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1.1.1 Blinking LED¶

Introduction¶

In this project, we will learn how to make a blinking LED by programming. Through your settings, your LED can produce a series of interesting phenomena. Now, go for it.

Required Components¶

In this project, we need the following components.

../_images/blinking_led_list.png

It’s definitely convenient to buy a whole kit, here’s the link:

Name

ITEMS IN THIS KIT

LINK

Raphael Kit

337

Raphael Kit

You can also buy them separately from the links below.

COMPONENT INTRODUCTION

PURCHASE LINK

GPIO Extension Board

BUY

Breadboard

BUY

Jumper Wires

BUY

Resistor

BUY

LED

BUY

Schematic Diagram¶

In this experiment, connect a 220Ω resistor to the anode (the long pin of the LED), then the resistor to 3.3 V, and connect the cathode (the short pin) of the LED to GPIO17 of Raspberry Pi. Therefore, to turn on an LED, we need to make GPIO17 low (0V) level. We can get this phenomenon by programming.

Note

Pin11 refers to the 11th pin of the Raspberry Pi from left to right, and its corresponding wiringPi and BCM pin numbers are shown in the following table.

In the C language related content, we make GPIO0 equivalent to 0 in the wiringPi. Among the Python language related content, BCM 17 is 17 in the BCM column of the following table. At the same time, they are the same as the 11th pin on the Raspberry Pi, Pin 11.

T-Board Name

physical

wiringPi

BCM

GPIO17

Pin 11

0

17
../_images/image48.png

Experimental Procedures¶

Step 1: Build the circuit.

../_images/image49.png

Step 2: Go to the folder of the code and run it.

  1. If you use a screen, you’re recommended to take the following steps.

Find 1.1.1_BlinkingLed.py and double click it to open. Now you’re in the file.

Click Run ->Run Module in the window and the following contents will appear.

To stop it from running, just click the X button on the top right to close it and then you’ll back to the code. If you modify the code, before clicking Run Module (F5) you need to save it first. Then you can see the results.

  1. If you log into the Raspberry Pi remotely, type in the command:

cd ~/raphael-kit/python

Note

Change directory to the path of the code in this experiment via cd.

Step 3: Run the code

sudo python3 1.1.1_BlinkingLed.py

Note

Here sudo - superuser do, and python means to run the file by Python.

After the code runs, you will see the LED flashing.

Step 4: If you want to edit the code file 1.1.1_BlinkingLed.py, press Ctrl + C to stop running the code. Then type the following command to open 1.1.1_BlinkingLed.py:

nano 1.1.1_BlinkingLed.py

Note

nano is a text editor tool. The command is used to open the code file 1.1.1_BlinkingLed.py by this tool.

Press Ctrl+X to exit. If you have modified the code, there will be a prompt asking whether to save the changes or not. Type in Y (save) or N (don’t save).

Then press Enter to exit. Type in nano 1.1.1_BlinkingLed.py again to see the effect after the change.

Code

The following is the program code:

Note

You can Modify/Reset/Copy/Run/Stop the code below. But before that, you need to go to source code path like raphael-kit/python. After modifying the code, you can run it directly to see the effect.

#!/usr/bin/env python3
import RPi.GPIO as GPIO
import time
LedPin = 17
def setup():
   # Set the GPIO modes to BCM Numbering
   GPIO.setmode(GPIO.BCM)
   # Set LedPin's mode to output,and initial level to High(3.3v)
   GPIO.setup(LedPin, GPIO.OUT, initial=GPIO.HIGH)
# Define a main function for main process
def main():
   while True:
      print ('...LED ON')
      # Turn on LED
      GPIO.output(LedPin, GPIO.LOW)
      time.sleep(0.5)
      print ('LED OFF...')
      # Turn off LED
      GPIO.output(LedPin, GPIO.HIGH)
      time.sleep(0.5)
# Define a destroy function for clean up everything after the script finished
def destroy():
   # Turn off LED
   GPIO.output(LedPin, GPIO.HIGH)
   # Release resource
   GPIO.cleanup()
# If run this script directly, do:
if __name__ == '__main__':
   setup()
   try:
      main()
   # When 'Ctrl+C' is pressed, the program destroy() will be  executed.
   except KeyboardInterrupt:
      destroy()

Code Explanation

#!/usr/bin/env python3

When the system detects this, it will search the installation path of python in the env setting, then call the corresponding interpreter to complete the operation. It’s to prevent the user not installing the python onto the /usr/bin default path.

import RPi.GPIO as GPIO

In this way, import the RPi.GPIO library, then define a variable, GPIO to replace RPI.GPIO in the following code.

import time

Import time package, for time delay function in the following program.

LedPin = 17

LED connects to the GPIO17 of the T-shape extension board, namely, BCM 17.

def setup():
   GPIO.setmode(GPIO.BCM)
   GPIO.setup(LedPin, GPIO.OUT, initial=GPIO.HIGH)

Set LedPin’s mode to output, and initial level to High (3.3v).

There are two ways of numbering the IO pins on a Raspberry Pi within RPi.GPIO: BOARD numbers and BCM numbers. In our projects, what we use is BCM numbers. You need to set up every channel you are using as an input or an output.

GPIO.output(LedPin, GPIO.LOW)

Set GPIO17(BCM17) as 0V (low level). Since the cathode of LED is connected to GPIO17, thus the LED will light up.

time.sleep(0.5)

Delay for 0.5 second. Here, the statement is delay function in C language, the unit is second.

def destroy():
   GPIO.cleanup()

Define a destroy function for clean up everything after the script finished.

if __name__ == '__main__':
   setup()
   try:
      main()
   # When 'Ctrl+C' is pressed, the program destroy() will be  executed.
   except KeyboardInterrupt:
      destroy()

This is the general running structure of the code. When the program starts to run, it initializes the pin by running the setup(), and then runs the code in the main() function to set the pin to high and low levels. When Ctrl+C is pressed, the program, destroy() will be  executed.

Phenomenon Picture¶

../_images/image54.jpeg