How to build an IR LED pen in more or less simple steps.

What

We're going to build a IR-LED in the top of a pen.
The LED will use a std 1.5V AA battery and be operated by a micro BTN(*).

(*) I asked for a switch at the local electronicparts shop but they explained to me that a pushbutton is a BTN, not a switch. We mere mortals just call them switches.

Why

Because you got inspired by Jhonny Lee and Uwe Schmidt and now want to play with the Wiimote and IR pens yourself.

So what do we need;

1) IR-Led I used a Kingbright L-53 F3C, Jhonny Chung Lee used a Vishay TSAL6400s (See discussion below on selecting an IR LED)
2) Micro BTN (switch :) The button should be one that makes contact when you press it
3) A 1.5 AA battery
4) A Marker big enough to contain all these items. I reccomned the PaperMate W10 series markers as they fit the bill perfectly.
5) Soldering iron and filler
6) Some basic tools (small cutters, strippers, pliers etc) and skills

Optional are;

Some batteryholder-springs and wires. Any thin wire should do, but it helps if they are flexible. The springs are helpful to make sure the contacts remian pressed to the battery. (The blue & red wires as shown in some pictures were the 'hard' telephonewires I tried initially, but that proved to be quite a challenge so I used the wires from the battery holder I had)
A piece of metal to get the battery out of the casing easier
Electrical tape to insulate some areas
Crimp sock (sp?) to insulate other area(s)
Unmentionables :)
An operating webcam to check the working(s) of the LED

i. Take the marker apart

Marker parts

iia. Remove the felt tip from the marker top

Tip

iib. Also remove the small pin from the tip. What remains is a base that suits a 5mm LED perfectly.

Tip

iii. Drill a hole for the switch (btn :) about halfway of the part of the tip that sticks in the pen base.

Tip hole

iv. Make an incision on the opposite side of the hole to allow easier fitment of the switch.

Tip incision

v. Solder the wires to the LED. Be careful not to let the LED get too hot. My choice was to use a red wire for the + lead (anode, usually the longer) and black for the - lead (kathode, usually the shorter).

LED

Here I made s mall judgment in error; I left the leads a tad too long. See my comments at the end.

At every step where the functionality of the LED may have been harmed I used the webcam in my laptop to check if the LED was still working. Any webcam will do. It will show the IR light that you can't see witht eh naked eye.
The light of the LED is marked with the red circle in the picture below.

LED check

vi. Next insulate the + lead. I used what I call a 'crimping sock'; the green stuff. It's material that crimps when heated.

Insulated

vii. Insert the LED in the tip from the outside in.

Insert LED

viii. Gently push the LED all the way down till it touches the base in the tip.

Down

ix. Check which contacts of the switch you need to use and then solder a red wire to one lead and the red wire from the LED the other.

Switch solder

x. Insert the switch in the hole and install (don't tighten yet!) the nut to keep it from falling out.
Switch installed

There are verious ways to attach the wires to the battery. I used the springparts from and old batterholder and a piece of metal to make getting the battery out of the base again easier.

xi. Solder the black wire to the spring and use electrical tape to attach it to the metal bit.
Bottom part

xii. Solder the red wire to another spring and use electrical tape to attach it to a flexible but but firm piece of material.

Top and bottom

xiii. Make an incision in the top of the base (where the tip slots in) to allow room for the switch.

Base incision

xiv. Put the metal bit in the base, insert the battery. Use a pencil to push it all the way down.

Insert battery

xv. Plug the top spring onto the battery and slide the top of the pen carefully into the base.
Take care not to entangle or clip the wires.

Done

Screw the nut(s) on the switch, put the cap on the tip and we're...

DONE.

Done

(slightly overexposed picture :)

Problems

One problem that is apparent in the picture at step xv is that the LED sticks out from the tip. this while there is such a snug fitting base in the tip for a 5mm LED.
The problem is that I did not shorten the leads on the LED so they ended up pushing the LED out.
I will correct that next time I take the pen apart or otherwise in the next version.

LED choice

There are a couple of attributes important when you choose a LED.

It's good to remember that the Wiimote's camera does not track the direct IR light from the LED, but the light that is reflected by the surface you use.

Given that reflection works according to the principle that the angle light falls on the reflective surface i the same as it will 'bounce off' a picture would explain that a LED which spreads light in a wider angle has a better chance of it's reflected light to reach the Wiimote than say a IR laser which ahs a very narrow spread of light.

On the other hand you want the light (and thus LED) to be as powerful as possible.
The two (wide spread and high power) don't seem top go together though.

Typically you'll find IR LED's with light ranging from 880nm to 950nm.
I believe that those around 950nm are said to work best.

To keep the design of the pen simple (as in the example above), you'll want to select a LED that has a Forward Voltage of about 1.2V and a max Voltage of 1.6V (or more). That way you do not need to install more components (resitors et al) in the circuit.

You can find more discussion on what makes good IR LED on the sites mentioned above.