Pixel ribbons

Think LEDs per meter. It makes a difference.

We were sitting around the conference table when Chuck (as in The Mr. Smith) said we’re building pixel trees for the next edition of the magazine. What’s a pixel tree? Think along the lines of a megatree, but every light is controllable. As Mr. Smith likes to say: any light, any color, any time. These are the trees that have moving patterns on them, can scroll pictures or text and truly wow your audience.

Light-O-Rama came out with something called the Cosmic Color Ribbon in 2009. The ribbon had 150 RGB based LEDs evenly spread across a five meter (16.4 feet) strip. Those LEDs were divided into 50 groups (called pixels) and each pixel was individually controllable through a custom controller and power supply provided by Light-O-Rama. Any pixel on this strip could be any color at any time. Cutting edge decorators have taken multiple Cosmic Color Ribbons, made them into the shape of a Christmas tree (think 12-24 vertical strips, skinny at the top, wide at the bottom) and dazzled the world with the moving designs of colorful lights. Now other vendors are doing similar tricks and the term pixel trees has come into existence.

Mr. Smith tasked us with building several different types of pixel trees using off-the-shelf components. We were excited and scared at the same time. This had super-geekfest written all over it.

We talked at length about how to build a pixel tree and decided to use pixel ribbons because they seemed the easiest. I was told to become the expert of pixel ribbons.

We could have used the well documented Light-O-Rama Cosmic Color Ribbons but for this issue of the magazine that was too easy. Instead, we located the individual components on our own.

I started looking for pixel ribbons and became overwhelmed. They come in different lengths, different pixels per meter, different colors, different voltages and different LED types, etc. Why can’t this be easy?

Pixel ribbons came configured in different ways
Pixel ribbons came configured in different ways

Pixel Density

The image is a good example of four different types of pixel ribbons.

  • The top white ribbon in the image: This is a Light-O-Rama Cosmic Color Ribbon. Look carefully for the four horizontal copper fingers at each end. Between the fingers are three white squares and these are the LEDs. Inside each of these square LEDs are three smaller LEDs (red, green and blue.) The other black items on the ribbon are the electronics required to decode the control signals and drive the LEDs. Between the copper fingers is equivalent to one pixel. It’s about three inches long and all three LEDs do the exact same thing. Think of them as being wired in parallel. There are 30 LEDs per meter of ribbon (39.37 inches) and since the LEDs are wired in groups of three it works out to ten controllable pixels per meter. Light-O-Rama Cosmic Color Ribbons are five meters long. At ten pixels per meter, a Cosmic Color Ribbon has 50 pixels over five meters.
  • The upper black ribbon in the image: This ribbon has the same LED spacing (the white squares) as the Cosmic Color Ribbon but look carefully at the horizontal copper fingers. Instead of four fingers there are three and the fingers are between each LED. There are 30 controllable pixels per meter. For a five meter ribbon, there are 150 pixels or three times more than the LOR Cosmic Color Ribbon
  • The white ribbon near the middle in the image: Notice the copper fingers are closer together. There are 60 controllable pixels per meter.
  • The bottom black ribbon in the image: The copper fingers are really close together. There are 144 controllable pixels per meter.

Data Flow

Since each pixel can be any color at any time, there’s a lot of information flowing between your sequence program and the pixel ribbon. Pixel ribbons are pretty smart. The pixel control information enters at one end and the pixels address themselves so each one is unique. The first pixel knows it is pixel 1, the next knows it’s pixel 2, etc. A little known trick is if there is a bad pixel, you can remove it by cutting on each side at the center of the copper fingers and solder the good halves back together. As an example if you had a 60 pixel ribbon and pixel 27 is bad, you can cut it out and the pixels will readdress from 1-59 with no gaps.

Look at the black ribbon and find the white arrows. The pixels address themselves in the direction of the arrows. The control information cable must be connected to the left side and the pixel addressing flows from left to right. What happens when you connect the control information cable at the wrong end of the ribbon (going against the flow of the data arrows?) There’s no harm done but there’s also no pixel activity either. Follow the arrows!
The white ribbon above has very small dataflow arrows. Look closely and you’ll see the center copper finger labeled DI or DO, depending on which side of the pixel LED you are on. DI means Data In and this is the direction the control information cable is injected. DO means Data Out and is where the data leaves the pixel. Notice the DO’s always flow into the DI’s. What happens when you connect the control information cable into a DO instead of DI? There’s no harm done but there’s also no pixel activity either. As we said earlier, the data signal enters at DI!

Those Copper Fingers

Note the copper fingers for soldering wires and the arrow showing the data flow
Note the copper fingers for soldering wires and the arrow showing the data flow

On the previous page did you catch the top ribbon has four copper fingers between pixels while the others have three? It has to do with the types of pixel LEDs being used. For our “three finger” ribbons we’re using something called a WS281x. If you want to know about all the different types of LED pixels and why they need three or four copper fingers, ask a geek.

Dummy Proof Voltage

Some ribbons need 12 volts DC and others require 5 volts DC. The latest generation of pixel ribbons use WS2812B LEDs meaning 5 volts DC. We went this route mainly because there’s built in protection should you wire the voltage backwards. How do we know? We did, by mistake, of course. When the ribbon refused to respond we checked our work, reversed the polarity and the ribbon worked fine. With other ribbons using a different type of pixel LED we managed to send them to the trashcan after a wiring mistake.

Power Needs of Pixel Ribbons

As if things were confusing enough, these ribbons love electricity. The more LEDs on a ribbon, the more power is required.

Ever wonder why most pixel ribbons are only five meters in length? The ribbon is really a long, thin and flexible circuit board. Electricity comes in one end and by the time it gets to the other end there’s not enough left to power another ribbon. You can tell when people try and cheat because the colors begin to fade when you lengthen a ribbon. It becomes very evident when all the pixels are 100% white, meaning all the reds, greens and blues are at maximum intensity. This is when the most power is being used and when there’s not enough available, the colors will fade.

Power Connector at Both Ends?

Because of the high density of pixels on some ribbons, you’ll find a power connector at both ends of the ribbon. The pros call it power injection since you’re adding power at unusual points. If there’s a power connector at both ends of the ribbon, this is a not-so-subtle hint to provide power to each end so all the pixels will be bright. We’ve built several pixel trees and are now in the habit of providing power to both ends of the ribbon if there’s more than 50 pixels. Be careful that you connect the control information signal at the proper end of the ribbon, though.

Power Supply Demands

To continue this geekfest, since pixel ribbons are low voltage devices you need to make sure your power supply is large enough. Confirm the voltage of the supply is the same as the voltage required by the ribbon. Look carefully at the ribbon package. You’ll typically see the length of the ribbon, voltage requirement as well as the total maximum power consumed in watts. Since you’ll probably be using multiple ribbons, make sure when you add up the maximum power for each that your power supply can provide that many watts. Break out the calculator if you have to.

Pixel Ribbon Sources

Check with the vendors mentioned in some of

our other pixel articles in PlanetChristmas Magazine. They will make sure you get new product at a good price and quickly swap out anything that goes bad.

You can also order pixel ribbons directly from the manufacturers in China. The prices typically look good until you factor in delivery time and shipping costs. We suggest ordering more than you need so if one ribbon goes bad or doesn’t work, you can replace it quickly while figuring out what to do with the sick one.
Now you’re the pixel ribbon expert!

This article was included in the April 2014 issue of PlanetChristmas Magazine.

By Fred Garvin

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