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

[joem]

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:

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?

[reverselandfill]

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 ?

[Fox]

That looks good! You should go through with it.

[joem]

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

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.

[reverselandfill]

@joem

since I found a lot of use for the front sync outputs on my Cadet 1

can you share some tips ?

[joem]

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.

[rempesm]

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.

[imageofsin]

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

[joem]

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.

[imageofsin]

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 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

[creatorlars]

@joem

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.

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.

[rempesm]

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!

[Fox]

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.

[jmsiener]

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.

[Jesse]

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.

120 Pcs Blunt Tip Dispensing Needle with Luer Lock, Elbow Blunt Needle and...

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

[gliss]

I’ve been building up Cadets to use with Syntonie’s sync system, so have started to create a board using the schematic here. Hope that’s okay? I’m happy to put it up on Github for the community once it’s finished if all goes well.

Some questions! I had hoped to include the discussed add-ons for bringing out the sync signals to the panel. I got a little confused though by this thread though: Sync extraction circuit - #22 by esnho which started talking about leaving some of the pulses uninverted. The schematic that @jmsiener designed inverts everything coming out of the LMH1980 – that’s what the Cadets are expecting, yes? Should that also be the case if I’m bringing the pulses out to the panel? Lastly, I was going to bring out v-sync, h-sync and odd/even, but that leaves one unused buffer. Anything clever I could do with this? Thanks all!

[Analogmonster]

I am working on something else right now intended to be LZX compatible so here are some pointers.

Search the forum for LMH1980, lars posted some examples. Frame extraction is a useful one. frame extraction pulse is inverted vsync ANDed with odd/even to give you a pulse at the beginning of the frame.

LMH1980 datasheet shows the timing diagrams. This shows that Vsync output is a short low pulse-this should be inverted. It shows Hsync output is a short low pulse-this should also be inverted. Odd/even is high when odd in interlaced formats, always high in progressive formats. Should not be inverted but best practice would be to buffer it in some way. If you are using an AND IC for frame extraction pulse you will have some spare gates and an AND gate can be used as a buffer by tying the 2 inputs together.

[jmsiener]

I wouldn’t say I’ve contributed anything here other than the desire to get something working. On the Syntonie discord Bastien enlightened me with these two circuits to buffer sync.

Top circuit is an opamp and -1V reference to invert and the bottom is a 74HC14 and opamp buffer to invert. I’ve got an LMH1980 on a breakout board looking like this:

I need to finish up the board. I figured I could use a 16 pin header and connect the horizontal/vertical sync hooked up to cv/gate on the 16 pin header and supply sync to one busboard.

I just need to get inspired again. The power supply situation in my case is garbage and was giving me artifacts in my output. Just so many things to get right and I’m writing this while holding my newly 2 year old daughter.

[jmsiener]

Hey y’all, I figured I’d share this little abomination I made on some protoboard to get my castle modules vibing in my case:

It takes the RCA sync from my VU007b and goes into an LMH1980 to extract sync, a 74HC14 to invert the signal, then into an LM6172 for buffering, and finally the CV/Gate pins on the 16 pin power header. Here’s a shot with the sync generator at 720p:

I’ve built somewhere in the neighborhood of 100+ eurorack modules, primarily panel/PCB combos, and this is the first project I’ve completely DIY’d with success, other than adding a summed output to my AteOhAte Toms. I had the idea initially almost a year ago and finally got around to executing it. I’m rather positive this idea could be shrunk down to something the size of a 5V PSU busboard adapter but I think this thing wrapped in plastic and gaff tape can be chucked into my case without remorse.

For the LMH1980 I used the example schematic in the data sheet and then @syntonie, who without his help this wouldn’t exist, helped me figure out the inverter and opamp buffer.

I think there’s room for improvement. I’m going to try swapping out the output resistors on my Castle VCOs to 75r 1/2W and see if that helps. I might try the same on my protoboard if that doesn’t clean up the output some more. There’s a little bit of fuzz/distortion/noise/idfk-how-to-describe-it on my falling edge of each bar, right side, (maybe it’s noticeable in the picture I shared) whereas the opposite, or left, side seems much sharper. I used 499r resistors between the opamp output and V/H sync power header connections.

PS-Sorry for derailing this thread with this post. It doesn’t exactly solve RCA to 14pin sync but it is good enough for a castle VCO, if anyone finds themselves in a similar situation.

[rempesm]

Not a derail, nice work!

I bet you could do the same thing to get RCA to 14 pin sync, just adjust the levels to match what that bus is expecting. H/V gate/CV sync is 1V, 14 pin sync is 5V. You probably only need to adjust the op amp buffer.

720p is a pretty demanding resolution for bandwidth, especially for sharp edges on instantaneous black/white square waves. I’m sure you’ll get some edge improvement by swapping to 75R 1/2W series output. This adjusts the inherent RC low pass filter created between the output resistor and the capacitance of the cable. There’s no inherent need to do that for your H/V sync pulses using 499R, they are relatively much slower than what a Castle Clock VCO can spit out.

I wouldn’t expect a pixel perfect edge with no noise as hard transitions are the most likely spot you’ll see the fuzzy bits of your power supply and any other interference in your setup.