How to make an infrared LED light pen

Simple instructions and shopping list for a great LED light pen.

If you want to experiment with Johnny Lee's Wiimote Whiteboard or other Wiimote hacking projects, I recommend starting by making your own IR LED light pen. My design shown here is sturdy, self-contained, cheap and easy to make.




Click here for printable shopping list and instructions (PDF).

Here's your shopping list (makes 2 pens):

ITEM	WHERE	PART #	COST
EXPO markers	Office Max	21671870	$6.00
IR LED x 2	Radio Shack	276-143	$4.00
LED holders	Radio Shack	276-080	$1.50
SPST momentary switches	Radio Shack	275-1571	$3.00
N-size batteries	Radio Shack	23-023	$5.00
N-size battery holder x 2	Radio Shack	270-405	$2.00
Soldering kit	Radio Shack	64-2802	$8.00

TOTAL: $29.50

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Directions:

1. Over a trash-can remove the marker tip and core with a pair of pliers (be careful as the ink can spray a bit).
2. Wipe out the inside of the marker to remove any remaining ink.
3. Drill a quarter-inch hole for the pushbutton switch at the spot where your thumb naturally rests on the grip. The pushbutton is a hair larger than 1/4" diameter so you'll need to grind at the edges a bit to widen the hole until the pushbutton fits in snugly.
4. With a fine piece of sandpaper, scuff up the surface of the LED - this helps diffuse the light to improve tracking.
5. Remove and discard the nut and washer from the LED holder.
6. Put the LED stems through the LED holder and slide the rubber plug onto the stems until it’s tight – having the LED on the outside of the LED holder helps more light shine out to improve tracking.
7. Solder an 8 inch length of red wire to the positive lead, which is the longer one (you can also tell by looking inside the bulb - the positive electrode is the smaller of the two).
8. Solder an 8-inch length of black wire to the negative lead.
9. Thread the wires through the body of the pen and use a set of pliers to screw the LED holder into the tip of the pen. This takes SIGNIFICANT force to expand the hole slightly, but the end result is nice and snug.
10. Fish the black wire through the hole for the pushbutton.
11. Snip the wire about an inch from the hole, then solder that to one terminal of your pushbutton.
12. Slip the remaining black wire back into the pen body and solder it to the other pushbutton terminal.
13. Gently press your pushbutton into place.
14. To leave more room for the battery, trim the excess wire leaving about an inch extending from the bottom of the pen body. Also trim the battery holder wires to about 1.5 inches each.
15. Solder the battery holder wires to those of the pen (red-to-red!) [NOTE: this is your first chance to test your connections. The IR LED is invisible to the eye but it IS visible to the CCD of digital cameras. Point your camera at the light, press the button and you should be able to see it light up on the camera's screen.]
16. Slide the battery and wire into the back of the pen and push the end cap back on as far as it'll go comfortably.

Good luck... let me know how it goes!