I drew up a little schematic, and with some jiggery-pokery and a thin speaker in place of a buzzer it just fits. I also found some super-bright LEDs, and a red magic marker. Red is much cooler. Anyways, on with the building!
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Step 1: The Stuff
That said, you will need:
a magic marker,
and a mini-usb port (mine broke so I went with the audio jack and rigged a custom charger).
The new stuff!
A pair of supercaps! these will be in series for a nice 5v, which is also what USB provides.
556 IC! Basically, it's a pair of conjoined 555's.
LED's! I found some cheap ones at that link.
An earbud speaker, or similar small noisy device.
Some capacitors and resistors; capacitors are 10, 0.1, and 0.01 uf. resistors will vary.
scissors, craft knife, pliers,superglue, a drill, and soldering stuff.
Step 2: Making the Body
Take apart the marker and pen. Grab the drill, and with something like a 1/4 in. bit drill out the stuff inside that held the felt tip in place. Make a hole in the end cap, as well.
Take apart the Tirefly, and drill a hole in the bottom.
Get rid of the tip of the pen, and cut the body to about 6 cm. Cut a slot in it about 2 cm long, since the switch will take up some space later.
Head back to the marker, and craft-knife two holes in the side to fit the switch and your recharge receptacle of your choice.
Stick the pen in the marker, and the Tirefly on the pen. Put some layers of tape around the base of the pen inside the marker; this will stop the top from extending too far.
Step 3: The Fancy Electronics
Since space is at a premium here, this will be soldered as compactly as possible. You can see in the pictures that I set the resistors and jumpers towards the inside connecting at a common positive side, and the more bulky capacitors along the outside. The supercaps will connect end-to-end, the negative of one going to the positive of the other, and as a unit (or UNIT) they fit together under the whole 556 assembly. Attach ground on the diagram to the negative side of the series supercaps, but don't do this for the positive side!
Step 4: It's Not Bigger on the Inside...
Also, you'll need to attach some wires. Make sure they're small, but not magnet wire size. Just something small.
Attach 2 to the negative terminal. One should be longer than the other; the long one will go up to the LED (make sure it will be long enough even when the pen is extended). The other will go to the charging port. The positive side of the supercaps will have 2 wires as well. One for the charging port, one for the switch. The positive side of the circuit should be attached to the other side of the switch, as well as the positive side of the LED. Thus, 6 wires in all.
Now, to squeeze it in...
Feed the wires in first. Leave them as long as you can, so you can easily guide them to the proper holes without having to deal with pushing the 556 inside. Using a pencil and some small pliers guide the charging port wires to the hole for your mini-usb, the positive terminal and positive side of the circuit to the hole for the switch, and the long wire to ground up into the tip.
Solder on the LED and resistor, and add the wire from the cathode of the LED to the switch from that end as well, guiding it to the switch hole. Again, make sure it is long enough to extend.
The end cap of the marker might have to be cut thinner, and then you can glue that in place. Molto Bene!
Step 6: Add Style!
Now you can head out into the world, secure in the knowledge that no door can stop you!