Joseph Ellsworth / temp-thermisterfor-ERT-J0

Calculate temperature based on resistance from thermistor with lookup chart

thermister_ert-j0eg1.cpp@6:3c9cb2bd08c6, 2016-04-02 (annotated)

Committer:
joeata2wh
Date:
Sat Apr 02 03:48:56 2016 +0000
Revision:
6:3c9cb2bd08c6
Parent:
5:88bf5a42812e 
basic data log working

Who changed what in which revision?

UserRevisionLine numberNew contents of line
joeata2wh 6:3c9cb2bd08c6 1 /* thermister_ert-j0eg1.cpp
joeata2wh 6:3c9cb2bd08c6 2 By Joseph Ellsworth CTO of A2WH
joeata2wh 6:3c9cb2bd08c6 3 Take a look at A2WH.com Producing Water from Air using Solar Energy
joeata2wh 6:3c9cb2bd08c6 4 March-2016 License: https://developer.mbed.org/handbook/MIT-Licence
joeata2wh 6:3c9cb2bd08c6 5 */
joeata2wh 6:3c9cb2bd08c6 6
joeata2wh 0:39f659087759 7 #include "mbed.h"
joeata2wh 1:cc492e6ba333 8 #include "ohms.h" // from library ohms_law
joeata2wh 5:88bf5a42812e 9 #include "thermister_ert-j0eg1.h"
joeata2wh 0:39f659087759 10 // Set of resistance values from data sheet used to lookup temperature to find
joeata2wh 0:39f659087759 11 // location in a 5V band.
joeata2wh 5:88bf5a42812e 12 const long thermisterResistance[] = {205200,154800,117900,90690,70370,50570,43440,34530,27640,22270,18060,14740,12110,
joeata2wh 0:39f659087759 13 10000,8309,6941,5828,4916,4165,3542,3027,2595,2233,1929,1672,1451,1261,1097,956,836,732,642,565,499};
joeata2wh 5:88bf5a42812e 14 const int thermisterBase = -40.0f;
joeata2wh 5:88bf5a42812e 15 const int thermisterStep = 5.0f;
joeata2wh 5:88bf5a42812e 16 const int thermisterMaxTemp = 125.0f;
joeata2wh 0:39f659087759 17
joeata2wh 0:39f659087759 18 float conv_c_to_f(float tempC) {
joeata2wh 5:88bf5a42812e 19 return (tempC * 1.8f) + 32.0f;
joeata2wh 5:88bf5a42812e 20 }
joeata2wh 5:88bf5a42812e 21
joeata2wh 5:88bf5a42812e 22 float conv_f_to_c(float tempF) {
joeata2wh 5:88bf5a42812e 23 return (tempF - 32.0f) * 0.55555555555f;
joeata2wh 5:88bf5a42812e 24 }
joeata2wh 5:88bf5a42812e 25
joeata2wh 5:88bf5a42812e 26 float ERTThermisterRead(PinName apin) {
joeata2wh 5:88bf5a42812e 27 #ifdef DEBUG3
joeata2wh 5:88bf5a42812e 28 printf("ERTThermisterRead start\r\n");
joeata2wh 5:88bf5a42812e 29 #endif
joeata2wh 5:88bf5a42812e 30 AnalogIn adcPin(apin);
joeata2wh 5:88bf5a42812e 31 float tmp = ERTThermisterReadTemp(adcPin);
joeata2wh 5:88bf5a42812e 32 #ifdef DEBUG3
joeata2wh 5:88bf5a42812e 33 printf("ERTThermisterRead temp=%f done\r\n", tmp);
joeata2wh 5:88bf5a42812e 34 #endif
joeata2wh 5:88bf5a42812e 35 return tmp;
joeata2wh 5:88bf5a42812e 36 }
joeata2wh 5:88bf5a42812e 37
joeata2wh 5:88bf5a42812e 38 // read the temp from thermister and print out
joeata2wh 5:88bf5a42812e 39 // both the reading and intermediate values.
joeata2wh 5:88bf5a42812e 40 float ERTThermisterReadPrint(Serial log, char *label, PinName apin) {
joeata2wh 5:88bf5a42812e 41 AnalogIn adcpin(apin);
joeata2wh 5:88bf5a42812e 42 float sensorValue = adcpin.read() * ERTThermisterAdcRef;
joeata2wh 5:88bf5a42812e 43 long sensorResist = calcResistV(22000, ERTThermisterAdcRef, sensorValue);
joeata2wh 5:88bf5a42812e 44 float t1C = ERTThermisterReadTemp(adcpin);
joeata2wh 5:88bf5a42812e 45 float t1F = conv_c_to_f(t1C);
joeata2wh 5:88bf5a42812e 46 log.printf("%s\tvin=%4.2f\tresist=%ld\tT1C=%4.1f\tT1F=%4.2f\r\n",
joeata2wh 5:88bf5a42812e 47 label, sensorValue, sensorResist, t1C, t1F);
joeata2wh 5:88bf5a42812e 48 return t1C;
joeata2wh 0:39f659087759 49 }
joeata2wh 0:39f659087759 50
joeata2wh 0:39f659087759 51
joeata2wh 0:39f659087759 52 /* Read Thermister Temperature using ADC and voltage dividor
joeata2wh 0:39f659087759 53 Lookup the range of resistance by finding the first resistance
joeata2wh 0:39f659087759 54 lower than our specified value which gives us temp with 5C spread
joeata2wh 0:39f659087759 55 then adjust by how far our sensor reading is above the lower
joeata2wh 0:39f659087759 56 bound of the range.*/
joeata2wh 5:88bf5a42812e 57 float ERTThermisterReadTemp(AnalogIn adcpin) {
joeata2wh 0:39f659087759 58 //sensorValue = avgRead(adcpin,3,2);
joeata2wh 5:88bf5a42812e 59 float sensorValue = adcpin.read() * ERTThermisterAdcRef;
joeata2wh 5:88bf5a42812e 60 long sensorResist = calcResistV(22000, ERTThermisterAdcRef, sensorValue);
joeata2wh 0:39f659087759 61 int tempCnt = thermisterBase;
joeata2wh 0:39f659087759 62 int tempndx = 0;
joeata2wh 5:88bf5a42812e 63 #ifdef DEBUG3
joeata2wh 5:88bf5a42812e 64 printf("start ERTThermisterReadTemp adc=%4.2f resist=%ld\r\n", sensorValue, sensorResist);
joeata2wh 5:88bf5a42812e 65 #endif
joeata2wh 5:88bf5a42812e 66 if (sensorResist >= thermisterResistance[0]) {
joeata2wh 5:88bf5a42812e 67 #ifdef DEBUG3
joeata2wh 5:88bf5a42812e 68 printf("resist too high\r\n");
joeata2wh 5:88bf5a42812e 69 #endif
joeata2wh 5:88bf5a42812e 70 return ERTThermisterErrorUnder;
joeata2wh 0:39f659087759 71 }
joeata2wh 0:39f659087759 72
joeata2wh 5:88bf5a42812e 73 #ifdef DEBUG3
joeata2wh 5:88bf5a42812e 74 printf("entering while loop sensorResist=%ld thermisterResistance[0]=%ld\r\n",sensorResist, thermisterResistance[0]);
joeata2wh 5:88bf5a42812e 75 #endif
joeata2wh 0:39f659087759 76 while (sensorResist < thermisterResistance[tempndx]) {
joeata2wh 0:39f659087759 77 tempndx++;
joeata2wh 0:39f659087759 78 tempCnt += thermisterStep;
joeata2wh 0:39f659087759 79 if (tempCnt >= thermisterMaxTemp) {
joeata2wh 5:88bf5a42812e 80 return ERTThermisterErrorOver;
joeata2wh 0:39f659087759 81 }
joeata2wh 0:39f659087759 82 }
joeata2wh 5:88bf5a42812e 83 tempCnt -= thermisterStep; // backup to begin of range
joeata2wh 5:88bf5a42812e 84 #ifdef DEBUG3
joeata2wh 5:88bf5a42812e 85 printf("tempCnt=%d\r\n", tempCnt);
joeata2wh 5:88bf5a42812e 86 #endif
joeata2wh 0:39f659087759 87 int lowTempResist = thermisterResistance[tempndx -1];
joeata2wh 0:39f659087759 88 int highTempResist = thermisterResistance[tempndx];
joeata2wh 0:39f659087759 89 int resistRangeDelta = lowTempResist - highTempResist;
joeata2wh 0:39f659087759 90 float degreesPerUnit = (float) thermisterStep / (float) (resistRangeDelta);
joeata2wh 0:39f659087759 91 int unitOverlow = lowTempResist - sensorResist;
joeata2wh 0:39f659087759 92 float degreeAdj = (float) unitOverlow * degreesPerUnit;
joeata2wh 5:88bf5a42812e 93 #ifdef DEBUG3
joeata2wh 5:88bf5a42812e 94 printf("degreeAdj=%f\r\n", degreeAdj);
joeata2wh 5:88bf5a42812e 95 #endif
joeata2wh 0:39f659087759 96 return (float) tempCnt + degreeAdj;
joeata2wh 0:39f659087759 97 }
joeata2wh 0:39f659087759 98
joeata2wh 5:88bf5a42812e 99 float ERTThermisterAvgReadTemp(AnalogIn adcpin, int numRead) {
joeata2wh 0:39f659087759 100 float sum = 0;
joeata2wh 0:39f659087759 101 int ndx;
joeata2wh 0:39f659087759 102 for (ndx = 0; ndx < numRead; ndx++) {
joeata2wh 0:39f659087759 103 wait(0.005);
joeata2wh 5:88bf5a42812e 104 sum += ERTThermisterReadTemp(adcpin);
joeata2wh 0:39f659087759 105 }
joeata2wh 0:39f659087759 106 return (float) ((float) sum / (float) ndx);
joeata2wh 0:39f659087759 107 }