DMX Addressing for Intelligent Lighting

[Gary 0]

I’ve been asked by a couple of members for a step-by-step introduction to DMX. I’d tried to put them off, explaining that I was no expert....”ahh, but you’ve got a down to earth way of explaining things”

 

Any DMX device, be it a humble 1 channel switch pack, or a 20 channel mega-bucks swirly lighting effect that even the BBC can only afford 2 of, needs to have its DMX address set. A DMX address means that a controller can send signals to that unit (Address) only, rather than all lights. If you set two units to have the same DMX address, they’ll normally copy each other. The DMX address cant be simply “typed in” to a unit. You’ve got to set the DMX address using a set of switches which you either set to off, or on.

 

I’ve seen some manufacturers instructions try to explain how to set a DMX address using pure mathematics eg: X to the power of 2, X to the power of 10 etc... it’s the bit that’s sometimes enough to get some DJ’s into a state anywhere between glazey-eyed and sheer panic.with the result being a dmx unit gets refunded and 2 more light screens and a rope light get sold.

 

I’d agree with anyone who says that the “2 to the power of” calculations often used by manufacturers for DMX address setting is confusing . Sometimes even the “abacus method” can be too so lets try the “Coins and Envelope” method (which I’ve used a couple of times previously at DJU MAX etc) this time.

 

The Coins and Paper Example:

Picture this. Here in the UK, we’ve got 8 coins... a 1p, 2p, 5p, 10p, 20p, 50p, £1, £2 (ok theres a £5 alledgedly, but lets ignore that).

 

Imagine all those coins lined up in ascending order...if you add up all the coins that you can see, you get...388.

 

Now, take one normal sheet of paper, and place it this side of the line of coins, but not covering/hiding any of them. Now, slide the 20p coin down under the paper. And again, add up all the coins you can still see...there 368 of course.

 

Slide the 1p coin down so its hidden by the paper, and you’re left with 367 when adding up the visible coins.

 

DMX addressing is no more complicated than this idea. The only difference is that DMX uses different “coin values”, each one double the value of the last, so combining the two ideas, a row of “DMX coins” would be 1,2,4,8,16,32,64,128 and 256.

 

For the sake of a simple example lets say that you’ve got a very simple DMX Dimmer simply controls the brightness (or dimness) of an attached lightbulb. This would be a one-channel DMX device.

 

So, lets say that you wanted to set a DMX device to have an address of 200. Obviously you wouldn’t want to use (switch on) the 256 switch, as you’ve gone over the target (you bust!) instantly. However, switch on the 128 switch, the 64 switch, you get ummm errrr 192..(not enough) flick the 8 switch on, and you’ve got 200. Congratulations – you’ve just set that DMX device to the DMX address of 200.

 

OK, so you’ve set the address of one of your DMX devices to 200, as in the example above. You’ve also wired up a big bright white light bulb onto your DMX dimmer pack. Now, using a controller (again in very simple terms) lets say that you want to have that light shine at half brightness.

 

A DMX controller basically sends a value, between zero and 255 to any DMX address. In our example, the only DMX address we’re using is 200. If we use the controller to send the full 255 to that dimmer, the white lamp will light up at full brightness, if we send zero to the dimmer, the lamp will switch off. If we send 128, the lamp will light up at half brightness...

 

 

Next!

All very nice this, having one bright (or dim) white light bulb, but you’re worried that the audience might get a bit bored with it, despite the fact that you’ve got the hang of sending 50 to the dimmer to get it to light at one 5th brightness, and sending 200 to it, to get 4/5ths brightness from it etc.

 

So, you decide to add a second DMX dimmer.

 

With DMX, when you’ve got two identical items, you’ve instantly got a choice on either setting the new device to any unused DMX address, in our example any thing OTHER than 200, or setting the identical device to the same DMX address eg: Both devices get called address 200. If you set two identical devices, with the same DMX address one device, will do exactly the same as the other. (there is a “dip switch” exception to this rule, which we’ll come onto later).

 

So, if you’ve got 2 DMX dimmers, both set to DMX address 200, and use a controller to send 255 to address 200, both your lightbulbs will come on at full brightness. Send 128 to DMX address 200, and both dimmer packs will light their bulb at half power. However, if you set the two devices to different addresses, say, address 200 and address 300, you can control them independently, eg: having one light on at half power, whilst the other light on at quarter power, or one light on, the other off etc.

 

Where a DMX unit has several functions eg: Different Gobo’s, different colours, a motorized pan mirror, a motorised tilt mirror, etc, its first channel is the only one that you need to set using the switches, all other channels are automatically assigned, consecutively. So, if you have a 6 channel DMX effect, and you set it to be address 100... The first function, perhaps the colour select will be on address 100, the gobo wheel on address 101, the colour wheel on address 102 etc...

 

Still with me? Hope so.

 

Now, lets say that your audience is still getting bored with your two independently controlled light bulbs on addresses 200 and 300. In a mad, rash moment you rush out and buy...a 4 channel DMX dimmer, which you’re planning on running on your show. As mentioned above, a device with more than one DMX channel on it, will only need you to set the first address for the device, lets use address 500 this time. So we’ll need to switch on the following switches...The 256 switch, the 128 switch, the 64 switch, the 32 switch, the 16 switch, and finally the 4 switch, there....that all adds up to 500.

 

The device will use the address that you’ve set (in this case 500), as its FIRST address. The device will automatically number/address is remaining channels in one step increments eg: its will set its second channel to 501, its next channel to 502, its next channel to 503.

 

So, our 4 channel DMX dimmer is on addresses 500, 501, 502 and 503. We can send any value from zero to 255 to any of those addresses. Just like posting a letter to house numbers 500,501,502, and 503 – with each letter containing a number between 0 and 255 in each one.

 

Of course, theres more to life than dimmers. Lets consider a very basic moonflower effect. One that’s got a bi-directional motor which spins clockwise and anti-clockwise, and a colour wheel inside with 10 different colours through which it can shine its standard, un-changeable pattern of dots. To make things interesting, we’ll say that the lamp in the moonflower is dimmable. This device would be described as a 3 channel DMX device, a channel for the motor, a channel for the colour selection, and a channel for the lamp dimmer.

 

Lets set the DMX moonflowers dip switches to set the unit onto address 400. As we’ve discussed, the first DMX channel (the bi-directional motor) will go onto address 400, the colour wheel will automatically go to address 401, and the lamp dimmer will be on 402.

 

Lets talk about the moonflowers lamp a moment on address 402 – if we send a zero value to it, it’ll be off, if we send 255 to it, it’ll be a full brightness. Easy peasy, lemon squeezey.

 

 

Mirror Pan/Tilt and Rotating Gobos

Now with DMX, we know that the maximum value that we can send to any of the 512 DMX addresses, is 256. So, halfway or “middle” would be 128

 

On some DMX lights which have a bi-directional motor with variable speed, the middle or “Stop” position is achieved by sending a value of 128 to them. In the case of our bi-directional, variable speed moonflower, if we send 128 to it, it doesn’t rotate either way – it stops. If we send 127 to the motor address (DMX channel 400), it will go very very slowly one way, or if we send 129 to it, it will go very very slowly the other direction. In contrast, sending 0 to the motor address (DMX channel 400) will spin the motor at its top speed one way, and sending 255 to the motor address, will get the motor spinning at top speed in the other direction.

 

It may help to think of this “middle value = no rotation” as one of those old large wooden ships wheels on an old sailing ship. With the ships wheel in the middle (value 128) the ship doesn’t steer left or right, turn the wheel left very slightly (127) and the ship will slowly turn to port very slowly. Turn the wheel all the way to the right (256) the ship will quickly wrench and veer its way starboard. This same “ships wheel” idea can also be applied to many DMX lights which offer variable speed rotating gobo’s, eg: 128 will be “No rotation”, 129 will be slow clockwise rotation, 255 will be maximum speed clockwise rotation, 0 would be maximum speed anti-clockwise etc.

 

This same idea of the middle 128 value being “No rotation in either direction” also applies to rotating gobos in some of todays lighting.

 

Gobos and colour wheels.

Theres no escaping a little bit of maths here unfortunately. With gobo and colour selection the faders range of values (0 to 255) is normally divided into however many gobos or colours that the unit offers. For example: If a lighting effect offered just two gobos (I wouldn’t bother buying one) then to select the first gobo, you’d send a value between 0 and 128. To switch to the second gobo, you’d send a value between 129 and 255. At the other end of the equipment scale, If a lighting effect offered 8 gobos then (urrmmm 255 divided by 8...equals....urmmm 31 values (out of 255) per gobo.

 

Below if a list of what values you could send to a lighting effect which offers 8 gobos.

 

Gobo# Value

Gobo 1 0 to 31

Gobo 2 32 to 63

Gobo 3 64 to 95

Gobo 4 96 to 127

Gobo 5 128 to 159

Gobo 6 160 to 191

Gobo 7 192 to 223

Gobo 8 224 to 255

 

If you wanted gobo 6, for example – it wouldn’t matter whether you sent a value of 160, 177, 184, or 191 – the unit would display gobo 6.

 

These same examples would hold true for selecting a colour from a unit offering 8 colours. So, if you wanted colour 3, you could send any value between 64, through to 95, and get colour 3. Its almost like getting a ruler with 255 millimeters on it and painting the first 31 millimeters in one colour, the next 31 millimeters in another colour, and so on. You’d simply pick a colour that you’d like, and read off any of the millimetre values shown within that colour.

 

 

I hope that the above examples have helped to clarify some of the numbers involved in DMX and hopefully take away some of the mystique and concerns which some people have (or maybe had) about DMX addressing, and values.

Edited May 11, 2005 by Gary

[DJ Marky Marc 0]

sounds good gary... when can you come over and program my DMX controler? http://www.dj-forum.co.uk/html//emoticons/biggrin.gif

[John Kidd 0]

Hi all,

 

I use a Martin Address calculator to find my DMX addresses as i rarely have 2 coins to rub together:-

 

Address Calculator

[tonyj 0]

QUOTE (John Kidd @ May 11 2005, 05:01 PM)

Hi all, I use a Martin Address calculator to find my DMX addresses as i rarely have 2 coins to rub together:- Address Calculator

God bless the internet http://www.dj-forum.co.uk/html//emoticons/biggrin.gif

 

John and Gary thanks for this info http://www.dj-forum.co.uk/html//emoticons/patriot.gif