This would increase usability while also reduce the risk to mess up net names and loosing sync with the simulation data.
For editing I would go back to edit mode, editing the original schematic file, leaving the schematic of the probing mode untouched. So, until I simulate again, I have a pair of read-only schematic and data. This would also be great for archiving slow running simulations. With the edit mode moving a wire doesn’t plot that node, the DC OP does not pop up etc.

Hi @Engelhardt,

What do you think of adding such option?

@Engelhardt I agree with Olli’s complaint that this is not nice behavior of Qspice, but I have an idea for a different solution: two pinning buttons or tick marks.

  • One would stop the autoscaling, and keep the scales fixed. This avoids having to re-adjust them after each simulation, as we often need to do. Another benefit might become available: if the waveform could be updated progressively (not erasing old data until new data is available) that would make it easy to visually spot small changes compared to the previous run.

  • The other would pin the plotted variables. That would make it possible to modify the schematic without having to overwrite and recall the plot file every time. You may not want to overwrite it because you still need important saved plot settings, and you don’t want to be distracted by having to manage different plot files.

These pinning buttons/tickmarks would probably best be on the global toolbar. It would be nice if they operate only on already existing plot panes and not on later created plot panes (that is until you untick+retick them again of course). That would make it possible to still probe around with autoscaling using a new pane while some important panes keep their fixed scaling at every run.
Some visible indication of “ticked” status per pane would then be nice.

If you hold down the ALT key, you are probing only.

Alt key down or not seems to make no difference. Puzzled, I installed the most recent update just now, but it still seems to makes no difference. Is there a special trick to this?

Anyway, writing the previous post got me to another idea that should be 1) easy to implement, and 2) has the advantage that needless distractions and frustrations about lost plot scale settings and changed plot variables are completely avoided, and 3) feels logical without needing extra GUI widgets.
This is the proposed behavior: when there is a plot file for the current simulation then the viewer uses the scale settings and the plotted variables exactly as saved, so both are automatically “pinned”, exactly as one would expect “saved plot settings” means. But this would happen only for plot panes that are in the plot file, and not for new plot panes, also exactly as one would expect. So by adding new plot panes, the user can still probe around and enjoy auto-scaling.

What I forgot to mention: when there is plot file, probing should then automatically open a new plot pane if there is not yet a “free” one. If a new trace needs to be added, the user can delete the plot file (there already is a menu item for this)

Edit: sorry, scratch that, its not a good idea at all as default behavior! It should always be possible to add a new trace to a pane with fixed scales! But if the user wants to open a new pane when probing, holding the ALT key down approach may be nice to enable this.

Additionally, I think it would be nice that if the user changes a plot scale using “Axis Setup”, then this means a plot file automatically gets created with an entry for that pane. That would then be the natural way to stop auto scaling. An extra button to enable/disable this might be good.

This is my understanding about hold down the ALT key for probing

  • The question from Olli : Probing may accidently move devices in the schematic.
  • Problem Description : After simulation is ran, left click to probe a node or device, if hold left click and move your mouse during probe, wire or device may also be moved.
  • Solution : Hold down ALT key and left click, this can prevent moving a wire or device. (requirement - this only work after a simulation is run and with an active waveform viewer)
  • Additional feature : This is also how you can measure differential voltage. Hold down ALT click on a node (keep pressing left click) and drag to other node, you will get a differential voltage (e.g. V(N001,N002)).

Hi KSKelvin,
Thank you for clearly stating how you understood the issue that Olli raised.
This made clear that this issue is misunderstood, and it also explains the puzzling but unhelpful ALT key advice. I will try to explain.

The issue is not that probing may move things in the schematic, its the other way around.
The issue that Olli raised is that moving things on the schematic will automatically cause probing and will add unwanted curves to the plot, “messing it up”.

A different issue I attempted to address simultaneously with my proposals is that autoscaling can’t be turned off when all you want is to probe around with a fixed scale settings, as you would do with an oscilloscope, and as is often superior to permanent autoscaling. The problem with autoscaling is that you loose a sense of scale. The plot file does not help: it restores scales but removes any new traces that you wanted to see on the fixed scales.

Both issues have in common that they are about automatic actions -that currently cannot be avoided- occurring in the waveform viewer and that result in the need for extra user actions to undo them. These extra steps are distracting and are indeed annoying because you have to repeat them again and again and again.
With the right options (e.g. tickmarks) both the waveform viewer and the user would have a lot less needless work to do, and using Qspice would become faster and more enjoyable.

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