Step 1: Get Materials
1.Alarm clock - mine is a cheap one that I got from Walgreens. It gets it's power from the mains and has a 9v battery for backup. I don't remeber how much it cost but it was probably less than $15.
2.Some basic knowledge of electronics and construction techniques. (really?)
Step 2: Get Materials
Step 3: Get Materials
Step 4: More Materials
5.Relay - 12vdc coil, and able to handle your bell supply power.
6.555 Timer - I think pretty much any standard variation will work.
7.2n3903 Transistor - (this may be superfluous)
8.1 M Ohm Resistor
9.Some hookup wire
10.Extension cord - this is optional, but if you use one make sure its the kind with 3 outlets so you can plug in the clock and two wall warts.
11.hardware and some sort of case to put it all in
solder, some sort of support (pcb, breadboard, etc.), soldering iron, multimeter (or just a voltmeter), wire stripper, screw drivers, a knife maybe
Step 5: !Warnings!
1. Just so we're clear, you need to exercise extreme caution when working on this project. Don't work on aynthing when it's plugged in!!! I've been electrocuted many times and it's never very fun. Make sure that the circuit is insulated when it is plugged in (by a case generally).
2. The 555 chip can be damaged by static discharge. In fact I usually buy doubles for this very reason. Don't wear static prone clothing and leave the chip in it's packaging until you're ready to use it.
3.The ground shown in the schematic is a floating ground, which means that it is exclusive to the circuit and SHOULD NOT be connected to earth ground (mains).
4.I'm not that knowledgable when it comes to electronics so this is presented as I did it. There is a lot of variation that could happen with different components and some things may not work together.
I think that's it... just use common sense.
Step 6: Open Your Clock
Carefully clip the ends of the wires to your meter. and plug the clock in (sorry for the safety contradiction). Your meter should read something like 16 volts. If not then your clock may not work, although with some basic electronics knowledge you could probably get it to work. But this setup may work anyways with a range from 10v to 18v approx.
Finally, with your meter still connected, get the alarm to go off. The voltage should drop to around 7-5v when the buzzer sounds. If so, then you have a winner.
Step 7: Wire It Up
Construct the circuit using your favorite method. and wire it to the other components as show in the schematic.