Spring 2016 3DOT Making Laser Tag Possible: Extending the IR emitter Range

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By: Kevin Moran (Electronics and Control Engineer)

 

 

One of the things I mentioned in the previous posts, was that by using an IR emitter (LED), the range was very limited. Testing showed an average range of 3-6 inches. In order to have a reasonable range for the emitter, it was necessary to concentrate that diffused light. One idea was to use lenses to concentrate the light, the opposite idea of a flashlight which spreads out a smaller area light.

There were many lenses to choose from such as:

∙ Convex: Helps light rays to converge into a single smaller area

∙ Concave: Causes light rays to diverge or spread out (Opposite of what we needed).

∙ Spherical: Which are less focused and produce a wider light beam

∙ Compound: Which increases the focus while decreasing image distortion

The lenses that were decided to use along with Spiderbot’s E&C engineering were the convex lenses, since our emitter had a short range due to the diffusion of the light rays, it was a good idea to concentrate those rays into a small area.

Calculations:

Looking online, we came across this formula that allowed us to calculate the distance that the IR LED would have to be from the lense in order to increase the range, to a distance that would work with our requirements

Using this formula and the values provided by the image below, we were able to calculate a suitable range.

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Using the diameter of the lenses I already had on me, along with the half angle provided by the datasheet of the IR LED. I came up with values to plug into this equation.

 

D = 11.3mm diameter (lens)

F = focal length

Θ = 40 (half angle intensity of the current emitter we are using)

D > 2*F*tan (Θ)

11.3mm > 2 * F * tan (40)

F < 6.73 mm

 

 

In conclusion in order to use the given lens diameter with our particular IR LED, the focal length (distance from LED to lens) has to be less than 6.73 mm. I asked the manufacturing engineer to provide with a small tube that can be used to further test these distances.  As can be appreciated by the picture below, the light intensity has increased as long as our range to about 16 inches. We will continue to test to extend this range even more.

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Sources:

http://alumnus.caltech.edu/~leif/infratag/lens_choice.html

http://physics.stackexchange.com/questions/146956/howtochoserightlensforconcentratingirsignal

http://micro.magnet.fsu.edu/optics/lightandcolor/lenses.html

Kent Hayes: Ordered the lenses for both teams