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Barometric Pressure Sensor BMP085



This simple program read data from pressure sensor bmp085 and calculating the temperature and real pressure using integer math. The microcontroler is Microchip's DSPIC33FJ256MC710, but it may work with any other.



#include "./dspic33.h"
#INCLUDE <math.h>

#use delay(clock=20000000)
//#use rs232(UART1,baud=19200,parity=N,bits=8,stream=uart1)
#use i2c(Master,Fast,sda=PIN_G3,scl=PIN_G2)

     #define LCD_RS_PIN      PIN_D1////
     #define LCD_RW_PIN      PIN_D2
     #define LCD_ENABLE_PIN  PIN_D3 ////
     #define LCD_DATA4       PIN_D12                                    ////
     #define LCD_DATA5       PIN_D13                                    ////
     #define LCD_DATA6       PIN_D4                                    ////
     #define LCD_DATA7       PIN_D5  

#include <LCD.C>
 int oss=0; //oversampling 0-low current 1-standart, 2,3- precision  
 signed int32 UT ;
 unsigned int32 UP;
 signed int16 AC1,AC2,AC3;
 unsigned int16 AC4,AC5,AC6;
 signed int16 B1,B2,MB,MC,MD;
 signed int32 X1,X2,B5,temperature,B6,X3,B3, pressure;
 unsigned int32 B4,B7;
 float altitude;
 signed int16 bmp085_read(int reg_address);
 void bmp085_write_control(int data);

void main()
    lcd_putc("\fDesigned by\n");
    lcd_putc("Martin Nikiforov");
    AC1=bmp085_read(0xAA);   // read parameters from bmp085's eeprom

 oss=3;//0-low current for more accuracy 1,2,3
   bmp085_write_control(0x2E);  //0x2E set to measure temperature   4,5ms                                                              
    UT=(unsigned int16)bmp085_read(0xF6); //read 0xF6 register temperature                             
    bmp085_write_control(0x34+(0x40*oss));  //0x34 - oss=0 set to measure pressure   4,5ms conv
                                            //oss=1 the value must be 0x74 oss =2 0xb4 , oss=3 0xF4
    UP=(unsigned int16)bmp085_read(0xF6);//pressure
    UP=(UP+(((unsigned int16)bmp085_read(0xF8))>>8))>>(8-oss);//XLSB extra precision byte
    X2=(((signed int32)MC)<<11)/(X1+MD);
    X1=(((signed int32)B2)*((B6*B6)/4096))/2048;
    X2=(((signed int32)AC2)*B6)/2048;
    B3=((((((signed int32)AC1)*4)+X3)*((int)pow(2,oss)))+2)/4;
    X1=(((signed int32)AC3)*B6)/8192;
    X2=(((signed int32)B1)*((B6*B6)/4096))/65536;
    B4=(((unsigned int32)AC4)*(unsigned int32)(X3+32768))>>15;
    B7=(unsigned int32)(((unsigned int32)UP)-B3)*(50000>>oss);
    else {pressure=(B7/B4)*2;}
    X1=(((unsigned int32)X1)*3038)/65536;                                         
    altitude=  44330.0*(1.0-pow((pressure/102325.0),(1/5.255)));
    //calculate altitude 102325.0 must be 101325.0 but where i live give me negative altitude
    printf(lcd_putc,"\aT=%4.1gC P=%5.1g\nAltitude%6.1g m\n",temperature/10.0,pressure/100.0,altitude);
  // screen refresh slowly when using \f

signed int16 bmp085_read(int reg_address)
    int msb,lsb;
    int16 data=0;
    i2c_write(0b11101110);    // Device address
    i2c_write(reg_address);  // Data to device
    i2c_start();            // Restart
    i2c_write(0b11101111);     // to change data direction
    msb=i2c_read(1);        // Now read from slave
    return (data);
void bmp085_write_control(int data)

    i2c_write(0b11101110);//     // Device address
    i2c_write(0xF4);  //control reg address
    i2c_write(data);   //write the data                 




Thank you for your program.
my project does not work properly
   but now perfect

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