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

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

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

The zip file should be unzipped first and then start the installation process. All the process here is done using the Linux command line. The command for unzipping the zip folder to is given below:

tar zxvf bcm2835-1.26.tar.gz

This command will unzip the .gz file into a folder named bcm2835-1.26 in which all the source files are present. Now the user should enter that 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

make

sudo make check

sudo make install

Once the installation is completed the library can be included as a header file in any C codes as

#include <bcm2835.h>

The each pin of the Raspberrypi board is declared inside this header file as their pin number or name etc. The functions for accessing those pins are also available in this header file. The pin out details of the raspberrypi board is given below:

Fig. 2: General Purpose I/O Pins Of Raspberry Pi board

 Fig. 3: Pin Number And Details Of Raspberrypi Board

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

Few functions from the library <bcm2835.h> can be used here and the details of them are given below:

Fig. 4: Functions Of Library <bcm2835.h> To Blink LED

The functions are used in the C code for blinking the LED which is given in Code 1 Tab.

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

cc blink.c -lbcm2835 -o blink

The binary file can be executed using the command:

./blink

As soon as the user enters the command the LED connected to the pin number 11 starts blinking. The execution can be terminated using CTRL + C

Project Source Code

###

 //------------------------------------------ led blinking code --------------------------------------------------//
#include <bcm2835.h>
#define PIN RPI_GPIO_P1_11
int main()
{
if (!bcm2835_init()) // initialize the library
return 1;
bcm2835_gpio_fsel (PIN, BCM2835_GPIO_FSEL_OUTP); // Set the pin to be an output
while (1)
{
bcm2835_gpio_write(PIN, HIGH); // Turn it on
bcm2835_delay(500); // wait a bit
bcm2835_gpio_write(PIN, LOW); // turn it off
bcm2835_delay(500); // wait a bit
}
bcm2835_close(); // close the library
return 0;
}
//------------------------------------------ led blinking code --------------------------------------------------//
 
###
 

Project Source Code

###

#include <bcm2835.h>
// Blinks on RPi Plug P1 pin 11 (which is GPIO pin 17)
#define PIN RPI_GPIO_P1_11
int main()
{

if (!bcm2835_init())
return 1;
// Set the pin to be an output
bcm2835_gpio_fsel(PIN, BCM2835_GPIO_FSEL_OUTP);
// Blink
while (1)
{
// Turn it on
bcm2835_gpio_write(PIN, HIGH);
// wait a bit
bcm2835_delay(500);
// turn it off
bcm2835_gpio_write(PIN, LOW);
// wait a bit
bcm2835_delay(500);
}
bcm2835_close();
return 0;
}
 
###
 

Circuit Diagrams

CIRCUIT_51

Project Components

Project Video

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Filed Under: Raspberry pi
Tagged With: led, Raspberry Pi
 

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