Showing posts with label C. Show all posts

Wednesday, November 14, 2012

by Rahul Kar on Leave a Comment

7 Segment Multiplexing With Raspberry Pi

7 segments can be driven using many different techniques in conjunction with software and hardware. Multiplexing is one of the most popular methods used to drive a 7 segment display when there are limited no of I/O pins.It uses the concept of POV(persistence of vision) where the human brain cannot detect the flickering of display when the refresh rate is very high(~50Hz).In this method the fundamental logic is to enable or disable the segment blocks at a very high speed at precise time slices.

In case of Raspberry Pi there are limited no of I/O pins, hence we will use multiplexing. WiringPi is perfect for this job as it uses Arduino like code and the code executes at a higher priority. Display used in this example is of common cathode type.Make sure you have the right 7 segment display,else you will end up getting random segments turned on.For pin mapping check the code below:-

Code:-

#include <wiringPi.h>
#include <stdio.h>
#define DISPLAY_BRIGHTNESS  500
#define DIGIT_ON  HIGH
#define DIGIT_OFF  LOW
#define SEGMENT_ON  LOW
#define SEGMENT_OFF HIGH
int SEGMENT_1=7; 
int SEGMENT_2=11;
int SEGMENT_3=13;
int SEGMENT_4=15;
int SEGMENT_A=3; 
int SEGMENT_B=5; 
int SEGMENT_C=18; 
int SEGMENT_D=19; 
int SEGMENT_E=23; 
int SEGMENT_F=24; 
int SEGMENT_G=25; 
void display_number(int num)
{
  pinMode(SEGMENT_1,OUTPUT);
  pinMode(SEGMENT_2,OUTPUT);
  pinMode(SEGMENT_3,OUTPUT);
  pinMode(SEGMENT_4,OUTPUT);
  long start=millis();
  for(int i=4;i>0;i--)
  {
    switch(i)
    {
    case 1:
      digitalWrite(SEGMENT_1,DIGIT_ON);
      break;
    case 2:
      digitalWrite(SEGMENT_2,DIGIT_ON);
      break;
    case 3:
      digitalWrite(SEGMENT_3,DIGIT_ON);
      break;
    case 4:
      digitalWrite(SEGMENT_4,DIGIT_ON);
      break;
    }
    print_number(num%10);
    num/=10;
    delayMicroseconds(DISPLAY_BRIGHTNESS); 
    print_number(10); 
    digitalWrite(SEGMENT_1,DIGIT_OFF);
    digitalWrite(SEGMENT_2,DIGIT_OFF);
    digitalWrite(SEGMENT_3,DIGIT_OFF);
    digitalWrite(SEGMENT_4,DIGIT_OFF);
  }
  while((millis()-start)<10);
}
void print_number(int num)
{
  pinMode(SEGMENT_A,OUTPUT);
  pinMode(SEGMENT_B,OUTPUT);
  pinMode(SEGMENT_C,OUTPUT);
  pinMode(SEGMENT_D,OUTPUT);
  pinMode(SEGMENT_E,OUTPUT);
  pinMode(SEGMENT_F,OUTPUT);
  pinMode(SEGMENT_G,OUTPUT);
  switch(num)
  {
  case 0:
    digitalWrite(SEGMENT_A,SEGMENT_ON);
    digitalWrite(SEGMENT_B,SEGMENT_ON);
    digitalWrite(SEGMENT_C,SEGMENT_ON);
    digitalWrite(SEGMENT_D,SEGMENT_ON);
    digitalWrite(SEGMENT_E,SEGMENT_ON);
    digitalWrite(SEGMENT_F,SEGMENT_ON);
    digitalWrite(SEGMENT_G,SEGMENT_OFF);
    break;
  case 1:
    digitalWrite(SEGMENT_A,SEGMENT_OFF);
    digitalWrite(SEGMENT_B,SEGMENT_ON);
    digitalWrite(SEGMENT_C,SEGMENT_ON);
    digitalWrite(SEGMENT_D,SEGMENT_OFF);
    digitalWrite(SEGMENT_E,SEGMENT_OFF);
    digitalWrite(SEGMENT_F,SEGMENT_OFF);
    digitalWrite(SEGMENT_G,SEGMENT_OFF);
    break;
  case 2:
    digitalWrite(SEGMENT_A,SEGMENT_ON);
    digitalWrite(SEGMENT_B,SEGMENT_ON);
    digitalWrite(SEGMENT_C,SEGMENT_OFF);
    digitalWrite(SEGMENT_D,SEGMENT_ON);
    digitalWrite(SEGMENT_E,SEGMENT_ON);
    digitalWrite(SEGMENT_F,SEGMENT_OFF);
    digitalWrite(SEGMENT_G,SEGMENT_ON);
    break;
  case 3:
    digitalWrite(SEGMENT_A,SEGMENT_ON);
    digitalWrite(SEGMENT_B,SEGMENT_ON);
    digitalWrite(SEGMENT_C,SEGMENT_ON);
    digitalWrite(SEGMENT_D,SEGMENT_ON);
    digitalWrite(SEGMENT_E,SEGMENT_OFF);
    digitalWrite(SEGMENT_F,SEGMENT_OFF);
    digitalWrite(SEGMENT_G,SEGMENT_ON);
    break;
  case 4:
    digitalWrite(SEGMENT_A,SEGMENT_OFF);
    digitalWrite(SEGMENT_B,SEGMENT_ON);
    digitalWrite(SEGMENT_C,SEGMENT_ON);
    digitalWrite(SEGMENT_D,SEGMENT_OFF);
    digitalWrite(SEGMENT_E,SEGMENT_OFF);
    digitalWrite(SEGMENT_F,SEGMENT_ON);
    digitalWrite(SEGMENT_G,SEGMENT_ON);
    break;
  case 5:
    digitalWrite(SEGMENT_A,SEGMENT_ON);
    digitalWrite(SEGMENT_B,SEGMENT_OFF);
    digitalWrite(SEGMENT_C,SEGMENT_ON);
    digitalWrite(SEGMENT_D,SEGMENT_ON);
    digitalWrite(SEGMENT_E,SEGMENT_OFF);
    digitalWrite(SEGMENT_F,SEGMENT_ON);
    digitalWrite(SEGMENT_G,SEGMENT_ON);
    break;
  case 6:
    digitalWrite(SEGMENT_A,SEGMENT_ON);
    digitalWrite(SEGMENT_B,SEGMENT_OFF);
    digitalWrite(SEGMENT_C,SEGMENT_ON);
    digitalWrite(SEGMENT_D,SEGMENT_ON);
    digitalWrite(SEGMENT_E,SEGMENT_ON);
    digitalWrite(SEGMENT_F,SEGMENT_ON);
    digitalWrite(SEGMENT_G,SEGMENT_ON);
    break;
  case 7:
    digitalWrite(SEGMENT_A,SEGMENT_ON);
    digitalWrite(SEGMENT_B,SEGMENT_ON);
    digitalWrite(SEGMENT_C,SEGMENT_ON);
    digitalWrite(SEGMENT_D,SEGMENT_OFF);
    digitalWrite(SEGMENT_E,SEGMENT_OFF);
    digitalWrite(SEGMENT_F,SEGMENT_OFF);
    digitalWrite(SEGMENT_G,SEGMENT_OFF);
    break;
  case 8:
    digitalWrite(SEGMENT_A,SEGMENT_ON);
    digitalWrite(SEGMENT_B,SEGMENT_ON);
    digitalWrite(SEGMENT_C,SEGMENT_ON);
    digitalWrite(SEGMENT_D,SEGMENT_ON);
    digitalWrite(SEGMENT_E,SEGMENT_ON);
    digitalWrite(SEGMENT_F,SEGMENT_ON);
    digitalWrite(SEGMENT_G,SEGMENT_ON);
    break;
  case 9:
    digitalWrite(SEGMENT_A,SEGMENT_ON);
    digitalWrite(SEGMENT_B,SEGMENT_ON);
    digitalWrite(SEGMENT_C,SEGMENT_ON);
    digitalWrite(SEGMENT_D,SEGMENT_ON);
    digitalWrite(SEGMENT_E,SEGMENT_OFF);
    digitalWrite(SEGMENT_F,SEGMENT_ON);
    digitalWrite(SEGMENT_G,SEGMENT_ON);
    break;
  case 10:
    digitalWrite(SEGMENT_A,SEGMENT_OFF);
    digitalWrite(SEGMENT_B,SEGMENT_OFF);
    digitalWrite(SEGMENT_C,SEGMENT_OFF);
    digitalWrite(SEGMENT_D,SEGMENT_OFF);
    digitalWrite(SEGMENT_E,SEGMENT_OFF);
    digitalWrite(SEGMENT_F,SEGMENT_OFF);
    digitalWrite(SEGMENT_G,SEGMENT_OFF);
    break;
  }
}
int main(void)
{
 printf("7 Segment Multiplexing using Raspberry Pi\n") ;
 if(getuid()!=0) //wiringPi requires root privileges  
 {  
  printf("Error:wiringPi must be run as root.\n");  
  return 1;  
 }  
 if(wiringPiSetup()==-1)  
 {  
  printf("Error:wiringPi setup failed!\n");  
  return 1;  
 }
 int counter=0;
 for(;;)
 {
  display_number(counter++);
                delay(1000);
  if(counter>9999)
   counter=0;
 }
  return 0;
}

Compile the code as...
gcc -o display segment.c -L/usr/local/lib -lwiringPi
Now execute it...
sudo ./display

Sunday, November 4, 2012

by Rahul Kar on Leave a Comment

PWM on Raspberry Pi

With only one hardware PWM pin on Raspberry Pi it can be quite a problem with Arduino users like me.There are various hardware solutions available to overcome this problem.Many ADC(analog to digital converters) IC are available which can be interfaced via I2C bus.In this post I will be using WiringPi library which can bit-bang any GPIO pins and generate PWM signal. Even though the PWM signals are generated by individual threads with high priority using a real-time scheduler, there may be instances where it may get temporarily descheduled for a fraction of a second and cause jitters.

Installing the Library:-
WiringPi is maintained under GIT for ease of change tracking.If you do not have GIT installed, then under any of the Debian releases, you can install it with-
sudo apt-get install git-core

To obtain WiringPi using GIT:
git clone git://git.drogon.net/wiringPi

If you have already used the clone operation for the first time, then

cd wiringPi
git pull origin
Will fetch an updated version then you can re-run the build script below.

To build/install there is a new simplified script:
cd wiringPi
./build

The new build script will compile and install it all for you - it does use the sudo command at one point, so you may wish to inspect the script before running it.

Example Code:-
This code uses both the hardware and software PWM functions.

//////---------------------------------------------------------------------------
////// Name:                   pwm.c
////// Compiled with:      gcc pwm.c -I/usr/local/include -L/usr/local/lib -lwiringPi -lpthread -o pwm
////// Schematic:              .------.
//////                         | o  o |
//////                     RPi | o  o |12
//////                         | o  o-|-----(->|)-----\/\/\/\--o GND
//////                         | o  o |11    LED1       220
//////                         | o  o-|-----(->|)-----\/\/\/\--o GND
//////                         | o  o |      LED2       220
//////                         | o  o-|
//////
////// Notes:
//////---------------------------------------------------------------------------
#include <stdio.h>
#include <stdlib.h>
#include <signal.h>
#include <wiringPi.h>
#include <softPwm.h>
void control_event(int sig);
int HARD_PWM_PIN=1; //Hardware PWM Pin(GPIO18-12)
int SOFT_PWM_PIN=0; //Software PWM Pin(GPIO0-11)
int DELAY_MS=10;
int main(void)
{
  (void)signal(SIGINT,control_event);
  (void)signal (SIGQUIT,control_event);
  printf("Hardware and software based PWM test on LED\n");
  if(getuid()!=0) //wiringPi requires root privileges
  {
    printf("Error:wiringPi must be run as root.\n");
    return 1;
  }
  if(wiringPiSetup()==-1)
  {
    printf("Error:wiringPi setup failed.\n");
    return 1;
  }
  pinMode(HARD_PWM_PIN,PWM_OUTPUT); //setup hardware pwm
  softPwmCreate(SOFT_PWM_PIN,0,100); //setup software pwm pin
  int up;
  int down;
  while(1)
  {
    for(up=1;up=5;down--)
    {
      pwmWrite(HARD_PWM_PIN,down);
      softPwmWrite(SOFT_PWM_PIN,down);
      delay(DELAY_MS*2);
    }
    delay(DELAY_MS*5);
  }
}
void control_event(int sig)
{
  printf("\b\bExiting...\n");
  pwmWrite(HARD_PWM_PIN,0);
  softPwmWrite(SOFT_PWM_PIN,0);
  delay(100); //wait a little for the pwm to finish write
  exit(0);
}

Limitations:- To minimize CPU usage the minimum default pulse width is set to 100μs thereby generating a PWM of 100 Hz. Lowering the range can give you a higher frequency at an expense of resolution and vice versa. Delays less than 100μs will dramatically increase the CPU usage and controlling other pins would be impossible.However, within these limitations controlling an LED or Motor is quite practical.

Friday, October 26, 2012

by Suriya Deepan on Leave a Comment

Running Pi headless - SSH tunneling part2

In this tutorial, I will demonstrate the following:-

1. Login through ssh
2. Changing pi's password
3. Navigating through file-system
4. Copying files on network
5. Shutdown, Reboot pi
6. Writing, compiling a C program

Download Notes

Raspberry Pi Blog