I deleted as much as I could but now i’m stuck with one issue which make no sense
OT: Do you really want to have a separate net AGND? Wouldn’t it make more sense to use a single GND net?
Creating different GNDs can be problematic for EMC reasons and should be avoided in general (there are some use cases, but they are rare and then you have to be careful. For example you should not route any track above plane GNDA to a place above GND).
The problem with 2 GNDs is that you create a dipole antenna with a IC in the middle that will use this antenna to radiate in a very hard to predict way
I honestly don’t know I just followed the schematic of these boards :
https://www.st.com/resource/en/schematic_pack/x-nucleo-ihm08m1_schematic.pdf (everything beside the connectors CNx)
https://www.st.com/resource/en/schematic_pack/mb1136-default-c04_schematic.pdf (the MCU sheet only)
I wouldn’t have used GNDA nor Earth but only GND if it wasn’t because of these CAD resources
Note : I’m a student
How accurate do you need your analog/ADC parts?
If you use a single GND, still make sure the power parts are in their own region, the analog parts are in their own region and the digital parts are in there own area.
That means you probably don’t make a EMC test and don’t really care if it radiates?
When you are student, why can’t you share your project?
I apologize for not answering earlier
Well I’m in intership and that project belongs to the company I’m in. But as you suggested I will delete a lot then share the it. It will just look like the schematic sheets from the nucleo boards then
I don’t know what EMC stands for to begin with, so for now I guess no.
Do you mean located on the board?
First, you probably want to remove that zip file from filetransfer website quickly. It as some 10+ backed up versions of your project in the “backup” directories.
Next your schematic is a bit of a mess. In KiCad global labels (and power symbols are global labels too) are connected though the whole project. There is no reason (and it is confusing too) to use both hierarchical labels into a hierarchical sheet, and then use global power labels on those sheets too.
This whole project has the feel of a beginner with KiCad trying to do a first project that is too complicated. After a bit of browsing though all your sheets I found the part below:
If you delete that part and update the PCB, then you have both a GND and a AGND net.
But you should really figure out what you want to do with those “different” GND nets. Designing a proper GND distribution is an extremely important part of any PCB and just copying stuff from other projects without understanding how to handle GND is a recipe for disaster.
Thank you for letting me know, I deleted it.
Oh I didn’t know. Could you give me few advice then? What labels should I remove?
That is exactly what it is. In my intership, I’m learning the job of a pcb designer and it became a bit too complicated while I’m still a beginner.
Thank you ! You were right, power symbols are global labels. I thought it was exclusive to the sheet, like local labels.
I honestly don’t know 
I don’t understand the purpose of having different gnd and how to determine them. I just copy what seemed useful from my development boards to make my custom board
So 3 days ago I was right 
:
Electromagnetic Compatibility.
Devices offered at market must meet formal requirements in this regard.
Long time ago (2002…2004) I was searching in internet for articles about how to design PCBs in accordance with EMC and signal integrity needs. One articles serie I qualified as the best (in my opinion). That articles later became not accessible for some years and then later they were once more accessible. I hope links I gave 3 years ago are still valid:
In my opinion if you read these articles you will learn enough about PCB design as for your needs.
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Yes you were right
Thank you ! So maybe yes but it will not be my job to do this. My intership is about to develop code for the microcontrollor (which I finished) and now I have to make my own board. This EMC wasn’t mentionned to me.
Thank you so much Piotr, I will definetly read this.
There is so many things to understand, I feel like my head will explose. Thank you for helping me
Yes it is. Designing for EMC is one of the many aspects that is inherent in any PCB that is designed for a commercial product, and as a student getting ready for “commercial job” you have to make it a part of your design.
Yes, I guess I already told you a few times you’re biting off bigger pieces then you can chew and swallow at a single time.
Code is also involved in EMC.
There are probably many rules how software should be written to be more EMC robust. As an example you can assume that bit in flash is more robust for electromagnetic disturbance then a bit in RAM.
So you can ask yourself a question: If I copied some data to RAM then should I assume that during 15 years my device is expected to continuously work can I assume that data is 100% stable or may be I should once a day/once a hour/once a minute to rewrite it.
As the last line of defense you can assume watchdog reset. EMC standards specify what the device behavior should be when exposed to electromagnetic fields. How you stand-up after watch-dog reset can decide if device pass or not pass EMC tests.
I recommend you use a single GND. This is simpler and a lot of time it is better than having multiple GNDs that you have to carefully connect and have to be careful with the signals going from one place to a other. A single GND is easier to do right.
Is it correct that you use a 2 layer board? If so, make a GND copper pour on both sides. Try to route as many tracks on the top layer, so that the bottom pour is connected very well. Where there are gaps, because a track goes in between, make sure you connect it to the top GND with vias.
Signals always need a return path. The return current always takes the path of lowest impedance. For higher frequencies, this path is closest to the track. Since you want the return path either:
- For differential pairs: In the other wire of the differential pair.
- For all other signals: In GND.
You have to make sure there is always a continuous GND connection near each wire. That includes a GND via near every signal via.
Keep in mind: The frequency of a signal is not the clock rate. The frequency depends on the slop of the edges, the steeper the slop the higher the frequency. You can easily have a 160 MHz frequency on a µC that uses a 8 MHz XTAL.
There is a lot of details i left out to not make it more complicated. I think it is already complicated enough for you.
My 3 cents about 2 layer boards.
Since I read those articles (from links I mentioned a moment ago) my 2 layer PCB strategy was to route 100% signal and power tracks on top with whole bottom being the continuous GND. I sometimes had to use some 0Rs to not break my GND continuity.
An example of such designed PCB I showed here:
Recently I started to use QFN microcontroller cases and as VCC routing as at the picture above became not possible I decided to use 4 layer PCBs as it is the only way to still have continuous GND layer.
I meant, this is not something that was mentioned in the work I have to do in my intership.
It’s not like I have the choice… I have to work on that even though a smaller project would have been better for beginner like me
Yes. And ok I will follow your advice for now and use a single GND.
From what i understand and what @paulvdh wrote, the project is too complex for your current skill level. You have to expect that the PCB may not work.
Getting help from someone with more experience, to at least look at your board, would be very helpful. If not, produce only a few prototypes and test them.
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