PSN-L Email List Message

Subject: RE: Interesting sensor pickup.
From: "Westfall, Ron" RWestfall@...........
Date: Fri, 4 May 2001 14:41:02 -0700


I believe I have heard other people on the list say they were using coils
from speakers.

For my coils, I used #34 magnet wire (real thin copper wire with a
transparent plastic coating, looks orange-reddish due to the copper) to wind
my coils.  I got a bunch of it from an electronic parts, ham radio supply

I used a wooden dowel, kitchen countertop laminate from the hardware store,
and brass bolts (non-magnetic) to create a coil form.

The size of my coils was limited by the horseshoe magnet I was using.  The
coil width had to be less than the width of the magnet gap.  The depth was
practically limited by the possible motion through the gap towards the
bottom of the U of the magnet.

I was using a metal lathe for another project and one night I set it up to
turn at a slow rate (I eventually sped it up to about 100 RPM).  I mounted
the coil form on a wood dowel in the lathe chuck.  I put the spool of wire
on a piece of pipe so it would turn freely.  I put on some gloves to protect
my fingers.  As the lathe turned, I fed the fine wire through the gloves to
keep enough tension for efficient wrapping and to direct where it was laid
down.  With my other hand I turned the reel of copper wire so that at no
time was the full force placed on the wire.  This approach worked pretty
good.  It required a couple of hours to wrap a coil, so over the course of a
couple of nights I wrapped 2 or 3 of them.

Even with so crude a wrapping mechanism, I found that moving the coil
through the gap of the horseshoe magnet by hand generated as much as 1 volt
on the output of the coil.  This produces good results on the seismograph.

If you are using a horseshoe magnet, part of the solution is to get a magnet
with a gap large enough for a reasonable size coil.

If this was any use to you, and you want more details (e.g. part details,
supply sources), let me know.

Ron Westfall

-----Original Message-----
From: Travis Farmer [mailto:travis5765@.............
Sent: Thursday, May 03, 2001 2:18 PM
To: Psn-L
Subject: Interesting sensor pickup.

On my Lehman sensor I have been using a homemade coil that provided moderate
output. I seem to have stumbled across something that works even better.
From an old (dead) hard drive,  I pulled the head positioning component and
gave it a try. I drew up a (bad) picture of the piece I am talking about. It
can be viewed at .
I rigged up a linkage to the seismo and gave it a slow 1"/sec swing. I got
an output of 0.026 V. the coil has a DC resistance of 18.1 Ohms.

Anybody else tried a setup like this?



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Larry Cochrane <cochrane@..............>