What time is it? The DS1307 Real Time Clock Chip knows. This tiny module will provide your project with an very accurate clock - sending the year, month, day, hour, minute and second as I2C serial data. The internal clock on an Arduino and most other microcontrollers tends to drift over time. After long periods, the internal clock may be off by several minutes or worse! Accurate clocks are important for logging data, synchronizing events, etc.