Nathan Hopkins / Mbed 2 deprecated Thermistor

Interfaced 9 MF51E103F3950 NTC 10k Thermistors to a Nucleo board for a science project.

Dependencies:   mbed

main.cpp@2:cda957297041, 2017-01-31 (annotated)

Committer:
smartsystemdesign
Date:
Tue Jan 31 17:51:43 2017 +0000
Revision:
2:cda957297041
Parent:
1:010d1ef2f3ab
Child:
3:cea064439566
Found calibrated resistor values based on an average of 3 temp readings.  See TempCalibration.xlsx.

Who changed what in which revision?

UserRevisionLine numberNew contents of line
smartsystemdesign 0:453df8530a88 1 // Using MF51E103F3950 NTC 10k Thermistor, with a B value of 3950
smartsystemdesign 0:453df8530a88 2 #include "mbed.h"
smartsystemdesign 0:453df8530a88 3
smartsystemdesign 0:453df8530a88 4 // which analog pin to connect
smartsystemdesign 0:453df8530a88 5 #define THERMISTORPIN A0
smartsystemdesign 0:453df8530a88 6 // resistance at 25 degrees C
smartsystemdesign 0:453df8530a88 7 #define THERMISTORNOMINAL 10000
smartsystemdesign 0:453df8530a88 8 // temp. for nominal resistance (almost always 25 C)
smartsystemdesign 0:453df8530a88 9 #define TEMPERATURENOMINAL 25
smartsystemdesign 0:453df8530a88 10 // how many samples to take and average, more takes longer
smartsystemdesign 0:453df8530a88 11 // but is more 'smooth'
smartsystemdesign 0:453df8530a88 12 #define NUMSAMPLES 5
smartsystemdesign 0:453df8530a88 13 // The beta coefficient of the thermistor (usually 3000-4000)
smartsystemdesign 0:453df8530a88 14 #define BCOEFFICIENT 3950
smartsystemdesign 0:453df8530a88 15 // the value of the 'other' resistor
smartsystemdesign 0:453df8530a88 16 #define SERIESRESISTOR 10000.0f
smartsystemdesign 0:453df8530a88 17
smartsystemdesign 0:453df8530a88 18 #define OFFSET_NUM_AVERAGES 20
smartsystemdesign 0:453df8530a88 19
smartsystemdesign 0:453df8530a88 20 Serial pc(USBTX, USBRX); // tx, rx
smartsystemdesign 0:453df8530a88 21 AnalogIn ain0(A0);
smartsystemdesign 0:453df8530a88 22 AnalogIn ain1(A1);
smartsystemdesign 0:453df8530a88 23 AnalogIn ain2(A2);
smartsystemdesign 0:453df8530a88 24 AnalogIn ain3(A3);
smartsystemdesign 0:453df8530a88 25 AnalogIn ain4(A4);
smartsystemdesign 0:453df8530a88 26 AnalogIn ain5(A5);
smartsystemdesign 2:cda957297041 27 AnalogIn ain6(PA_5); // Note: on the Nucleo F401, this is connected to the LED.
smartsystemdesign 2:cda957297041 28 AnalogIn ain7(PA_6);
smartsystemdesign 0:453df8530a88 29 AnalogIn ain8(PA_7);
smartsystemdesign 0:453df8530a88 30
smartsystemdesign 0:453df8530a88 31 float offsets[9] = {0};
smartsystemdesign 2:cda957297041 32 float resistors[9] = {9984.270169f, 9999.947582f, 9999.962164f, 9999.960999f, 9999.958757f, 9999.918074f, 9999.969933f, 9999.966487f, 9999.977766f};
smartsystemdesign 0:453df8530a88 33
smartsystemdesign 0:453df8530a88 34 int main()
smartsystemdesign 0:453df8530a88 35 {
smartsystemdesign 0:453df8530a88 36 pc.baud(115200);
smartsystemdesign 0:453df8530a88 37
smartsystemdesign 0:453df8530a88 38 pc.printf("\nThermistor test\n");
smartsystemdesign 0:453df8530a88 39 float rawReading[9] = {0};
smartsystemdesign 0:453df8530a88 40 float reading[9] = {0};
smartsystemdesign 0:453df8530a88 41
smartsystemdesign 0:453df8530a88 42 // Find offset values (take average 20 readings for offset):
smartsystemdesign 0:453df8530a88 43 float sum = 0;
smartsystemdesign 0:453df8530a88 44 // for(uint8_t i = 0; i < OFFSET_NUM_AVERAGES; i++) {
smartsystemdesign 0:453df8530a88 45 // sum += ain0.read();
smartsystemdesign 0:453df8530a88 46 // }
smartsystemdesign 0:453df8530a88 47 // offsets[0] = (sum / OFFSET_NUM_AVERAGES);
smartsystemdesign 0:453df8530a88 48 //
smartsystemdesign 0:453df8530a88 49 // sum = 0;
smartsystemdesign 0:453df8530a88 50 // for(uint8_t i = 0; i < OFFSET_NUM_AVERAGES; i++) {
smartsystemdesign 0:453df8530a88 51 // sum += ain1.read();
smartsystemdesign 0:453df8530a88 52 // }
smartsystemdesign 0:453df8530a88 53 // offsets[1] = (sum / OFFSET_NUM_AVERAGES);
smartsystemdesign 0:453df8530a88 54 //
smartsystemdesign 0:453df8530a88 55 // sum = 0;
smartsystemdesign 0:453df8530a88 56 // for(uint8_t i = 0; i < OFFSET_NUM_AVERAGES; i++) {
smartsystemdesign 0:453df8530a88 57 // sum += ain2.read();
smartsystemdesign 0:453df8530a88 58 // }
smartsystemdesign 0:453df8530a88 59 // offsets[2] = (sum / OFFSET_NUM_AVERAGES);
smartsystemdesign 0:453df8530a88 60 //
smartsystemdesign 0:453df8530a88 61 // sum = 0;
smartsystemdesign 0:453df8530a88 62 // for(uint8_t i = 0; i < OFFSET_NUM_AVERAGES; i++) {
smartsystemdesign 0:453df8530a88 63 // sum += ain3.read();
smartsystemdesign 0:453df8530a88 64 // }
smartsystemdesign 0:453df8530a88 65 // offsets[3] = (sum / OFFSET_NUM_AVERAGES);
smartsystemdesign 0:453df8530a88 66 //
smartsystemdesign 0:453df8530a88 67 // sum = 0;
smartsystemdesign 0:453df8530a88 68 // for(uint8_t i = 0; i < OFFSET_NUM_AVERAGES; i++) {
smartsystemdesign 0:453df8530a88 69 // sum += ain4.read();
smartsystemdesign 0:453df8530a88 70 // }
smartsystemdesign 0:453df8530a88 71 // offsets[4] = (sum / OFFSET_NUM_AVERAGES);
smartsystemdesign 0:453df8530a88 72 //
smartsystemdesign 0:453df8530a88 73 // sum = 0;
smartsystemdesign 0:453df8530a88 74 // for(uint8_t i = 0; i < OFFSET_NUM_AVERAGES; i++) {
smartsystemdesign 0:453df8530a88 75 // sum += ain5.read();
smartsystemdesign 0:453df8530a88 76 // }
smartsystemdesign 0:453df8530a88 77 // offsets[5] = (sum / OFFSET_NUM_AVERAGES);
smartsystemdesign 0:453df8530a88 78 //
smartsystemdesign 0:453df8530a88 79 // sum = 0;
smartsystemdesign 0:453df8530a88 80 // for(uint8_t i = 0; i < OFFSET_NUM_AVERAGES; i++) {
smartsystemdesign 0:453df8530a88 81 // sum += ain5.read();
smartsystemdesign 0:453df8530a88 82 // }
smartsystemdesign 0:453df8530a88 83 // offsets[5] = (sum / OFFSET_NUM_AVERAGES);
smartsystemdesign 0:453df8530a88 84 //
smartsystemdesign 0:453df8530a88 85 // sum = 0;
smartsystemdesign 0:453df8530a88 86 // for(uint8_t i = 0; i < OFFSET_NUM_AVERAGES; i++) {
smartsystemdesign 0:453df8530a88 87 // sum += ain6.read();
smartsystemdesign 0:453df8530a88 88 // }
smartsystemdesign 0:453df8530a88 89 // offsets[6] = (sum / OFFSET_NUM_AVERAGES);
smartsystemdesign 0:453df8530a88 90 //
smartsystemdesign 0:453df8530a88 91 // sum = 0;
smartsystemdesign 0:453df8530a88 92 // for(uint8_t i = 0; i < OFFSET_NUM_AVERAGES; i++) {
smartsystemdesign 0:453df8530a88 93 // sum += ain7.read();
smartsystemdesign 0:453df8530a88 94 // }
smartsystemdesign 0:453df8530a88 95 // offsets[7] = (sum / OFFSET_NUM_AVERAGES);
smartsystemdesign 0:453df8530a88 96 //
smartsystemdesign 0:453df8530a88 97 // sum = 0;
smartsystemdesign 0:453df8530a88 98 // for(uint8_t i = 0; i < OFFSET_NUM_AVERAGES; i++) {
smartsystemdesign 0:453df8530a88 99 // sum += ain8.read();
smartsystemdesign 0:453df8530a88 100 // }
smartsystemdesign 0:453df8530a88 101 // offsets[8] = (sum / OFFSET_NUM_AVERAGES);
smartsystemdesign 0:453df8530a88 102
smartsystemdesign 0:453df8530a88 103 // Single reading for offset:
smartsystemdesign 0:453df8530a88 104 // offsets[0] = ain0.read();
smartsystemdesign 0:453df8530a88 105 // offsets[1] = ain1.read();
smartsystemdesign 0:453df8530a88 106 // offsets[2] = ain2.read();
smartsystemdesign 0:453df8530a88 107 // offsets[3] = ain3.read();
smartsystemdesign 0:453df8530a88 108 // offsets[4] = ain4.read();
smartsystemdesign 0:453df8530a88 109 // offsets[5] = ain5.read();
smartsystemdesign 0:453df8530a88 110 // offsets[6] = ain6.read();
smartsystemdesign 0:453df8530a88 111 // offsets[7] = ain7.read();
smartsystemdesign 0:453df8530a88 112 // offsets[8] = ain8.read();
smartsystemdesign 0:453df8530a88 113
smartsystemdesign 0:453df8530a88 114 // Find average of offsets and store in offsets array:
smartsystemdesign 0:453df8530a88 115 sum = 0;
smartsystemdesign 0:453df8530a88 116 float average = 0;
smartsystemdesign 0:453df8530a88 117
smartsystemdesign 0:453df8530a88 118 for(uint8_t i = 0; i < 9; i++) {
smartsystemdesign 0:453df8530a88 119 sum += offsets[i];
smartsystemdesign 0:453df8530a88 120 }
smartsystemdesign 0:453df8530a88 121
smartsystemdesign 0:453df8530a88 122 average = sum / 9;
smartsystemdesign 0:453df8530a88 123
smartsystemdesign 0:453df8530a88 124 for(uint8_t i = 0; i < 9; i++) {
smartsystemdesign 0:453df8530a88 125 offsets[i] = offsets[i] - average;
smartsystemdesign 0:453df8530a88 126 }
smartsystemdesign 0:453df8530a88 127
smartsystemdesign 0:453df8530a88 128 while(1) {
smartsystemdesign 0:453df8530a88 129 // Take reading and apply offset, then use voltage divider equation:
smartsystemdesign 0:453df8530a88 130 // rawReading[0] = 1 / (ain0.read() - offsets[0]) - 1;
smartsystemdesign 0:453df8530a88 131 // rawReading[1] = 1 / (ain1.read() - offsets[1]) - 1;
smartsystemdesign 0:453df8530a88 132 // rawReading[2] = 1 / (ain2.read() - offsets[2]) - 1;
smartsystemdesign 0:453df8530a88 133 // rawReading[3] = 1 / (ain3.read() - offsets[3]) - 1;
smartsystemdesign 0:453df8530a88 134 // rawReading[4] = 1 / (ain4.read() - offsets[4]) - 1;
smartsystemdesign 0:453df8530a88 135 // rawReading[5] = 1 / (ain5.read() - offsets[5]) - 1;
smartsystemdesign 0:453df8530a88 136 // rawReading[6] = 1 / (ain6.read() - offsets[6]) - 1;
smartsystemdesign 0:453df8530a88 137 // rawReading[7] = 1 / (ain7.read() - offsets[7]) - 1;
smartsystemdesign 0:453df8530a88 138 // rawReading[8] = 1 / (ain8.read() - offsets[8]) - 1;
smartsystemdesign 0:453df8530a88 139
smartsystemdesign 0:453df8530a88 140 rawReading[0] = 1 / ain0.read() - 1;
smartsystemdesign 0:453df8530a88 141 rawReading[1] = 1 / ain1.read() - 1;
smartsystemdesign 0:453df8530a88 142 rawReading[2] = 1 / ain2.read() - 1;
smartsystemdesign 0:453df8530a88 143 rawReading[3] = 1 / ain3.read() - 1;
smartsystemdesign 0:453df8530a88 144 rawReading[4] = 1 / ain4.read() - 1;
smartsystemdesign 0:453df8530a88 145 rawReading[5] = 1 / ain5.read() - 1;
smartsystemdesign 0:453df8530a88 146 rawReading[6] = 1 / ain6.read() - 1;
smartsystemdesign 0:453df8530a88 147 rawReading[7] = 1 / ain7.read() - 1;
smartsystemdesign 0:453df8530a88 148 rawReading[8] = 1 / ain8.read() - 1;
smartsystemdesign 0:453df8530a88 149
smartsystemdesign 0:453df8530a88 150 for(uint8_t i = 0; i < 9; i++) {
smartsystemdesign 0:453df8530a88 151 reading[i] = resistors[i] / rawReading[i];
smartsystemdesign 0:453df8530a88 152 }
smartsystemdesign 0:453df8530a88 153
smartsystemdesign 0:453df8530a88 154 // pc.printf("Thermistor resistance ");
smartsystemdesign 0:453df8530a88 155 // pc.printf("%f\t", reading0);
smartsystemdesign 0:453df8530a88 156
smartsystemdesign 0:453df8530a88 157 // Apply Steinhart equation:
smartsystemdesign 0:453df8530a88 158 for(uint8_t i = 0; i < 9; i++) {
smartsystemdesign 0:453df8530a88 159 float steinhart;
smartsystemdesign 0:453df8530a88 160 steinhart = reading[i] / THERMISTORNOMINAL; // (R/Ro)
smartsystemdesign 0:453df8530a88 161 steinhart = log(steinhart); // ln(R/Ro)
smartsystemdesign 0:453df8530a88 162 steinhart /= BCOEFFICIENT; // 1/B * ln(R/Ro)
smartsystemdesign 0:453df8530a88 163 steinhart += 1.0 / (TEMPERATURENOMINAL + 273.15); // + (1/To)
smartsystemdesign 0:453df8530a88 164 steinhart = 1.0f / steinhart; // Invert
smartsystemdesign 0:453df8530a88 165 steinhart -= 273.15f; // convert to C
smartsystemdesign 0:453df8530a88 166 // pc.printf("Temperature %d: %f *C\t", i, steinhart);
smartsystemdesign 0:453df8530a88 167
smartsystemdesign 0:453df8530a88 168 // Print commas for plotting (except at end):
smartsystemdesign 0:453df8530a88 169 if(i == 8) {
smartsystemdesign 0:453df8530a88 170 pc.printf("%.4f", steinhart);
smartsystemdesign 0:453df8530a88 171 }
smartsystemdesign 2:cda957297041 172 else if(i == 6)
smartsystemdesign 2:cda957297041 173 continue; // bad analog input (on LED)
smartsystemdesign 0:453df8530a88 174 else {
smartsystemdesign 0:453df8530a88 175 pc.printf("%.4f,", steinhart);
smartsystemdesign 0:453df8530a88 176 }
smartsystemdesign 0:453df8530a88 177 }
smartsystemdesign 0:453df8530a88 178
smartsystemdesign 0:453df8530a88 179 pc.printf("\n");
smartsystemdesign 1:010d1ef2f3ab 180 wait(1);
smartsystemdesign 0:453df8530a88 181 }
smartsystemdesign 0:453df8530a88 182 }