LinearTemp.cpp

00001 /* Copyright (c) <2012> <P. Patel>, MIT License
00002  *
00003  * Permission is hereby granted, free of charge, to any person obtaining a copy of this software 
00004  * and associated documentation files (the "Software"), to deal in the Software without restriction, 
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00006  * sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is 
00007  * furnished to do so, subject to the following conditions:
00008  *
00009  * The above copyright notice and this permission notice shall be included in all copies or 
00010  * substantial portions of the Software.
00011  *
00012  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING 
00013  * BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND 
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00018  
00019 // --------------------- Median Filtered Linear Temperature Sensor Reader ----------------------------
00020  
00021 #include "LinearTemp.h"
00022 #include "mbed.h"
00023 
00024 // Constructor using two calibration points to define linear multiplier and offset
00025 LinearTemp::LinearTemp(PinName pin, float temp1, unsigned short read1, float temp2, unsigned short read2):_pin(pin) {
00026     _temp = 0.0;                                     // Zero the temperature
00027     _multiplier = (temp2 - temp1) / (read2 - read1); // Calculate multiplier as slope
00028     _offset = temp1 - (_multiplier * read1);         // Calculate offset
00029 }
00030 // Constructor using user defined multiplier and offset
00031 LinearTemp::LinearTemp(PinName pin, float multiplier, float offset):_pin(pin) {
00032     _temp = 0.0;                                     // Zero the temperature
00033     _multiplier = multiplier;                        // Set multiplier
00034     _offset = offset;                                // Set offset
00035 }
00036 
00037 // Populates an array with temperature readings, sorts, and returns median
00038 float LinearTemp::readTemp() {
00039     _tempArr[0] = _pin.read_u16();
00040     for (int i = 1; i < 9; i++) { 
00041         _tempArr[i] = _pin.read_u16();
00042         unsigned short tmp = _tempArr[i];
00043         int j;            
00044         for (j = i - 1; j >= 0; j--) {
00045             if (tmp>=_tempArr[j]) break;
00046             _tempArr[j + 1] = _tempArr[j];
00047         }
00048         _tempArr[j + 1] = tmp;
00049     }
00050     _temp = (_tempArr[4] * _multiplier) + _offset;
00051     return _temp;
00052 }
00053 // Returns last calculated temperature value
00054 float LinearTemp::getTemp() {
00055     return _temp;
00056 }