Composite -> scart adapter wanted

Discussions about Sinclair ZX80 and ZX81 Hardware
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sirmorris
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Joined: Thu May 08, 2008 5:45 pm

Composite -> scart adapter wanted

Post by sirmorris »

I have a very useful RGB/SCART(Peritel) -> VGA adapter which I use for most of my old computers. I'd like some way to get the composite output from my nailed-to-a-plank development zeddy board onto my vga monitor through this adapter without having to go through my rf->vga box. The quality is terrible and it occupies too much space, and an extra plug socket.

I have a chroma board which would be perfect but I don't want to nail this to the plank so it's not really feasible to use it in this situation.

So what I need is composite -> scart. There don't seem to be any search terms on fleabay which turn up useful items, everything is scart->hdmi these days.

Has anyone else ever wondered this? I want something tiny and cheap. I don't want to do what everyone else seems to do which is use an old VCR.

Ta.
C

sirmorris
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Re: Composite -> scart adapter wanted

Post by sirmorris »

Just for laughs (and because, well you know - educated guess) I put the composite signal into the G(reen) input on my sony broadcast monitor. Yaay! I get a nice clear picture of an inverted K. I was banking on the fact that the monitor would accept sync-on-green as there is no separate sync input.

My RGB -> VGA adapter has a separate sync so, would it 'simply' be a case of grabbing the nearest LM1881 and feeding the separated sync to the sync input and then the unchanged video signal to the R,G and B channels?

That would be sweet.

C

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1024MAK
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Re: Composite -> scart adapter wanted

Post by 1024MAK »

sirmorris wrote:My RGB -> VGA adapter has a separate sync so, would it 'simply' be a case of grabbing the nearest LM1881 and feeding the separated sync to the sync input and then the unchanged video signal to the R,G and B channels?
It may be even simpler :mrgreen:. Depending on the available signal level (current drive) and how fussy (or not) the RGB -> VGA adapter is, you could just feed an amplified composite video signal to both the sync and say the green channel. If that works okay, try for white by connecting up the red and blue channels also to the composite video signal.

Most real TV's are happy to decode the sync from a composite video signal on pin 20 of the SCART connector.

If your RGB -> VGA adapter (which type do you have anyway?) does not like having a video signal, yes a LM1881 may help.

Mark

sirmorris
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Re: Composite -> scart adapter wanted

Post by sirmorris »

This is my cheap ol' converter.

I tried the same trick with the video into the G/Y input but no dice - I saw a clear screen for a fraction of a second on a couple of occasions. I think it can work but I suspect sync issues. It doesn't work nicely with (cough)acornatom(cough) RGB with its 60hz refresh rate - lots of flickering and rolling. I may be able to 'reconfigure' it with a screwdriver but haven't looked.

I'll try the 'signal on every pin' thing tonight :D

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1024MAK
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Re: Composite -> scart adapter wanted

Post by 1024MAK »

Ah, the GBS-8200 are a bit too fussy when it comes to their sync inputs.

The Atari ST community had difficulty getting it to sync to the Atari ST's RGB video output. So feeding a composite video signal into the sync input will not work (at least, not on the version 4 and earlier boards).

Mark

XorA
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Re: Composite -> scart adapter wanted

Post by XorA »

If you don't mind another adapter

http://www.ebay.co.uk/itm/LTS-LTAVB0VA6 ... Sw6BtVSmyK

Is what I use for my zeddy on VGA. You can get them much cheaper than that one if your search!

G

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-B-
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Re: Composite -> scart adapter wanted

Post by -B- »

I use this setup to get composite to VGA.
image.jpeg
Composite to VGA
(1.33 MiB) Downloaded 342 times
The SCART to HDMI adapter is fully SCART compliant and will detect composite, RGB or Y/C input and was £20 on eBay. The HDMI to VGA adapter was another £5.
image.jpeg
No lag detected
(2.11 MiB) Downloaded 342 times
-B-

sirmorris
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Re: Composite -> scart adapter wanted

Post by sirmorris »

Hmm, that looks like an option - thanks!

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PokeMon
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Re: Composite -> scart adapter wanted

Post by PokeMon »

It works with my SONY broadcast monitor when using RGB setting and G input in the same quality as using composite.
I assume that your signal does not support the back porch and result in a dark picture with default brightness/contrast settings.
I complained the missing back porch on the CHROMA interface for ZX81 which forced me to use additional sync input and change to external sync.

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