Lesson 2 Flowing LED Lights

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Introduction

In this lesson, we will learn how to make eight LEDs blink as flowing water based on Raspberry Pi.

Newly AddedComponents

Schematic Diagram

In this experiment, connect 220Ωresistors to the anode (the longer pin of the LED) respectively, then the resistors to Pin 11, 121315161822 and 24 of Raspberry Pi, and connect the cathode (the short pin) of the LEDs to GND. We can see from the schematic diagram that the anode of LED connect to a current-limiting resistor and then to Raspberry Pi. Therefore, to turn on an LED, we need to make pins high level. This process can be realized by programming.

Build the Circuit

  • For C Language Users:

Command 

1.Go to the folder of the code.

cd /home/pi/electronic-kit/for-raspberry-pi/c/Lesson_2_FlowingLedLights

2.Compile the code.

gcc 2_FlowingLedLights.c -lwiringPi 

Note: When using the gcc command, if you do not use -o, it will automatically output as a.out.

3.Run the executable file.

sudo ./a.out

Now, you will see these 8 LEDs are lit one by one from left to right, and then one by one from right to left.

Code

1.#include <wiringPi.h>  
2.#include <stdio.h>  
3.  
4.const int LedPin[]={0,1,2,3,4,5,6,10};   //Define 8 LED pin   
5.  
6.int main(void)  
7.{  
8.    // When initialize wiring failed, print message to screen  
9.    if(wiringPiSetup() == -1){  
10.        printf("setup wiringPi failed !");  
11.        return 1;   
12.    }  
13.      
14.    for(int j=0;j-1;i--)  
28.        {         
29.            // LED off  
30.            digitalWrite(LedPin[i], LOW);  
31.            delay(100);  
32.        }  
33.    }  
34.  
35.    return 0;  
36.}  

Code Explanation

4.const int LedPin[]={0,1,2,3,4,5,6,10}; 

Create an array, LedPin to define the eight LEDs then connect them to GPIO0~GPIO6, GPIO10 respectively.

14.    for(int j=0;j

Use a for loop to set all 8 pins connected to LEDs to OUTPUT mode and LOW level.

21.        for(int i=0;i

Light up the LEDs in GPIO0~6 and GPIO10 successively. i increases progressively from 0 to 7, LED0 to LED7 changes accordingly, making it like a flowing LED light from left to right.

27.        for(int i=7;i>-1;i–)  
28.        {         
29.            // LED off  
30.            digitalWrite(LedPin[i], LOW);  
31.            delay(100);  
32.        }  

Close the LEDs in GPIO0~6 and GPIO10 successively. i increases progressively from 7 to 0, LED0 to LED7 changes accordingly, making it like a flowing LED light from right to left.

  • For PythonLanguage Users:

Command

1.Go to the folder of the code.

cd /home/pi/electronic-kit/for-raspberry-pi/python

2.Run the code.

sudo python3 2_FlowingLed.py

Now, you will see these 8 LEDs are lit one by one from left to right, and then one by one from right to left.

Code

1.import RPi.GPIO as GPIO    
2.import time     
3.  
4.pins = [17,18,27,22,23,24,25,8]  
5.  
6.# Define a setup function for some setup  
7.def setup():  
8.    GPIO.setmode(GPIO.BCM)     
9.    for i in range(0, 8, 1):  
10.        GPIO.setup(pins[i], GPIO.OUT, initial=GPIO.LOW)  
11.  
12.# Define a main function for main process  
13.def main():  
14.    while True:  
15.        # print ('...LED ON')  
16.        # Turn on LED  
17.        for i in range(0, 8, 1):  
18.            GPIO.output(pins[i], GPIO.HIGH)  
19.            time.sleep(0.1)  
20.             
21.        # print ('LED OFF...')  
22.        # Turn off LED  
23.        for i in range(7, -1, -1):  
24.            GPIO.output(pins[i], GPIO.LOW)  
25.            time.sleep(0.1)  
26.  
27.# Define a destroy function for clean up everything after the script finished   
28.def destroy():  
29.    # Turn off LED     
30.    for i in range(0, 8, 1):  
31.            GPIO.output(pins[i], GPIO.LOW)  
32.    # Release resource  
33.    GPIO.cleanup()                      
34.  
35.# If run this script directly, do:  
36.if __name__ == '__main__':  
37.    setup()  
38.    try:  
39.        main()  
40.    # When 'Ctrl+C' is pressed, the child program   
41.    # destroy() will be  executed.  
42.    except KeyboardInterrupt:  
43.        destroy()  

Code Explanation

9.    for i in range(0, 8, 1):  
10.        GPIO.setup(pins[i], GPIO.OUT, initial=GPIO.LOW)  

Use a for loop to set all 8 pins connected to LEDs to output mode and LOW level. 

17.        for i in range(0, 8, 1):  
18.            GPIO.output(pins[i], GPIO.HIGH) 
19.  time.sleep(0.1)

Variable i increases progressively from 0 to 8, increasing by 1 every time. Accordingly, set the pins in the array pins[i] to HIGH respectively to light up the LEDs and the lighting time is 0.1s. Then, you will see 8 LEDs light up one by one.

23.        for i in range(7, -1, -1):  
24.            GPIO.output(pins[i], GPIO.LOW)  
25.            time.sleep(0.1)  

Variable i decreases progressively from 7 to -1, decreasing by 1 every time. Then LED0~LED7 change accordingly, making it like a flowing LED light from right to left.