USB monitor connection for multi monitor setup

Discussion in 'Displays' started by xxtraloud, Mar 13, 2018.

  1. xxtraloud

    xxtraloud Limp Gawd

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    I need an advice from the monitor experts. What I have is a laptop with

    - intel HD 520
    - one HDMI port
    - 2 USB 3.0 ports
    - 1 USB type C (3.0) port

    I am trying to setup two monitors, one monitor is newer and has DVI/displayport, the other VGA, and I think VGA. I looked into usb-c to DVI/display port adapter but it's unclear if they can drive two monitors. I would like the most flexible setup that I can use in the future if I change monitors. For example if I endup having two monitors with DVI/displayport.

    - is there a usb 3.0 (type c preferred) that allows to connect two monitors in EXTENDED mode and costs max $35/30EURO? Would it be better to get a regular USB or type c adapter? I am wondering if type c will become the standard for new PC laptops.
    - should I just buy two separate adapters? A usb to dvi/vga/dp and an hdmi to dvi/vga/dp?
     
    Last edited: Mar 13, 2018
  2. rtangwai

    rtangwai [H]ard|Gawd

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    What make/model of laptop do you have? That Type C port could be Thunderbolt, which changes your situation considerably.
     
  3. xxtraloud

    xxtraloud Limp Gawd

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    It's an LG Gram 2016 model, no it's not a thunderbolt, it's simply a type C 3.0.
     
  4. DanNeely

    DanNeely 2[H]4U

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    For multiple displays off a single USB port, you'd probably need to look for a full up USB dock, and even the cheapest of those is probably going to be a bit over your target budget. Excluding ones without video out they seem to start around $80.

    If the convenience of only having to connect one cable instead of 2 is worth paying the premium is up to you.
     
  5. xxtraloud

    xxtraloud Limp Gawd

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    That makes sense. So I was thinking something like this
    https://www.amazon.com/Multiport-KP...rd_wg=94rgh&psc=1&refRID=Y9Q5Z1H8T7SHZM7840H7

    or this

    https://www.amazon.fr/Multiport-Cab...pID=5197HzXiBBL&preST=_SY300_QL70_&dpSrc=srch

    https://www.amazon.com/HuDieM-Multi...D=41k8YcvVU8L&preST=_SY300_QL70_&dpSrc=detail

    These are 3.1 but should be compatible with 3.0, correct? One of the two adapters description says "the adapter is not compatible with devices which do not support the protocol of DP Alt Mode" Not sure what that means.
     
  6. DanNeely

    DanNeely 2[H]4U

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    The first and third of those say they can only support 1 display at a time (#3 also lacks support for encrypted video, so no netflix/etc).

    The middle one only supports 2 displays at once if one is VGA and both top out at 1080p (Dunno if you'll find anything that can do 1440 and something else at the $30 price range though).

    Maybe. There's a major "Yes, but..." here. USB3.1 gen1 added support for alt modes, and if it was designed for 3.1 gen 2 you're only able to give it half the expected bandwidth which might impact running 2 screens at once.

    Alt modes allow a computer to send things other than USB data directly over USB wires (without needing to package it as USB data in the PC and unpack it at the other end). The catch is that your computer has to support it, if it can't send a displayport signal to the USB-C port you're probably not going to get any video out. The latter is partially a supposition on my part, but between the warning and it not having any display port out, I assume it works by looking like a displayport hub to the PC and then just converting outputs from there internally.

    PS don't feel bad about being confused. for version 3.1 the USB standards group changed thier standard from being universal because it always just worked to being universally confusing by trying to support every mutually incompatible standard on the planet to become the One Cable to Rule Them All.

    PPS All 3 of those adapters only work with DP Alt mode, as will probably anything else at that price level. If your laptop doesn't have it, you're back to needing a $100ish dock that can do video on its own instead of just passing a signal through.
     
    Last edited: Mar 15, 2018
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  7. xxtraloud

    xxtraloud Limp Gawd

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    Thank you Dan for the precious info. I don't need to run anything beyond 1080, so that should not be a problem. Is there anyway I can determine if my usb-c port supports DP alt mode? I can't find any info online regarding my laptop. I don't necessarily need DP, I can use DVI + VGA for the two monitors I have. Is DP alt mode only needed for monitors that only have DP ports?
     
  8. DanNeely

    DanNeely 2[H]4U

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    Dunno if there's a good way to check what if any alt modes your ports support without testing hardware (perhaps a new question in the general hardware forum?). If you listed your laptop someone else might have better sleuthing luck.

    The adapters that say they need DP-alt mode to work and don't have a DP out I can guarantee won't work without DP-alt mode support on the laptop. As far as the computer is concerned they're a 2 or 3 way displayport hub, and then they just attach DP-HDMI/etc adapters to each of the hubs DP outputs internally. I strongly suspect the same is true for any that say they need DP alt mode to work even if one of their outputs is DP unless they explicitly say the other ports will work without it.

    DP alt mode is the only easy way to get multiples of 1080p video out a single 5 GB usb port (because it lets the wires in the connector run at much faster displayport speeds). For anything else you've only got the bandwidth to run one monitor without compression and need to have a decent sized buffer (which inevitably adds input lag) because USB data doesn't have high enough innate QoS levels to guarantee the data stream will never be interrupted long enough to drop a frame.

    Without it you're down to cheap 1 monitor per USB adapters that can at least ignore the bandwidth issue, and more complex systems that have made the $100 docks doable long before DP alt mode was a thing.
     
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