Makerfire&reg; Raspberry Pi RTC Module Real Time Clock Module DS1307 Chip with Coin Battery User Manual: https://www.wiki.52pi.com/index.php?title=DS1307_RTC_Module_with_BAT_for_Raspberry_Pi_SKU:_EP-0059 The RTC module is specifically designed for Raspberry Pi A+/B+/2/3. It communicated with Raspberry Pi through I2C Interface. There is a Maxim DS1307 and CR1220 button cell on the board to keep the real time for a long time after the Raspberry Pi has its power down. Set a serial port, TTL convenient way online debugging RTC chip: DS1307, Battery:CR1220; Work Voltage: 5V