Lesson 2 RGB LED Module

Introduction

RGB LED modules can emit various colors of light. Three LEDs of red, green, and blue are packaged into a transparent or semitransparent plastic shell with four pins led out. The three primary colors of red, green, and blue can be mixed and compose all kinds of colors by brightness, so you can make an RGB LED emit colorful light by controlling the circuit.

_images/image100.png

Required Components

  • 1 * Raspberry Pi

  • 1 * Breadboard

  • Several Jumper wires

  • 1 * RGB LED module

  • 1 * 4-Pin anti-reverse cable

Experimental Principle

In this experiment, we will use PWM technology to control the brightness of RGB.

Pulse Width Modulation, or PWM, is a technique for getting analog results with digital means. Digital control is used to create a square wave, a signal switched between on and off. This on-off pattern can simulate voltages in between full on (5 Volts) and off (0 Volts) by changing the portion of the time the signal spends on versus the time that the signal spends off. The duration of “on time” is called the pulse width. To get varying analog values, you change, or modulate, that pulse width. If you repeat this on-off pattern fast enough with an LED for example, the result is as if the signal is a steady voltage between 0 and 5v controlling the brightness of the LED.

_images/image101.png

We can see from the top oscillogram that the amplitude of DC voltage output is 5V. However, the actual voltage output is only 3.75V through PWM, for the high level only takes up 75% of the total voltage within a period.

Here are the three basic parameters of PWM:

_images/image102.png

1. The term duty cycle describes the proportion of “on” time to the regular interval or “period” of time

  1. Period describes the reciprocal of pulses in one second.

  2. The voltage amplitude here is 0V-5V.

Here we input any value between 0 and 255 to the three pins of the RGB LED to make it display different colors.

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

The schematic diagram of the module is as shown below:

_images/image103.png

Experimental Procedures

Step 1: Build the circuit according to the following method.

Raspberry Pi

GPIO Extension Board

RGB LED Module

3.3V

3V3

VCC

GPIO0

GPIO17

R

GPIO1

GPIO18

G

GPIO2

GPIO27

B
02_RGB_LED_bb

For C Users:

Step 2: Change directory.

cd /home/pi/SunFounder_SensorKit_for_RPi2/C/02_rgb_led/

Step 3: Compile.

gcc rgb_led.c -lwiringPi

Note

If it does not work after running, or there is an error prompt wiringPi.h: No such file or directory, please refer to WiringPi to install it.

Step 4: Run.

sudo ./a.out

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 message to 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;
}

For Python Users:

Step 2: Change directory.

cd /home/pi/SunFounder_SensorKit_for_RPi2/Python/

Step 3: Run.

sudo python3 02_rgb_led.py

Code

#!/usr/bin/env python3
import RPi.GPIO as GPIO
import time

colors = [0xFF0000, 0x00FF00, 0x0000FF, 0xFFFF00, 0xFF00FF, 0x00FFFF]
R = 11
G = 12
B = 13

def setup(Rpin, Gpin, Bpin):
   global pins
   global p_R, p_G, p_B
   pins = {'pin_R': Rpin, 'pin_G': Gpin, 'pin_B': Bpin}
   GPIO.setmode(GPIO.BOARD)       # Numbers GPIOs by physical location
   for i in pins:
      GPIO.setup(pins[i], GPIO.OUT)   # Set pins' mode is output
      GPIO.output(pins[i], GPIO.HIGH) # Set pins to high(+3.3V) to off led

   p_R = GPIO.PWM(pins['pin_R'], 2000)  # set Frequece to 2KHz
   p_G = GPIO.PWM(pins['pin_G'], 1999)
   p_B = GPIO.PWM(pins['pin_B'], 5000)

   p_R.start(100)      # Initial duty Cycle = 0(leds off)
   p_G.start(100)
   p_B.start(100)

def map(x, in_min, in_max, out_min, out_max):
   return (x - in_min) * (out_max - out_min) / (in_max - in_min) + out_min

def off():
   GPIO.setmode(GPIO.BOARD)
   for i in pins:
      GPIO.setup(pins[i], GPIO.OUT)   # Set pins' mode is output
      GPIO.output(pins[i], GPIO.HIGH)    # Turn off all leds

def setColor(col):   # For example : col = 0x112233
   R_val = (col & 0xff0000) >> 16
   G_val = (col & 0x00ff00) >> 8
   B_val = (col & 0x0000ff) >> 0

   R_val = map(R_val, 0, 255, 0, 100)
   G_val = map(G_val, 0, 255, 0, 100)
   B_val = map(B_val, 0, 255, 0, 100)

   p_R.ChangeDutyCycle(100-R_val)     # Change duty cycle
   p_G.ChangeDutyCycle(100-G_val)
   p_B.ChangeDutyCycle(100-B_val)

def loop():
   while True:
      for col in colors:
         setColor(col)
         time.sleep(1)

def destroy():
   p_R.stop()
   p_G.stop()
   p_B.stop()
   off()
   GPIO.cleanup()

if __name__ == "__main__":
   try:
      setup(R, G, B)
      loop()
   except KeyboardInterrupt:
      destroy()

You will see the RGB LED light up, and display different colors in turn.

_images/image105.jpeg