Diff: BMP180.cpp

Revision:

0:70d1d5ec30c8

Child:

2:79d0d565c3af

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/BMP180.cpp	Sun Mar 08 16:11:49 2015 +0000
@@ -0,0 +1,183 @@
+/**
+@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);
+    }
+}
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