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8 to 1 scart switch

@[email protected]@me

Dec 15, 2016
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Hi all,
I'm thinking about building my own 8 to 1 SCART switch (for the PAL format, in France), supporting both RGB & CBVS, in order to have all my retro game consoles connected to the TV without having to remove / change / re-plug cables each time.
One of the reasons is that commercial devices are either expensive either not with 8 inputs (and cascading several is ugly to the eye).

Anyway, I started some research on how to do such a thing, and I found this schematic, using the MAXIM MAX9655 chip :

https://www.maximintegrated.com/en/images/appnotes/4522/4522Fig03.gif

I had a look at the datasheet, and all seems to be doing what I want, but as it does only work for 2 inputs, I'm wondering if it would be a safe thing to casacade such ICs (in a way there is always 3 MAX9655 between any input and the output), while keeping a good signal and not to much delay ?

Thanks in advance for your tips :)
 

kellys_eye

Jun 25, 2010
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You would have to 'parallel' the outputs to get eight-into-one but the safest way would be via an 'enable' signal on the MAX device. Clearly it doesn't have one so this would need to be implemented at the output - any device that could 'pass' the signal but be enabled/disabled and driven through an 3-of-8 decoder would work.
 

@[email protected]@me

Dec 15, 2016
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Dec 15, 2016
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It seems like the MAX 9656 has such an output enable pin (the outputs are as 3 state buffers in the datasheet). The other functionality it offers is not useful for me, but shouldn't prevent me from doing what I need.
what do you mean by "parallel" the outputs ? Do I really need to be able to hi-Z some outputs ?
The intended goal is to have 4 MAXs for the 8 inputs, put the 4 outputs to 2 other MAXs, and finally the 2 output to a last one, and towards the TV (like some kind of bintree).
 

kellys_eye

Jun 25, 2010
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The parallel solution was what I initially proposed (but requiring the /EN signals from a 3-of-8 decoder).
 

@[email protected]@me

Dec 15, 2016
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Someone gently reminded me the parts I'm showing here (MAX9655 & MAX9656) are no longer available for sale :( I'll have to find another way of doing what I want
 

@[email protected]@me

Dec 15, 2016
81
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Dec 15, 2016
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I finally managed to break open an old SCART switch, and it seems that simple relays may be largely sufficient :) (they use mechanical switches with 12 contacts at once). So adios the MAX4399 or MAX9655 :) thanks for your help, I'll post the schematics here once I'm done
 
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