Factors to Consider When Designing an RGB Pixel Matrix

Over the years we at HolidayCoro have been asked why we only sell a single pixel matrix product - our 18" x 24" pixel with either 150 or 162 pixels.  Well, actually, we've produced a fair number of custom matrix based panel items for customers over the years and the main reason we don't offer all these variations for sale is because each project is so different.  The article hopes to provide information on factors that we consider when working with customers on designing a pixel matrix and hopefully this will help those building their own or working with us to custom produce one.

• What exactly is the purpose of the pixel matrix?
• Is this matrix intended to be dense enough that viewers will be able to see objects scrolling or displayed on it such as text, icons or logos?  
• What is the viewing distance from the matrix to the viewer?  If you've ever looked at a big screen TV up close, you can understand the relationship the size of the pixels (lights) have to the distance they are being viewed from.
• What is the viewing angle?  A curve pixel panel (such as a pixel megatree) can look odd if all the pixels in the matrix are not visible to the viewer.
• What is the shape of the matrix?  Is the matrix a cone, in the case of a pixel megatree, where the pixels at the top are in a much higher density than those at the bottom of the tree?  Is the matrix cylindrical?  flat? concave or convex?  All these designs have an effect on the final output, pixel density and mounting methods.
• Technical factors to consider include:
• Number of pixels - This is an important factor to consider and the number shouldn't be random - it should be based on the design requirements.  Look closely at how many pixels you'll need and their spacing from each other.  If needed, build a sample mock-up and view it from the distance and angle you expect your viewer to view it from. 
• Pixel height and width - Also consider how many pixels you may need to display certain items such as a text font which often require a 5x8 pattern.  Again, keep in mind that you will also need to have the pixels close enough that the human eye can make out the pattern - just because it might look good in the sequencing software doesn't mean that will translate into the real world.  
• Multi-Panel Alignment - If the matrix will be comprised of several panels, be sure to carefully consider the spacing within a panel and how it relates to the spacing induced between two adjoining panels.  This may mean that you will need to increase the center-to-center spacing of the lights to match that of the panel-to-panel gap.
• Mounting or support - An important part of any matrix is how you will mount it - because a matrix tends to be a flat area (excluding pixel megatrees), you'll need to think hard about what system you'll use to mount the substrate on to which the pixels are mounted. If that surface catches the air, there could be problems with it blowing over or toppling the support structure.  Also consider that you'll need to store this mounting system in the off-season - so if the panels need to go into an attic, consider the opening going to the attic.
• Substrate mounting - In most cases, you'll need to mount your pixels to a substrate - not only to support them but to maintain a clean and even spacing - there isn't anything worse than a matrix that has mis-aligned pixels.  How you mount those pixels can vary - it could be holes in coro like we do at HolidayCoro or it could be screwed or glued to wood slats or plywood - this all depends on your pixel type.
• Pixel type - The type of pixel you select will often be a by-product of the distance and viewing angle of the people viewing your matrix.  These pixels could be in a strip form, node form or module form and each has it's pros and cons and there is no one pixel that is best suited for all matrix types.
• Channels - Keep in mind that you'll often have many, many DMX channels on a matrix display and it makes sense to select pixel counts that fall within a set number of DMX universes - so don't design a pixel display that requires 180 pixels (18 wide by 10 high) if it could have been done in 163 pixels (18 wide by 9 high) which fits neatly into a single DMX universe and thus saves you a controller or controller output and also makes your sequencing easier to setup and manage.
• Repairs - Factor in that pixels DO fail and that you'll need to fix them.  So consider how easy it will be to remove and replace pixels.
• Cost / Budget - A matrix can grow in cost quite quickly when you factor in hundreds to thousands of pixels, so be sure to ask yourself the overall value of the matrix and how well it accomplishes its goal.  If this is just for announcing the radio station and song titles, a simple matrix will do - if you need to scroll logos or animations, you'll need a larger and more expensive matrix.
• Big isn't always better - Since pixels have come down in price and complexity, we've seen a number of pixel matrix panels (and pixel megatrees) in displays that just completely over-shadow and "hog" the display.  We believe that a well balanced display should be the ideal and that one mega-element can leave your audience so fixated on one area that they fail to see other areas and animation. 
• Software & Sequencing - Building a matrix panel is only one part of the process and the other major part is generating the sequencing for that panel.  Since it is nearly impossible to "hand" sequence matrix displays, you'll want to consider applications like LightShow Pro's matrix animator or Light-o-Rama's Superstar lights or other freeware applications that have been coming into the market.  You may even want to design your pixel display hardware, then start sequencing it before you buy or build it to evaluate how complex it will be to sequence the matrix. 

The Good, Bad and the Future: Pixel Nodes



Channel Letter Sign with 8mm Pixel Nodes

8mm Tri-Color RGB Node with 12mm Case

First, a little background on the 8mm, tri-color LED node.  For anyone that has been to Asia (mainly China), you'll notice that they have many signs produced that use these nodes.  These signs are what we would, in the US, call Channel Letter signs.  In the US, we normally have channel letter sign that has an acrylic face with sheet metal sides and back that form a box, which is then illuminated with either neon (older) or LED modules (newer).  This channel letter design in the US produces a smooth clean, single color letter. 

While China also has the same type of channel letter signs, they also have the same sign but instead of an acrylic face they again use sheet metal for the face.  In that sheet metal they then punch ~12mm holes.  In these holes they install either dumb or intelligent RGB nodes.  This creates a sign that can be addressed either as a matrix (intelligent pixels) or just as a single color (dumb).  This type of sign design is nearly non-existent in the US currently.  So, why does this matter?  Well, this explains first why the physical case of nodes are generally 12mm in diameter.  It also explains why the little "fingers" that are on the side of the nodes are only about 1/16 of an inch between the top and bottom - they are design to fit into thin gauge sheet metal and pretty much nothing else. 

Here is the problem - they often are not exactly the same diameter, either from a single vendor, even within a single string or very often from vendor to vendor.  So you might have nodes with diameters of .40", .42", .44", .46" and so on.  So, if you want to make, say, a scrolling matrix panel (see sample panel video we've produced for a customer to the right) with pixel nodes. 

What we found is that when we produced these panels from ABS plastic, a hard, stiff plastic sheet, they would hold perfectly but only if you cut the hole with .01-.02" of the actual diameter of the node.  Any more and the node would either fall out or would be wonky and not point straight out.  Any less and it was impossible to get the node in at all - in fact many people had to use lubricant just to get some of the nodes in a string into the holes (which were all exactly the same diameter).  So, it was clear that if we wanted to sell a product that would hold and mount RGB nodes from any vendor, that we would need a different method of mounting them. 

At first this seems simple - just find some plastic that can hold them, right?  Well, it turns out that isn't the case.  In holding pixel nodes, you have a number of factors to consider:

• They need to be held tightly so as not to point different directions, causing different levels of light output.
• The material needs to be able to "adjust" to slightly different sized nodes from different vendors.
• The material needs to stand up to UV and a wide range of temperatures (-20 to 130f).
• The material needs to be at a cost point that the final product is reasonably priced.
• The material needs to be strong enough to handle 5-15 pounds of nodes.
• The material needs to be strong enough when mounted to a frame or other material to resist tearing, sagging, stretching or failing in high wind loads.
• And finally the material needs to be easy to machine on our CNC equipment.

It's a tall order and that's why we've yet to offer a "standard", non-custom mounting frame.  So, starting in February, we spent countless hours researching the tens of thousands of materials out there that could be a possible match for the magical material so we can bring products based on nodes to you.  As of March 8th, 2013, we have narrowed the field down to two companies that make very specialized plastics that meet our needs and we are working with them to produce and test the plastics that we hope will solve this problem.  We hope to have material in the April/May time frame after testing is completed and products shortly there after.

  

So, what do we plan to produce with this magical plastic?  Well that's a good question.  We know that lots of you out there want a method of creating a simple scrolling matrix screen like what is shown in the video above, so that's a pretty much no-brainier - we'll offer complete kits to build exactly that. 

We also plan to offer a mini-tree that also holds the nodes and is curved like a circular tree with the nodes "studded" through out - this would be offered as a dumb and smart mini-tree kit.

As is often the case, once we have a starter product, often customers are the source of some of the best ideas out there that we could never imagine.  So, if you have ideas for a product that incorporates RGB nodes, smart or dumb, feel free to email us or leave feedback below on the blog.

29-Mar-2013 - Update:  We have released the matrix panel here:  http://www.holidaycoro.com/Pixel-Matrix-Mounting-p/265.htm
 

Thanks,

David

HolidayCoro.com