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Frequency doubling

Discussion in 'Electronic Design' started by [email protected], Nov 30, 2007.

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  1. Guest

    Hi folks

    I'm looking for suggestions. I have a 15.625 KHz analog video signal
    which I need to double so it can be displayed on a VGA monitor.

    Anyone here know the best (or easiest) approach to achieve this?
  2. Phil Allison

    Phil Allison Guest

    ** Errrrr - buy a video standards converter box ??

    Too radical an idea ?

    ........ Phil
  3. Guest

    No, where's the fun in that? :)

    I was thinking of building one myself. Not quite sure what's the best
    approach, tho.. that's why I'm fishing for ideas here. My first
    thought was ADC->Some microcontroller fast enough to repeat signal
    twice->DAC (with 8-bit quality on the converters) but maybe that's a
    bit overkill for such a trivial task.

  4. Frank Buss

    Frank Buss Guest

    I think you need even more for this task. So you have an FBAS signal and
    you want to display it on a VGA monitor? Just doubling the frequency
    doesn't work, your idea reading it and repeating it twice per frame is
    good. But you have to convert it from FBAS to RGB, too. And
    microcontrollers fast enough for a 50MHz pixel clock may be expensive. You
    should consider using a FPGA.
  5. I have done it in FPGA.
    This has been discussed here some year(s?) ago.
    IF you have YCrBb you can read in a line and write it back at double speed.
    lowpass - ADC - blockram - DAC -lowpass,
    but you can sample CrCb half at half the frequency,
    as color is less detail (note sign, CrCb can be negative).
    If you have composite, a good PAL or NTSC decoder in FPGA is not trivial,
    use an analog one perhaps to get to YCrCb.

    Also somebody found some links with really cheap converters.
    Probably cheaper then one mcan make them oneself.
    Personally I would not bother, all will go digital soon, and old analog
    TVtronics will be gone.
  6. PeterD

    PeterD Guest


    1. Get a good PC
    2. Get a good video capture board.
    3. Install same in PC
    4. Run 15.625 (???) video into the capture board.
    5. Connect VGA monitor into the computer's video output
    7. Watch your TV!

    How simple do you want it? Or are you looking for a passive solution?

  7. A Frame buffer.

  8. First is the conversion clock, or "dot" clock which should be
    synchronous with the line rate. This means a PLL to lock to the Hz
    rate. You'll need ADC(s) of 10 bits minimum.
    Is your input composite? Then you'll need a composite-to-YUV decoder
    in the FPGA firmware. You might be able to find this on open cores,
    but I've implemented this from scratch, and like Jan said, it's not

    Not wanting to discourage the DIY approach, but in case you give up:

  9. Phil Allison

    Phil Allison Guest

    ** Hey asshole - YOU asked for the EASIEST approach !!!!

    Now, you reveal that you are a REALLY another publicly masturbating,
    PITA, fuckwit TROLL.

    Why didn't YOU just say so in the first place ??

    Makes it SOOOO much easier when you know what sort of human excrement
    you are talking to.

    ....... Phil
  10. You do not need to store a whole frame, one line is enough.
  11. Guest

    Just buy a converter box. Like Phil said, YOU asked for the easiest
    Or buy a LCD TV.
    Doing this yourself is not as trivial as it seems.
    You can look into the AL250 chips, I tried making a RGBI to VGA
    converter with one, and all I ended up with was a purple mess and a
    bad clock recovery system.
    This isn't so trivial as you think, it's a bit more involved than just
    doubling the sync signals.
    Converter boxes are available at any computer store and are pretty
  12. Guest


    ....aaaaand "ignore". There.

  13. Guest

    I know, I just expected something a bit more exciting from the than "buy a box."
    Ok, I see. Maybe we're on the same boat, as my signal is RGBI as
    well. Sorry I didn't have the chance to mention that earlier.

    Maybe you've been playing with the Amiga's RGB as well?

  14. Guest

    Electronics is heavily commoditized now, often you're better off
    speccing than designing.
    Nah, I was fooling around with the C128 RGBI. I don't remember if the
    Amiga gave you RGBI, I have a vague memory of a db-23 video connector
    with analog RGB on it. Maybe there was RGBI to use cheaper monitors?

    If you want I can tell you more about my AL250 project. It's dead now.
    Too boring, and too much work.
    How do you plan on getting the pixel clock? If you design an internal
    card for the 2000, you're golden.
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