The $2 Thermistor Temperature Sensor

A thermistor makes for a very inexpensive temperature sensor, under $2 for the thermistor and the 10k ohm resistor, not counting the $45 for the Arduino and LCD display:

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#include <LiquidCrystal.h>
#include <math.h>

/*
LCD Connections:
rs (LCD pin 4) to Arduino pin 12
rw (LCD pin 5) to Arduino pin 11
enable (LCD pin 6) to Arduino pin 10
LCD pin 15 to Arduino pin 13
LCD pins d4, d5, d6, d7 to Arduino pins 5, 4, 3, 2

Thermistor Connections:
Thermistor Pin 1 to +5v
Thermistor Pin 2 to Analog Pin 0
10k ohm resistor pin 1 to Analog Pin 0
10k ohm resistor pin 2 to Gnd
*/

LiquidCrystal lcd(12, 11, 10, 5, 4, 3, 2);
int backLight = 13;    // pin 13 will control the backlight

void setup(void) {
pinMode(backLight, OUTPUT);
digitalWrite(backLight, HIGH); // turn backlight on. Replace ‘HIGH’ with ‘LOW’ to turn it off.
lcd.begin(20, 4);              // rows, columns.  use 16,2 for a 16×2 LCD, etc.
lcd.clear();                   // start with a blank screen
lcd.setCursor(0,0);            // set cursor to column 0, row 0
}

double Thermistor(int RawADC) {
double Temp;
// See See http://en.wikipedia.org/wiki/Thermistor for explanation of formula
Temp = log(((10240000/RawADC) – 10000));
Temp = 1 / (0.001129148 + (0.000234125 * Temp) + (0.0000000876741 * Temp * Temp * Temp));
Temp = Temp – 273.15;           // Convert Kelvin to Celcius
return Temp;
}

void printTemp(void) {
double fTemp;
double temp = Thermistor(analogRead(0));  // Read sensor on Pin 0
lcd.clear();
lcd.setCursor(0,0);
lcd.print(“Temperature is:”);
lcd.setCursor(0,1);
lcd.print(temp);
lcd.print(” C, “);
fTemp = (temp * 1.8) + 32.0;    // Convert to Fahrenheit
lcd.print(fTemp);
lcd.print(” F”);
if (fTemp > 68 && fTemp < 78) {
lcd.setCursor(0,3);
lcd.print(“Very comfortable”);
}
}

void loop(void) {
printTemp();
delay(1000);
}

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