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PCB Design for USB Ports.

post #1 of 8
Thread Starter 
As part of my case mod, I've decided to create a PCB for my front panel USB ports. I'm going to be using surface mount components only: Kycon USB Ports, and the traces will route to these 2.54mm pitch IDC headers.
Connected to those headers will be StarTech 5-pin USB IDC cables which, in turn, connect to an NZXT IU01 USB Expansion. Finally, that will connect to my motherboard.

Now, I have two queries, for which most of the information above will be irrelevant:

1) What's the best freeware software to use for designing the PCB? Needs to be easy to use, since I'm not an electrical engineer and I don't want to have to go through a steep learning curve just to do a one-off design. I also need it to be able to print the traces at 1:1 scale.
I was looking to use one of the various free apps provided by the multitude of PCB manufacturers on the Internet. More specifically, I've downloaded ExpressPCB, but I figured I'd ask here first in case someone knows a better solution.

2) USB IDC headers have 5 pins. USB sockets have 4 pins. You can see where this is going.
I know that pins 1-4 are VBUS, D-, D+ and Ground. From what I can tell, the 5th pin is S-Ground (for Signal Ground?). While I was thinking about what the best solution to the "how should I mount the USBs" problem, I saw this. It looks to me as though the 5th pin connects to the metal housing of the USB port.
Is that correct?
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post #2 of 8
I expect the 5th pin connects via the outer shielding on the cable to the housing of the port. You can easily check that with a multi-meter. And most IDC headers have 9 pins, with one missing to force correct alignment.
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post #3 of 8
Thread Starter 
Quote:
Originally Posted by allikat View Post
I expect the 5th pin connects via the outer shielding on the cable to the housing of the port. You can easily check that with a multi-meter. And most IDC headers have 9 pins, with one missing to force correct alignment.
That's where I'm confused. What does that mean?
Do I just make another copper trace from the metal housing of the USB socket that leads to the 5th pin on the IDC header?

Also, yep, my motherboard has 9 pins and so does the NZXT IU01. Does that mean I should link two USB socket shells per S-GND pin? If so, would it be better to have an individual trace for both, or "daisy chain" them?
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post #4 of 8
I can snap pictures of one top and bottom for you tomorrow if nobody else beats me too it. I don't even think its connected on the cable side most of the time.
post #5 of 8
1) ive used circuit wizard its really easy to use to make custom pcb's etc i made a guitar pedal using it lol, i might still have it somewhere in which case i can probably send it to you some how.
2) i think thats right, but doesnt seem to make much sense if you think about it.
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post #6 of 8
Quote:
Originally Posted by [Adz] View Post
2) USB IDC headers have 5 pins. USB sockets have 4 pins. You can see where this is going.
I know that pins 1-4 are VBUS, D-, D+ and Ground. From what I can tell, the 5th pin is S-Ground (for Signal Ground?). While I was thinking about what the best solution to the "how should I mount the USBs" problem, I saw this. It looks to me as though the 5th pin connects to the metal housing of the USB port.
Is that correct?
The last pin is the shield for the cable (helps reduce EMI), which connects to ground. For external connections the shield connects via the metal housings of the connectors. While this isn't absolutely necessary for the USB to work, it serves to ensure signal integrity over long cable runs. On your PCB, I'd suggest running all the shield grounds through a common ground, this will ensure that all the cables are fully shielded; even if they are connected to the keyed side of a 9-pin USB header.
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post #7 of 8
I looked over a PCI USB card, and all the socket housings share a common ground, which would go to the 9th pin of an internal motherboard connector. Usually this would run via a foil wrap around the wires inside the cable which shields them from interference.
You have the individual wires in their individual insulators, covered with the foil wrap, then the outside coating over that.
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post #8 of 8
Thread Starter 
Since the header cables are pre-wired with all 5 pins, I'll assume that the interference protection on that part is covered. I've now got Circuit Wizard that Ski mentioned earlier, so later during the day I'm going to come up with a rough circuit plan and post it here to see if I've got the right idea.
The general concept that I've got is that I'm going to link the housing for each USB socket together, and that is going to link to the 5th pin on all 6 IDC connectors. I'm not sure if that makes sense, but it should be clearer once I'd done the design
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