#include <SoftwareSerial.h>
#include <LiquidCrystal.h>

SoftwareSerial mySerial(3, 2); // RX, TX

// 初始化 LCD 引脚
LiquidCrystal lcd(12, 11, 5, 4, 3, 2);

//for Timer
unsigned long previousMillis = 0;
long interval = 2000;

//for voltage sensor
int analogInput = A0;
float R1 = 30000.0; //  
float R2 = 7500.0; // 

//for smoothing
const int numReadings = 20;
float readings[numReadings];      // the readings from the analog input

char buff[5];

void setup() {
  pinMode(analogInput, INPUT);
  Serial.begin(9600);

  Serial.println("Type AT commands!");
  mySerial.begin(9600);

  // 初始化 LCD
  lcd.begin(16, 2);
  lcd.print("Voltage Reader");
  lcd.setCursor(0, 1);
  lcd.print("Initializing...");
  delay(2000);
  lcd.clear();
}

void loop() {
  unsigned long currentMillis = millis();

  if (currentMillis - previousMillis > interval) {
    previousMillis = currentMillis;

    float volt = readAvg();
    Serial.println(volt, 1);
    sendData(volt);

    // 在 LCD 上显示电压
    lcd.setCursor(0, 0);
    lcd.print("Voltage: ");
    lcd.setCursor(9, 0);
    lcd.print(volt, 1);
    lcd.print(" V");
  }
}

float readCorrectVoltage() {
  // read normal Arduino value
  int adcVal = analogRead(A0);

  // read correct supply voltage
  float supply = readVcc() / 1000.0;

  float voltage = adcVal * 5.0 / 1024.0;  //AS's way
  float voltCorrected = supply / 5 * voltage;  //AS's way

  return voltCorrected;
}

long readVcc() {
  long result;
  // Read 1.1V reference against AVcc
#if defined(__AVR_ATmega32U4__) || defined(__AVR_ATmega1280__) || defined(__AVR_ATmega2560__)
  ADMUX = _BV(REFS0) | _BV(MUX4) | _BV(MUX3) | _BV(MUX2) | _BV(MUX1);
#elif defined (__AVR_ATtiny24__) || defined(__AVR_ATtiny44__) || defined(__AVR_ATtiny84__)
  ADMUX = _BV(MUX5) | _BV(MUX0);
#elif defined (__AVR_ATtiny25__) || defined(__AVR_ATtiny45__) || defined(__AVR_ATtiny85__)
  ADMUX = _BV(MUX3) | _BV(MUX2);
#else
  ADMUX = _BV(REFS0) | _BV(MUX3) | _BV(MUX2) | _BV(MUX1);
#endif
  delay(2); // Wait for Vref to settle
  ADCSRA |= _BV(ADSC); // Convert
  while (bit_is_set(ADCSRA, ADSC));
  result = ADCL;
  result |= ADCH << 8;
  result = 1126400L / result; // Calculate Vcc (in mV); 1126400 = 1.1*1024*1000
  return result;
}

float readNominalVoltage() {
  int value = analogRead(analogInput);
  float vout = (value * 5.0) / 1024.0; // see text
  float vin = vout / (R2 / (R1 + R2));

  return vin;
}

float readAvg() {
  float total = 0.0;

  // initialize all the readings to 0:
  for (int thisReading = 0; thisReading < numReadings; thisReading++) {
    readings[thisReading] = 0.0;
  }

  for (int readIndex = 0; readIndex < numReadings; readIndex++) {
    readings[readIndex] = readCorrectVoltage();
    total = total + readings[readIndex];//incremental total
    delay(1);
  }

  float averageV = total / numReadings;   // the average

  return averageV;
}

float read_running_average() {
  int total = 0;

  // initialize all the readings to 0:
  for (int thisReading = 0; thisReading < numReadings; thisReading++) {
    readings[thisReading] = 0;
  }

  for (int readIndex = 0; readIndex < numReadings; readIndex++) {
    readings[readIndex] = analogRead(analogInput);
    total = total + readings[readIndex];//incremental total
  }

  int average = total / numReadings;   // the average
  float vout = (average * 5.0) / 1024.0; // see text
  float vin = vout / (R2 / (R1 + R2));
  return vin;
}

void sendData(float volt) {
  dtostrf(volt, 4, 1, buff);

  String data = "#" + String(buff) + "~";
  mySerial.print(data);
}