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Dummy Plugs for Graphics Cards

Discussion in 'bit-tech Folding Team' started by ArthurBuse, 27 Apr 2009.

  1. ArthurBuse

    ArthurBuse CustomBitChimps member

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    If you want to run Folding at Home with more than one graphics card connected,
    then if you are using Windows Vista, you will need a monitor attached to each
    graphics card, or use a dummy plug to make it seem so.

    You need to tell Windows to spread the picture over all your graphics cards.
    Windows XP will happily assume each graphics card has a monitor attached
    and try to spread the picture over a monitor which you do not have. Windows
    Vista checks to make sure.

    You can make a dummy plug using three resistors and either a 15-pin D-plug or a
    DVI-I to VGA adapter, which is included with most graphics cards. You can
    solder the resistors to the 15-pin D-plug, or simply stick them in the holes of
    the DVI-I to VGA adapter.

    Here the link to the diagram you are going to need so you know where to put your resistors.

    http://soerennielsen.dk/mod/VGAdummy/index_en.php is the diagram.

    Actually, you can get away with only having the middle resistor, the one connecting
    pins 2 and 7. But at some future date it might not work and you won't remember why.

    How does it work?
    The graphics card sends separate picture information on three separate channels,
    red, green, and blue. Each of the three channels has a pair of pins
    pin 1 is Red Signal
    pin 2 is Green Signal
    pin 3 is Blue Signal
    pin 6 is Red Ground
    pin 7 is Green Ground
    pin 8 is Blue Ground

    If there is a monitor attached, it takes a few milliamps of current from the
    graphics card. The computer tests wether a current is flowing from
    the Green Signal on pin 2. If there is, it is assumed that an old-fashioned
    VGA or SVGA monitor is connected. The resistor connecting pins 2 and seven
    causes the same amount of current to flow as a monitor would.

    Why 75 ohms?
    If you are sending water down a pipe, it flows smoother if the pipework is the
    same diameter all the way. If you are sending electricity at radio frequency, it
    flows smoother if all the components have the same impedance. Television gear
    has an impedance of 75 ohms.

    In the UK, Maplin M75R metal oxide resistors are the easiest to buy, but the wire is a bit thin to stick in the holes of a DVI-I to VGA adapter. It is said that 1/2 watt carbon
    resistors have thicker wire that is just the right size. In the USA, 75 ohm resistors
    are harder to find. You can use 68 ohms or 82 ohms instead. Anything between
    50 and 100 ohms will probably work. If you use less than 50, you will be drawing
    too much current, perhaps. If you use too high a value, perhaps not enough current will
    flow to simulate a monitor being connected.

    It does not matter which end of a resistor is which. I have arranged mine like this so
    you can see the colours are the same, and the bodies stop the wires touching.
    You only need one dummy plug per graphics card, even if it has two monitor sockets.
    Windows tries to detect what model of monitor is attached, and fails. Windows XP
    calls it a "Default Monitor" and Vista calls it a "non-generic pnp monitor".

    [​IMG]
    Resistors stuck in DVI Adapter, wide part of VGA socket uppermost.


    [​IMG]
    Resistors stuck in DVI Adapter, view from other side.
    [​IMG]
    Close up of Maplin M75R resistor. violet, green, black, gold, brown.
    The top three colours should be the same whichever type you buy. The other two colours show the tolerance, which does not matter.
     
    yodasarmpit and Spaceraver like this.
  2. DocJonz

    DocJonz Another CPC refugee .....

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    Nice one 'Arthur' - always handy to have this thread - I had saved a link to it on the CPC Forum, but ........ :duh:

    [​IMG]
     
  3. 1Razor

    1Razor Living life one day at a time....

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    Cheers 'Arthur', will definitely come in handy if Win7 is a good as the Beta appears to be and it's cheap enough!
     
  4. Thaifood

    Thaifood Member

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    waiting for my resistors! :)
     
  5. saspro

    saspro IT monkey

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    There's a 1 year free Windows 7 trial out today.
     
  6. 1Razor

    1Razor Living life one day at a time....

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    Just tried accessing it, all info states it's for open release on 5th May unless you're a TechNetPlus subscriber and you can get it now. Don't fancy paying £240 just to download it now.....I'll wait. Thanks for the info though. :thumb:
     
  7. saspro

    saspro IT monkey

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    Opps :duh: I've had it since yesterday (Technet & F1 Cheesecake)
     
  8. Fisher.

    Fisher. partially impartial

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    Picked it up a few days back (my company may or may not do large amounts of legal work for MS) but haven't had a chance to test it myself.

    ...and how do you like the word filter? Cheesecake, you say?
     
  9. saspro

    saspro IT monkey

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    Don't like it.
     
  10. Sgt_Barnes

    Sgt_Barnes "It was like that when i found it"

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    Does Windows 7 require dummy plugs to run multi GPUs with a single screen? I have 2 cards running in XP and all i had to do was extend the desktop and use Rivatuner to fold with both. Just wondering as i will be getting 7 when it comes out so will i need to get plugs at the same time?
     
  11. Unicorn

    Unicorn Uniform November India

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    You do as far as I know... any folding I did on the beta was strictly CPU based and I never got a chance to run the GPU2 client on there, but seeing as drivers etc for it are all Vista X64 I'd imagine the dummy plugs are needed.
     
  12. Fisher.

    Fisher. partially impartial

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    It'll grow on you;)
     

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