How do I Convert, Split and Merge DMX? What if I Do it Wrong? – Learn Stage Lighting .com

How do I Convert, Split and Merge DMX? What if I Do it Wrong?

If you’re using more than a few DMX fixtures, or have them spread out across your stage, you’re going to want to split your DMX signal.

And if you’re wiring up fixtures from different product lines, chances are you’ll need to convert connectors, signal type, and perhaps merge some DMX streams from different consoles!

Splitting, merging or converting DMX the wrong way can result in some really big problems, from fixtures dropping out to fixtures flickering, flashing, moving and doing all sorts of things that you don’t want to see during your church service, theatrical show or corporate event.

If you are brand-new to DMX, check out this post explaining the basics of DMX before you read the post below!  Thanks!

Converting DMX

Let’s start with converting DMX between 3 and 5 pin connectors.

Why Do I Need to Convert Between 3 pin and 5 pin?

If you’ve worked with a fair number of DMX devices, you’ll notice that some use 3 pin XLR jacks, some use 5 pin XLR jacks, and some use both to receive and then pass on DMX.

So which is right?

DMX daisy chain

A basic DMX daisy-chain.
Thanks to navet.

The DMX protocol states that 5 pin is right, but then again, DMX only uses 3 of the pins.

In fact, many of the 5 pin cables commercially available are actually imposters- they only have 3 wires inside!   Shocking, I know!  Read more about DMX basics here if you’re interested.

But really, it doesn’t matter.  Any connector designed for low-voltage can be used.  In fact, some fixtures even have an Ethernet RJ-45 plug in for DMX also, and that’s just there to confuse us further.  (Learn more about running DMX over ethernet here)

So that brings us to conversion.  You may find yourself in a situation where you need to convert between 3 pin and 5 pin in order to wire up all of your fixtures.  There are 3 great ways to do this:

  1. You can use a fixture with both 3 and 5 pin XLR in/out jacks to do the conversion.  Just go 3 pin on the DMX in, and 5 pin on the DMX out or vice-versa, and you’ll be great.  The jacks are wired together.   Just don’t use this to split DMX, by using both connectors for output, or merge DMX using the input.  We’ll talk about all that further down the page.
  2. You can use a 3 to 5 pin adapter cable, such as this one, or this one, or both, if you’ve got to go back!  These are always a good little trick to have on hand, because you never know when you’re going to need one.
  3. You can use your opto-splitter if it has 3 and 5 pin outs like this one.  Just don’t double up on the 3 and 5 pin of the same output if your splitter, if it has 3 and 5 pin plugs on each output.

Obviously, it is cheapest and easiest to simply convert DMX using a fixture that has both 3 and 5 pin XLR’s.  Since that may not always be convenient, however, using adapters or a splitter can also work great and they’re great tools to have around if you own a lot of lighting.

Splitting DMX

Splitting DMX is a whole different ball game.  You may sometimes find yourself in a situation where you need to split your signal, such as:

  • Having lights in all sorts of places.  It just makes it much easier sometimes to split instead of having to run cables for DMX in and out to all the far-reaching areas or your show!
  • Having more than 32 devices on one line.  The DMX standard only allows 32 devices per daisy chain of lights in order to preserve signal strength.
  • If you are going over 1800 feet in cable length.
  • In the professional world, we often split DMX to each lighting position just in case a fixture goes haywire or a cable gets tripped/snagged/unplugged, etc.  That way, a fault doesn’t take down more of the lighting rig than it has to!

Now that we’ve gone over the situations where you need to split DMX, let’s touch on how NOT to split DMX.

DMX cannot be split with a y-cable, because this is data we are working with, and that just doesn’t turn out well!  I’m hesitant to mention this, but, in a pinch you can use a y-cable knowing that it severely degrades the signal strength of your DMX, especially if you make either of the “y’s” longer than a couple inches.  So just don’t use a y-cable, it’s really not a good idea for your stress level!

A DMX Splitter is an essential part of a professional’s toolbox, and is great for those of you just starting out too.  It is the proper way to split DMX signal, since we are working with data.  Think about it – you don’t make y-cables for your ethernet connections, you use a router, or more comparable, an unmanaged switch.

 

Sometimes called an Iso-Splitter, Opto-Splitter, Fleenor, or any other nickname made up by a production company.  These handy little boxes or rack mount units take the DMX signal in through their input, and split it out electronically by copying the data stream.  Then, the splitter shoots the signal as a light-beam of signal across a small gap inside the unit – electrically isolating your signal.  So, now we’ve got properly duplicated signal that is safe from electrical faults on other lines, and has been amplified to full strength again.

If you have a lot of lights or are buying more and more fixtures that require a DMX input, an opto-splitter is a great investment that will both make your life easier and keep more hair on your head when it comes to troubleshooting.

A great model that I have had success with is the inexpensive Enttec D-Split, which is under $150 for 4 outputs of split data – 2 in 3 pin, and 2 in 5 pin.  Check out my full review of the D-Split here!

If you require a truss-mounted split, this unit by American DJ is also good, but only has 3 pin inputs and outputs, and is more expensive than the Enttec.

Merging DMX

Lastly, we hit the topic of DMX merging.  Though much less talked about than splitting, DMX merging allows you to use 2 consoles on the same lighting rig, or use 1 dimmer rack for 2 rooms with 2 consoles, or other strange scenarios like that.

Note that ETC dimmer racks and many others have 2 DMX inputs, so you don’t have to merge to accomplish this.  Check out your lighting system before purchasing a merger, and make sure you can’t do what you need to without a merger!

merge dmx

From Fuzzy Gerdes on Flickr

Merging DMX is not a overly common thing to do, and so I’ll keep this brief and to the point.  You can merge DMX with a active “box” just like splitting DMX, but it sure does not work to use a “y” cable!  Using a “y” cable to merge DMX will cause your data to interact in ways you didn’t know it could as it is combining at different points in the electrical phase.  It just gets ugly.  Don’t do it.  Ever.  Thanks.

Anyways, before we get too complicated, know this.  DMX merging is like DMX splitting, and you’re gonna need a special box to make it happen.  Since DMX merging is not nearly as common as splitting, there are a lot less products on the market, and they are more expensive.  But, if you need to merge, you need to merge.

This merger by Leviton is a good buy, and merges DMX in a similar, but opposite way that a splitter splits.  Mergers have to choose internally what signal to use when there is a conflicting request, like both consoles bringing up the same channel at different levels.  The Leviton merger uses HTP, or highest takes precedence to determine this, but more expensive units let you choose between LTP and HTP.

Read more about HTP and LTP and how they work here.

Closing it all up

DMX splitting, converting and merging can either be a blessing or a nightmare.  If done correctly, these 3 data manipulations can really make your life easier, solve problems, and help make your lighting system less prone to errors.  Done incorrectly, and you’ll have a world of trouble on your hands – hopefully that’s not how you found this post!

Remember that even though it uses 3 pin cable sometimes, you can’t use a y-split like a microphone cable.  Keep this in mind, and you’ll go far.  Happy splitting, merging and converting!


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  • David says:

    We are using dmx for lighting in a restaurant and can’t discover all lights there is more than 32 do I need to devide them up. Thank you

    • David says:

      Hey David,

      This is most likely your problem, though it is very difficult to diagnose over the internet.
      Though I can’t say for sure, it’s most likely that your problem is at least partially caused by the high amount of fixtures in a single chain. I would definitely add a split.

      Thanks!
      -David


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