#include <SPI.h>
#include <SD.h>

const float BETA = 3950; // Beta coefficient of the thermistor
const int chipSelect = 10; // Pin connected to the CS line of the SD card

void init_ADC(void);
unsigned char start_ADC(void);
uint16_t read_ADC(void);
void Temp(uint16_t value); // Function declaration

void setup() {
  Serial.begin(9600);
  init_ADC();
  start_ADC();

  // Initialize SD card
  if (!SD.begin(chipSelect)) {
    Serial.println("SD card initialization failed!");
    return;
  }
  Serial.println("SD card initialized.");

  // Open the file and write the header if needed
  File dataFile = SD.open("temperature.txt", FILE_WRITE);
  if (dataFile) {
    dataFile.println("Time, Temperature (C)"); // Write header if this is a new file
    dataFile.close();
  } else {
    Serial.println("Error opening temperature.txt");
  }
}

void loop() {
  // Read ADC and store temperature data
  uint16_t x = read_ADC();
  Temp(x); // Pass ADC value to Temp function
  
  delay(1000); // Log temperature every second
}

void init_ADC() {
  volatile char *admux = (volatile char *)0x7C;
  volatile char *adcsra = (volatile char *)0x7A;
  *admux = 0x40; // Internal 1.1V voltage reference with external capacitor at AREF pin
  sei();         // Enable global interrupt;
  *adcsra = 0xA7; // 11000111: 128 prescaler, ADC enable, start ADC
}

unsigned char start_ADC() {
  volatile char *adcsra = (volatile char *)0x7A;
  *adcsra = *adcsra | 0x40; // Starting the ADC
}

uint16_t read_ADC() {
  volatile char *adcsra = (volatile char *)0x7A;
  volatile unsigned char *L = (volatile unsigned char *)0x78;
  volatile unsigned char *H = (volatile unsigned char *)0x79;
  uint16_t value;
  while ((*adcsra & 0x10) == 0); // Wait for conversion to be completed
  value = (*H << 8) | *L;  // Combine the upper and lower bits to get 10-bit result
  *adcsra = *adcsra | 0x10; // Clear the flag
  return value;
}

void Temp(uint16_t value) {
  float analogValue = float(value); // Convert to float
  float celsius = 1 / (log(1 / (1023. / analogValue - 1)) / BETA + 1.0 / 298.15) - 273.15;

  // Print temperature to serial monitor
  Serial.print("Temperature: ");
  Serial.print(celsius);
  Serial.println(" C");

  // Open the file to append the temperature data
  File dataFile = SD.open("temperature.txt", FILE_WRITE);
  if (dataFile) {
    // Write temperature to SD card file
    dataFile.print(millis() / 1000); // Log time in seconds since program start
    dataFile.print(", ");
    dataFile.print(celsius);
    dataFile.println(" C");
    dataFile.close(); // Close the file to save the data
  } else {
    Serial.println("Error opening temperature.txt");
  }
}