Arduino: 24 hours digital clock
This is an Arduino powered 24-hour digital clock that uses the RTC chip DS1307 for timekeeping. DS1307 has a small battery backup so that it keeps the correct time even the rest of the circuit is not powered. The time is displayed on 5×7 LED dot matrix.
The ATMEGA168 controller and the rest of the circuit is powered by a 9 volt 650 mA power supply with a LM7805 regulator IC.