BMP085 Barometric Pressure Sensor Breakout
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
Document
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; }
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