Author Topic: Possible to split the RGB output?  (Read 1573 times)

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Offline geebus

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Possible to split the RGB output?
« on: 00:39, 02 November 19 »
Hi all, I'm looking to be able to record the output from the amstrad(s) whilst still using the standard monitor. So effectively having the machine running as it would normally do, but with an offshoot going to a capture card.
I was thinking of making a cable that just splits the output to two connectors but wondering if that would have the effect of halving the output to each plug (if both were in use)?
Anyone have any prior knowledge of doing the same or similar that could help?

Offline Bryce

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Re: Possible to split the RGB output?
« Reply #1 on: 16:35, 02 November 19 »
Yes, you'll effectively half the voltage on each colour because you are doubling the impedance. To do it properly you'd need an active splitter that gave two outputs at the correct levels.

In reality it won't actually be half, for several reasons that require complicated maths to explain, but you will end up with two dull versions of the screen.

Bryce.

Offline GUNHED

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Re: Possible to split the RGB output?
« Reply #2 on: 16:56, 02 November 19 »
Well, that's a bit off the topic.... maybe... But shouldn't it be possible to split into one RGB and one monochrome rail. Since these use different signals there shouldn't be signal loss. But I never tried it.
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Offline Bryce

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Re: Possible to split the RGB output?
« Reply #3 on: 21:11, 02 November 19 »
Not quite, because the monochrome signal is derived from mixing the R,G and B signals together. So loading the composite line will also pull them down, although less as they are mixed via current limiting resistors.

Bryce.

Offline geebus

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Re: Possible to split the RGB output?
« Reply #4 on: 13:40, 03 November 19 »
Thanks for confirming Bryce.
I think what i'll do is try find a way to capture the output and not use a normal monitor, just move the capture to a 2nd screen and have the amstrad under that. Making it look like two separate computers.
Or I could make a little device that takes the input and puts a boost into both outputs. But that'll be a project for another time I think.

Offline Bryce

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Re: Possible to split the RGB output?
« Reply #5 on: 15:08, 03 November 19 »
Because you're not trying to convert or upscale the signal, you can make a purely analogue version that doesn't care about refresh rates etc. They are pretty simple and the internet is full of examples such as this:

http://streampowers.blogspot.com/2013/05/simple-vga-monitor-splitter-and.html

Yours would be even simpler as you only need one Sync signal. But make sure it's being powered from the CPC 5V and GND, otherwise you may have sync issues.

Bryce.