badassery.ino

#include <LiquidCrystal.h>

const int buttonPin = 2;

/* volatile means tells compiler not to optimize these
 * since they might be updated from an ISR
 */
volatile int hours, minutes, seconds;

LiquidCrystal lcd(12, 11, 6, 5, 4, 3);

void setup() {
  
  //TIMER
  //why use a library when you could write directly to registers?!
  TCCR1A = 0;// disable PWM and diconnect digital pin 11 from timer1
  TCCR1B = 0;// use falling edge
  TCNT1  = 0;//initialize counter value to 0
  
  // set compare match register for 1hz increments
  OCR1A = 15624;// = (16*10^6) / (1*1024) - 1 (must be <65536)
  TCCR1B |= (1 << WGM12); //actually clear overflow register on match
  TCCR1B |= (1 << CS12) | (1 << CS10); // Set CS10 and CS12 bits for 1024 prescaler
  TIMSK1 |= (1 << OCIE1A); // jump to the input capture interrupt vector on match

  //RESET BUTTON
  EICRA |= 0x3; // rising edge of INT0
  EIMSK |= 0x1; // enable INT0

  // set up the LCD's number of columns and rows
  lcd.begin(16, 2);
}

void loop() {
  lcd.setCursor(0, 1);
  char t[9];
  sprintf(t, "%2.2i:%2.2i:%2.2i", hours, minutes, seconds);
  lcd.print(t);
}

ISR(INT0_vect){
  hours = 0;
  seconds = 0;
  minutes = 0;
}

// Interrupt is called once a millisecond,
SIGNAL(TIMER1_COMPA_vect)
{
  seconds++;
  if (seconds % 60 == 0 && seconds > 0) {
    seconds = 0;
    minutes++;
  }
  if (minutes % 60 == 0 && minutes > 0) {
    minutes = 0;
    hours++;
  }
}