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DMX help

Discussion in 'Lighting and Electrics' started by Shawncfer, Jul 2, 2009.

  1. Shawncfer

    Shawncfer Active Member

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    What is it?

    I've googled it, and I've looked in the control booth Wiki (but neither really helped).

    I know this is a stupid question, but I've rigged lights, cut gels, and operated a board. I've never had to set a whole system up, or fix one.

    I'm assuming from what I've read that a DMX just carries the signal from the board to the dimmers. So is that right? Or am I making myself look more stupid?

    and Second: Ive ran lights at a club that were already set up. I didnt have to rig them or change gels out or anything, just the board. And now Im also doing some work at my schools theatre for band/choir/dance preformances. And I've noticed that where ever the lights are theres a chanel number with a 1 foot cable hanging down from there. And obviously you run the lights through there to the dimmer and yah. BUT, Ive noticed at some theatres they dont have that little box that drops the cables down. So do they hang lights where they need them and just run a REALLY long extention cable all the way to the dimmers? or is there another box they plug it in located in the center of the lights where they just run extentions to there and then run it to the dimmer? (sort of like what I thought a DMX was in the first question)

    I'm sorry for being annoying, I'm just intrigued!
     
  2. NickJones

    NickJones Active Member

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    Not a stupid question, I have had to explain this to a few people in the past, DMX is a protocol. Its the language that makes your console talk to your dimmers, LEDs & MLs. It's that simple, I can see why the Wiki wouldn't help.

    DMX may also reffer to DMX cable, the cable that carries the DMX data, like a ethernet cable (Cat5) does for your computer.
    Hope I cleared it up,
    Nick
     
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  3. soundlight

    soundlight Well-Known Member

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    DMX is the control protocol for controlling dimmers, moving lights, and dmx accessories for lights such as color scrollers and gobo rotators. The wiki should help here.

    When you bring up a fader on a lighting console and the appropriate dimmer comes up, the information link between the console and dimmer that carries the information that tells the dimmer rack what dimmer to bring up is the DMX protocol.

    Circuits (the actual thing you plug the light in to) are sometimes on pigtails (those 1' extension cables), sometimes actually on a raceway (big long box with plugs in it that runs the length of a pipe/batten), and sometimes in boxes near the lights, but you need short extension cords to get to them. For some smaller theatres, they do actually run cable from the dimmers, but this is only for low-budget theatres with smaller houses where it's at least semi-practical. These are often semi-permenant but sometimes taken down between shows to re-run elsewhere.
     
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  4. Shawncfer

    Shawncfer Active Member

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    Thats exactly what we have, pigtails on a raceway.

    Now back to the DMX, yall both helped me understand what it is, but I just wanna check, the lightboard doesnt run straight into the dimmers, it runs into a DMX first correct?

    And the DMX allows the board to communicate with the dimmer telling which dimmer to come on at what percent. right?
     
  5. porkchop

    porkchop Well-Known Member

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    You have really good questions, there's no shame in asking. It sounds like you have a good idea of the basics you just need a few more details.

    First of all DMX is the signal. Basically there is a 5-pin XLR cable (could be 3-pin but it's supposed to be 5-pin) running from the board to the dimmers and to any intelligent fixtures you have. It transmits 512 values between 0 and 255. I believe it does this 40 times a second but I could be wrong. The 0 to 255 value represents the intensity of any light plugged into the respective dimmer, or if the cable is plugged into an intelligent fixture is a data instruction to make the light do something (this is the only data source so all light functions are communicated this way). This can be expanded upon if you search for DMX you will probably find some very in depth information.

    As far as the numbers they are the number dimmer controlling that plug. If you plug a light into dimmer 42 say and then send the DMX signal to the dimmer rack that you want dimmer 42 at full you will see your light come on (Or at least that's what's supposed to happen).

    What you will probably notice is that channel 42 on your lighting console may or may not control dimmer 42. This is because of something called the patch. Which is stored on your lighting console. The best way to think of the patch is like a giant spreadsheet where the first column is the channel number and the second column is the dimmer(s) that the channel controls. Other things that you will see on different boards are: universe number (if you don't type that in with dimmer number), a maximum level to send to that dimmer, and a profile for an intelligent fixture. I'm sure there's others but that's what I can think of off the top of my head. The presentation of this varies widely from manufacture to manufacture and even between the same company's consoles but with that idea you at least get the idea.

    Hope that covers it, feel free to ask more if it doesn't
     
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  6. len

    len Well-Known Member

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    I usually explain what dmx is this way:

    imagine puppets, the kind with strings (marionettes). Each string represents a data channel or address. Typically, a control console has 512 channels (strings), or multiple sets of 512 channels (universes). You as the puppet master control each string and as you raise and lower the fader, twiddle the knob, press the preset, etc., it raises and lowers the string, and makes the puppet do what it's supposed to. The difference is that dmx is done with electrons, not actual string. The other difference is that instead of raising an arm on a puppet, you're sending commands to a fixture and the microprocessor in the fixture (even dimmer racks have them) translates that into some mechanical action (activating a dimmer, spinning a color wheel, etc.).
     
  7. TimmyP1955

    TimmyP1955 Active Member

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    DMX is not a thing, it is a communication protocol, or a "message" that is "written" in a particular "language". If you are familiar with MIDI, think of it as similar to that. The lighting console sends out a signal - a message that is written in the DMX language. This DMX signal is fed via DMX cable (basically like mic cable with less capacitance) into the dimmer pack (or LED PAR or moving fixture), which reads the message and interprets what instructions it is being given in this message. It then carries out the instructions. For a dimmer, the message might be "fade channel 3 up to 50%". For a moving fixture, the message might be "change color to gel holder 2, then fade up to 100%, then simultaneously pan 45 degrees clockwise and incline 90 degrees".
     
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  8. Shawncfer

    Shawncfer Active Member

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    Alright. So I got it figured out now.

    DMX is just the SIGNAL that goes From the board, through the 5 pin XLR, and into the dimmer.

    Now question two!

    When talking about conventional fixures, the signal (DMX) goes through the 1 XLR cable, right? So after all (lets pretend our board has 30 channels) 30 channels on the board go into one xlr cable, how does it split up into each dimmer once it arrives where ever the dimmers are located?

    and

    When talking about moving fixtures, if we have 10 intelegents and one board for the intelegents, does each one require its own cable? Going out from the light board for intelegents?

    For example, If im using a lightboard for intelegent lights, does it have 10 outputs for 10 different lights? or is there 1 output and somewhere along the lines it splits going to the different lights? or what?
     
  9. Kinkele

    Kinkele Member

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    DMX ( Digital Multi Plex, before that was AMX, Analog Multi Plex) can handle 512 things on one cable. On the receiving end it can pass in and out of various devices and keep going. Each device has a selectable address or a starting address that tells it which of the 512 addresses to listen to. A dimmer rack may start at DMX address 1. If it is a rack of 96 dimmers the dimmers are 1-96. if a similar rack is set for a starting address of 101 then the dimmers are DMX addresses 101 thru 196. If you continue the signal out of the rack and on to a scroller, then address the scroller as 201 then it listens to DMX 201. You can continue this on to a moving light. Each moving light has its own specific number of dmx addresses needed. If the mover is very simple it may need only 14 addresses; intensity, shutter, gobo, color, pan, tilt. ect. Each individual thing you want to control needs an address. Moving lights get compicated which is why the consoles have fixture libraries of moving lights.

    Once everything has an address, then the console has a patch. In the patch you get to change the order of the DMX addresses into something that makes more sense to you, the operator. Some operators make all the front light on channels 1-10, fill on 11-20. Whatever order make it easy for you. "Patch" "dimmer" 101 @"channel" 1. Now the light plugged in to dimmer 101 will come on when you bring up channel 1 on the console.

    Patches can also be defaulted 1 to 1, 2 to 2, 3 to 3....this is good to do during setup to check your lights.

    Moving lights and moving light consoles get more complicated. I have done it the most basic way. Assign a moving light to DMX 301. Patch the 14 dmx addresses it needs individually; 301 @ channel 11, 302 @ 12, 303 @ 13...ect. Then on a basic console I have to figure out what function in the moving light each channel does. This is a good way of understanding what is actually happening. Sometimes a moving light responds to very specific percentages; The "control" function is on channel 14 is set to 25 % for 2 seconds, while the intensity channel is set to 0% then the fixture will reset. This is why there are moving light consoles. They just create a reset button.

    I hope that was clear. I have to go. My 14 yr old is doing some CKY band with 6 movers and 24 dimmers.
     
  10. NickJones

    NickJones Active Member

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    As for the movers, your console sends a message for example, you have a moving light with the attributes as follows (its more complex than this but it should give you an idea):
    1. Move Left & Right
    2. Tilt Forward & Backwards
    3. Dimmer
    4. Colour

    So lets say your console sends a messsage to the Mover, the message is Channel 1 @ 50
    Channel 2 @ 25
    Channel 3 @ 100
    Channel 3 @ 0

    Now lets decode.
    The first channel is set to 50, meaning that the moving light moves to the middle, as it is 50, and 50 is halfway between 0 and 100.
    The second channel is at 25, and this is the moving forward and backwards channel, if directly up is 50% (90 Degrees), then 25% will mean that the light is at 45 degrees.
    Channel 3 is our dimmer, its at 100% so its at full.
    Channel 4 is at 0, that's open white, so no colour there.

    Okay, so now I will confuse you.

    DMX doesn't understand 0-100% instead it uses any value between 0-225, meaning 225 is full, and 0 is nothing. Most consoles allow you to enter a value in percentage, rather than the DMX value.

    On most moving light consoles, typing the channel is both inaccurate and a bore, so instead, you can use encoder wheels, to move the left & right and tilt up & down, all these do is when you turn the wheel the increase/decrease the value.

    It's not called up & down, its called Tilt,
    It's not called left and right, its called Pan,

    Most lights have 2 channels for pan & 2 channels for tilt this makes it more accurate.

    Most lights have no dimmer, as the light (called a lamp) is not dimmable. So instead the have mechanical dimmers that basicly just cover up the light.

    As they can't be dimmed movers have to have the lamp "struck" meaning the light turns on.

    I think I covered everything.

    Nick
     
  11. Shawncfer

    Shawncfer Active Member

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    Alright so I'm starting to get it now. But finaly I just wanna make sure I got this, according to kinkele, at the end of tv xlr cable, it will plug into dimmer 1, then from there, another smaller 5 pin xlr will come out dimmer 1 and into 2. Then out 2 and into 3 and etc. Once it gets to the end of the dimmer rack, it can then go to moving lights and pass through some of those and even then to those gel switchers that I can't think of the name right now and it can change the different gels. Pretty much anything cept pyro and laser? And I can just keep running it through as long as I have under 512 dimmers or whatever hooked up. And I know that the moving lights count for about 14 if those dmx channels so as long as everything combined is under 512?
     
  12. NickJones

    NickJones Active Member

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    You got a bit lost...
    The cable is supposed to have a 5 Pin XLR adapter, [​IMG] looks like this, that is known as a DMX Cable,

    Each device in the chan is given and "adress" like an email adress, and this means that when you send the signal to pull up channel 10 to 100%, whatever dimmer or mover is adressed to channel 10 will listen and do what it says, so the cable doesn't have to run to anything in any particular order.

    Each device has an input and an output, meaning they can all be linked.

    And the gel switchers are known as "Scrollers"

    It's not used in Pyro as it doesn't have adequate saftey features.

    Moving lights can use up to about 30 different channels.

    Nick
     
  13. soundlight

    soundlight Well-Known Member

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    NickJones, I think he meant "the" not "tv". There's no "a" in his post.

    Each individual dimmer in a rack does not take DMX. There is a processor in the rack that takes the DMX and tells each dimmer what to do via internal wiring and commands that are not DMX. You would not want to pay for DMX tranceiver electronics for every single channel of dimming you have! Each dimmer rack though does have DMX. If you have a bunch of eight-channel dimmers, each of these takes DMX. The first one "daisy chains" to the second one, second to the third, etc. So if you have 24 channels of dimming in a rack which has three 8-channel rackmount dimmers, you only need to connect each rackmount unit to eachother, not a cable between each of the 24 dimmers. And for something like a large ETC Sensor rack, an individual "CEM" (name of the internal processor for ETC Sensor dimmers) can control up to 96 dimmers.

    This "daisy chaining" term that I'm talking about is the term for connecting one dimmer rack or fixture to the next dimmer rack or fixture by connecting the DMX out of one to the DMX in of another.

    The length of a DMX signal chain (say, daisy chaining a whole bunch of moving lights together) is technically limited to 32 devices in one run of DMX (this is a limitation set in the standard, and should be followed to prevent weird signal issues from coming up).

    If you have more than 32 devices (be that dimmers or moving lights or rotators or whatever), you have to use something called a DMX Optosplitter. The "opto" part of that is for the special optical isolation that's used to split the DMX. These devices can have anywhere from just two DMX outputs to at least 10. This way you can connect more devices to one DMX signal.

    The gel switcher things you're talking about are scrollers. Most gel scrollers are powered from their own central power supply. This power supply takes a DMX input and a power input, and puts them both on the same 4-pin cable. This goes out and gets daisy chained to each of the scrollers so that they don't have to have individual power runs as well as DMX runs.
     
  14. Shawncfer

    Shawncfer Active Member

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    Sorry I did mean the. I'm just typing on a phone so it auto corrects it.

    So I got the basic idea that it runs through the dimmers and then through other stuff.

    The only thing I messed up is that it doesnt go through each dimmer, instead a processor which then divides it amongst the dimmers. And then I can daisy chain through one processor of one dimmer rack to another processor of another dimmer rack and then it can go through those processors (if needing more than one) and into moving lights.

    Now for the gel scrollers. Can it run through the dimmer processor and into the moving lights and then into the scrollers or do you need a separate board and DMX signal for the scrollers?
    Posted via Mobile Device
     
  15. n1ist

    n1ist Well-Known Member

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    The order doesn't matter; the DMX chain can go to the dimmer processor and then to the movers, or it can go to the movers first. Each device has an address (usually set with dipswitches or up/down buttons on the device) that tells it which of the 512 channels start looking at. A splitter (1 cable in, many out) lets you get around the limitation of 32 devices per DMX chain (there's not enough "oomph" in the board to drive more than 32 things, and the splitter regenerates the signal).

    Some gel scrollers take DMX directly; others have a special power supply box that takes DMX (and power, of course) and converts it into what the actual scrollers use, and connects to the scrollers with a special cable).

    One other tidbit - at the end of a DMX chain (on whichever device is plugged in last), you need to terminate the signal, either with a terminator plug, or some devices have a switchable terminator. This makes sure the signal doesn't get any interference from reflections at the end.

    As for the XLR connectors, the DMX standard specs a 5-pin XLR. Much lower-end gear uses a 3-pin XLR instead. Some stuff even uses RJ45 connectors. There are adapters that go between them. You need to use DMX cable, not regular mic cord, to ensure signal fidelity.

    /mike
     
  16. Shawncfer

    Shawncfer Active Member

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    Alright alright, but
    still, can I run the same cable to the color scrollers? Or does it have to be a separate dmx signal from a different board? And was I right about you plug the 5pin xlr to the processor which then sends it to all the different dimmers? And what if I don't have anything plugged into a certain dimmer? Does it skip over that dimmer when giving addresses or does it still get an address in the 512 rangr and. Just don't patch it into my board?
    Posted via Mobile Device
     
  17. GreyWyvern

    GreyWyvern Apollo Staff

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    The same cable can't be run straight to the scrollers, but it doesn't have to be a seperate DMX signal from a different board (although it can be done that way). Scrollers use 4-pin data cable to get their signal which also supplies the power needed to operate them. The 5-pin cable you would daisy-chain from your other devices, would go into a power supply unit and could continue on to other devices. You could think of the PSU as a special dimmer for scrollers, rotators, and other such devices.

    Yes, you are right about it going to the processor which then decodes it and controls the dimmers. The dimmers don't know if they have anything plugged into them or not. They are a fixed thing in the sense that they are always there and are assigned a dimmer number. Yes, you can just skip over "empty" dimmers in your patch on the board.

    Sounds like you are getting the hang of it. Keep the questions coming. At the risk of sounding cliche', the only bad question is the one that isn't asked.

    Dave
     
  18. soundlight

    soundlight Well-Known Member

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    Color scrollers: you use the same signal to plug in to the Color Scroller power supply (not many scrollers take DMX directly). The power supply has a DMX in and out just like a moving light, and you set the address on each scroller.

    And yes, you plug the DMX cable in to the dimmer's processor, and that sends commands to each dimmer. The dimmer doesn't care if it doesn't have anything plugged in to it, it still gets a signal from the processor if the DMX signal tells the processor to give it one.

    Let's do a basic example here to clarify the scroller issue:
    You have two racks of dimmers, each has 24 dimmers in it, so 48 dimmers total. Each dimmer has a light attached to it at the circuit on stage. You've put color scrollers on 8 of these lights for a particular show, so you need to control them as well. You're "patching" things "straight" or "1 to 1", so fader one means channel one means dimmer one means circuit one and fader two means channel two means dimmer two means circuit two, etc, etc. So you have to start addressing your scrollers at 49 or above, seeing as the dimmers take up channels 1-48. So the scrollers will be addresses 49-56. Here's how you connect it all up - the DMX cable runs from the console to the dimmer or to the scroller power supply first. Order of connection has no meaning in terms of the actual DMX signal. So you can either hook the cable up to the dimmer rack and then to the power supply, or to the power supply and then to the dimmer rack. After those connections are made, you have control of the dimmers but not the scrollers.

    The scroller power supply is simply a device for bundling power and data - think of it like one of those fertilizer connections for a garden hose that has a little side connection for a bucket of fertilizer to be sucked in to the hose and mix with the water. The water in the garden hose is the power, and the fertilizer that you're sucking in from the bucket is the DMX. Once the water and fertilizer mix, they travel down the same hose. This is how a scroller power supply works, only with power and DMX data. So once you connect the DMX to the scroller power supply, that's like putting fertilizer in the water.

    Each scroller power supply has a send and return in order to complete the circuit. You connect the power supply's send to the first scroller with a 4-pin DMX cable, then connect the first scroller to the second, then the second to the third, then the third to the fourth, etc...all the way to scroller #8 in this example. Then, you send the output of scroller 8 back to the return connection of the power supply in order to ensure problem-free operation.

    With the addressing that I set up, you're going to be able to control Scroller #1 with channe 49 on the board, Scroller #2 with channel 50 on the board, etc...all the way up to Scroller #8 which will be controlled by channel 56 (unless the scrollers have more than one channel for a fan speed or color mixing or whatever, then you have to allocate more channels for them...but most just have one channel).

    So the scrollers are controlled by the same console, they just require the special power supply in order to be fed power and data.
     
    Last edited: Jul 3, 2009
  19. Shawncfer

    Shawncfer Active Member

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    Okay so let's pretend in order that I'm sending DMX through the dimmers first, from there it runs to a power supply, and put of the power supply comes a 4 pin xlr cable instead of 5. From there it runs into all the color scrollers and a gobo rotator first if I have one and then the moving lights and from there I plug it back into the power supply and then from there I terminate that signal if I have nothing else I need it for with a terminator thing like one of yall mentioned before. Or do I need an individual power supply for each set of items like the gobo rotators and color scrollers and others? Or can it just be one power supply for all? And if I put the power supply before the dimmer racks it won't affect it at all?
    Posted via Mobile Device
     
  20. soundlight

    soundlight Well-Known Member

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    The power supply is only used for scrollers and certain types of gobo rotators. Moving lights take straight DMX.

    If you go in to the dimmers first then to the power supply with the DMX, you then take the DMX out of the scroller power supply and that DMX signal goes to the moving lights.

    Lemme draw up a diagram, back shortly with a .pdf.
     

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