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2.4 Colorful Light

In this lesson, we’ll explore how to create various colors using an RGB LED and the Raspberry Pi Pico 2. By adjusting the intensity of the red, green, and blue components, we can mix light to produce a wide range of colors. This concept is based on the additive method of color mixing.

What is Additive Color Mixing?

Additive color mixing involves combining different colors of light to produce new colors. When red, green, and blue light are combined in various intensities, they can create any color in the visible spectrum. For example:

• Red + Green = Yellow

• Red + Blue = Magenta

• Green + Blue = Cyan

• Red + Green + Blue = White

What You’ll Need

In this project, we need the following components.

It’s definitely convenient to buy a whole kit, here’s the link:

Name	ITEMS IN THIS KIT	LINK
Newton Lab Kit	450+	Newton Lab Kit

You can also buy them separately from the links below.

SN	COMPONENT	QUANTITY	LINK
1	Raspberry Pi Pico 2	1	BUY
2	Micro USB Cable	1
3	Breadboard	1	BUY
4	Jumper Wires	Several	BUY
5	Resistor	3(1-330Ω, 2-220Ω)	BUY
6	RGB LED	1	BUY

Circuit Diagram

The PWM pins GP13, GP14 and GP15 control the Red, Green and Blue pins of the RGB LED respectively, and connect the common cathode pin to GND. This allows the RGB LED to display a specific color by superimposing light on these pins with different PWM values.

Wiring Diagram

The RGB LED has 4 pins: the long pin is the common cathode pin, which is usually connected to GND; the left pin next to the longest pin is Red; and the two pins on the right are Green and Blue.

We use a higher resistance for the red LED because it is typically brighter than the green and blue LEDs at the same current.

Writing the Code

We’ll write a MicroPython program that controls the intensity of each color using Pulse Width Modulation (PWM) to produce different colors.

Note

• Open the 2.4_colorful_light.py from newton-lab-kit/micropython or copy the code into Thonny, then click “Run” or press F5.

• Ensure the correct interpreter is selected: MicroPython (Raspberry Pi Pico).COMxx.

import machine
import utime

# Initialize PWM for red, green, and blue pins
red = machine.PWM(machine.Pin(13))
green = machine.PWM(machine.Pin(14))
blue = machine.PWM(machine.Pin(15))

# Set the PWM frequency
red.freq(1000)
green.freq(1000)
blue.freq(1000)

def map_value(x, in_min, in_max, out_min, out_max):
    # Map a value from one range to another
    return int((x - in_min) * (out_max - out_min) / (in_max - in_min) + out_min)

def set_color(r, g, b):
    # Set the color by adjusting duty cycles
    red.duty_u16(map_value(r, 0, 255, 0, 65535))
    green.duty_u16(map_value(g, 0, 255, 0, 65535))
    blue.duty_u16(map_value(b, 0, 255, 0, 65535))

# Example: Set the color to orange
set_color(255, 165, 0)

When the code is running, the RGB LED will emit an orange light.

Understanding the Code

1. Import Libraries:

   • machine: To access hardware-specific functions.

   • utime: For time-related functions (not used in this example but useful for animations).

2. Initialize PWM Objects:

   • Create PWM objects for the red, green, and blue pins connected to the RGB LED and set the PWM frequency to 1000 Hz for all colors.

   # Initialize PWM for red, green, and blue pins
   red = machine.PWM(machine.Pin(13))
   green = machine.PWM(machine.Pin(14))
   blue = machine.PWM(machine.Pin(15))
   
   # Set the PWM frequency
   red.freq(1000)
   green.freq(1000)
   blue.freq(1000)
   

3. Define map_value Function:

   • Since the duty_u16 method accepts values from 0 to 65535, but color values are typically in the range 0 to 255, we need to map the 0-255 range to 0-65535.

   • The map_value function scales the input value accordingly.

   def map_value(x, in_min, in_max, out_min, out_max):
       # Map a value from one range to another
       return int((x - in_min) * (out_max - out_min) / (in_max - in_min) + out_min)
   

4. Define set_color Function:

   This function takes RGB values (each from 0 to 255) and sets the duty cycle for each color channel after mapping.

   def set_color(r, g, b):
       # Set the color by adjusting duty cycles
       red.duty_u16(map_value(r, 0, 255, 0, 65535))
       green.duty_u16(map_value(g, 0, 255, 0, 65535))
       blue.duty_u16(map_value(b, 0, 255, 0, 65535))
   

5. Set the Desired Color:

   Call set_color(255, 165, 0) to set the RGB LED to orange. You can change the values to any RGB color you like.

Example: Color Cycling

Let’s enhance the code to cycle through different colors.

1. To find the RGB values for different colors, you can use any graphic software or an online color picker. For example:

   • Red: (255, 0, 0)

   • Green: (0, 255, 0)

   • Blue: (0, 0, 255)

   • White: (255, 255, 255)

   • Purple: (128, 0, 128)

2. Write the code.

   We define a list of RGB tuples representing different colors. The while True loop cycles through each color, sets the RGB LED to that color, and waits for 1 second before moving to the next color.

   import machine
   import utime
   
   # Initialize PWM for red, green, and blue pins
   red = machine.PWM(machine.Pin(13))
   green = machine.PWM(machine.Pin(14))
   blue = machine.PWM(machine.Pin(15))
   
   # Set the PWM frequency
   red.freq(1000)
   green.freq(1000)
   blue.freq(1000)
   
   def map_value(x, in_min, in_max, out_min, out_max):
       return int((x - in_min) * (out_max - out_min) / (in_max - in_min) + out_min)
   
   def set_color(r, g, b):
       red.duty_u16(map_value(r, 0, 255, 0, 65535))
       green.duty_u16(map_value(g, 0, 255, 0, 65535))
       blue.duty_u16(map_value(b, 0, 255, 0, 65535))
   
   # List of colors to cycle through
   colors = [
       (255, 0, 0),     # Red
       (0, 255, 0),     # Green
       (0, 0, 255),     # Blue
       (255, 255, 0),   # Yellow
       (0, 255, 255),   # Cyan
       (255, 0, 255),   # Magenta
       (255, 255, 255)  # White
   ]
   
   while True:
       for color in colors:
           set_color(*color)
           utime.sleep(1)
   

When this code is running, the RGB LED will cycle through a sequence of colors: red, green, blue, yellow, cyan, magenta, and white.

Each color will be displayed for 1 second before transitioning to the next one in the list.

Conclusion

By controlling the intensity of the red, green, and blue components of an RGB LED using PWM, we can create a vast array of colors. This project demonstrates the principles of additive color mixing and provides a foundation for creating colorful light displays with microcontrollers.

References

• machine.PWM