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Blinking an LED

✎

Modified 2020-08-28 by unknown

Step 1: Blinking the LED in the REPL

✎

Modified 2020-08-28 by unknown

There are two types of signals that an LED can provide: High and Low signals. To turn on the LED, we need to provide High signal on the pin we choose, while to turn off the LED we will give a Low signal.

After we power up the Pi, navigate to the code editor, and open up the terminal, we can type in this line and press Enter:

gpio -g mode 6 out

In this line, the -g option is the option to define the GPIO BCM pin as explained earlier. We can use this page to figure out the numbering. In this case, our LED is connected to Pin 6 on the Pi, so we designate the corresponding GPIO6 to run the Output mode, which means that it can provide High or low signal.

Next, we write the signal on GPIO6 to be High by running this command:

gpio -g write 6 1

At this point, you should see the LED turned on. Similarly, the following command will turn it off by writing the Low signal:

gpio -g write 6 0

Lastly, we can use the gpio blink command to blink the LED:

gpio -g blink 6

In the above command, we command pin 6 for a blink, turn on 1 second, turn off 1 second, and so on. Press CTRL+C to stop the command.

Step 2: Blinking the LED using a bash script

✎

Modified 2020-09-16 by Dev Ramesh

An alternative way to blink the LED is to use the gpio commands in bash. Before using them, we need to know the path to the gpio command by using the which command in the terminal:

which gpio

You should get an output of /usr/bin/gpio path.

Now we are ready to make the bash script. The first step is to create a file such as blink.sh with the touch command.

touch blink.sh

Then, navigate to the blink.sh file through the navigator on the left side of the screen editor, open it, and fill in the following script:

while :
do
        /usr/bin/gpio -g toggle 6
        sleep 1
done

Before we proceed, let’s take a closer look to the lines we just wrote. The first line while： created an infinite loop that runs the following two lines over and over again. The toggle option is an option to write the opposite condition: if the pin is Low, it will be written High, and vice versa. The sleep 1 means to delay the program for 1 second before it continues.

Can you think of a way to change the frequency of blinking by modifying one number in the above script?

After writing our script, we can press CTRL+X followed by confirmation by pressing the Y button to save it. After that, make the script executable (to give us the permission to run it with the +x option) with the chmod (change mod) command.

chmod +x blink.sh

At last, we can run the program with the bash command:h

bash blink.sh

./blink.sh

The LED should blink. Don’t forget to stop it using Ctrl+C.

Additional Reference

✎

Modified 2020-08-28 by unknown

GPIO commands

Blinking the LED tutorial