LinearTemp.h

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, 
00005  * including without limitation the rights to use, copy, modify, merge, publish, distribute, 
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 
00014  * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, 
00015  * DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, 
00016  * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
00017  */
00018  
00019  // --------------------- Median Filtered Linear Temperature Sensor Reader ------------------------
00020  
00021 #ifndef LINEAR_TEMP
00022 #define LINEAR_TEMP
00023 
00024 #include "mbed.h"
00025 /** This library is designed to work with devices like the LM335 temperature sensor.  There are only
00026  * two requirements for compatibility of a device with this library: 1) It must be a sensor device
00027  * that has an analog voltage output. 2) The physical quantity measured must vary linearly with 
00028  * the analog voltage.  The LM335 which creates an analog voltage proportional to temperature
00029  * can work very well with this library using the nominal multiplier of 0.0050354 and offset of 
00030  * -273.15 or by providing two calibration points to the constuctor to generate a linear response.  It
00031  * samples the sensor 9 times and uses the median to minimize the effect of poor ADC readings and sudden
00032  * changes. 
00033  * 
00034  * Example:
00035  * @code
00036  * LinearTemp mysensor(p20, 0.0050354, -273.15);        // Setup a LM335 temp sensor on pin 20
00037  * DigitalOut myled(LED1);
00038  * 
00039  * int main() {
00040  *     while(1) {
00041  *         // Light LED if filtered temperature is greater than 45 degrees Celsius
00042  *         if (mysensor > 45) myled = 1;
00043  *         else myled = 0;
00044  *     }
00045  * }
00046  * @endcode
00047  */
00048 class LinearTemp {
00049 public:
00050     /** Create a calibrated temperature sensor object connected to an Analog input pin
00051      * @param pin Analog input pin to which an LM335 or comparable linear temp sensor is connected
00052      * @param temp1 Temperature (float in degrees C or F) of first calibration point
00053      * @param read1 Mbed ADC reading (unsigned short) of first calibration point
00054      * @param temp2 Temperature (float in degrees C or F) of second calibration point
00055      * @param read2 Mbed ADC reading (unsigned short) of second calibration point
00056      */
00057     LinearTemp(PinName pin, float temp1, unsigned short read1, float temp2, unsigned short read2);
00058     /** Create a calibrated temperature sensor object connected to an Analog input pin
00059      * @param pin Analog input pin to which an LM335 or comparable linear temp sensor is connected
00060      * @param multiplier Conversion multiplier to go from ADC reading as unsigned short to temperature (change in degrees / change in unsigned short)
00061      * @param offset Conversion offset (positive or negative)
00062      */
00063     LinearTemp(PinName pin, float multiplier,  float offset);
00064     /** Returns a new median-filtered, converted reading from the sensor
00065       * @returns New temperature (float) in degrees C or F as designated by the calibration points
00066       */
00067     float readTemp();
00068     /** Return the last calculated and stored temperature
00069       * @returns Last stored temperature (float) in degrees C or F as designated by the calibration points
00070       */
00071     float getTemp();
00072     #ifdef MBED_OPERATORS
00073     /** An operator shorthand for readTemp() to calculate filtered temperature
00074      */
00075     operator float() {
00076         return readTemp();
00077     }
00078     #endif
00079 private:
00080     AnalogIn _pin;
00081     unsigned short _tempArr[9];
00082     float _temp;
00083     float _multiplier;
00084     float _offset;
00085 };
00086 #endif