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
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