I'm not at all an expert on the hardware side, I'm a software engineer but this raised my curiosity.
The Universal Serial Bus Specification Revision 2.0 specification states
6.8 USB Grounding The shield must be terminated to the connector plug for completed assemblies. The shield and chassis are bonded together. The user selected grounding scheme for USB devices, and cables must be consistent with accepted industry practices and regulatory agency standards for safety and EMI/ESD/RF
whatever that means
What I found out is that the literature states that connecting a shield directly to the signal ground on a device side can create unwanted ground currents or interfere with EMI/ESD behavior. There are recommendations for placing a resistor, a ferrite bead to limit highâfrequency noise being conducted onto the shield (Texas Inst.), or other stuff between the shield and ground instead of a direct connection, or even leaving the shield floating on the peripheral side to avoid ground loop currents flowing between host and device grounds.
This seems to be because if the host and device grounds are at slightly different potentials, a direct DC connection could allow current to circulate through the shieldâs metal, potentially injecting noise or creating interference ??
This topic was started at @outbackhut request, I have nothing to do with it and as far as I'm concerned the topic from which it was split was solved and there is nothing more to discuss.
The connector shield on the Uno R3 is connected to UGND of the ATMEGA16U2 chip through a BLM21 ferrite bead with 0.27 Ohm resistance. It has been suggested without proof that this is not the way it should be done.
Yes Iâm confused but still wondering if it should or should not be connected to GND. Seems there is a good argument in the literature to not connect it directly but there is also documentation on connection through some components as wellâŚ
To me it seems like the answer is "it depends " but Iâm not clear on what.
The USB 2.0 specification was clear about how to build the cables and connectors re the shield but not on how they would be connected to various grounds on the host/device. Consequently the confusion. USB C does a better job.
OP asked if he/she could feed an Uno via Vin and USB simultaneously;
First answer said generally no, but yes if carefully share grounds. Original Uno has a circuit that handles that;
OP then asked if the barrel jack and the USB socket share the same ground;
Answers were âdepends on who make the boardâ and âyesâ;
The subject then changes to wether it is necessary or not to ground the USB shield and splitted to this hockey fight like topic.
@outbackhut (who might be asleep in Australia by this time) says it depends if the board will be constantly manipulated or not. @jim-p says itâs nonsense. We now have a third opinion by @EmilyJane in posts #26 and #28.
Sameways here, since when we use EasyEDA, the USB female connector has its shell clearly marked as GNDâŚ
I was trying to understand whatâs your expert opinion on grounding the usb shield - seems both options are documented in the literature and I understood from your postings here that you lean towards never doing it.
So my scientific curiosity was triggered and I wanted to understand your view.
Seems you are not interested in that discussion so Iâll leave it there.
No such request is required. When a tangential discussion occurs in a topic, and that tangent is not aligned with the goals of the topic author, the moderators will split it off to a dedicated topic so that it doesn't cause harm to the original topic author.
If for some inexplicable reason you are bothered by having tangential posts split to a different topic, then in the future be careful that your replies are tightly focused on the specific subjects of discussion specified by the topic author, and that the posts are appropriate within the context (e.g., not going into low level details far beyond what is needed to address the subjects raised by the topic author, and not helpful at their level of experience).
Note that it is expected that topics will wander a bit on this informal discussion site. The level of wandering that is appropriate will depend on the goals and conduct of the topic creator. I'm sure most of us are prone to going off on tangents when it comes to technical subjects we personally find interesting. In cases where there was no malicious intent or violation of the fundamental standards of behavior for this forum, there are no repercussions for the accounts of those whose posts are subject to a topic split. In this case, it would be a good idea to reflect on the situation as it might provide insight into how we can more effectively participate in the forum going forward. However, we should not be overly concerned by the split.
As @pert has said in reply #37 no request is needed. I noted that the discussion had strayed away from the original topic, it seemed to me that what was being discussed was worthwhile but not really related to what the author of the other topic had asked about, so I split it. When this happens it's often the case that the exact point to make the split is not clear because the wandering off topic happens gradually over a number of posts. In this case I judged that yours was the first reply of the new discussion, but I could easily have made the split at a different point. As the discussion was, at that point, entirely between you and @outbackhut it would have been ideal if I could have made both of you the OP, but the forum software does not allow that. This is why you appear as the OP in this topic. If you do not wish to engage further that's OK, but it is clear others do so I am leaving the topic here for them.
Edit:
To be clear, there is no suggestion of any wrongdoing by anyone here.
Yes, that sounded interesting and that's why I thought it was an appropriate thread to ask my clarification question since we had two contributors expressing different view points and the limited literature I had reviewed supported both views.
I'm always puzzled with hardware stuff, my mind is not so used to "it depends" without much info on how to make the decision. So it's interesting to understand how experienced people do pick a way and why.
Personally I stand on including EMF protection if at all possible. It costs next to nothing and barely takes up space. I like the way some official boards do it, and some clones do it, but the reverse is true where some official boards arenât perfect, and most clones are terrible.
