Cheap DMX interface = USB to RS-485 converter?

[bulldog_99_00]

Hi,

I am a new user and am studying my DMX interface options.

I'm on a budget, so I'm considering buying the Enttec Open DMX.

The Open DMX is an unbuffered interface. Does that mean that it's just a USB to RS-485 converter? Or does it construct the DMX packets as well?

Thank you

[Mattotone]

its a straight convertor, the host does all the processing, Iv used one for years and no problems, i only use 15 fixtures (52 channels).
The pro version is buffered and will take some work away from the host (in regards to timings).

[Boycordoba]

Hey there! I've built my own USB-DMX interface as well. I used two output drivers in order to get to different powered outputs as if in a DMX splitter. Din't have any problem with that.

Now, I did have a problem when programmig my DMX receivers. I have no problems receiveng and decoding the signal at all. The actual problem is with Freestyler and the OPEN DMX interfaces, where Freestyler sends a STOP bit that's just too long after the START BYTE (0). In that case the microcontroller reads that STOP BIT as if it was another byte and then I need to filter that byte out.

That would'nt be an issue if I was always going to use the fixture with Freestyler and an OPEN DMX interface, but, the problem arises when I use a console or another type of adapter I.E: ENTTEC PRO that use the correct DMX timing. In these cases, the channels get shifted by one position. For example: if I want to control a fixture with channel 1, then I have to set the fixture's DIP switch to 0.

Now, the question: is there a way to modify the lenght of that STOP BIT in Freestyler, so that it conforms to the correct timing?
It seems it's a problem with the source code. Apparently Freestyler opens the port, closes the port to send the BREAK Signal, open the port to send the MAB Signal, with the port open sends the START BYTE, closes the port and then opens the port again to send the DMX String.

I hope it makes any sense and maybe I can get an answer.

Thanks,
Fernando
Cordoba - Argentina

[Boycordoba]

I forgot to mention in my previous post that I also own an ENTTEC OPEN DMX interface. The problem I mention here does not only happen with th interface I built, but also with the ENTTEC.

Thanks.
Fernando

[Boycordoba]

Well, the problem is the MAB (mark-after-break).

Since I cannot (or at least I don't know how to) modify the values in Freestyler, I built my own DMX sender with PIC16F628A. Now I can modify any value I want to test the DMX thread and I could determine that the channel shifting is result of the too long MAB. Changing the lenght of the BREAK signal didn't change anything, but with a MAB as long as Freestyler's (2mS) the channel shifted.

So, is there a way to modify that? Anyone has a clue on how to modify the BREAK and/or MAB lenght in Freestyler when using OPEN DMX interfaces?

Thanks,
Fernando