HOME Schematics Hobby Corner Dave's Circuits Electronic Resources Book Corner Contact Info


  Experimenter's Corner

  Previous Issues

Optical Fiber Pressure & Motion Test Circuit
By: Dave Johnson

Optical fibers have been used for detecting motion and pressure for quite a few decades now.  If you would like to experiment with this interesting technique, you can use the circuit below.

The circuit uses an off-the-shelf bright red LED light source, designed for plastic optical fibers.  It also uses a matching phototransistor light detector.  The devices are designed for plastic fiber.  I would suggest you keep the total fiber length less than 50 feet.  Bending or stepping on the fiber will produce a detectable output signal.
This method relies on the phenomenon of “microbending.”  Light is routed through the fiber more efficiently when the fiber is perfectly straight.  When it is forced to move through small angles, a bit of the light is lost through the sides.  When the fiber cable is moved or when pressure is applied, small changes in the intensity of the light detected can be observed.  This technique has been used to monitor ground motion caused by humans and vehicles.

The circuit is powered by a +5v source.  A single resistor, R1, controls the LED current. The Amplifier circuit has a low DC gain but a high X100 gain to AC signals.

 
 

Please send comments to me


January 2011

Page 1 Back
Envelope
Circuit
Diagnosis
Experimenter's
Corner
Good Idea
done Badly
What the World
needs Now
Wily Widget
 


Imagineering Ezine    Discover Solar Energy Dave Johnson & Associates Faraday Touch Switches



 About Us   |  Advertise on DiscoverCircuits.com   |   Report Broken Links  |    Link to DiscoverCircuits.com  |   
Privacy Policy


Discovercircuits.com endeavors to credit original designers.   Please alert us by eMail so we can
delete links to material that have been copied without your permission
.   Thank you.


© Copyright of all original material on this website is the property
of David A. Johnson, P.E. (Dave Johnson & Associates ) unless otherwise noted.  

Linking is ALLOWED but COPYING any content or graphics to your web site is EXPRESSLY PROHIBITED.
All material is provided "as is" without guarantees or warranty of any kind, either expressed or implied.