Max length of running a dmx daisy chain.
- Thread starterstonehedge99
- Start date
Hi Stonehede99
Buy the Chinese DMX cable. The fact that you are using equipment that uses 3 pin XLR sort of desinates that it isn't the top of the line. The Chinese 120 ohm cable will be about as good as you are going to find, that you can get in, or shipped to Sri Lanka.
You will have to forgive many who post on CB. They can tend to be a bit snobbish, when it comes to DMX and it's use. In an ideal world their snobishness is good. Also their comments are good and valid for many of the readers of this type of post. Especially those who live where they can get the best. Many of the CB readers are trying to function with a very tight budget. There are some things that can be cut in quality in order to save a buck or two. DMX is one of those things in theatre lighting that the user should go with the best they can afford.
In the case of places where most of this equipment is not available or is just now becoming available, you go with the best that you can get. Many who have posted in this thread have no idea of the situation in Sri Lanka. While much of what has been posted is good advice, it ignores that your choices are probably Chinese DMX cable of slightly less quality, Cat 5, audio cable zipcord or fence wire. The Chinese DMX cable is probably your best bet of what is available to you.
Tom Johnson
Buy the Chinese DMX cable. The fact that you are using equipment that uses 3 pin XLR sort of desinates that it isn't the top of the line. The Chinese 120 ohm cable will be about as good as you are going to find, that you can get in, or shipped to Sri Lanka.
You will have to forgive many who post on CB. They can tend to be a bit snobbish, when it comes to DMX and it's use. In an ideal world their snobishness is good. Also their comments are good and valid for many of the readers of this type of post. Especially those who live where they can get the best. Many of the CB readers are trying to function with a very tight budget. There are some things that can be cut in quality in order to save a buck or two. DMX is one of those things in theatre lighting that the user should go with the best they can afford.
In the case of places where most of this equipment is not available or is just now becoming available, you go with the best that you can get. Many who have posted in this thread have no idea of the situation in Sri Lanka. While much of what has been posted is good advice, it ignores that your choices are probably Chinese DMX cable of slightly less quality, Cat 5, audio cable zipcord or fence wire. The Chinese DMX cable is probably your best bet of what is available to you.
Tom Johnson
stonehedge99
Active Member
Hi Tom,
Thanks for understanding my situation and explaining. Will this chinese cable @ 120 ohms work for a 360 ft run with 20 fixtures on that line ?
I actually did feel the talk about inverse law and square wave went over my head in terms of understanding. I understand they exist, but like you said in places where they have access to the best. Here i dont even know if the dmx cable i order from the USA will even reach me. The technicians here at my place are mostly illiterate, can speak proper english, at least the tech guys in the dmx lighting world and suppliers etc are hardly well read, most of them actually manpower labourers.
I think anyhow the technical perfection detail will still help those that are looking for it when they visit this thread.
Regards
Thanks for understanding my situation and explaining. Will this chinese cable @ 120 ohms work for a 360 ft run with 20 fixtures on that line ?
I actually did feel the talk about inverse law and square wave went over my head in terms of understanding. I understand they exist, but like you said in places where they have access to the best. Here i dont even know if the dmx cable i order from the USA will even reach me. The technicians here at my place are mostly illiterate, can speak proper english, at least the tech guys in the dmx lighting world and suppliers etc are hardly well read, most of them actually manpower labourers.
I think anyhow the technical perfection detail will still help those that are looking for it when they visit this thread.
Regards
The DMX standard says that with 120 ohm cable and proper termination that you should be able to daisy chain up to 32 receiving devices and for much greater distances than 360 feet.
Having said that, here are a few things to watch out for. The more connectors in the chain, the more possibility for problems. Not all devices that use DMX for control signals use the proper chips for that task. Some of the very cheap DMX devices use digital circuitry that is not RS485 tranceivers. The more of these type of devices in the chain, the greater the potential for problems. I personally don't know these devices, but they have been mentioned in general on the lightnetwork forum by Mats Karlsson, who I consider to be just about the most intelligent overall lighting person around.
The solution to your problem if 20 devices causes too much load, is an optosplitter. I realize that might not be the easiest thing to purchase in Sri Lanka. There are many different splitters available. The best is Doug Fleenor, but there are some pretty good Chinese units marketed under Elation, neo-neon and ohers. I think that your best bet might be an Enttec. That might not be the correct spelling, but I believe that it is built in Australia, so it might be easier to purchase than something from the US or Europe. It has one input and 4 outputs. It comes with either 3 or 5 pin XLRs, and sells for $100US in the US.
I would go with the Chinese cable, use the longest continuous lengths on the long distances, to reduce the number of connectors. Check each device to make sure there isn't a terminator switch that is turned on. Terminate the end of the line with a proper 120 terminator or a resistor across pins 2 and 3. Then if you have a chance, purchase an Enttec optosplitter and have it ready to upgrade your system to a greater reliability as you go along.
I hope this helps, just use common sense and check your install as you go.
Tom Johnson
Having said that, here are a few things to watch out for. The more connectors in the chain, the more possibility for problems. Not all devices that use DMX for control signals use the proper chips for that task. Some of the very cheap DMX devices use digital circuitry that is not RS485 tranceivers. The more of these type of devices in the chain, the greater the potential for problems. I personally don't know these devices, but they have been mentioned in general on the lightnetwork forum by Mats Karlsson, who I consider to be just about the most intelligent overall lighting person around.
The solution to your problem if 20 devices causes too much load, is an optosplitter. I realize that might not be the easiest thing to purchase in Sri Lanka. There are many different splitters available. The best is Doug Fleenor, but there are some pretty good Chinese units marketed under Elation, neo-neon and ohers. I think that your best bet might be an Enttec. That might not be the correct spelling, but I believe that it is built in Australia, so it might be easier to purchase than something from the US or Europe. It has one input and 4 outputs. It comes with either 3 or 5 pin XLRs, and sells for $100US in the US.
I would go with the Chinese cable, use the longest continuous lengths on the long distances, to reduce the number of connectors. Check each device to make sure there isn't a terminator switch that is turned on. Terminate the end of the line with a proper 120 terminator or a resistor across pins 2 and 3. Then if you have a chance, purchase an Enttec optosplitter and have it ready to upgrade your system to a greater reliability as you go along.
I hope this helps, just use common sense and check your install as you go.
Tom Johnson
Tex
Active Member
High End Systems would disagree. 3 pin connectors show up in all levels of dmx devices, even though they don't meet the standard.
Sent from my GT-P7510 using Tapatalk
True, very true, but they are even changing and must have read the USITT standards.
Don't get me wrong, I have several items that started out 3 pin, but I have changed their connectors to 5 pin. There are many decent devices that use 3 pin XLR, but at the same time, the really crappy ones almost never use 5 pin XLR. The whole 3 pin versus 5 pin is a discussion/argument that will persist for ever and is really good material for folks that would rather argue lighting than actually spend all of their time doing it. Oops! did I just open a huge door to get flamed. Oh well, I have an asbestos suit made from all that wire I took out of Electro-Control fresnels, in order to bring them up to date.
Tom Johnson
The opto-splitter in question is this one. Enttec sells it for 125 USD. You will most likely also need a 3-pin to 5-pin adapter, for instance this one, if you want to use the opto-splitter with your 3 pin cable. I'm not familiar with the general price of shipping or customs to Sri Lanka, but I'm guessing it's probably a lot. Unfortunately, you won't find anything reliable cheaper (barring Chinese off-brand stuff, which is a dice roll).
Good luck with all of this.
stonehedge99
Active Member
Will this product help. Its a little cheaper too..
It splits one input into 8 outs and amplifies the signal too ???
Will this help ?
Thanks
When it comes to splitters, there are ones that just split the signal by using multiple transceiver chips. One is used for the input or receiving the signal. The output of that chip is then sent to how many ever outputs through one chip per output in the transmission mode. This type of splitter uses only one power supply for all of the chips.
The most advanced splitter goes a bit further. It uses one chip for receive, one each chip for each output to transmit, but also uses and isolation chip on each of the output chips and uses separate power supplies to power the input circuitry, and one for each output. Those are referred to as Optoisolated splitters or generally in a shorter form as "optosplitter".
The advantage of the opto splitter is the security it provides to the devices attached. Let us say that you have many different types of devices that require the DMX signal. You may want to put all of the moving heads of one manufacture on one output. On another output, you may want to put all of your scroller power supplies. Other devices such as "shoebox dimmers" may go on several different outputs based on their location. Now if say one of the shoebox dimmers shorts internally putting mains power on the DMX line, It will only destroy the other devices on that output of the optosplitter. All of the devices on the other outputs will be protected because there is no direct signals with voltage on them that connect between ouputs.
The type that has no isolation through optical coupling risk the possibility of every device being damaged when one device shorts internally or cables shorting to higher voltages.
The device that you are looking at on ebay is almost for sure to be the non-optoisolation type distributor. Considering the price and the single power input. That having been said and considering the low cost and the 3 pin connectors, that you seem to have on the rest of your system, and the fact that they can probably ship from China to Sri Lanka, more easily than from the US or Europe, I would say that it would be worth your while. It mentions in the add and the broken english, "485". I think that means that it is splitting and distributing RS485, the transmission standard of DMX.
While isolation is desireable, having the ability to splitt some of your signals will certainly help with the distances. I think that I am going to buy one just to have as a backup for other things that I do at my theatre. I have 24 outputs of DMX, all isolated through out my theatre, and a couple of 4 output portable that I can use as neccessary. The price of that Chinese one is low enough for me to just buy one and take it apart to see how they have done it.
Tom Johnson
stonehedge99
Active Member
Hey Tom,
I did a lot of searching and found that unit. It seems to be very cheap. But This unit seems to have protection for upto 1000v on the dmx line, something similar to opto isolation ????
Anyway heres one for almost the same price in the UK and this one is from a very prominent theatre supply house with the best part being this IS Opto Isolated. Check it out here.
Thanks
I did a lot of searching and found that unit. It seems to be very cheap. But This unit seems to have protection for upto 1000v on the dmx line, something similar to opto isolation ????
Anyway heres one for almost the same price in the UK and this one is from a very prominent theatre supply house with the best part being this IS Opto Isolated. Check it out here.
Thanks
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Both of the units that you indicated would probably be a better choice than the Chinese one that we discussed earlier. The one from the UK appears to have a drawing on the case, that would indicate that there is power isolation as well as the DMX signal isolation. It would be my guess that there are two seperate outputs that are power isolated, and each of those outputs has two seperate DMX outputs. This is common of the Elation splitters, only they do eight outputs divided into to four power isolations.
The New Zealand unit uses USB power which is 5 volts DC, and is the same voltage required to operate the DMX tranceiver chips. I therefore doubt that it has power isolation.
If I were you, I would purchase which ever unit can be delivered to Sri Lanka the easiest and the quickest. I think any of them would do a Good job for you. If I had to prioritize them based on what I can read and observe, I would rate the one in the UK best, the New Zealand next and the Chinese last. Just looking at a map, I would think that the one from China would be the easiest transportation wise and the UK and new Zealand routes are about the same distance, but the UK route would have more land line transportation. Good Luck, I think that you are pretty well versed at this point to get the DMX installed and pretty reliable.
Tom Johnson
stonehedge99
Active Member
Ive ordered the dmx splitter/booster box. Hopefully it will arrive soon.
Meanwhile a small question that cropped up. Now that ill be sending one dmx signal from my controller into the distro box and then the dmx splits into 8 outs. Ofcourse ill be just using about 3 out runs from there. So output 1 will run for 100 ft, output 2 for 100', and the third also the same. Im planning to terminate each run at the end of the 100' run. Is this ok or termination is only ideal for a one single length run ?
Thanks
Meanwhile a small question that cropped up. Now that ill be sending one dmx signal from my controller into the distro box and then the dmx splits into 8 outs. Ofcourse ill be just using about 3 out runs from there. So output 1 will run for 100 ft, output 2 for 100', and the third also the same. Im planning to terminate each run at the end of the 100' run. Is this ok or termination is only ideal for a one single length run ?
Thanks
You treat each output of the opto-isolator as an individual DMX run. So if you use outputs 1-3, at the end of each chain on each output you'll want a terminator. Distance has no factor in regards to terminating your signals. If your total DMX cable run on a given output is 20' or 200', you'd still use a terminator at the end of each chain.
Example:
Output 1 ---> Dimmer Pack ---> Dimmer Pack ---> Dimmer Pack ---> Dimmer Pack ---> Terminator
Output 2 ---> Scroller PSU ---> Scroller PSU ---> Terminator
Output 3 ---> Scroller PSU ---> Scroller PSU ---> Terminator
Output 4 ---> LED ---> LED ---> LED ---> LED --> LED --> Terminator
Output 5 ---> Unused (no terminator needed)
Output 6 ---> Unused (no terminator needed)
Output 7 ---> Unused (no terminator needed)
Output 8 ---> Unused (no terminator needed)
The nice thing about a proper splitter such as this is if something quirky happens on output #4 -- a bad cable with a shorted wire that causes devices to do weird things, the problem will only be witnessed on the devices connected to that output. Devices on output #6, #2, or any other output will still function normally.
stonehedge99
Active Member
Hi Guys,
I have got the DMX booster splitter with me and i have bought a small 12v power adapter to power it. I wanted to ask. Is this power adapter meant only for optional backup or the dmx booster always needs power to work. This is the chinese one ive metioned above see here.
Can someone tell me if this needs to be powered all the time by 12v and any idea what they mean by "12v-24v" printed on the splitter ????
I have got the DMX booster splitter with me and i have bought a small 12v power adapter to power it. I wanted to ask. Is this power adapter meant only for optional backup or the dmx booster always needs power to work. This is the chinese one ive metioned above see here.
Can someone tell me if this needs to be powered all the time by 12v and any idea what they mean by "12v-24v" printed on the splitter ????
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