I’m new to Spice in Kicad and can’t figure out how to measure current and wattage. Is it possible, and how so? Thanks!
Current is easier, although it would be a nice feature to get the probe to add the current automatically if clicked on a component instead of a node.
Anyway, you need to add the desired signal manually from the list as shown below:
Wattage is voltage*current, but I’m not sure that the KiCad Simulator currently supports plotting a function consisting of multiple voltages and/or currents. Maybe someone else here knows? If not, I can show you how to farm out this task to LTspice (if you have it available).
I do not know much of ngSpice (yet), but it seems logical to me that it would be possible to define some mathematical formula to add a new variable in a text box in KiCad and pass that along to ngSpice (just like the “.ac dec 20 10 10Meg” ) and ngspice adds it to it’s netlist. You would have to read the ngSpice manual to dertermine if this is possible and how to handle it.
Edit / Oops:
This probably would not work. See:
https://forum.kicad.info/t/how-to-improve-the-kicad-ngspice-interface/15880/12?u=paulvdh
Your reply gives me hope, but I can’t get it to work yet.
First, I may not have the absolute latest version, so I will download from the nightly updates and hope that is my problem.
That said, going from your step 1 to step 2 is easy. I can’t make the jump to step 3. There is stuff missing there. Like a button allowing me to select a signal to add. I get the window but no options.
To cover my bases, I did check Help and Online manuals but found nothing.
Comparing directly to LTSpice and OrCAD spice, having a button to press to show current and wattage seems like a very big thing to add to the list of things to improve in this spice program.
Another approach may be:
I think there are voltage to voltage sources, and voltage to current sources and other weird converters as predefined spice components. With those and a resistor or so you can probably add a “probe and measurement” conversion section to your schematic & netlist. which can then be probed.
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Heads up thinkin’! That’s a good idea for a workaround. I guess the most straightforward way is to use a behavioral voltage source. You would then need to know your node names for the voltage across the component(s), or label them yourself.
I whipped up something really quick. The netlist generator does not like if nodes don’t connect to anything so I had to add dummy resistors R3 and R4 for everything to parse correctly. Probably a bug. I dunno. Not gonna really deal with it since I got scolded last time for posting observations instead of filing bug reports. Anyway, here are my results:
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