1.1.2 RGB LED

Introduction

In this project, we will control an RGB LED to flash various colors.

Schematic Diagram

After connecting the pins of R, G, and B to a current limiting resistor, connect them to the GPIO17, GPIO18, and GPIO27 respectively. The longest pin (GND) of the LED connects to the GND of the Raspberry Pi. When the three pins are given different PWM values, the RGB LED will display different colors.

T-Board Name

physical

wiringPi

BCM

GPIO17

Pin 11

0

17

GPIO18

Pin 12

1

18

GPIO27

Pin 13

2

27

_images/rgb_led_schematic.png

Experimental Procedures

Step 1: Build the circuit.

_images/image61.png

Step 2: Go to the folder of the code.

cd /home/pi/raphael-kit/c/1.1.2/

Step 3: 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.

Step 4: 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?.

Code

#include <wiringPi.h>
#include <softPwm.h>
#include <stdio.h>
#define uchar unsigned char
#define LedPinRed    0
#define LedPinGreen  1
#define LedPinBlue   2

void ledInit(void){
    softPwmCreate(LedPinRed,  0, 100);
    softPwmCreate(LedPinGreen,0, 100);
    softPwmCreate(LedPinBlue, 0, 100);
}

void ledColorSet(uchar r_val, uchar g_val, uchar b_val){
    softPwmWrite(LedPinRed,   r_val);
    softPwmWrite(LedPinGreen, g_val);
    softPwmWrite(LedPinBlue,  b_val);
}

int main(void){

    if(wiringPiSetup() == -1){ //when initialize wiring failed, printf messageto screen
        printf("setup wiringPi failed !");
        return 1;
    }

    ledInit();
    while(1){
        printf("Red\n");
        ledColorSet(0xff,0x00,0x00);   //red
        delay(500);
        printf("Green\n");
        ledColorSet(0x00,0xff,0x00);   //green
        delay(500);
        printf("Blue\n");
        ledColorSet(0x00,0x00,0xff);   //blue
        delay(500);
        printf("Yellow\n");
        ledColorSet(0xff,0xff,0x00);   //yellow
        delay(500);
        printf("Purple\n");
        ledColorSet(0xff,0x00,0xff);   //purple
        delay(500);
        printf("Cyan\n");
        ledColorSet(0xc0,0xff,0x3e);   //cyan
        delay(500);
    }
    return 0;
}

Code Explanation

#include <softPwm.h>

Library used for realizing the pwm function of the software.

void ledInit(void){
    softPwmCreate(LedPinRed,  0, 100);
    softPwmCreate(LedPinGreen,0, 100);
    softPwmCreate(LedPinBlue, 0, 100);
}

The function is to use software to create a PWM pin, set its period between 0x100us-100x100us.

The prototype of the function softPwmCreate(LedPinRed, 0, 100) is as follows:

int softPwmCreate(int pin,int initialValue,int pwmRange);
  • Parameter pin: Any GPIO pin of Raspberry Pi can be set as a PWM pin.

  • Parameter initialValue: The initial pulse width is that initialValue times100us.

  • Parameter pwmRange: the period of PWM is that pwmRange times100us.

void ledColorSet(uchar r_val, uchar g_val, uchar b_val){
    softPwmWrite(LedPinRed,   r_val);
    softPwmWrite(LedPinGreen, g_val);
    softPwmWrite(LedPinBlue,  b_val);
}

This function is to set the colors of the LED. Using RGB, the formal parameter r_val represents the luminance of the red one, g_val of the green one, b_val of the blue one.

The prototype of the function softPwmWrite(LedPinBlue, b_val) is as follows:

void softPwmWrite (int pin, int value) ;
  • Parameter pin: Any GPIO pin of Raspberry Pi can be set as a PWM pin.

  • Parameter Value: The pulse width of PWM is value times 100us. Note that value can only be less than pwmRange defined previously, if it is larger than pwmRange, the value will be given a fixed value, pwmRange.

ledColorSet(0xff,0x00,0x00);

Call the function defined before. Write 0xff into LedPinRed and 0x00 into LedPinGreen and LedPinBlue. Only the Red LED lights up after running this code. If you want to light up LEDs in other colors, just modify the parameters.

Phenomenon Picture

_images/image62.jpeg