Lesson 6 RGB LED

Introduction

RGB LEDs can emit various colors of light. They are manufactured by packaging three LEDs of red, green, and blue into a transparent or semitransparent plastic shell and lead out four pins. The three primary colors of red, green, and blue can be mixed to all kinds of colors by brightness, so you can make RGB LEDs emit light with all kinds of colors by controlling the circuit.

Components

– 1*Raspberry Pi

– 1*Network cable（or USB wireless network adapter）

– 1*RGB LED

– 1*Resistor

– Several jumper wires

Experimental Principle

The three primary color red, green and blue of  a RGB LED can compose various colors by brightness. We can adjust the brightness of LED with PWM technology. Raspberry Pi has only one channel hardware PWM output, but we need three channels to control the RGB LED. As a result, it is difficult to realize with the hardware PWM of Raspberry Pi. Do not worry! Fortunately the softPwm library simulates PWM (softPwm) for us with software method. Based on this, we only need to include the header file softPwm.h, then call the API it provided to easily achieve multi-channel PWM output to control the RGB LED to display all kinds of colors.

There are two types of package for RGB LEDs. One is patch type, and the other is dual-in-line type. The difference between them is color resolution. The former has better color resolution.

RGB LEDs can be categorized into common anode type and common cathode type. In this experiment, we use common cathode RGB LED.

Experimental Procedures

Step 1: Connect the circuit as shown in the following diagram

Step 2: Edit and save the code with vim (see path/Rpi_ultraKit /06_rgb/rgb.c)

Step 3: Compile the code

gcc  rgb.c  -lwiringPi  -lpthread

Step 4: Run the program

./a.out

Now you should see the RGB LED light up, and flash different colors in turn.

Further Exploration

You can modify the parameters of the function ledColorSet( ) by yourself, and then compile and run the code to see the color changes of the RGB LED.

Experimental Summary

In this experiment, you have learnt how to control RGB LEDs with the softPwm of Raspberry Pi in this experiment. Try to apply the softPwm to DC motor speed regulation.

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)
{
 int i;

 if(wiringPiSetup() == -1){ //when initialize wiring failed,print messageto screen
  printf("setup wiringPi failed !");
  return 1;
 }
 //printf("linker LedPin : GPIO %d(wiringPi pin)\n",LedPin); //when initialize wiring successfully,print message to screen

 ledInit();

 while(1){
  ledColorSet(0xff,0x00,0x00);   //red
  delay(500);
  ledColorSet(0x00,0xff,0x00);   //green
  delay(500);
  ledColorSet(0x00,0x00,0xff);   //blue
  delay(500);

  ledColorSet(0xff,0xff,0x00);   //yellow
  delay(500);
  ledColorSet(0xff,0x00,0xff);   //pick
  delay(500);
  ledColorSet(0xc0,0xff,0x3e);
  delay(500);

  ledColorSet(0x94,0x00,0xd3);
  delay(500);
  ledColorSet(0x76,0xee,0x00);
  delay(500);
  ledColorSet(0x00,0xc5,0xcd);
  delay(500);

 }

 return 0;
}