Electronic Circuits and electronic circuits, electronic schematics plus an extensive resource for hobbyists, inventors and engineers

DiscoverCircuits.com has links to 45,000+ electronic circuits, cross-referenced
into 500+ categories.    We have searched the web to help you find quick design ideas.

HOME Schematics Hobby Corner Dave's Circuits Electronic Resources Contact Info
Imagineering Ezine    Discover Solar Energy Dave Johnson & Associates Faraday Touch Switches
Welcome to DiscoverCircuits.com - online since 2002

See Media Kit for
Advertising Opportunities

Attention Designers:  Please alert us by eMail if we have linked to sites
where your original material has been copied without your permission.
We will change to the LINK to your site.  
Thank you.

 

DiscoverCircuits.com -- Hobby Corner
Last Updated on: Wednesday, October 18, 2017 05:04 AM

Hobby Circuits List

The contents & graphics of Discovercircuits.com are copyright protected.
LINKING to Dave's circuits is permitted but DO NOT COPY any files to your WEB SITE server

More  Alarm Circuits

Earthquake Alarm Circuit
designed by David Johnson, P.E.

Geophones are dandy motion sensors.  They are metal cans containing a powerful magnet, suspended with springs inside a coil of wire.  The magnet functions as a floating mass.  The slightest vertical motion of the device causes the coil to move relative to the magnet. 

This induces a small voltage in the wire coil.  These devices have been used for decades by oil and gas companies to conduct surveys of underground rock and strata, using induced seismic shocks. Although millions of them have been manufactured over the years they are often hard to find.  You can make your own geophone by suspending a strong magnet with a rubber band, so it hangs inside a coil of wire containing several hundred turns. Any vertical movement will produce a detectable voltage in the coil.  To reduce false signals produced by air movements, I suggest that the assembly be housed inside a pipe or some other container. 

The hobby circuit below shows how this do-it-yourself geophone can be used as an early warning earthquake alarm.  The electronic circuit uses a low power dual op Amp from National Semiconductor.  The weak voltage from the coil is first Amplified by the left side circuit.  That signal is fed to voltage comparator.  The output of the comparator is routed through a filter network then to a n-channel FET switch.  The switch can be used directly to turn on a beeper or it could be connected to a computer system.  I included a LED light as a visual indicator.  The LED will turn on whenever the circuit detects motion.  With the components shown, the overall sensitivity is less than one millivolt peak to peak at the coil.  By decreasing the value of R5, you can decrease the sensitivity so any desired level.

 

Commercial Geophone

Click on Drawing Below to view PDF version of Schematic

More  Alarm Circuits

Hobby Circuits List
eMail David A. Johnson, P.E. about this circuit

 


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.