I’m a little confused about whether I should assign a standard footprint to my custom schematic symbol or leave it blank and assign it with the foot print assignment tool. Also I appear to get two footprints when I import from the schematic to the PCB. One footprint has all my rats nest connections, the other has none. I could just delete it, but it reappears on every import and I can’t quite figure out where the second one is coming from. Any help would be greatly appreciated.
These are just alternative methods to achieve the same goal. Just pick whatever suits you.
Open both the schematic and the PCB editors simultaneously, and select something. KiCad’s cross probing should show you instantly what parts it thinks are connected.
Thanks @paulvdh If I have a footprint defined on the symbol, and I also map a footprint using the assignment tool would that cause two footprints to be included? Or does one take precedent over the other.
If you use certain part more than once it usually makes sense to add it to your personal library and make it “fully defined”, i.e. the symbol has the footprint link saved in the library. Why would you want to do it manually again and again?
Also I appear to get two footprints when I import from the schematic to the PCB.
Ah, the cross probing helped a lot. It showed I had an incorrect footprint added to another custom symbol which was why it was appearing and nothing connected.
Also, each schematic symbol should only have one footprint link. (It is probably not even possible to add more then one footprint link to a schematic symbol). You can examine the properties of schematic symbols individually, or use Schematic Editor / Tools / Edit Symbol Fields for a spreadsheet like overview (with editing and cut& paste possibility). In KiCad, the schematic symbol is the “root part”, and a link to a footprint is added to a schematic symbol as an attribute.
Very often there are several ways to do a certain task in KiCad. It’s possible there are 5 or more different ways to get to a certain result.
If you are talking about assigning the footprint to the schematic symbol when you create the symbol before saving I would apply the following logic.
If the symbol is quite generic and might have different possible footprints assigned to it, e.g. switch, I would leave it blank when I create the symbol and would assign the footprint when using it in the schematic.
If the symbol is very specific and is being created for a unique or very specific component with a unique/unusual footprint I would add it to the symbol and then save the symbol.
In general you would assign all the footprints at the schematic stage prior to starting work on the PCB, but sometimes you may have space constraints so may need to adjust your choice of component/footprint. This can be often be achieved by doing a component placement to see where components can fit then adjusting component package/size and hence footprint choice to make things fit. At this stage you might want to make that change from within the PCB layout.
I used to assign footprints to the first resistor and first capacitor I put in a schematic, and then make copies of those for all the others. That way footprints are already assigned to all of them. But in the end it does not matter much. There are so many ways in KiCad to assign footprints in bulk that doing this for the first parts does not save much time. Maybe the difference is a minute or two on a whole project.
