Gemma+NeoPixel 0: Wheel

This post describes the Wheel function that is part of the strandtest example included within the NeoPixel library.

I’m writing it as a preamble to a planned series of articles about my experiments with an Arduino Gemma and a NeoPixel ring with 16 RGB LEDs.

The Wheel function takes a value from 0 to 255 (inclusive) and maps that onto a red-green-blue color wheel. Internally, it computes a value for the red, green, and blue components of the result. Those three parts are combined by the strip.Color function to return a 32-bit value representing that color.

The Wheel function may eventually be included in the NeoPixel library, but for now, include it in each of your sketches.

uint32_t Wheel(byte WheelPos) {
  WheelPos = 255 - WheelPos;
  if(WheelPos < 85) {
    return strip.Color(255 - WheelPos * 3, 0, WheelPos * 3);
  }
  if(WheelPos < 170) {
    WheelPos -= 85;
    return strip.Color(0, WheelPos * 3, 255 - WheelPos * 3);
  }
  WheelPos -= 170;
  return strip.Color(WheelPos * 3, 255 - WheelPos * 3, 0);
}

From a quick code reading, we can see that the numbers from 0 to 255 are divided into three sections: 0-85, 86-170, and 171-255. But what we care about more than the math are the colors that result.

Let’s build a table showing how an input value is transformed. I wrote a little Python code to take each number from 0 to 255 and give the resulting red, green, and blue values. In addition, I added the HTML hex color code and the color itself. Maybe it’ll help you when incorporating Wheel into your own designs.

The color wheel only includes red, green, and blue combinations. There is no black and no white. You may need to use other techniques or in addition to the Wheel function.

Get ready for some scrolling!