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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.
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:
Test wiringPi exist or not
You can test whether the wiringPi library has already been installed by running following command in terminal：
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
Fritzing File Dowload link: http://osoyoo.com/driver/pi3_start_learning_kit_lesson_3/osoyoo-raspi-lesson3.fzz.zip
3)Download sample code from our website with following command
cd ~ wget http://osoyoo.com/driver/pi3_start_learning_kit_lesson_3/testwiringpi.c
Copy the code from https://osoyoo.com/driver/pi3_start_learning_kit_lesson_3/testwiringpi.c to testwiringpi.c
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
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 we can we know which number system applies to our program. Here are some simple rules:
If you decide use Physical Pin number system, you need use add following statement
If you want use BCM pin number system, you need add following statement:
In this lesson, we will use wiringPi library to access GPIO pins, so it is used WPI number system.
Main function main() invokes print_message() function first, and the terminal will show the print message, and then set LEDPIN as output mode, at last, go on while loop statement and conditionals. The program will change Led pin level times and times to make the LED blink and send print message to terminal.
4)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
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.
DownLoad Url osoyoo.com