VGA signal 'splitter' ?

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Trepan
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VGA signal 'splitter' ?

Post by Trepan » Tue Nov 04, 2008 5:38 am

I know these exist for sale but I am looking at building something that would require a more custom solution.

Basically, a normal VGA signal is passed out of the system at a high resolution rate.

I'm going to have several monitors that have lower resolution, and I want to make a multi-monitor setup.

What I need here is a way to read the incoming VGA signal and chop it into a bunch of smaller 'squares' of resolution.. eg comes out of the device at 1600 x 960 and I want to split it into 4 separate outputs of 800*480 each for a different part of the original 1600x960.

I don't know a lot about video hardware so I'm not sure how to go about doing this. Obviously there is a way, but I'd really like to know how it works/how to build something similar.

For the sake of argument we can pretend that the original signal is coming from the output of a laptop VGA jack and will be used to control multiple screens, 6 - 10 of them.

Thanks guys

Bigglez
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Re: VGA signal 'splitter' ?

Post by Bigglez » Tue Nov 04, 2008 7:27 am

Trepan wrote:Basically, a normal VGA signal is passed out of the system at a high resolution rate.

I'm going to have several monitors that have lower resolution, and I want to make a multi-monitor setup.

What I need here is a way to read the incoming VGA signal and chop it into a bunch of smaller 'squares' of resolution.. eg comes out of the device at 1600 x 960 and I want to split it into 4 separate outputs of 800*480 each for a different part of the original 1600x960.
Multi-screen displays (video wall) have been around
for many years. The better ones use special monitors
to reduce the 'picture frame' effect where the screens
touch. Large single plasma displays or LCD/DLP
projectors are superior.

What monitors are you using for the screens? Are they
all the same brand and model?

The input signal is stored in a digital memory
that has dual-ports (so that data can be read
as other data is written). The input writes to the
full memory array, but separate sections are
read concurrently for each dedicated display monitor.

For analog monitors the digital data is convertered
to analog and sync is either added to one channel
or as a fourth line plus R-G-B. Composite video
is typically not used to save cost and complexity.
R-G-B gives better performance and the
option to go to higher scan or refresh rates.

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MrAl
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Re: VGA signal 'splitter' ?

Post by MrAl » Tue Nov 04, 2008 8:12 am

Trepan wrote:
Basically, a normal VGA signal is passed out of the system at a high resolution rate.

Hi,

You know you might be dealing with a 125MHz clock right?
LEDs vs Bulbs, LEDs are winning.

Bigglez
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Re: VGA signal 'splitter' ?

Post by Bigglez » Tue Nov 04, 2008 8:19 am

MrAl wrote:
Trepan wrote: Basically, a normal VGA signal is passed out of the system at a high resolution rate.
You know you might be dealing with a 125MHz clock right?
Actually, a VGA standard PIXEL clock is closer to
25MHz (50MHz worse case for VGA 800x600 72Hz).
More info here.

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MrAl
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Re: VGA signal 'splitter' ?

Post by MrAl » Tue Nov 04, 2008 8:29 am

Bigglez wrote:
MrAl wrote:
Trepan wrote: Basically, a normal VGA signal is passed out of the system at a high resolution rate.
You know you might be dealing with a 125MHz clock right?
Actually, a VGA standard PIXEL clock is closer to
25MHz (50MHz worse case for VGA 800x600 72Hz).
More info here.
Hi,

Yeah, but he's talking about 1600x960 right? The higher the resolution
the higher the clock right? The card has to pump more information out
in the same amount of time.
25MHz is for a 600x480 screen.
I could be wrong because i havent looked at this stuff in quite a long
time now, but 1600 x 960 x 60 = 92.16MHz, and this doesnt include
any sync time yet.
LEDs vs Bulbs, LEDs are winning.

Bigglez
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Re: VGA signal 'splitter' ?

Post by Bigglez » Tue Nov 04, 2008 8:41 am

MrAl wrote: Yeah, but he's talking about 1600x960 right?
Perhaps. The OP might be taking on more than
a weekender project here. Once the system is
working at VGA rates it can be scaled to SVGA,
PIXEL clock speed is the least of the concern.

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MrAl
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Re: VGA signal 'splitter' ?

Post by MrAl » Tue Nov 04, 2008 10:19 am

Bigglez wrote:
MrAl wrote: Yeah, but he's talking about 1600x960 right?
Perhaps. The OP might be taking on more than
a weekender project here. Once the system is
working at VGA rates it can be scaled to SVGA,
PIXEL clock speed is the least of the concern.
Hi again,

I think i have to disagree again here because the pixel clock
seems like a major defining characteristic of the system because
it defines the bandwidth of the parts required to handle the
signals.
For example, if the pixel clock was only 1MHz i think this would
be easy to design because lots of parts work at that frequency
and usually dont require special proximity attention, whereas
signals i've estimated to be upwards of 150MHz (for 1600x960)
definitely do require special parts and techniques, and again
due to dimensional consideration probably can only be done
effectively with surface mount parts. This is why before i
got into a lengthly discussion of approaches to this project
i thought i would mention one of the key points, and that is
fairly high frequency signal processing and of course the
reader can deduce some of the consequences of this alone
before proceeding with the task.

BTW, i dont usually ask questions or make points just for
the heck of hearing myself type :smile:
LEDs vs Bulbs, LEDs are winning.

Bigglez
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Re: VGA signal 'splitter' ?

Post by Bigglez » Tue Nov 04, 2008 10:42 am

MrAl wrote: I think i have to disagree again here because the pixel clock
seems like a major defining characteristic of the system because
it defines the bandwidth of the parts required to handle the
signals.
Do you have a schematic or block diagram? I'm
not following your concern about "bandwidth".
MrAl wrote:BTW, i dont usually ask questions or make points just for
the heck of hearing myself type
I usually don't post unless I have input or a question.

psycho
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Post by psycho » Tue Nov 04, 2008 7:00 pm

I haven't done it, but I would be willing to bet that an FPGA could easily handle this. There may already be something out there to base it on.

Just my .02

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MrAl
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Re: VGA signal 'splitter' ?

Post by MrAl » Wed Nov 05, 2008 5:55 am

Bigglez wrote:
MrAl wrote: I think i have to disagree again here because the pixel clock
seems like a major defining characteristic of the system because
it defines the bandwidth of the parts required to handle the
signals.
Do you have a schematic or block diagram? I'm
not following your concern about "bandwidth".
Sorry but i almost cant believe you dont understand what bandwidth means
in this context. It's hard for me to believe that you've never considered
the 'bandwidth' of an electronic part before. What could there be
that is too hard to understand about that?
Or could it be that you dont see the difference between using 2MHz
electronic parts and 200MHz electronic parts, in which case i would
simply ask why not.
psycho wrote:I haven't done it, but I would be willing to bet that an FPGA could easily handle this. There may already be something out there to base it on.
Just my .02
Just an FPGA, and no other high speed parts?
LEDs vs Bulbs, LEDs are winning.

Trepan
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Re: VGA signal 'splitter' ?

Post by Trepan » Thu Nov 13, 2008 5:23 am

Bigglez wrote:
Trepan wrote:Basically, a normal VGA signal is passed out of the system at a high resolution rate.

I'm going to have several monitors that have lower resolution, and I want to make a multi-monitor setup.

What I need here is a way to read the incoming VGA signal and chop it into a bunch of smaller 'squares' of resolution.. eg comes out of the device at 1600 x 960 and I want to split it into 4 separate outputs of 800*480 each for a different part of the original 1600x960.
Multi-screen displays (video wall) have been around
for many years. The better ones use special monitors
to reduce the 'picture frame' effect where the screens
touch. Large single plasma displays or LCD/DLP
projectors are superior.

What monitors are you using for the screens? Are they
all the same brand and model?

The input signal is stored in a digital memory
that has dual-ports (so that data can be read
as other data is written). The input writes to the
full memory array, but separate sections are
read concurrently for each dedicated display monitor.

For analog monitors the digital data is convertered
to analog and sync is either added to one channel
or as a fourth line plus R-G-B. Composite video
is typically not used to save cost and complexity.
R-G-B gives better performance and the
option to go to higher scan or refresh rates.
Thanks to everyone for all of the replies. I'd like to clear some things up and hopefully answer some questions to help clarify.

I was thinking of multiple TFT LCD screens, this is for an industrial application. The screens aren't necessarily going to be 'attached' physically but they will all be the same brand etc. Some of them may be attached, some may not. They don't have frames so that's not an issue as I'd be getting some OEM screens with no frame. They will be digital monitors and I haven't decided if they would end up being touchable or not but that's another matter entirely.

This is definitely not a weekend project and is a long term project I'm working on developing. I'm just trying to flush out the details. I'm nowhere close to building it yet, it's an idea I have kicking around at this point. I have lots of time to learn about SVGA etc where necessary, I just really don't know where to start.

Some of the comments have been quite informational. It's something I'm building for myself, not to make a profit from that's for sure. I imagine something like this does exist already but I'd like to take a stab and building it myself.

I'm trying to picture a block diagram of what has been discussed here. I'm going to try to step through each step of the operation below:


1) A digital SVGA signal coming from a given output at a high rate of resolution.
2) This image is 'read' at the speed it comes in at (which will need to be determined and synced to)
3) The signal is sliced up 6 ways (for example), a little window of lower resolution each which is a different window of the large screen input. This signal could end up being either VGA or SVGA each.
4) each individual signal is passed on to their respective monitors and displayed.

I understand #2 but not sure how to go about it. For #3, I'm not sure how to go about doing such a thing. I guess for #3 that all of the outputs can be sent at the same time and speed. Perhaps I don't need anything overly complicated to do the 'splitting', that part I'm not sure of. Surely something digital that could read the resolution down to the pixel level and then pipe the output to one of X (6-8 or what have you) number of outputs depending on their position on the 'big screen'.

I know exactly what I want to do but maybe I'm having trouble explaining it properly. Essentially I want to build the part that would accept the 'whole' SVGA signal and output the multiple smaller screen sizes, each to a separate SVGA/VGA output.

This to me is where it's a bit of a black box and where I need the assistance. I'm not even sure to begin. I imagine my problem is I'm not sure what the parts would even be called that would do these types of operations, so I don't know what ICs/data sheets to look at and where to start to develop it.

Thanks in advance!

Bigglez
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Re: VGA signal 'splitter' ?

Post by Bigglez » Thu Nov 13, 2008 1:39 pm

Trepan wrote: I was thinking of multiple TFT LCD screens
....
They will be digital monitors
So the satellite monitors have DVI connectors?
Trepan wrote: I'm trying to picture a block diagram of what has been discussed here.
....
1) A digital SVGA signal coming from a given output at a high rate of resolution.
2) This image is 'read' at the speed it comes in at (which will need to be determined and synced to)
3) The signal is sliced up 6 ways (for example), a little window of lower resolution each which is a different window of the large screen input. This signal could end up being either VGA or SVGA each.
4) each individual signal is passed on to their respective monitors and displayed.
The input has greater data rates than any of the
outputs so you must use a memory to allow
conversion from one to the other. The memory
has to be large enough to hold one frame of the
input (high resolution) data.

The satellite outputs will only use a portion of the
data from the input, because they are at a lower
resolution, slower data speed, and looking at different
portions of the original data.

This requires a dual port memory, or a ping-pong
memory with two pages. While one is written with
the newly arriving data the other page is being read
(selectively) by each of the satellites.
The memory pages are swapped at each new
input frame, so the last data can be processed
while the newly arriving data is stored.

The memory is parallel but the data arriving and leaving
is serial, so conversion is necessary.

All of the satellites can be sync'd but these are probably
async to the input data. By using flat panel monitors
the likelyhood of coupling or interference from one to
another is greatly reduced.

By using digital (not analog) signal on inputs and outputs
will simplify your design, in that you will not need to do
any conversion from analog to digital, or the other way.

The address of each satellite monitor is probably something
you would make user definable, and you will need a
supervisor system to mange this task.

A good way to impliment your idea is to use a PC
chassis and install a separate VGA graphics board
for each satellite (some graphics cards already allow
two separate monitors to be connected). The PC
chassic has all the power supplies and hardware
for the project, which is now a (massive) software
task.

fripster
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Post by fripster » Tue Nov 18, 2008 4:54 am

....or you buy the whole thing at BlackBox: The "multivision' system: type KVP2200-M

I would not even think of trying such a hack myself.... but who am i?

fripster ;-)
Once a WireHead, Always a WireHead

Bigglez
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Post by Bigglez » Tue Nov 18, 2008 8:47 am

fripster wrote:....or you buy the whole thing at BlackBox: The "multivision' system: type KVP2200-M
The OP wrote:I know these exist for sale but I am looking at building something that would require a more custom solution.
The OP wrote:I don't know a lot about video hardware so I'm not sure how to go about doing this. Obviously there is a way, but I'd really like to know how it works/how to build something similar.
Part of the question was to understand how they work.
It helps to read the entire thread form the begining.

Trepan
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Re: VGA signal 'splitter' ?

Post by Trepan » Wed Dec 03, 2008 7:03 am

Bigglez wrote:
Trepan wrote: I was thinking of multiple TFT LCD screens
....
They will be digital monitors
So the satellite monitors have DVI connectors?
Trepan wrote: I'm trying to picture a block diagram of what has been discussed here.
....
1) A digital SVGA signal coming from a given output at a high rate of resolution.
2) This image is 'read' at the speed it comes in at (which will need to be determined and synced to)
3) The signal is sliced up 6 ways (for example), a little window of lower resolution each which is a different window of the large screen input. This signal could end up being either VGA or SVGA each.
4) each individual signal is passed on to their respective monitors and displayed.
The input has greater data rates than any of the
outputs so you must use a memory to allow
conversion from one to the other. The memory
has to be large enough to hold one frame of the
input (high resolution) data.

The satellite outputs will only use a portion of the
data from the input, because they are at a lower
resolution, slower data speed, and looking at different
portions of the original data.

This requires a dual port memory, or a ping-pong
memory with two pages. While one is written with
the newly arriving data the other page is being read
(selectively) by each of the satellites.
The memory pages are swapped at each new
input frame, so the last data can be processed
while the newly arriving data is stored.

The memory is parallel but the data arriving and leaving
is serial, so conversion is necessary.

All of the satellites can be sync'd but these are probably
async to the input data. By using flat panel monitors
the likelyhood of coupling or interference from one to
another is greatly reduced.

By using digital (not analog) signal on inputs and outputs
will simplify your design, in that you will not need to do
any conversion from analog to digital, or the other way.

The address of each satellite monitor is probably something
you would make user definable, and you will need a
supervisor system to mange this task.

A good way to impliment your idea is to use a PC
chassis and install a separate VGA graphics board
for each satellite (some graphics cards already allow
two separate monitors to be connected). The PC
chassic has all the power supplies and hardware
for the project, which is now a (massive) software
task.
This is perfect. I only really have one other question. How do I send only the portion of the screen I want to each satellite screen? I imagine I need to somehow define a window inside of the 'bigger picture' in terms of pixels and then only that portion would get sent on port 1 to screen 1 for example. another portion gets sent only on port 2 the same way I guess?

Just wondering what would actually do the dividing up of the big picture.

Thanks!

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