PSN-L Email List Message

Subject: Newbie trying to get started
From: Steinar Midtskogen steinar@.............
Date: Fri, 20 Jun 2008 22:07:01 +0200


Hello List,

I'm in the process of setting up a seismometer.  I was considering a
few options for building one based on internet descriptions, until I
found the SEP seismometer which at 315 seemed likely to turn out
cheaper than all parts needed to build one myself: 

 http://www.mutr.co.uk/product_info.php?products_id=9047

So I got this seismometer and a quick start.  I built a box for it,
and I set up a datalogger.  For the datalogger I'm using a Linksys
NSLU2 which is running SlugOS Linux.  It's a little box with a 266MHz
ARM processor and 32 MB RAM, plenty for the task.  It has ethernet and
two USB ports.  I've plugged a card reader into one port, to which
I've connected two flash cards which makes up the filesystem
configured as RAID 1 for added reliability, and the other is used to
connect to the seismometer by a serial cable.

So far, so good.  Now I only need to add some software.  I've searched
a bit for existing software, but it turns out to be mostly Windows or
DOS applications with no source code provided, which wont run on an
ARM processor.  I think that to use a full blown leftover pc running
Windows for the task is both impractical and expensive.  I guess I
have to write some code myself.

I wrote a small program which logs the data from the seismometer.  I
currently plot what I get on this web page (using gnuplot):

 http://voksenlia.net/met/seismometer/

What's remaining is some processing prior to plotting.  I most likely
need to process my data with a lowpass filter.  But then I've run into
a problem.  I know very little about signal processing, and I don't
know what type of filter I should use for the best results.  Existing
software uses filters it seems, but I haven't found any source code
which could help me out.  So I turn to this list.

I have a 16 bit A/D converter sampling at 20 Hz.  My seismometer has a
natural period of about 16 seconds.  How should I process the data?

-- 
Steinar ; NIL DIFFICILE VOLENTI ; http://latinitas.org ; http://voksenlia.net
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