Sync Generator for 120FPS project

Dear Live production gurus,

I am working on a post-production project that requires we shoot using an Ursa Mini 4K at 120FPS. These are the project settings on the camera:

IMG_4951.jpg (46.32 KiB) Viewed 3830 times

The project requires we sync 4 separate LED panels to flash in sequence for exactly 1 frame of video each. To do this we want to use a sync generator like the "Blackmagic Mini Converter Sync Generator". I want to know if it work with a Project Frame Rate of "60 fps", Sensor Frame Rate "120 fps" and Sensor Area "Windowed"?

I am also curious about the type of signal coming from the Sync Generator. We want to run the LEDs using an Arduino and I am wondering how we will interpret the signal coming from the Sync Generator. Will it be an SMPTE signal?

Any help would be much appreciated.

The sync generator can output either a black burst of tri-level reference signal. These are analog signals, and are very extensively documented online.

Thanks jack I’ll do some digging into documentation for tri-level reference signals.

Does anyone think we will run into any issues using a sync generator with these frame rates?

I'm not sure I'm understanding exactly what you're trying to do. Can you give more detail on what you're attempting, and your desired outcome?

Hey Jack

Thanks for your interest in this, i'll PM you.

I have made a post about this project over on the arduino forums if anyone is up for helping thanks: https://forum.arduino.cc/index.php?topic=517477.0

To add on your post on the Arduino forum,

First in your code you define a delay as INT DELAY = 8.3333
You are trying to define a float to a int.. The Integer will have a value of 8. As there is no decimal in a interger.

I even doubt if the compiler code behind DELAY does handle a float. But what you could do is use delayMicroseconds... Search for it by google.. It does give you more control as we are not talking about miliseconds but microseconds. Do note that the Delay function is not very accruarate for timing.
If you would create a square wave based on this and you measure this square wave with a logic analyser, you will see that there is some time difference between the puls lengths.. So not quite accurate.. You might want to investigate a more cleaner way with a direct control of timer and compare function that is not handled by the big arduino overhead code.


Also yes you can extract the Sync pulse of the sync generator. But the generator at best will spit out 50/60 pulses per second. There is no120fps sync puls.. So let's assume that the camera will lock to the genlock when it is in high speed mode.. (This is a maybe.. Absolutely not guaranteed).. The question would be.. How does it sync.. does it flywheel sync once every X frames? Does it sync each 2nd pulse?

You are trying to trigger something that a Phantom has numerous trigger functions for. But broadcast grade cameras are not really made for..

Still a very intresting project from a technical standpoint. So i will follow this project from the sideline..

Thanks man!

I made a post over on the arduino forums to represent the tests I've done in regards to your mention of delayMicroseconds.

More problems after more problems. I hope I start to see a light at the end of the tunnel soon.

Merry Xmas everyone!

I received a reply from my contact in Blackmagic support who has done some tests with off speed frame rates. They said:

I've just tested this here and the it looks like the URSA Mini does lose the Ref input when you enable the off-speed frame rate. I apologise I wasn't aware of this behaviour.
I tested two of URSA Mini cameras synced together and at 50 FPS they were perfectly synced, I then increased the frame rate to 100 fps and left the ref signal from our Sync generator plugged in, after one hour I checked the cameras and they were still in sync.
I believe this means that you should be still ok with the Sync generator, it is possible after a few hours the camera will drift and you will lose the sync.

This is very promising. It could mean that sync generator is still the correct tool to use and my next step is going to be using the LM1981 chip to extract the sync pulse and feed it into either the Arduino or some kind of PLL as was suggested by a user on the arduino forums.