real time clck -RTC DS 1307- to Arduino

Question

I am trying to connect the ds1307 to Arduino to get the the time on the LCD and I used this circuit in my project and I tried the example code in the library but it didn't work. What could the problem be?

the code:

#include <Wire.h>
#include "RTClib.h"

RTC_DS1307 RTC;

void setup () {
    Serial.begin(57600);
    Wire.begin();
    RTC.begin();

  if (! RTC.isrunning()) {
    Serial.println("RTC is NOT running!");
    // following line sets the RTC to the date & time this sketch was compiled
    //RTC.adjust(DateTime(__DATE__, __TIME__));
  }

}

void loop () {
    DateTime now = RTC.now();

    Serial.print(now.year(), DEC);
    Serial.print('/');
    Serial.print(now.month(), DEC);
    Serial.print('/');
    Serial.print(now.day(), DEC);
    Serial.print(' ');
    Serial.print(now.hour(), DEC);
    Serial.print(':');
    Serial.print(now.minute(), DEC);
    Serial.print(':');
    Serial.print(now.second(), DEC);
    Serial.println();

    Serial.print(" since 1970 = ");
    Serial.print(now.unixtime());
    Serial.print("s = ");
    Serial.print(now.unixtime() / 86400L);
    Serial.println("d");

    // calculate a date which is 7 days and 30 seconds into the future
    DateTime future (now.unixtime() + 7 * 86400L + 30);

    Serial.print(" now + 7d + 30s: ");
    Serial.print(future.year(), DEC);
    Serial.print('/');
    Serial.print(future.month(), DEC);
    Serial.print('/');
    Serial.print(future.day(), DEC);
    Serial.print(' ');
    Serial.print(future.hour(), DEC);
    Serial.print(':');
    Serial.print(future.minute(), DEC);
    Serial.print(':');
    Serial.print(future.second(), DEC);
    Serial.println();

    Serial.println();
    delay(3000);
}

============================

Answer 1

It won't work if there are no pullups on the lines, because I2C uses an open drain bus.

Add a 2.2kΩ resistor (can be anything between this and 10kΩ, a lower value is better for long lines and higher clock speed) from SCL to +5V and also another one from SDA to +5V (so one between DS1307 pins 5 and 8, another one between pins 6 and 8) .

The resistors (marked Rp) are shown below:

If you need the square wave out, you will also need a pullup on this too, details are in the datasheet.