saturday, 9 may 2009

posted at 08:16

Gub and Penny went out with a friend last night, so with the girls in bed I got a solid five hour block all to myself. At the end of the night I'd achieved something I'm quite proud of:

This is my ancient Amiga 500 hooked up to my nice tv via the RGB-to-HDMI converter I got for my birthday.

I built two cables. The first is the main one that I'll need for all the things I intend to do with this converter. It turns the somewhat unwieldy SCART input on the converter into a rather more convenient DE9 connector. I've done my own version of the Game Station X connector - I've left out the Luma and Chroma lines but added a ground line. So in short, this cable is carrying the red, green and blue video lines, left and right audio, ground and a +5V line - everything I need.

There's not much to it. The only tricky bit is that SCART has a line (BLNK on pin 16) that selects whether the input is composite or RGB. The line needs to be fed 1-3V to select RGB; leaving it unconnected gives composite. Connecting it to the +5V line via a 180-ohm resistor makes a nice voltage divider and provides the needed signal.

The second cable is one that takes the video off the Amiga and turns it into my custom format. I originally intended to modify the cable I built years ago to connect the Amiga to my 1084S monitor (which died long ago), but on opening it I found that the cable was a five-core cable and wasn't carrying the +5V line. A quick dig around in the garage revealed a short length of six-core phone cable, so I used this to build a new cable. I also had to cannibalise a 2xRCA-2xRCA cable to provide the audio (which doesn't come through the video port on the Amiga but instead via two RCA ports), so I now have this rather peculiar looking plug with two distinct cables coming out of it.

The most surprising thing about all this is that it worked first time. I dabble but I am most certainly not an electronics guy. There was a few tricky bits where I just took the option that seemed most obvious, but I really expected it not to work because I hadn't understood some obscure detail. I'm excited that I'm able to do this! I keep old game systems around because I like to play the games from time to time, but most people when hooking their old machines up to a new tv and seeing it looking crap would be powerless to do anything about it. I like that I know enough to be able to buy or build things that can make it work!

It does seem that my Amiga has suffered from its long storage. Half the time it doesn't start at all, and sometimes it crashes at boot:

But damn, that text is crisp!

Next is the Nintendo 64 mod to get the RGB lines out. I'm hoping to find some time for it this weekend.