File content as of revision 0:70d1d5ec30c8:

/**
@file BMP180.cpp

@brief Member functions implementations

*/
#include "mbed.h"
#include "BMP180.h"

BMP180::BMP180(PinName sdaPin, PinName sclPin)
{
    i2c = new I2C(sdaPin,sclPin); // create new I2C instance and initialise
    i2c->frequency(400000);       // I2C Fast Mode - 400kHz
    leds = new BusOut(LED4,LED3,LED2,LED1);
}

Measurement BMP180::readValues()
{
    // algorithm for taking measurement is taken from datasheet
    int UT = readUncompensatedTemperatureValue();
    int UP = readUncompensatedPressureValue();
    // once you have the uncompensated T and P, you can calculate the true T and P
    // using the equations from the datasheet
    int T = calcTrueTemperature(UT);
    int P = calcTruePressure(UP);

    Measurement measurement;
    measurement.temperature = T*0.1;  // scaled by 0.1 C
    measurement.pressure = P*0.01;    // Put pressure in mb

    return measurement;
}

int BMP180::readUncompensatedTemperatureValue()
{
    // from algorithm in datasheet - p15
    sendByteToRegister(0x2E,0xF4);
    wait_ms(5);  // 4.5 ms delay for OSS = 1
    char MSB = readByteFromRegister(0xF6);
    char LSB = readByteFromRegister(0xF7);
    // combine in 16-bit value
    int UT = (MSB << 8) | LSB;
    return UT;

}

int BMP180::readUncompensatedPressureValue()
{
    // from datasheet
    char byte = 0x34 + (oss << 6);
    sendByteToRegister(byte,0xF4);
    wait_ms(8);  // 7.5 ms delay for OSS = 1

    char MSB = readByteFromRegister(0xF6);
    char LSB = readByteFromRegister(0xF7);
    // just do 16-bit, not 19-bit
    int UP = (MSB << 16 | LSB << 8) >> (8 - oss);
    return UP;
}

int BMP180::calcTrueTemperature(int UT)
{
    // equations from data sheet
    X1 = (UT - calibration.AC6) * calibration.AC5/32768;
    X2 = calibration.MC * 2048 / (X1 + calibration.MD);
    B5 = X1 + X2;
    int T = (B5 + 8)/16;
    return T;
}

int BMP180::calcTruePressure(int UP)
{
    // equations from data sheet
    B6 = B5 - 4000;
    X1 = (calibration.B2 * (B6*B6/4096))/2048;
    X2 = calibration.AC2*B6/2048;
    X3 = X1 + X2;
    B3 = (((4*calibration.AC1 + X3) << oss)+2)/4;
    X1 = calibration.AC3*B6/8192;
    X2 = (calibration.B1*(B6*B6/4096))/65536;
    X3 = ((X1+X2)+2)/4;
    B4 = calibration.AC4*(unsigned int)(X3+32768)/32768;
    B7 = ((unsigned int)UP - B3)*(50000>>oss);
    int P;
    if (B7 < 0x80000000)
        P = (B7*2)/B4;
    else
        P = (B7/B4)*2;
    X1 = (P/256)*(P/256);
    X1 = (X1*3038)/65536;
    X2 = (-7357*P)/65536;
    P = P + (X1+X2+3791)/16;

    return P;

}

// configure the barometer
void BMP180::init()
{
    i2c->frequency(400000); // set Fast Mode I2C frequency

    char data = readByteFromRegister(ID_REG);  // Section 4 - datasheet
    if (data != 0x55) { // if correct ID not found, hang and flash error message
        error();
    }
    
    readCalibrationData(); 
    oss = 1;  // standard oversampling setting

}

// Reads factory calibrated data
void BMP180::readCalibrationData()
{
    char eeprom[22];
    readBytesFromRegister(EEPROM_REG_ADD,22,eeprom);
    // store calibration data in structure
    calibration.AC1 = (int16_t) (eeprom[0] << 8) | eeprom[1];
    calibration.AC2 = (int16_t) (eeprom[2] << 8) | eeprom[3];
    calibration.AC3 = (int16_t) (eeprom[4] << 8) | eeprom[5];
    calibration.AC4 = (uint16_t) (eeprom[6] << 8) | eeprom[7];
    calibration.AC5 = (uint16_t) (eeprom[8] << 8) | eeprom[9];
    calibration.AC6 = (uint16_t) (eeprom[10] << 8) | eeprom[11];
    calibration.B1 = (int16_t) (eeprom[12] << 8) | eeprom[13];
    calibration.B2 = (int16_t) (eeprom[14] << 8) | eeprom[15];
    calibration.MB = (int16_t) (eeprom[16] << 8) | eeprom[17];
    calibration.MC = (int16_t) (eeprom[18] << 8) | eeprom[19];
    calibration.MD = (int16_t) (eeprom[20] << 8) | eeprom[21];
}


// reads a byte from a specific register
char BMP180::readByteFromRegister(char reg)
{
    int nack = i2c->write(BMP180_W_ADDRESS,&reg,1,true);  // send the register address to the slave
    if (nack)
        error();  // if we don't receive acknowledgement, flash error message

    char rx;
    nack = i2c->read(BMP180_W_ADDRESS,&rx,1);  // read a byte from the register and store in buffer
    if (nack)
        error();  // if we don't receive acknowledgement, flash error message

    return rx;
}

// reads a series of bytes, starting from a specific register
void BMP180::readBytesFromRegister(char reg,int numberOfBytes,char bytes[])
{
    int nack = i2c->write(BMP180_W_ADDRESS,&reg,1,true);  // send the slave write address and the configuration register address

    if (nack)
        error();  // if we don't receive acknowledgement, flash error message

    nack = i2c->read(BMP180_W_ADDRESS,bytes,numberOfBytes);  // read bytes
    if (nack)
        error();  // if we don't receive acknowledgement, flash error message

}

// sends a byte to a specific register
void BMP180::sendByteToRegister(char byte,char reg)
{
    char data[2];
    data[0] = reg;
    data[1] = byte;
    // send the register address, followed by the data
    int nack = i2c->write(BMP180_W_ADDRESS,data,2);
    if (nack)
        error();  // if we don't receive acknowledgement, flash error message

}

void BMP180::error()
{
    while(1) {
        leds->write(15);
        wait(0.1);
        leds->write(0);
        wait(0.1);
    }
}