Sync to a TTL pulse and maximum strobe rate

Wed Jun 20, 2018 6:39 pm

Hello,

I'd like to sync a Skypanel to a squarewave shutter sync pulse from a camera (in order to strobe the Skypanel). I'm assuming I'd need to build some kind of DMX interface that sees the square wave and sends out a simple DMX signal to make the Skypanel strobe once. My questions around this are:

- Does anyone know of a device that takes a square wave signal (or even simple pulse of a voltage going high/low) and can then output a DMX signal?

- How quickly can a Skypanel be strobed? Assuming that this is probably dependent on the level of light output but is 500 Hz possible? Or 1000 Hz?

Best,

Stuart
stuetr
 
Posts: 2
Joined: Thu Jun 16, 2016 5:02 pm

Re: Sync to a TTL pulse and maximum strobe rate

Tue Jul 10, 2018 10:59 pm

Hi Stuart,

Thanks for your post.

I'm not aware of any device out there that takes a square wave signal and then outputs DMX, but maybe some else out there has an idea for this.

In regard to how fast the SkyPanel can be strobed, there are several limitations. The first is the speed of DMX. If you are trying to sync to a shutter, DMX might not be the best protocol as it is not incredibly fast. Furthermore, there is no way, given SkyPanel's hardware, to allow for such a fast strobe or syncing to a shutter. I don't think it would be possible.

Sorry I am not able to help you further on this one.

- Mike Wagner
Senior Product Manager, ARRI
Mike Wagner
 
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Joined: Mon Nov 23, 2015 8:42 pm

Re: Sync to a TTL pulse and maximum strobe rate

Sat Aug 04, 2018 7:45 pm

Stuart,
While there may not be anything available on the market to meet your needs you mentioned building something yourself. If you are handy with electronics and willing to learn a little bit of programming there are hobbyist programmable micro-controllers called Arduinos that should help you bridge the gap between TTL and DMX.

The micro-controllers have pins purpose built to read TTL levels and return High and Low (on and off) through programming. There are some prebuilt DMX add ons available for purchase called shields (a quick google search for arduino DMX shield will give you a lot of choices) that are compatible with programming libraries that handle the grunt work of using an arduino to build a custom DMX controller.

Basically the devil is in the details though and you have to make sure the TTL voltage signal is in range for the arduino (usually 5v or 3.3v depending on the model chip) and source other electronic components like connectors and any TTL logic voltage converters if they are needed. Building a device like this from scratch is possible but it is a big time sink especially if you have no programming or electronics experience.

I have used Arduino and DMX shields (as well as raw components) to build my own portable DMX controllers and flicker gags and as far a I can tell strobing speeds over DMX vary based on the light fixture. DMX sends data at 9600 baud which according to google is 9.6kHz but if you send a whole universe of DMX data (512 bytes with the start bits) the refresh rate is 44Hz according to Wikipedia. However, DMX has no minimum number of bytes you have to send along with the start frames so if you use the sky panel in the bare minimum number of DMX channels and only send 3-4 channels out over the stream then you can achieve a higher refresh rate as long as the light fixture's hardware can keep up with it.

There are obviously a lot more variables and building your own hardware requires a lot of testing. It took me 7 months to get my flicker effect generators for kino Celebs to a stable build (then firmware 3 for sky panels was released and made any more development totally pointless). If you still want to try rolling your own hardware solution shoot me a direct message and I can point you to some great resources for Arduino and DMX as well as programming and some of the curve balls that come up in the dev process.


Joe
joemartin
 
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