Network hub as DMX splitter?

[Snowcat]

'lo again folks.

Have been asked to setup a small scale "permanent" install into the schools assembly hall and was intending to use the "Cat5e as DMX line" trick. Unfortunately they're being a little difficult when it comes to buying DMX splitters to allow for the distances and multiple directions I'm going to have to run cables in.

However, it turns out we have a stockpile of obsolete network hubs (ie - signals at one port get mirrored to all others) that are laying around doing nothing and it's got me thinking...

Could a normal Cat5e HUB (not switch) be used as a DMX splitter?

Before I break out the cables and soldering iron, Has anyone tried this before me? Thoughts? Warnings? Better way of doing this?

Thanks as always!

[remco_k]

Could a normal Cat5e HUB (not switch) be used as a DMX splitter?

No.

DMX is about the same as RS485, and not ethernet.
Using a network hub (or switch) will not work at all. I even think some things might die.

You _really_ need a DMX splitter, and for each cable end a DMX terminator.
If you have real short cable runs (less than a few meters) you could think of a home made passive DMX splitter. Wich I do not prefer by the way...
Can you give us more info about the complete system you are about to install?
All cable lengths and runs?

[Snowcat]

Damn... I was worried about that. Quietly hoped that the hub would simply pass on the data without trying to interpret it (The hubs I'm thinking of are a good 10 years old at least).

The assembly hall rig is effectively a larger version of what I have in the Studio Theatre here. :-

an ancient set of parcans and fresnels controlled by a DMX dimmer pack. Old skool Gels and clamps agogo
8x Stairville PAR64 LED Parcans
2x Stairville MV250H moving heads mounted to vertical bars halfway along each wall

The hall itself is the "traditional" 2 badmington courts wide x 1 long with a raised stage at one end and a 5 row deep balcony at the other. I'm intending to have the control point at the centre front of the balcony overlooking the floor and stage.


Apologies for the crappy old photo. Only one I have to hand.

With the lack of splitters, I'm thinking of running the daisy chain anti-clockwise around the room as you see it there.
Leave a long loose coil on the balcony (that can be packed away from mischief makers during the day), across the top of the curtain rail and cutting down at the vertical bar, back up and along to a disused speaker grille I can poke a hole through to get back stage. Can be less elegant backstage but need to get the Dimmer pack (Massive old Strand thing with retrofit DMX) at ground level and then back up into the ceiling for the the LEDs. After that, back out the other Grille then curtain rail and opposite Vertical bar on the way back.

To me, that's one helluva run for a single line and there's the risk of a single bad connection or fixture killing the entire rig. I also have to allow for hired equipment that occasionally gets linked into the same system for larger shows and the like (a REAL High School Musical for instance. ). In a perfect world, I would have a splitter connected directly to the interface and then run a backbone line along either wall to meet roughly in the middle backstage. Maybe use splitters to divert DMX physically up or down to reach the fixtures themselves.

A signal break on one side would hopefully be covered from the opposite side. A 2 pronged attack rather than a long lap of the room.

In the grand scheme there aren't a massive number of fixtures but we're talking maybe 150-200+ metres of cable once all the detours are accounted for. The network hubs were previously used to provide data for the boarding houses on the edge of campus so I know they would be capable of getting a signal that distance. I've also been busy soldering together DMX terminators after realising my mistake before...

Unfancy but reliable equipment preferred here. Very much a Thomann junkie since I started working at the School.

[Snowcat]

Looks like I'm going to be pricing wireless equipment after all. The head high-ones have nixed any setup that involves visible cables or ducting. *facepalm*

There are crawl spaces and myriad small tunnels etc underneath the surface but running cables to everywhere I need is going to be a nightmare. Also, I'm not allowed to run ANYTHING up there without a fully qualified sparky with me and that's going to mean even MORE money. The joys of HSE and insurance...

Looking like 1x Transmitter and 3x receiver (Left bar, Right Bar and main backstage). At least I won't have any problems with the control booth location.

Thanks again for the advice!

[Snowcat]

... and here I am again a few months later and post show.

In the end, I managed to run a trio of DMX splitters (Backstage, Left and right wall on long leads and a third servicing 2 temp towers just in front of the balcony). The "Permanent" part being limited to the left and right walls being hung and DMX'd along the top of the curtain rails then temp fly-leads to the control point @ centre balcony. the 2 moving heads (Stairville MV-250H) have their own auto paterns when not controlled which is enough for proms/parties etc. Plug into the mains and let them run...

I also got lucky and managed to find an ancient backbone line that already ran from the balcony to backstage. Cat5e based that I simply re-ended as 3-Pin XLR/DMX. The result was ugly as sin but works well enough for what I needed. For the Senior school play that began this project a small amount of kit was hired in and then everything Frankenstein'ed together and programmed within Freestyler. I would've preferred a lot more time and a lot more control but the end results seem alright.

("After Juliet" - Dollar Academy, March 2009 - Pictures taken throughout rehearsals and show)











Apologies for the lack of video but hopefully these shots ("Borrowed" from the Schools own website) give a taste of the end result.

Thanks again for everyones help! I'll probably be by again when the next show comes around...