Accelerometru ADXL345

Placa pentru Analog Device ADXL345. ADXL345 este un accelerometru mic, subtire, cu un consum redus de energie, pe 3 axe cu masuratoare de rezolutie mare (13 biti) pana la ±16 g. Datele de iesire digitale sunt formatate in complement fata de doi si sunt accesibile prin fie un SPI (cu 3 sau 4 fire) sau o interfata digitala I2C.
 

ADXL345 este foarte potrivit pentru masuratori ale acceleratiei statice a gravitatiei in aplicatii care sesizeaza bascularea, ca si acceleratia dinamica rezultand din miscare sau socuri. Rezolutia sa mare (4 mg/LSB) permite masurarea schimbarilor de inclinatie mai mici de 1,0°.
 

Mai multe functii de sesizare speciale sunt furnizate. Sesizarea activitatii si inactivitatii depisteaza prezenta sau lipsa miscarii si daca acceleratia pe oricare axa excede un nivel setat de catre utilizator. Sesizarea batailor usoare depisteaza bataile simple sau duble. Sesizarea caderii libere depisteaza daca aparatul este in cadere. Aceste functii pot fi mapate pe unul din doi pini de iesire de intrerupere. Un buffer first in, first out (FIFO) cu 32 de nivele integrat, in curs de patentare, poate fi folosit pentru a stoca datele pentru a minimiza interventia procesorului gazda. Modurile cu consum redus permit administrarea energiei inteligenta, bazata pe miscare, cu sesizare de praguri si masuratori active de acceleratie cu disipare de energie extrem de scazuta.

#include "wire.h"
#include "adxl345.h"


ADXL345 adxl; //variable adxl is an instance of the ADXL345 library

void setup(){
  Serial.begin(9600);
  adxl.powerOn();

  //set activity/ inactivity thresholds (0-255)
  adxl.setActivityThreshold(75); //62.5mg per increment
  adxl.setInactivityThreshold(75); //62.5mg per increment
  adxl.setTimeInactivity(10); // how many seconds of no activity is inactive?
 
  //look of activity movement on this axes - 1 == on; 0 == off 
  adxl.setActivityX(1);
  adxl.setActivityY(1);
  adxl.setActivityZ(1);
 
  //look of inactivity movement on this axes - 1 == on; 0 == off
  adxl.setInactivityX(1);
  adxl.setInactivityY(1);
  adxl.setInactivityZ(1);
 
  //look of tap movement on this axes - 1 == on; 0 == off
  adxl.setTapDetectionOnX(0);
  adxl.setTapDetectionOnY(0);
  adxl.setTapDetectionOnZ(1);
 
  //set values for what is a tap, and what is a double tap (0-255)
  adxl.setTapThreshold(50); //62.5mg per increment
  adxl.setTapDuration(15); //625μs per increment
  adxl.setDoubleTapLatency(80); //1.25ms per increment
  adxl.setDoubleTapWindow(200); //1.25ms per increment
 
  //set values for what is considered freefall (0-255)
  adxl.setFreeFallThreshold(7); //(5 - 9) recommended - 62.5mg per increment
  adxl.setFreeFallDuration(45); //(20 - 70) recommended - 5ms per increment
 
  //setting all interupts to take place on int pin 1
  //I had issues with int pin 2, was unable to reset it
  adxl.setInterruptMapping( ADXL345_INT_SINGLE_TAP_BIT,   ADXL345_INT1_PIN );
  adxl.setInterruptMapping( ADXL345_INT_DOUBLE_TAP_BIT,   ADXL345_INT1_PIN );
  adxl.setInterruptMapping( ADXL345_INT_FREE_FALL_BIT,    ADXL345_INT1_PIN );
  adxl.setInterruptMapping( ADXL345_INT_ACTIVITY_BIT,     ADXL345_INT1_PIN );
  adxl.setInterruptMapping( ADXL345_INT_INACTIVITY_BIT,   ADXL345_INT1_PIN );
 
  //register interupt actions - 1 == on; 0 == off  
  adxl.setInterrupt( ADXL345_INT_SINGLE_TAP_BIT, 1);
  adxl.setInterrupt( ADXL345_INT_DOUBLE_TAP_BIT, 1);
  adxl.setInterrupt( ADXL345_INT_FREE_FALL_BIT,  1);
  adxl.setInterrupt( ADXL345_INT_ACTIVITY_BIT,   1);
  adxl.setInterrupt( ADXL345_INT_INACTIVITY_BIT, 1);
}

void loop(){
  
  int x,y,z;  
  adxl.readAccel(&x, &y, &z); //read the accelerometer values and store them in variables  x,y,z

  // Output x,y,z values - Commented out
  Serial.print("X: ");
  Serial.print(x);
  Serial.print("  Y: ");
  Serial.print(y);
  Serial.print("  Z: ");
  Serial.println(z);
}

Raspberry PI
 

Daca nu iti este clar ce este un accelerometru si care sunt aplicatiile lui practice, aici gasesti un document in limba romana care iti explica mai multe - http://robofun.ro/forum/viewtopic.php?f=16&t=158 (microcontroller-ul folosit este Arduino, vezi mai jos pentru un tutorial pentru conectarea cu Raspberry PI) 

Cod Sursa

// gcc -o read_adxl readings_general.c

#include "stdio.h"
#include "stdlib.h"
#include "fcntl.h"
#include "unistd.h"
#include "string.h"
#include 
#include 
#include 
#include 

#define SRF02_I2C_ADDR 0x70
#define ADXL345_I2C_ADDR 0x53

void selectDevice(int fd, int addr, char * name)
{
   if (ioctl(fd, I2C_SLAVE, addr) < 0)
   {
      fprintf(stderr, "%s not presentn", name);
      //exit(1);
   }
}

void writeToDevice(int fd, int reg, int val)
{
   char buf[2];
   buf[0]=reg; buf[1]=val;
   if (write(fd, buf, 2) != 2)
   {
      fprintf(stderr, "Can't write to ADXL345n");
      //exit(1);
   }
}

int main(int argc, char **argv)
{
   unsigned int range;
   int count, b;
   short x, y, z;
   float xa, ya, za;
   int fd;
   unsigned char buf[16];
   char str[80] = {};
   char system_str[256] = {};

   if ((fd = open("/dev/i2c-1", O_RDWR)) < 0)
   {
      // Open port for reading and writing
      fprintf(stderr, "Failed to open i2c busn");
      exit(1);
   }
   /* initialise ADXL345 */

   selectDevice(fd, ADXL345_I2C_ADDR, "ADXL345");

   writeToDevice(fd, 0x2d, 0);
   writeToDevice(fd, 0x2d, 16);
   writeToDevice(fd, 0x2d, 8);
   writeToDevice(fd, 0x31, 0);
   writeToDevice(fd, 0x31, 11);

   while (1) {
      /* select ADXL345 */

      selectDevice(fd, ADXL345_I2C_ADDR, "ADXL345");

      buf[0] = 0x32;
      if ((write(fd, buf, 1)) != 1)
      {
         // Send the register to read from
         fprintf(stderr, "Error writing to i2c slaven");
         //exit(1);
      }
      if (read(fd, buf, 6) != 6)
      {
         //  X, Y, Z accelerations

         fprintf(stderr, "Unable to read from ADXL345n");
         //exit(1);
      }
      else
      {
         x = buf[1]<<8| buf[0];
         y = buf[3]<<8| buf[2];
         z = buf[5]<<8| buf[4];
         xa = (90.0 / 256.0) * (float) x;
         ya = (90.0 / 256.0) * (float) y;
         za = (90.0 / 256.0) * (float) z;

         printf("X: %4.0f   Y: %4.0f   Z: %4.0fn", xa, ya, za);
      }
      usleep(9000);
   }
   return 0;
}

  Descarca tutorial conectare Raspberry PI (PDF)

Specificatii:
 

• 2,0-3,6V CC voltaj de alimentare
• energie ultra scazuta: 40uA in modul masuratoare, 0,1uA in mod standby la 2,5V
• detectie de bataie/bataie dubla
• detectie de cadere libera
• interfete SPI si I2C

Linkuri:
 

Schema

Datasheet

Exemplu de control I2C (ATmega328)

Cod exemplu (ATmega328)

Exemplu mbed

Exemplu Bildr

Proiect "Pedometru IoT"