skip navigational linksPJRC
Shopping Cart Checkout Shipping Cost Download Website
Home MP3 Player 8051 Tools All Projects PJRC Store Site Map
You are here: Teensy Teensyduino Libraries DS1307RTC

PJRC Store
Teensy 3.2, $19.80
Teensy LC, $11.65
Teensy 2.0, $16.00
Teensy++ 2.0, $24.00
Main Page
Teensy 3.2 / 3.1
Getting Started
How-To Tips
Code Library

DS1307RTC Library

DS1307RTC allows you to access real time clock (RTC) chips compatible with the DS1307. It is intended to be used with the Time library.


Hardware Requirements

DS1307RTC works with the DS1307, DS1337 and DS3231 real time clock chips.

The DS1307 chip only works with 5 volt power. The DS1337 and DS3231 can use 3.3 or 5 volts.

Teensy 3.0 has a built-in RTC, so the DS1337 offers little benefit. However, the DS3231 includes a temperature compensated crystal, so it is recommended for applications requiring high accuracy.

The ChronoDot board provides the DS3231 chip in an easy-to-use package. For use with Teensy 3.0, you must add pullup resistors for the SDA and SCL signals.

Basic Usage


Reads the current date & time as a 32 bit "time_t" number. Zero is returned if the DS1307 is not running or does not respond.


Sets the date & time, using a 32 bit "time_t" number. Returns true for success, or false if any error occurs.;

Read the current date & time as TimeElements variable. See the Time library for TimeElements details. Returns true on success, or false if the time could not be read.


Sets the date & time, using a TimeElements variable. Returns true for


Returns true if a DS1307 compatible chip was present after using the 4 functions. If an error occurs, this can be used to distinguish between a DS1307 that is not running vs no chip connected at all.

Example Program

DS1307RTC includes 2 examples, to read or set the time.

You can open this example from File > Examples > DS1307RTC > ReadTest.

#include <DS1307RTC.h>
#include <Time.h>
#include <Wire.h>

void setup() {
  while (!Serial) ; // wait for serial
  Serial.println("DS1307RTC Read Test");

void loop() {
  tmElements_t tm;

  if ( {
    Serial.print("Ok, Time = ");
    Serial.print(", Date (D/M/Y) = ");
  } else {
    if (RTC.chipPresent()) {
      Serial.println("The DS1307 is stopped.  Please run the SetTime");
      Serial.println("example to initialize the time and begin running.");
    } else {
      Serial.println("DS1307 read error!  Please check the circuitry.");

void print2digits(int number) {
  if (number >= 0 && number < 10) {