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.

Experimental Conditions

– 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_UniversalStartKit/02_8led/8Led.c)

Step 3: Compile the code

            gcc  8Led.c  -lwiringPi

Step 4: Run the program

            ./a.out

Now, when you press Enter, 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.

8Led.c

#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;
}

Python Code

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

pins = [11, 12, 13, 15, 16, 18, 22, 7]

def setup():
	GPIO.setmode(GPIO.BOARD)        # Numbers GPIOs by physical location
	for pin in pins:
		GPIO.setup(pin, GPIO.OUT)   # Set all pins' mode is output
		GPIO.output(pin, GPIO.HIGH) # Set all pins to high(+3.3V) to off led

def loop():
	while True:
		for pin in pins:
			GPIO.output(pin, GPIO.LOW)	
			time.sleep(0.5)
			GPIO.output(pin, GPIO.HIGH)

def destroy():
	for pin in pins:
		GPIO.output(pin, GPIO.HIGH)    # turn off all leds
	GPIO.cleanup()                     # Release resource

if __name__ == '__main__':     # Program start from here
	setup()
	try:
		loop()
	except KeyboardInterrupt:  # When 'Ctrl+C' is pressed, the child program destroy() will be  executed.
		destroy()