/*
 *  Arduino-Nano  12 V  UPS / INVERTER
 *  50 Hz SPWM 23.4 kHz carrier  –  3-stage charger  –  20×4 I²C LCD
 *  ONE button ON/OFF  –  NTC + FAN  –  single CT  –  mains detect relay
 *
 *  License: MIT  –  use on your own risk
 */

#include <Wire.h>
#include <LiquidCrystal_I2C.h>
#include <math.h>

LiquidCrystal_I2C lcd(0x27, 20, 4);   // I²C address change if required

//------------------------- USER CONSTANTS ---------------------------
const float VBULK      = 14.4;
const float VFLOAT     = 13.5;
const float VBAT_LOW   = 10.8;        // inverter shutdown
const float VBAT_HIGH  = 15.0;        // over-voltage shutdown
const float TEMP_MAX   = 70.0;        // °C on heatsink
const float CT_BURDEN  = 33.0;        // ohm
const float CT_RATIO   = 1000.0;      // 1000:1 CT
const float ACSENS     = (5.0/1023.0);

//------------------------ PIN DEFINITIONS ---------------------------
#define H1  3
#define L1  4
#define H2  5
#define L2  6
#define FAN 7
#define RELAY 8
#define CHG_PWM 10          // charger buck
#define BTN 2
#define BEEP 9

//------------------------ GLOBALS ----------------------------------
volatile bool systemON = false;
volatile bool mainsPresent = false;
volatile bool chargerMode = false;

const uint8_t sineTable[256] PROGMEM = {
  128,131,134,137,140,143,146,149,152,155,158,161,164,167,170,173,
  176,179,182,184,187,190,193,195,198,201,203,206,208,211,213,216,
  218,220,223,225,227,229,231,233,235,237,239,241,242,244,246,247,
  249,250,251,253,254,255,255,256,257,258,258,259,259,260,260,260,
  260,260,260,260,259,259,258,258,257,256,255,255,254,253,251,250,
  249,247,246,244,242,241,239,237,235,233,231,229,227,225,223,220,
  218,216,213,211,208,206,203,201,198,195,193,190,187,184,182,179,
  176,173,170,167,164,161,158,155,152,149,146,143,140,137,134,131,
  128,125,122,119,116,113,110,107,104,101, 98, 95, 92, 89, 86, 83,
   80, 77, 74, 72, 69, 66, 63, 61, 58, 55, 53, 50, 48, 45, 43, 40,
   38, 36, 33, 31, 29, 27, 25, 23, 21, 19, 17, 15, 14, 12, 10, 9,
    7, 6, 5, 3, 2, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0,
    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 2, 3,
    5, 6, 7, 9,10,12,14,15,17,19,21,23,25,27,29,31,
   33,36,38,40,43,45,48,50,53,55,58,61,63,66,69,72,
   74,77,80,83,86,89,92,95, 98,101,104,107,110,113,116,119,122,125
};

volatile uint16_t spwmIndex = 0;

//------------------------ PROTOTYPES -------------------------------
void timer2Init();
float readVbat();
float readTemp();
float readAmps();
bool readMains();
void updateLCD(float vbat, float amp, float temp);
void beep(uint8_t n);
void shutdown();
void updateCharger(float vbat);

//------------------------ SETUP ------------------------------------
void setup() {
  // Initialize pins
  pinMode(H1, OUTPUT); 
  pinMode(L1, OUTPUT);
  pinMode(H2, OUTPUT);
  pinMode(L2, OUTPUT);
  pinMode(FAN, OUTPUT);
  pinMode(RELAY, OUTPUT);
  pinMode(CHG_PWM, OUTPUT);
  pinMode(BEEP, OUTPUT);
  pinMode(BTN, INPUT_PULLUP);
  
  // Ensure all outputs are OFF
  digitalWrite(H1, LOW);
  digitalWrite(L1, LOW);
  digitalWrite(H2, LOW);
  digitalWrite(L2, LOW);
  digitalWrite(FAN, LOW);
  digitalWrite(RELAY, LOW);
  digitalWrite(CHG_PWM, LOW);
  digitalWrite(BEEP, LOW);

  // Initialize LCD
  Wire.begin();
  lcd.init();
  lcd.backlight();
  lcd.setCursor(0,0); lcd.print("Nano-UPS  50Hz");
  lcd.setCursor(0,1); lcd.print(" 23.4k SPWM");
  delay(1500);

  timer2Init();        // start SPWM
  ADC_ENABLE();
  beep(2);
}

//------------------------ MAIN LOOP --------------------------------
void loop() {
  static uint32_t tmr = 0;
  static uint32_t chargerTmr = 0;
  
  if (millis() - tmr >= 200) {          // 5 Hz refresh
    tmr = millis();
    
    float vbat = readVbat();
    float temp = readTemp();
    float amp  = readAmps();
    mainsPresent = readMains();

    //----- Button ON/OFF (long press >700 ms) ----------------------
    static bool lastBtn = HIGH;
    static uint32_t btnT = 0;
    bool b = digitalRead(BTN);
    
    if (!b && lastBtn) {  // Button pressed
      btnT = millis();
    }
    if (b && !lastBtn && (millis() - btnT > 700)) {  // Released after long press
      systemON = !systemON;
      if (systemON) beep(1);
    }
    lastBtn = b;

    //----- Protection checks ---------------------------------------
    if (vbat < VBAT_LOW || vbat > VBAT_HIGH || temp > TEMP_MAX) {
      shutdown();
    }

    //----- Mode selection ------------------------------------------
    if (mainsPresent) {
      digitalWrite(RELAY, HIGH);      // mains route
      chargerMode = true;
    } else {
      digitalWrite(RELAY, LOW);       // inverter route
      chargerMode = false;
      digitalWrite(CHG_PWM, LOW);     // Turn off charger
    }

    //----- Charger control -----------------------------------------
    if (chargerMode && systemON) {
      if (millis() - chargerTmr >= 100) {  // 10 Hz charger update
        chargerTmr = millis();
        updateCharger(vbat);
      }
    } else {
      digitalWrite(CHG_PWM, LOW);
    }

    //----- FAN control ---------------------------------------------
    digitalWrite(FAN, temp > 45);

    //----- LCD update ----------------------------------------------
    updateLCD(vbat, amp, temp);
  }
}

//------------------------ ADC READINGS -----------------------------
float readVbat() {
  uint16_t a = analogRead(A0);
  return a * ACSENS * 4.0 * (16.0 / 15.0);   // divider 1/4 + calib
}

float readTemp() {
  uint16_t a = analogRead(A1);
  if (a == 0) return 25.0;  // Avoid division by zero
  float r = 10000.0 * (1023.0 / a - 1.0);   // NTC 10k @25°C β=3950
  float t = 1.0 / (log(r/10000.0)/3950.0 + 1.0/298.15) - 273.15;
  return t;
}

float readAmps() {
  uint16_t a = analogRead(A2);
  float v = (a - 512) * ACSENS;
  return abs(v) * CT_RATIO / CT_BURDEN;    // amps
}

bool readMains() {
  uint16_t a = analogRead(A3);
  return (a > 400);                         // ~1 V AC detected
}

//------------------------ CHARGER CONTROL --------------------------
void updateCharger(float vbat) {
  static uint8_t pwmValue = 0;
  
  if (vbat < VBULK) {
    // Bulk charging
    pwmValue = 255;  // Full power
  } else if (vbat < VFLOAT) {
    // Absorption charging
    pwmValue = 128;  // Half power
  } else {
    // Float charging
    pwmValue = 64;   // Low power
  }
  
  analogWrite(CHG_PWM, pwmValue);
}

//------------------------ LCD --------------------------------------
void updateLCD(float vbat, float amp, float temp) {
  lcd.setCursor(0,0);
  lcd.print("Vbat "); lcd.print(vbat,1); lcd.print("V   ");
  
  lcd.setCursor(0,1);
  lcd.print("Amp  "); lcd.print(amp,1); lcd.print("A   ");
  
  lcd.setCursor(0,2);
  lcd.print("Temp "); lcd.print(temp,0); lcd.print("C   ");
  
  lcd.setCursor(0,3);
  if (systemON) {
    lcd.print(mainsPresent ? "UPS  " : "INV  ");
  } else {
    lcd.print("OFF  ");
  }
  
  // Calculate load percentage (assuming max 10A = 100%)
  int loadPercent = constrain((int)(amp * 10), 0, 100);
  lcd.print("Load "); lcd.print(loadPercent); lcd.print("%   ");
}

//------------------------ BEEP / SHUTDOWN ---------------------------
void beep(uint8_t n) { 
  for(uint8_t i = 0; i < n; i++) {
    digitalWrite(BEEP, HIGH);
    delay(80);
    digitalWrite(BEEP, LOW);
    delay(80);
  }
}

void shutdown() {
  systemON = false;
  digitalWrite(H1, LOW);
  digitalWrite(L1, LOW);
  digitalWrite(H2, LOW);
  digitalWrite(L2, LOW);
  digitalWrite(CHG_PWM, LOW);
  digitalWrite(RELAY, LOW);
  
  lcd.clear();
  lcd.setCursor(0,0);
  lcd.print("SYSTEM SHUTDOWN!");
  lcd.setCursor(0,1);
  lcd.print("Check battery/temp");
  
  beep(6);
  while(1) {
    // Flash LED or provide status indication
    digitalWrite(BEEP, HIGH);
    delay(100);
    digitalWrite(BEEP, LOW);
    delay(2000);
  }
}

//------------------------ TIMER-2 SPWM ------------------------------
ISR(TIMER2_OVF_vect) {
  if (!systemON || chargerMode) {  // mute bridge when charging or off
    OCR2A = 0;
    OCR2B = 0;
    digitalWrite(H1, LOW);
    digitalWrite(L1, LOW);
    digitalWrite(H2, LOW);
    digitalWrite(L2, LOW);
    return;
  }
  
  uint8_t sa = pgm_read_byte(&sineTable[spwmIndex]);
  uint8_t sb = pgm_read_byte(&sineTable[(spwmIndex + 128) & 255]);
  
  OCR2A = sa;   // PWM 1
  OCR2B = sb;   // PWM 2
  
  // H-bridge control with dead time
  if (sa > 5) {
    digitalWrite(L1, LOW);
    digitalWrite(H1, HIGH);
  } else {
    digitalWrite(H1, LOW);
    digitalWrite(L1, HIGH);
  }
  
  if (sb > 5) {
    digitalWrite(L2, LOW);
    digitalWrite(H2, HIGH);
  } else {
    digitalWrite(H2, LOW);
    digitalWrite(L2, HIGH);
  }
  
  spwmIndex = (spwmIndex + 1) & 255;  // Wrap around
}

void timer2Init() {
  // Timer-2 fast-pwm 23.4 kHz non-inverting
  TCCR2A = _BV(COM2A1) | _BV(COM2B1) | _BV(WGM20) | _BV(WGM21);
  TCCR2B = _BV(WGM22) | _BV(CS20);    // prescaler = 1
  OCR2A = 0;  // Start with PWM off
  OCR2B = 0;
  TIMSK2 = _BV(TOIE2);   // enable overflow interrupt
}

// MACROS (moved to end to avoid potential issues)
#define ADC_ENABLE()  (ADCSRA |=  _BV(ADEN))
#define ADC_START()   (ADCSRA |=  _BV(ADSC))