Author Topic: vga to green screen gt85 how?!  (Read 2628 times)

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Offline hz138

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vga to green screen gt85 how?!
« on: 15:48, 16 June 12 »
hi,
 i want to use the amstrad green screen with a vga output for a old school effect.
 i want to connect the gt85 screen to a vga output from a fileserver pc.
 i have the 6 pinout din but do
not know which pins to use on the vga for sync(choice), lum, ground(choice).
 can you help?
cheers ;D

Offline Bryce

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Re: vga to green screen gt85 how?!
« Reply #1 on: 17:49, 16 June 12 »
The first thing you need is to combine the V and H Sync signals from the VGA output to create a C-Sync signal. The other thing that's important is that your VGA card can be configured down to 15Hz, if your VGA card can't do that, then it's not going to work anyway.

For the correct circuitry, take a look at a VGA to SCART solution like this one: VGA to TV converter

Bryce.

Offline Badstarr

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Re: vga to green screen gt85 how?!
« Reply #2 on: 20:00, 17 June 12 »
I tried this many years ago with an old pentium system and I never quite managed to get it to work. The problem as Bryce points out was that the VGA card wouldn't produce a signal at a low enough frequency and after following some scant internet information at the time I was able to override the refresh rate but this caused a raft of other problems. It was about 12 years ago so I'm unsure exactly how I went about this I was looking forward to using an emulator on a second VGA card on the GT65 but at the time it seemed to be a no go. As I remember the only "stable-ish" output image I achieved induced a migraine and didn't update correctly and Windows whinged a lot about it. I abandoned the idea as I didn't want to risk damaging my GT65. There are probably a lot more options available today, obviously there is the link Bryce posted (this actually looks quite familiar and could be at least similar to the solution I attempted to use) or you could probably buy some sort of solution that would convert the the VGA signal to a more GT65 friendly one and make some modifications there. Maybe an ancient gaphics card could make things easier too?
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Offline ralferoo

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Re: vga to green screen gt85 how?!
« Reply #3 on: 13:21, 18 June 12 »
Maybe an ancient gaphics card could make things easier too?
If it's too old, maybe not... I think you'd be best to find a graphics card that already has a TV out (like a lot of ~10 year old nvidia ones, e.g. geforce and geforce 2 vintage) as if it's generating a TV out, it must already be doing the right frequencies.

It possible though that it's still generating at VGA scan rates and doing the opposite of a scan doubler - effectively it'd read 2 lines into a RAM and output 1 at half the data rate. It's quite possible some TV out capable cards do that because IIRC they display the same picture at overscan VGA resolution on the monitor at the same time.

Offline Bryce

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Re: vga to green screen gt85 how?!
« Reply #4 on: 14:14, 18 June 12 »
The Matrox cards were very good for adjusting the frequency. nvidia cards could also do this with the old drivers, but I think they removed that feature in later drivers.

Bryce.

Offline hz138

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Re: vga to green screen gt85 how?!
« Reply #5 on: 14:05, 22 June 12 »



thanks a lot for the responses. 8)
hmmmmmm, sounds like looads of greif and it still might not work which is a shame. :-[

this convertor \http://www.octoate.de/wp/articles/connect-cpc-to-vga-display/

is what brought me here but i guess that won't work as is or without mods.

cheers

Offline hz138

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Re: vga to green screen gt85 how?!
« Reply #6 on: 14:34, 22 June 12 »
what about a ibm or canon green screen will that run from a modern pc or will i  still have problems with the refresh rate?

cheers

Offline Bryce

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Re: vga to green screen gt85 how?!
« Reply #7 on: 14:50, 22 June 12 »


thanks a lot for the responses. 8)
hmmmmmm, sounds like looads of greif and it still might not work which is a shame. :-[

this convertor \http://www.octoate.de/wp/articles/connect-cpc-to-vga-display/

is what brought me here but i guess that won't work as is or without mods.

cheers

That's the exact opposite to what you asked. Which do you want - CPC connected to VGA screen or VGA PC connected to GT65?

The octoate mod works fine (for CPC connected to VGA monitor) without any mods required.

Bryce.

Offline hz138

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Re: vga to green screen gt85 how?!
« Reply #8 on: 15:08, 22 June 12 »
i know its the opposite but i dont know if it works both ways or is easy to mod.

Offline Bryce

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Re: vga to green screen gt85 how?!
« Reply #9 on: 15:18, 22 June 12 »
No, it definitely only works in one direction. There is no way of modding that device to work in the other direction.

Bryce.

Offline hz138

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Re: vga to green screen gt85 how?!
« Reply #10 on: 15:38, 22 June 12 »
ok thanks.

what about a ibm or canon green screen will that run from a modern pc or will i  still have problems with the refresh rate?

cheers

Offline Bryce

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Re: vga to green screen gt85 how?!
« Reply #11 on: 16:18, 22 June 12 »
The question is a bit vague. Which monitor exactly? What inputs does it have? Is it Composite or CGA? Point me to a Datasheet.

Bryce.

Offline hz138

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Re: vga to green screen gt85 how?!
« Reply #12 on: 19:10, 22 June 12 »
i have got not idea!

if i can't use the gt85 with out guarranteed sucess then i will have to try and source another monitor so any help you can offer would be useful!

 :)


Offline hz138

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Re: vga to green screen gt85 how?!
« Reply #13 on: 15:53, 23 June 12 »
ok found a canon green screen. with male 9 pin din so a vga to din lead will work with modern pc or not?

 :-\