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vga to ethernet converter

Discussion in 'Electronic Design' started by Rune Christensen, Sep 1, 2004.

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  1. Hello

    Does anyone know if it's possible to build a VGA to ethernet converter? A
    device that converts a VGA signal to a digital videostream.

    I want to be able to operate a computer from a remote position also when the
    computer boots. So I will be able to change bios settings, starting mode of
    Windows, etc.

  2. That is inlikely possible. Especially when I consider the high
    analog bandwidth required for comfortable viewing.
    At 1600x1200 with 24bit colors, the bandwidth is in the order of
    350MHz per color.

  3. Iwo Mergler

    Iwo Mergler Guest

    Yes it is possible.

    As Rune pointed out, the easy approach is most likely
    unsuccessful, as the bandwidth of a video signal may
    well be several hundred MHz.

    If I had to design such a beast, I would start with
    a frame grabber, similar to the innards of a LCD monitor.
    I would then compress the video stream for transmission
    via Ethernet.

    For simple applications (BIOS, simple GUI, etc.), a differential
    encoding or simply a reduced frame rate would be sufficient.
    A 10MBit/s ethernet link could reliably transmit about one
    640x480x24 frame per second.

    For complex GUIs / moving pictures, you may have to use a
    real compression algorithm, maybe MPEG2.

    Kind regards,

  4. Does it have to be Windows? There are ways to do this if you can access
    bios and/or the o/s via a serial console. Not possible with Windows
  5. Ian

    Ian Guest

    Some "server management" cards do just this. Needs to either snoop the bus for VGA
    accesses or fully emulate a VGA adapter (i.e. they /are/ the VGA adapter for the
    machine). Quite expensive to buy, quite hard to make...
  6. Ken Taylor

    Ken Taylor Guest

    Do you actually need to change BIOS settings remotely as well? Programs such
    as VNC allow you to remotely take control of the PC, which also gets over
    the keyboard/mouse interface that your VGA-Ethernet converter forgets. Only
    applies once the OS is up and running though, hence the BIOS question.

  7. Richard

    Richard Guest - KVM over IP $$$

    If Ethernet / IP aren't required, there are Cat-5 KVM extenders for <$1K
    that will run 500 feet. See Raritan or Avocent for these as well.
  8. Tim Shoppa

    Tim Shoppa Guest

    It's not really Ethernet, but there are companies that sell
    adapters that let you run VGA signals over CAT-5 cable for distances
    of hundreds/thousands of feet. There's a converter box at one end,
    and another converter box at the other end.

    For example

    If anyone wants to spill the beans on what's inside these, I'm curious.
    I would guess that of the 4 CAT-5 pairs, three are for R, G, and B, and
    the fourth pair is used to carry sync info. But maybe it's much more
    complicated? Or maybe it's just 3 single-ended-analog-to-differential
    converters on one end and termination and differential-to-single-ended
    conversion on the other for RGB? You could convert the H&V syncs to any
    number of intermediate signals on their way to the other end... that's
    "just" 2 digital lines.

  9. "Ian"
  10. Ian Stirling

    Ian Stirling Guest

    Devices to do this are readily available.
    Just google for network webcams.
  11. Zak

    Zak Guest

    Or google for "KVM over IP". IBM and HP have servers that can do this
    via an internal management card.

  12. INS122595

    INS122595 Guest

    We done similar projects, the critical point is if many VGA standard need be


  13. Andrew Dyer

    Andrew Dyer Guest

    some 'server' type computers have a BIOS that will allow you to do
    the basics over a serial port. After the computer comes up you
    can run something like windows' RDP or VNC for a remote desktop.
    This isn't all that simple - assume your video stream is
    800x600x8bits per pixel x 60 hz (~230 mbits/sec). To make it
    work, you'll have to run gigabit ethernet, drop bits or frames,
    compress or some mixture of these.

    Next problem is how to get at the screen data - you could implement a
    whole vga subsystem (don't forget BIOS and drivers), snoop the PCI bus
    (need to track the state of a real vga chip which can be tricky), get a
    digital copy of the VGA output data (not all vga chips have digital out)
    or recapture the data from an analog copy (probably don't have access to
    the pixel clock, so you need PLLs to recapture the data).
  14. Tim Shoppa

    Tim Shoppa Guest

    Ah, not too far from what I thought. Although I am surprised at how
    they only use 3 of the 4 pairs, and use a funky encoding of common
    mode voltages on the red, green, and blue pairs to send the sync.

    I suppose that the sync really is sent differentially, in sort-of a
    three-phase way. They claim this reduces EMI, they're probably right but
    I've never analyzed this situation before.

    Maybe the fourth pair is reserved for a back-channel (mouse, keyboard) by
    some applications?

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