Altitude.h

00001 /*
00002     MPL3115A2 Barometric Pressure and Tempurature Sensor Library
00003     By: Michael Lange
00004     Date: March 31, 2014
00005     License: This code is public domain.
00006  
00007     This class encapsulates an altitude reading from the sensor.
00008  
00009  */
00010  
00011  
00012 #ifndef ALTITUDE_H
00013 #define ALTITUDE_H
00014 
00015 #include "mbed.h"
00016 
00017 //! Casting a float to a char truncates, therefore negative numbers become positive.
00018 //! This will properly cast a float in the range -128 to 127 to a char.
00019 #define float_to_char(x) (((x)<0)?(-(char)(x)):((char)(x)))
00020 
00021 //! Altitude provides a wrapper around altitude data coming from the sensor. The class handles
00022 //! working with compressed data from the sensor and provides convenient functions for retreiving
00023 //! the data in various units (with room to add more if needed).
00024 class Altitude
00025 {
00026 public:
00027 
00028     //! The size of the compressed data buffer from the sensor. Used in an I2C read.
00029     static const int size = 3;
00030     
00031     //! The units we support converting the sensor data to.
00032     enum unitsType { METERS, FEET };
00033 
00034     Altitude();
00035     Altitude(float a, unitsType units = FEET);
00036     Altitude(const char* compressed);
00037     Altitude(const char msb, const char csb, const char lsb);
00038 
00039     //! Allows using the object directly in an I2C read operation.
00040     operator char*(void) { return _compressed; }
00041     //! Same as calling altitude with METERS as the parameter.
00042     operator float(void) { return _altitude; }
00043 
00044     //! Returns the altitude in the units you specifiy, defaulting to FEET if none specified.
00045     float altitude(unitsType units = FEET);
00046     //! Call to decompress the sensor data after an I2C read.
00047     void setAltitude();
00048     void setAltitude(const char* compressed);
00049     void setAltitude(const char msb, const char csb, const char lsb);
00050     void setAltitude(float a, unitsType units = FEET);
00051 
00052     //! Returns the altitude as a string in the units specified, defaulting to FEET if none specified.
00053     const char* print(unitsType units = FEET);
00054     
00055     //! Converts meters to feet.
00056     static float MetersToFeet(float meters) { return meters * 3.28084; }
00057     //! Converts feet to meters.
00058     static float FeetToMeters(float feet) { return feet / 3.28084; }
00059     
00060 private:
00061     float _altitude;
00062     char  _compressed[3];
00063     char  _printBuffer[9];
00064 };
00065 
00066 #endif // ALTITUDE_H