DMX gateway

I have a small change to make to an existing site where they want to add some feature lighting controlled via DMX.

As I have never used DMX before, is there anything I need to know?

I am assuming at the moment that I will be able to supply the lighting from a spare relay channel, and set levels via a DMX module, therefore the cabling is simply the mains cabling from relay to lighting and the signal cable just CAT5 from DMX module to the lighting modules. Is that about right? (I don't believe there are any additional power supplies needed on the DMX side as with DALI are there? I just daisy-chain the signal cable between modules, of which there will be about 4?)

It won't be me doing the install anyway but the installer doesn't know DMX either and seem to be looking to me as the expert....

 

I've found the following which is quite helpful (to me anyway):
http://www.lighting.philips.com/gl_en/controls/training/Introduction to DMX.pdf

Thanks for your advice, it sounds simple enough as long as they get the wiring topology right! (We'll see....)

 

Additional question: If the architect just wants to set the lights once to a desired level, and from then on we only ever switch on to that level (or off), do DMX controlled fittings generally hold their level after being set on power loss or does it need re-setting? If it's device dependant, is there a key phrase I should be looking for in their spec?

 

OK, I'm happy to go with your assumptions.

So the question is, within a DMX module and C-Bus, what's the best way to store a desired level and use that as the only "on" level?

There doesn't seem to be a way to set maximum levels within the DMX, otherwise it would be easy (set a group on or off, and for "on" let the actual on level be set by the maximum). So in the absence of that feature, any suggestions?

It looks like at some point I'm going to sit with the architect tweaking levels until he's happy, at which point I need some way to store them for recall whenever I turn on the power to the LEDs.

 

I would do this from the C-Bus side of things. If you configure your key input unit to use the Memory Toggle 2 key microfunction as the Short Press event (all the others can be Idle) then the level of the C-Bus Group will toggle between Off and the Recall 2 level each time you press the button.

The other way to configure a key for this function is to use the default Preset 1 function, where a short press recalls the level (either Recall 1 or 2) and a long press turns the group off.

 

If only it were that simple!

At present I have a bus coupler in the room, 2 channels in use, one of which is used to dim the main room lights. However we also control the room from a head end PC. I'm going to need to have the feature lighting off if the room lights are off, but not necessarily the other way around. There won't be a switch for the feature lighting, it'll be on automatically if the room is occupied and some other conditions are met.

I'm going to have to give this some thought, but to complicate things further I believe there will be three sets of LEDs which will switch together but at different levels.

 

Scenes are a good way to define a lot of levels for different groups. Most units that support scenes have a storage capacity for at least 40 group-level pairs in a single scene. If you are translating C-Bus groups to DMX, and are controlling with a head end PC, you should be able to initiate a scene after any power recovery (assuming you can detect the loss and recovery of power), or just send the scene regularly, but at a low rate (if you can't detect loss and recovery).

 

I think scenes are going to be the way to go but at present I don't have anything on the network that support scenes. I've not really played much with scenes, what's going to be the minimum I'm going to require? I'm thinking about sticking a PAC in but that might well be overkill....

[EDIT]
I should add that whatever I use will have to go into an electrical panel, not on the wall somewhere useful, so ideally wants to be a DIN mounted module not a switch. I think that's probably means PAC is my best (only?) option but I'd welcome alternative suggestions!

Also: I need to have some way to commission this with the architect so some way to set anything up to 12 group address values from within the room; the PAC will give me that via a laptop and Toolkit.
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