main.cpp

00001 // Using MF51E103F3950 NTC 10k Thermistor, with a B value of 3950
00002 #include "mbed.h"
00003 
00004 // which analog pin to connect
00005 #define THERMISTORPIN A0
00006 // resistance at 25 degrees C
00007 #define THERMISTORNOMINAL 10000
00008 // temp. for nominal resistance (almost always 25 C)
00009 #define TEMPERATURENOMINAL 25
00010 // how many samples to take and average, more takes longer
00011 // but is more 'smooth'
00012 #define NUMSAMPLES 5
00013 // The beta coefficient of the thermistor (usually 3000-4000)
00014 #define BCOEFFICIENT 3950
00015 // the value of the 'other' resistor
00016 #define SERIESRESISTOR 10000.0f
00017 
00018 #define OFFSET_NUM_AVERAGES 20
00019 
00020 Serial pc(USBTX, USBRX); // tx, rx
00021 AnalogIn ain0(A0);
00022 AnalogIn ain1(A1);
00023 AnalogIn ain2(A2);
00024 AnalogIn ain3(A3);
00025 AnalogIn ain4(A4);
00026 AnalogIn ain5(A5);
00027 AnalogIn ain6(PA_5); // Note: on the Nucleo F401, this is connected to the LED.
00028 AnalogIn ain7(PA_6);
00029 AnalogIn ain8(PA_7);
00030 
00031 Timer timer;
00032 
00033 float offsets[9] = {0};
00034 float resistors[9] = {9984.270169f, 9999.947582f, 9999.962164f, 9999.960999f, 9999.958757f, 9999.918074f, 9999.969933f, 9999.966487f, 9999.977766f};
00035 
00036 int main()
00037 {
00038     pc.baud(115200);
00039 
00040     pc.printf("\nThermistor test\n");
00041     float rawReading[9] = {0};
00042     float reading[9] = {0};
00043     
00044 // Find offset values (take average 20 readings for offset):
00045     float sum = 0;
00046 //    for(uint8_t i = 0; i < OFFSET_NUM_AVERAGES; i++) {
00047 //        sum += ain0.read();
00048 //    }
00049 //    offsets[0] = (sum / OFFSET_NUM_AVERAGES);
00050 //    
00051 //    sum = 0;
00052 //    for(uint8_t i = 0; i < OFFSET_NUM_AVERAGES; i++) {
00053 //        sum += ain1.read();
00054 //    }
00055 //    offsets[1] = (sum / OFFSET_NUM_AVERAGES);
00056 //    
00057 //    sum = 0;
00058 //    for(uint8_t i = 0; i < OFFSET_NUM_AVERAGES; i++) {
00059 //        sum += ain2.read();
00060 //    }
00061 //    offsets[2] = (sum / OFFSET_NUM_AVERAGES);
00062 //    
00063 //    sum = 0;
00064 //    for(uint8_t i = 0; i < OFFSET_NUM_AVERAGES; i++) {
00065 //        sum += ain3.read();
00066 //    }
00067 //    offsets[3] = (sum / OFFSET_NUM_AVERAGES);    
00068 //
00069 //    sum = 0;
00070 //    for(uint8_t i = 0; i < OFFSET_NUM_AVERAGES; i++) {
00071 //        sum += ain4.read();
00072 //    }
00073 //    offsets[4] = (sum / OFFSET_NUM_AVERAGES);
00074 //
00075 //    sum = 0;
00076 //    for(uint8_t i = 0; i < OFFSET_NUM_AVERAGES; i++) {
00077 //        sum += ain5.read();
00078 //    }
00079 //    offsets[5] = (sum / OFFSET_NUM_AVERAGES);
00080 //            
00081 //    sum = 0;
00082 //    for(uint8_t i = 0; i < OFFSET_NUM_AVERAGES; i++) {
00083 //        sum += ain5.read();
00084 //    }
00085 //    offsets[5] = (sum / OFFSET_NUM_AVERAGES);
00086 //
00087 //    sum = 0;
00088 //    for(uint8_t i = 0; i < OFFSET_NUM_AVERAGES; i++) {
00089 //        sum += ain6.read();
00090 //    }
00091 //    offsets[6] = (sum / OFFSET_NUM_AVERAGES);
00092 //
00093 //    sum = 0;
00094 //    for(uint8_t i = 0; i < OFFSET_NUM_AVERAGES; i++) {
00095 //        sum += ain7.read();
00096 //    }
00097 //    offsets[7] = (sum / OFFSET_NUM_AVERAGES);
00098 //    
00099 //    sum = 0;
00100 //    for(uint8_t i = 0; i < OFFSET_NUM_AVERAGES; i++) {
00101 //        sum += ain8.read();
00102 //    }
00103 //    offsets[8] = (sum / OFFSET_NUM_AVERAGES);
00104 
00105 // Single reading for offset:
00106 //    offsets[0] = ain0.read();
00107 //    offsets[1] = ain1.read();
00108 //    offsets[2] = ain2.read();
00109 //    offsets[3] = ain3.read();
00110 //    offsets[4] = ain4.read();
00111 //    offsets[5] = ain5.read();
00112 //    offsets[6] = ain6.read();
00113 //    offsets[7] = ain7.read();
00114 //    offsets[8] = ain8.read();
00115     
00116 // Find average of offsets and store in offsets array:
00117     sum = 0;
00118     float average = 0;
00119     
00120     for(uint8_t i = 0; i < 9; i++) {
00121         sum += offsets[i];
00122     }
00123     
00124     average = sum / 9;
00125     
00126     for(uint8_t i = 0; i < 9; i++) {
00127         offsets[i] = offsets[i] - average;
00128     }
00129 
00130     timer.start();
00131 
00132     while(1) {
00133 // Take reading and apply offset, then use voltage divider equation:
00134 //        rawReading[0] = 1 / (ain0.read() - offsets[0]) - 1;
00135 //        rawReading[1] = 1 / (ain1.read() - offsets[1]) - 1;
00136 //        rawReading[2] = 1 / (ain2.read() - offsets[2]) - 1;
00137 //        rawReading[3] = 1 / (ain3.read() - offsets[3]) - 1;
00138 //        rawReading[4] = 1 / (ain4.read() - offsets[4]) - 1;
00139 //        rawReading[5] = 1 / (ain5.read() - offsets[5]) - 1;
00140 //        rawReading[6] = 1 / (ain6.read() - offsets[6]) - 1;
00141 //        rawReading[7] = 1 / (ain7.read() - offsets[7]) - 1;
00142 //        rawReading[8] = 1 / (ain8.read() - offsets[8]) - 1;
00143         
00144         rawReading[0] = 1 / ain0.read() - 1;
00145         rawReading[1] = 1 / ain1.read() - 1;
00146         rawReading[2] = 1 / ain2.read() - 1;
00147         rawReading[3] = 1 / ain3.read() - 1;
00148         rawReading[4] = 1 / ain4.read() - 1;
00149         rawReading[5] = 1 / ain5.read() - 1;
00150         rawReading[6] = 1 / ain6.read() - 1;
00151         rawReading[7] = 1 / ain7.read() - 1;
00152         rawReading[8] = 1 / ain8.read() - 1;
00153         
00154         for(uint8_t i = 0; i < 9; i++) {
00155             reading[i] = resistors[i] / rawReading[i];
00156         }
00157                 
00158 //        pc.printf("Thermistor resistance ");
00159 //        pc.printf("%f\t", reading0);
00160 
00161 // Apply Steinhart equation:
00162 
00163         for(uint8_t i = 0; i < 9; i++) {
00164             float steinhart;
00165             steinhart = reading[i] / THERMISTORNOMINAL;     // (R/Ro)
00166             steinhart = log(steinhart);                  // ln(R/Ro)
00167             steinhart /= BCOEFFICIENT;                   // 1/B * ln(R/Ro)
00168             steinhart += 1.0 / (TEMPERATURENOMINAL + 273.15); // + (1/To)
00169             steinhart = 1.0f / steinhart;                 // Invert
00170             steinhart -= 273.15f;                         // convert to C
00171 //            pc.printf("Temperature %d: %f *C\t", i, steinhart);
00172 
00173 // Print commas for plotting (except at end):
00174 
00175             if(i == 6)
00176                 continue;   // bad analog input (on LED)
00177             else {
00178                 pc.printf("%.4f,", steinhart);
00179             }
00180         }
00181         pc.printf("%.2f\n", timer.read()/60.0f); // print time from boot in minutes
00182 
00183         wait(1);
00184     }
00185 }