A reliable (modified) alarm clock that will wake the dead. I put this together after having several wind-up alarms break on me. It's basically an electronic alarm clock modified to trigger an alarm bell. Since I'm pretty much comatose when I sleep this is just what I needed.
Step 1: Get Materials
Here's what you need to make this:
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
3.Some sort of doorbell or alarm bell that is loud - The electromagnetic kind work well.(If you use something different then you may have to change wall wart #2) I got mine from eBay. It's like the buzzer type of old doorbell but with a hammer and bell attached.
Step 3: Get Materials
4.(2) Wall wart type power transformers. #1 is 9v DC output (somewhere around 350 ma) and #2 is 9v AC (@500 ma).
Step 4: More Materials
The rest you need is:
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!
OK, a couple of 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
With it unplugged, open your clock (no touchy capacitors) and solder two lengths of wire on to the buzzer disc/ speaker (where the 2 wires from the clock circuitry are soldered on). Run the two new wires out of the case (I used the power cord hole) and button the case back up.
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
(you may want to breadboard this first to make sure it works.)
Construct the circuit using your favorite method. and wire it to the other components as show in the schematic.
Step 8: Button It Up
Make a case for the guts (wood works well for this). I made a box with the necessary holes and put the circuit, relay, wall warts, and outlet end of the extension cord in there. I mounted the bell to the top with screws and the clock with velcro. That's pretty much it...
Step 9: Take It for a Test Drive
Set the alarm for some time in the future and enjoy!