Show voltage drop in Simulator

[MarkOnKicad]

Probably a newbie question here but i can’t find an answer anywhere.

Is it possible to show the Voltage Drop over an individual component in the Simulator output?

For example if i have a 12VDC Voltage Source and 2 resistors in series connected to the Source (1 and 2 Ohms resp.), and lets say the circuit has 4A flowing through it, then i would like to see the voltage drop over these resistors of 4 and 8 Volts resp. (by Ohms law).
Ngspice seems to output only the voltage drop towards Ground (12 and 8 Volts resp.).

I know that in ltspice you can add a probe over an individual component and thus get the voltage drop over that component. Is there something like that in kiCad?

I am using kiCad 5.1.5 on Ubuntu 20.04.

[holger]

The interface between Eeschema and ngspice is currently rather limited.

So this option is not (yet) available.

[paulvdh]

I’m not entirely sure if this works, but I think you can create a formula in a text box in Eeschema which subtracts two voltages, and then draw a graph of that in the simulator.

[holger]

It is possible if you use the plotting capabilities of an external ngspice executable.

It is not possible (I have just checked that again with 5.99) with the internal ngspice simulator.

I am just working on a .probe command for ngspice which will include a differential voltage probe.

The alternative would be an enhancement of the interface in Eeschema. Somebody would have to catch this opportunity and do it.

[gkeeth]

Another possibility is to use a VCVS with unity gain to measure the voltage drop across a component and output a ground-referenced voltage.

It’s a bit tedious but it can be done.

But yes, short answer is not possible using the current eeschema-ngspice interface without a workaround of some sort.

[holger]

Please see also

Spice simulation: probing between two nodes

How do I probe across two nodes of a circuit, i.e., measuring voltage between two nodes. For example, I want to see AC waveform between two nodes. Thanks!

Add differential signals Ngspice

Hi everybody. This is my first thread so please be patient. Right now I’m designing a single-ended to full-differential OPA filter. [imagen] But I don’t know how to measure or add the differential output from the filter in the spice simulator. I want to see the transfer function from the single-ended input to the differential output. You think you can help me? Thanks

[Ste]

Another workaround can be found here:

Simulation plotting references?

Hey, there. Currently, Eeschema <-> ngspice interface is somewhat limited so you can’t plot differential voltages directly in KiCad’s Simulator app. One workaround is to generate the difference voltage within the simulation itself and plot it. There are several ways to do this. Although E-source would probably be the most “correct” way, it requires a non-standard symbol with two extra control pins. Therefore, I opted to use a B-source in the attached example project (in ZIP file below) whic…

[MarkOnKicad]

Thank you everyone for the replies and workarounds.

I solved my problem by going to ngspice directly. I copied the spice file from kiCad and added a print and plot statement to get the differential measurements. Works fine.

It is unfortunate that it’s not yet possible to do differential measurements without altering the scheme in kiCad. I think this might be a good addition to kiCad for the future.

Thanks again everyone.