Doorbell Notifications

We have a fairly large backyard at our house and if you're in the back, there is no possible way to hear the doorbell.  

But, we tend to have our cell phones most of the time.

So, I built this device to monitor for the doorbell being pressed.

I noticed many projects that replaced the doorbell with an embedded controller, and I didn't really want to replace mine.  

This project is powered from the existing doorbell circuit and watches for the button press at the front door.

It then uses Prowl to send a notification to the cell phone.

When the doorbell is pressed, about 1 second later the phone chirps to tell you the doorbell was pressed.

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I'm thinking Intermediate Skill is fine for this project, but if you disagree, please let me know so it can be accurate.

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Basic theory is this:

We need a notification when the doorbell is touched:  

• A doorbell press connects 20v AC between two connections on my doorbell.  
• Build a 1/2 wave rectifier to get about 20V DC.
• Then use a resistor divider to bring it down to about 5V.
• Feed it through an optocoupler just to be safe.
• Read the resulting DC voltage rise from one of the pins on your embedded controller.  

We need to power the circuit so I don't have to plug it in anywhere else:

• Two of the other pins have a constant 20V AC signal on them.
• Feed 20v AC through a bridge rectifier with a big smoothing capacitor.
• Take the resulting 20V DC and put it through a Buck Converter.
• Use the Buck Converter to step down to 4V (or something reasonable for your controller).
• Power the controller from this DC voltage.