The 5 pin DMX Cable Religion

[dosxuk]

Another way to look at the "why not just use 3 pin XLRs - they're just connectors on a bit of cable" argument is to reply with "Why not use 16A Cee form connectors on a bit of mains flex - at the end of the day they're 3 pin connectors with some three core cable in the middle". I'm sure that over very short distances you could even make some bits of DMX kit work. At the end of the day, DMX is a standard which all DMX compaitable equipment should follow. Just because there are alternative connectors and cable does not mean they should be used.

[robloxley]

Here are some cables on eBay that seem to be far cheaper than even the ones that you make yourself that were pointed on in the forums. Are these not as good?

They appear to have cheap connectors and unspecified cable, so no.

[Ynot]

Having been away for a few days, and then read this whole thread, it seems that some people are missing one very important fact. DMX is a standard. It's the way in which things are done. If we can't all agree to adopt that standard, then there is no guarantee that things will continue to work as intended.

 

So if you want to use 3pin XLR connectors, or a different pin-out from everyone else, or some old cable that happened to be lying in your workshop, then go ahead. I don't care. Do what you want. but don't call it DMX, cos it isn't. It doesn't meet the standard. It might be close to the standard. It might vaguely resemble the standard. But since it doesn't meet the standard, it isn't DMX. It is "something that is not DMX".

 

Is that clear?

Sorry, Bruce - but I gotta step up here.

 

The DMX standard is the protocol. ie how the signals are sent and interpreted. If you connected the wires to the controller (desk) and the fixture by means of a 3-way choc-block at each end, the control protocol would STILL be DMX.

 

However, I'd agree that the standard interface quoted by the industry is 5-pin XLR.

 

What that means is that no matter how you connect the kit together, you're still using DMX signals to control to remote gear.

 

Personally, I'd much rather see a complete standard across the board - ie 5-pin all the way - but the realist in me accepts that we'll need converters and reversal leads for many years to come. It's just one of those things in this great game of life.

 

After all, a standard car tyre is round, black, with tread on the outside. But that doesn't stop manufacturers using different colour black (or white) rubber, different tread patterns, different diameter and widths, etc etc. They all work on a car, but some won't fit some makes, and some will stop you better in the wet. Doesn't mean they're anything less than a tyre, does it...?

 

 

Tony

[Oovis]

Lets start with some black magic. Take a random piece of cable, plug it into a test instrument called a TDR, and it tells you how long the cable is.

 

Every time I've had dealings with them in the day job (telecoms), the figure has been different to what it should have been, although they do tend to give you the distance to the nearest JCB!

 

 

Hmm, a handy tool then if you have a fetish for diggers! :P

[bruce]

The DMX standard is the protocol. ie how the signals are sent and interpreted. If you connected the wires to the controller (desk) and the fixture by means of a 3-way choc-block at each end, the control protocol would STILL be DMX.

 

However, I'd agree that the standard interface quoted by the industry is 5-pin XLR.

 

My understanding is that the 5-pin connector was specified within the spec - but as the USITT DMX512 spec and guidance notes are not available online, I cannot comment further. I could well be wrong. But if the connector was not specified, then it _should_ have been...

 

After all, a standard car tyre is round, black, with tread on the outside. But that doesn't stop manufacturers using different colour black (or white) rubber, different tread patterns, different diameter and widths, etc etc. They all work on a car, but some won't fit some makes, and some will stop you better in the wet. Doesn't mean they're anything less than a tyre, does it...?

 

That's not a very good analogy. There is no "standard" car tyre. A car tyre is designed for a specific vehicle, or group of vehicles - nobody would expect the tyre from my land rover to be able to be of any use on my wife's Golf cabrio...

 

DMX, on the other hand, is a communications protocol. It's intended to link devices together in a vendor-agnostic way. Varying the connectors and/or polarity doesn't help anyone.

 

I work in data communications. These days, everyone has encountered Ethernet - it's the ubiquitous way of joining computers, switches, routers and all the rest. You just plug it in and it works. I can't remember the last time I had an interworking problem. You don't have to worry about whether you're plugging an intel motherboard into a 3com switch or a linksys router.

 

But it wasn't always that way - I remember when we had to spend ages doing interoperability tests between equipment from different vendors, all of which nominally adhered to the same standard. We had huge "compatibility matrices", and bizarre situations where equipment from vendor A would interwork with B and C, but not D, unless there was also an E on the network...

 

These days are gone, but it took concerted pressure from the user community on the manufacturers to ensure that the standard - rather than the manufacturer's interpretation of the bits of the standard that they liked - was implemented.

[Ynot]

My understanding is that the 5-pin connector was specified within the spec - but as the USITT DMX512 spec and guidance notes are not available online, I cannot comment further. I could well be wrong. But if the connector was not specified, then it _should_ have been...

I understand what you're saying, and I can't make a 100% accurate statement about what's in the spec, but I'd be very surprised to find that USITT would make a categoric statement that "5-pin it is and 5-pin it shall be else it's not DMX", especially considering the likelihood that before it was fully adopted there were probably manufacturers fitting whatever took their fancy (probably for fiscal reasons).

That's not a very good analogy. There is no "standard" car tyre. A car tyre is designed for a specific vehicle, or group of vehicles - nobody would expect the tyre from my land rover to be able to be of any use on my wife's Golf cabrio...

OK - fair enough.

Here's another - alluded to in an earlier post on this thread.

The socket on my wall here has 230v on the live/neutral pins. The socket is rated at 13A max, with a 13A (theoretical value) trip at the distro and it has square pins. The plug I plug in, matched that socket, is fused at 13A and powers my wife's hairdryer, for eample.

 

If I were to swap that socket for a 15A round pin socket and the plug for a 15A plug, or even a 16A Ceeform socket/plug, I could still use the same cable, and power the same appliance. there would be no difference in the voltage available on the outlet. The basic spec of the signal (ie the electrickery) out of that socket is exactly the same if using the same appliance.

That's the point I'm trying to make - that whilst there arestandards of connectors, and each one can be specified in turn for different applications, it's the signal that is the overall standard in this sort of environment. In this example, it's 13A, 230V. For DMX, it's the DMX protocol. Changing the connector changes not the protocol.

 

DMX, on the other hand, is a communications protocol. It's intended to link devices together in a vendor-agnostic way. Varying the connectors and/or polarity doesn't help anyone.

 

I work in data communications. These days, everyone has encountered Ethernet - it's the ubiquitous way of joining computers, switches, routers and all the rest. You just plug it in and it works. I can't remember the last time I had an interworking problem. You don't have to worry about whether you're plugging an intel motherboard into a 3com switch or a linksys router.

 

But it wasn't always that way - I remember when we had to spend ages doing interoperability tests between equipment from different vendors, all of which nominally adhered to the same standard. We had huge "compatibility matrices", and bizarre situations where equipment from vendor A would interwork with B and C, but not D, unless there was also an E on the network...

Also :P I also work in the comms industry - and I can recall when the early KiloStream network terminating units were produced with sometimes three different interfaces on the back, depending on the client's needs. The spec actually stated for this showed, for example, RS232 as the interface - it described the actual plug and what wiring went where. Others were similar. But the basic transmission of data through that NTU was essentially the same, regardless of the plugs used. So yes, that's an example of two or more different standards for the same transmission protocol. It may be that this is what USITT has done - designed the transmission standard then stated therewas a standard INTERFACE in the 5-pin XLR. But there's nothing to stop anyone connecting the standard DMX signal in any way they choose, in a non-standard or Heath-Robinson way (as in 3-way choc-block!!)

 

Don't get me wrong - I think I've already said that I support 5-pin as the ideal (we recently wired in multiple DMX drops around the theatre, ALL in 5-pin) BUT I'm also not going to hold my breath waiting for big-boys Martin and all the little boys underneath them to cotton on and retrospectively change everything they've made and anything they make in the future. I also said I believed that albeit a small one, many lower-end manufacturers build using 3-pin simply because it's cheaper, and their gear isn't used in an error-sensitive environment (eg discos & clubs), so in their opinion, why should they change up?? (Devil's advocate, there!!)

[Oovis]

My understanding is that the 5-pin connector was specified within the spec - but as the USITT DMX512 spec and guidance notes are not available online, I cannot comment further. I could well be wrong. But if the connector was not specified, then it _should_ have been...

I understand what you're saying, and I can't make a 100% accurate statement about what's in the spec, but I'd be very surprised to find that USITT would make a categoric statement that "5-pin it is and 5-pin it shall be else it's not DMX", especially considering the likelihood that before it was fully adopted there were probably manufacturers fitting whatever took their fancy (probably for fiscal reasons).

 

Look at post #24 in this thread and you'll see a quote from the USITT DMX FAQ saying exactly that. You must use 5-pin connectors to call it DMX.

 

Here's another - alluded to in an earlier post on this thread.

The socket on my wall here has 230v on the live/neutral pins. The socket is rated at 13A max, with a 13A (theoretical value) trip at the distro and it has square pins. The plug I plug in, matched that socket, is fused at 13A and powers my wife's hairdryer, for eample.

 

If I were to swap that socket for a 15A round pin socket and the plug for a 15A plug, or even a 16A Ceeform socket/plug, I could still use the same cable, and power the same appliance. there would be no difference in the voltage available on the outlet. The basic spec of the signal (ie the electrickery) out of that socket is exactly the same if using the same appliance.

That's the point I'm trying to make - that whilst there arestandards of connectors, and each one can be specified in turn for different applications, it's the signal that is the overall standard in this sort of environment. In this example, it's 13A, 230V. For DMX, it's the DMX protocol. Changing the connector changes not the protocol.

 

Hmm.. If your trip is rated at 13A it's a very odd one. I would expect 16A or 32A. If it's 16A this would be a radial circuit so you could, in theory, swap the connectors like this. You'd have a trip 1A over the rating of the connectors though.

 

If, however, you're on a 32A trip your sockets are on a r1ng ma1n. British Standard 7671 says all sockets on this type of circuit must be of the type so there's still a standard to adhere to in this instance. You can't install 13, 15 and 16 as you suggest.

 

Being really pedantic, your socket has 230V across the phase and neutral pins, not on them....

 

Your argument is that DMX covers the protocol of data transmission, not the connectors, but the DMX page from the USITT site Here says this;

 

DMX512 is a standard that describes a method of digital data transmission between controllers and lighting equipment and accessories. It covers electrical characteristics (based on the EIA/TIA–485 standard), data format, data protocol, and connector type. This standard is intended to provide for interoperability at both communication and mechanical levels with controllers made by different manufacturers.

 

(My emphasis added)

 

I'll get my coat..

 

Edit; added link to USITT page

[maeterlinck]

They go further on the FAQ page:

 

Is any connector besides an XLR–5 allowed?

No ! Using anything besides the XLR–5 connectors as prescribed in all versions of the standard is not allowed and defeats the interoperability the standard is intended to provide. Equipment using an XLR–3 connector is not compliant with the standard and should not be marked as such. In very special circumstances, the ANSI version of the standard allows for the use of a non–XLR style connector. One of the provisions for this is that the manufacturer must supply an adapter.

From: http://www.usitt.org/standards/DMX512_FAQ.html#FAQ_05

 

I still think it's fair to say, that, as with other protocols (and the means to interpret them) there a is a degree of tolerance built in. We can use this tolerance to do things not technically allowed by the spec for whatever reason. My feeling is that these allowances are aimed at end users and not manufactures, hence Martin's 3pin usage is a pain in the arse.

 

 

Edit: To include the URL to the FAQ

[Ynot]

I'd be very surprised to find that USITT would make a categoric statement that "5-pin it is and 5-pin it shall be else it's not DMX"

Look at post #24 in this thread and you'll see a quote from the USITT DMX FAQ saying exactly that. You must use 5-pin connectors to call it DMX

 

Your argument is that DMX covers the protocol of data transmission, not the connectors, but the DMX page from the USITT site Here says this;

DMX512 is a standard that describes a method of digital data transmission between controllers and lighting equipment and accessories. It covers electrical characteristics (based on the EIA/TIA–485 standard), data format, data protocol, and connector type. This standard is intended to provide for interoperability at both communication and mechanical levels with controllers made by different manufacturers.

OK - I am therefore officially surprised! :)

 

Here's another - alluded to in an earlier post on this thread.

The socket on my wall here has 230v on the live/neutral pins. The socket is rated at 13A max, with a 13A (theoretical value) trip at the distro and it has square pins. The plug I plug in, matched that socket, is fused at 13A and powers my wife's hairdryer, for eample.

 

If I were to swap that socket for a 15A round pin socket and the plug for a 15A plug, or even a 16A Ceeform socket/plug, I could still use the same cable, and power the same appliance. there would be no difference in the voltage available on the outlet. The basic spec of the signal (ie the electrickery) out of that socket is exactly the same if using the same appliance.

That's the point I'm trying to make - that whilst there arestandards of connectors, and each one can be specified in turn for different applications, it's the signal that is the overall standard in this sort of environment. In this example, it's 13A, 230V. For DMX, it's the DMX protocol. Changing the connector changes not the protocol.

 

Hmm.. If your trip is rated at 13A it's a very odd one. I would expect 16A or 32A. If it's 16A this would be a radial circuit so you could, in theory, swap the connectors like this. You'd have a trip 1A over the rating of the connectors though.

 

If, however, you're on a 32A trip your sockets are on a r1ng ma1n. British Standard 7671 says all sockets on this type of circuit must be of the type so there's still a standard to adhere to in this instance. You can't install 13, 15 and 16 as you suggest.

Well, you missed the bit I've now highlighted in bold - the (theoretical value) bit - to allay just such an argument against saying "Well, it's a 32A trip anyway!" :P :D

Being really pedantic, your socket has 230V across the phase and neutral pins, not on them....

Yup - twas indeed - I'm sure you know what I meant, tho! ;)

 

At the end of the day, as I keep trying to point out, is that with ANY so-called 'standard' is only standard as long as the users want it to be. In the real world, things get changed. Yes, if we push hard enough, we, as an industry group, COULD change them for the better. But that takes time, effort, often money and always inclination, and to be perfectly frank, I can't see that many people being worried enough about this 3-pin/5-pin issue to make enough noise about it to make a real difference.... Can you?

 

So instead of worrying about it ad nauseam, let's just accept what can't (at this moment) be changed, make do with what we have, and adapt what we haven't, and just get on with the job in hand.

 

Fair enough?

 

 

They go further on the FAQ page:

 

Is any connector besides an XLR–5 allowed?

No ! Using anything besides the XLR–5 connectors as prescribed in all versions of the standard is not allowed and defeats the interoperability the standard is intended to provide. Equipment using an XLR–3 connector is not compliant with the standard and should not be marked as such. In very special circumstances, the ANSI version of the standard allows for the use of a non–XLR style connector. One of the provisions for this is that the manufacturer must supply an adapter.

 

Forgive me, but is this FAQ not just a schedule of opinions?

I don't have time to delve into it just now, but will take a look later, but certainly the quote above does appear to be just that - an interpretation of the standard.

 

The bit that makes me chuckle is the end bit...

In very special circumstances, the ANSI version of the standard allows for the use of a non–XLR style connector. One of the provisions for this is that the manufacturer must supply an adapter

Which says that it's OK to use non 5-pin XLR as long as the manufacturer supplies a converter. So does that mean it's DMX512 protocol up to the point where it's converted, and NOT after that?

Because that would be a rather ridiculous statement to make and support!!

 

By the way - I've also seen kit with inch & a quarter JACK sockets as DMX in/out (NJD Predator, for one).

Tony

[bruce]

The bit that makes me chuckle is the end bit...

In very special circumstances, the ANSI version of the standard allows for the use of a non–XLR style connector. One of the provisions for this is that the manufacturer must supply an adapter

Which says that it's OK to use non 5-pin XLR as long as the manufacturer supplies a converter. So does that mean it's DMX512 protocol up to the point where it's converted, and NOT after that?

No. It's simply saying that the external presentation for any DMX device should be 5pin. In "special circumstances" - and I'm guessing they mean things like wet or hostile environments - a different connector may be appropriate, but if a converter is supplied as part of the system, then the external presentation is still within the spirit of the standard.

[Oovis]

Forgive me, but is this FAQ not just a schedule of opinions?

I don't have time to delve into it just now, but will take a look later, but certainly the quote above does appear to be just that - an interpretation of the standard.

 

It's the interpretation of the standard by the people who wrote it.

[pritch]

If anyone wants me I'll be out the back, making up a 5-pin XLR to Powerlock cable.

[dbuckley]

I dont have the released version of the DMX512-A spec, but do have a draft version, and can state categorically that for a device to be called DMX512-A compatible it must use a 5 pin XLR.

 

Alternative connectors are allowed only when it is physically impossible to mount a 5 pin XLR on the product, and if you do use an alternative connector, it may not be any type of XLR (so XLR 3s ruled out again).

 

Going back into history, the 1990 spec specified that (Section 9, Connectors) "Where connectors are used, they shall utilize 5-pin "XLR" style microphone connectors" and in Section 11, Marking and Identification, "Equipment conforming to this standard may be marked and identified with USITT DMX512/1990 or DMX512/1990".

 

This isn't FAQ interpretation territory, since 1990 the (until very recently) current version of the DMX512 specification has mandated 5 pin XLRs. Those still using XLR 3s are already one and half decades out of date, how much longer will this madness continue...

 

It is possible the 1986 version of the standard was less stroppy on the issue, but I dont have that version to check.

 

And just another bit from the standard - for fixed installations, two pair cable is mandatory.

 

If anyone wants me I'll be out the back, making up a 5-pin XLR to Powerlock cable.

 

You'd be better off using Speakons, as then you can connect both pairs

[Matt Riley]

If anyone wants me I'll be out the back, making up a 5-pin XLR to Powerlock cable.

 

You'd be better off using Speakons, as then you can connect both pairs :P

 

powerlock = flippin big (mainly american used) 3 phase connector (the one you use when cee125 is too small, each core on seperate connectors, 400-600 amp capacity)

 

Powercon = neutrik 1 pair 16 amp (ish) connector similar to speakon

 

Lost in translation?

[dbuckley]

Lost in translation?

 

Yep. I saw PowerCon..... Perhaps (if I push hard enough) they'll mate :P