Diff: main.cpp

Revision:

0:eaea12966d34

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/main.cpp	Fri Jan 22 17:21:52 2016 +0000
@@ -0,0 +1,86 @@
+/* FRDM-Thermistor-Demo
+This is a Thermistor to Temerature conversion demo 
+for the @NXP (@freescale) FRDM-K64F demo board
+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
+           
+
+*/
+ 
+
+#include "mbed.h"
+
+#define THERMISTORNOMINAL 100000      // 100k 
+// 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    
+  
+AnalogIn Thermistor(A3);
+
+Serial pc(USBTX, USBRX);
+
+
+// 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 get_temperature()
+{
+    float temperature, resistance;
+    float steinhart;
+    int a;
+    
+    a = Thermistor.read_u16();       // Read 16bit Analog value
+    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;
+}
+   
+ 
+
+
+int main()
+{
+    pc.baud(115200);    
+    pc.printf("\r\nThermistor Test - Build " __DATE__ " " __TIME__ "\r\n");
+  
+    while(1) {  
+       pc.printf("Temperature %f *C\r\n",get_temperature()); 
+
+       wait(.5); 
+    }
+}