This is a Maxim DS3231 real-time clock IC with a non-rechargeable backup battery - neatly mounted on a small board that can be used with almost any project. Header pins are already installed so you can easily connect jumper wires, or you can solder your own connections onto the other side of the module. (We also have a neat Raspberry Pi-specific module for the same price). It's very easy to use, and with our Arduino tutorial you'll be up and running in no time.
Please note - If you are using a non-rechargeable battery (such as the free CR2032 we give you) - you must remove the diode from the board, as indicated by the white arrow below:
A backup battery is included, however we do not guarantee the life and you should use a fresh CR2032 before finalising your project. The board also has a small Atmel AT24C32 32K EEPROM which is handy for storing data, settings and so on.
The module is both 3.3V and 5V tolerant, so you can use it with almost any other development platform that uses the I2C bus. It uses the same commands as the DS1307 and we have our own Arduino tutorial to get you started.
The main benefit over the cheaper DS1307 is the increased accuracy, the DS3231 is down to +/-3.5ppm whereas the DS1307 can vary wildly depending on the temperature, quality and accuracy of the external crystal and capacitors.