VGA Video from a Sega Dreamcast

I have a bipolar relationship with video games. Growing up, I was not allowed to touch them (only watch my friend play Zelda on the original NES, with its shiny gold cartridge), and once I got to college and had some money saved up I didn't go buy the PS2, which was new at the time, but the old classics like the Neo Geo. In much the same way that old cars are much more appealing from a tinkerer's perspective, I could actually understand how a Nintendo, Genesis, and Playstation worked and that itself made the system more interesting, regardless of how much I actually cared about the games. As my knowledge of computers and architecture grew, so correspondingly did my interest in more advanced machines. So far, I'm up to about the PS2/Gamecube, which isn't to say I fully understand everything by a long shot, but at least I can wrap my head around the basic principles. I particularly appreciate Sony's machines, even if I think they're architecturally inferior, since they publish their latest silicon in respectable journals and conferences. For example, here is the PS1 CPU, and the PS2 CPU, and the PS3 CPU.

The Sega Dreamcast was a half generation behind the PS2, and in my mind is a marvelous piece of engineering. Designed in the later 1990's, it was exceptionally powerful and forward-thinking, especially considering that it was developed before industry standard consumer graphics platforms were mature. Although it looks unmistakeably dated, it was probably the last machine that featured graphics better than PCs. One of its forward thinking features is its ability to natively render the framebuffer at 640x480, 60Hz which is full VGA resolution, about equivalent to 480p but in 4:3 format. To get a hold of this video stream usually meant purchasing a breakout box from Sega, but ingenious hackers discovered the pinout of the A/V port, allowing direct connection of the video.

It's not entirely clear to me the purpose of the diodes on the sync lines-I can only guess that they give some ESD protection. It was discovered that the 74HCT244s, which are just octal buffers, are not strictly necessary with most displays, and you can drive the H and V sync directly through to the display with 4.7k pullup resistors.

So, the first job is to find a spot on the back of the Dreamcast enclosure to fit the mod, which consists of an HD15 female connector, two RCAs for stereo audio, and a toggle switch.

A few minutes with a drill and a dremel makes short work of the soft ABS plastic.

Although not strictly the most professional technique, I like to make simple circuits inline with heatshrink and wire. Because the Dreamcast is pretty dense internally, I soldered the necessary wires to the copper side of the PCB, and routed them through the ventilation holes in the front of the RF shield by the controller sub-module. Here are the series blocking caps, which are 220u electrolytics in parallel with 2.2u metal films, and below that are the sync resistors.

Even though it's a bit clumsy to route the wires all the way from the back to the front and back again, there's no real signal loss/matching issues since these are VGA bandwidth (and they'll most likely drive a VGA cable which is 10x longer than these wires). All together and ready to go:

And finally, from the back, all closed up.

As I mentioned, I take no credit for the technical discovery of this trick, I just was bored one weekend and searched for information, then hacked my own machine.