Ralph A Posted May 16, 2015 Share Posted May 16, 2015 I have two fans that I want to use Dumb DMX lights on. Each will have 16 of the little white dumb DMX controllers for the fan. So that is 48 channels per fan. I wanted to know if I could run both of the fans on a single universe, since both fans would only be a total of 96 channels? Seems like I remember you could not have more than 21 or so devices on a single universe. Is it possible to run both on one Universe?Thanks! Link to comment Share on other sites More sharing options...
Dennis Laff Posted May 16, 2015 Share Posted May 16, 2015 32 DEVICES PER UNIVERSE. Link to comment Share on other sites More sharing options...
pyrotech Posted May 16, 2015 Share Posted May 16, 2015 A DMX universe can have a maximum of 512 channels. That's it. However many devices you want on a single universe is completely up to you (as long as you don't go over 512)! Therefore, for your application, you said that each fan uses 48 channels. You can put a total of 10 fans on 1 universe. 48 channels each fan X 10 total fans = 480 total channels (if you were to add an 11th fan, the total channel count would be....528) Hope that helps. Tim Link to comment Share on other sites More sharing options...
jerrymac Posted May 16, 2015 Share Posted May 16, 2015 No more than 512 circuits and no more than 32 different devices per universe, which ever occurs first. In the example of 3 channel controllers you can still only connect 32 to a single universe although you would only be consuming 96 circuits. Link to comment Share on other sites More sharing options...
Ralph A Posted May 16, 2015 Author Share Posted May 16, 2015 Thanks guys for the answers!! I could not remember the max devices per universe. Getting older. That will work out perfect for my application. So just out of curiosity, if you put more than 32 devices on a single universe what happens? Commands start acting erratic? Link to comment Share on other sites More sharing options...
Dennis Laff Posted May 16, 2015 Share Posted May 16, 2015 Never had that many but I figure it must go crazy . Link to comment Share on other sites More sharing options...
Ralph A Posted May 16, 2015 Author Share Posted May 16, 2015 Thanks! Maybe I should try it someday. Link to comment Share on other sites More sharing options...
pyrotech Posted May 17, 2015 Share Posted May 17, 2015 I think there is some confusion going on here. Hopefully, I can clear it up. First off, as everyone has said, a single DMX universe can have a maximum of 512 channels. The confusion is with the number of devices on a DMX universe. If you have a device that has only one channel, you could absolutely have 512 DEVICES on a single universe. The 32 device limit that everyone keeps commenting on is NOT a limitation of the DMX universe. It is a limitation of a single daisy-chained cable run. You cannot (should not) exceed 32 device hops on a single cable run. But, if you have independent outputs, or a DMX splitter, you can have as many runs as you want (each run cannot exceed 32 devices) and therefore, you can theoretically have 512-single channel devices on one universe! Hope this clears up any confusion. 1 Link to comment Share on other sites More sharing options...
plasmadrive Posted May 18, 2015 Share Posted May 18, 2015 (edited) I think there is some confusion going on here. Hopefully, I can clear it up. First off, as everyone has said, a single DMX universe can have a maximum of 512 channels. The confusion is with the number of devices on a DMX universe. If you have a device that has only one channel, you could absolutely have 512 DEVICES on a single universe. The 32 device limit that everyone keeps commenting on is NOT a limitation of the DMX universe. It is a limitation of a single daisy-chained cable run. You cannot (should not) exceed 32 device hops on a single cable run. But, if you have independent outputs, or a DMX splitter, you can have as many runs as you want (each run cannot exceed 32 devices) and therefore, you can theoretically have 512-single channel devices on one universe! Hope this clears up any confusion.Actually that is not 100% accurate. http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=3&cad=rja&uact=8&ved=0CC8QFjAC&url=http%3A%2F%2Fwww.analog.com%2Fmedia%2Fen%2Ftechnical-documentation%2Fapplication-notes%2FAN-960.pdf&ei=BhFaVcLwHIesogS_1YGgAQ&usg=AFQjCNFle7iI08Z6RfZras1e7_L97L-Wqw&sig2=SQ5EEtr43Cxjxff4vphjfQ&bvm=bv.93564037,d.cGU RS-485 AND THE UNIT LOAD CONCEPT The input impedance of the RS-485 receiver is specified as larger than or equal to 12 kΩ. This impedance is defined as having one unit load (UL). The RS-485 specification specifies the capability to sustain up to 32 ULs.Some RS-485 receivers are specified as having ¼ UL or ⅛ UL. A receiver specified to have ¼ UL means that the receiver only loads the bus by ¼ of the standard UL and, therefore, 4 times as many of these receivers can be connected to the bus (4 × 32 = 128 nodes).Similarly, if an RS-485 receiver is specified to have ⅛ UL, the receiver only loads the bus by ⅛ of the standard UL and, therefore, 8 times as many of these receivers can be connected to the bus (8 × 32 = 256 nodes). See Table 1 for UL and receiver input impedance details. Edited May 18, 2015 by plasmadrive Link to comment Share on other sites More sharing options...
EmmienLightFan Posted May 18, 2015 Share Posted May 18, 2015 A DMX universe can have a maximum of 512 channels. That's it. However many devices you want on a single universe is completely up to you (as long as you don't go over 512)! This is untrue. Actually that is not 100% accurate. http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=3&cad=rja&uact=8&ved=0CC8QFjAC&url=http%3A%2F%2Fwww.analog.com%2Fmedia%2Fen%2Ftechnical-documentation%2Fapplication-notes%2FAN-960.pdf&ei=BhFaVcLwHIesogS_1YGgAQ&usg=AFQjCNFle7iI08Z6RfZras1e7_L97L-Wqw&sig2=SQ5EEtr43Cxjxff4vphjfQ&bvm=bv.93564037,d.cGU RS-485 AND THE UNIT LOAD CONCEPT The input impedance of the RS-485 receiver is specified as larger than or equal to 12 kΩ. This impedance is defined as having one unit load (UL). The RS-485 specification specifies the capability to sustain up to 32 ULs.Some RS-485 receivers are specified as having ¼ UL or ⅛ UL. A receiver specified to have ¼ UL means that the receiver only loads the bus by ¼ of the standard UL and, therefore, 4 times as many of these receivers can be connected to the bus (4 × 32 = 128 nodes).Similarly, if an RS-485 receiver is specified to have ⅛ UL, the receiver only loads the bus by ⅛ of the standard UL and, therefore, 8 times as many of these receivers can be connected to the bus (8 × 32 = 256 nodes). See Table 1 for UL and receiver input impedance details. In simple terms, when you have that many devices on an RS485 network, the signal is weakened to the point where it won't work. Most proper lights (Like in a theatre lighting setup with expensive dimmers/intelligent fixtures) have circuitry between the DMX connections that help to boost signal and remove interference. Most of the cheaper RGB dimmers and stuff we use have a simple resistor between the in and out or are just wired directly. This works, but is seriously frowned upon by professional lighting people. They also would NEVER use cat5 for DMX cable, although it is also twisted pairs, like DMX cable, but has 8 wires not 3. Most of the time, with any DMX device, you will be able to pass the 32 limit mark, so it doesn't really matter, but there is a chance there will be problems. Link to comment Share on other sites More sharing options...
plasmadrive Posted May 18, 2015 Share Posted May 18, 2015 (edited) This is untrue. In simple terms, when you have that many devices on an RS485 network, the signal is weakened to the point where it won't work. Most proper lights (Like in a theatre lighting setup with expensive dimmers/intelligent fixtures) have circuitry between the DMX connections that help to boost signal and remove interference. Most of the cheaper RGB dimmers and stuff we use have a simple resistor between the in and out or are just wired directly. This works, but is seriously frowned upon by professional lighting people. They also would NEVER use cat5 for DMX cable, although it is also twisted pairs, like DMX cable, but has 8 wires not 3. Most of the time, with any DMX device, you will be able to pass the 32 limit mark, so it doesn't really matter, but there is a chance there will be problems.We have put up to 60 device locations on a single DMX universe without issue on professionally installed Archtectural installations. The 32 limit was from a long time ago with 1 UL devices and if you use the correct devices (1\2 UL or better) as I posted about, you should be fine with more. Most stage lighting from the past are 1 UL per fixture. I am not sure about the newer stuff or what current manufacturers are doing as far as Unit Loading of the receivers. We always used 1/2 UL chips or better for our custom boards. You do have to watch out for Stub Length vs. speed I don't get what you mean by "Most of the cheaper RGB dimmers and stuff we use have a simple resistor between the in and out or are just wired directly." The terminating resistors at the beginning and end of the string are also per spec and not just for hobby use. (is that what you mean by the resistors between in and out?) Many manufacturers have switchable terminators on their lights and others are self terminating if i remember correctly. RS485 is inherently noise immune but there are "Fail-safe Biasing" schemes that will enhence the reliability of the receiving unit. There are also units out there where the RS485 is electrically isolated to insure no ground loops. As for the Cat5 never being used... that is also old school. They don't usually use it on the road in the trusses because it is pretty light weight and won't stand up to the riggers of stage lighting resets, but for permanent installs, it is becoming more and more common, especially for multiple universes on a single cable. Cat5 is 100 ohm impedence and Low capacitance and works VERY WELL for any RS485 signal. We used it a lot for waste water treatment plant installs for instrumentation. Those are permanent installs of course. There are of course many other factors involved with the whole RS485 transmission scheme and the USITT spec for DMX512, but those are for another day.. Edited May 18, 2015 by plasmadrive Link to comment Share on other sites More sharing options...
Little_b Posted May 18, 2015 Share Posted May 18, 2015 I've been learning as much as I can about DMX this year and still a little confused on some of the "vocab words." When you say 32 devices what are you referring to? Is it for example you had 32 RGB Pixel Candy Canes of say 20 pixels each? So the "Hop" is in between them? Or is it say, 32 Sandevices e6804's? Link to comment Share on other sites More sharing options...
plasmadrive Posted May 19, 2015 Share Posted May 19, 2015 Each "drop" or "stub" off the DMX data line is considered a "device". For example, I have 12 of the WS2812B pixels on one of 10 props. Each of the 10 props has a DMX to WS2812B converter and those converters would be considered "devices". This would equal 10 "devices" or 10 "stubs". the total channel count would be 10x3x10 or 360 channels, but only 10 "devices". What happens after the RS485 receiver chip is not counted as devices. Link to comment Share on other sites More sharing options...
Ralph A Posted May 19, 2015 Author Share Posted May 19, 2015 WOW, look what I started. I should be more careful with my questions! Thanks for all the information guys!!! Link to comment Share on other sites More sharing options...
plasmadrive Posted May 19, 2015 Share Posted May 19, 2015 WOW, look what I started. I should be more careful with my questions! Thanks for all the information guys!!!Your question was a good one.. there is nothing "started". Just trying to keep the accuracy of the subject up. All the posts on this have been good IMHO. This is how disussions happen.... its all a good exchange of info.. nothing more.. Link to comment Share on other sites More sharing options...
Ralph A Posted May 19, 2015 Author Share Posted May 19, 2015 Your question was a good one.. there is nothing "started". Just trying to keep the accuracy of the subject up. All the posts on this have been good IMHO. This is how disussions happen.... its all a good exchange of info.. nothing more..Thanks, I was just funning about. I always enjoy your input. Most of the time its a bit over my head, but thats how I learn more!! 1 Link to comment Share on other sites More sharing options...
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