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Electronics Building a custom KVM

Discussion in 'Modding' started by z4114, 30 Jan 2009.

  1. z4114

    z4114 FACE!

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    I want to build my own custom KVM that will transfer DVI-I, USB, and 4 jacks worth of audio. I ran across an article on engadget about making your own composite video switcher and i'm guessing the process could work backwards as well.

    I want to use the CBT3244A as the IC what does the switching. I know there will need to be a lot of these chips (DVI-I is 29 pins) but that doesn't bother me. I just want to know if this is something feasible.

    Thanks for your help.
     
  2. Alex6969

    Alex6969 If it's fixed, I can break it.

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    Yes very feasible. I've been wanting to make a USB switch for quite some time.
     
  3. Moriquendi

    Moriquendi Bit Tech Biker

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    There are two problems with your proposal. First, DVI uses TMDS, that's Transition Minimised Differential Signalling which means that each signal in fact used two wires that operate above and below 0V, you cant just put a digital switch in it and expect it to work. The second problem is that DVI operates at 165MHz and at speeds like that differences in line length will start to cause problems.

    With composite video the signal is analog which means that distortions and delays will show up as poor image quality. DVI is digital and encoded meaning that distortion and delays would make the data garbage and stop the thing working.

    So I don't think it is in fact feasible however you can get DVI KVMs that include USB and audio though only one stereo signal, audio switchers are pretty cheap though.

    Moriquendi
     
  4. ConKbot of Doom

    ConKbot of Doom New Member

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    DVI actually pushes > 1gbps down the data lines, the clock is 165 MHz however. TI makes a 4:1 HDMI/DVI switch IC and it has pin contol (i.e. bring a pin high or low to control which input is selected) but it is in a 100TQFP package, with .5mm lead pitch. Not gonna rig that up on a breadboard.
     
  5. z4114

    z4114 FACE!

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    So if I forget about DVI and just use VGA, I should be ok? I figure I can drop $20 on parts just for the experience and if it works, all the better.
     
  6. ConKbot of Doom

    ConKbot of Doom New Member

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    The VGA frequencies are still quite high (whatever your vertical resolution * your horizontal,) but much lower then DVI, so why not give it a shot. 1280 *1024 would give a ~1.3 MHz signal.

    Your layout will be important, but it wont be affected by it not being a transmission line, etc... as much as the DVI.

    Keep your wiring short/neat, preferrably with some grounds to separate the high freqnecy stuff. (the RGB lines mainly and the H, V lines to a lesser extent) and you should be able to come up with something workable.
     

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