#include "RTClib.h"

const int dataPin = 2;   /* DS */
const int clockPin = 3;  /* SHCP */
const int latchPin = 4;  /* STCP */

RTC_DS1307 rtc;
DateTime now;
uint8_t hour, minute, second;

void setup () {
  Serial.begin(115200);

  pinMode(dataPin, OUTPUT);
  pinMode(clockPin, OUTPUT);
  pinMode(latchPin, OUTPUT);

  if (! rtc.begin()) {
    Serial.println("Couldn't find RTC");
    Serial.flush();
    abort();
  }
}

void update_time()
{
  DateTime now = rtc.now();

  hour = now.hour();
  minute = now.minute();
  second = now.second();
}

void write_time()
{
  digitalWrite(latchPin, LOW);
  shiftOut(dataPin, clockPin, MSBFIRST, hour);
  shiftOut(dataPin, clockPin, MSBFIRST, minute);
  shiftOut(dataPin, clockPin, MSBFIRST, second);
  digitalWrite(latchPin, HIGH);
}

void loop () {
  update_time();
  write_time();
}