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

[Steve Batson]

John,

Yes, this is Luis' RGB2VGA board used with the DENano FPGA. 

Since you have just finished it, I'd test it out first to see if you see any jitter or other problems. However Roger did a lot of investigation and found these values produce voltages in line with the VGA Standard and to help the board properly sync from the CoCo output. I don't have all the technical details, I just know it worked for Roger and works for me.

These are what Roger came up with and I simply duplicated what he found. Also, the Variable resistor, he recommended a 10K Multi Turn for finer control when tuning for the best appearance. Another thing to know is that there are some additional wires recommended but they were not needed on Roger's or my case and jitter did not go away until removed.

Top Left

82 Ohms - Grey-Red-Black-Gold-Brown
R22
R23
R25

* * * Bottom Left

1.2K Brown-Red-Black-Brown-Brown
R18
R19
R20
R21

* * * Top Right 10

R9  47
R10 47

390 ohms
R1
R4
R7

820 ohms
R2
R5
R8

1.8K ohms
R3
R6
Rx (this is the resistor soldered to R7 and the GPIO1 Connector)

* * * Bottom Right

2K Red-Black-Red-Gold
R17
R14
R12
R11

1K Brown-Black-black-Brown-Brown
R15
R16




On Jul 9, 2015, at 9:31 PM, John B <trymyz at gmail.com> wrote:

> Steve,
> 
> Are you referring to Luis' RGB2VGA board?  The reason I ask is I literally
> (15 min ago) just finished assmebling my board.  I used the resistors he
> outlined on his page under the "Modifications" section.
> https://sites.google.com/site/tandycocoloco/rgb2vga  Are those the
> resistors that produced the video jitter?  If so, can you give us the new
> values that fixed the issue?
> 
> Thanks,
> 
> John
> 
> On Thu, Jul 9, 2015 at 11:45 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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> 
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