This is a great battery-backed (battery is NOT included) real time clock (RTC) that allows your microcontroller project to keep track of time even if it is reprogrammed, or if the power is lost.  Perfect for data logging, clock-building, time stamping, timers, and alarms.  Works great with an Arduino and Raspberry Pi.

The DS1307 RTC is accessed via the I2C protocol.

Note: This product does not come with a CR1220 coin cell battery.