PSN-L Email List Message

Subject: Re: Homade Geophone
From: james fisher kd6iwd@.........
Date: Thu, 4 Aug 2005 20:32:11 -0700 (PDT)

Hi everyone, thought I would describe my homemade
"geophone". I noted that a voltmeter magnetic meter
movement had a coil of wire suspended in a very high
intensity magnetic field. the gap between the coil and
the magnet is only 1 or 2 mm. The coil is free to
rotate- indicating voltage by the attached meter
pointer. If you move the pointer the coil also moves
yelding a small current. I glued a right angle 
bracket on the meter needle using a THIN piece of
aluminum cut out of a aluminum soda can with a
ordinary pair of scissors. Remove rough edges with
fine sandpaper.  For my experiment I placed a small
weight on the aluminum bracket. after amplifing the
output I could detect footsteps. The bracket could be
placed in contact with a pendulum arm and it might
pick up the movement of the pendulum. This is a rather
sensitive device because the high intensity alinco
magnet is used with only a 1 or 2  mm air gap across
the magnetic poles.

best regards



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