[Coco] RGB-to-VGA converter

[Steven Hirsch]

On Mon, 31 Aug 2009, J.P. Samson wrote:

> On Aug-31-09, at 6:13 AM, Christian Lesage wrote:
>> Steven Hirsch wrote:
>>> 
>>> I rolled my own solution for displaying CoCo video on a modern LCD display 
>>> and I agree completely - a great improvement in the viewing experience.
>> 
>> Could you provide us with some details?
>
>
> For anyone who's interested, I've pulled up some of the relevant messages...

Thanks VERY much for pulling that up.  Couldn't locate the thread in my 
mail reader.

I did eventually try building a low-pass filter per Roy's specification in 
an attempt at cleaning up some slight vertical "banding", but it seemed to 
reduce the sharpness quite noticably without really doing much to mitigate 
the bands.  Perhaps I didn't get the component values quite right.  At any 
rate, the artifacts are not that bothersome to me so the solution has 
worked out quite well.

I've been on a concerted campaign to eliminate CRT monitors from my work 
area.  The Wei-Ya box handles my C128 in 80-column mode along with the 
CoCo.  I picked up a cheapie no-name composite-to-VGA converter for C64 
and 128 in 40-column mode, Atari 800 and TI-99a.

The Apples are a tougher problem.  The original Apple II and IIe generate 
a notoriously non-standard NTSC color signal.  Most converters produce 
miserable results from the composite baseband output.  There are a few 
cards in the works that generate real VGA timings and I'm looking forward 
to purchasing or building one of them.

The Apple //gs has an RGB output that's a bit more mainstream, but 
required a rather expensive re-scanning converter (>$200, unfortunately), 
Looks great on a 17" LCD monitor in most of its modes!  As an added bonus, 
the converter works incredibly well on Amiga video.  The higher resolution 
interlaced modes from an A2000 are just about unusable on a CRT monitor 
due to flicker.  The upconverter rescans these and presents a rock-solid, 
gorgeous display.  Works better than any of the legacy scan converters as 
far as I'm concerned.

All of these devices feed inputs on a Belkin KVM switcher, but there is 
obviously some input cable switching required as well.

My other project is elimination of multiple keyboards.  So far, I've found 
adapters that permit me to use a PC keyboard with my Amigas and the Apple 
//gs.  The CoCo is still waiting patiently for a Cloud-9 keyboard adapter. 
Mark has the hardware design finished, but the firmware is still on the 
to-do list (last I checked).  I did chase down an earlier design by Dana 
Peters (I think Mark's original adapter may have been based on this) and 
might take a whack at wire-wrapping one together.

Someone else in the community was working on a keyboard adapter, but I've 
lost his e-mail address and cannot for the life of me remember who it was.

Steve


> .....
>
> On Nov-15-08, 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!
>> 
>> 40-column text does not fill the display, but 80-column mode runs right to 
>> the edges and looks terrific.  These little boards are about $70 from the 
>> distributor and require a 12VDC wall-wart power supply.  I mounted mine in 
>> a Radio Shmacked project box.
>> 
>> FWIW, I'm using a Dell 17" LCD display.
>
> .....
>
>> 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.
>> 
>> The converter board has a PC mounted power jack for the wall-wart and a 
>> female VGA connector for the monitor.  No assembly required except for a 
>> box if you so choose.
>> 
>> I have seen Roy's converter on a web page, but was not aware of it when I 
>> started the project to replace all my aging/dying CRTs.  Also, I have the 
>> impression that it's specific for the CoCo and I need something that would 
>> work with any 15Khz. analog RGB source.  I did have to build a little board 
>> to convert digital RGBI from the C128 to analog RGB.  It just sits between 
>> the Commodore and the Wei-Ya converter (I do have to switch plugs when 
>> going from the C128 to the CoCo).

--