[Coco] Finally RGB from a coco 2

[Zippster]

Hi Darren,

The comparators weren’t behaving as I expected on the first prototype, so I’m laying out a second
one with optional hysteresis on the LM339s to enhance stability, and individual voltage dividers instead
of the very hard to adjust networks I had on the first one.

I may add a header for a piggyback board with a circuit using an AD725 ic for composite and s-video
(artifact support) that will hopefully be the clearest composite possible on a CoCo2 (in addition to the VGA).

There’s also a collaborative project I’m working on with Brendan Donahe.  An MC6847 VGA board using an
Altera Cyclone IV FPGA. I just ordered our development prototype PCBs last week.  This one will support 
artifacts directly once we have it developed.

We will definitely have some 6847 VGA options eventually.  :)

- Ed


> On Jul 1, 2015, at 3:56 PM, Darren A <mechacoco at gmail.com> wrote:
> 
> I think I would rather wait for Ed's 6847-to-VGA project. Any updates on
> the progress Ed?
> 
> - Darren
> 
> 
> On Wed, Jul 1, 2015 at 1:05 PM, Zippster <zippster278 at gmail.com> wrote:
> 
>> I don’t know.
>> 
>> I asked Fred about schematics on Atari Age, he declined, saying he wanted
>> to offer kits and upgrades.
>> 
>> My guess would be the transistor circuit inverts Y and level (amplitude)
>> adjusts Y, øA, and øB.
>> The small board probably handles component to RGB matrix conversion, the
>> the HDMI converter
>> box as scan-doubler to 31.4khz for the monitor.
>> 
>> - Ed
>>