Re: analog video signals

On May 26, 4:40 pm, "Bob Myers" <nospample...@xxxxxxxxxxxxxxx> wrote:
<b...@xxxxxxxxxxxxxx> wrote in message

news:1180199179.608594.63050@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

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
called.

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
levels.



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

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.

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
microcontroller.

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



.

Relevant Pages

  • Re: Power Supply
    ... If his current video board has only analog VGA output, and if his new monitor has a DVI input, he would be well advised to upgrade his video to a card that has DVI output for his stated objective, e.g. "I am interested mainly in ... A lot depends on the adjustment of the LCD monitor as well as the analog VGA cable connecting the monitor to the computer. ...
    (alt.sys.pc-clone.dell)
  • Re: Old monitor, new video card. Compatible?
    ... My card has 2 connections, one analog, one DVI. ... > I finally hook it up to the LCD monitor. ... analog output of the video card. ...
    (alt.comp.hardware.pc-homebuilt)
  • Re: Old monitor, new video card. Compatible?
    ... My card has 2 connections, one analog, one DVI. ... >> I finally hook it up to the LCD monitor. ... > analog output of the video card. ...
    (alt.comp.hardware.pc-homebuilt)
  • Re: Digital vs. analog Flat panel displays
    ... Analog displays require that the original digital signal from the ... video card processor be converted to an analog signal (still in the video ... This analog siganl then travels over the VGA cable to the monitor ... unit in the video card is sent straight out over the digital video cable to ...
    (alt.comp.periphs.mainboard.asus)
  • Separating Composite video signal???
    ... I have a small monitor that has separate video signals, video, horz/vert ... I have read about a IC chip that will separate the sync signals, ...
    (sci.electronics.repair)