/*
 Project: 4 digit 7 segment display module /common cathode/ Thermistor 10 KOhm
 Function: Temperature displayed on 4 digit 7 segment display
 */
/****************************************************************************/
const int digitPins[4] = {4,5,6,7}; //4 common cathode pins of the display
const int clockPin = 11;    //74HC595 Pin 11 SHcp
const int latchPin = 12;    //74HC595 Pin 12 STcp
const int dataPin = 13;     //74HC595 Pin 14 DS
const int sensorPin =A0;    //Thermistor 10 KOhm attached to analog pin A0
const byte digit[10] =      //seven segment digits in bits
{
  B11000000, //0
  B11111001, //1
  B10100100, //2
  B10110000, //3
  B10011001, //4
  B10010010, //5
  B10000010, //6
  B11111000, //7
  B10000000, //8
  B10010000  //9
 };
int digitBuffer[4] = {0};
int digitScan = 0;
double Thermistor(int RawADC) {
  double Temp;
  Temp = log(10000.0 * ((1023.0 / RawADC - 1)));
  Temp = 1 / (0.001129148 + (0.000234125 + (0.0000000876741 * Temp * Temp )) * Temp );
  Temp = Temp - 273.15;
  Temp = (Temp * 9.0) / 5.0 + 32.0;
  return Temp;
}
/**********************************************************************/
void setup(){                
  for(int i=0;i<4;i++)
  {
    pinMode(digitPins[i],OUTPUT);
  }
  pinMode(sensorPin, INPUT);
  pinMode(latchPin, OUTPUT);
  pinMode(clockPin, OUTPUT);
  pinMode(dataPin, OUTPUT);  
 Serial.begin(9600);
}
 
//writes the temperature on display
void updateDisp(){
  for(byte j=0; j<4; j++)  
    digitalWrite(digitPins[j], HIGH);
 
  digitalWrite(latchPin, LOW);  
shiftOut(dataPin, clockPin, MSBFIRST, B00000000);
 digitalWrite(latchPin, HIGH);
 
delayMicroseconds(1000);
  digitalWrite(digitPins[digitScan], LOW); 
 
  digitalWrite(latchPin, LOW);  
 
    shiftOut(dataPin, clockPin, MSBFIRST, ~digit[digitBuffer[digitScan]]);
 if(digitScan==2){
    shiftOut(dataPin, clockPin, MSBFIRST, ~(digit[digitBuffer[digitScan]] & B01111111)); //print the decimal point on the 3rd digit
    }
 
  digitalWrite(latchPin, HIGH);
  digitScan++;
  if(digitScan>3) digitScan=0; 
}

void loop(){ 
double temp;
  int val = analogRead(sensorPin);
  temp = Thermistor(val);
  float celsius = (temp-32)*5/9;
 //Fahrenheit temperature display - uncomment if you want to use it
 /* digitBuffer[3] = (int(temp) % 100) / 10;
  digitBuffer[2] = (int(temp) % 100) % 10;
  digitBuffer[1] = (int(temp) % 1000) / 100;
  digitBuffer[0] = int(temp) / 1000;
  updateDisp();
  delay(2);
  */
  //Celsius temperature display - comment if you do not want to use it
  digitBuffer[3] = (int(celsius) % 100) / 10;
  digitBuffer[2] = (int(celsius) % 100) % 10;
  digitBuffer[1] = (int(celsius) % 1000) / 100;
  digitBuffer[0] = int(celsius) / 1000;
  updateDisp();
  delay(2);
}