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A Signal Generator based on VGA Output

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BadElvis

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Hey, this is my first post! I wanted to buy a signal generator, but they are so expensive that I decided to build one myself. I thought I would be nice to use a graphics adapter's vga output, because it is rather fast and the D/A conversion is done by the graphics card. I only need to amplify the signal.

The problem is, when the cathode ray travels back to start a new row or frame, the output on red/green/blue channel is 0. I have to bridge this time interval. My question is, how can I do this?

Maybe it is possible to delay one of the channels in order to use the delayed signal when another signal is blanking? The switching circuitry could be controlled by the v- and h-sync signals that are also provided by vga. Maybe there is also another possibility to work around the blanking. Thanks for your ideas!

BadElvis
 

chuckey

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It depends on what you want to use the signal generator for. If you are using it to find the response of filters, you could use a synchronised detection system, so you only measure your wave form during the active line periods. If you are hoping for a continous sine wave output, there really is no hope. The vertical and horizontal blanking is applicable to all the colour channels and the delays required for the vertical blanking are huge and must have a linear phase/frequency plot right across you wanted frequency band. You could if you just want a high frequency sinewave just ignore the blanking and think that the energy content is some what lower then if it was a continous sinewave.
Frank
 

BadElvis

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Hey Frank!

Thanks for your response. I already feared that it is very difficult. The beauty would be of course, that the graphics adapter does the digital part and that you could generating an arbitrarily long signal on your screen by playing a movie for example. If it were not for the blanking.

I might drop the idea of using the VGA and think about following one of the various building instructions online.
 

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