Film-Tech Forum ARCHIVE: Is there a manual for GPO signals somewhere

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Posted by Yasar Arabaci (Member # 8562) on 10-31-2014, 12:30 PM:

Hi,

I am very new to projectionist business. In the movie theather I work, we have barco projectors and doremi dcp-2000 servers. In those servers, we use a macro to automate intermissions. It goes something like this;

GPO #2 Pulse at 400ms
Delay 1 seconds
Playback: PAUSE
Delay 1 seconds
IMB dowser: close
delay 575 seconds
IMB dowser: open
Delay 1 seconds
Playback: PLAY
Delay 1 seconds
GPO #0 Pulse at 400ms

I find most of it self explanatory and I can see that GPO lines open and close the lights. However, I can't find where is this behaviour documented. I am curious whether there are other useful GPO's like #2 and #0 and what happens if I make them pulse at different frequency.

Thanks in advance.

Yaşar Arabacı

Posted by Dave Macaulay (Member # 813) on 11-01-2014, 08:25 AM:

This should be in the digital forum.
There are 8 GPO outputs on Doremi external servers, the IMS1000 has 6. There are also inputs.
You probably have some sort of interface device between the server and dimmer. That is normal to protect the server circuitry from damage - the output drivers are not very powerful.
You can use the outputs for anything you like. The programmer used a 400ms pulse because many dimmers ignore short pulses to avoid having interference activate them.
The inputs can be used for lots of things as well, typically fire alarm signals or remote pause and play buttons.
The projector also has GPIO. I think only 4 outputs are actually usable (several are predefined and used internally or for 3D sync). These should definitely be buffered, their circuitry is on a very expensive PCB. I have only seen projector GPO used in one system, for exhaust control by defining an output as on when lamp is on.
Our practice has been to use a Jnior module for I/O. They work with any server, do basic I/O reliably, plus they have a powerful scripting language and a protocol translation capability when such stuff is needed.

Posted by Yasar Arabaci (Member # 8562) on 11-02-2014, 05:38 AM:

quote: Dave Macaulay
This should be in the digital forum.

Sorry, my bad.

So, If I understood correctly, GPO's are user defined and I should check where they are connected, right?

Posted by Marcel Birgelen (Member # 6801) on 11-02-2014, 07:06 AM:

Yes indeed, that's the whole idea with GPO signals. They're fully "user customizable", so whatever is being triggered by those signals entirely depends on what's connected to those GPO pins.

The number of milliseconds isn't a frequency as such, it simply defines the duration of the pulse/signal being sent. Like Dave already explained, some circuits either don't react to short pulses due to design limitations or on purpose, to avoid interference. So a small increase or decrease of this value will probably do nothing.

Posted by Carsten Kurz (Member # 5396) on 11-02-2014, 10:18 AM:

The Doremi field installer manuals have circuit excerpts that show the server-side/IMB/IMS GPIOs and make suggestions how to use them.

Note that a lot of cinemas use JNIOR external GPIO boxes connected to the theater network through ethernet. I have seen them very often while the server-side GPIOs are left unused. There are various reasons why they do it that way.

This GPIO system existed already in the analog days, every cinema processor for film projection had similiar options, and a lot of cinemas had automation devices in use that did what nowadays servers/SPLs do. Some digital cinemas still run combinations of external automation controllers and serverside automation.

- Carsten