Ryan Blace was looking for a way to manually turn on or off his electric hot water system, as the manual control in fitted timer box was a little too close to the mains current for his liking. Instead, he created an Arduino-controlled solution that has a servo which physically controls the switch in the original timer box - for example:
Although it can be simple to use a mains-rated relay, it can be prudent to avoid doing so when unsure about working with mains current or from a legal perspective you may not be licensed to do so. Either way, this is another example of using an Arduino board to solve a problem. For more information, visit his site here.
To get started with your own timing projects, use our real-time clock module based on the DS3232 - with a temperature-controlled oscillator it is highly accurate, and has an onboard backup battery for when the power dies and 236 bytes of non-volatile memory for user data.