Open Source SCART switch project

[numbski]

https://github.com/Numbski/open-source- ... witch/wiki

In case anyone wants to play along. I know retroswim did one a while back, but I feel like he used a bunch of unshielded wire, despite building up a custom pcb, and used an arduino (or really, an atmega with arduino sketch loaded) to drive a display. I'd like to get this one to a place where it is mostly-automatic, and can be soldered by a beginner. I can do SMD, but not everyone is quite that good with an iron. The end goal is a 12 port switch that is mostly hole-through soldering, that way those that are more solder-adept can do bus switches up on breakout boards for the less-solder-inclined.

I have my eagle library up on github as well, small as it is right now - but it has the critical piece in it, the female vertical pcb mount scart socket:

https://github.com/Numbski/eagle-library

So yeah. Pieces that might go in later would be an rgb amp, but I'm not sure how to implement logic to the end of, if 1 display, bypass the amp, if 2 displays use it - as I have a perfect 1:2 RGB amp here someplace (forgot which one, I think it is a popular one for SNES RGB bypasses?).

First up is a cheap 3-port manual switch, and I will gradually build up the project from there. I'm home sick on disability, which means I have lots of time, but very little productive time to work with. This will be very much stop-and-go for me. If you feel like playing along and helping, have at it!

[citrus3000psi]

Nice Idea.

I designed a scart box a long time ago using a basic bus switches and a manual knob.

https://imgur.com/a/R1FLG

I had started to design up a new switch box with HDMI, toslink, component, scart but since scrapped it. As I don't try and keep my consoles connected anymore. I was going to use the MAX7461 for sync detection.

[numbski]

That looks amazing. Did you keep your brd and sch files?


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[Ryoandr]

I made a ghetto CBT3245 8/2, and it actually works good. Got the cheapass multi scart at flea markets, and used a rotary switch for selecting the input.


i don't need no stinky custom pcb or steel casing

[Syntax]

I just convert old db9 15 or 25 printer switch boxes.
Means no lines are ever crossed. You can pick the boxes up for less than $5.
Rotary switches all the way.
If there were db25 to scart female adapters id be laughing.

[numbski]

I just convert old db9 15 or 25 printer switch boxes.
Means no lines are ever crossed. You can pick the boxes up for less than $5.
Rotary switches all the way.
If there were db25 to scart female adapters id be laughing.

I actually have two of those sitting here, but i am very hesitant. Looks like they use very thin wires. That, and the wires are colored by port, nit by pin. Will make it a serious PIA to convert.


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[Syntax]

The pin layout seems daunting but it's easy.
You can't fuck it up its super simple.
Use your own shielded wires.

Here's 2 HDMI switches I made because 20 wire HDMI switches just don't exist.

[citrus3000psi]

That looks amazing. Did you keep your brd and sch files?


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I designed this in a program called express pcb. The first pcb program I ever used. Its a proprietary format and can't export gerbers. I probably have the file somewhere, I can dig it up if you want me to. The design is very simple though.

[numbski]

That looks amazing. Did you keep your brd and sch files?


Sent from my iPhone using Tapatalk

I designed this in a program called express pcb. The first pcb program I ever used. Its a proprietary format and can't export gerbers. I probably have the file somewhere, I can dig it up if you want me to. The design is very simple though.

My bus switches arrived today - getting ready to play around with how infant this to function. Seems like watching the sync line for a signal and switching after x seconds is a decent plan. Going the pushbutton or maybe even rotary route first go since i have that handy.

[numbski]

I made a ghetto CBT3245 8/2, and it actually works good. Got the cheapass multi scart at flea markets, and used a rotary switch for selecting the input.


i don't need no stinky custom pcb or steel casing

So how did you go about amplifying for two outputs? Did you just use a 2:1 amp that was on at all times, or did you use a manual switch to bypass the amp when only one output was connected?

[Ryoandr]

So how did you go about amplifying for two outputs? Did you just use a 2:1 amp that was on at all times, or did you use a manual switch to bypass the amp when only one output was connected?

just a 7374 wired for 2 outputs like in the datasheet, on at all times.

[Darksakul]

Reminds me when I had repurpose a old manual VGA KVM switch that handled AT Keyboards, and made adapters to send audio through instead.

Spoiler

Hot glue only there for strain relief of the cables.

Even if DB 25 to scart adapters don't exist (yet) I image it not hard to wire up.

[robotvendingmachine]

I bought the Scart splitter from eBay and will buy the bus chips shortly.

[Syntax]

Reminds me when I had repurpose a old manual VGA KVM switch that handled AT Keyboards, and made adapters to send audio through instead.

Spoiler

Hot glue only there for strain relief of the cables.

Even if DB 25 to scart adapters don't exist (yet) I image it not hard to wire up.

Its a lazy way to do it, not recommended as its better to use shielded cable with these rotary switches.
Too many analogue signals in close proximity...

[numbski]

Reminds me when I had repurpose a old manual VGA KVM switch that handled AT Keyboards, and made adapters to send audio through instead.

Spoiler

Hot glue only there for strain relief of the cables.

Even if DB 25 to scart adapters don't exist (yet) I image it not hard to wire up.

Its a lazy way to do it, not recommended as its better to use shielded cable with these rotary switches.
Too many analogue signals in close proximity...

I know - kabeldirect on amazon makes me so sad. Such beefy cables and connectors, bhp the infernal buzzing from crosstalk...

[numbski]

https://github.com/Numbski/open-source- ... witch/wiki

Updated - bus switch breakout boards arrived today. Realized I will need to desolder the existing wire from the circuit board since it is soldered directly to input 3. Oops. Fixable, just need to work out in my head how I want to handle it, and handle bringing all 3 inputs back to that wire.

[numbski]

Back to working on this a bit today, and I'm thinking I won't be able to avoid something - if I want to design this at the end to be auto-switching, an AVR is going to be mandatory. Even if it is just programmed with a relatively simple arduino sketch that watches the alarm lines of the MAX7461's for each port, it has to be there.

The problem I see is mutual-exclusivity. We want to make sure that at any given point in time, only one source can send to the destination. Ben Heck's design didn't even account for this, oddly. I guess he assumed that with the lights and a little common sense, no one would try using two video sources concurrently.

Not that an AVR is particularly expensive, and you can use an existing arduino as an ISP to program a smaller AVR for the task.

If manual switching, then for the three port I can just use an on-on-on toggle switch (have a bag of them laying here for NESRGB palette switching) to switch between the ports.

Was hoping to keep a mostly-dumb auto-switching solution, but if I don't use an AVR and simply rely on the inverted logic of the MAX7461 alarm lines, there's nothing to say that two consoles couldn't be on at the same time, shutting off the MAX7461 alarm, telling it's bus switch to send.

I'm more of a networking and perl coding kind of guy, so if you see a more simplistic solution to this, please speak up.

Hoping to get my prototype wired up by the weekend. I ordered my MAX7461's and breakout boards from China, so those are taking a looong time to show up. In the meantime, I was thinking of sketching up a simple SCART to DIP adapter board and having a bunch run off at OSH Park. That way I can breadboard this whole thing.

[citrus3000psi]

Was hoping to keep a mostly-dumb auto-switching solution, but if I don't use an AVR and simply rely on the inverted logic of the MAX7461 alarm lines, there's nothing to say that two consoles could be on at the same time, shutting off the MAX7461 alarm, telling it's bus switch to send.

You can get creative with resistor values and create pull ups/downs and let one MAX7461 overwrite other MAX7461 and so on down the chain.

Honestly AVR ares easy so the circuit itself might be less complicated with one on board. Checkout circuits.io its an easy to use online AVR sim.

[nam9]

just a 7374 wired for 2 outputs like in the datasheet, on at all times.

Interesting! How did you handle audio?
I am interested in a building low cost 1:2 scart distribution amp..

[Ryoandr]

just a 7374 wired for 2 outputs like in the datasheet, on at all times.

Interesting! How did you handle audio?
I am interested in a building low cost 1:2 scart distribution amp..

audio is just Y-splitted. I guess you could build some proper amp splitter, there should be plenty of info on the web.