RelogioTimer1

  #include "TimerOne.h"
  #include <LiquidCrystal_I2C.h>
  byte hora = 0;
  int hora1 = 0;
  byte minu = 0;
  int minu1 = 0;
  byte segu = 0;
  int segu1 = 0;
  unsigned long tempo = 0;
  unsigned long valor = 0;
//#include <LiquidCrystal.h>

//LiquidCrystal lcd(6, 7, 4, 5, 2, 3); //Configura os pinos do Arduino para se comunicar com o LCD
 LiquidCrystal_I2C lcd(0x38,  2, 1, 0, 7, 6, 5, 4, 3, POSITIVE);  // Set the LCD I2C address
  //---------------------------------
  void setup()
  {
    lcd.begin(16,2);
    Serial.begin(9600);
    pinMode(13, OUTPUT);
    Timer1.initialize(1000000);         // initialize timer1, and set a 1/2 second period
    Timer1.attachInterrupt(callback);  // attaches callback() as a timer overflow interrupt
  }
  //--------------------------------------
  void callback()
  {
    digitalWrite(13, digitalRead(13) ^ 1);
    tempo++;
    if (tempo >= 86400) tempo = 0;
  }
  //--------------------------------------
  void loop()
  {
    if (Serial.available() > 0)
    {
      valor =  Serial.parseInt();
      tempo = tempo + valor;
    }
    hora = tempo / 3600;
    hora1 = hora * 3600;
    minu1 = tempo - hora1;
    minu = minu1/60;
    segu1 = minu*60 + hora1;
    segu = tempo - segu1;

    lcd.setCursor(1,0);
    if (hora < 10)
      lcd.print("0");
    lcd.print(hora);
    lcd.print(":");
    if (minu < 10)
      lcd.print("0");
    lcd.print(minu);
    lcd.print(":");
    if (segu < 10)
      lcd.print("0");
    lcd.print(segu);
  }