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What is a Null Pixel
Unlike regular LED strings, Pixels allow each individual RGB LED to be turned on and off separately. In order to have each RGB LED be capable of individual control, it must have data signaling go to the Pixels to command them. Pixels have power wires connected to them to power them, but Pixels also use high speed serial data communications over additional wires in the cable to them. The serial data signal can only go a certain distance before the signal is to week or distorted to allow proper function of the Pixels. If the signal is too weak or distorted, the Pixels may not respond properly and flash erratically or not light at all.
Null Pixels are placed on the power and signal lines between the Pixel Controller and the first Pixel that is located at a distance from the controller. The Null Pixel basically is a regular Pixel that is not used for lighting, but merely repeats the signal and sends it down the line to the next Pixel. It is possible to splice multiple Null Pixels into a line if the distance is great. By inserting Null Pixels in the signal lines you regenerate the data signals and the clock signals and allow them to go further away from the controller.
When splicing in Null Pixels, pay close attention to the wire color codes and the Pixel Orientation. There is an input and an output side to every pixel.
4 Wire Pixels vs 3 Wire Pixels
The distance you can go depends on many factors including the proximity to other power and data wires, wire shielding and if you use twisted pair wire or not. You should always test your Pixel layout with the proper length wires to see if there will be an issue and the need for additional Null Pixels.
Managing Null Pixels in Pixel Controllers and Sequencing Software
Pixels work by receiving all of the data for the entire string, using the data meant for that specific RGB LED and then passing the remainder of the data down the string to the next Pixel which repeats the process. You need to account for the Null Pixels in either the Sequencing Software or the Pixel Controller.
If your Pixel Controller has a setting for Null Pixels, like the E682 does, then you just set the controller up with the correct number of Null Pixels and then in the Sequencing Software you just sequence for the active Pixels in your design and ignore the existence of the Null Pixels. The Null Pixels do not add additional channels to your sequence.
If you Pixel Controller does not have a setting for Null Pixels, like many low cost controllers, then you must account for the fact that there are Null Pixels in your sequence and adjust your sequences to ignore the Null Pixels. The Null Pixels do add additional channels to your sequence.
Different Styles of Pixels
Dumb RGB or Intelligent Pixels??
Things You Will Need To Get Started With Pixels
Pixel Wiring Colors
Choosing a Pixel Voltage: 5V vs 12V