Timer schematic/simulation


I’m modeling a timer circuit, starting with pspice “vsource” and “0” for the ground. I’m able to
get through ERC and the ngspice simulation gives expected square wave result.

Now I want to get a little bit more “fancy” and add connectors so that I can see how things will
look in PCB editor. I guess I don’t quite understand how to use “labels” and get everything to
work. With the current iteration, I get through ERC, but ngspice gives “warning, can’t find model gnd”.
So it looks like I need to somehow associate the pspice “0” with GND, but how to do that is unclear.
For connector P2, I went to the spice model tab and was able to input 15V under the source tab.
But for connector P1, I can’t see how to get GND correct.

Normally it does not make sense to simulate connectors. So you should exclude them from simulation.

If you really want to simulate a connector, you will have to attach a SPICE model to it. This may be a subcircuit consisting of a series resistance (a few Ohms at most for the contact resistance) and a capacitance pin-to-pin or pin-to-ground.

In your case, with such low frequencies, simulating a connector is not helpful and does not change the result. So exclude it.

I think in this case OP wants the connector symbols to simulate as the voltage source, so they are trying to add a voltage source model to the screw terminals.

@gregg_a_g, I think the issue you’re running into is that sources inherently need two pins. So I have a few suggestions:

  1. use a symbol that has two screw terminals, rather than two symbols that each have one screw terminal. You should be able to attach the source model without issues
  2. or add an explicit voltage source to your schematic like you had in the first version. You can mark the symbol as not on PCB.
  3. It might be possible to write a subcircuit model that wraps a voltage source and internally connects one pin of the voltage source to ground. This would let you have a “1 pin voltage source” in your schematic, which you could attach to the P2 connector as a subcircuit model.

Thanks for the replies, gentlemen!

I found a nice Kicad 6 “intro” - Getting Started with KiCad Version 6 : Beginner’s Tutorial to Schematic and PCB Design - CIRCUITSTATE Electronics

As I read through, it seemed pretty clear that “simulation” and “PCB layout” have a bit of
mutual exclusivity. It seems best to have two versions - one for sim, and one for layout.
That’s really easy enough to do, but I didn’t realize that until I saw your two replies and
read through the documentation a little more closely.

Really like the Kicad 6.0!