Introduction

Nowadays,there are more and more navigation device with GPS function can be avilabled in electronic market.But along with high precision micro pressure sensor came, a problem solved that we can not know the current altitude,even we can using GPS to determine the location of the equipments.Bosch Sensortec developed a smart, ultra small size, high precision digital sensor BMP180 to fit high precision measurement and data acquisition for intelligence with high accuracy output of pressure (or height) and temperature measurement data.

Applications

Specification

Pin Definition

The definition of Barometric Pressure Sensor sensor pin is

Pin Definition

Documents

Characteristic Curve

Sample

TOY0058 diagram

The result in Serial Monitor

Sample Code

/**************************************************************************************/
/**********************DFRobot.com*****************************/
/***write by Tom Riddler          Jun.16.14***/
/***if you got any progream,please contact me terminaterfxy@hotmail.com***/

#include <Wire.h>
#define BMP180ADD 0xEE>>1  // I2C address of BMP180
                           //write is (0xEE)     read is (0xEF)
unsigned char OSS;
/**********************MSB      LSB******/
int ac1;           // 0xAA     0xAB
int ac2;           // 0xAC     0xAD
int ac3;           // 0xAE     0xAE
unsigned int ac4;  // 0xB0     0xB1
unsigned int ac5;  // 0xB2     0xB3
unsigned int ac6;  // 0xB4     0xB5
int b1;            // 0xB6     0xB7
int b2;            // 0xB8     0xB9
int mb;            // 0xBA     0xBB
int mc;            // 0xBC     0xBD
int md;            // 0xBE     0xBF
float temperature;
double pressure;
double pressure2;
long b5;
double altitude;



void setup()
{
  Serial.begin(9600);
  Wire.begin();
  OSS = 2;  // Oversampling Setting           0: single    1: 2 times    2: 4 times   3: 8 times
  BMP180start();
}

void loop()
{
  calculate();
  show();
  delay(1000);
}

/** calculate centure **/
void calculate()
{
  temperature = bmp180GetTemperature(bmp180ReadUT());
  temperature = temperature*0.1;
  pressure = bmp180GetPressure(bmp180ReadUP());
  pressure2 = pressure/101325;
  pressure2 = pow(pressure2,0.19029496);
  altitude = 44330*(1-pressure2);                            //altitude = 44330*(1-(pressure/101325)^0.19029496);
}

/** print reslut **/
void show()
{
  Serial.print("Temperature: ");
  Serial.print(temperature, 1);                            //10 hexadecimal
  Serial.println(" C");
  Serial.print("Pressure: ");
  Serial.print(pressure, 0);                               //10 hexadecimal
  Serial.println(" Pa");
  Serial.print("altitude:");
  Serial.print(altitude);
  Serial.println("m");
}

/**BMP180 satrt program**/
void BMP180start()
{                     /*MSB*/
  ac1 = bmp180ReadDate(0xAA);                      //get full data
  ac2 = bmp180ReadDate(0xAC);
  ac3 = bmp180ReadDate(0xAE);
  ac4 = bmp180ReadDate(0xB0);
  ac5 = bmp180ReadDate(0xB2);
  ac6 = bmp180ReadDate(0xB4);
  b1  = bmp180ReadDate(0xB6);
  b2  = bmp180ReadDate(0xB8);
  mb  = bmp180ReadDate(0xBA);
  mc  = bmp180ReadDate(0xBC);
  md  = bmp180ReadDate(0xBE);
}

/***BMP180 temperature Calculate***/
short bmp180GetTemperature(unsigned int ut)
{
  long x1, x2;
  x1 = (((long)ut - (long)ac6)*(long)ac5) >> 15;  //x1=((ut-ac6)*ac5)/(2^15)
  x2 = ((long)mc << 11)/(x1 + md);                //x2=(mc*2^11)/(x1+md)
  b5 = x1 + x2;                                   //b5=x1+x2
  return ((b5 + 8)>>4);                           //t=(b5+8)/(2^4)
}

/***BMP180 pressure Calculate***/

long bmp180GetPressure(unsigned long up)
{
  long x1, x2, x3, b3, b6, p;
  unsigned long b4, b7;

  b6 = b5 - 4000;

  x1 = (b2 * (b6 * b6)>>12)>>11;
  x2 = (ac2 * b6)>>11;
  x3 = x1 + x2;
  b3 = (((((long)ac1)*4 + x3)<<OSS) + 2)>>2;

  x1 = (ac3 * b6)>>13;
  x2 = (b1 * ((b6 * b6)>>12))>>16;
  x3 = ((x1 + x2) + 2)>>2;
  b4 = (ac4 * (unsigned long)(x3 + 32768))>>15;

  b7 = ((unsigned long)(up - b3) * (50000>>OSS));
  if (b7 < 0x80000000)
    p = (b7<<1)/b4;
  else
    p = (b7/b4)<<1;

  x1 = (p>>8) * (p>>8);
  x1 = (x1 * 3038)>>16;
  x2 = (-7357 * p)>>16;
  p += (x1 + x2 + 3791)>>4;

  return p;
}


/*** Read 1 bytes from the BMP180  ***/

int bmp180Read(unsigned char address)
{
  unsigned char data;

  Wire.beginTransmission(BMP180ADD);
  Wire.write(address);
  Wire.endTransmission();

  Wire.requestFrom(BMP180ADD, 1);
  while(!Wire.available());

  return Wire.read();
}

/*** Read 2 bytes from the BMP180 ***/
int bmp180ReadDate(unsigned char address)
{
  unsigned char msb, lsb;
  Wire.beginTransmission(BMP180ADD);
  Wire.write(address);
  Wire.endTransmission();
  Wire.requestFrom(BMP180ADD, 2);
  while(Wire.available()<2);
  msb = Wire.read();
  lsb = Wire.read();
  return (int) msb<<8 | lsb;
}

/*** read uncompensated temperature value ***/
unsigned int bmp180ReadUT()
{
  unsigned int ut;
  Wire.beginTransmission(BMP180ADD);
  Wire.write(0xF4);                       // Write 0x2E into Register 0xF4
  Wire.write(0x2E);                       // This requests a temperature reading
  Wire.endTransmission();
  delay(5);                               // Wait at least 4.5ms
  ut = bmp180ReadDate(0xF6);               // read MSB from 0xF6 read LSB from (16 bit)
  return ut;
}

/*** Read uncompensated pressure value from BMP180 ***/
unsigned long bmp180ReadUP()
{
  unsigned char msb, lsb, xlsb;
  unsigned long up = 0;

  Wire.beginTransmission(BMP180ADD);
  Wire.write(0xF4);                        // Write 0x34+(OSS<<6) into register 0xF4
  Wire.write(0x34 + (OSS<<6));             // 0x34+oss*64
  Wire.endTransmission();
  delay(2 + (3<<OSS));                     // Wait for conversion, delay time dependent on OSS

  Wire.beginTransmission(BMP180ADD);
  Wire.write(0xF6);                        // Read register 0xF6 (MSB), 0xF7 (LSB), and 0xF8 (XLSB)
  Wire.endTransmission();

  Wire.requestFrom(BMP180ADD, 3);
  while(Wire.available() < 3);             // Wait for data to become available
  msb = Wire.read();
  lsb = Wire.read();
  xlsb = Wire.read();
  up = (((unsigned long) msb << 16) | ((unsigned long) lsb << 8) | (unsigned long) xlsb) >> (8-OSS);//16 to 19 bit
  return up;
}

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