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3.3 Controlling an RGB LED Strip

In this lesson, we’ll learn how to control an RGB LED strip (specifically the WS2812 type) using the Raspberry Pi Pico 2 and MicroPython.

The WS2812 is a smart LED that integrates a control circuit and an RGB chip into a 5050-sized LED package. Each LED has its own built-in controller, which allows us to control each LED individually using a single data line. This means we can change the color and brightness of each LED on the strip independently.

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

WS2812 RGB 8 LEDs Strip

1

BUY

Circuit Diagram

sch_ws2812

Wiring Diagram

wiring_ws2812

Be cautious with the current draw. While the Pico’s VBUS pin can supply power for a small number of LEDs (like 8), using more LEDs may require an external power supply to prevent overloading the Pico.

Writing the Code

Note

  • You can open the file 3.3_rgb_led_strip.ino from newton-lab-kit/arduino/3.3_rgb_led_strip.

  • Or copy this code into Arduino IDE.

  • Select the Raspberry Pi Pico 2 board and the correct port, then click “Upload”.

  • The Adafruit_NeoPixel library is used here, you can install it from the Library Manager.

    ../_images/lib_neopixel.png 
#include <Adafruit_NeoPixel.h>

#define PIXEL_PIN    0    // Digital IO pin connected to the NeoPixels
#define PIXEL_COUNT  8    // Number of NeoPixels

// Declare our NeoPixel strip object
Adafruit_NeoPixel strip(PIXEL_COUNT, PIXEL_PIN, NEO_GRB + NEO_KHZ800);

void setup() {
  strip.begin();           // Initialize the NeoPixel library
  strip.show();            // Turn OFF all pixels ASAP
}

void loop() {
  // Set the color of each pixel
  strip.setPixelColor(0, strip.Color(255, 0, 0));   // Red
  strip.setPixelColor(1, strip.Color(0, 255, 0));   // Green
  strip.setPixelColor(2, strip.Color(0, 0, 255));   // Blue
  strip.setPixelColor(3, strip.Color(255, 255, 0)); // Yellow
  strip.setPixelColor(4, strip.Color(0, 255, 255)); // Cyan
  strip.setPixelColor(5, strip.Color(255, 0, 255)); // Magenta
  strip.setPixelColor(6, strip.Color(255, 255, 255)); // White
  strip.setPixelColor(7, strip.Color(0, 0, 0));     // Off

  strip.show();  // Update the strip with new contents
  delay(1000);   // Wait for a second

  // Turn off all pixels
  strip.clear();
  strip.show();
  delay(1000);   // Wait for a second
}

After uploading the code, you should see the LEDs light up with different colors, stay on for a second, then turn off for a second.

Understanding the Code

  1. Include the Library:

    #include <Adafruit_NeoPixel.h>

  2. Define Constants:

    • PIXEL_PIN: The GPIO pin connected to the data input of the LED strip (GP0).

    • PIXEL_COUNT: The number of LEDs on the strip.

  3. Initialize the Strip:

    NEO_GRB + NEO_KHZ800: Specifies the color order and communication speed.

    Adafruit_NeoPixel strip(PIXEL_COUNT, PIXEL_PIN, NEO_GRB + NEO_KHZ800);

  4. In setup() function:

    • strip.begin(): Initializes the NeoPixel library.

    • strip.show(): Ensures all pixels are off.

  5. In loop() function:

    • strip.setPixelColor(index, color): Sets the color of a specific pixel.

    • strip.Color(r, g, b): Creates a 24-bit color value from red, green, and blue components (0-255).

    • strip.show(): Sends the updated color data to the strip.

    • strip.clear(): Clears the pixel data in memory (turns off the pixels on the next show()).

Advanced Example: Color Wipe Animation

Let’s create a simple animation where each LED lights up in sequence.

  • colorWipe(): Lights up each pixel in sequence with the specified color.

  • Calls colorWipe() with different colors to create an animation.

#include <Adafruit_NeoPixel.h>

#define PIXEL_PIN    0
#define PIXEL_COUNT  8

Adafruit_NeoPixel strip(PIXEL_COUNT, PIXEL_PIN, NEO_GRB + NEO_KHZ800);

void setup() {
  strip.begin();
  strip.show(); // Initialize all pixels to 'off'
}

void loop() {
  colorWipe(strip.Color(255, 0, 0), 50); // Red
  colorWipe(strip.Color(0, 255, 0), 50); // Green
  colorWipe(strip.Color(0, 0, 255), 50); // Blue
}

void colorWipe(uint32_t color, int wait) {
  for(int i=0; i<strip.numPixels(); i++) {
    strip.setPixelColor(i, color);
    strip.show();
    delay(wait);
  }
}

After uploading the code, you should see the LEDs light up one by one in red, then green, then blue.

Advanced Example: Rainbow Cycle Animation

  • rainbowCycle() Function: Cycles through the colors of the rainbow across all pixels.

  • The nested loops create a smooth transition of colors.

  • Wheel() Function: Generates rainbow colors across 0-255 positions.

#include <Adafruit_NeoPixel.h>

#define PIXEL_PIN    0
#define PIXEL_COUNT  8

Adafruit_NeoPixel strip(PIXEL_COUNT, PIXEL_PIN, NEO_GRB + NEO_KHZ800);

void setup() {
  strip.begin();
  strip.show(); // Initialize all pixels to 'off'
}

void loop() {
  rainbowCycle(20); // Rainbow cycle with 20ms delay per step
}

void rainbowCycle(int wait) {
  uint16_t i, j;

  for(j=0; j<256*5; j++) { // 5 cycles of all colors on the wheel
    for(i=0; i< strip.numPixels(); i++) {
      strip.setPixelColor(i, Wheel(((i * 256 / strip.numPixels()) + j) & 255));
    }
    strip.show();
    delay(wait);
  }
}

// Input a value 0 to 255 to get a color value.
// The colors are a transition r - g - b - back to r.
uint32_t Wheel(byte WheelPos) {
  if(WheelPos < 85) {
    return strip.Color(WheelPos * 3, 255 - WheelPos * 3, 0);
  } else if(WheelPos < 170) {
    WheelPos -= 85;
    return strip.Color(255 - WheelPos * 3, 0, WheelPos * 3);
  } else {
    WheelPos -= 170;
    return strip.Color(0, WheelPos * 3, 255 - WheelPos * 3);
  }
}

After uploading the code, the LED strip should display a rainbow of colors cycling smoothly.

Further Exploration

  • Create Custom Animations:

    • Experiment with different colors and animations.

    • Combine multiple animation functions.

  • Respond to Sensors:

    Use input from sensors to change the LED colors or patterns.

  • Build a Visualizer:

    Create a music visualizer that changes the LEDs based on sound input.

Power Considerations

  • Current Draw:

    • Each LED can draw up to 60mA at full brightness.

    • For 8 LEDs, that’s up to 480mA.

    • Ensure your power source can supply the required current.

  • External Power Supply:

    • For larger strips or higher brightness, use an external 5V power supply.

    • Connect the ground of the external power supply to the Pico’s ground.

Conclusion

In this lesson, you’ve learned how to control a WS2812 RGB LED strip using the Raspberry Pi Pico and the Adafruit NeoPixel library. By manipulating individual pixels, you can create stunning visual effects for your projects.