Coding4Fun

Using IR Pens

Since the Wii remote camera is sensitive to sources of IR light, if we want to track the location of a stylus on a display, we need to create a stylus with a tip that emits IR light. To do this, we need a couple of components:

• An IR light emitting diode (LED)

• A normally open momentary switch button

• One AAA battery

• Some thin wire (26 AWG or higher)

• A casing to hold everything, such as a dry-erase marker

Building the pen for this project is as much an art as it is a science. If you think the whiteboard is something you'll want to come back to, enhance, and use repeatedly, by all means take the time to fit the assembled circuit in the casing of a whiteboard marker, as shown in Figure 9-1.

Figure 9-1. Completed IR pen in dry-erase marker

However, if you struggle with getting the circuit into the marker's cavity, look for alternative casings that may give a little more space to work with. For example, sometimes your circuit can be too bulky in your first attempt to fit in the tight space of a whiteboard marker. A slightly roomier option is to use a spare parts tube from a computer toolkit as the body, and insert a whiteboard marker tip in place of a cap to give it the feeling of a stylus, as seen in Figure 9-2.

Figure 9-2. Completed IR pen in spare parts tube

Spare parts tubes are available ...