1Hz

//  DS1307 Square-wave machine sketch for Arduino
 
#include "Wire.h"
#define DS1307_I2C_ADDRESS 0x68 // each I2C object has a unique bus address, the DS1307 is 0x68
 
void setup()
{
  Wire.begin();
}
 
void sqw1() // set to 1Hz
{
  Wire.beginTransmission(DS1307_I2C_ADDRESS);
  Wire.write(0x07); // move pointer to SQW address
  Wire.write(0x10); //  sends 0x10 (hex) 00010000 (binary)
  Wire.endTransmission();
}
 
void sqw2() // set to 4.096 kHz
{
  Wire.beginTransmission(DS1307_I2C_ADDRESS);
  Wire.write(0x07); // move pointer to SQW address
  Wire.write(0x11); //  sends 0x11 (hex) 00010001 (binary)
  Wire.endTransmission();
}
 
void sqw3() // set to 8.192 kHz
{
  Wire.beginTransmission(DS1307_I2C_ADDRESS);
  Wire.write(0x07); // move pointer to SQW address
  Wire.write(0x12); // sends 0x12 (hex) 00010010 (binary)
  Wire.endTransmission();
}
 
void sqw4() // set to 32.768 kHz (the crystal frequency)
{
  Wire.beginTransmission(DS1307_I2C_ADDRESS);
  Wire.write(0x07); // move pointer to SQW address
  Wire.write(0x13); // sends 0x13 (hex) 00010011 (binary)
  Wire.endTransmission();
}
 
void sqwOff()
// turns the SQW off
{
  Wire.beginTransmission(DS1307_I2C_ADDRESS);
  Wire.write(0x07); // move pointer to SQW address
  Wire.write(0x00); // turns the SQW pin off
  Wire.endTransmission();
}
 
void loop()
{
  sqw1();
  do {} while (1);
}