/**
  Assumes a 10K@25℃ NTC thermistor connected in series with a 10K resistor.
*/
#include <SD.h>
#define CS_PIN 10
String filename = "Arduino_Project.txt";
File curFile;

void setup() {
  Serial.begin(9600);
  if (!SD.begin(CS_PIN)) {
    Serial.println("Card initialization failed!");
    while (true);
  }
}

void loop() {
  // Turn an analog signal into a temperature measurement  
  int tempValue = analogRead(A0);
  float temperature = 1 / (log(1 / (1023. / tempValue - 1)) / 3950 + 1.0 / 298.15) - 273.15;
  
  Serial.print("The current temperature is: ");
  Serial.print(temperature);
  Serial.println(" C");

  // Save the temperature reading to the SD card
  curFile = SD.open(filename, FILE_WRITE); 
  if (curFile) {
    curFile.println(temperature);
    curFile.close();
  } else {
    Serial.println("error writing to file");
  }

  // Read all logged temperatures and average them
  curFile = SD.open(filename, FILE_READ);
  if (curFile) {
    float tempSum = 0.0;
    int tempCount = 0;
    while (curFile.available()) {
      tempSum += curFile.readStringUntil('\n').toFloat();
      tempCount++;
    }
    curFile.close();

    Serial.print("The average temperature measured is: ");
    Serial.print(tempSum/tempCount);
    Serial.println(" C \n");
  } else {
    Serial.println("error reading from file");
  }
  delay(2000);
}