Schematics Question on DC External VGA

I am in the planning stages of building my own VGA adapter, because I can't justify spending $60 on a video hookup for a system I paid $10 for at the Good Will. Also I love learning new things. It will be my first electronics project, so the internal mod is out of the question for now.

I have seen two schematics, this one:


and the more often referred to GameSX version: http://www.gamesx.com/grafx/dricas.gif

From my limited understanding of electronics, the only difference seems to be that GameSX utilizes this 74HCT244 buffer/line driver.

I am wondering if the added buffer/line driver is necessary or optional. Is it only needed in order to beef up the signal for a longer cable? Will the simplified version work for a short cable?

 

The buffer is a good idea from an EE standpoint but I've built this circuit without the logic chip and it worked just fine.

 

Thanks! Sounds good. Perhaps this time next week I will be playing through VGA.

Right now I have it going through a composite to RF modulator on a 42" LCD... Just because it's not as bad as the composite to HDMI converter I have. The RF signal is grainy as hell, but at least it's not too blurred or stretched.

 

I have added a VGA port to my dreamcast with no components at all, works perfectly, it was mentioned in another thread here and tried it, works great.

 

Keep us posted on this! I also share ur frustration w overpriced VGA adapters on eBay, etc. I'd also prefer making an external adapter instead of hacking around inside my unit. I'm curious where you'll find a suitable connector for the DC side.

 

It's optional - lots of people have made VGA boxes without them, and based on looking at the signals with a scope on both the original Sega box and one without the buffer there doesn't seem to be any significant difference in signal amplitude. I suspect that the primary reason for that chip was not as a buffer, but to disable the sync signals to the VGA display when the VGA box was turned off (that's what the connection between the switch and pin 19 of the buffer chip does).

This might seem like a paranoid precaution now, when 99% of monitors are microprocessor controlled and will just refuse to display signals they don't like - but back in 1998 there were still quite a few fixed-frequency VGA monitors around, and some of them could actually be physically damaged by being driven at the wrong line rate.

 

Just wondering if the OP had any luck getting this to work.. pls keep up posted, ty

 

If it helps, my first real mod on anything besides backlighting gameboys, was to do an internal DCVGA mod found right here on AG. To my surprise..... It turned out well. My skills are VERY lacking too. I'm a noob. http://www.assemblergames.com/forums/showthread.php?21585-Dreamcast-Internal-VGA-modification