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Re: doing math on plots


The current eeschema-ngspice interface is very limited.

How would one plot, for example, the difference between two vectors?
I tried this in a text box:

.save foo=(‘v(/input)-v(/output2)’)
.tran 10u 50m

but "foo" does not show up in the list of vectors to display in the plot window.

Here you might have a look at https://forum.kicad.info/t/spice-plotting-difference-of-voltages/19545/2

Another thing, I found that one can use parameters for values, for
example {Rx} for a resistor value and then add a textbox with ".param
Rx=100k". Would it be possible to simultaneous get plots for a set of
different values of Rx?

Here you might try external ngspice. KiCad 5.1.x has a direct interface, where you generate a netlist from your circuit and then may call ngspice. This will offer the full ngspice capabilities and plotting via ngspice or gnuplot. I have described an example at http://ngspice.sourceforge.net/ngspice-eeschema.html#external .

Unfortunately this interface has disappeared in KiCad 5.9.9 . I still will have to make a wish list bug report to get this back.


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