PSN-L Email List Message
Subject: Re: Modified sound card and datalogging and geophones
From: Gordon Couger gcouger@..........
Date: Wed, 20 Jul 2005 00:37:54 -0500
Have you considered using a mixer with local oscillator
frequency that puts the unwanted image above the range of the
It inverts the spectrum but that's no problem with computers as
fast as we have.
> In a message dated 18/07/2005 19:31:08 GMT Daylight Time,
> mike8s2@......... writes:
> installed some larger-capacitance-value coupling
capacitors on my
> 24-bit sound card so I could resolve lower frequencies.
What is a
> good datalogging app to
> use with this?
> Hi Greg,
> I suggest that you look at Larry's website at
> http://psn.quake.net/ and read some of the articles. Look at
> websites on http://psn.quake.net/dave/map.htm
> A soundcard by itself has a frequency range of about 10
Hz to 24 KHz
> and it is basically an AC only device. The 10 Hz lower
> limited by the input C + R circuit. The standard PC drivers
> sample rate from 8,000 to 48,000 sps. Using this, you end up
> massive files on a daily basis and no quick way of monitoring
> haven't seen an application which enables you to use the
> at really low sample rates, say 20 / sec and return them to a
> Assuming that you are in the States, you can buy a $25 10
> from Dataq, but it is usual to use 12 to 16 bit ADCs.
Following on a
> geophone, you will need a low noise amplifier and a filter. See
> http://users.viawest.net/~aloomis/seismom.htm or
> It is usual to limit amateur seismic sensors to
frequencies of less
> than 10 Hz. This cuts out most of the urban traffic and
> noise, which is of no interest to most of us and may swamp
> else above 20 Hz.
> You also need a timing system which is good to better
than 1 sec.
> Unfortunately, most computers are fitted with something called a
> 'software clock', which can vary by minutes per day. The
first seismic P
> waves travel at maybe 10 km / sec, so a 1 minute error would
> location error of ~380 miles. This really is useless for
> and why you need a dedicated data recording program which
> into account.
> The P and S waves are of most interest to us, since they
> to determine the distance of the quake from your station.
> P waves are at about 1 Hz and S waves are at about 0.5 Hz,
> quakes have higher frequency components.
> The 'cheap' 4.5 Hz geophones can be extended down to
about 0.5 Hz
> with a special amplifier, but they will also pick up local
> regional quakes on their own.
> It is also possible to make a really cheap vibration
> seismometer using piezo disks and added weights. I use one
> 0.25 Hz to 10 Hz, but I need a FET input opamp and good
> to do this.
> *Do 'read up' about earthquakes and seismometers before
> There is a lot to learn!*
> To go beyond this very basic advice, I would need to know
> are located, your knowledge of electronics, what tools /
> skills you have and how much you are prepared to spend. I am
> inquisitive, merely practical. Commercial seismometer systems
> several 10's of thousands of $, but amateur systems may be
made from a
> few $100 upwards. You can exchange construction time + skills
> made equipment, but the effort may be considerable. The real
art lies in
> not making too many mistakes.....
> I hope that this hslps...
> Chris Chapman
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