Hi,

I need some input from any DMX gurus onboard

We are adding on some DMX garden lighting to a Crestron project. Usually we create DMX 'shows' using a desk or software controller, save these into a playback controller and trigger the playback unit from the Crestron system. We do this as previously when we have programmed Crestron to directly control DMX (using their RS232 connected bridge unit) we found that doing colour fades, even on just one RGB LED Strip, ate up processing power, and we ran it in a different program slot on the processor to minimise impact on the main program.

Crestron however now have a sACN module in their database that can be used to send DMX values to an sACN to DMX bridge over ethernet, which begs the question "why not try programming the show on the Crestron processor and cut out the middle man?"

The reason the the last attempt at this was so processor hungry (even for just 3-channels) seemed to be that for every colour increment of the fade change, DMX values for three channels were being transmitted over RS232 and onto the DMX bus, and I'm not sure if this was necessary.

My question regarding DMX protocol therefore is: if you are asking a fitting to colour change, is it necessary to transmit a DMX value for every intensity increment for each of the RGB channels to do this, or within the DMX protocol is there a 'fade time' command that can be issued to offload the process to the fitting rather than sending all the incremental values?

I know when programming a show on the desk i can allocate a slider to 'fade time', but i don't then know if this just means the desk is sending out all the value increments spaced depending on the fade time slider value, or whether it is sending a target colour value and a fade value for the colour transition to the fittings?

Can any of the collective advise?

TIA

Nick

Correct, constant commands are sent over the DMX bus for fading and changing colors.

This is typically why an external program or controller is used because it’s way too busy to rely on an automation controller alone.

The Engineering Solutions Response Box is a great controller to use. I’ve been using it in my projects for years. I believe they even host a Crestron module on their website.

Thanks for this, I wont bother going any further along the lines of direct-from-Crestron control for this project. Your answer has probably saved me from many hours of headaches!

We have previously used playback units from iSplay and Chauvet with success, however this time I am considering an Enntec sPlay unit.

I see a lot of the DMX fittings seem to have macros built-in that perform colour fade and switching sequences which can be triggered by a value on a DMX channel. I guess if I needed something fairly basic this would be more suited to direct Crestron control as i only need to send one time values to select, start, and stop the fitting macro?

This job however needs more of a 'show' element as it features around thirty fittings garden-wide that need to present a coordinated effect.

Nick,

Do yourself and customer a favor and at least check these guys out. Only device I will use with DMX.

[Link: response-box.com]

Very helpful support as well. Plain. simple, ASCII codes too. Has some scenes built-in, but you can create your own scenes, save them, for a simple 232 string recall.

I also use these and have developed an extensive module for controlling any DMX 3, 4 or 5 channel strip or fixture. The module has 36 preset colors, the ability to change all 5 channel values on the fly, 12 preset sequences with controllable fade and interval times as well as 12 user definable and savable colors. It is chatty by nature as it is controlling all of the DMX conversation but I have not found it overwhelming. I suppose it depends on the processor used and the size/efficiency of your other programming. Using it's own program slot is not a bad idea if you have a large number of fixtures but I am sure there will be a limit to what any processor (Crestron or a native lighting processor) can handle.

The benefit to using an external DMX controller is that you can program everything in an environment designed to do just that and then simply trigger your presets using Crestron or some other control system.