1.1.2 RGB LED

Introduction

In this project, we will use PWM to control RGB LEDs to display different colors.

Components

An RGB LED contains three LEDs in one package - red, green, and blue. By adjusting the brightness of each color, we can mix them to create various colors. On the Raspberry Pi, we use PWM (Pulse Width Modulation) to control LED brightness. Since Raspberry Pi has limited hardware PWM outputs, we use the softPwm library to simulate PWM signals through software. This allows us to control all three channels of the RGB LED simultaneously, creating a wide range of colorful lighting effects.

Connect

T-Board Name	physical	wiringPi	BCM
GPIO17	Pin 11	0	17
GPIO18	Pin 12	1	18
GPIO27	Pin 13	2	27

Code

For C Language User

Go to the folder of the code.

cd ~/Basic-Starter-Kit-for-Raspberry-Pi/c/1.1.2/

Compile the code.

gcc 1.1.2_rgbLed.c -lwiringPi

Note

When the instruction “gcc” is executed, if “-o” is not called, then the executable file is named “a.out”.

Run the executable file.

sudo ./a.out

After the code runs, you will see that RGB displays red, green, blue, yellow, pink, and cyan.

Note

If it does not work after running, or there is an error prompt: “wiringPi.h: No such file or directory”, please refer to C code is not working?.

This is the complete code

#include <wiringPi.h>
 #include <softPwm.h>
 #include <stdio.h>

 // Define GPIO pins for the RGB LED.
 #define LED_PIN_RED    0
 #define LED_PIN_GREEN  1
 #define LED_PIN_BLUE   2

 // Define PWM range for colors (0-255).
 #define PWM_RANGE 255

 // Define a structure to hold color values and names.
 typedef struct {
     const char* name;
     unsigned char red;
     unsigned char green;
     unsigned char blue;
 } Color;

 // Array of colors to display in sequence.
 const Color COLORS[] = {
     {"Red",    0xff, 0x00, 0x00},
     {"Green",  0x00, 0xff, 0x00},
     {"Blue",   0x00, 0x00, 0xff},
     {"Yellow", 0xff, 0xff, 0x00},
     {"Purple", 0xff, 0x00, 0xff},
     {"Cyan",   0xc0, 0xff, 0x3e}
 };
 const int NUM_COLORS = sizeof(COLORS) / sizeof(COLORS[0]);

 /**
 * @brief Initializes wiringPi and sets up software PWM for RGB LED pins.
 * @return 0 on success, 1 on failure.
 */
 int setupHardware() {
     // Attempt to initialize the wiringPi library.
     if (wiringPiSetup() == -1) {
         printf("Failed to setup wiringPi!\n");
         return 1;
     }

     // Create software PWM on each of the RGB pins with a range of 0-255.
     softPwmCreate(LED_PIN_RED,   0, PWM_RANGE);
     softPwmCreate(LED_PIN_GREEN, 0, PWM_RANGE);
     softPwmCreate(LED_PIN_BLUE,  0, PWM_RANGE);

     return 0;
 }

 /**
 * @brief Sets the RGB LED to a specific color.
 * @param red   The red intensity (0-255).
 * @param green The green intensity (0-255).
 * @param blue  The blue intensity (0-255).
 */
 void setLedColor(unsigned char red, unsigned char green, unsigned char blue) {
     softPwmWrite(LED_PIN_RED,   red);
     softPwmWrite(LED_PIN_GREEN, green);
     softPwmWrite(LED_PIN_BLUE,  blue);
 }

 /**
 * @brief The main application loop to cycle through a predefined set of colors.
 */
 void colorCycleLoop() {
     int colorIndex = 0;
     while (1) {
         // Get the current color from the array.
         const Color* currentColor = &COLORS[colorIndex];

         printf("Displaying color: %s\n", currentColor->name);

         // Set the LED to the current color.
         setLedColor(currentColor->red, currentColor->green, currentColor->blue);

         // Wait for 500ms before changing to the next color.
         delay(500);

         // Move to the next color, and loop back to the start if at the end.
         colorIndex = (colorIndex + 1) % NUM_COLORS;
     }
 }

 /**
 * @brief Main function.
 * @return Integer status code. 0 for success, 1 for error.
 */
 int main(void) {
     // Initialize the hardware.
     if (setupHardware() != 0) {
         return 1; // Exit if setup fails.
     }

     // Start the color cycling loop.
     colorCycleLoop();

     return 0; // This is unreachable.
 }

For Python Language User

Go to the code folder and run.

cd ~/Basic-Starter-Kit-for-Raspberry-Pi/python

python 1.1.2_rgbLed.py