Recently I’ve been working an Arduino real time clock with a 4 digit 7 segment display. The real time clock chip is a DS1302
In the bottom left is the 4 digit 7 segment display, the bottom right the DS1302 RTC chip and the top right an Arduino Pro Mini. The device is powered over the serial cable which can also be used with a small Java command-line program to synchronize the clock and set an alarm which is currently only implemented in software.
The code for the Arduino and the Java application can be found at this Git Repo.