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dmx terminator


cobra513
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Does a dmx terminator have to be 120 ohm or can it be a lower or higher value, if so by how much. Does cat5e cable length affect size of terminator. I currently have a 150 ohm resistoras the terminator and seem to have issues of certain lights working randomly and randomly having certain lights that don't work.

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I cant find it right off the bat, but I think there is a discussion here about that.

However, if it helps, the characteristic impedence of cat5e @100Mhz is 100 Ohms.

I would rework your terminator to 100 Ohms and see if that helps...

Also, what are you using to drive your DMX?

Bob

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Sorry this is my first year with both LOR and DMX. Bob not too sure what your asking about but here's what I've got. 6 poles each holding 3 5050 rgb led's connected to a 3 channel dmx contoller daisy chained together and connected to a 2nd LOR usb rs485b adapter being run by LOR software. This is a smaller version of Tim Fischer's North Poles and is a redesign of the corostar from Holiday coro. Steve I would have but RS didn't have any, I grabbed 2 or 3 different sizes and started with the 150 ohm since it seemed to be the closest.

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Not sure if this is what your looking for:

http://www.dfd.com/whyterm.html

" The DMX512 specification states the cable should have a characteristic impedance of 120 ohms (although most DMX512 techies agree a value between 100 and 120 ohms is satisfactory). A value of 120 ohms is usually specified for proper DMX512 termination. "

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Sorry this is my first year with both LOR and DMX. Bob not too sure what your asking about but here's what I've got. 6 poles each holding 3 5050 rgb led's connected to a 3 channel dmx contoller daisy chained together and connected to a 2nd LOR usb rs485b adapter being run by LOR software. This is a smaller version of Tim Fischer's North Poles and is a redesign of the corostar from Holiday coro. Steve I would have but RS didn't have any, I grabbed 2 or 3 different sizes and started with the 150 ohm since it seemed to be the closest.

Actually you answered the question. The LOR USB485B is what i was trying to get to.

I also know that RS didnt have the 120 Ohm resistors but they (or at least mine did ) have 100 and 10 Ohm.

While your looking for specifically a single 120 Ohm resistor you can put a 100+10+10 in series and get 120 Ohms.

Pin 1 ------ 100 ------- 10 -------- 10 ---------- Pin 2

This will at least tell you if the terminator solves your issue.

Bob

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My original was a 1/4 watt 150 ohm, was able to pick up a variety today and since i wasn't sure of what wattage to get i got 100 ohm in 1,1/2, and 1/4 watt,10 ohm in 1 and 1/4 watt, 47 ohm in 1/2 watt, and 22 ohm in 1/2 watt. will the wattage make a difference or can i just use either of the wattage and just keep it between 100 and 120 ohms. Thanks for the help guys.

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This is what the Lynx Express uses for a terminator. 1/4 watt 120 ohm should do it. I know it you search you will find a range of ohms that will work. I would think 150 would work just fine.

http://www.mouser.com/Search/ProductDetail.aspx?R=271-120-RCvirtualkey21980000virtualkey271-120-RC

I have had random issues when using animated sequences with DMX this year. I initialy thought it was a terminator but after switching to musical sequences everything is testing good.

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  • 2 weeks later...

Well I've tried all versions of terminators I had from 1/4 watt 100 ohm to 1 watt 120 ohm still same issue. Don't think it's a length issue as i'm only about 40' to first pole and about 20' between each of the six. All my sequences are musical so far. Thought maybe it was an issue of running the cat 5 to close to my power cords (had initial cable in with a bundle of power cords and speaker cords ) so I moved it so it was atleast 6" from the power cords in most places (gets a little closer in a couple of spots). Whats happening is really random, one time one wont work at all, next it may work fine or fail to show a particular color or be out of sequence for the color, sometimes for only part of a song other times for the whole thing and then be fine. Not always the same pole and it is usually only one at a time but i think I've had as many as 2 do it at once and more often than not it is one of the same three poles. I also tried entering the chain from different poles and splitting the cat 5 into 2 sets of three always same issue. Any ideas would be welcome but if worse comes to worse I'm just gonna run as is as this Sat the 24th is my start date.

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That's right except I have 6 dmx devices each with a 3 channel controller set at different addresses on 1 universe starting with 2,3,4 for first one 5,6,7 for second and so on. Just to clarify it looks like this

-> USB485B -> LOR Protocol -> LOR device

Computer

-> USB485B -> DMX Protocol -> 3 channel DMX device ->3 channel DMX device ->3 channel DMX device ->3 channel DMX device ->3 channel DMX device ->3 channel DMX device ->Terminator

Edited by cobra513
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The only thing I question in this setup is using the USB485B for DMX. Last year I tested that device with some of my DMX controllers and its output was a mess. I know they are supposed to work but they didn't for me. There was some talk that mine were older models from 07-09 and may have slower chips that don't work for DMX.

I have used an Entec Pro, Lynx USB dongle and Lynx Etherdongle (E1.31) for DMX and have had great luck. This year I am running all DMX.

The four things I would check are:

1. USB485B (see if you can get another DMX dongle to test with. An Entec open would even work great for this.

2). Do some research on those 3 channel DMX adapters as I thought I heard some discussion at one time about them being one channel off but I don't remember the specifics or if it was truly these.

3). Check any couplers or Y adapters in your cables.

4). I had animation sequences gave me fits this year while testing. Musical sequences have been rock solid.

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Tried my programing dongle from holiday coro, same result. Only other one I have is the other usb485b for my LOR controller right now. Think I'm just goin to run as is and try to figure it out later.

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When I used the Holiday Coro dongle I was able to control ONE device via LOR without issue. However, when I added the other seven, that is when the 1 channel shift seemed to occur.

I will add that I used my Serial 485 LOR dongle and communicated DMX without issues.

I do see some wierd events (fast flash, random on/off etc) when I use XLights via my J1Sys D2 bridge on the HC 3-channel controllers but via LOR they are spot on..

Bob

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  • 1 month later...

Ok now that the season is over and I have my lights down I'm back to trying to track down this issue. First I left these lights to take down last and tried them with no other power or speaker cords in the yard, they would randomly have 1 that would not light at all usually #2,3,or 6 when show would run, same as before. Since this didn't fit with show I let them run on their default setting of fading through colors. I would notice every so often they would go crazy flashing white very fast, I would unplug the power and plug it back in and they would be ok for awhile then do it again later. I tore the poles apart removing the controllers, plugs and lights and double checked all the conections and wires,found a couple of minor wire issues fixed them and hooked them back up. I also originally had them addressed to same address as what was in the sequence so I bumped them down 1 since I was using the 485b. This seems to have fixed the random issue of one not working as long as I don't use a terminator, the minute I put one in (no matter what size) the lights go nuts even if there is no data cable attached, 1 or 2 sometimes 3 flashing different colors or white, as soon as I take the terminator out they behave ok. From reading the forumns I know this is not normal so I'm back to wondering whats up. Sorry this is so long but wanted to provide as much info as possible.

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I hate to even point this out, but have you checked your wiring and cables for bad connections, solders, or wiring order? Im sensing this is a cable issue more than a user error. You have done all that you can to terminate the dmx line to no luck. Have you taken everything back to square 1 and checked the cables?

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Didn't check with using the terminator til I had all 6 hooked back up although each one worked ok without the terminator when checked individually. I'll hav to go back and check from square one again when I get some time, maybe this weekend. Thanks

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  • 2 weeks later...

Ok finally wa able to spend so more time on this. I did have some wiring issues( thought I was being careful) and was able to fix them but still have an issue that I think I know where problem is. Now when I run the sequences they work fine as long as I have no twinkle or shimmer go to them, when I do that it seems to throw off the response by the lights by 1 channel more than the usb485b already does. I'm thinking the usb485 is the culprit here.

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Doing shimmers and twinkles on a DMX network is not easy; the computer spends extra CPU cycles trying to emulate what the LOR network does automatically. Your computer may be struggling to keep up, and missing a few beats here and there in the process.

 

Compounding the issue is running the USB485 in DMX mode; besides the addressing problems, the older versions have response issues.

 

The DMXKing dongles, the DMX Fusion Pro and the Enttec Pro units are the top USB-DMX converters out there; they always work just the way you expect them to.

 

And when it comes out in March, the Holidaycoro version should be just as reliable.

 

If you have access to one of these units (and NOT the Enttec Open model), you might want to try it out.

 

They're always a good investment and might save you chasing down and troubleshooting erratic lighting.

 

 

Besides the above units, I especially like the LOR iDMX1000 unit for running a DMX network. Yes, it's pricey, but you can not only run the Hardware Utility with it, but you can store non-musical sequences in it's onboard memory. If you need to run those type of stand-alone shows, that is.

 

In addition, it has some internal code that makes shimmers and twinkles work better on a DMX network.

I believe it's limited to the first 128 addresses that you are doing shimmers and twinkles for, wherever they are in the DMX network.

Edited by Ken Benedict
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I ran shimmer a lot this year on my LED window frames.  I used the LOR IDMX and it worked flawlessly.. as far as I could tell. 

 

I did get some minor timing issues when I went to S3 3.9 though... at least I thought I did.. but no one could tell. Seemed to me like it was tens of miliseconds behind where it was with 3.8.  Might have been in my head, but I don't think it was... LOL  

 

Even the voices told me I was right!    :rolleyes: 

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  • 2 months later...

Ok finally wa able to spend so more time on this. I did have some wiring issues( thought I was being careful) and was able to fix them but still have an issue that I think I know where problem is. Now when I run the sequences they work fine as long as I have no twinkle or shimmer go to them, when I do that it seems to throw off the response by the lights by 1 channel more than the usb485b already does. I'm thinking the usb485 is the culprit here.

 

Termination rarely makes a difference excluding rare situations (LOR doesn't even use it).  The tools you need are a scope (to see if there is some sort of interference) and/or a digital logic analyzer (for decoding the DMX packets to see if the source of the problem is on the output side). 

 

Here are some resources that might help:

 

http://www.holidaycoro.com/kb_results.asp?ID=17

 

http://blog.holidaycoro.com/2013/03/dmx-lor-protocols-and-rs-485.html

 

Maybe that helps...

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