Re: Apple ][ to VGA monitor adapter board - looking for best color decoding method

["Michael J. Mahon" <mjmahon@aol.com>]

ferdimh@gmx.de wrote:
> Hi all!
>
> With the understanding of the decoder circuit (I got the schematics
> from Marcus Heuser - thank you!)
> I was able to optimize color displays. The principle of the Shift
> register/latch circuit delivers a very poor picture if a different
> resistor network is connected to get RGB output. This was unusable, my
> method was far better. But, based on the resistor network  of the PAL
> color card, I was able to recalculate my values and got to this:
> http://img87.imageshack.us/my.php?image=comparisonau3.jpg
> The lower monitor is a 14'' NTSC device connected to the video out,
> the upper monitor is a 12'' IBM VGA connected to my card.
> I also tried some games:
> http://img301.imageshack.us/img301/1107/pacmanxj0.jpg (HIRES)
> http://img87.imageshack.us/img87/2020/airheart1vgand9.jpg (DHIRES)

The color fidelity is great, and even the transitions are pretty
good (NTSC-like)!

The "chroma sharpness" of the conversion is responsible for the
"serrated" horizontal colored lines and areas, but that is a standard
(if unattractive) feature of "RGB" Apple II displays.

It might be fun some time to detect the color burst and use it to
switch in a low-pass filter on the color only--but that would entail
converting to "component" first so only the chroma channels could be
band-limited, then converting to RGB.  When the low-pass was switched
in, an additional delay would need to be added to the luminance signal
to compensate for the filter's group delay.

This approach would give the "best of both worlds":  A crisp text
display and a pleasantly blended color display, which most Apple
graphics designers used for their "proof" displays.

> I'm just wondering how to continue. I might finish the PCB layout
> tomorrow, so I need to decide whether I make a prototype on my own -
> which is a lot of work (566 pads/204 vias) to be done or if I decide
> to let some guys make the PCB. But a 268mm x80mm is going to be
> expensive in prototype volumes (i.e. 1 or 2). It seems that PCBs are
> way cheaper in the US than in Europe...why? I might actually let them
> make in the US and ship them here.

That's probably the cheapest way.  Competition is fierce in the US,
and it really helps lower the prices.  The same is true for most
consumer electronics, BTW.  I once had a Sony VP tell me that they
mostly sell their TVs in the US a little above cost to build volume,
since the market is so competitive, and then get their profit from
other regions!

Quite a switch on the 1970's ploy of going to Japan to get consumer
electronics cheaper.  ;-)  47th Street Photo in New York has better
prices!  (Of course, most consumer electronics don't even come from
Japan anymore.)

-michael

NadaPong: Network game demo for Apple II computers!
Home page:  http://members.aol.com/MJMahon/

"The wastebasket is our most important design
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