Diff: thermister_ert-j0eg1.cpp

Revision:

0:39f659087759

Child:

1:cc492e6ba333

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/thermister_ert-j0eg1.cpp	Mon Mar 07 23:17:16 2016 +0000
@@ -0,0 +1,61 @@
+#include "mbed.h"
+#include "ohms.h"
+
+// Set of resistance values from data sheet used to lookup temperature to find
+// location in a 5V band. 
+static long thermisterResistance[] = {205200,154800,117900,90690,70370,50570,43440,34530,27640,22270,18060,14740,12110,
+                  10000,8309,6941,5828,4916,4165,3542,3027,2595,2233,1929,1672,1451,1261,1097,956,836,732,642,565,499};                  
+static int thermisterBase = -40;
+static int thermisterStep = 5;
+static int thermisterMaxTemp = 125;
+const float adc_ref = 3.30;
+
+
+
+float conv_c_to_f(float tempC) {  
+  return (tempC * 1.8) + 32.0;
+}
+
+
+/* Read Thermister Temperature using ADC and voltage dividor 
+ Lookup the range of resistance by finding the first resistance
+ lower than our specified value which gives us temp with 5C spread
+ then adjust by how far our sensor reading is above the lower
+ bound of the range.*/
+float readTemp(AnalogIn adcpin) {    
+    //sensorValue = avgRead(adcpin,3,2);
+    float sensorValue = adcpin.read() * adc_ref;    
+    long sensorResist =  calcResistV(22000, adc_ref, sensorValue);
+    int tempCnt = thermisterBase;   
+    int tempndx = 0;
+    
+    if  (sensorValue >= thermisterResistance[0]) {
+      return -255;
+    }
+    
+    while (sensorResist < thermisterResistance[tempndx]) {     
+       tempndx++;
+       tempCnt += thermisterStep;
+       if (tempCnt >= thermisterMaxTemp) {
+         return 255;
+       }
+    }
+    tempCnt -= thermisterStep; // backup to begin of range    
+    int lowTempResist = thermisterResistance[tempndx -1];
+    int highTempResist = thermisterResistance[tempndx];
+    int resistRangeDelta = lowTempResist - highTempResist;
+    float degreesPerUnit = (float) thermisterStep / (float) (resistRangeDelta);
+    int unitOverlow = lowTempResist - sensorResist;
+    float degreeAdj = (float) unitOverlow * degreesPerUnit;
+    return (float) tempCnt + degreeAdj;
+}
+
+float avgReadTemp(AnalogIn adcpin, int numRead) {
+  float sum = 0;
+  int ndx; 
+  for (ndx = 0; ndx < numRead; ndx++) {
+    wait(0.005);
+    sum += readTemp(adcpin);
+  }
+  return (float) ((float) sum / (float) ndx);
+}