DMX... adapters/ termination /pockettester

[Haytech]

To connect some DMX devices it´s useful to have some adapters.

 

5pin male XLR to 3pin female XLR

3pin male XLR to 5pin female XLR

 

they are available at your wholesalers, or you solder your own:

 

take some digital cable (110 ohms),NCMX5, NCMF3 or NCMX3, NCFX5

 

configuration of full patched USITT1990:

 

configuration of half patched USITT1990 (most used DMX connection):

 

configuration (Adpater):

the 3pin XLR connections don´t match with USITT1990 but they are tolerated in the industry.

[ice]

And if you want to do it right; use proper DMX wiring (that has a resistance of 110 ohms) and a terminator (120 ohms specificated by RS-485).

 

This is a good scheme for a terminator:

 

It should be soldered between the data- and data+ (2 and 3) and uses 2 220 ohm resistors, and one multicoloured LED. By placing the resistors in a parallel connection they will resemble one ~110 ohm resistor, and the LED is going to tell you what you're broadcasting. All channels 0 will give colour 1, all channels 255 will give colour 2, and everything in between... you get that, right?

 

Proper wiring solves a load of problems with DMX, it's simple but delicate protocol! Long live ethernet, wohoh!

[Haytech]

if you want to do it right; use proper DMX wiring (that has a resistance of 110 ohms)

 

Indeed :!:

[daoops]

hmm, I think I actually read in the DMX512 page where they just had a test about the differense between CAT5 and DMX cable. And they found none, except the quality when using it for outdoor and traveling. For installation they actually recommended CAT5 cable.

[PatrickK]

Since cat 5 cable comes in two flavours, did they use shielded or unshielded cable?

I assume they used shielded, but let's get it straight before anyone buys a couple of miles of unshielded cable. :wink:

[daoops]

Here is the test made from ESTA

 

http://www.esta.org/tsp/DMXoverCat5_P2.pdf

 

Also a link to alot of DMX512 stuff

 

http://www.dmx512.com

 

Moderation: DMX512 link corrected

[ice]

Why use CAT5 instead of DMX wiring? Perhaps it's cheaper (I don't know), but that would be the only advantage I could think of. Don't get me wrong; we use it too, but we've connected several XLRs to it so there only one cable needed for DMX, smoke and haze channels (I don't run smoke and DMX off the console).

[Kirkup_xp]

Cat5 is extremely cheap compared to 'proper' DMX cabling. Another reason is that many new buildings have Cat5 prewired around the building.

If you had a 4 universe console, you could (I assume*) use the 4 pairs in Cat5 to provide the 4 signals? That could certainly be cheaper than 4 runs of 110ohm!

 

*I haven't checked out the practicalities of this, so don't take my word as gospel.

[daoops]

Here in norway is under half the price with Cat5 cables. And you can actually run 2 DMX cables in one shielded CAT5 cable. In other words. Lets say you are installing a concert stage. It's about 100m from FOH to the stage. And you need at least 2 DMX universes. This would have alot to say in money if you were using CAT5 vs. DMX cable

[ice]

Anyone has a proper conclusion for that article? It gives the sheets and test-results, but I can't make nothing useful out of that with my little knowledge of electric wiring. Thanx in advance.

[Haytech]

Hi,

Cat5/7 shielded twisted pair cables are suited for installation purposes.

For example: SFTP4x2xAWG24

 

Other AES/EBU 110Ω cables are better for "live" situations as they are "flexible"

 

We use normal microphone cables for DMX connections as we don´t want to build up a seperate DMX cable park works fine too.

This option dosn´t match the USITT1990 nor DIN5693

[daoops]

Don't the manufactors say that regular XLR (microphone) cables is not to be use as DMX ? But that is probably because of the resistance.

And there is the question.. If you use a cable that has to low or high resistance, is it possible to custombuild a termination plug to suit the DMX requirements ?

And normally it's only special fixtures that demands this.

 

"We use normal microphon cables for DMX connections as we don´t want to build up a seperate DMX cable park works fine too. "

 

It works fine but it's unstable. The dimmers may start to flicker, and you can damage fixtures like movingheads and scanners.

 

The thing with CAT5 cables that I really like is that you can get hold of cables with 4,8, 12,16, and up to 256 pairs. So you can actually have in one cable (and it is actually not that expencive), 102 DMX512 and 170 DMX256 cables in one cable Thats what I call a multi-cable :twisted:

And you can build the DMX into a patch-system, so that you are preperd for Ethernet, ChilliNet and the other new systems. You can even combine it with the sound. And all in one cable, with shielding enough for them all.

And the signal won't even leak.

 

Think this was a little off-topic now though, but...

[ice]

Lol, now everyone is going to buy CAT5 cable anyway; you have to when you go ethernet! The multi-cable is indeed very useful as we currently use it the same way.

I don't really get the argument of 110 ohm cables being more flexible; we've got some CAT5 wiring for AVIOM systems which is just as flexible as our DMX wiring?

[Haytech]

It works fine but it's unstable.

we use microphone cables in live situations for DMX since 10 years and it works stable.

 

The dimmers may start to flicker, and you can damage fixtures like movingheads and scanners.

Our DMX system (22 devices) hasn´t such problems with the DMX wiring.

How do I damage my scanners and movinghead´s with a wrong DMX signal of max. current DC5V ?

[daoops]

Our DMX system (22 devices) hasn´t such problems with the DMX wiring.

How do I damage my scanners and movinghead´s with a wrong DMX signal of max. current DC5V ?

 

Basic because of the simple formula.

 

Resistance*Current=Voltage

 

In other words.. if you need DC5V and have less resistance.. Well then the current will be higher to meet the required voltage. Then the fixture will get other inputs than it is manufactured for. Therefor.. It will work, but for how long ?? And different electronic equiptment act's different when this happened.

And other will do just fine. So it isn't said that it will be damaged, but CAN be damaged.

[Haytech]

ThankÂs Daoops for tutoring me ohmic laws ...

 

DMX - is a inverted signal of DMX + so in the cable accures due to capacitance a pulse.

110Ω Cables are used to minimize the possibilities to get a own-pulsing cable.

 

To match european laws driver chips have to be 15kV electrostatic discharge save.

 

Some of the fixtures driverchips such as LTC485 doesn´t have this protection.

[Haytech]

Here are is my DMX Tester works very fine ...

 

[bemi]

Hi,

 

as i understand the only prob about microphone-cables as DMX-Lines is the wrong impedance. This results in reflections inside the cable, so that the receiver (probably) may not receive a proper signal (that may result in wrong DMX-values). And wrong DMX-values may destroy Scanners or Moving-Heads ("flickering pan, tilt, beamshape" may be harmful).

 

In addition to that there may be peaks on the DMX-Line, but maximum 10Volts (when 2 +5V-Peaks cross each other), but that won't destroy any DMX-Inputs, IMHO. Besides you have a signal loss because of the wrong impedance.

 

Because of the small difference of impedance DMX(AES-EBU)-Cable/Microphone-Cable (110/perhaps 90-95) you can ignore these problems. Most important: terminate your DMX-Line (otherwise you really have reflections)!

[frogsurf]

Lol, now everyone is going to buy CAT5 cable anyway; you have to when you go ethernet! The multi-cable is indeed very useful as we currently use it the same way.

 

No need to daisy chain with ethernet. You can octopus it or chain a signal using hubs. Not to mention the massive format...

 

It works fine but it's unstable.

we use microphone cables in live situations for DMX since 10 years and it works stable.

 

The dimmers may start to flicker, and you can damage fixtures like movingheads and scanners.

Our DMX system (22 devices) hasn´t such problems with the DMX wiring.

How do I damage my scanners and movinghead´s with a wrong DMX signal of max. current DC5V ?

 

Some types of fixtures are fickle to cross talk with unsheilded data wire. Mostly low end stuff like technobeams etc...

[ice]

And wrong DMX-values may destroy Scanners or Moving-Heads ("flickering pan, tilt, beamshape" may be harmful).

 

A scanner or movinghead calculates the movement it has to make to get from current to new position. That means flickering signal does make the fixture unusable, but it won't destroy it. I'll simply calculate movement to the next position, but before it reaches that position it has to recalculate to the new position. Exactly the same as a nice clean fade, only the endpoint keeps on changing rapidly.

 

It's a common mistake that only low-end stuff would be affected by bad cabling. Highend fixtures usually have more sensitive signal sensing and thus are more likely to react to a bad signal. Low end equipment uses less sensitive readings in combination with algorithms which make sure that doesn't affect operation. I've allready experienced a rig of new MAC250's and old 518 scanners with a long, unshielded microphone calbe. The new macs wouldn't react, pro518 worked like a charm; new proper cable and terminator fixed everything.

[Morn]

A question came up for myself when reading this...

 

With how many Ohm do terminate your microphone cable DMX line?

[Franck]

120 Ohm

 

Microphone cables are not the best idea. Look for proper DMX data cables.

 

By the way... nice tool for DMX testing: http://www.zero88.com/en/products/3/87