I actually made this out of pure boredom one night, and it actually turned out pretty well! All this is a small assortment of bits and pieces that anyone who works with electronics is bound to having lying about. Here is the bill of matrial (tools mixed in):
-Soldering iron w/ solder
-Perf board (or similar ridged plastic that can have holes poked in)
-3 LED's (you can use more or less if you like, but three sits nicely on perf board)
-1 resistor (this will change per LED's. I needed a 220 ohm. Here is a LED calculator for help)
-1 tac button
-9 volt battery clip (you can use the top of another 9 volt, if you need to!)
-Superglue and/or epoxy
-Hot glue gun with glue sticks
-One pack of Sugru
Step 1: The Circuit
Below (or above, not sure where it will wind up!) is the circuit used. It's rather simple, and was more or less tossed together on eChalk.
Step 2: Building the Thing
Making the circuit is a snap: the issue lies in making the "Box" that houses the wiring and give it some shape. This is made with three small chunks of perf board and a 9v battery clip. The perf board chunks are just cut down to size so the whole assembly will be about the same dimensions as the battery itself.
On one chunk of perf board, super glue your tac button onto that. While you wait for the super glue to dry on that, wire up the three LED's and resistor to another chunk of perf board. Hopefully, your super glue will be dried at this point, and you will be able to wire up the tac button. Keep in mind to try and keep the lengths of wire/leads short, so you can get it all folded up in a small spot. The other end of your tac button will go to the battery clip (again, note polarity!). The last bit of wiring is for the other side of the batter clip to go to the LED's/resistor (depending on what you wired where). Test this quickly by tapping the battery bay to the battery ad press the tac button. If you have light, then move on! If not, review the circuit, and find the issue. Don't worry, this is low voltage, and won't hurt you unless you lick it.
With the wiring done, you can now glue the other bit of perf board on the whole set up, and start gluing everything together. Refer to the pictures for what goes where. Once the perf board are glued in place, go ahead and fill the middle cavity with hot glue. This will not only insulate the wires, and prevent shorts, but will give the flashlight a more solid feel.
And now onto the touch ups. I would highly recommend cutting the outside with epoxy, as this (when dried) will give the whole thing a very rugged build. Again, wait for the glue to dry, and break out the sugru! One pack should do the trick. Go ahead and warp it over the whole thing. It's best to start wrapping with it off the battery, then stick it on the battery, and finish wrapping. This will shape any access sugru on or near the battery clips to fit over and around a battery. Make sure to press the tac button from time to time to make sure it's still free to move!. Once it's wrapped, you can use a wet sponge or cloth to "buff" the sugru to give it a smooth finish.
And after another portion of wait (24 hours this time, per sugru's cure time) your good to go! This little thing is bright enough to use as a basic flashlight in most situations, and is tiny! Enjoy the light, and thanks for the view!