gscartsw RGB-SCART project

If you're really concerned about quality you should go with relays or RGB amplifier ICs with 3-state outputs, and impedance controlled PCB traces.

 

If needed, RGB amplifier can be installed into SCART connector, like Tim did in his NESRGB.
I am really concerned about quality but I am not going to be crazy about it. If nobody sees the difference - it's not important. It means I am not going to use mysterious "gold-coated" SCART connectors and ENIG here.
This switch will be of much higher quality than any released SCART switch. I recently disassembled 5x Component consumer switch which has high ratings and works well, and I must say it's very cheap inside. There are cheap components which distort signal more. It's not $1000 switch after all.

 

Just trying to help.. I hate to see mediocre solutions being built and put into circulation.

Using video amplifiers arranged as a non-inverting voltage summer/"mixer" could be less expensive than analog switches. A mixer would give you "automatic" switching without having to rely on the SCART status pin, and if they needed to be they can be forced off with open-collector drivers or a SPST switch.

Anyways I'm pretty sure that these Maxim switches are meant to be used AFTER the signal has been buffered and biased and I didn't notice any mention of biasing or using a bipolar supply? Like RetroSwim pointed out I think you're going to have problems with AC-coupled signals. If you are biasing the signal, then you really need an amplifier because the impedance mismatch will be horrific.

 

the consoles will already output amplified RGBS ready for TV's to take so i don't see the need to amplify further. or am i missing something?

 

What RetroSwim pointed out was taken care of even before he wrote it, I checked that.

 

You're missing probably a lot--putting a bunch of coax wires in parallel creates a huge amount of capacitance both on the input and output of these analog switches. Amplifiers for each input are necessary to 1) minimize capacitance by isolating the signals, which maximizes the bandwidth 2) to allow the signals to be terminated so signals don't reflect and 3) to bias the signals for the switching elements to minimize distortion.

Could you share how it's "taken care of"? Are you using a negative supply?
Even if you use +- 3.3V any signals with large DC biases (such as many poor RGB mods) will be clipped.

 

Do you want to see schematics?
I don't get what you're trying to prove here , are you interested in such switch?

 

No a schematic isn't necessary, I'm just curious to know that the signal isn't distorted which is a big deal IMO. I would be interested in an active SCART switch but only if there's good signal integrity.

 

For audio multiplexers Vss is supplied with -5V.

All other information you want to know is here:

 

OK, so AC coupled video will clip without biasing or a +- 3.3V supply. Good to know.

 

Today finished soldering of first switch. Runs fine, tried my SMD1 SAT and SNES. Picture is just fine, no problems, no degradation.
I didn't got sound multiplexers yet, so no sound.

 

Looking good man!!

Best practices, yeah, absolutely.

But for this application, I think the video is low bandwidth enough that any artefacts won't be noticeable by the human eye.

Heck, I have a cheapo KVM switch somewhere that's just a 35-pole wafer switch with all plain hookup wire interconnects (no mini-coax for RGB), and you don't get any visual degradation until you pass 800x600, where you start seeing loss of contrast, ghosting, etc.

 

very nice work

 

If you're only viewing 240p video over short cables then it may well be acceptable, but it's standard practice for a reason. Controlled PCB impedance costs nothing and will make a difference at pixel edges under instrumentation (including capture cards). If you think it's overkill look at the analog switch's bandwidth. A proper design will at least let you use some of it by switching arbitrarily well.

In the KVM floating wires ideally don't affect the transmission line because they don't have significant capacitance or inductance. The degradation is probably more from the switch and cables.

 

something like this but with RCA jacks instead of scart would be really handy for me

 

You shouldn't use Composite, if you want quality.
Also this can be used:

 

I seriously doubt this, but do you think it would be possible to plug one of these into another? I have about 13 systems that use SCART so 8 ports aren't enough.

 

Yes, you will be able to daisy-chain these. I also have more than 8 consoles here. 8 was optimal number for one switch.

 

Great! Can't wait to see the final units.