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Last Updated on: Thursday, November 30, 2017 07:43 AM

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Optical Fiber Indicator
Designed by Dave Johnson

Problem:  Design a a simple battery powered device that would quickly spot check to see if a fiber cable was active with light and determine which one of the 4 wavelengths was being used.

Solution:  The concept was to have four germanium photodiodes along the front of a suitable plastic box.  Each photodiode would have a narrow band optical filter placed in front so it would respond only to light in that specific narrow wavelength.  A comparator circuit would monitor the light from each photodiode and light a simple LED and sound a beeper if the light from an optical fiber matched the selected band.  The user would just have to pass the end of the fiber over the four detectors to determine an active fiber and the wavelength of light being used. The whole circuit could be powered by 3 volts from two AA cells. 

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DC Magazine, September 2009, Page 7:  Wave Length Indicator


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