Creating a Simple Temperature Sensor with an Arduino

The first step towards automation that I wanted to incorporate was a temperature sensor. I bought some 10k ohm resistors and thermistors. Using a simple wiring schematic one can take an analog measurement through a micro-controller and determine the temperature in kelvin. Once you have that data value you can just convert it to your preferred unit, which I just converted to Celsius and then Fahrenheit for simplicity.

    At first I wanted to use fancy display, or many LEDs to display the temperature but I realized that it would quickly use up too many pins on an Arduino. So instead I took the temperature and divided it by an integer of 10, which the number gets truncated after the decimal so you end up with the first (10's place) of a temperature. Then by subtracting the difference of the original by the new truncated number will return 1-9, or the second digit. It is probably easier to understand in code versus writing. 

 // Uncomment this line for the function to return Fahrenheit instead.

 //Temp = (Temp * 9.0)/ 5.0 + 32.0; // Convert to Fahrenheit

 return Temp;  // Return the Temperature

}

void printDouble(double val, byte precision) {

  // prints val with number of decimal places determine by precision

  // precision is a number from 0 to 6 indicating the desired decimal places

  // example: printDouble(3.1415, 2); // prints 3.14 (two decimal places)

  Serial.print (int(val));  //prints the int part

  if( precision > 0) {

    Serial.print("."); // print the decimal point

    unsigned long frac, mult = 1;

    byte padding = precision -1;

    while(precision--) mult *=10;

    if(val >= 0) frac = (val - int(val)) * mult; 

    else frac = (int(val) - val) * mult;

    unsigned long frac1 = frac;

    while(frac1 /= 10) padding--;

    while(padding--) Serial.print("0");

    Serial.print(frac,DEC) ;

  }

}

#define ThermistorPIN 0   // Analog Pin 0

//These pins are used for indicating the temperature, one counts how many times each 

//                                                    color blinks with the blue one blinking first

//Ex: if blue blinks 6 times and UV twice, the temp=62

int led10 = 13; //blue led for giving first digit of water temperature by blinking x amount of times

int led1 = 12; //UV or purple LED for blinking x amount of times to display 2nd digit

void setup() {

  Serial.begin(115200);

  pinMode(led10, OUTPUT);     

  pinMode(led1, OUTPUT);     

}

double temp;

int temp10; // Value used to first digit of temperature (10s place, 10,20,30,etc.)

int temp1; // Value used for second digit of temperature (values 1-9) 

void loop() {

  temp=Thermistor(analogRead(ThermistorPIN));           // read ADC and convert it to Celsius

  //Serial.print(", Celsius: "); printDouble(temp,3);     // display Celsius

  temp = (temp * 9.0)/ 5.0 + 32.0;                      // converts to Fahrenheit

  //Serial.print(", Fahrenheit: "); printDouble(temp,3);  // display Fahrenheit

 //*By dividing the temp by an integer it will truncate the remaining numbers after a decimal point

 //**    so 62/10 would return 6

 temp10 = temp/10; 

//*Then to find the second digit we can subtract the difference 

 //**    of the two so 62-60 = 2

 temp1 = temp-temp10;

 //*This method was useful to make a temperature display that does not

 //**  use up too many pins and it still easy to understand 

 //Now time to display the temperature through blinking LEDs

 //First is the blue light for the first digit

 for (int i=1; i<=temp10; i++) //Blink once for every int value, could have started at 0 and just used a 

                                                                                //less than (<)

 {

   digitalWrite(led10, HIGH);  // turn the LED on (HIGH is the voltage level)

   delay(250);                  // wait for a 250ms, more than enough time to recognize a flash

   digitalWrite(led10, LOW);    // turn the LED off by making the voltage LOW

   delay(800);                  // wait 800ms, can be adjusted however too slow is tedious and 

                                                                        //too fast is easy to miss a blink

 }

 //A delay here can be helpful for a gap between the two colors

 //Second is the UV light for the second digit 

 for (int i=1; i<=temp1; i++) //Blink once for every int value, could have started at 0 and just 

                                                                                //used a less than (<)

 {

   digitalWrite(led1, HIGH);  // turn the LED on (HIGH is the voltage level)

   delay(250);                  // wait for a 250ms, more than enough time to recognize a flash

   digitalWrite(led1, LOW);      // turn the LED off by making the voltage LOW

   delay(800);                  // wait 800ms, can be adjusted however too slow is tedious and too 

                                                    //fast is easy to miss a blink

 }

 delay(2000);                                          

I found that because the unit was outdoors the temperature of the tank was almost always the same temperature as the air. It did have a bit of lag time but it wasn't too much. So I didn't keep that one until I stared heating the water.