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Tips for driving WS2811 LED strips (Part 1)

12 Mar 2015  | Lee Goldberg

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Due to their versatility, commodity-level pricing and the eye-popping visual effects they create, programmable LED strips have become a staple ingredient for both Maker-style projects and more conventional LED lighting applications. But as I quickly discovered when using them as a "Mood LED" for my Smart Hat project3, the serial protocol bus used to address and control the LEDs can be somewhat complicated and tricky to use. I've summarised some of the key design issues and located a few resources to help shorten your climb up the learning curve when you need to include LED strips in one of your projects.

Figure 1: The NeoPixel LED Strip in its native habitat. Courtesy of Adafruit Labs.

There are several types of LED strips but this article will focus on driving LED arrays which use WS28114 and WS28124 driver chips. This is in part because products like Adafruit's NeoPixel strips which use them tend to be less expensive than similar products which use LPD8806 drivers. The cost was only one of the reasons I used Adafruit's NeoPixel strips (they are based on the '2811) for my Smart Hat project. I also like NeoPixels because they have consistently high quality and come in a wide variety of pixel densities and offer several form factors besides the traditional strip such as rings, matrixes, and several different types of individual pixels.

Figure 2: NeoPixel variants. Courtesy of Adafruit Labs.

On the other hand, commanding a WS2811 device via its serial control bus is not a straightforward task. Part of this is because it uses a single combined clock and data line to ripple the instructions for each LED down the serial daisy chain bus which runs between each pixel (figure 3). This means that that pixels can't be addressed individually so any change requires refreshing the instructions loaded into all the pixels upstream of the one you want to update.

Figure 3: WS2811 LED controllers pass instructions from the host MCU from pixel to pixel using a daisy-chain serial bus. Courtesy of World Semiconductor.

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