This is the SparkFun Real Time Clock (RTC) Module, this little breakout that uses the DS1307 to keep track of the current year, month, day as well as the current time. The module comes fully assembled and includes a small CR1225 Lithium coin cell battery that will run the RTC for a minimum of 9 years (17 years typical) without an external 5V power supply.
The DS1307 RTC is accessed via the I2C protocol. We've written a test-bed to program the modules, this code should give you some insight on how to interface the module to any microcontroller using our example software I2C and BCD routines.
This rev of the Real Time Clock module finally adds I2C resistors and a larger battery pad to fix the problems with the battery shorting to the board.
Get Started with the RTC Module Hookup Guide
