I did it. I finally finished the IR pen needed make my screen interactive. Several weeks ago I marveled at Johnny Chung Lee’s YouTube video homemade invention that turned any screen into an interactive whiteboard. I blogged about it here.
Then, I took apart an old highlighter and threw away the insides. 
I then went to Radio Shack and bought an InfraRed LED and momentary mini-switch.
With some wires, I soldered them to two ends of a AAA battery holder I salvaged from a couple old penlights.
When you connect the wires from the battery holder to the LED, make sure you hook them to the correct ends. LEDs work only one direction. The longer Cathode wire is positive and the shorter anode end is negative.
I used a soldering iron to drill 2 holes all the way through the front end of the barrel. One hole was smaller to fit the switch. The other hole was larger because it’s a tight fit for the switch and this hole allowed to to easily place the switch.
The LED kind of flopped around in the tip of the IR pen, so I put some electrical tape on the end to stabilize it and cover the bare wires.
Since the human eye cannot see infrared light, how do you check to make sure your circuit works. Surprisingly, digital cameras do see IR light, so you can just look at the led through a digital camera display to tell whether it is working or not.
The AAA battery fits nicely into the barrel. I stuck back in the cap I had pulled out at the beginning in order to gut the highlighter. 
Now that I had the IR pen finished, the hard part was done. I went to Wal-Mart and bought a Wii remote for $40 and a Bluetooth dongle for $10.
The next step was to connect them all together. I visited Johnny Chung Lee’s web site and downloaded the program he wrote to connect the two. I unzipped the program to a folder and created a shortcut to it on my desktop.
I pressed buttons 1 and 2 at the same time to put it in search mode. 4 lights on the Wii will blink to show it is ready. I opened My Bluetooth Places on my Windows XP computer and clicked “Add a Bluetooth Device.d” The wizard opened, and I clicked the “Search” button. The computer and the Wii remote happily connected and showed an icon for the Wii. The “Next” button showed the service. I checked to Wii and clicked the “Finish” button. They were connected.
I then opened Johnny’s Wii whiteboard program and the 4 blinking lights on the wii changed to 1 steady light. I pointed the Wii at my laptop screen. Just like in Johnny’s video, I clicked the calibrate button. I used the IR pen to touch the 4 calibration points. I could then use the IR pen like a mouse.
Performance: I got better results with the pen when the Wii sat at about a 45 degree angle to the screen, so my hand or the pen doesn’t block the Wii’s view. It is not very precise, so small buttons on the screen are a problem. It is also hard to tell where the cursor is, and you have to sometimes lift the LED away from the screen surface to get it to work. I found that if I hold down the button when starting on a non-interactive part of the window or screen (like the edge of the desktop), it will show the cursor. I can then drag the cursor to where I want it, and then click again to “left-click the mouse.” It works great for drawing or on programs with large buttons. 
I have only tried it so far on my small laptop screen, so I may get better performance with a large, projected screen.
I’ll try it with my projector at school. I’ll see whether my students can use it. Then, I’ll get back with you to let you know how it went.
The Wii interactive whiteboard is not perfect, but it has great possibilities. Hey, for $50, its not bad at all, and my students can now directly interact with digital content on our projector screen.
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