Diff: LinearAnalogSensor.h

Revision:

0:78eeca1c1944

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+++ b/LinearAnalogSensor.h	Wed Aug 07 19:37:12 2013 +0000
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+/* Copyright (c) <2012> <P. Patel>, MIT License
+ *
+ * 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.
+ */
+ 
+ // --------------------- Median Filtered Linear Temperature Sensor Reader ------------------------
+ 
+#ifndef LINEAR_ANALOG
+#define LINEAR_ANALOG
+
+#include "mbed.h"
+/** This library is designed to work with devices like the LM335 temperature sensor.  There are only
+ * two requirements for compatibility of a device with this library: 1) It must be a sensor device
+ * that has an analog voltage output. 2) The physical quantity measured must vary linearly with 
+ * the analog voltage.  The LM335 which creates an analog voltage proportional to temperature
+ * can work very well with this library using the nominal multiplier of 0.0050354 and offset of 
+ * -273.15 or by providing two calibration points to the constuctor to generate a linear response.  It
+ * samples the sensor 9 times and uses the median to minimize the effect of poor ADC readings and sudden
+ * changes. 
+ * 
+ * Example:
+ * @code
+ * LinearAnalogSensor mysensor(p20, 0.0050354, -273.15);        // Setup a LM335 temp sensor on pin 20
+ * DigitalOut myled(LED1);
+ * 
+ * int main() {
+ *     while(1) {
+ *         // Light LED if filtered temperature is greater than 45 degrees Celsius
+ *         if (mysensor > 45) myled = 1;
+ *         else myled = 0;
+ *     }
+ * }
+ * @endcode
+ */
+class LinearAnalogSensor {
+public:
+    /** Create a calibrated temperature sensor object connected to an Analog input pin
+     * @param pin Analog input pin to which an LM335 or comparable linear temp sensor is connected
+     * @param numSamples Number of samples over which to apply a median filter
+     * @param temp1 Temperature (float in degrees C or F) of first calibration point
+     * @param read1 Mbed ADC reading (unsigned short) of first calibration point
+     * @param temp2 Temperature (float in degrees C or F) of second calibration point
+     * @param read2 Mbed ADC reading (unsigned short) of second calibration point
+     */
+    LinearAnalogSensor(PinName pin, int numSamples, float temp1, unsigned short read1, float temp2, unsigned short read2);
+    /** Create a calibrated temperature sensor object connected to an Analog input pin
+     * @param pin Analog input pin to which an LM335 or comparable linear temp sensor is connected
+     * @param numSamples Number of samples over which to apply a median filter
+     * @param multiplier Conversion multiplier to go from ADC reading as unsigned short to temperature (change in degrees / change in unsigned short)
+     * @param offset Conversion offset (positive or negative)
+     */
+    LinearAnalogSensor(PinName pin, int numSamples, float multiplier,  float offset);
+    /** Returns a new median-filtered, converted reading from the sensor
+      * @returns New temperature (float) in degrees C or F as designated by the calibration points
+      */
+    float read();
+    /** Return the last calculated and stored temperature
+      * @returns Last stored temperature (float) in degrees C or F as designated by the calibration points
+      */
+    float getLast();
+    #ifdef MBED_OPERATORS
+    /** An operator shorthand for readTemp() to calculate filtered temperature
+     */
+    operator float() {
+        return read();
+    }
+    #endif
+private:
+    AnalogIn _pin;
+    unsigned short * _arr;
+    float _reading;
+    float _multiplier;
+    int _numSamples;
+    float _offset;
+};
+#endif
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