This real time clock (RTC) module is upon on the Dallas DS1307 clock/calender chip. The module also includes an Atmel AT24C32, a non-volatile 4-Kbyte EEPROM. Both devices are unified by the single I2C serial bus.
The RTC can be maintained by using a CR2032 lithium button cell (not supplied), the cell holder is mounted on the underside of the PCB. The module can be modified to use a rechargeable lithium-ion cell, LIR2032, by replacing just two resistors.
Provision is made for a 3-pin DS18B20 digital temperature sensor (not included).