PSN-L Email List Message

Subject: Re: Seismic detector circuit schematics
From: John Popelish jpopelish@........
Date: Tue, 01 Mar 2005 18:42:07 -0500

> John Lahr  wrote:

(I have edited your post to plain test to make it read
easier in the archive, since it contains so much useful information.
Hope that is okay.)

> Hi John,
> I've posted some schematics on my web site as well.
> Amplifier/Filter circuit from Chris Chapman:
> Linear Variable Differential Transformer sensor from Chris Chapman:
> Folded pendulum seismometer electronics package from David H. Youden:
> Basic optical sensor circuit for a self-centering 
> SG type pendulum from Chris Chapman:
> Micorphone amplifier for use with gunshot location system using
> a TLE2426ILP to avoid need for dual power supply from Fred Fischer:
> Is the use of a 1/2 rail virtual ground a good idea for seismic
> amplifiers?

I don't see why not.

> What is a newer part for this purpose?
(snip Digikey search)

That is the only single part rail splitter I have seen, 
but any rail-to-rail or single supply opamp 
that tolerates a fair amount of capacitance on its output
will do this job with a two resistor divider across the rails 
fed into a follower configuration.  An opamp that don't 
tolerate capacitance so well needs an additional 
low value resistor between the opamp output 
and the derived ground rail to make sure it is stable,
since there will be bypass caps between the positive 
and negative rails and this derived ground, 
scattered around the board.

No special part needed, unless you are going for 
the absolute minimum number of components.  
You just have to add up the worst case total 
ground current and make sure the opamp is capable 
of supplying that without current limiting.

> Symmetric differential capacitive sensor from Randall Peters:
> Folded pendulum design from Brady Romberg's team at the
> Colorado School of Mines:
> Cheers,
> John Lahr

Thanks for this library of links.  
I have something to study for the next few days.

John Popelish

Public Seismic Network Mailing List (PSN-L)

[ Top ] [ Back ] [ Home Page ]