After acquiring a Maxim iButton reader and tag, Instructables user "kenyer" decided to use it as as the basis for a garage door opening button. After some experimentation he discovered how to connect the iButton reader to an Arduino using the 1-wire bus, and ended up making an entire system that also has a digital clock (without using a real-time clock IC) displayed using an LCD. Here's his system at work:
Even if you're not interested in his primary goal, the explanation of making a clock without an RTC is a good read, so click here for more information. And for more, we're on twitter and Google+, so follow us for news and product updates as well.
Although an Arduino can timekeep on its' own, when he power goes out so does the time, instead - consider using our super-accurate real-time clock module. Based on the DS3232, it has a temperature-controlled crystal oscillator for accurate time keeping, battery backup and 236 bytes of non-volatile memory for user data. For more information, see our modules page.