Arduino sketch that will put a DS3231 time keeping chip into a low power mode where it outputs a 1Hz square wave (pull up needed)

gistfile1.txt

#include "Wire.h"
#define DS3231_I2C_ADDRESS 0x68

#define DS_REG_CR (0x0e)    // Control Reg
#define DS_REG_SR (0x0f)    // Status Reg

// Pins connected to the DS2321
// We want to know these so we can put them HI_Z when not talking to the board to get a real power measurement. 
#define D_SCLK A5
#define D_SDAT A4
#define D_VIN  A3
#define D_GND  A2

// Base code stolen from 
// http://tronixstuff.com/2014/12/01/tutorial-using-ds1307-and-ds3231-real-time-clock-modules-with-arduino/

// Convert normal decimal numbers to binary coded decimal
byte decToBcd(byte val)
{
  return( (val/10*16) + (val%10) );
}
// Convert binary coded decimal to normal decimal numbers
byte bcdToDec(byte val)
{
  return( (val/16*10) + (val%16) );
}
void setDS3231time(byte second, byte minute, byte hour, byte dayOfWeek, byte
dayOfMonth, byte month, byte year)
{
  // sets time and date data to DS3231
  Wire.beginTransmission(DS3231_I2C_ADDRESS);
  Wire.write(0); // set next input to start at the seconds register
  Wire.write(decToBcd(second)); // set seconds
  Wire.write(decToBcd(minute)); // set minutes
  Wire.write(decToBcd(hour)); // set hours
  Wire.write(decToBcd(dayOfWeek)); // set day of week (1=Sunday, 7=Saturday)
  Wire.write(decToBcd(dayOfMonth)); // set date (1 to 31)
  Wire.write(decToBcd(month)); // set month
  Wire.write(decToBcd(year)); // set year (0 to 99)
  Wire.endTransmission();
}

// Set reg r to v

void setReg( uint8_t r, uint8_t v ){
  Wire.beginTransmission(DS3231_I2C_ADDRESS);  
  Wire.write(r); 
  Wire.write( v);    
  Wire.endTransmission();  
}

void setCR()
{

  // Set Alarm 
  setReg(0x07 ,  0b10001111);    // Enable (A1M1), Set alarm 1 match to every second

  // sets Control Register on DS3231  
//  setReg(0x0e , 0b01000101);    // SQ enabled on VBAT, Alarm output on SQW pin (INITCN), Enable Alarm 1 (A1IE)

    setReg(0x0e , 0b01000000);    // SQ enabled on VBAT, Square wave enabled with 1hrz

  //Wire.write( 0b00000100);    // Assign SQ to INT pin, but without alarm enable, no output on SQW
  
  // now address is 0x0f (status reg)
//  setReg( 0x0f , 0b00000000);    // Disable the 32khz output to save power
  setReg( 0x0f , 0b00001000);    // Enaable the 32khz output 
  
}


void readDS3231time(byte *second,
byte *minute,
byte *hour,
byte *dayOfWeek,
byte *dayOfMonth,
byte *month,
byte *year)
{
  Wire.beginTransmission(DS3231_I2C_ADDRESS);
  Wire.write(0); // set DS3231 register pointer to 00h
  Wire.endTransmission();
  Wire.requestFrom(DS3231_I2C_ADDRESS, 7);
  // request seven bytes of data from DS3231 starting from register 00h
  *second = bcdToDec(Wire.read() & 0x7f);
  *minute = bcdToDec(Wire.read());
  *hour = bcdToDec(Wire.read() & 0x3f);
  *dayOfWeek = bcdToDec(Wire.read());
  *dayOfMonth = bcdToDec(Wire.read());
  *month = bcdToDec(Wire.read());
  *year = bcdToDec(Wire.read());
}

uint8_t readR(uint8_t r) {
  Wire.beginTransmission(DS3231_I2C_ADDRESS);
  Wire.write(r); // set DS3231 register pointer to 00h
  Wire.endTransmission();
  Wire.requestFrom(DS3231_I2C_ADDRESS, 1);
  // request seven bytes of data from DS3231 starting from register 00h
  return(Wire.read() & 0x7f);
}

void displayTime()
{
  byte second, minute, hour, dayOfWeek, dayOfMonth, month, year;
  // retrieve data from DS3231
  readDS3231time(&second, &minute, &hour, &dayOfWeek, &dayOfMonth, &month,
  &year);
  // send it to the serial monitor
  Serial.print(hour, DEC);
  // convert the byte variable to a decimal number when displayed
  Serial.print(":");
  if (minute<10)
  {
    Serial.print("0");
  }
  Serial.print(minute, DEC);
  Serial.print(":");
  if (second<10)
  {
    Serial.print("0");
  }
  Serial.print(second, DEC);
  Serial.print(" ");
  Serial.print(dayOfMonth, DEC);
  Serial.print("/");
  Serial.print(month, DEC);
  Serial.print("/");
  Serial.print(year, DEC);
  Serial.print(" Day of week: ");
  switch(dayOfWeek){
  case 1:
    Serial.println("Sunday");
    break;
  case 2:
    Serial.println("Monday");
    break;
  case 3:
    Serial.println("Tuesday");
    break;
  case 4:
    Serial.println("Wednesday");
    break;
  case 5:
    Serial.println("Thursday");
    break;
  case 6:
    Serial.println("Friday");
    break;
  case 7:
    Serial.println("Saturday");
    break;
  }
}

void displayRegs(void) {
  Serial.print("CR:");
  Serial.print( readR(DS_REG_CR) , BIN );
  Serial.print(" SR:");
  Serial.println( readR(DS_REG_SR) , BIN );
  
}


void powerUpDS(void) {
  digitalWrite( D_GND, 0 ); 
  pinMode( D_GND, OUTPUT);   
  
  pinMode( D_VIN, OUTPUT);   // This pin is connected to Vin
  digitalWrite( D_VIN , 1 ); // Power the board so we can talk to it.   
  
  delay(100);                // Give a moment for the board to stabilize

  //pinMode( D_SCLK, OUTPUT);   // This pin is connected to Vin
  //pinMode( D_DAT, OUTPUT);   // This pin is connected to Vin

  
}


void powerDownDS(void) {
  //pinMode( A0, INPUT);   // This pin is connected to Vin
 // pinMode( D_SCLK, INPUT);   // This pin is connected to SCLK
 // pinMode( D_SDAT, INPUT);   // This pin is connected to SDAT

 
  pinMode( D_GND, INPUT);   // This pin is connected to SDAT

  digitalWrite( D_VIN , 0 );  // ...otherwise we wll see pullup?  
  pinMode( D_VIN, INPUT);   // This pin is connected to SCLK
}

void setup()
{


  powerUpDS();
  Wire.begin();
  Serial.begin(9600);
  // set the initial time here:
  // DS3231 seconds, minutes, hours, day, date, month, year
  //setDS3231time(00,0,0,0,1,1,17);
  setCR();
  powerDownDS();
}


void loop()
{
  powerUpDS();
  displayTime(); // display the real-time clock data on the Serial Monitor,
  displayRegs();
  powerDownDS();

  delay(10000); // every 10 second
}