If you are looking for a simple vertical seismometer, take a look at the  one 
built by Roger Sparks.
 
_http://www.elltel.net/sparksite/CSpring%20Seismometer.html_ 
(http://www.elltel.net/sparksite/CSpring%20Seismometer.html) 
 
It has a period of several seconds, which I has been able to digitally  
extend to many  seconds.
 
It is virtually impossible to get a long period simply by hanging a mass  
from a vertical spring. For example, the spring has to stretch one meter to get  
a natural period of two seconds. The period of such a sensor is the same as a  
pendulum of the same length as the extension of a vertical spring.
 
Bob





If you are looking for a simple vertical seismometer, take a look at th=
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one built by Roger Sparks.
 
http://w=
ww.elltel.net/sparksite/CSpring%20Seismometer.html
 
It has a period of several seconds, which I has been able to digit=
ally=20
extend to many  seconds.
 
It is virtually impossible to get a long period simply by hanging a mas=
s=20
from a vertical spring. For example, the spring has to stretch one meter to=20=
get=20
a natural period of two seconds. The period of such a sensor is the same as=20=
a=20
pendulum of the same length as the extension of a vertical spring.
 
Bob