Lesson 2 LED Flowing Lights

Introduction

In this lesson, we will learn how to make eight LEDs blink in various effects as you want based on Raspberry Pi.

Components

– 1*Raspberry Pi

– 1*Breadboard

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

– 8*LED

– 8*Resistor (220Ω)

– Jumper wires

Experimental Principle

Set GPIO0 to GPIO7 to low in turn by programming, then LED0 to LED7 will light up in turn. You can make eight LEDs blink in different effects by controlling their delay time and the order of lighting up.

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 /02_8led/8Led.c)

Step 3: Compile the code

gcc  8Led.c  -lwiringPi

Step 4: Run the program

./a.out

Now, eight LEDs will light up circularly and render different effects.

Further Exploration

We can write the blinking effects of LEDs in an array. If you want to use one of these effects, you can call it in the main() function directly.

Code

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

//make led_n on
void led_on(int n)
{
 digitalWrite(n, LOW);
}

//make led_n off
void led_off(int n)
{
 digitalWrite(n, HIGH);
}

int main(void)
{
 int i;

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

 for(i=0;i<8;i++){
  printf("linker LedPin : GPIO %d(wiringPi pin)\n",i); //when initialize wiring successfully,print message to screen
 }

 for(i=0;i<8;i++){       //make 8 pins' mode is output
  pinMode(i, OUTPUT);
 }

 while(1){
  for(i=0;i<8;i++){   //make led on from left to right
   led_on(i);
   delay(100);
   led_off(i);
  }
 // delay(500);
  for(i=8;i>=0;i--){  //make led off from right to left
   led_on(i);
   delay(100);
   led_off(i);
  }
 }

 return 0;
}