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HD15 - Reading video signal from VGA Port

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PeterDove

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Hi All,

I have a project in which I need to read the video signal coming from the back of the laptop ( VGA port ) and convert it into a large LED array. Can anyone tell me where I can get some information on decoding the information coming from the port and what the various pins are for?

Thanks

Peter
 
It's analogue RGB with seperate horizontal and vertical sync - the speeds of which depend on the mode in use (but always much faster than normal TV).

This isn't at all a trivial job!!!!.
 
To be honest this is a very straight forward Google. Essentially you've got ground, Red, Green and Blue signals and then horizontal sync and vertical sync. VGA is an analogue signal.

You need to learn about the video signal

https://www.epanorama.net/documents/pc/vga_timing.html

You might want to try and build it as a frame buffer type solution as this link illustrates for VGA to TV conversion.

**broken link removed**

David.
 
You need some pretty zippy ADC's to digitize VGA ouput, especially at any decent resolution. Between the speed and memory required I don't see you doing this on anything but an FPGA board, micro controllers aren't going to be able to handle it. If you're having trouble finding the specs for a VGA cable then this project might be a tad bit over your head.
 
Why the need to digitise it though? I was thinking about this earlier and given that it's an analogue signal and you have sync timebases, if you knew the frequency of the sync components (which are part of the spec), then it should be reasonably trivial(!) :)

For a single scan line, say you have 1024 x 800 LED's the first row would be illuminated in sequence based upon the delta from the sync component.

Then again, I suspect that the POV might not be sufficient for this and that the array would need refreshing during the display of a frame hence the frame store/display would be the more reliable way. Any sync issues with my earlier thoughts would make the timing critical. :)

Rip apart an LCD projector or TFT and wire that up to LED's ;)

David.
 
djtaylor1 said:
Why the need to digitise it though? I was thinking about this earlier and given that it's an analogue signal and you have sync timebases, if you knew the frequency of the sync components (which are part of the spec), then it should be reasonably trivial(!) :)

For a single scan line, say you have 1024 x 800 LED's the first row would be illuminated in sequence based upon the delta from the sync component.

Then again, I suspect that the POV might not be sufficient for this and that the array would need refreshing during the display of a frame hence the frame store/display would be the more reliable way. Any sync issues with my earlier thoughts would make the timing critical. :)

Rip apart an LCD projector or TFT and wire that up to LED's ;)

David.

Thanks for the ideas! I probably need to keep reading for a while to get it to make sense to me - my first challenge is simple to be able to read the signal!
 
How about you state your complete project requirements so we know how complex the system will end up being.

Things to know are the input VGA resolution and frame rate, the output resolution and frame rate, color depth, equipment available, etc., etc.
 
To be honest, this would make a good final project for a degree student, it's more difficult than you might think - the simple approach by djtaylor1 wouldn't work.
 
Do your sanity a favor, start with 320X200 at a 60hz refresh rate, and use an analog pre-processor to add the RGB signals into a single grayscale channel.
Just creating a 320X200 LED array is a massive undertakeing, the digitizing issues aside.
 
Sceadwian said:
Do your sanity a favor, start with 320X200 at a 60hz refresh rate, and use an analog pre-processor to add the RGB signals into a single grayscale channel.
Just creating a 320X200 LED array is a massive undertakeing, the digitizing issues aside.

This is what I was thinking. The only thing I am having trouble with is understanding getting the signal out of the port and interpreting it. I have decided to drop this for now and focus on a simpler PIC to RS232 com port using the Max232 chip. I still need to do the VGA project at some point but its not life and death - will try to more research.

If anyone has any time on their hands to do the basic code etc then I would be willing to donate some money to them :) Not a lot but I can do $100 or so. I am pretty good at being able to take example code and flying with that. I program for a living, C++, Delphi, Java, Assembler(some), VB etc - so its not all new stuff.

Peter
 
To make your VGA converter, you will need to use a CPLD or FPGA which will require you to learn a Hardware Description Langage such as VHDL or Verilog. They are not too difficult to learn, but neither of them are anything like coding a program in the traditional sense. There are plenty of tutorials for both languages floating around the internet. I suggest you run through a few of them before you start your VGA design.
 
phalanx said:
To make your VGA converter, you will need to use a CPLD or FPGA which will require you to learn a Hardware Description Langage such as VHDL or Verilog. They are not too difficult to learn, but neither of them are anything like coding a program in the traditional sense. There are plenty of tutorials for both languages floating around the internet. I suggest you run through a few of them before you start your VGA design.

Thanks for the tip - just recently came across a couple of VGA examples for FPGA!

Peter
 
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