Arduino hasn’t internal clock. It means some operations connected with time (delaying for specified interval) are possible, but date and time controlling isn’t so easy.
To let Arduino know, what time is it exactly, there is external clock device needed. Such a device is Dallas DS1307, available on Nettigo.eu in form of Arduino-connectable module. This module has a battery back-up, so once set, the time isn’t deleted after shutting Arduino down.
The module is already soldered, but connecting to Arduino remains open issue. It looks like the following:
In the left upper corner there is 4-pin header socket with 2.54 mm raster. Unfortunately we still haven’t cables for this socket in stock. You have to scare it up or connect through ICSP socket using goldpins. Those elements are provided with the module, but need soldering (simple even for beginners).
Using the cable we can connect the module to any controler supporting I2C protocol.
ICSP socket (from which the module is powered) has two positions to which it could be soldered. The first is for Arduino Duemilanove and its clones (taking pinout and size into account) or Seeeduino Mega. With such a connection the module is incompatible with Arduino Mega (relative position of ICSp pins and I2C bus output is different).
Of course, it always remains to solder wires instead of goldpins and ICSP and then we are able to connect with every microcontroler supporting I2C. How the module with soldered socket and goldpins looks show the pictures below: