Let’s say I have a pin header on my PCB that connects all 40 pins from the Raspberry Pi. Some of those pins are ground. As far as I understand, the whole PCB can act as ground once a ground plane is added, and I just need to attach the GND symbol in the schematic.
Do I need to add the GND symbol for every ground pin from the header? And whenever I need ground for example, for buttons or other components, is it enough to just add the GND symbol?
Is there anything else I need to be aware of? I assume I don’t need to manually route the ground connections, right?
You still have to connect every pin that needs to be grounded to the GND symbol or the GND rail. Otherwise those pins will have no net, and trigger an ERC warning (no net and not no connect). The GND fill will not connect to those pins if they have no net.
No, a no connect flag on the pin would also cause the GND fill to avoid the pin.
The key point is the schematic has to specify all the correct connections. The board will then obey the specifications, or signal a DRC error. This is why we tell beginners that a schematic is very desirable and not to skip making it. Without a schematic, the layout editor cannot provide you with checking.
Not only the above AND the comments from @retiredfeline , but you cannot be certain that all the GNDs are connected internally. By not connecting one or more to the Gnd net, you may find one or some of the parts of the circuit just don’t work.
Also, Kicad is designed so, once you perform the “Update PCB from Schematic”, you are only able to connect tracks between footprints so they match exactly the wires (or labels) between the symbols in the schematic. So, if a pin is not connected to anything, you will not be able to connect a track to the pad that is represented by that schematic pin.
I do not understand why you ask this question. For KiCad itself, there is absolutely nothing special about GND. It is just a three letter combination that is used as a name to identify a net.
If you want a connector pin to connect to anything, then you have to draw the connection. Putting a label next to it, but without the connecting wire does not help.
Yes. You need to connect the GND symbols, or GND labels. For KiCad all Power symbols are treated as power inputs (because multiple for the same net are used, they can not be power outputs). and the name creates a global net label. In KiCad local and global labels connect to the same net if the names are the same.
If you create a GND plane on the PCB, then all GND pins that are within the boundaries of that zone will connect to it. But I do recommend you do Schematic Editor / Tools / Update PCB from Schematic and just experiment with what happens on your PCB and what connections are (or are not) recognized. Your first attempt do not have to be “serious”. Just some quick imports, draw a random zone and random PCB outline (The PCB editor does have some strange behavior if you do not draw the PCB outline on Edge.Cuts) is enough to “get started”. Later you can decide whether to clean up your work and continue or just delete the whole PCB and do a clean import.
A common beginners mistake is to route tracks though the GND plane, and that is not good. The GND plane should not have big interruptions, small holes for via’s (small groups, never a long row of via’s) or for “dog bones” where a track jumps under another track though the GND plane are acceptable, but keep those GND interruptions as small as practical. (5mm is a guideline for the maximum interruption. For more background, to see the 2h20minute video from Rick Hartley of "how to design a proper GND on Youtube. This topic is important enough for a 2hour video.
Thank you all very much for your help with this. I think it makes all sense now to me.
Electronics is a fairly new subject for me, and I’m learning new things every day.
I really appreciate your help, thanks a lot!
Thank you for answering in detail, you made my weekend.
Summary
Proper GND plane design is essential, especially when dealing with CAN transceivers. The PCA82C250T has served me well in many layouts, offering excellent noise immunity. Keeping the transceiver close to the GND return path can greatly reduce EMI and ensure signal integrity in noisy environments.
