PSN-L Email List Message

Subject: Re: Vertical design/1-sec
From: Ben Bradley benbradley@..............
Date: Fri, 20 Dec 2002 13:12:28 -0500

   Hi everyone, I'm new to the list, though I've read through much of the list archives. My interest in making a seismometer was kindled a few months ago, and some web searching turned up many interesting things, such as this list. 

At 01:29 PM 12/19/02 -0700, meredithlamb wrote:
>Larry, Jim and all, 
>For those searching for a "possible" vertical seismometer, 
>and/or exploring variations: 

>Of course, with Georgia Tech being a teaching institution, it 
>could just be that this instrument is more meant to inspire just 
>enough curiosity about it, that people like me (and others) might 
>go further into it...ha. 

   This design is interesting in that appears simple to assemble as well as being low in cost, and so one can get it up and running quickly. The first thing I would do with it is replace the photoresistive sensor with a photodiode, phototransistor, or optointerrupter (simply a phototransistor and light-emitting diode aligned in one package with a gap between them). The cost is about the same (a dollar or so), and photoresistive elements, depending on models, can take many milliseconds to respond to changes in light, limiting frequency response, posibly below the maximum of interest. A photodiode/phototransistor has more than adequate frequency response.

   For a rather more complex and sensitive vertical seismometer, there is the device described here:

The Scientific American article on it is here:


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