31 December 2013

Customer Question: Should I use a centralized or de-centralized controller for an element?

HolidayCoro sales/support often sees common, open-ended questions from our customers and here on our blog we post detailed responses publicly so that other people will be able to learn from the decision making process we use to answer these questions.

Today's question is:  "I am making 16 pyramids and would like to light them up using 3 or 4 Basic Rectangle RGB LED Waterproof Module per pyramid.  The pyramids will be in the front yard each about a yard apart.  My Question - should I buy 16x Item #30 Basic 3 Channel RGB DMX Controller or should I buy 2x Item #24 Basic RGB 27 Channel DMX Controller.  Is there any advantage to either in this situation?"

For this given project it has already been determined that basic or dumb RGB lights should be used as opposed to pixels and this is often the case when an element doesn't need the control that pixels offer or when there are larger distances between elements.  So the question becomes - should the basic RGB DMX controller be centralized in the form of a 27 channel (9 RGB outputs) DMX controller or individual 3 channel (1 RGB output) DMX controller in each element?  The issue comes down mainly to two factors - cost and complexity:

  • Cost - The number of RGB lights won't change between the two methods, so we'll exclude that from the calculations, though what does mainly matter are wiring, power supplies, controllers.  Also, we need to determine he power consumption of the RGB Modules, which in this case consume about 100ma (1/10th of an amp) at 12v DC - or 16 elements x 4 modules is 6.4 amps total.  So, we'll take the number of individual elements here - 16 and do some comparison math with the two options: 
    • Centralized - This method allows us to have one (or two in this case) centralized controllers - the costs involved are:
      • $114 ($57 x 2) - 27 Channel DMX controllers
      • $26 ($13 x 2) - 45w (3.75amps at 12v) power supply.  This solution would power each 27 channel controller with a single power supply.  It's a little tight on the power at 3.2 amps total per controller (32 modules per controller) but it should work.
      • $20 ($10 x 2) - Waterproof housing.  The 27 channel controller isn't waterproof, so you'll need a waterproof/resistant housing and this varies by region, water/snow conditions and budget.
      • $20 (100ft @ $.10 per foot x 2) - CAT5 wiring.  You'll need to get the output of the controller out to the individual elements and CAT5 would be a good solution here as the current consumption of the lights is below the current carying ability of CAT5 at a bout 3 to 4 amps and it has 8 wires, so you could double up each wire for the 4 wires required for RGB lights.
      • ~$180 - Total
    • De-Centralized - This method allows us to have an individual, 3 channel DMX controllers in each element - the costs involved are:
Of course there are other minor costs - shrink wrap, solder, tools, shipping, etc and we've not included those in the calculations above.  So, on the surface, they look pretty much about the same from a cost basis, so let's take a closer look and consider all the other factors:
  • Complexity
    • Interconnections - Left out from above on both are how you'll interconnect the wiring from the element to the controllers.  
      • Centralized - With the centralized solution, you could solder the CAT5 wire directly to the lights in the element and then have elements with 20, 15, 10 and 5 ft lengths of cable coming off them and then you'd fish that wire into the controller case and screw it down to the terminals on the controller.  The problems with this solution are that it makes future adjustments in length complicated since you've already set the length of the cable from the element to the controller when you built the element.  Additionally, you'll have to deal with elements that have attached wire and then manually wire up each element to the controller, adding to your display setup time.  An additional down side to this method is that you also have more wire spread out over your display which can present safety/tripping hazards.  The upside to this method is that it doesn't really require any additional connectors - just tin the wires where they go into the controller screw terminals.
      • De-Centralized - If you've placed the individual CAT5 controllers in each element, that means that you can simply attach a 3 way splitter to each CAT5 plug, then plug in the necessary CAT5 cable between each element (5ft lengths in this case) in a daisy chain arrangement.  Then you just build a power injector for each of the two bands of 8 elements and this allows you to run the power and the DMX signal from one element to the next.  The amount of wire is limited as it only goes from one element to the next.  The down side is that you need to ensure that you control water ingress in to the CAT5 connectors and use a corrosion control spray - usually mounting the controller up-side down under the element would be more than sufficient to manage water ingress.  The real beauty of the Power+DMX over CAT system is that you can assembly your display quickly just by plugging into each element to the element next to it.

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