xalixo
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Re: RCA video out to VGA adaptor

Wed Mar 21, 2012 12:53 pm

Hi,

a lot of people have mentioned that HDMI to VGA adaptors won't work, except for the really expensive ones, which makes sense because HDMI uses a digital signal, but VGA signals are analogue. The R-Pi also has an RCA video out port on it, which is analogue so would it be possible to just connect a VGA screen to that using an adaptor like this? I know its still expensive (£15) but its still a lot cheaper than the £40-£50 HDMI adaptors. Also does anyone know why the VGA to RCA video adaptors only cost about £1 whereas RCA video to VGA cost so much more.

Sorry if something like this has been posted before, I did a search but couldn't find anything.

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rurwin
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Re: RCA video out to VGA adaptor

Wed Mar 21, 2012 1:00 pm

The VGA connection has between 3 and 5 signals in it. The RCA composite connection has one signal, which is a mixture of those 3-5.

Say I have some sand in three different colours. Would you prefer the job of mixing them together into one big heap, or taking one big heap and separating out the different colours?

xalixo
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Re: RCA video out to VGA adaptor

Wed Mar 21, 2012 2:04 pm

Thanks for the explanation rurwin. It makes sense.

So I assume there's no reason why one of these type of adaptors wouldn't work with the Rasberry pi. If so would it be the cheapest way to get a pi outputting to VGA?

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Jongoleur
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Re: RCA video out to VGA adaptor

Wed Mar 21, 2012 2:11 pm

I had a quick google on the subject.  Its not pretty.

Have a read through this discussion http://www.electrondepot.com/e.....22475-.htm

Quoting from one of the posts in the above discussion:


What probably hasn't been explained to you is the complexity of pulling
apart the composite signal then reconstructing it in to VGA  (which is a
form of RGB format).

The most popular way is to digitise the composite video in to a video frame
buffer… and the reconstruct the VGA (RGB) analogue signal.

So you are going from analogue (composite) –> digital –>digital
process–>analogue (VGA).

This is a very high speed process and surface mount IC's with 100's of pins
or more.


All you need to convert VGA to composite is some passive resistors and capacitors, thats why its cheap.  Going the other way requires active signal processing (its what happens in a TV between the composite input and the screen) and that isn't so cheap. In essence, its hard work and not to be undertaken lightly.

I do recall some sort of bodgework for a Beagleboard, but it wasn't said to work well…

xalixo said:


So I assume there"s no reason why one of these type of adaptors wouldn"t work with the Rasberry pi. If so would it be the cheapest way to get a pi outputting to VGA?



Cheap converters are "ok" for allowing a video source to be connected to a VGA input only projector, but the quality of text on a computer screen will be eye-wrenching.

The other thing is that this has been discussed to death elsewhere on the forum.  Have a look around.  I'm now closing this discussion down.

edit: for clarification and to answer xalixos last post.
I'm just a bouncer, splatterers do it with more force.....

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