[Coco] RGB --> VGA for CoCo: A success story

[Steven Hirsch]

On Sat, 15 Nov 2008, J.P. Samson wrote:

>>> On Nov 15, 2008, at 11:24 AM, Steven Hirsch wrote:
>>>> This morning I finally got motivated and built an adapter to run RGB 
>>>> video from my CoCo 3 into the Wei-Ya ACV-011 RGB-->VGA converter.  I'm 
>>>> pleased to report that it works quite well!
>>> 
>>> Any plans to do a write-up on how you put this together, Steven?  How's 
>>> the quality?  Have you ever used Roy's converter to be able to compare 
>>> results?
>> 
>> There's not a whole lot to write up...  It's just a matter of building a 
>> cable with a 10-pin ribbon cable header on one end.  If you are not sharing 
>> the converter with other classic machines, you just splice the other end to 
>> the header supplied with the converter board.  The signals are just 1:1, 
>> connect Gnd, R, G, B, H-sync and V-sync and you're good to go.  The pinout 
>> for the bottom of the CoCo 3 is widely available.
>
> Nice and easy, that's for sure.  I'd guess that Roy's converter does a better 
> job, since it is specifically designed for the CoCo 3 and includes a filter 
> to absorb some of the vertical banding that is an artifact of the computer's 
> RGB output.  Roy's adapter has difficulty clearly resolving some color 
> combinations, though, making such text hard to read.

A quick followup on the subject:  I built an RLC low-pass filter based on 
Roy's design (thanks for the schematic, Roy!) and gave it a try.  Results 
in my situation were not very good.  It did not eliminate visible banding 
(which was very slight to begin with), but did throw away enough in-band 
video signal to blur the text display noticably.

Disclaimer:

This is not to be taken as a comment on the performance Roy's converter 
box (which I have never used)!  The input impedance of the Wei-Ya RGB 
board may vary from his design and that can have a sizable effect on the 
filter characteristics.  I know that many folks are happy with Roy's 
converter and I'll take it on faith that it does a fine job.

I just picked up another SCART cable, so the next thing to try will be 
running the CoCo into my Highway 100 converter.

Steve



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