Lesson 2 RGB LED

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Introduction

There are two kinds of packages for RGB LED (as shown below) in this kit. One is Surface Mount Device (SMD) type, and the other is Dual In-line Package (DIP) type.

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, 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.

Components

– 1 * Raspberry Pi

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

– 1 * RGB LED module

– Several jumper wires

Experimental Principle

The three primary colors can be mixed into various colors by brightness. The brightness of LED can be adjusted with PWM. Raspberry Pi has only one channel for hardware PWM output, but it needs three channels to control the RGB LED, which means it is difficult to control the RGB LED with the hardware PWM of Raspberry Pi. Fortunately, the softPwm library simulates PWM (softPwm) by programming. Thus, you only need to include the header file softPwm.h (for C language users), and then call the API it provided to easily achieve multi-channel PWM output to control the RGB LED so as to display all kinds of colors.

RGB LEDs can be categorized into common anode type and common cathode type. In this experiment, the latter is used.

Experimental Procedures

Step 1: Build the circuit

                                  Raspberry Pi                          RGB LED

                                          GPIO0 ————————-  R

                                          GPIO1 ————————-  G

                                          GPIO2 ————————-  B

                                           GND  ————————– ” – “

Step 2: Edit and save the code (see path/Rpi_SensorKit_code/04_RGB/rgb.c)

Step 3: Compile

              gcc  rgb.c –lwiringPi -lpthread

Step 4: Run

              ./a.out

Here you should see the RGB LED flashing different colors in turn.

Further Exploration

Try to modify the parameters of the function ledColorSet( ) to change the color of the LED.

rgb.c

#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;
}

Python Code

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

colors = [0xFF0000, 0x00FF00, 0x0000FF, 0xFFFF00, 0xFF00FF, 0x00FFFF]
pins = {'pin_R':11, 'pin_G':12, 'pin_B':13}  # pins is a dict

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'], 2000)
p_B = GPIO.PWM(pins['pin_B'], 5000)

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

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

try:
	while True:
		for col in colors:
			setColor(col)
			time.sleep(0.5)
except KeyboardInterrupt:
	p_R.stop()
	p_G.stop()
	p_B.stop()
	for i in pins:
		GPIO.output(pins[i], GPIO.HIGH)    # Turn off all leds
	GPIO.cleanup()