Check out this neat seven segment LED clock project using a variety of Adafruit components.

I just finished making a clock for my work area using a 7 segment display, RTC (real time clock) and the RTC library.  The nice thing about using this RTC is that it has a backup battery so if you lose power, it still maintains the time.

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Fairly easy setup.  Both the RTC and the 7 segment display use 12c to communicate with the Arduino.  Because they have different addresses this is ok.  Adafruit has this handy chart of a lot of sensors and things and what their addresses are.    The 7 segment display I used has an address of 0×70 and that is not yet on the chart, but can be found in the library RTClib.

Used in this project are the Adafruit 0.56″ 4-Digit 7-Segment Display w/I2C Backpack, DS1307 Real Time Clock breakout board kit, and Adafruit Perma-Proto Half-sized Breadboard PCB.