Difference between revisions of "BMP085 Barometric Pressure Sensor Breakout"

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(Example code)
Line 27: Line 27:
 
==Example code==
 
==Example code==
 
  #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());
  Serial.print("Temperature: ");
+
Serial.print("Temperature: ");
  Serial.print(temperature, DEC);
+
Serial.print(temperature, DEC);
  Serial.println(" *0.1 deg C");
+
Serial.println(" *0.1 deg C");
  Serial.print("Pressure: ");
+
Serial.print("Pressure: ");
  Serial.print(pressure, DEC);
+
Serial.print(pressure, DEC);
  Serial.println(" Pa");
+
Serial.println(" Pa");
  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);
  ac3 = bmp085ReadInt(0xAE);
+
ac3 = bmp085ReadInt(0xAE);
  ac4 = bmp085ReadInt(0xB0);
+
ac4 = bmp085ReadInt(0xB0);
  ac5 = bmp085ReadInt(0xB2);
+
ac5 = bmp085ReadInt(0xB2);
  ac6 = bmp085ReadInt(0xB4);
+
ac6 = bmp085ReadInt(0xB4);
  b1 = bmp085ReadInt(0xB6);
+
b1 = bmp085ReadInt(0xB6);
  b2 = bmp085ReadInt(0xB8);
+
b2 = bmp085ReadInt(0xB8);
  mb = bmp085ReadInt(0xBA);
+
mb = bmp085ReadInt(0xBA);
  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;
  x2 = ((long)mc << 11)/(x1 + md);
+
x2 = ((long)mc << 11)/(x1 + md);
  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;
  b6 = b5 - 4000;
+
b6 = b5 - 4000;
  // Calculate B3
+
// Calculate B3
  x1 = (b2 * (b6 * b6)>>12)>>11;
+
x1 = (b2 * (b6 * b6)>>12)>>11;
  x2 = (ac2 * b6)>>11;
+
x2 = (ac2 * b6)>>11;
  x3 = x1 + x2;
+
x3 = x1 + x2;
  b3 = (((((long)ac1)*4 + x3)<<OSS) + 2)>>2;
+
b3 = (((((long)ac1)*4 + x3)<<OSS) + 2)>>2;
  // Calculate B4
+
// Calculate B4
  x1 = (ac3 * b6)>>13;
+
x1 = (ac3 * b6)>>13;
  x2 = (b1 * ((b6 * b6)>>12))>>16;
+
x2 = (b1 * ((b6 * b6)>>12))>>16;
  x3 = ((x1 + x2) + 2)>>2;
+
x3 = ((x1 + x2) + 2)>>2;
  b4 = (ac4 * (unsigned long)(x3 + 32768))>>15;
+
b4 = (ac4 * (unsigned long)(x3 + 32768))>>15;
  b7 = ((unsigned long)(up - b3) * (50000>>OSS));
+
b7 = ((unsigned long)(up - b3) * (50000>>OSS));
  if (b7 < 0x80000000)
+
if (b7 < 0x80000000)
    p = (b7<<1)/b4;
+
  p = (b7<<1)/b4;
  else
+
else
    p = (b7/b4)<<1;
+
  p = (b7/b4)<<1;
  x1 = (p>>8) * (p>>8);
+
x1 = (p>>8) * (p>>8);
  x1 = (x1 * 3038)>>16;
+
x1 = (x1 * 3038)>>16;
  x2 = (-7357 * p)>>16;
+
x2 = (-7357 * p)>>16;
  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);
  Wire.send(address);
+
Wire.write(address);
  Wire.endTransmission();
+
Wire.endTransmission();
  Wire.requestFrom(BMP085_ADDRESS, 1);
+
Wire.requestFrom(BMP085_ADDRESS, 1);
  while(!Wire.available());
+
while(!Wire.available());
  return Wire.receive();
+
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);
  Wire.send(address);
+
Wire.write(address);
  Wire.endTransmission();
+
Wire.endTransmission();
  Wire.requestFrom(BMP085_ADDRESS, 2);
+
Wire.requestFrom(BMP085_ADDRESS, 2);
  while(Wire.available()<2);
+
while(Wire.available()<2);
  msb = Wire.receive();
+
msb = Wire.read();
  lsb = Wire.receive();
+
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
  // This requests a temperature reading
+
// This requests a temperature reading
  Wire.beginTransmission(BMP085_ADDRESS);
+
Wire.beginTransmission(BMP085_ADDRESS);
  Wire.send(0xF4);
+
Wire.write(0xF4);
  Wire.send(0x2E);
+
Wire.write(0x2E);
  Wire.endTransmission();
+
Wire.endTransmission();
  // Wait at least 4.5ms
+
// Wait at least 4.5ms
  delay(5);
+
delay(5);
  // Read two bytes from registers 0xF6 and 0xF7
+
// Read two bytes from registers 0xF6 and 0xF7
  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;
  // Write 0x34+(OSS<<6) into register 0xF4
+
// Write 0x34+(OSS<<6) into register 0xF4
  // Request a pressure reading w/ oversampling setting
+
// Request a pressure reading w/ oversampling setting
  Wire.beginTransmission(BMP085_ADDRESS);
+
Wire.beginTransmission(BMP085_ADDRESS);
  Wire.send(0xF4);
+
Wire.write(0xF4);
  Wire.send(0x34 + (OSS<<6));
+
Wire.write(0x34 + (OSS<<6));
  Wire.endTransmission();
+
Wire.endTransmission();
  // Wait for conversion, delay time dependent on OSS
+
// Wait for conversion, delay time dependent on OSS
  delay(2 + (3<<OSS));
+
delay(2 + (3<<OSS));
  // Read register 0xF6 (MSB), 0xF7 (LSB), and 0xF8 (XLSB)
+
// Read register 0xF6 (MSB), 0xF7 (LSB), and 0xF8 (XLSB)
  Wire.beginTransmission(BMP085_ADDRESS);
+
Wire.beginTransmission(BMP085_ADDRESS);
  Wire.send(0xF6);
+
Wire.write(0xF6);
  Wire.endTransmission();
+
Wire.endTransmission();
  Wire.requestFrom(BMP085_ADDRESS, 3);
+
Wire.requestFrom(BMP085_ADDRESS, 3);
  // Wait for data to become available
+
// Wait for data to become available
  while(Wire.available() < 3);
+
while(Wire.available() < 3);
  msb = Wire.receive();
+
msb = Wire.read();
  lsb = Wire.receive();
+
lsb = Wire.read();
  xlsb = Wire.receive();
+
xlsb = Wire.read();
  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]

Revision as of 01:49, 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

#include <Wire.h>
  1. 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