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analog video signals

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.

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

Eeyore

Jan 1, 1970
0
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.

Component video.

http://en.wikipedia.org/wiki/Component_video

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

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 ?????


Graham
 
B

BobG

Jan 1, 1970
0
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?
 
H

Homer J Simpson

Jan 1, 1970
0
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.

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

Look on Amazon.com 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.
 
B

Bob Myers

Jan 1, 1970
0
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.
 
M

Marra

Jan 1, 1970
0
What rubbish I have designed microcontrollers into numerous video
projects.

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

Michael A. Terrell

Jan 1, 1970
0
Marra said:
What rubbish I have designed microcontrollers into numerous video
projects.

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


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
 
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.




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.
 
E

Eeyore

Jan 1, 1970
0
Marra said:
What rubbish I have designed microcontrollers into numerous video
projects.

I have used PIC micros to do it.

How fast is your bit clock ?

Graham
 
E

Eeyore

Jan 1, 1970
0
BTW, if you spread out the horizontal retrace pulses,

What "horizontal retrace pulses" ?

Do you make this stuff up as you go along ?

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

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

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

Graham
 
J

Jasen

Jan 1, 1970
0
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.

colloquially "VGA"
technically it's "RGB" with separete sync signals
RGB is a class of component video
Also, is there a microcontroller that could generate such signals?

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....

Bye.
Jasen
 
J

Jasen

Jan 1, 1970
0
[vga timing]
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?
maybe.

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.

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

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)
 
M

Michael A. Terrell

Jan 1, 1970
0
Eeyore said:
What "horizontal retrace pulses" ?

Do you make this stuff up as you go along ?


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
 
M

Marra

Jan 1, 1970
0
How fast is your bit clock ?

Graham

I never said it was for PC video.

One project was to use a PIC to drive an on screen display for a CCTV
system.
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.
 
E

Eeyore

Jan 1, 1970
0
Marra said:
I never said it was for PC video.

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.

One project was to use a PIC to drive an on screen display for a CCTV
system.
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.

A big issue is syncing the two video streams.

Graham
 
K

Kit

Jan 1, 1970
0
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.

Graham

I hear that the Propeller from Parallax can create VGA signals, with
ok quality.
-Kit
 
B

Bob Myers

Jan 1, 1970
0
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.

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.
 
R

Rich Grise

Jan 1, 1970
0
....

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?

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.

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.

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!
Rich
 
B

Bob Myers

Jan 1, 1970
0
Rich Grise said:
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.

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.
 
R

Rich Grise

Jan 1, 1970
0
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.

Oh, well, that's different!

Never Mind!

Emily Litella ;-)
 
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