Introduction to Python and Microcontrollers

Rainbow Light

Make all 8 LEDs on the RGB LED Module display a smooth, evenly-spaced rainbow that continuously shifts — combining the LED Pixel module with the color-wheel technique from Gradient Color Light.

Component List

Same module, board, and circuit as LED Pixel.

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Circuit

Same circuit as LED Pixel — see that page for the schematic and wiring diagrams.

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Code

File: 02_input_and_output/code/Rainbow_light.py

from machine import Pin
import neopixel
import time
pin = Pin(48, Pin.OUT)
np = neopixel.NeoPixel(pin, 8)

brightness=0.1         #brightness: 0-1.0
red=0                  #red
green=0                #green
blue=0                 #blue

def wheel(pos):
    global red,green,blue
    WheelPos=pos%255
    if WheelPos<85:
        red=(255-WheelPos*3)
        green=(WheelPos*3)
        blue=0
    elif WheelPos>=85 and WheelPos<170:
        WheelPos -= 85;
        red=0
        green=(255-WheelPos*3)
        blue=(WheelPos*3)
    else :
        WheelPos -= 170;
        red=(WheelPos*3)
        green=0
        blue=(255-WheelPos*3)
        
while True:
    for i in range(0,255):
        for j in range(0,8):
            wheel(i+j*255//8)
            np[j]=(int(red*brightness),int(green*brightness),int(blue*brightness))
            np.write()
        time.sleep_ms(5)

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How to Run

Online

1. Open Thonny → 02_input_and_output/code/.
2. Double-click Rainbow_light.py.
3. Click Run current script — the 8 LEDs display a rainbow that shifts smoothly along the strip.

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Code Explanation

The color wheel function

def wheel(pos):
    global red,green,blue
    WheelPos=pos%255
    if WheelPos<85:
        red=(255-WheelPos*3)
        green=(WheelPos*3)
        blue=0
    elif WheelPos>=85 and WheelPos<170:
        WheelPos -= 85
        red=0
        green=(255-WheelPos*3)
        blue=(WheelPos*3)
    else:
        WheelPos -= 170
        red=(WheelPos*3)
        green=0
        blue=(255-WheelPos*3)

Same idea as Gradient Color Light’s wheel(), but using a 0–255 range (since np[j] expects 0–255 color bytes, not 0–1023 PWM duty values) and setting red/green/blue globals instead of writing to PWM pins directly.

Spread the wheel across all 8 LEDs

for i in range(0,255):
    for j in range(0,8):
        wheel(i+j*255//8)
        np[j]=(int(red*brightness),int(green*brightness),int(blue*brightness))
        np.write()
    time.sleep_ms(5)

For LED j, the wheel position is offset by j*255//8 — so each of the 8 LEDs sits at an evenly-spaced point around the wheel (1/8th of the way apart) instead of all showing the same color. As i increases, every LED’s position shifts together, sliding the rainbow along the strip. brightness (0.0–1.0) scales the final RGB values down before they’re written.

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Key Concepts

• Per-LED phase offset: adding j*255//8 to the wheel position spreads one color cycle evenly across 8 LEDs instead of showing one color at a time
• Brightness scaling: multiplying each color channel by a 0–1.0 brightness value dims the whole strip without changing the color math

See Class neopixel for the full API reference.

Further Exploration

• Change brightness to 1.0 for full intensity, or near 0 for a dim glow.
• Change the divisor in j*255//8 to make the rainbow repeat more than once across the strip.

Back to Module

Adapted from Python_Tutorial.pdf Project 6.2

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