Re: Apple RGB monitor- VGA interface

[supertimer@aol.com (Supertimer)]

In a previous article, rubywand@swbell.net (Rubywand) says:

>Scott G. writes ...
>
>> .... I searched the net and found dozens of
>> companies that make little devices that will take a 30kHz
>> (VGA/SVGA) output and transform it to 15kHz for connection
>> to "TV" analog RGB devices (NTSC rate).  These typically
>> sell for $25 and are designed to connect PC and Mac computers
>> to projection displays.
>> 
>> If such a device is possible for so little money, would it
>> not be possible to build the reverse device?  One that would
>> take analog RGB output from a GS or an Amiga and pipe it to
>> a VGA/SVGA/Mac monitor?  There is an market for such a thing.
>> It would be different from the Second Sight too, because it
>> will allow the display of ALL of the GS's modes ....

The Amiga has been there and done that.  They are called scan doubler
cards.  I'm surprised that nobody ever made one for the GS.  I mean,
it uses the same type of monitor and all.

>display the usual 200-line GS screen as 400
>lines on a 30KHz VGA/SVGA monitor. It should look very nice and, as you
>mention, all GS display modes would be available.
>
>     Of course, once you've gone to the trouble of developing such an
>interface, there would be a temptation to add embellishments (e.g. a way
>to display 400 unique lines, more colors, etc.).  It would not be too
>surprising to discover that Second Sight began as a 'simple' VGA monitor
>interface.

The Second Sight is not a scan doubler.  It actually shadows the
output of the GS by reading screens and redisplaying them through
the VGA chip.  The result is a choppy display because the Second
Sight is not fast enough to keep up with every frame.  The irony
is that by trying to be more, the Second Sight does a poorer job
than a real scan doubler when displaying regular GS video.

If a scan doubler is to be built, it can be a solution for the
Second Sight problem as well.  Amiga scan doublers typically have
a pass-tru that lets true VGA signals bypass the screen doubler.
A simple port can be added to the GS scan doubler that lets Second
Sight video bypass it.  Regular GS modes would go through the scan
doubler while the Second Sight VGA ones would go to the pass-thru
port.  The Second Sight would not be needed, but Second Sight users
would be supported.

>
>     In quantities of a thousand or so, the basic GS-to-VGA monitor
>interface circuit might be commercially doable at a sale price below
>$75, especially, if it's an Apple club project or other such situation
>where no one actually expects to be paid much for the time he/she
>contributes.

One cost cutting option is to locate a maker of an Amiga scan
doubler and try to convince it to make a GS one.  If the same video
signals are available through the GS slot, a redesign of an Amiga
card to interface with a GS slot might be simpler than an all from
scratch design.