How to blink the LED using Raspberry Pi -(Part 07/38)

In this project the Raspberrypi board is loaded with Ubuntu and is accessed remotely using VNC . The Raspberrypi board is also connected to the internet . There are 26 connectors that can be taken out from the connector port of the Raspberrypi board. All connector pins are taken out using 13*2 pin female connectors and on the other end of the wire 26 pin Burg stick male connectors are connected. Burg stick male connectors allow each pin on the Raspberrypi board to be connected to the holes on a breadboard.

To access the pins coming out of the Broadcom controller of the Raspberrypi board using the C language, a C library called “bcm2835” is available. The first step in the C coding process to access the GPIO of the Raspberrypi board is to install the “bcm2835” library. The bcm2835 library is available for download as a zip file that needs to be copied to the /home/pi folder . The zip file appears as bcm2835-1.26.tar.gz in the /home/pi folder.

The zip file must be unzipped first and then start the installation process. The entire process here is done using the Linux command line . The command to unzip the zip folder is given below:

tar zxvf bcm2835-1.26.tar.gz

This command will unzip the .gz file into a folder called bcm2835-1.26 in which all the source files are present. Now the user must enter this folder to continue the installation process. To enter the folder use the following command;

cd bcm2835-1.26

Now use the following commands one by one to finish the installation process.

./configure

to do

sudo do check

sudo make install

Once the installation is complete, the library can be included as a header file in any C code, such as

#include

Each pin of the Raspberrypi board is declared within this header file as its pin number or name, etc. Functions to access these pins are also available in this header file. Raspberrypi board pinout details are given below:

Fig. 2: Raspberry Pi board general purpose I/O pins

Figure 3: Raspberrypi board pin number and details

The following section discusses how to write C code to blink an LED connected to any general-purpose output pin of the Raspberrypi, say pin number 11 (GPIO_0).

Few library functions can be used here and details of them are provided below:

Fig. 4: Library functions to blink the LED

Functions are used in code C to blink the LED provided in the Code 1 tab.

User can use vim editor to write the code and save it to a file, say “blink.c”. On the command line itself, use the following command to compile the code with the new library file to generate the “blink” executable file

cc blink.c -lbcm2835 -o blink

The binary file can be executed using the command:

./blink

As soon as the user types the command, the LED connected to pin number 11 starts blinking. Execution can be terminated using CTRL + C

Project source code

 ###

 //------------------------------------------ led blinking code --- -----------------------------------------------//
 #include <bcm2835.h>
 #define PIN RPI_GPIO_P1_11
 main int
 {
 if (!bcm2835_init ) // initialize the library
 return 1;
 bcm2835_gpio_fsel (PIN, BCM2835_GPIO_FSEL_OUTP); //Configure the pin as output
 while (1)
 {
 bcm2835_gpio_write(PIN, HIGH); //Turn it on
 bcm2835_delay(500); // wait one moment
 bcm2835_gpio_write(PIN, DOWN); // Turn this off
 bcm2835_delay(500); // wait one moment
 }
 bcm2835_close ; //close the library
 return 0;
 }
 //------------------------------------------ LED blinking code -- - ----------------------------------------------- //

 ###

Project source code

 ###

 #include <bcm2835.h>
 // Flashes on pin 11 of the RPi Plug P1 (which is pin 17 of the GPIO)
 #define PIN RPI_GPIO_P1_11
 main int
 {
 if (!bcm2835_init )
 return 1; 
//Configure the pin as output
 bcm2835_gpio_fsel(PIN, BCM2835_GPIO_FSEL_OUTP);
 // Blink
 while (1)
 {
 //Turn it on
 bcm2835_gpio_write(PIN, HIGH);
 // wait one moment
 bcm2835_delay(500);
 // Turn this off
 bcm2835_gpio_write(PIN, DOWN);
 // wait one moment
 bcm2835_delay(500);
 }
 bcm2835_close ;
 return 0;
 }

 ###

Circuit diagrams

CIRCUIT_51

Project Components

Project video