Circuit Board Schematics for a 'DIY Switcher'

[JDP]

Hi All,

 

As part of a small project I need to create a small basic switcher.

 

We don't have a budget for a Folsom or MX70, so I was wondering if anyone has a schematic for a small, basic switcher which could be created? This would preferably use something basic like push switches as a control surface, with electronics allowing a source switch of VGA, Composite and DVI signals..

 

I am fully able to create circuit boards, solder them, and work at component value. And I have an account with Rapid Electronics and RS :o

 

I know its an ask, and I am not expecting anything apart from recommendations of something expensive, but thought it would be worth a shot

 

Cheers

 

John

[Shez]

Do you just need to be able to switch multiple VGA inputs to one VGA output, multiple DVI inputs to one DVI output and multiple composite inputs to one composite output; or do you need to convert any of those inputs to a different format?

If it's just switching, the elctronics won't be to hard but if you want a box that can convert signal formats, provide glitch-free switching etc, I think you may struggle more than a little bit to build one.

[JDP]

Hi Shez,

 

It would ideally have a VGA, DVI and Composite input, switching to a DVI output. If needbe I can loose the composite.

 

Glitch free I am not really worried about, an AB switcher or similar would work, unless anyone else has something more 'fancy'?

[Tesseract]

Computer, capture cards, puredata + linux, arduino if you really want a hardware controller.

Except that'd probably end up being more expensive than buying one.

 

So, just buy, unless you want something really simple EDIT: Sorry, didn't read your post properly. I don't think there's any chance. That said, there is at least one website out there which has circuit diagrams for some pretty good DIY AV equipment. Don't know if they have video mixers though. I'll see if I can find it again and check. :/ EDIT2: Doesn't look like it. You could try designing one yourself, but. :D

[broadcast_techie]

John,

Crash switching composite feeds of the same format can be a case of simple switches. If you want clean switching you will need to design something with a framestore on each input. To be honest, composite / VGA shouldn't be that difficult to deal with, but by the time you get into the DVI / SDI world you have to be really careful with the pcb design and component choices.

Also you haven't said what output you need, or what the purpose of this switcher is...

 

Kris

[dbuckley]

A good few years ago Elektor magazine had a composite video mixer project. It required that the sources be syncronised. But once you get past that it all got quite easy - seperate out the video into, well, video and sync, and then the video was just mixed like audio, or switched between sources at an appropriate moment to do all the usual selection of wipes etc. Quite clever. Check with your local librarian

[Stuart91]

It required that the sources be syncronised.

 

Video sources capable of synchronisation tend only to appear in more professional devices - e.g. no consumer-grade camcorder that I'm aware of has the facility, the composite video output from most graphics cards doesn't either. So if you have the money to buy such devices, obtaining something like an MX70 shouldn't be too much of an obstacle...

 

I can appreciate that a project like this might be a fun task for an electronic hobbyist, but I can't see much usefulness for someone trying to get video mixing on a budget...

[dbuckley]

Oh absolutely. If you have (or can get) synced sources then grab an old Grass Valley off eBay and get the real deal, but I assumed (perhaps wrongly) that the OP was trying to learn something here.

 

Mind you, when I were much younger, even CCTV cameras had sync inputs :)

[Jivemaster]

Synchronised cameras also come from the CCTV industry, they have an LV AC feed and sync off one of the zero crossings. That way they can switch with mechanical switches.

 

http://www.milinst.com/DMX/dmxtext.htm and down the page.

[Stuart91]

Oh absolutely. If you have (or can get) synced sources then grab an old Grass Valley off eBay and get the real deal

 

I'd agree with that course of action. Although I did investigate this route a while ago. The problem for us was that even if we got cameras with sync, we still had the issue of not being able to connect anything else to the system. (Tricky when a customer says something like "We want the Wii up on the big screen") The cost of even a few frame synchronisers (to connect kit that doesn't accept a sync signal) seemed to be prohibitively expensive - unless there are some cheaper models that I missed...

[Dmills]

I have seen loads of synchronisers on ebay for not much money.

 

Note that if you are building a simple 2 bus mixer, you only need two synchronisers irrespective of the number of inputs, as you can crash switch the input to whichever unit is not presently live to output when you select the source, it gets harder if you want to support DSK and the like.

 

Now, I will grant you that this is all for composite or component, taking SDI, VGA and DVI gets tricky quickly, especially if you need to be able to scale or if the required output rate differs from the input (say video input (50Fields/s) and VGA (60ish or more, non interlaced), there is a reason kit that does that is expensive!

 

Incidentally I remember one of the electronics rags publishing a synchroniser design back in the day, but there are probably much neater ways to do it now.

 

If I HAD to build the thing for some reason, I would probably look into a handful of video capture cards with appropriate inputs, and do the bulk of the job in software on a decent PC!

 

Regards, Dan.