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VGA signal fading

Discussion in 'Beginner Electronics' started by Coyoteboy, May 29, 2007.

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  1. Coyoteboy

    Coyoteboy Guest

    I'm looking to create a VGA fader - I have a projector that takes a VGA
    signal from a PC, but I want to be able to fade that signal down to black
    between projections, manually using a slider. I know there are production
    items out there but they are in the region of upper hundreds and over-spec'd
    for what I need. I just need to be able to fade in and out one input.

    I cant find, on a brief hunt, the VGA signal spec but I would guess its got
    a sync line and 3 AC signals for pixel brightness. I hear it may be ~0.7v
    p-p but i dont have that confirmed. Would it be fairly simple to create a
    variable gain amp to maintain 1:1 or lower gain to fade the signals to black
    without losing sync with the projector (it pops up a blue screen when the
    cable is unplugged). Obvioulsly one amp on each analogue line.

    Any hints/pointers would be of great help!

  2. Charles

    Charles Guest

    I don't think you can gracefully fade a digital signal.
  3. VGA is analog.
  4. Charles

    Charles Guest

    Yes it is. But how about the synch pulses? Decreasing amplitude might
    reduce contrast to a point, but then synchronization will be lost.
  5. PeterD

    PeterD Guest

    Standard VGA is analog, not digital.

    A quick version would require a triple ganged pot, perhaps 150 ohms
    each (one for each color signal). I guess three sliders with some sort
    of homemade handle to gang 'em together might do just fine.
  6. Charles

    Charles Guest

    That makes sense.
  7. Why would one even think about fading the sync pulses?
    They're on separate lines in the VGA connector.
  8. Coyoteboy

    Coyoteboy Guest

    I'm concerned about shorting the signals to ground. I'll experiment with a
    cheap video card and see what is required to pull the signal low without a
    full short. It'd be fairly easy to set this up with a set of digital pots
    too, is my thinking, and enjoy the lack of mechanical failures (as a
  9. Where are you?!?!
  10. Cliff Woodcraft

    Cliff Woodcraft

    Jan 18, 2011
    I have made a VGA fader, which works quite well because nobody seems to make one. I am wondering whether to go into production for the benefit of anyone else in a similar predicament
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