Revision 2:79d0d565c3af, committed 2015-03-13

Comitter:

eencae

Date:

Fri Mar 13 18:44:57 2015 +0000

Parent:

1:e6c317e0f3a4

Child:

3:0e92710a46f9

Commit message:

-Added in test data from data sheet (algorithm matches solution presented in data sheet).; -Swapped int for int32_t to be sure of size.; -Replaced dividing by powers of 2 by bit-shifting.;

Changed in this revision

--- a/BMP180.cpp	Sun Mar 08 16:14:36 2015 +0000
+++ b/BMP180.cpp	Fri Mar 13 18:44:57 2015 +0000
@@ -17,12 +17,12 @@
 Measurement BMP180::readValues()
 {
     // algorithm for taking measurement is taken from datasheet
-    int UT = readUncompensatedTemperatureValue();
-    int UP = readUncompensatedPressureValue();
+    int32_t UT = readUncompensatedTemperatureValue();
+    int32_t 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);
+    int32_t T = calcTrueTemperature(UT);
+    int32_t P = calcTruePressure(UP);
 
     Measurement measurement;
     measurement.temperature = T*0.1;  // scaled by 0.1 C
@@ -31,7 +31,7 @@
     return measurement;
 }
 
-int BMP180::readUncompensatedTemperatureValue()
+int32_t BMP180::readUncompensatedTemperatureValue()
 {
     // from algorithm in datasheet - p15
     sendByteToRegister(0x2E,0xF4);
@@ -39,12 +39,13 @@
     char MSB = readByteFromRegister(0xF6);
     char LSB = readByteFromRegister(0xF7);
     // combine in 16-bit value
-    int UT = (MSB << 8) | LSB;
+    int UT = (MSB << 8) | LSB;   
+    //int32_t UT = 27898;  // test data from datasheet
+    //printf("\n\nUT = %d\n",UT);
     return UT;
-
 }
 
-int BMP180::readUncompensatedPressureValue()
+int32_t BMP180::readUncompensatedPressureValue()
 {
     // from datasheet
     char byte = 0x34 + (oss << 6);
@@ -53,44 +54,59 @@
 
     char MSB = readByteFromRegister(0xF6);
     char LSB = readByteFromRegister(0xF7);
+    char XLSB = readByteFromRegister(0xF7);
     // just do 16-bit, not 19-bit
+    //int UP = (MSB << 16 | LSB << 8 | XLSB) >> (8 - oss);
     int UP = (MSB << 16 | LSB << 8) >> (8 - oss);
+    
+    //int32_t UP = 23843;   // test data from datasheet
+    //printf("UP = %d\n",UP);
     return UP;
 }
 
-int BMP180::calcTrueTemperature(int UT)
+int32_t BMP180::calcTrueTemperature(int32_t UT)
 {
     // equations from data sheet
-    X1 = (UT - calibration.AC6) * calibration.AC5/32768;
-    X2 = calibration.MC * 2048 / (X1 + calibration.MD);
+    X1 = ((UT - calibration.AC6)*calibration.AC5) >> 15;
+    X2 = (calibration.MC << 11) / (X1 + calibration.MD);
     B5 = X1 + X2;
-    int T = (B5 + 8)/16;
+    int32_t T = (B5 + 8) >> 4;
+    //printf("X1=%d\nX2=%d\nB5=%d\n*****\nT=%d\n******\n",X1,X2,B5,T);
     return T;
 }
 
-int BMP180::calcTruePressure(int UP)
+int32_t BMP180::calcTruePressure(int32_t UP)
 {
     // equations from data sheet
     B6 = B5 - 4000;
-    X1 = (calibration.B2 * (B6*B6/4096))/2048;
-    X2 = calibration.AC2*B6/2048;
+    //printf("\n********\nB6=%d\n",B6);
+    X1 = (calibration.B2 * ((B6*B6) >> 12))>>11;
+    X2 = (calibration.AC2*B6)>>11;
     X3 = X1 + X2;
-    B3 = (((4*calibration.AC1 + X3) << oss)+2)/4;
-    X1 = calibration.AC3*B6/8192;
-    X2 = (calibration.B1*(B6*B6/4096))/65536;
+    B3 = (((calibration.AC1*4 + X3) << oss)+2)/4;
+    //printf("X1=%d\nX2=%d\nX3=%d\nB3=%d\n",X1,X2,X3,B3);
+    X1 = (calibration.AC3*B6)>>13;
+    X2 = (calibration.B1*((B6*B6)>>12))>>16;
     X3 = ((X1+X2)+2)/4;
-    B4 = calibration.AC4*(unsigned int)(X3+32768)/32768;
-    B7 = ((unsigned int)UP - B3)*(50000>>oss);
-    int P;
+    B4 = (calibration.AC4*(uint32_t)(X3+32768))>>15;
+    //printf("X1=%d\nX2=%d\nX3=%d\nB4=%u\n",X1,X2,X3,B4);
+    B7 = ((uint32_t)UP - B3)*(50000>>oss);
+    //printf("B7=%u\n",B7);
+    int32_t 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;
+    //printf("P=%d\n",P);
+    X1 = (P>>8)*(P>>8);
+    //printf("X1=%d\n",X1);
+    X1 = (X1*3038)>>16;
+    //printf("X1=%d\n",X1);
+    X2 = (-7357*P)>>16;
+    //printf("X2=%d\n",X2);
     P = P + (X1+X2+3791)/16;
-
+    //printf("P=%d\n",P);
+    
     return P;
 
 }
@@ -105,15 +121,18 @@
         error();
     }
     
-    readCalibrationData(); 
-    oss = 1;  // standard oversampling setting
+    readCalibrationData();
+    oss = 1;  // standard power oversampling setting
+    //oss = 0;  // used when testing data sheet example
 
 }
 
 // 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];
@@ -127,6 +146,13 @@
     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];
+    
+    // test data from data sheet
+    //calibration.AC1 = 408;calibration.AC2 = -72;calibration.AC3 = -14383;calibration.AC4 = 32741;calibration.AC5 = 32757;
+    //calibration.AC6 = 23153;calibration.B1 = 6190;calibration.B2 = 4;calibration.MB = -32768;calibration.MC = -8711;calibration.MD = 2868;
+    //printf("AC1=%d\nAC2=%d\nAC3=%d\nAC4=%u\nAC5=%u\nAC6=%u\nB1=%d\nB2=%d\nMB=%d\nMC=%d\nMD=%d\n",
+    // calibration.AC1,calibration.AC2,calibration.AC3,calibration.AC4,calibration.AC5,calibration.AC6,
+    // calibration.B1,calibration.B2,calibration.MB,calibration.MC,calibration.MD);
 }
 
 

--- a/BMP180.h	Sun Mar 08 16:14:36 2015 +0000
+++ b/BMP180.h	Fri Mar 13 18:44:57 2015 +0000
@@ -106,10 +106,10 @@
 
 private:
     void error();
-    int readUncompensatedTemperatureValue();
-    int readUncompensatedPressureValue();
-    int calcTrueTemperature(int UT);
-    int calcTruePressure(int UP);
+    int32_t readUncompensatedTemperatureValue();
+    int32_t readUncompensatedPressureValue();
+    int32_t calcTrueTemperature(int32_t UT);
+    int32_t calcTruePressure(int32_t UP);
     void sendByteToRegister(char byte,char reg);
     char readByteFromRegister(char reg);
     void readBytesFromRegister(char reg,int numberOfBytes,char bytes[]);
@@ -121,8 +121,8 @@
     BusOut* leds;
     Calibration calibration;  // variable to store calibration data
     // variables for calculation
-    int X1,X2,X3,B3,B5,B6;
-    unsigned int B4,B7;
+    int32_t X1,X2,X3,B3,B5,B6;
+    uint32_t B4,B7;
     int oss;  // oversampling setting
 };