Re: IGS Monitor from Composite Source?

[nyder <nyder.23@gmail.com>]

On May 6, 12:19 am, "Michael J. Mahon" <mjma...@aol.com> wrote:
> mdj wrote:
> > On May 6, 2:39 pm, demp...@actrix.gen.nz (David Empson) wrote:
>
> >>Steve ][ <s...@hotmail.com> wrote:
>
> >>>Just wondering if anyone knows of a way to take a "composite RCA"
> >>>video signal and convert it into something that would display on the
> >>>IIGS Analog RGC monitor.
>
> >>I assume you meant Analog RGB and that was just a typo.
>
> >>In theory, yes. You would need a fancy video conversion box which
> >>decoded the composite signal and produced an RGB signal for the monitor.
> >>This would be an analog process and the signal quality would be much
> >>lower than a genuine Analog RGB source, and probably worse than looking
> >>at the same signal on a good quality composite colour monitor.
>
> > How so? A composite colour monitor has to decode the composite signal
> > to RGB to display it so I don't see how it would look any worse, other
> > than the higher-fidelity of most RGB displays.
>
> Just because the adapter boxes that cost less than $500 are not
> "Sony quality" chroma demodulators.
>
> Of course, the *big* drop in quality comes from doing the chroma
> separation inherent in composite video, with the consequent bandwidth
> limitation.
>
> >>I don't know if any such box exists. It would be simpler than a
> >>hypothetical "composite to VGA" converter, because it doesn't need to do
> >>a frequency conversion as well.
>
> > There are plenty of chips out there that'll decode NTSC into component
> > forms. I doubt you'd need a lot in the way of support circuitry to
> > drive it.
>
> No, it's a mess.  There are filters and delay lines involved, so any
> chip you find will have lots of pins and lots of external components.
> Chroma separation and demodulation is either an analog process or a
> pretty complex DSP process, so there's no free lunch.
>
> > If your intention is to convert Apple II composite to RGB that might
> > be a little trickier, as some modern decoders tend to be confused by
> > the quasi-NTSC nature of the Apple II video signal.
>
> That might be an issue for a "modern" digital/DSP solution--it might
> not lock to the Apple II signal.  An analog solution would not have
> a problem with that.
>
> -michael
>
> NadaNet file server for Apple II computers!
> Home page:  http://members.aol.com/MJMahon/
>
> "The wastebasket is our most important design
> tool--and it's seriously underused."

I need to test this chip to see how well it does with a composite
signal, but according to the datasheet, it's splits all 6 signals out
of the 1 video input.  Thats Hsync, Vsync, Csync, R, G, B.

I just haven't got around to trying it out yet.


Thats why I was asking where the composite signal was coming from,
because there might be a way to get a better signal, like tapping it
before it gets mixed.

But like it was said, you aren't going to get the best quality working
off a composite signal.   At least it's a 15khz signal, and if it
wasn't modulated (rf modulator) then it's all video signal.

I'll try to test it out this week and see how the chip can handle it.
I thought I could do it easily with the eval board, but I just noticed
it doesn't have any poles for the R,G,B, so I'm either going to add to
it, or make a test board with one of the chips.

Not sure what you are looking for exactly, but truthly you might be
better off picking up a monitor with composit in, like an amiga 1084
or something.  I just picked up 2 of them in the last week off of
craigslist here in Seattle.  For free, so keep your eyes open.

I'll let you know how my tests with the chip goes.