Author Topic: This is how I utilized low-power IR LED to build an IR pen  (Read 4748 times)

Offline peaceful1123

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Hi, folks. Iím from Hong Kong but unfortunately cannot buy a high power IR LED to build an IR pen. Hereís the approach I used to solve the problem.

First of all, my projected computer image (~1.3m X 1m) on the wall was set such that the center of the image was at the same height from the ground (~1.6m) as normal eye-sight.

Then, I modified an ordinary LED torch light (~10cm long) such that it consisted of 4 low-power IR LED (1.5V, 100mA working at >250mA with no resistor). Unlike most of you, I didnít use the tip you called pointing at the screen. I simply stood right in front of the screen, held the IR pen like holding a pencil in the way that the LEDs pointed towards you and the Wiimote.

Lastly, my Wiimote was set right in front of the center of the screen 3m apart.

If youíve studied Ergonomics good enough, youíd have noticed that human tend to hold a pencil pointing slightly upwards if the drawing point is higher than their eye-sight. Whereas, we tend to hold a pencil slightly downwards if the drawing point is below our eye level. This tilt angle was noticed to compensate the cursor position error generated by not using LEDs as the tip. Besides, since the length of the IR pen was much smaller than the distance between Wiimote and the screen, it provided resolution good enough for normal Windows applications.

This approach differs from the traditional method in the way that you can stand right in front of the screen and hold the IR pen like a pencil but not a magic wand. In addition, LED power is fully utilized because the LEDs are pointing directly at Wiimote. The drawback is that the center of the projected image and Wiimote must be set in a straight line at the eye level for the best result, and the Wiimote cannot be placed at the left or right of the screen.

This is the third IR pen I built with low-power IR LED and I wish all of you enjoy my findings.

Offline UndCon

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Reply #1 on: August 12, 2008, 06:41:12 AM
Nice setup - I used almost the same size of screen when I tried mine but I had a different position of the Wiimote.