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 Forum index » DIY Hardware and Software » Video synthesis and manipulation
RGB matrix mixer [DRAFT]
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NOISEBOB



Joined: Oct 13, 2019
Posts: 17
Location: NOISE

PostPosted: Fri Oct 18, 2019 1:31 pm    Post subject:  RGB matrix mixer [DRAFT] Reply with quote  Mark this post and the followings unread

Posted Image, might have been reduced in size. Click Image to view fullscreen.

fresh idea.. matrix mixer for red, green and blue.

would this work?


edit: fixed some bad errors, original schem had pwr and gnd short circuiting and used NPN where they were supposed to be PNP. if you want to see the wrong one it is here: http://shitcore.org/imgbrd/db/157143040955.png

inspired by this: https://web.archive.org/web/20060112082440/http://www.anatekcorp.com/driving.htm
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PHOBoS



Joined: Jan 14, 2010
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PostPosted: Sat Oct 26, 2019 11:07 am    Post subject: Reply with quote  Mark this post and the followings unread

I hardly have any experience with controlling RGB signals but I do see some flaws.

I think the input impedance should indeed be 75 ohms, although I am not sure how important this is, but it could form a voltage
divider with the output to get the correct voltage. In your schematic you have 3x 75 ohms in parallel resulting in 25 ohms.

If a pot is at 0 ohms the corresponding transistor is connected directly between +5V and GND and it probably will result in a hot
but unhappy trannie. If a pot is above 0 ohms but still at a pretty low value it might develop a smoking habid and although
smoking pot can be fun that is usually a different kind of pot.

The transistors might need a current limiting resistor on the base but there could be some current limiting on RGB outputs
that is already enough. Also because of the way they are configured it might not be needed at all.

What you have now looks more of a current mixer btw and you probably want a voltage mixer. Then again this current will be
converted to a voltage when you plug it into something.

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NOISEBOB



Joined: Oct 13, 2019
Posts: 17
Location: NOISE

PostPosted: Sat Oct 26, 2019 1:59 pm    Post subject: Reply with quote  Mark this post and the followings unread

PHOBoS wrote:
and although
smoking pot can be fun that is usually a different kind of pot.


LOL


yeah i know this circuit has lots of errors, the kind folk over at AAC pointed it out already.


i think i need to read up on how transistors and shit actually work. and breadboard some more.

thanks for the input. it is appreciated a lot.

Smile
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PHOBoS



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PostPosted: Sat Oct 26, 2019 4:08 pm    Post subject: Reply with quote  Mark this post and the followings unread

Had a look over at AAC. Yeah you basically want 3 of those mixers, but I don't know the frequency of the RGB signals. I'd assume that for a
single color it would actually just be DC so you don't want any AC coupling (no caps on the inputs).

The voltage level for RGB signals is only 0.7V which could become a bit of a problem. It might not be a bad idea to first boost the signals and
attenuate them again after mixing. You probably also need to limit them because if you're summing the signals you could get a max voltage
of 2.1V, I'm not sure if that could damage anything.

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