VGA Feedback Loop

Discussion in 'The Projects Forum' started by Eskapist, Sep 15, 2015.

  1. Eskapist

    Thread Starter New Member

    Jan 4, 2012
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    0
    Hey AAC.

    I think this is my first post here (I'll see in a while. Hehe)

    A friend and I are making a VGA Video "Synthesizer" with an Arduino Uno. Things work great but we need to get a feedback loop running on each of the RGB channels in order to make some nice "glitch". Is there a way to do this? It does not have to be perfect sync or color.

    - Eskapist.
     
  2. AnalogKid

    Distinguished Member

    Aug 1, 2013
    4,542
    1,251
    Your question has 10% of the information needed for an answer. Please fill in the remaining 90%.

    ak
     
  3. Eskapist

    Thread Starter New Member

    Jan 4, 2012
    4
    0
    Hey AnalogKid.

    Sorry for the confusion. I've made a picture - Hopefully it will explain it better.
    Basically we create graphics using some simple code on the arduino. We then manipulate each channel with analog effects like filters. We are trying to come up with a way for the signal to be fed back into itself, with a delay, creating a feedback effect on the output.

    Untitled-1.jpg
     
  4. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    A video delay line is a relatively complex circuit, but the innergoogle has some. A fractional-line delay probably will producee mush; a full line delay will give some synchronized effects. But for the really cool effects you need a full frame delay (or a graphics card with a CPU behind it thumping away).

    The innergoogle also has products: http://www.ovation.co.uk/DelayLine/DelayLine.html

    ak
     
  5. Brownout

    Well-Known Member

    Jan 10, 2012
    2,375
    998
    In days of yore, one could produce "reverberation" effects with a device called a "Bucket Brigade." It's essentially an anlalog shift register. With feedback taps, it can produce multiple, diminishing copies of the original signal to add to the original for the kind of effect you want. I've never seen it used on video before, but I see no reason why it wouldn't work. One show-stopper might be low clock frequency of ~1.5Mhz, however. A possible work-around might be 3 strings in parallel and a 3-phase clock for 4.5Mhz operation.
     
    Last edited: Sep 15, 2015
  6. AnalogKid

    Distinguished Member

    Aug 1, 2013
    4,542
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    BBD's were barely acceptable to the golden-eared audio crowd, and never fast enough for video (NTSC needed at least 10.8 MHz). Similar to acoustic delay lines made with springs, Anderson and others made glass "ultrasonic" video delay lines. A 1-line delay (approx 63 us) was about 4" long. Ultrasonic in this case was a 20 MHz carrier. When computer memory expanded beyond 1024 bits per chip (!) and TRW popped out its 8-bit video-speed A/D and D/A, analog delay tech faded rapidly. One six-foot equipment rack was the perfect size to hold one frame of video.

    ak
     
  7. Brownout

    Well-Known Member

    Jan 10, 2012
    2,375
    998
    I offered a work around to the "never fast enough" issue. Required frequency actually depends on several factors, like image size, refresh rate, etc.
    I assume the OP knows about computer memory size and has a reason he doens't what to do this in software. I never claimed it is a perfect solution, but one that might be worth a look.
     
    Last edited: Sep 15, 2015
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