Revision 0:61bbd81782de, committed 2015-01-10

Comitter:

wim

Date:

Sat Jan 10 19:10:17 2015 +0000

Commit message:

First version of HP03SA library.

Changed in this revision

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/HP03SA.cpp	Sat Jan 10 19:10:17 2015 +0000
@@ -0,0 +1,321 @@
+/* mbed HP03SA Library, for an I2C Pressure and Temperature sensor which provides derived Altitude values
+ * Copyright (c) 2015, v01: WH, Initial version, ported in part from Elektor weatherstation (Sept 2011), Author: W. Waetzig
+ *                          See http://www.elektor-labs.com/project/usb-long-term-weather-logger-100888.12037.html
+ *                          Code also based on several other public sources:   
+ *                          See http://en.wikipedia.org/wiki/Atmospheric_pressure
+ *                          See https://learn.sparkfun.com/tutorials/bmp180-barometric-pressure-sensor-hookup-?_ga=1.94307604.888266135.1310146152
+ *
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+#include "mbed.h"
+#include "HP03SA.h"
+
+/** Create an HP03SA interface for mbed pins
+  *
+  * @param i2c    I2C Bus 
+  * @param XCLR   Clock enable control line
+  */ 
+HP03SA::HP03SA(I2C *i2c, PinName XCLR) : _i2c(i2c), _xclr(XCLR) {
+
+  _init();
+}
+
+/**  Init the HP03SA
+  *  
+  */
+void HP03SA::_init() {
+  char buffer[18];
+
+  //HP03S initialization
+
+  _xclr=0;   //XCLR low for coefficients readout
+      
+  // Select C1 register
+  buffer[0] = 0x10;                                // Register address for _C1 MSB is 0x10
+  _i2c->write(HP03SA_EEPROM_SA, buffer, 1, true);  // Repeated Start
+  // Read calibration parameters
+  _i2c->read(HP03SA_EEPROM_SA, buffer, 18);   
+  
+  _C1 = (buffer[0] << 8)  | buffer[1];  // _C1 MSB, LSB
+  _C2 = (buffer[2] << 8)  | buffer[3];  // _C2 MSB, LSB
+  _C3 = (buffer[4] << 8)  | buffer[5];  // _C3 MSB, LSB
+  _C4 = (buffer[6] << 8)  | buffer[7];  // _C4 MSB, LSB
+  _C5 = (buffer[8] << 8)  | buffer[9];  // _C5 MSB, LSB
+  _C6 = (buffer[10] << 8) | buffer[11]; // _C6 MSB, LSB
+  _C7 = (buffer[12] << 8) | buffer[13]; // _C7 MSB, LSB
+  _A  =  buffer[14];                    // _A 
+  _B  =  buffer[15];                    // _B 
+  _C  =  buffer[16];                    // _C 
+  _D  =  buffer[17];                    // _D               
+
+  _pres_base_x10 = PBASE_X10;
+  _temp_base_x10 = TBASE_X10;
+
+  // Execute Dummy reads after init()
+  sample();
+  sample();   
+}  
+
+/** Read ADC value (either pressure or temperature depending on Control Register setting)
+  *
+  * @return int   pressure or temperature 
+  */ 
+int HP03SA::_readADC (void) {
+    char buffer[2];
+
+    // Select ADC register
+    buffer[0] = 0xFD;                              // Register address for ADC
+    _i2c->write(HP03SA_BARO_SA, buffer, 1, true);  // Repeated Start
+    // Read ADC
+    _i2c->read(HP03SA_BARO_SA, buffer, 2);   
+
+    return ((buffer[0] << 8) | buffer[1]);         // MSB, LSB
+}
+
+/** Read Pressure and Temperature
+  *
+  * @return none 
+  */ 
+void HP03SA::_readTempPres(void) {
+    char buffer[2];    
+    
+    _xclr=1;   // ADC-XCLR
+    
+    // Read ADC with pressure value
+    buffer[0] = 0xFF;             // Control Register address  
+    buffer[1] = 0xF0;             // function = select + start-conversion PRES
+    _i2c->write(HP03SA_BARO_SA, buffer, 2);
+    wait_ms(40);                  // delay for ADC-conversion
+    _D1  = _readADC();
+
+    // Read ADC with temperature value
+    buffer[0] = 0xFF;             // Control Register address
+    buffer[1] = 0xE8;             // function = select + start-conversion TEMP
+    _i2c->write(HP03SA_BARO_SA, buffer, 2);
+    wait_ms(40);                  // delay for ADC-conversion
+    _D2  = _readADC();
+
+    _xclr=0;   // ADC-XCLR                 
+}
+
+/** Calculate Pressure and Temperature
+  *
+  * @return none 
+  */ 
+void HP03SA::_calcTempPres(void) {
+    long int _D2_C5;
+    int _corr;    
+
+    // Temperature and Pressure calculations from HP03S datasheet version 1.3
+    // with 2nd-order corrections using the parameters _A, _B, _C, _D
+    // Measured values are: _D1(pressure) and _D2(temperature)
+    // Correct offset-calculation (_off)
+
+    _D2_C5 = _D2 - _C5;
+    if (_D2_C5 >= 0) 
+        _corr = _A;     // _A
+    else
+        _corr = _B;     // _B
+
+    _dUT = _D2_C5 - ((_D2_C5 >> 7) * (_D2_C5 >> 7) * (_corr >> _C)); // _C
+
+//  _off = (   (_C4 - 1024) * _dUT / 16384 + _C2 ) * 4;
+//  _off = ((( (_C4 - 1024) * _dUT ) >> 14 ) + _C2 ) << 2;
+    _off = ((( (_C4 - 1024) * _dUT ) >> 14 ) + _C2 ) << 2;
+
+//  _sens = _C3 * _dUT / 1024 + _C1 ;
+    _sens = (( _C3 * _dUT ) >> 10 ) + _C1 ;   
+
+//  _x = (_D1 - 7168) * _sens / 16384 - _off;
+    _x = (((_D1 - 7168) * _sens ) >> 14 ) - _off;    
+
+//  _pres = x * 10 / 32 + _C7;
+    _pres_x10 = (( _x * 10 ) >> 5 ) + _C7;  // Pressure in hPa x 10
+
+//  _temp = _dUT * _C6 / 65536 + 250;
+    _temp_x10 = (( _dUT * _C6 ) >> 16 ) - (_dUT >> _D) + 250; // _D, Temp in Celsius x 10
+}
+
+
+/** Calculate Altitude
+  *
+  * @return none 
+  */ 
+void HP03SA::_calcAlt(void) {
+// Calculation based on ISA model
+// http://en.wikipedia.org/wiki/Atmospheric_pressure
+//
+//  h = (1 - pow((P/Pref), RL/gM)) * Tref / L
+//
+//    h     altitude above Mean Sea Level in m
+//    P     atmospheric pressure at altitude h
+//    Pref  sea level standard atmospheric pressure 101325 Pa
+//    L     temperature lapse rate, = g/cp for dry air  0.0065 K/m
+//    Tref  sea level standard temperature  288.15 K (= 15.0 + 273.15)
+//    g     Earth-surface gravitational acceleration    9.80665 m/s2
+//    M     molar mass of dry air   0.0289644 kg/mol
+//    R     universal gas constant  8.31447 J/(mol•K)
+//    RL/gM 0.19026674
+//    gM/RL 5.25578009f
+
+//ISA calculation  
+//  _alt = 44330.76923f * (1.0f - pow( ((float) _pres_x10 / _pres_base_x10), RLGM));
+  _alt = (TBASE_X10 / LBASE_X10) * (1.0f - pow( ((float) _pres_x10 / _pres_base_x10), RLGM));
+      
+//Correction for temperature
+//  _temp_base_x10 = TBASE_X10 - ( (float) _alt * LBASE_X10 );
+//  _temp_base_x10 = TBASE_X10;
+  
+  _alt = (float) _alt * ((float)_temp_x10 + 2731.5f) / _temp_base_x10; 
+}
+
+/** Get Pressure and Temperature sample
+  *
+  * @return none 
+  */ 
+void HP03SA::sample(void) {
+  _readTempPres();
+  _calcTempPres();
+  _calcAlt();  
+}    
+
+/** Get Absolute Atmospheric Pressure in hPa x 10
+  * Note: sample() must be called before getAtmPressure()  
+  * Checked using http://luchtdruk.com/luchtdruk-in-nederland.html
+  *
+  * @return int Pressure in hPa x 10 
+  */ 
+int HP03SA::getAbsPressure(void) {
+  return _pres_x10;
+}
+
+/** Get Sealevel Atmospheric Pressure in hPa x 10
+  * This produces pressure readings that can be used for weather measurements.
+  * Note: sample() must be called before getSeaPressure()  
+  *  
+  * @param  int alt_meter Altitude above Mean Sea Level where measurement is taken
+  * @return int Pressure at sea level in hPa x 10 
+  */ 
+int HP03SA::getSeaPressure(int alt_meter) {
+//    return ( (float) _pres_x10 / pow (1.0f - ((float) alt_meter / 44330.0), 5.255) );    
+    return ( (float) _pres_x10 / pow (1.0f - ((float) alt_meter * LBASE_X10 / TBASE_X10), GMRL) );
+}
+
+/** Get Temperature as int in °Celsius x 10
+  * Note: sample() must be called before getTemperature()  
+  *
+  * @return int Temperature in °Celsius x 10
+  */ 
+int HP03SA::getTemperatureInt(void) {
+  return _temp_x10;
+}
+
+/** Get Temperature as float in °Celsius
+  * Note: sample() must be called before getTemperature()  
+  *
+  * @return float Temperature in °Celsius
+  */ 
+float HP03SA::getTemperature(void) {
+  return (float) _temp_x10 / 10.0f;  
+}
+
+
+/** Convert Temperature from °Celsius into °Fahrenheit
+  *
+  * @param  float celsius in °Celsius  
+  * @return float temperature in °Fahrenheit
+  */ 
+float HP03SA::celsiusToFahrenheit(float celsius) {
+  
+  return ((celsius * 9.0f) / 5.0f) + 32.0f; // Convert to Fahrenheit
+}
+
+
+/** Get Altitude in meters using ISA
+  * Note: sample() must be called before getAltitude()  
+  *
+  * @return int Altitude in meters above Mean Sea Level (MSL)
+  */ 
+int HP03SA::getAltitude(void) {
+  return _alt;
+}
+
+/** Get Altitude in feet using ISA
+  * Note: sample() must be called before getAltitudeFt()  
+  *
+  * @return int Altitude in feet above Mean Sea Level (MSL)
+  */ 
+int HP03SA::getAltitudeFt() {
+  return (float)_alt * 3.28084f;
+}
+    
+/** Get Status
+  *
+  * @return bool Sensor ready 
+  */ 
+bool HP03SA::getStatus(void) {
+  char buffer[2];      
+  int status;
+    
+  _xclr=1;   // ADC-XCLR
+
+  // Read ADC with pressure value (dummy operation to check status)
+  buffer[0] = 0xFF;             // Control Register address  
+  status=_i2c->write(HP03SA_BARO_SA, buffer, 1);
+
+  _xclr=0;   // ADC-XCLR  
+ 
+  return (status==0);           // True when device found   
+}
+
+/** Set QNH Pressure to calibrate sensor
+  *
+  * @param int pressure_x10 at Mean Sea Level in hPa x 10
+  *            The getAltitude() reading will be 0 m for the set pressure.
+  */  
+void HP03SA::setPressure(int pressure_x10) {
+  _pres_base_x10 = (float) pressure_x10;
+}
+
+/** Set QNH Altitude in meter to calibrate sensor
+  *
+  * @param int alt_meter Altitude in meters above Mean Sea Level (MSL) for current pressure  
+  *            The getAltitude() reading will be 'alt_meter' m for the current pressure.  
+  */ 
+void HP03SA::setAltitude(int alt_meter) {
+    
+// Compute _temp_base derived from the temp at set altitude and temp lapse
+//  _temp_base_x10 = ((float) _temp_x10 + 2731.5f) + ((float) alt * LBASE_X10);    
+ 
+// Compute pressure at Mean Sea Level from the pressure at the set altitude
+  _pres_base_x10 = (float) _pres_x10 * pow( TBASE_X10 / (TBASE_X10 - ((float) alt_meter * LBASE_X10)), GMRL);
+}
+
+/** Set QNH Altitude in feet to calibrate sensor
+  *
+  * @param int alt_feet Altitude in meters above Mean Sea Level (MSL) for current pressure
+  *            The getAltitudeFt() reading will be 'alt_feet' ft for the current pressure.   
+  */ 
+void HP03SA::setAltitudeFt(int alt_feet){
+  setAltitude(alt_feet / 3.28084f);
+}
+
+  

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/HP03SA.h	Sat Jan 10 19:10:17 2015 +0000
@@ -0,0 +1,293 @@
+/* mbed HP03SA Library, for an I2C Pressure and Temperature sensor which provides derived Altitude values
+ * Copyright (c) 2015, v01: WH, Initial version, ported in part from Elektor weatherstation (Sept 2011), Author: W. Waetzig
+ *                          See http://www.elektor-labs.com/project/usb-long-term-weather-logger-100888.12037.html
+ *                          Code also based on several other public sources: 
+ *                          See http://en.wikipedia.org/wiki/Atmospheric_pressure
+ *                          See https://learn.sparkfun.com/tutorials/bmp180-barometric-pressure-sensor-hookup-?_ga=1.94307604.888266135.1310146152
+ *
+ * The HP03S pressure sensor from Hope Microelectronics contains a piezoresistive transducer and
+ * integrated 16-bit A/D converter (ADC), along with control logic and an I2C interface. 
+ * The transducer outputs one voltage that depends on pressure and one that depends on temperature.
+ * These analogue values are alternately converted by the ADC and the results made available on the I2C interface. 
+ * During the manufacturing process eleven sensor-specific calibration values with a length of two bytes are stored 
+ * in the device’s EEPROM, and these can also be retrieved by the microcontroller.
+ * The correction-parameters are read out from the device in used in the calculation.
+ * A 32 kHz clock with an amplitude of 3 V is required to drive the ADC. This could be derived from the mbed PwmOut.
+ * The HP03SA has an absolute pressure range between 300-1100 hPa. Operating temp is -20 to +60 degrees Celsius.
+ * Note: 1 atm = 1013.25 hPa = 1013.25 mbar
+ *
+ * Unit conversions see http://www.hoperf.com/docs/guide/160.htm
+ *
+ *   bar Bar                                          convert to 100,000 Pascals exactly
+ *   psi Pounds per Square Inch                       convert to 6894.76 Pascals
+ *   mb or mbar Millibar                              convert to 100 Pascals (1 hPa) exactly
+ *   hPa Hectopascal                                  convert to 100 Pascals exactly
+ *   kPa Kilopascal                                   convert to 1,000 Pascals
+ *   MPa Megapascal                                   convert to 1,000,000 Pascals
+ *   Kgf/cm² or kg/cm² Kilogram force per Square Centimetre convert to 98,066.5 Pascals
+ *   N/m² Newton per Square Meter                     convert to 1 Pascal (SI unit for pressure)
+ *   torr Torr                                        convert to 133.322 Pascals
+ *   mtorr Millitorr                                  convert to 0.133322 Pascals
+ *   mm Hg                                            convert to 133.322387415 Pascals
+ *   1 atm 1 Atmosphere                               convert to 101325 Pascals exactly (760 mm Hg)
+ *   1 atm 1 Atmosphere                               convert to 1013.25 hPa exactly 
+ *   Dynes/cm² or D/cm² Dynes per Square Centimetre   convert to 0.1 Pascals exactly
+ *   oz/in² Ounces per Square Inch                    convert to 430.922 Pascals
+ *   tsi (UK) or tfsi (UK) Tonnes Force per Square Inch (Long, UK) convert to 15444300 Pascals
+ *   tsi (USA) or tfsi (USA) Ton Force per Square Inch (Short, USA) convert to 13789500 Pascals
+ *   tsf (USA) or tfsf (USA) Tons Force per Square Foot (Short, USA) convert to 95760.5 Pascals
+ *   psf Pounds per Square Foot                       convert to 47.8803 Pascals
+ *   g/cm² or gf/cm² Grammes Force per Square Centimetre convert to 98.0665 Pascals
+ *
+ * The Altitude calculation is based on the ICAO Standard Atmosphere model ISA. The code has 
+ * certainly not been thoroughly validated! Use at own risk.
+ *
+ * QNH is the barometric altimeter setting that causes an altimeter to read 
+ * airfield elevation above mean sea level when on the airfield. In ISA temperature
+ * conditions the altimeter will read altitude above mean sea level in the vicinity of the airfield.
+ * Note: Remember QNH as mnemonic for "nautical height"
+ * Average sea-level pressure is 101.325 kPa (1013.25 hPa or mbar) or 29.92 inches (inHg) or 
+ * 760 millimetres of mercury (mmHg). In aviation weather reports (METAR), QNH is transmitted 
+ * around the world in hectopascals or millibars (1 hectopascal = 1 millibar), except in the 
+ * United States, Canada, and Colombia where it is reported in inches (to two decimal places) of mercury. 
+ *
+ * 
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+#ifndef MBED_HP03SA_H
+#define MBED_HP03SA_H
+
+#include "mbed.h"
+
+/** An interface for the HP03S I2C pressure and temperature sensor
+ *
+ * @code
+ * #include "mbed.h"
+ * #include "HP03S.h"
+ * 
+ * // I2C Communication
+ * I2C i2c(p28,p27); // SDA, SCL
+ *
+ * // Serial Communication*
+ * Serial pc(USBTX,USBRX);
+ *
+ * // Instantiate HP03SA
+ * HP03SA hp03sa(&i2c, D_XCLR); // I2C bus, XCLK Pin 
+ * // Generate the 32kHz master clock for HP03SA
+ * PwmOut mclk(p21);
+ *
+ * int main() {
+ *   pc.printf("Hello World!\n");
+ * 
+ *   //Init MCLK for HP03SA
+ *   mclk.period_us(30);       //32768 KHz
+ *   mclk.pulsewidth_us(15);   //32768 KHz
+ *
+ *   while(1) {
+ *     // Take reading from sensor            
+ *     hp03sa.sample();
+ *    
+ *     // Show Pressure    
+ *     pc.printf("Absolute atmospheric pressure is %.1f [hPa]\r\n", (float) hp03sa.getAbsPressure() / 10.0f);
+ *     pc.printf("Sealevel atmospheric pressure is %.1f [hPa]\r\n", (float) hp03sa.getSeaPressure(20) / 10.0f); // About right where I live..
+ *   
+ *     // Show Temperature
+ *     pc.printf("Ambient temperature is %.1f [C]\r\n", (float) hp03sa.getTemperature() / 10.0f);       
+ *
+ *     // Show Altitude meters
+ *     pc.printf("Altitude estimated at %d [m]\r\n", hp03sa.getAltitude());       
+ * 
+ *     // Show Altitude Ft
+ *     pc.printf("Altitude estimated at %d [ft]\r\n", hp03sa.getAltitudeFt());
+ *
+ *     wait(1.0);
+ *   }
+ * }
+ * @endcode
+ */
+
+// Device I2C Slave addresses
+#define HP03SA_BARO_SA   0xEE 
+#define HP03SA_EEPROM_SA 0xA0
+
+//ISA computation constants
+#define RLGM        0.19026674f          // ISA Exponent (R * L) / (g * M)
+#define GMRL        5.25578009f          // ISA Exponent (g * M) / (R * L) 
+#define LBASE_X10   0.065f               // ISA Temp Lapse (i.e. drop) in K per meter x10
+#define TBASE_X10   (150.0f + 2731.5f)   // ISA Ref Temp in K x10
+#define PBASE_X10   (1013.25f * 10.0f)   // ISA Ref Pres in hPa x10
+  
+/** Create an HP03SA Class instance
+  *
+  */ 
+class HP03SA {
+
+public:
+
+  /** Create an HP03SA device instance
+    *
+    * @param i2c    I2C Bus 
+    * @param XCLR   Clock enable control line
+    */ 
+   HP03SA(I2C *i2c, PinName XCLR);
+
+  /** Get Status
+    *
+    * @return bool Sensor ready 
+    */ 
+   bool getStatus(void);
+
+  /** Get Pressure and Temperature sample
+    *
+    * @return none 
+    */ 
+   void sample(void);
+
+  /** Get Absolute Atmospheric Pressure in hPa x 10
+    * Note: sample() must be called before getAbsPressure()
+    *
+    * @return int Pressure in hPa x 10
+    */ 
+   int getAbsPressure(void);
+
+  /** Get Sealevel Atmospheric Pressure in hPa x 10
+    * Note: sample() must be called before getSeaPressure()
+    *
+    * @param  int alt_meter Altitude above Mean Sea Level where measurement is taken
+    * @return int Pressure at sea level in hPa x 10   
+    */ 
+   int getSeaPressure(int alt_meter);
+
+  /** Get Temperature as int in °Celsius x 10
+    * Note: sample() must be called before getTemperature()  
+    *
+    * @return int Temperature in °Celsius x 10
+    */ 
+   int getTemperatureInt(void);
+
+  /** Get Temperature as float in °Celsius
+    * Note: sample() must be called before getTemperatureFl()  
+    *
+    * @return float Temperature in °Celsius
+    */ 
+   float getTemperature(void);
+
+  /** Get Altitude in meters using ISA
+    * Note: sample() must be called before getAltitude()  
+    *
+    * @return int Altitude in meters above Mean Sea Level (MSL)
+    */ 
+   int getAltitude(void);
+
+  /** Get Altitude in feet using ISA
+    * Note: sample() must be called before getAltitudeFt()  
+    *
+    * @return int Altitude in feet above Mean Sea Level (MSL)
+    */ 
+   int getAltitudeFt();
+
+  /** Set QNH Pressure to calibrate sensor
+    *
+    * @param int pressure_x10 at Mean Sea Level in hPa x 10
+    *            The getAltitude() reading will be 0 m for the set pressure.
+    */ 
+   void setPressure(int pressure_x10 = PBASE_X10);
+
+  /** Set QNH Altitude in meter to calibrate sensor
+    *
+    * @param int alt_meter Altitude in meters above Mean Sea Level (MSL) for current pressure
+    *            The getAltitude() reading will be 'alt_meter' m for the current pressure.   
+    */ 
+   void setAltitude(int alt_meter = 0);
+
+
+  /** Set QNH Altitude in feet to calibrate sensor
+    *
+    * @param int alt_feet Altitude in meters above Mean Sea Level (MSL) for current pressure
+    *            The getAltitudeFt() reading will be 'alt_feet' ft for the current pressure.   
+    */ 
+   void setAltitudeFt(int alt_feet = 0);
+
+
+   /** Convert Temperature from °Celsius into °Fahrenheit
+     *
+     * @param  float celsius in °Celsius  
+     * @return float temperature in °Fahrenheit
+     */ 
+    float celsiusToFahrenheit(float celsius);
+ 
+private: 
+
+  /** Init HP03SA device
+    *
+    * @return none    
+    */ 
+   void _init();
+
+  /** Read ADC value (either pressure or temperature depending on Control Register setting)
+    *
+    * @return int   pressure or temperature 
+    */ 
+   int _readADC (void);
+
+  /** Read Pressure and Temperature
+    *
+    * @return none 
+    */ 
+   void _readTempPres(void);
+  
+  /** Calculate Pressure and Temperature
+    *
+    * @return none 
+    */ 
+   void _calcTempPres(void);
+ 
+  /** Calculate Altitude
+    *
+    * @return none 
+    */ 
+   void _calcAlt(void);
+
+  //I2C interface and ADC control
+  I2C *_i2c;
+  DigitalOut _xclr;
+
+  //Raw values, computed values
+  int  _D1,  _D2;        // measured values: pressure,temperature.  
+  int  _dUT, _off;       // auxiliary variables
+  int  _sens, _x;        // auxiliary variables  
+  int  _temp_x10;        // temperature in Celsius x 10
+  int  _pres_x10;        // pressure in hPa x 10  
+  int  _alt;             // altitude in m  
+  float _pres_base_x10;
+  float _temp_base_x10;
+    
+  //Calibration coefficients
+  int _C1,  //Sensitivity coefficient  
+      _C2,  //Offset coefficient
+      _C3,  //Temp coefficient of sensitivity
+      _C4,  //Temp coefficient of offset
+      _C5,  //Reference temperature
+      _C6,  //Temp coefficient of temperrature
+      _C7;  //Offset fine tuning
+  //Sensor correction-parameters A, B, C, D    
+  int _A, _B, _C, _D;  
+};
+   
+#endif
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