Difference between revisions of "BMP085 Barometric Pressure Sensor Breakout"

Revision as of 01:22, 7 August 2012

Introduction

This is a breakout board for BOSCH BMP085 digital barometric pressure sensor.This breadboard-friendly board break out all pins of BMP085 to 6-pin pitch header.BMP085 offers a meauring range of 300 - 1100hPa with an absolute accuracy of 2.5hPa and a noise of down to 0.03hPa.At the same time,the BMP085 features low power consumption of down to 3uA.The sensors supports a voltage between 1.8 and 3.6V. It's designed to be connected directly to microcontroller via I2C bus. The very small and ultra-thin package make the BMP085 the sensor of choice for any mobile application requiring precise barametric pressure meaurement.

Features

• Digital two wire (I2C) interface
• Wide barometric pressure range
• Flexible supply voltage range
• Ultra-low power consumption
• Low noise measurement
• Fully calibrated
• Temperature measurement included
• Ultra-flat, small footprint

Usage

Here is the guide illustrates how to connect an Arduino to the BMP085 breakout board.

Example code

#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; 
short temperature;
long pressure;
void setup()
{
 Serial.begin(9600);
 Wire.begin();
 bmp085Calibration();
}
void loop()
{
 temperature = bmp085GetTemperature(bmp085ReadUT());
 pressure = bmp085GetPressure(bmp085ReadUP());
 Serial.print("Temperature: ");
 Serial.print(temperature, DEC);
 Serial.println(" *0.1 deg C");
 Serial.print("Pressure: ");
 Serial.print(pressure, DEC);
 Serial.println(" Pa");
 Serial.println();
 delay(1000);
}
// 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 given ut.
// Value returned will be in units of 0.1 deg C
short bmp085GetTemperature(unsigned int ut)
{
 long x1, x2;
 x1 = (((long)ut - (long)ac6)*(long)ac5) >> 15;
 x2 = ((long)mc << 11)/(x1 + md);
 b5 = x1 + x2;
 return ((b5 + 8)>>4);  
}
// 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;
 return p;
}
// Read 1 byte from the BMP085 at 'address'
char bmp085Read(unsigned char address)
{
 unsigned char data;
 Wire.beginTransmission(BMP085_ADDRESS);
 Wire.send(address);
 Wire.endTransmission();
 Wire.requestFrom(BMP085_ADDRESS, 1);
 while(!Wire.available());
 return Wire.receive();
}
// 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.send(address);
 Wire.endTransmission();
 Wire.requestFrom(BMP085_ADDRESS, 2);
 while(Wire.available()<2);
 msb = Wire.receive();
 lsb = Wire.receive();
 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.send(0xF4);
 Wire.send(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.send(0xF4);
 Wire.send(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)
 Wire.beginTransmission(BMP085_ADDRESS);
 Wire.send(0xF6);
 Wire.endTransmission();
 Wire.requestFrom(BMP085_ADDRESS, 3);
 // Wait for data to become available
 while(Wire.available() < 3);
 msb = Wire.receive();
 lsb = Wire.receive();
 xlsb = Wire.receive();
 up = (((unsigned long) msb << 16) | ((unsigned long) lsb << 8) | (unsigned long) xlsb) >> (8-OSS);
 return up;
}

How to buy

Click here to buy BMP085 Barometric Pressure Sensor Breakout