Rainbow

Now let's bring some real color to this class!

Recall our color wheel MicroSim:

Let me introduce you to one of the most colorful functions in the MicroPython world. It is the famous wheel function. When you think of the color wheel, think of the wheel function. Wouldn't it be nice to just take a stroll around the color wheel and walk through all the colors of the rainbow! Well, wheel is here to help you do just that!

The wheel functions looks like this:

wheel(color_number_0_to_255)

You just give it a number from 0 to 255 and it will return a red, green and blue number that will span the spectrum from red, orange, yellow, green, blue, indigo and violet and then back to red again.

Here is the entire elegant wheel function in all its glory:

def wheel(pos):
    # Input a value 0 to 255 to get a color value.
    # The colors are a transition r - g - b - back to r.
    if pos < 0 or pos > 255:
        return (0, 0, 0)
    if pos < 85:
        return (255 - pos * 3, pos * 3, 0)
    if pos < 170:
        pos -= 85
        return (0, 255 - pos * 3, pos * 3)
    pos -= 170
    return (pos * 3, 0, 255 - pos * 3)

Here is a markdown table with the values for 10 common colors from the wheel function. The wheel function creates a smooth transition from red to green to blue and back to red as the input value goes from 0 to 255.

Common Colors in the Wheel Function

Color Name	Wheel Position	RGB Values
Red	0	(255, 0, 0)
Orange	32	(159, 96, 0)
Yellow	64	(63, 192, 0)
Green	85	(0, 255, 0)
Teal	127	(0, 129, 126)
Cyan	128	(0, 128, 127)
Blue	170	(0, 0, 255)
Purple	191	(63, 0, 192)
Magenta	213	(126, 0, 129)
Pink	234	(189, 0, 66)

This table shows how the wheel function generates a spectrum of colors by adjusting the RGB values based on the input position (0-255). Each position produces a unique combination of red, green, and blue values, creating the full color wheel.

I suggest you bookmark this page because for fun projects we will come back to this function frequently.

Testing the Wheel Program

Here is a full test program that will demonstrate how the wheel function is used in practice.

from machine import Pin
from neopixel import NeoPixel
from utime import sleep
from urandom import randint
# get the configuration information

NUMBER_PIXELS = 30
strip = NeoPixel(Pin(0), np)
# we have each pixel step through the color wheel
color_wheel_step = int(256 / NUMBER_PIXELS)

def wheel(pos):
    # Input a value 0 to 255 to get a color value.
    # The colors are a transition r - g - b - back to r.
    if pos < 0 or pos > 255:
        return (0, 0, 0)
    if pos < 85:
        return (255 - pos * 3, pos * 3, 0)
    if pos < 170:
        pos -= 85
        return (0, 255 - pos * 3, pos * 3)
    pos -= 170
    return (pos * 3, 0, 255 - pos * 3)

current_color = 0
print('Drawing rainbow in', np, 'steps with step size of: ', color_wheel_step)
for i in range(0,NUMBER_PIXELS):
    strip[i] = wheel(current_color)
    current_color = current_color + color_wheel_step
    print(i, current_color, wheel(current_color))
    strip.write()
    sleep(.03)