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sync generators
MUFF WIGGLER Forum Index -> Video Synthesis  
Author sync generators
bod
Hi folks,

I’m new round here, but have been tinkering with video synthery nonsense for a while, albeit with a 3 year break until yesterday! Until now I’ve been using lm1881 chips to extract the sync signal from a video feed, and hacking vga signals as per brian mckenna’s vga synth he made many moons ago. Theres a few things on my site but its mostly poorly documented, especially now that I’ve somehow locked my self out of the site…. Not very useful.

Anyway, I was wondering what people are using for video sync generators for standalone units? The wee vga synth I use (or used, and is now needing rebuilt), required a vga input to steal the V and H sync signals from, and mix the RGB signals from the synth back in. Whilst I don’t expect you to give away your secrets, but do you have any suggestions? The sync generator chips I looked at around 5 years ago seem even more scarce now, but theres a few fancy looking SOIC chips that look suitable, I just need to stop drinking coffee long enough to be able to solder them!

I was thinking of just continuing with the vga hacks, but figured with all these wonderful new modules that people are producing there may be a better or at least “easier” method. Theres some great stuff on here, I’m looking forward to going through it all tonight!

Cheers,

Bod.
lizlarsen
Hey bod! Welcome to the forum!!! applause

The LZX Video Sync Generator module is an NTSC/PAL sync generator which has external locking capability, a DC restored video input, and several sync outputs. It has a 14-pin header on the back of the module which distributes several 5V sync signals and is well documented here:
http://www.lzxindustries.net/technical
So if you are doing DIY modules which need the sync signals, they are accessible there.

The LZX VSG uses an AVR Atmega chip clocked via 13.5MHz crystal and with some external logic chips used to achieve external lock. An LM1881 is used to strip the sync, to pass on to this logic. That is a great chip, so easy to use! The LZX VSG doesn't just strip the external sync though, it locks the timing of the internal clock to match the phase of the external sync. This is a bit more stable way to do it, and defeats things like macrovision protection, etc. There are also tons of op-amp buffers and logic buffers to distribute signals going out of the module. I can't share the source code, but this is the basic principle at work.

I think most people doing video synthesis and working with sync with modules right now, are using this module. Together with LZX Color Video Encoder, it forms the basic I/O for video in the LZX system.

In the past, lots of "DIY" type systems would use a rackmount or standalone box sync generator to generate all the necessary signals. If you search for "NTSC Sync Generator" on eBay, they are not hard to find! You'll want to make sure the one you get has the features you want, for your DIY projects.
daverj
Back in the 70s and 80s I made internal sync generators (no genlock) using a Fairchild chip called the 3262. But it's been obsolete a very long time. I have also made sync generators by combining a PIC chip with a PLD chip (programmable logic), which worked in PAL and NTSC. The CPU and PLD both required programming. I also made one using an LM1881 and an FPGA (gate array) that did internal sync and genlock.

The genlock for my upcoming video synth system (finally shipping around January) is a fairly complex beast which includes several specialized video chips, a gate array, a digitally controlled oscillator, and a CPU running at 80Mhz. All surface mount. It not only locks to NTSC and PAL (auto-detecting the format), but fills in any missing sync pulses. It also creates black burst and some sync signals that are used by other modules. It's far too complex to sell as a kit or for somebody to breadboard. But that and one of my Output Amp modules will be a good core system for homebrew synths, since they take care of the important stuff like creating the sync and turning the output of any processing circuit back into recordable video.

One good way to get a sync generator and genlock for a homebrew system is to look for an old Panasonic analog SEG on ebay, like the WJ4600 or WJ5500. They both have full sync generators, with genlock, and put out all of the standard sync pulses (HD, VD, Blanking, Composite Sync, Burst Flag, and Subcarrier). The newer SEGs have TBCs built in and don't genlock or put out all the sync signals. So they are good for working with video, but not for supplying sync to homebrew synths.
bod
Great, thanks very much guys!! Lots of things to think about and tinker with!! Mr. Green my partner in crime is a broadcasting technician at the BBC and has been pestering me to update the box and make it a bit more substantial, so when it comes to the sync standards i have him to keep me straight, but my background is synth design, repair and building, so we have a pretty good base to leap off from, although I have to drag him back a bit and point out we don't have the same budget as he does at work..... EVS desks are pocket change to them!

I might have to sell a kidney to afford some of your modules just now, but it will no doubt save a lot of hassle in the long run and let me concentrate on modifying the more common ground synth modules I'm used to, to work on video.

I've coded a few attiny chips to generate VGA sync signals so that i can have a standalone unit without the computerand from previous experiments have found that you can throw pretty much anything at the RGB lines as long as its within 0-5v. but, having said that, we normally ran video from the laptop at the same time so it was never really an issue and the box mixed everything together.

The great thing is that the uk has gone digital in respect of tv broadcasting so there is loads of surplus analogue equipment to be had for buttons as the tv stations sell off their out of date equipment.

So many options, so little time... So much fun to be had!!
lizlarsen
Quote:
save a lot of hassle in the long run and let me concentrate on modifying the more common ground synth modules I'm used to, to work on video.


That's one of the most exciting things about these new systems, I think -- finally getting the signals in and out with an interface designed for doing this kind of stuff. We love talking about DIY and adapting schematics here, so please post any notes.

LZX will be offering some Sandin IP module clones in PCB, kit, or assembled versions as well if you are interested in kits.

Looking forward to hearing more about your projects.
bitSmasher
bod wrote:
I've coded a few attiny chips to generate VGA sync signals so that i can have a standalone unit without the computerand from previous experiments have found that you can throw pretty much anything at the RGB lines as long as its within 0-5v. but, having said that, we normally ran video from the laptop at the same time so it was never really an issue and the box mixed everything together
Could you take something like a cheapo composite to VGA converter (ie $30 on ebay) and hijack the RGB lines?
lizlarsen
Yes you could.
bod
bitSmasher wrote:
bod wrote:
I've coded a few attiny chips to generate VGA sync signals so that i can have a standalone unit without the computerand from previous experiments have found that you can throw pretty much anything at the RGB lines as long as its within 0-5v. but, having said that, we normally ran video from the laptop at the same time so it was never really an issue and the box mixed everything together
Could you take something like a cheapo composite to VGA converter (ie $30 on ebay) and hijack the RGB lines?


thats one way i've done it in the past. you still need the laptop output to supply the sync signals, but the scan convertors are really just RGB to PAL/NTSC encoders. i dont think i've come across one that generates its own, but i could be wrong!
i have a couple of old monitors in the studio that i use so a PAL output has never been an issue, and pretty much all the projectors we've used at gigs have vga inputs.
i might tear one apart this evening to have a good look at whats in there again, as my notes have mostly been lost in the dump that is the attic of my house....
bitSmasher
Sorry I mean the composite in > VGA out converters, that'd have to generate individual H + V sync signals on the output... and would they generate the sync regardless of the input?
So you'd just use it as a sync generator, inputting nothing to but taking the H + V out then adding your own signals to the R G B lines of whatever you're inputting to record/display.

It's something I'm definitely going to play with once I get a workshop space set up again. Don't wanna derail your thread too much though!
bod
Ah, I should try reading the question!!

Never tried that to be honest, but you can get simple VGA testers that will put out sync signals, search on hackaday for VGA tester, there are a number of kits and DIY options to be had from various places.
bod
bitSmasher wrote:
. Don't wanna derail your thread too much though!


No harm in that, it's a thread about sync generators, and you had a question on said subject! Mr. Green
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