One of the benefits of the Arduino development platform is the ease of making an accurate clock, and the following example by Instructables member Matt_wes is not only easy to make but also quite useful.
Instead of making do with pocket-sized LED displays, this clock uses digits that are 16 cm tall and would be visible from quite a distance away. Thanks to the power required for each segment, they are switched via MOSFETS to deal with the current.
However the effort is worth it, as you can see below. This could also be used for countdowns, score-keeping and much more - just change the Arduino sketch.
The most important part of any clock project is the inclusion of an accurate real-time clock IC. Here at Freetronics we have the Maxim DS3232 real-time clock IC module:
Apart from keeping accurate time for years due to the temperature-controlled oscillator and having a tiny coin-cell for backup, it is very simple to connect to your Arduino project. A driver library allows your program to easily set or read the time and date.
Perfect for clock projects, dataloggers or anything that needs to know the date and time. Furthermore it contains a digital thermometer and 236 bytes of non-volatile memory to store user settings and other data. For more information, check out the module page here.