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I have a monitor that takes USB-C for video input and passes mouse and keyboard back.

I need to connect to this through a bulkhead, and most connectors seem to be USB-A. Though they mention being USB 3.0 compatible, I don't know if all the wires will be there, or only what is required for "normal USB". It looks like both pinouts have similar Tx and Rx cables, so maybe it will be OK.

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  • \$\begingroup\$ What kind of video are you referring to? \$\endgroup\$
    – Eugene Sh.
    Commented Feb 15, 2023 at 18:14
  • \$\begingroup\$ computer monitor \$\endgroup\$
    – new2cad
    Commented Feb 15, 2023 at 18:17
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    \$\begingroup\$ This isn't what I am asking about. Is it DisplayPort? Interestingly a very similar question was asked today a bit earlier: electronics.stackexchange.com/questions/654176/… \$\endgroup\$
    – Eugene Sh.
    Commented Feb 15, 2023 at 18:18
  • \$\begingroup\$ I'm seeing a few USB-C bulkhead adapters for less than $10 from the usual reputable sources, in case that was on the table. \$\endgroup\$
    – vir
    Commented Feb 15, 2023 at 18:27
  • \$\begingroup\$ Sure I was looking mccmaster carr and was not happy with what I saw, nothing at mouser, but maybe I missed it \$\endgroup\$
    – new2cad
    Commented Feb 15, 2023 at 18:35

2 Answers 2

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This is potentially problematic in a few ways.

  1. The monitor may not be a pure USB device, it may be using an alternate mode like displayport. This cannot be supported over an A connector. Depending on the device this may result in either reduced performance or no video at all.
  2. Even if the monitor is a USB device, USB C is a reversable connector. Responsibility for handling reversal falls on the device with the USB C socket. So if your monitor is a USB device and has a USB C Socket you are ok, but if the monitor has a USB C plug there may be issues.
  3. Volt drop and signal integrity may become an issue, but if the cables are short this is unlikely to be an issue.
  4. A cable with a USB A plug and a USB C plug will be coded with the USB C end as "downstream". If your bulkhead adapter has two A sockets (rather than the A socket on one side and B socket on the other that it should have) then you will likely have to use a C plug to A socket adapter in combination with an A plug to A plug adapter to make it work.

USB C couplers may also be problematic. The USB C standard was not designed to accomodate them, and they may either only work one way round or not work at all depending on the design of the devices and the coupler.

IMO if you need to pass your signals through bulkheads or similar, USB C is probablly not the right technology for the job.

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  • \$\begingroup\$ Yeah both monitor and PC have USB C Sockets. I believe it is using display port 1.4 over usbc \$\endgroup\$
    – new2cad
    Commented Feb 15, 2023 at 19:00
  • \$\begingroup\$ Yeah, displayport is not going to work over USB A connectors, the monitor might fall back to a "video over USB" mode, but at best it will perform much worse than a displayport connection and at worst it may not work at all. \$\endgroup\$
    – Peter Green
    Commented Feb 15, 2023 at 19:04
  • \$\begingroup\$ That makes sense, I was hoping that the 2 tx/rx pairs in the pinout were just the same things be different names, but I guess the VBUS and CC1 lines are doing something \$\endgroup\$
    – new2cad
    Commented Feb 15, 2023 at 19:11
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Shouldn't be a problem.

What could be a problem is the voltage drop - in case you are using this concoction to provide power across it, since the multiple connectors etc would add to the overall resistance of the entire chain.

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    \$\begingroup\$ Doesn't video over USB-C use alternate mode? If so, it can't be initiated as it happens through vendor-defined messages on the CC line. And the initiation will likely allocate high-speed pairs that are missing as well (USB-C has 4 high-speed pairs, USB A has only 2). \$\endgroup\$
    – Codo
    Commented Feb 15, 2023 at 18:34
  • \$\begingroup\$ Oh well, if its going the vendor defined message route, then all bets are off. \$\endgroup\$
    – Kripacharys
    Commented Feb 15, 2023 at 19:11

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