Diff: Thermistor.cpp

Revision:

0:000a8be2414d

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/Thermistor.cpp	Wed Mar 09 13:52:45 2016 +0000
@@ -0,0 +1,75 @@
+ /*
+ * Thermistor Temperature library
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+#include "mbed.h"
+#include "Thermistor.h"
+
+
+    Thermistor::Thermistor(PinName pin) : _pin(pin) {  // _pin(pin) means pass pin to the AnalogIn constructor
+        init();
+    }
+ 
+    void Thermistor::init() {
+        ThermistorNominal = THERMISTORNOMINAL;
+        TemperatureNominal = TEMPERATURENOMINAL;
+        BCoefficient = BCOEFFICIENT;
+        SeriesResistor = SERIESRESISTOR;
+    }
+ 
+     // This is the workhorse routine that calculates the temperature
+    // using the Steinhart-Hart equation for thermistors
+    // https://en.wikipedia.org/wiki/Steinhart%E2%80%93Hart_equation
+    float Thermistor::get_temperature()
+    {
+        float temperature =0, resistance =0;
+        float steinhart =0;
+        double a=0;
+        int smooth = 5;             // Number of samples to smooth
+        
+        for(int i=0;i<smooth;i++) {
+            a += _pin.read_u16();       // Read 16bit Analog value
+        }
+        a = a/smooth;                   // Get average of samples    
+ //       pc.printf("Raw Analog Value for Thermistor = %d\r\n",a);
+      
+        /* Calculate the resistance of the thermistor from analog votage read. */
+        resistance = (float) SeriesResistor / ((65536.0 / a) - 1);
+ //       pc.printf("Resistance for Thermistor = %f\r\n",resistance);
+       
+        steinhart = resistance / ThermistorNominal;         // (R/Ro)
+        steinhart = log(steinhart);                         // ln(R/Ro)
+        steinhart /= BCoefficient;                          // 1/B * ln(R/Ro)
+        steinhart += 1.0 / (TemperatureNominal + 273.15);   // + (1/To)
+        steinhart = 1.0 / steinhart;                        // Invert
+        temperature = steinhart - 273.15;                   // convert to C
+    
+        return temperature;
+    }
+     
+    void Thermistor::set_ThermistorNominal(float thermnom) {
+        ThermistorNominal = thermnom;
+    }    
+    void Thermistor::set_TemperatureNominal(float tempnom){
+        TemperatureNominal = tempnom;
+    }    
+    void Thermistor::set_BCoefficient(float bcoefficient){
+        BCoefficient = bcoefficient;
+    }    
+    void Thermistor::set_SeriesResistor(float resistor){
+        SeriesResistor = resistor;
+    }    
+    
+
+
+