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LED Light

 
This project was for Amazon.  It is an LED book light that attaches to Amazon's flagship eBook reader "Kindle" to help users read in the dark.  I was responsible for the electrical design on this project.  This project had two interesting challenges to overcome.
  • First, the customer wanted to use a costly IC and PCB to ensure that the LED would maintain the same luminosity over the life of the useful life of the batteries.  In a nut shell, they didn't want the light to grow dim as the batteries began to die.  They also wanted the same luminosity if the light was powered by batteries or by an AC power supply.  The high cost of the IC put the project success at risk.
  • Second, I had to devise a way to measure the luminosity at various points over a given area.  In other words, I had to find a way to show how evenly the light from the LED spread over a surface.
 
I overcame the first issue by creating a plot that showed the performance of the light in each of the possible electrical configurations.  This one page plot also contained the unit cost of each of the configurations.  Upon reviewing the information the customer could easily see that the best solution was the simple (and least costly) electrical design.
 
I overcame the second issue by building a light box using an array of photo sensitive resistors.  Using a multi-meter, some fancy math and MS Excel I was able to print plots that represented the intensity of light over a given region.  I was able to do this with $40 in parts, a little soldering, and some time.
 
Here are some pictures of the LED light which attaches to a device with magnets.  The light automatically turns on when the light is opened more than 25 as shown in the last picture.