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bdwillie

Parallel DMX hookup?

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After running traces on a few of my DMX dumb RGB controllers, it seems that the DMX in and DMX out are just point to point circuit card runs with no electronics in between.  If that is the case, what is stopping me from having a box in the yard that has one DMX in, and three DMX out jacks, paralleled with shielded cable?  All three would be used, so no open jack to pick up interference.  This would save quite a bit of hassle ( and Cable) on set up.  Yes I know this would not increase my channel count on that universe,  no where near the 512 anyway!

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In practice it usually works to split the signal as you say, I do the same with my lights. However it can cause problems with signal reflection corrupting the first packet on the line in some cases. It really just depends on the cable lengths before and after the split, as well cable quality. That being said it doesn't hurt to try it, the worst that will happen is the lights just wont get the right data and might act sporadic. 

If you do try it and you have problems with the signal, there are devices that will split and repeat the signal, effectively isolating the outputs from each other and the input. The commercial ones can be a bit costly though, and are not usually worth the money to buy in our case. You can make one though if you know a little bit about electronics. It just takes a few Opto Isolators, DC to DC converters and RS485 Differential Transceivers.

Also here is a good technical DMX512 Primer, with some other Tips and Tricks as well.

http://www.dfd.com/primer.html

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1 hour ago, bdwillie said:

After running traces on a few of my DMX dumb RGB controllers, it seems that the DMX in and DMX out are just point to point circuit card runs with no electronics in between. 

That is correct.

The RS-485 standard specifies point to point to point etc with a terminator at both ends of the circuit.  However lots of people violate the standard in various ways.  Lots of people don't put a terminator on the ends, and quite a few have splits in the cable path.  Do they get away with it?  Generally yes, but the more you violate the standard, the more likely to cause problems.  The longer the splits are, the more likely to cause problems.  With that said, there are active splitters that do what you want.  I've never looked into them,  but I remember them being mentioned here on the forum.

 

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12 hours ago, k6ccc said:

  there are active splitters that do what you want.  I've never looked into them,  but I remember them being mentioned here on the forum.

 

time to go searching!  THanks!

 

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