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This example works to synchronize the DS3231 RTC clock chip with Network Time Protocol (NTP) or local computer time by way of microUSB connection to a computer.

To synchronize the clock:

  1. Ensure that you have the DS3231 library installed on your system.
  2. Power your main processor board and connect the DS3231 RTC chip to it (if necessary). Attach your processor board to your computer and make sure it is visible as a virtual COM port.
  3. Download PCsync.ino or copy and paste its contents into a new sketch and upload it to your board.
  4. Verify on the serial port monitor that your board is outputting a date and time value. If you have just powered your RTC for the first time, the date and time will be shortly after January 1, 2000. (The serial port baudrate should be set to 57600.)
  5. To synchronize manually: Send the current unix time preceded by a T over the serial port (ie, T1484241080). It is best to send a time just a few seconds in advance of the current time because it does take a few seconds for it to initialize. The current unix time stamp can be found at or
  6. To synchronize automatically: After uploading PCsync.ino to the device, close the serial port monitor. Download and run PCsync.exe. This will automatically detect and communicate with the RTC and set the clock to within 1 second of either the local computer time or, if the computer is connected to the internet, the US Network Time Protocol service. The time will be set in UTC, not whatever the local timezone is.
  7. If desired, verify that your clock is set correctly by monitoring your device on the serial port and comparing the output time to Remember that the time on will be shown in your current time zone and the clock will be set in UTC.


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