[WIP] RCA Sync to 14-pin Sync (mostly)

Forum DIY
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In some comment somewhere, I mentioned that something like this should be fairly easy to make (in order to sync anything that needs 14-pin sync but not the blanking signal), and, well, now I want to try my hand at making it. This is pretty much just the LMH1980 reference circuit hooked up to some Schmitt inverters:

rca-to-14pin-1
rca-to-14pin-11236Ă—820 14.6 KB

I think the single inverter per output is right since according to my notes the 14-pin sync format is positive-going signals, but the sync output by the lmh1980 is negative going, right?

This should let you sync the Cadet 4 Ramp Generator and Cadet 9 VCO in an RCA-sync system. Also, I think I’m going to tack on some jumpers that when closed will also send H and V sync to the CV and Gate lines on the power header, so that it could also (optionally) be used to sync Castle VCOs.

I’m also thinking of maybe making it be a module (instead of just a PCB that you need to mount (or leave dangerously dangling) in your case. Then it should be easy to also add some H, V, and Frame sync output jacks like the Cadet 1. But maybe that’s a bit too much feature creep. I also haven’t decided on whether it should be through-hole or SMD. The LMH1980 is SMD, so maybe the whole thing should be, since I already have to deal with that one part? It could make for a nice small board if SMD, probably.

Technically, since it uses an LMH1980, this should also convert from HD RCA sync to 14-pin sync, but I’m not sure how useful that’ll be… The Cadet 4 Ramps definitely would need to be recalibrated (and maybe have some parts swapped) to be useful for HD rates, and the Cadet 9 VCO might need to be recalibrated too (I can’t remember what its trimpot is for).

So, what do you think? Would this be useful to you? And if so, any requests/suggestions? And from an electrical standpoint, do I have it right?

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Great idea!

I sort of wanted to make such a pcb as an addon for my sync busboard, but had not started yet.
Maybe we can make something together, like a module & busboard thing, where the module connects to the busboard and distributes the sync signals ?

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That looks good! You should go through with it.

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I figured I probably wasn’t the only person thinking about this. :slight_smile:

Module + busboard could be interesting… I don’t think we’d need a different busboard from your sync busboard, would we? Then a 14-pin cable like the kind you’d use from the sync busboard to a module could be used to connect this sync converter module to the busboard. Or did you have something else in mind? I could even see it being a PCB that plugs directly into your sync busboard – if we keep it to pretty much the schematic I posted it might be able to be small enough so that could make sense.

I think I’m leaning towards definitely making this a module, since I found a lot of use for the front sync outputs on my Cadet 1. I’ll try to play around with some layout soon and see what feels good.

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can you share some tips ?

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The thing I’ve used them for the most is syncing audio oscillators. All the oscillators I tried did OK syncing to frame or v-sync, and one even managed to handle h-sync OK (Intellijel Dixie 2+, though it was nowhere as nice a proper video oscillator). I also use the front sync outputs to sync my Castle VCOs since they’re not on the same power bus as my Cadet 1.

Another thing I’ve done is use a voltage controlled switch (a Doepfer one) to switch between video signals, and I used the frame sync to time it to that to reduce tearing, using a spare VCA as a makeshift AND function that AND’ed the frame sync and a randomly generated trigger.

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Frame sync output is also a way to clock sequencers without frame tearing. You probably will want to divide the frame sync down before clocking the sequencer.

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Hey!
Any updates? I’m super excited for this module.
I assume you’re in the prototyping stage, but just wanted to ask :slight_smile:
Ty!

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Nothing of note to report yet. (Perhaps I announced my plans a little too early, whoops.) I’ve worked on it a bit, but I’m trying to get a bunch of different boards (from various projects) ready for one big pcb order, so I haven’t yet reached the pcb stage.

Relatedly, I’m looking for easy ways to solder the LMH1980. I’d love to have it put on by the PCB manufacturer, but it looks like none of the one’s I checked have that one unsurprisingly (or maybe I’m just not checking right? – I’ve never done PCBA before). I’ve tried a couple of times on other projects to hand-solder (both drag-soldering and pin-by-pin) something with a finer pitch than an SOIC, and I failed miserably, and unfortunately the LMH1980 is a VSSOP. I have a hot air gun that I’ve used for some desoldering a few times, so I think I’ll try that, which will be a first for me. But if anyone has advice on how best to hot-air-solder it, or any other advice on easy ways to solder it, I’m all ears.

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Massively appreciate the detailed update! If you haven’t started on the pcb (and are very busy w other projects) I don’t mind doing the board for you. Designing PCBs + soldering is my favorite thing to do, and I really want this module :slightly_smiling_face: Which ECAD are you using by the way? I’m on Kicad 6. I’m a master SMT solderist too so I dont mind ordering the boards + chips, putting the packages on, then shipping them to you. Anyways- let me know if I have your blessing. To be 1000% crystal clear; it’s entirely yours, I just want to help bring this to fruition sooner! Thanks bud :sparkles:

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Get one of those ChipQuik flux pens and some of their high flux rework solder. You’ll find everything just snaps in place sooner after hitting it with hot air, and the flux really aids in cleaning up any bridges, etc. Without a fast reflow (i.e., not enough flux on the board or in the solder) a hot air tool can easily make a mess or end up burning the FR4 before reflow happens.

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Low temp indium solder can help, too. I used that on the QFNs for the Capsules I built up and it made those a snap. Something like this:

https://www.chipquik.com/store/product_info.php?products_id=210001

But yes, get comfortable with using plenty of flux!

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Also recommending Chip Quik. I use both a flux pen as well as a liquid dropper and have used Chip Quik - low temp solder before.

When needed, I also have solder wicking copper braid on hand for removing any pesky bridges that do happen to remain after the hot air reflow. A jeweler’s loupe also comes in handy for inspection. I have a cheap pair that are worn like glasses and have LEDs.

As for PCBA, some service providers can order your BOM or allow for you to ship the obscure parts to them directly. The cost of PCBA may not be worth it for one part unfortunately.

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Real talk, I want to build this on some board and just hot glue it to the bottom of my case. Sacrilege to some but really, I just want these castle modules I built to play well with my VU007b. Do you think this circuit would be good to go other than your plans of adding all of the features you’ve mentioned?

The only snafu I’m encountering is finding vssop to dip adapter to actually get this built up on a one off perf board.

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Get low temp solder paste in a syringe, they’re called “Luer lock” syringes - you can buy really fine tips for them on Amazon.

If the paste is too thick an old timer trick is to add a bit of 97% iso alcohol, but honestly just warming the syringe up tends to work just fine. We take it out of the fridge an hour or 2 before use.

The other move is to order a stencil & apply paste using a credit card or a cut of the stainless material that the stencil is cut out of. That works a real treat for super fine pitch stuff. If you don’t get around to it I can make you a 1980 stencil the next time I order JLCPCB, should be just a few weeks & we’re laying out a few stencils anyways so it wouldn’t be any trouble

[EDIT] whoops just seeing im replying to an old post