mine.cpp

#include <EEPROM.h>
float tempC;
int reading;
int tempPin = 0;
int EAdress = 0;

void setup () {
  analogReference(INTERNAL);
}

void writeTemp(float temp) {
  EEPROM.write(EAdress, temp);
  EAdress += 4;
}

void loop () {
  reading = analogRead(tempPin);
  tempC = reading / 9.31;
  writeTemp(tempC);
  delay(15 * 60 * 1000 / 30); // 15 minutes * 60 seconds * 1000 milliseconds / 30 seconds
}