Difference between revisions of "BMP085 Barometric Pressure Sensor Breakout"

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(Example code)
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==Example code==
 
==Example code==
 +
For Arduino 1.0+
 +
 
  #include <Wire.h>
 
  #include <Wire.h>
#define BMP085_ADDRESS 0x77  // I2C address of BMP085
+
#define BMP085_ADDRESS 0x77  // I2C address of BMP085
const unsigned char OSS = 0;  // Oversampling Setting
+
const unsigned char OSS = 0;  // Oversampling Setting
// Calibration values
+
// Calibration values
int ac1;
+
int ac1;
int ac2;  
+
int ac2;  
int ac3;  
+
int ac3;  
unsigned int ac4;
+
unsigned int ac4;
unsigned int ac5;
+
unsigned int ac5;
unsigned int ac6;
+
unsigned int ac6;
int b1;  
+
int b1;  
int b2;
+
int b2;
int mb;
+
int mb;
int mc;
+
int mc;
int md;
+
int md;
// b5 is calculated in bmp085GetTemperature(...), this variable is also used in bmp085GetPressure(...)
+
// b5 is calculated in bmp085GetTemperature(...), this variable is also used in bmp085GetPressure(...)
// so ...Temperature(...) must be called before ...Pressure(...).
+
// so ...Temperature(...) must be called before ...Pressure(...).
long b5;  
+
long b5;  
short temperature;
+
short temperature;
long pressure;
+
long pressure;
void setup()
+
void setup()
{
+
{
 
  Serial.begin(9600);
 
  Serial.begin(9600);
 
  Wire.begin();
 
  Wire.begin();
 
  bmp085Calibration();
 
  bmp085Calibration();
}
+
}
void loop()
+
void loop()
{
+
{
 
  temperature = bmp085GetTemperature(bmp085ReadUT());
 
  temperature = bmp085GetTemperature(bmp085ReadUT());
 
  pressure = bmp085GetPressure(bmp085ReadUP());
 
  pressure = bmp085GetPressure(bmp085ReadUP());
Line 64: Line 66:
 
  Serial.println();
 
  Serial.println();
 
  delay(1000);
 
  delay(1000);
}
+
}
// Stores all of the bmp085's calibration values into global variables
+
// Stores all of the bmp085's calibration values into global variables
// Calibration values are required to calculate temp and pressure
+
// Calibration values are required to calculate temp and pressure
// This function should be called at the beginning of the program
+
// This function should be called at the beginning of the program
void bmp085Calibration()
+
void bmp085Calibration()
{
+
{
 
  ac1 = bmp085ReadInt(0xAA);
 
  ac1 = bmp085ReadInt(0xAA);
 
  ac2 = bmp085ReadInt(0xAC);
 
  ac2 = bmp085ReadInt(0xAC);
Line 81: Line 83:
 
  mc = bmp085ReadInt(0xBC);
 
  mc = bmp085ReadInt(0xBC);
 
  md = bmp085ReadInt(0xBE);
 
  md = bmp085ReadInt(0xBE);
}
+
}
// Calculate temperature given ut.
+
// Calculate temperature given ut.
// Value returned will be in units of 0.1 deg C
+
// Value returned will be in units of 0.1 deg C
short bmp085GetTemperature(unsigned int ut)
+
short bmp085GetTemperature(unsigned int ut)
{
+
{
 
  long x1, x2;
 
  long x1, x2;
 
  x1 = (((long)ut - (long)ac6)*(long)ac5) >> 15;
 
  x1 = (((long)ut - (long)ac6)*(long)ac5) >> 15;
Line 91: Line 93:
 
  b5 = x1 + x2;
 
  b5 = x1 + x2;
 
  return ((b5 + 8)>>4);   
 
  return ((b5 + 8)>>4);   
}
+
}
// Calculate pressure given up
+
// Calculate pressure given up
// calibration values must be known
+
// calibration values must be known
// b5 is also required so bmp085GetTemperature(...) must be called first.
+
// b5 is also required so bmp085GetTemperature(...) must be called first.
// Value returned will be pressure in units of Pa.
+
// Value returned will be pressure in units of Pa.
long bmp085GetPressure(unsigned long up)
+
long bmp085GetPressure(unsigned long up)
{
+
{
 
  long x1, x2, x3, b3, b6, p;
 
  long x1, x2, x3, b3, b6, p;
 
  unsigned long b4, b7;
 
  unsigned long b4, b7;
Line 121: Line 123:
 
  p += (x1 + x2 + 3791)>>4;
 
  p += (x1 + x2 + 3791)>>4;
 
  return p;
 
  return p;
}
+
}
// Read 1 byte from the BMP085 at 'address'
+
// Read 1 byte from the BMP085 at 'address'
char bmp085Read(unsigned char address)
+
char bmp085Read(unsigned char address)
{
+
{
 
  unsigned char data;
 
  unsigned char data;
 
  Wire.beginTransmission(BMP085_ADDRESS);
 
  Wire.beginTransmission(BMP085_ADDRESS);
Line 132: Line 134:
 
  while(!Wire.available());
 
  while(!Wire.available());
 
  return Wire.read();
 
  return Wire.read();
}
+
}
// Read 2 bytes from the BMP085
+
// Read 2 bytes from the BMP085
// First byte will be from 'address'
+
// First byte will be from 'address'
// Second byte will be from 'address'+1
+
// Second byte will be from 'address'+1
int bmp085ReadInt(unsigned char address)
+
int bmp085ReadInt(unsigned char address)
{
+
{
 
  unsigned char msb, lsb;
 
  unsigned char msb, lsb;
 
  Wire.beginTransmission(BMP085_ADDRESS);
 
  Wire.beginTransmission(BMP085_ADDRESS);
Line 147: Line 149:
 
  lsb = Wire.read();
 
  lsb = Wire.read();
 
  return (int) msb<<8 | lsb;
 
  return (int) msb<<8 | lsb;
}
+
}
// Read the uncompensated temperature value
+
// Read the uncompensated temperature value
unsigned int bmp085ReadUT()
+
unsigned int bmp085ReadUT()
{
+
{
 
  unsigned int ut;
 
  unsigned int ut;
 
  // Write 0x2E into Register 0xF4
 
  // Write 0x2E into Register 0xF4
Line 163: Line 165:
 
  ut = bmp085ReadInt(0xF6);
 
  ut = bmp085ReadInt(0xF6);
 
  return ut;
 
  return ut;
}
+
}
// Read the uncompensated pressure value
+
// Read the uncompensated pressure value
unsigned long bmp085ReadUP()
+
unsigned long bmp085ReadUP()
{
+
{
 
  unsigned char msb, lsb, xlsb;
 
  unsigned char msb, lsb, xlsb;
 
  unsigned long up = 0;
 
  unsigned long up = 0;
Line 189: Line 191:
 
  up = (((unsigned long) msb << 16) | ((unsigned long) lsb << 8) | (unsigned long) xlsb) >> (8-OSS);
 
  up = (((unsigned long) msb << 16) | ((unsigned long) lsb << 8) | (unsigned long) xlsb) >> (8-OSS);
 
  return up;
 
  return up;
}
+
}
  
 
==How to buy==
 
==How to buy==
 
Click here to buy [http://www.geeetech.com/bmp085-breakoutbarometric-pressure-sensor-p-530.html BMP085 Barometric Pressure Sensor Breakout]
 
Click here to buy [http://www.geeetech.com/bmp085-breakoutbarometric-pressure-sensor-p-530.html BMP085 Barometric Pressure Sensor Breakout]

Latest revision as of 01:51, 10 December 2012

Introduction

Bmp085.jpg

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

Document

BMP085 Datasheet

Usage

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

BMP085-3.jpg

BMPtable.jpg

Example code

For Arduino 1.0+

#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.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)
Wire.beginTransmission(BMP085_ADDRESS);
Wire.write(0xF6);
Wire.endTransmission();
Wire.requestFrom(BMP085_ADDRESS, 3);
// Wait for data to become available
while(Wire.available() < 3);
msb = Wire.read();
lsb = Wire.read();
xlsb = Wire.read();
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