Reading GPIO state in beagle bone black

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1

Hi,

i am new to beagle bone black board…

i flashed new Debian Image to BBB and worked on simple LED blinking program in C. it is working fine(external LED connected in bread board), in Linux ubuntu

next example i am trying to control that external LED using external switch :

like this :

system("echo out > /sys/class/gpio/gpio68/direction) for LED.
system ("echo in > /sys/class/gpio/gpio67/direction) for switch.

using these coding lines i am making LED high and Low in C file

system("echo 1 > /sys/class/gpio/gpio68/value)

system("echo 0 > /sys/class/gpio/gpio68/value)

based on the switch status i need to make LED ON and LED OFF…

how to read the state of GPIO in beagle bone black in C file???

please help me any one …

2

The easy way is going to be reading the value file for the gpio pin you have set as input. In C:

FILE * f = fopen("/sys/class/gpio/gpio67/value", “r”);
int val;
(void) fscanf(f, “%d”, &val);

tada the variable val now holds a one or zero based on the state of the gpio pin.

Another tutorial: https://www.dummies.com/computers/beaglebone/setting-beaglebone-gpios-as-inputs/

For simple stuff like this, usually a quick Google search will have the answers :wink:

3

Hi,

thanks for reply, i understand the concept and hardware connections from that link what u shared…

Let me check once working of program to control the LED blinking using push botton

4

Hi,

i am new to beagle bone black board..

i flashed new Debian Image to BBB and worked on simple LED blinking program
in C. it is working fine(external LED connected in bread board), in Linux
ubuntu

next example i am trying to control that external LED using external switch
:

like this :

system("echo out > /sys/class/gpio/gpio68/direction) for LED.
system ("echo in > /sys/class/gpio/gpio67/direction) for switch.

You don't really need to fork a process like that. You can just do this
direcly in C:

#include <stdio.h>

typedef enum direction {in, out} Direction;

void SetDirection(int GPIO, Direction dir)
{
    char filename[36];
    FILE *fp;
    
    snprintf(filename,sizeof(filename),"/sys/class/gpio/gpio%d/direction",GPIO);
    fp = fopen(filename,"w");
    switch (dir) {
    case in: fprintf(fp,"in\n"); break;
    case out: fprintf(fp,"out\n"); break;
    }
    close(fp);
}

Then in your code:

#define LED 68
#define SWITCH 67

SetDirection(LED,out);
SetDirection(SWITCH,in);

using these coding lines i am making LED high and Low in C file
system("echo 1 > /sys/class/gpio/gpio68/value)
system("echo 0 > /sys/class/gpio/gpio68/value)

typedef enum value {LOW=0, HIGH=1} Value;

void WriteGPIO(int GPIO, Value v)
{
    char filename[32];
    FILE *fp;
    
    snprintf(filename,sizeof(filename),"/sys/class/gpio/gpio%d/value",GPIO);
    fp = fopen(filename,"w");
    fprintf(fp,"%d\n",(int) v);
    close(fp);
}
    
Then in your main program:

WriteGPIO(LED,HIGH); /* Led on */
WriteGPIO(LED,LOW); /* Led off */

based on the switch status i need to make LED ON and LED OFF...

how to read the state of GPIO in beagle bone black in C file???

How about this:

Value ReadGPIO(int GPIO)
{
    char filename[32];
    FILE *fp;
    Value v;
    
    snprintf(filename,sizeof(filename),"/sys/class/gpio/gpio%d/value",GPIO);
    fp = fopen(filename,"r");
    fscanf(fp,"%d",(int *)&v);
    close(fp);
    return (v);
}

Then:

if (ReadGPIO(SWITCH) == HIGH) {
    /* switch input is high ... */
}

5

Insiders tip welcome?

Compiling against libpruio this is a 10-liner. Check out the examples section of the docs.

Regards

6

Hi TJF and Robert and Rob

it is working fine. i am able to control the LED blinking by externally connected switch…

Thank to all for reply and guiding me.