Revision 0:000a8be2414d, committed 2016-03-09

Comitter:

unix_guru

Date:

Wed Mar 09 13:52:45 2016 +0000

Child:

1:601e1435dfb8

Commit message:

Created Thermistor Library for re-use

Changed in this revision

--- /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;
+    }    
+    
+
+
+ 

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/Thermistor.h	Wed Mar 09 13:52:45 2016 +0000
@@ -0,0 +1,99 @@
+#ifndef THERMISTOR_H
+#define THERMISTOR_H
+///
+/// @mainpage Thermistor Temperature library
+///
+/// This is a Thermistor to Temerature conversion library 
+///
+/// Much thanks to @Adafruit for this tutorial:
+/// https://learn.adafruit.com/thermistor/using-a-thermistor
+///
+/// The 100K Thermistor is configured with a 4.7k series resistor 
+/// tied to vcc (3.3v)  like this:
+///
+///    +3.3v
+///      |
+///      \
+///      /  4.7k series resistor
+///      \
+///      /
+///      |
+///      .-----------O To Anlog pin on FRDM board
+///      |
+///      \
+///      /
+///  Thermistor  100k Nominal
+///      \
+///      /
+///      |
+///     ---
+///     GND
+///  
+///
+/// @author Michael J. Ball
+///  unix_guru at hotmail.com
+///  @unix_guru on Twitter
+///  March 2016
+/// 
+/// @code 
+/// Thermistor bed(PTB10);
+/// printf("Temperature is %f Celcius", bed.get_temperature());
+///
+/// ...
+/// @endcode
+///
+/// @license
+/// 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"
+
+
+#define THERMISTORNOMINAL 100000      // 100k default 
+// temp. for nominal resistance (almost always 25 C)
+#define TEMPERATURENOMINAL 25   
+// The beta coefficient of the thermistor (usually 3000-4000)
+#define BCOEFFICIENT 3950
+// the value of the 'other' resistor
+#define SERIESRESISTOR 4700    
+  
+
+class Thermistor {
+public:
+    Thermistor(PinName pin);  
+    /** Receives a PinName variable.
+     * @param pin mbed pin to which the thermistor is connected
+     */
+ 
+
+    float get_temperature();
+    /**  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
+     */
+    void init();                                    // Set default Steinhart-Hart values
+    void set_ThermistorNominal(float thermnom);     // Change the thermistors nominal resistance
+    void set_TemperatureNominal(float tempnom);     // Change the thermistors nominal temperature
+    void set_BCoefficient(float bcoefficient);      // Change the thermistors BCoefficient
+    void set_SeriesResistor(float resistor);        // Change the value of the series resistor
+ 
+private:
+    AnalogIn _pin;
+    float ThermistorNominal;
+    float TemperatureNominal;
+    float BCoefficient;
+    float SeriesResistor;
+};
+ 
+#endif