[Coco] Cross Post from the Facebook Page about the RGB2VGA Board

Steve Batson steve_batson at yahoo.com
Mon Jul 20 00:03:33 EDT 2015 

John,

I agree with Ed. It is darn good. Keep in mind that Roger's resistor values were found through a lot of work on his part. He did mention that some changes to the code could probably clean it up more, but the code used to build the .JIC file doesn't seem to be available. When he tried to compile what is available, he had issues. That's when he was told to use the included .JIC file. Like Ed, I do have mine pretty darned stable but it's not perfect. When I adjust the POT, I can get it to look really good on most stuff, but haven't found a sweet spot for everything.

From everything I've seen so far and from what Roger found, I think there are two main things going on.

1) There is some noise needs to be dealt with in the FPGA Code, possibly in combination with further tweaking with the board components. And while I'm not a Video Expert or electrical engineer, I find it extremely interesting that there are no RF filtering circuits on the RGB2VGA board. I would think that any noise that makes it way to the card could ride the signals right out to the VGA port. Possibly there are still some signal level issues that are creating some noise or allowing to the vga port.

2) I'm almost certain that some of the noise I'm seeing, and sounds like you too, is RF Interference. The waves or rolling effect. And I think you are on the right track of looking to a shorter ribbon cable as it may be picking it up from outside from computer or monitor powers supplies. The reason I say this is that when I move the cable around and reposition it, it sometimes gets better and sometimes worse. I'm thinking a shorter cable, or maybe a shielded cable will help. You must have come to this conclusion about the same time I did. :)

Anyway, as several of us have mentioned, it's still an outstanding product and much better than most of us had before. And not having a working RGB Monitor, it's awesome to be able to use with LCD monitors of today.

In any case, if enough of us keep at it, we should be able to get this thing darn near perfect. I think Roger has a a pretty solid understanding of it now as is evident from his work. Now with Ed involved, there are two very talented people looking at it. I will help anyway I can, test, etc. but currently Roger and Ed have much more knowledge than I do about the CoCo and hardware interfacing to it.

I'll be building a second board soon to use as a spare, maybe it will be cleaner...we'll see. If even newer resistor or other changes come up, I could test those.


Steve

On Jul 19, 2015, at 7:23 PM, John B <trymyz at gmail.com> wrote:

> I agree, definitely very good quality.  The screen is acceptable.  Maybe I
> am too picky about these things and expect it to be perfect.  I have a few
> things to try.  One being another monitor and the other being a shorter
> cable from the CC3 to the board.  This one is almost 2 feet.
> 
> On Sun, Jul 19, 2015 at 10:15 PM, Zippster <zippster278 at gmail.com> wrote:
> 
>> If you’re running without the ground fix (much more stable), and Roger’s
>> resistor
>> values, I think that is about as good as it gets with this particular PCB
>> without
>> improvements to the FPGA code.
>> 
>> Although I seem to be able to dial in an acceptable screen for any mode no
>> problem,
>> but finding one that’s perfect across all of them…. well, I guess it is
>> what it is.
>> 
>> Still darn good though.  :)
>> 
>> - Ed
>> 
>> 
>> 
>>> On Jul 19, 2015, at 9:02 PM, John B <trymyz at gmail.com> wrote:
>>> 
>>> I did both.  The ground fix makes the text more unstable.
>>> 
>>> On Sun, Jul 19, 2015 at 10:00 PM, Zippster <zippster278 at gmail.com>
>> wrote:
>>> 
>>>> Hi John,
>>>> 
>>>> Are you running with or without the ground fix on the hsync input?
>>>> 
>>>> - Ed
>>>> 
>>>> 
>>>>> On Jul 19, 2015, at 8:41 PM, John B <trymyz at gmail.com> wrote:
>>>>> 
>>>>> Steve,
>>>>> 
>>>>> I built a second board this weekend with the new resistor values.  Your
>>>>> sheet was quite handy.  Thank you again.  The text has definitely
>>>>> stabilized but a few other things are off.  The left edge of the screen
>>>> is
>>>>> kind of wavy and gray lines are wavy.  For example in KQ3, everything
>>>> else
>>>>> is stable, except the gray lines (lines in the stairs and wall).  They
>>>> seem
>>>>> to shimmer.  I have adjusted the potentiometer but going to far either
>>>> way
>>>>> causes other issues with the image.  I know you recommeneded a
>> multi-turn
>>>>> potentiometer.  Which one are you using?  Anyway, I will most likely
>> try
>>>> a
>>>>> higher quality monitor and see if the image improves.  Currently I am
>>>> using
>>>>> a cheap Dell 17 inch that was in the attic.  Maybe I am being too picky
>>>> and
>>>>> this is as good as it gets.
>>>>> 
>>>>> John
>>>>> 
>>>>> On Sun, Jul 12, 2015 at 4:53 PM, John B <trymyz at gmail.com> wrote:
>>>>> 
>>>>>> I am pretty sure it will stabilize with new resistor values.  Compared
>>>> to
>>>>>> composite, it looks pretty darn good now.  OSH Park only sold the
>>>> boards in
>>>>>> lots of 3 so I have 2 spares.  I will definitely complete the other
>> one
>>>>>> with the new values.  Haven't decided if I will build the third one
>> yet.
>>>>>> 
>>>>>> On Sun, Jul 12, 2015 at 1:04 AM, Steve Batson via Coco <
>>>>>> coco at maltedmedia.com> wrote:
>>>>>> 
>>>>>>> John,
>>>>>>> 
>>>>>>> Trust me, unless you have something else wrong with the board,
>> Roger's
>>>>>>> recommended resistor changes will clean things right up. Mine looks
>>>> awesome
>>>>>>> and I simply duplicated his changes. Since I had a few resistor
>>>> changes, I
>>>>>>> may end up buying another board and building one up fresh with the
>>>> right
>>>>>>> resistors the first time. The board will certainly look better and it
>>>> won't
>>>>>>> hurt to have a spare. I'm not going to buy a spare FPGA
>>>>>>> though...hehehehe...that's a bit pricey.
>>>>>>> 
>>>>>>> On Jul 11, 2015, at 9:48 PM, John B <trymyz at gmail.com> wrote:
>>>>>>> 
>>>>>>>> Definitely great news.  Hopefully the new resistors will take care
>> of
>>>> my
>>>>>>>> jitter/wavy lines and text problem.  I will find out next week.
>>>>>>>> 
>>>>>>>> On Sun, Jul 12, 2015 at 12:42 AM, Steve Batson via Coco <
>>>>>>>> coco at maltedmedia.com> wrote:
>>>>>>>> 
>>>>>>>>> I changed the last 4 resistors and didn't really notice much
>>>>>>> difference,
>>>>>>>>> but since values were based on Roger's research and testing and
>> that
>>>>>>> his
>>>>>>>>> board is now solid, I figured I'd do the same. I've Tested all of
>> the
>>>>>>>>> features and it's incredible results.
>>>>>>>>> 
>>>>>>>>> The output is rock solid. Colors are Rich. Text looks fantastic in
>>>> 32,
>>>>>>> 40
>>>>>>>>> and 80 columns. I've tested Zaxxon, Grabber, Tetra3, Brewmaster,
>>>> Donkey
>>>>>>>>> King. And The biggie, Sockmaster's port of the Original Donkey Kong
>>>>>>> and it
>>>>>>>>> Looks Awesome! Very happy with the results of this thing. It was a
>>>> lot
>>>>>>> of
>>>>>>>>> work, but it was well worth it.
>>>>>>>>> 
>>>>>>>>> 
>>>>>>>>> 
>>>>>>>>> 
>>>>>>>>> On Jul 9, 2015, at 8:45 PM, Steve Batson <
>>>> steve at batsonphotography.com>
>>>>>>>>> wrote:
>>>>>>>>> 
>>>>>>>>>> I figured I'd post the following here too. Some discussion
>> occurred
>>>> on
>>>>>>>>> the FB page, but a lot of discussion was done between Roger and
>>>> Myself
>>>>>>> in
>>>>>>>>> email as Roger made several discoveries that stabilized some very
>>>>>>> annoying
>>>>>>>>> jitter problems with video.
>>>>>>>>>> 
>>>>>>>>>> RGB2VGA Stabilized!
>>>>>>>>>> First thanks to Felipe for a very cool Solution to bring the CoCo3
>>>>>>> video
>>>>>>>>> to Modern VGA Monitors. Originally, I missed a few resistors that I
>>>>>>> somehow
>>>>>>>>> thought were optional and Felipe straightened me out on those.
>>>>>>>>>> Then I was getting Jitter just like Roger was experiencing. I had
>>>>>>>>> several email discussions with Roger as he was doing some research
>>>> and
>>>>>>>>> experimenting based on what he found about the VGA standards and
>>>> found
>>>>>>> that
>>>>>>>>> changing some resistor values stabilized the output from his
>> board. I
>>>>>>> have
>>>>>>>>> pretty much duplicated Roger's resistor values on my board with the
>>>>>>>>> exception of 4 that I'm waiting to come in, but mine is crisp and
>>>>>>> jitter is
>>>>>>>>> gone. I will most likely change those 4 resistors when the parts
>> come
>>>>>>> in
>>>>>>>>> unless it doesn't make sense.
>>>>>>>>>> Anyway, Finally fantastic output on my VGA monitor. Very Cool!!!
>>>>>>>>>> Very Big thanks to Roger!!!
>>>>>>>>>> 
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