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In previous lesson Introduction Of Raspberry Pi GPIO , we learned what is GPIO pins ,GPIO naming and location map in Raspberry Pi. Now we start to learn how to program GPIO pins and control outside device through GPIO.

Introduction for WiringPi

If you want to use Raspberry Pi to control other devices such as sensors, motors, LEDs etc, you need to exchange signal with these devices. This is called Input/Output(I/O). That is the job of GPIO pins.

In order to send/get data from GPIO pins, theoretically  people can use ARM Assembly or C language to directly access the I/O address, registers, memories or trigger related I/O interrupt. However, such programming practice is super complicated, inconvenient and requires deep understanding about ARM CPU hardware detail.

Fortunately,  experts invented a developing tool called “utility” or “library”. With the help of utility/library, complicated I/O detail programming are sealed into some black boxes called “Functions” which makes GPIO programming  simple and easy.

There are many free Open source GPIO libraries in the Internet. In this lesson, we will teach you how to install “wiringPi” library which is very popular among  C programmers.

We don’t want to talk much of the technical detail about wiringPi. If you want to get more wiringPi information , please read  following link:

The GPIO utility

Test wiringPi exist or not

You can test whether the wiringPi library has already been installed  by running following command in terminal：

gpio  -v

If the message appears in your terminal, the wiringPi is installed in your Pi.

If the message appears as follow, the wiringPi has not been installed yet.

Install wiringPi through git

Step 1) Update your pi package repository (these 2 commands are recommended to do regularly)
sudo apt-get update
sudo apt-get upgrade

Step 2)  run following command to install wiringpi library

sudo apt-get install wiringpi

Sample project for WiringPi

After installation wirngPi, you can test a project with LED on your raspberry Pi via wiringPi.

1) Experimental Principle
Connect LED with raspberry Pi GPIO, and then the program output high or low level to this GPIO to control the LED blink.

B17 in above graph means BCM GPIO#17 or Physical pin#11 or wiringPi#0(zero).

Note: B means BCM(Broadcom pin number). If you don’t know what is BCM pin#, Physical pin#, wiringPi#, please review our lesson 2: Introduction Of Raspberry Pi GPIO

2) Connection Graph

Fritzing File Dowload link: http://osoyoo.com/driver/pi3_start_learning_kit_lesson_3/osoyoo-raspi-lesson3.fzz.zip

3)Understand 3 kinds GPIO number system

Add wiringPi and stdio file which is used in this project at the beginning of the code. the LED connect with wPi#0 (physical pin#11 or GPIO/BCM 17). There are three ways of naming including physical, wiringPi and BCM. To learn more information about raspberry Pi GPIO, please visit: https://osoyoo.com/2017/06/26/raspberry-pi-basic-tutorial-introduction-of-raspberry-pi-gpio/. You can enter the following command to see the GPIO layout

gpio readall

Above pin map shows Raspberry Pi actually has 3 pin number system. Physical Pin number, WPI(WiringPi) pin number and BCM pin number.  For example , Physical Pin#7 in BCM system is called GPIO 17 while in WPI system , it is called GPIO 0(zero).
So how can we know which number system applies to our program? Here are some simple rules:
In python:
If you decide use Physical Pin number system, you need use add following statement

GPIO.setmode(GPIO.BOARD)

If you want use BCM pin number system, you need add following statement:

GPIO.setmode(GPIO.BCM)

In C or C++:
C/C++ use wiringPi  library to access GPIO pins and WiringPi library uses WPI number system.

4)Download C sample code from our website with following command

cd ~
wget http://osoyoo.com/driver/pi3_start_learning_kit_lesson_3/testwiringpi.c

5)Compile Code with following command:

gcc -Wall -o app testwiringpi.c -lwiringPi

Explanation: C language is high level language. Before running the project, the code need to compile as an executable file.
gcc: is GNU Compiler Collection. If you want to write your own C code and compile to run it, you need to master gcc.
-Wall: to get more error when compile the code
-o: to name the compiled file. You can name the file as your like. here we name as app
testwiringpi.c: means the original file which is compiled
-lwiringPi: is to load the library wiringPi (l is short for library)

4)Run Project, enter the following command and press “enter” to run the project

sudo  ./app

5)After running the code, your terminal will show print message as codef firstly, and then the LED blink and the ternimal will show LED status.


6)You can also use Python to do the same job.

i) Download Python Code by following command:

wget http://osoyoo.com/driver/pi3_start_learning_kit_lesson_3/testwiringpi.py

Run the python code by following command:

python testwiringpi.py