I was wondering if I could make my own DMX cables by soldering XLR ends on to CAT 5 network cable? Does anyone see any problems with that?
Thanks,
Corey
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I do. For dmx it needs to have a certain impedience rating. Now idont know cat 5 but I can tell you it prob. Won't work. And if it does you may end ip hurting your lights and also you may run into signal problems later on. My two watts on it. Sincerely,
Getting the data from point A to point B. Ah, so many ways to do that. So many wrong ways to do it as well.
DMX makes it tempting to do things the wrong way. Why? 3-pin DMX. Why? 3-pin DMX is wired the same as 3-wire balanced XLR microphone cables. And even more so, they look identical. You can't tell by looking at the cable unless you look at the cable itself.
Add to the confusion of XLR audio, where it's Pin 2 hot(+) and Pin 3 Cold(-), which is similar to DMX, which is Pin 2(+) and Pin 3(-). And in both cases, pin 1 is shell. The main difference is that DMX runs in the opposite direction as typical microphone cabling. No doubt the intention was to run it down an audio snake using an unused input channel.
Also keep in mind that Cat5 is typically re-assembled and re-sent one it hits a hub or switch completely. With DMX, while a fixture may try to repair a degraded signal, it's not a total "restoration". With Cat5, we're dealing with those bits in a more critical manner with tiny voltate differences. With DMX, it's what, 5 volts? I forget. All we need to see is "positive or negative" voltage, and a weak signal, as long as still in the proper phase, can be properly interpretted. With Cat5, weak signals that degenerate too much are flat out lost and discarded or generate a CRC or some other transmission/receive error.
But microphone cabling is at 600 ohms, dealing with very low impedence devices. DMX is 120 ohms, properly rated for data transmissions.
But wait, Cat 5 is a data cable. Right. And how does it work? Well, Pin 1 is TX+ while pin 3 is TX-, Pin 4 is RX+ and Pin 5 is RX-. More twists per foot. More is better, right? Right, but we're talking different types of signalling.
Why do we have + and - signals? Simple. Same reason why we do that in audio. With Pin 2 + and Pin 3 -, the signal is transmitted down the wire with Pin 3 being 180-degrees out of phase. At the console, the signal is recombined, and any noise would have been induced in phase, and when the Pin 3 signal is brought back in phase, the noise is removed and we have a clean(er) signal.
This same principle applies for why DMX does the same thing. When driving a signal at what can be typically LONGER cable runs than would be typically data approved(we like SHORT cables for serial connections, the shorter the better), it is necessary to do the + and - signals to ensure greated integrity. When the signal hits a DMX fixture, it may clean up the source signal a tiny bit before passing it along IF the fixture is on. Otherwise, it passes it through untouched.
But isn't ethernet and DMX digital? Right. Both are. But, DMX is shielded cabling, trying to keep that RF out. DMX also doesn't have any error correction in the protocol, it's a one-way stream. The shield is there to try to keep out RF amd EM interference, but mainly RF.
In the case of ethernet, we're dealing with significantly higher data speeds and significantly smaller yet faster data on the wire. Using Layer 1, we determine topology(say, cat 5, so we're using hubs or switches), Layer 2 we establish framing and transport of those packets, and when we climb up to Layer 3, we get to the TCP portion(yes, UDP) portion of the TCP/IP protocol, which includes error correction protocols. If a packet drops, the remote end says "hey, I didn't get it" and then your end sees this and re-transmits. Repeat until final check-sums are reported and are in agreement. DMX doesn't do any of this.
Also, Cat 5 is unshielded, but the impedence of the cabling and twists per foot help get rid of any induced noise into the wires. Cat 5 has maximum single cable run distances, which can be exceeded but are used mainly to establish smart data practices. You can easily run a Cat 5 cable 200 yards with no problem. Would I do that? No. But I do have a pair of 200-foot cables Cat5e cables that I use for a video application.
So, while the Cat 5 could or would work, the lack of a shield is going to result in errors. The wrong impedence loading will also result in errors. Do you want your lights freaking out during an event? cat5 is cheap. Bought in bulk, DMX cable is cheap. I just bought a 300foot reel of Accucable at a really good price. I just am trying to do things right, and I don't want to run DMX down my 56-channel audio whip anymore. I'll run another single cable next to my whip. So, what do I have? 1 Cat 5 for a video app(moving to up to 4), a Cat5 for my Aviom system, and a DMX cable. These run next to a 56-pair audio whip. While I have been doing fine using audio XLR cabling for my DMX application, I just dont' want to do that anymore. If you know me better, you know I strive for the right way and work hard to do it right, so I can be lazy later.
My advise: don't do it.
Just keep in mind, the original DMX application was using 5-wire XLR connectors, but 3 points were not used. It was still Pin1 shield, 2 TX+, 3 TX-. The 5 pin to 3-pin adaptor is simply a direct move to the appropriate connector. But 5-pin XLR is more expensive than 3-pin XLR. Not to be critical, but we should stick to the original DMX specification that specified 5-pin and this would end these issues.
Wow, that sure is a long way to say no. Maybe I should have added a spoiler alert!
DMX makes it tempting to do things the wrong way. Why? 3-pin DMX. Why? 3-pin DMX is wired the same as 3-wire balanced XLR microphone cables. And even more so, they look identical. You can't tell by looking at the cable unless you look at the cable itself.
Add to the confusion of XLR audio, where it's Pin 2 hot(+) and Pin 3 Cold(-), which is similar to DMX, which is Pin 2(+) and Pin 3(-). And in both cases, pin 1 is shell. The main difference is that DMX runs in the opposite direction as typical microphone cabling. No doubt the intention was to run it down an audio snake using an unused input channel.
Also keep in mind that Cat5 is typically re-assembled and re-sent one it hits a hub or switch completely. With DMX, while a fixture may try to repair a degraded signal, it's not a total "restoration". With Cat5, we're dealing with those bits in a more critical manner with tiny voltate differences. With DMX, it's what, 5 volts? I forget. All we need to see is "positive or negative" voltage, and a weak signal, as long as still in the proper phase, can be properly interpretted. With Cat5, weak signals that degenerate too much are flat out lost and discarded or generate a CRC or some other transmission/receive error.
But microphone cabling is at 600 ohms, dealing with very low impedence devices. DMX is 120 ohms, properly rated for data transmissions.
But wait, Cat 5 is a data cable. Right. And how does it work? Well, Pin 1 is TX+ while pin 3 is TX-, Pin 4 is RX+ and Pin 5 is RX-. More twists per foot. More is better, right? Right, but we're talking different types of signalling.
Why do we have + and - signals? Simple. Same reason why we do that in audio. With Pin 2 + and Pin 3 -, the signal is transmitted down the wire with Pin 3 being 180-degrees out of phase. At the console, the signal is recombined, and any noise would have been induced in phase, and when the Pin 3 signal is brought back in phase, the noise is removed and we have a clean(er) signal.
This same principle applies for why DMX does the same thing. When driving a signal at what can be typically LONGER cable runs than would be typically data approved(we like SHORT cables for serial connections, the shorter the better), it is necessary to do the + and - signals to ensure greated integrity. When the signal hits a DMX fixture, it may clean up the source signal a tiny bit before passing it along IF the fixture is on. Otherwise, it passes it through untouched.
But isn't ethernet and DMX digital? Right. Both are. But, DMX is shielded cabling, trying to keep that RF out. DMX also doesn't have any error correction in the protocol, it's a one-way stream. The shield is there to try to keep out RF amd EM interference, but mainly RF.
In the case of ethernet, we're dealing with significantly higher data speeds and significantly smaller yet faster data on the wire. Using Layer 1, we determine topology(say, cat 5, so we're using hubs or switches), Layer 2 we establish framing and transport of those packets, and when we climb up to Layer 3, we get to the TCP portion(yes, UDP) portion of the TCP/IP protocol, which includes error correction protocols. If a packet drops, the remote end says "hey, I didn't get it" and then your end sees this and re-transmits. Repeat until final check-sums are reported and are in agreement. DMX doesn't do any of this.
Also, Cat 5 is unshielded, but the impedence of the cabling and twists per foot help get rid of any induced noise into the wires. Cat 5 has maximum single cable run distances, which can be exceeded but are used mainly to establish smart data practices. You can easily run a Cat 5 cable 200 yards with no problem. Would I do that? No. But I do have a pair of 200-foot cables Cat5e cables that I use for a video application.
So, while the Cat 5 could or would work, the lack of a shield is going to result in errors. The wrong impedence loading will also result in errors. Do you want your lights freaking out during an event? cat5 is cheap. Bought in bulk, DMX cable is cheap. I just bought a 300foot reel of Accucable at a really good price. I just am trying to do things right, and I don't want to run DMX down my 56-channel audio whip anymore. I'll run another single cable next to my whip. So, what do I have? 1 Cat 5 for a video app(moving to up to 4), a Cat5 for my Aviom system, and a DMX cable. These run next to a 56-pair audio whip. While I have been doing fine using audio XLR cabling for my DMX application, I just dont' want to do that anymore. If you know me better, you know I strive for the right way and work hard to do it right, so I can be lazy later.
My advise: don't do it.
Just keep in mind, the original DMX application was using 5-wire XLR connectors, but 3 points were not used. It was still Pin1 shield, 2 TX+, 3 TX-. The 5 pin to 3-pin adaptor is simply a direct move to the appropriate connector. But 5-pin XLR is more expensive than 3-pin XLR. Not to be critical, but we should stick to the original DMX specification that specified 5-pin and this would end these issues.
Wow, that sure is a long way to say no. Maybe I should have added a spoiler alert!
In regards to your link:
I will read those papers later.
But honestly, if they want to ensure acceptance, they could develop a DMX-512 over Cat5 protocol, which would require Cat5(or better) as a transport medium, while the original DMX signal would have to be modulated and demodulated(uh, modem...) at the sending and receiving ends, respectively.
Now, we're talking permanent installations. Come on, a spool of Accucable is 300 feet, which is what I bought. The investment is trivial. Pop 5 pin connectors on it and have a 3-pin adaptor handy for each end. If some show use multiple DMX runs(say, opener and main), run 4 DMX runs. Again, we're talking trivial expenses in the bigger scheme of things.
The rest of use are "Road Warriors" and have to roll in, set up, do show and pull it down and roll back out. Chances are if a tour rolls in, they ain't gonna use house wiring anyways. They'll even run their own com cables for their intercomm.
If you're building facilities, just think ahead with planning. Just run extra cabling, it NEVER hurts.
I'm all for saving money. This ain't it. Need a good guy to talk to about getting DMX cabling? I'll hook you up.
I will read those papers later.
But honestly, if they want to ensure acceptance, they could develop a DMX-512 over Cat5 protocol, which would require Cat5(or better) as a transport medium, while the original DMX signal would have to be modulated and demodulated(uh, modem...) at the sending and receiving ends, respectively.
Now, we're talking permanent installations. Come on, a spool of Accucable is 300 feet, which is what I bought. The investment is trivial. Pop 5 pin connectors on it and have a 3-pin adaptor handy for each end. If some show use multiple DMX runs(say, opener and main), run 4 DMX runs. Again, we're talking trivial expenses in the bigger scheme of things.
The rest of use are "Road Warriors" and have to roll in, set up, do show and pull it down and roll back out. Chances are if a tour rolls in, they ain't gonna use house wiring anyways. They'll even run their own com cables for their intercomm.
If you're building facilities, just think ahead with planning. Just run extra cabling, it NEVER hurts.
I'm all for saving money. This ain't it. Need a good guy to talk to about getting DMX cabling? I'll hook you up.