// I tested this 5/14/25, it works irl!!!! Now with RTC + PPM

#include <Wire.h>
#include "RTClib.h"

#define MQ2pin 2 // or 26, either is fine
#define Buzzer 5 // can be any
#define RL 10.0  // load resistor in kΩ
#define Ro 3.3   // default Ro in clean air (kΩ), approximated
int dangerPPM = 2000; // 2000 ppm threshold for LPG alert

RTC_DS3231 rtc;

char daysOfTheWeek[7][12] = {"Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday"};

// function to read Rs using analog voltage
float readRs(int analogPin, float RL) {
  int adc = analogRead(analogPin);
  float voltage = adc * (3.3 / 1023.0);  // 5 represents the voltage
  float rs = (3.3 - voltage) * RL / voltage;
  return rs;
}

// function to estimate LPG PPM based on Rs/Ro ratio
float estimateLPGppm(float rs, float ro) {
  float rs_ro_ratio = rs / ro;

  // LPG curve approximation from datasheet
  float m = -0.38;
  float b = 1.15;

  float logRatio = log10(rs_ro_ratio);
  float logPPM = (logRatio - b) / m;
  float ppm = pow(10, logPPM);

  return ppm;
}

void setup() {
  Serial.begin(9600);
  pinMode(Buzzer, OUTPUT);
  Serial.println("MQ2 warming up!");

  // allow the MQ2 to warm up
  delay(20000);

  // start RTC
  if (!rtc.begin()) {
    Serial.println("Couldn't find RTC");
    while (1) delay(10);
  }

  if (rtc.lostPower()) {
    Serial.println("RTC lost power, setting time to compile time");
    rtc.adjust(DateTime(F(__DATE__), F(__TIME__)));
  }
}

void loop() {
  // get sensor reading and convert to PPM
  float rs = readRs(MQ2pin, RL);
  float ppm = estimateLPGppm(rs, Ro);

  // get RTC time
  DateTime now = rtc.now();
  String yearStr = String(now.year(), DEC);
  String monthStr = (now.month() < 10 ? "0" : "") + String(now.month(), DEC);
  String dayStr = (now.day() < 10 ? "0" : "") + String(now.day(), DEC);
  String hourStr = (now.hour() < 10 ? "0" : "") + String(now.hour(), DEC); 
  String minuteStr = (now.minute() < 10 ? "0" : "") + String(now.minute(), DEC);
  String secondStr = (now.second() < 10 ? "0" : "") + String(now.second(), DEC);
  String dayOfWeek = daysOfTheWeek[now.dayOfTheWeek()];
  String timestamp = dayOfWeek + ", " + yearStr + "-" + monthStr + "-" + dayStr + " " + hourStr + ":" + minuteStr + ":" + secondStr;

  // print readings
  Serial.print("Timestamp: ");
  Serial.println(timestamp);
  Serial.print("Sensor Rs: ");
  Serial.print(rs);
  Serial.print(" kΩ, Estimated LPG PPM: ");
  Serial.println(ppm);

  // if ppm exceeds threshold, activate buzzer
  if (ppm >= dangerPPM) {
    Serial.println("Danger: Gas concentration exceeded safe limit");
    digitalWrite(Buzzer, HIGH); // buzzer on 
    delay(20000); // give the miner time to react
    digitalWrite(Buzzer, LOW); // buzzer off 
  }

  delay(15000); // sample every 15 seconds
}