BMP 180 Module,Environment

BMP180 module can measure the barometric pressure and temperature, barometric pressure changes with the altitude, it can also measure the altitude! BMP180 is the next generation of Bosch. Though BMP085 and BMP180 have the same interface in firmware and the code is in common, BMP180 module is the lowest-cost sensor in measuring the barometric pressure, temperature and altitude.

Technical Data

Voltage: 3v to 5.5v

Current: 1.1vA to 20vA

Pressure range: 300 to 1100hpa

Features

Pressure sensing range: 300-1100 hPa (-500m to 9000m above sea level);

Up to 0.03hPa / 0.25m resolution;

Temperature range: -40 to +85°C

Temperature accuracy: ±2°C

Low power: 5μA in standard mode

Accuracy: resolution is 0.06hpa(0.5m) in low power mode

Resolution is 0.03hpa(0.25m) in high linear mode

Usage

[code]

//Arduino 1.0+ Only

/*Based largely on code by Jim Lindblom

Get pressure, altitude, and temperature from the BMP085.

Serial.print it out at 9600 baud to serial monitor.

#include <Wire.h>

#define BMP085_ADDRESS 0x77 // I2C address of BMP085

const unsigned char OSS = 0; // Oversampling Setting

// Calibration values

int ac1;

int ac2;

int ac3;

unsigned int ac4;

unsigned int ac5;

unsigned int ac6;

int b1;

int b2;

int mb;

int mc;

int md;

// b5 is calculated in bmp085GetTemperature(...), this variable is also used in bmp085GetPressure(...)

// so ...Temperature(...) must be called before ...Pressure(...).

long b5;

void setup(){

Serial.begin(9600);

Wire.begin();

bmp085Calibration();

}

void loop()

{

float temperature = bmp085GetTemperature(bmp085ReadUT()); //MUST be called first

float pressure = bmp085GetPressure(bmp085ReadUP());

float atm = pressure / 101325; // "standard atmosphere"

float altitude = calcAltitude(pressure); //Uncompensated caculation - in Meters

Serial.print("Temperature: ");

Serial.print(temperature, 2); //display 2 decimal places

Serial.println("deg C");

Serial.print("Pressure: ");

Serial.print(pressure, 0); //whole number only.

Serial.println(" Pa");

Serial.print("Standard Atmosphere: ");

Serial.println(atm, 4); //display 4 decimal places

Serial.print("Altitude: ");

Serial.print(altitude, 2); //display 2 decimal places

Serial.println(" M");

Serial.println();//line break

delay(1000); //wait a second and get values again.

}

// Stores all of the bmp085's calibration values into global variables

// Calibration values are required to calculate temp and pressure

// This function should be called at the beginning of the program

void bmp085Calibration()

{

ac1 = bmp085ReadInt(0xAA);

ac2 = bmp085ReadInt(0xAC);

ac3 = bmp085ReadInt(0xAE);

ac4 = bmp085ReadInt(0xB0);

ac5 = bmp085ReadInt(0xB2);

ac6 = bmp085ReadInt(0xB4);

b1 = bmp085ReadInt(0xB6);

b2 = bmp085ReadInt(0xB8);

mb = bmp085ReadInt(0xBA);

mc = bmp085ReadInt(0xBC);

md = bmp085ReadInt(0xBE);

}

// Calculate temperature in deg C

float bmp085GetTemperature(unsigned int ut){

long x1, x2;

x1 = (((long)ut - (long)ac6)*(long)ac5) >> 15;

x2 = ((long)mc << 11)/(x1 + md);

b5 = x1 + x2;

float temp = ((b5 + 8)>>4);

temp = temp /10;

return temp;

}

// Calculate pressure given up

// calibration values must be known

// b5 is also required so bmp085GetTemperature(...) must be called first.

// Value returned will be pressure in units of Pa.

long bmp085GetPressure(unsigned long up){

long x1, x2, x3, b3, b6, p;

unsigned long b4, b7;

b6 = b5 - 4000;

// Calculate B3

x1 = (b2 * (b6 * b6)>>12)>>11;

x2 = (ac2 * b6)>>11;

x3 = x1 + x2;

b3 = (((((long)ac1)*4 + x3)<<OSS) + 2)>>2;

// Calculate B4

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;

long temp = p;

return temp;

}

// Read 1 byte from the BMP085 at 'address'

char bmp085Read(unsigned char address)

{

unsigned char data;

Wire.beginTransmission(BMP085_ADDRESS);

Wire.write(address);

Wire.endTransmission();

Wire.requestFrom(BMP085_ADDRESS, 1);

while(!Wire.available())

;

return Wire.read();

}

// Read 2 bytes from the BMP085

// First byte will be from 'address'

// Second byte will be from 'address'+1

int bmp085ReadInt(unsigned char address)

{

unsigned char msb, lsb;

Wire.beginTransmission(BMP085_ADDRESS);

Wire.write(address);

Wire.endTransmission();

Wire.requestFrom(BMP085_ADDRESS, 2);

while(Wire.available()<2)

;

msb = Wire.read();

lsb = Wire.read();

return (int) msb<<8 | lsb;

}

// Read the uncompensated temperature value

unsigned int bmp085ReadUT(){

unsigned int ut;

// Write 0x2E into Register 0xF4

// This requests a temperature reading

Wire.beginTransmission(BMP085_ADDRESS);

Wire.write(0xF4);

Wire.write(0x2E);

Wire.endTransmission();

// Wait at least 4.5ms

delay(5);

// Read two bytes from registers 0xF6 and 0xF7

ut = bmp085ReadInt(0xF6);

return ut;

}

// Read the uncompensated pressure value

unsigned long bmp085ReadUP(){

unsigned char msb, lsb, xlsb;

unsigned long up = 0;

// Write 0x34+(OSS<<6) into register 0xF4

// Request a pressure reading w/ oversampling setting

Wire.beginTransmission(BMP085_ADDRESS);

Wire.write(0xF4);

Wire.write(0x34 + (OSS<<6));

Wire.endTransmission();

// Wait for conversion, delay time dependent on OSS

delay(2 + (3<<OSS));

// Read register 0xF6 (MSB), 0xF7 (LSB), and 0xF8 (XLSB)

msb = bmp085Read(0xF6);

lsb = bmp085Read(0xF7);

xlsb = bmp085Read(0xF8);

up = (((unsigned long) msb << 16) | ((unsigned long) lsb << 8) | (unsigned long) xlsb) >> (8-OSS);

return up;

}

void writeRegister(int deviceAddress, byte address, byte val) {

Wire.beginTransmission(deviceAddress); // start transmission to device

Wire.write(address); // send register address

Wire.write(val); // send value to write

Wire.endTransmission(); // end transmission

}

int readRegister(int deviceAddress, byte address){

int v;

Wire.beginTransmission(deviceAddress);

Wire.write(address); // register to read

Wire.endTransmission();

Wire.requestFrom(deviceAddress, 1); // read a byte

while(!Wire.available()) {

// waiting

}

v = Wire.read();

return v;

}

float calcAltitude(float pressure){

float A = pressure/101325;

float B = 1/5.25588;

float C = pow(A,B);

C = 1 - C;

C = C /0.0000225577;

return C;

}

[/code]

Resource

Program

Datasheet