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analog video signals

Discussion in 'Electronic Basics' started by [email protected], May 26, 2007.

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  1. Guest

    I was just wondering if anyone knows what the analog video signals
    going from the computer to the monitor look like or what they are

    Also, is there a microcontroller that could generate such signals?
  2. Eeyore

    Eeyore Guest

    Component video.

    Microcontollers are too slow for such a task. Display controllers are a specfic
    kind of faily dumb (as a rule) processor of sorts.

    As ever........ What is it you actually want to do ?????

  3. BobG

    BobG Guest

    There are a couple of projects on avrfreaks that use an AVR
    microcontroller and 2 outputs as a 2 bit dac to generate NTSC timing
    and video... puts 120 pix x 90 pix in B&W on a TV. If you told me you
    were trying to do that, I'd have bet against you ever getting it to
    work. I suppose I have to believe it... there was a picture of the
    screen... maybe it was all bogus?
  4. Look on for "The Cheap Video Cookbook" by Donald E. Lancaster.
    There's a second book in the series also, "Son of Cheap video".

    These may tell you more.
  5. Bob Myers

    Bob Myers Guest

    There are a lot of things that could qualify as "analog video,"
    but the sort which most commonly are found going from a PC
    to its monitor (the "VGA" interface) are three separate signals
    (one each for red, green, and blue) which have an amplitude of
    0.7V p-p, and in which the most positive excursion of the signal,
    with respect to the blanking level, is considered "white". (Note
    that you will often see the "white" level for each channel as 0.7V
    positive with respect to the video return pins, but technically
    VGA is an AC-coupled system and the white level is supposed to
    be referenced to the blanking level, not "ground.") Oh, and this
    assumes a 75 ohm termination impedance.

    The vertical and horizontal sync signals are seperate, each on its
    own physical line, and are positive-true pulses at standard TTL
    A microcontroller by itself would likely not be fast enough to
    generate anything but the crudest video; for even the lowest
    standard format (640 x 480 at 60 Hz), you need a pixel rate
    of a bit over 25 MHz. Simple pattern generation (color bars,
    etc.) can often be done with just a microcontroller, though.
    Actually, I put together just such a generator a number of years
    back, for the purpose of EMI testing of monitors. What is
    it you're trying to do, exactly?

    Bob M.
  6. Marra

    Marra Guest

    What rubbish I have designed microcontrollers into numerous video

    I have used PIC micros to do it.
    So long as you keep the timing tight it works fine.

  7. Really? My monitor is 2048 * 1536 resolution. Lets see you drive
    THAT with a PIC. BTW, I want true color, not that 16 bit crap.

    Service to my country? Been there, Done that, and I've got my DD214 to
    prove it.
    Member of DAV #85.

    Michael A. Terrell
    Central Florida
  8. Guest

    Right now, I just want to understand how it works a little better - I
    don't have a specific project.

    BTW, if you spread out the horizontal retrace pulses, will this
    actually slow down the speed at which lines get updated? And,
    similarly, if you spread out the vertical syncs, will this slow down
    the speed at which it moves down a line? If so, I was thinking maybe
    you could send analog video to an LCD monitor with really spread
    out horizontal and vertical sync signals using a cheap

    For instance, instead of doing 1 frame in 1/60 of a second, you might
    take a minute to draw the frame.
  9. Eeyore

    Eeyore Guest

    How fast is your bit clock ?

  10. Eeyore

    Eeyore Guest

    What "horizontal retrace pulses" ?

    Do you make this stuff up as you go along ?

    You have not been doing any thinking at all have you ?

    What you should do is some *LEARNING* and stop wasting other ppls' time.

  11. Jasen

    Jasen Guest

    colloquially "VGA"
    technically it's "RGB" with separete sync signals
    RGB is a class of component video
    I expect so, getting more than a blank screen or horizontal bars
    could be a challenge on the lesser micros, although even there it
    may be possible to do some trickery with a fast synchronous serial
    port and emit a monochrome image....

  12. Jasen

    Jasen Guest

    [vga timing]
    LCD is more forgiving than cathode ray, if it has a video input that
    runs at the normal TV scan rates it can probably handle those rates on
    the VGA input too.
    probably not. I doubt that the electronics inside the monitor is designed
    to go that slow.

    Another option may be to interface your microcontroller with an old ISA bus
    VGA card... you won't need all 118 lines, just 17 address lines (16 if you
    don't need colour text mode) 8 data, and maybe 8 others.
    the card may need the -12V supply for the output to work. (I had one
    like that in a PC)

  13. That's it Donkey. Attack, rather than explain.

    The proper term is "Horizontal Sync", and it can only be varied
    within the limits of the monitor you use. I have never seen a monitor
    that could take one minute for a single horizontal scan. It has to be
    real time, because the monitor needs all of the signals synchronized to
    create the image you want.

    Service to my country? Been there, Done that, and I've got my DD214 to
    prove it.
    Member of DAV #85.

    Michael A. Terrell
    Central Florida
  14. Marra

    Marra Guest

    I never said it was for PC video.

    One project was to use a PIC to drive an on screen display for a CCTV
    The PIC cut into the picture to display time and camera information.

    Clearly for PC type resolution you need to go for a proper video card.
    Or use a PIC with some dedicated video hardware.
  15. Eeyore

    Eeyore Guest

    I wasn't assuming it was specifically but you'll have a bit clock when you make
    such a signal with a uP or whatever.

    A big issue is syncing the two video streams.

  16. Kit

    Kit Guest

    I hear that the Propeller from Parallax can create VGA signals, with
    ok quality.
  17. Bob Myers

    Bob Myers Guest

    You can certainly generate slow video - i.e., longer line and
    frame times, which is what I think you're getting at in the above -
    but the LCD monitor very likely will not accept it. The LCD panel
    itself has a fairly limited range of timings over which it will operate,
    and generally the scaler/controller IC typically found in the front
    end also will accept only a certain range of timings. Most often,
    the bottom end of that range isn't too far removed from the
    60 Hz VGA standard (640 x 480 pixels, 25.175 MHz pixel
    rate, and about 31.5 kHz horizontal (line) rate).

    Bob M.
  18. Rich Grise

    Rich Grise Guest

    These will depend on how you set the parameters for your sync generator,
    and you'd have to modify the horizontal and vertical scan oscillators
    and probably deflection amps to make them scan slower.

    This is called "slow-scan TV" - it's a way to put a TV pic on an audio
    bandwidth. But you need a very long persistence phosphor.

    Have Fun!
  19. Bob Myers

    Bob Myers Guest

    Phosphor? What's that? :)

    Actually, these days (with memory and other digital
    bits so cheap), it's a lot more common simply to decode
    the SSTV and shove it into a frame buffer, then display
    it on a standard monitor, running at a more normal rate.

    Bob M.
  20. Rich Grise

    Rich Grise Guest

    Oh, well, that's different!

    Never Mind!

    Emily Litella ;-)
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