So when I bought my house, I noticed it had probably the most boring doorbell on the planet. Then I saw the adafruit's Wave Shield and saw inspiration.
This is my first actually completed hobby electronics project, so I'm pretty proud of it, even if it's really simple.http://youtu.be/lDCDayKyOQA
(Is it possible to embed a youtube video on these forums?)
Pre-R3 Arduino UnoWave Shield 1.1Velleman 3 Watt Mono Amplifier # K 8066
Power for the doorbell comes from a 16V transformer off mains power (120V). It's run through a 50V 4A bridge diode rectifier into an electrolytic cap and a ceramic cap to smooth the pulsed DC, then two diodes to drop the voltage by ~3V before powering the mono amplifier and being split off for the UNO's Vin.
The doorbell is connected like any other button, sending 5V out to the doorbell and in to a digital pin configured as an interrupt. Using a pullup resistor and pulling the pin to ground wasn't used to lower the demand on the linear regulator running on voltage that's a bit higher than I'd like. To further reduce power usage, the atmega328 is put into PWR_DOWN sleep in between doorbell rings.
Also, thanks to adafruit_support for providing help!
My next project is a little more ambitious, a thermostat that can use a wireless sensor for temperature readings.