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PICList Thread
'PIC: fluxgate compass'
1997\08\05@083813 by Mike Harrison

picon face
Dear all
In all the excitement regarding magnetic direction devices, has anyone
mentioned fluxgate devices with arc-minute accuracy? (specious claim -
indefensible really).
I read Electronics and Wireless World 5 years back now, got the kit and
built one sensitive to micro-gauss for monitoring the earths magnetic field
for incipient aurorae.
The company supplying the coil, Telcon metals, still exists as far as I know
and thus so should the supplier of the kit. It strikes me as being the
perfect thing for a PIC project. What's more it has a follow-up article
using it as the core of an electronic compass. In the kit you use an
oscillator and dividers to drive a square way across a coil and pick the
saturation effects up using orthogonal sense coils on the rising and falling
edges of the excitation wave. To drive it with a PIC and transistor array-
too easy sir. What *and* use an 8 bit ADC to measure the  output signal ?
Given a sufficient kick I may even bother to dig up the reference.
Email me if sufficiently desperate.
Mike
***************************************************************************
M. Harrison                                     TEL 44 1235 445288
Space Science division                          Fax 44 1235 445848
Rutherford Appleton Lab                         email spam_OUTm.c.harrisonTakeThisOuTspamrl.ac.uk
Building R25 Room 2.124                         .....mikeKILLspamspam@spam@leyenda.demon.co.uk
Chilton
Oxon OX11 0QX UK
***************************************************************************

1997\08\05@093917 by Kalle Pihlajasaari

flavicon
face
Hi Mike and other flux gaters,

> In all the excitement regarding magnetic direction devices, has anyone
> mentioned fluxgate devices with arc-minute accuracy? (specious claim -
> indefensible really).
> I read Electronics and Wireless World 5 years back now, got the kit and
> built one sensitive to micro-gauss for monitoring the earths magnetic field
> for incipient aurorae.

Time flies, it was in 1991.

> The company supplying the coil, Telcon metals, still exists as far as I know
> and thus so should the supplier of the kit. It strikes me as being the
> perfect thing for a PIC project. What's more it has a follow-up article
> using it as the core of an electronic compass. In the kit you use an
> oscillator and dividers to drive a square way across a coil and pick the
> saturation effects up using orthogonal sense coils on the rising and falling
> edges of the excitation wave. To drive it with a PIC and transistor array-
> too easy sir. What *and* use an 8 bit ADC to measure the  output signal ?

Sounds like the ideal Job for the 16C711 chips I have waiting here.
I have already wound my core according to the instructions in the
second article but never had the time to build the drive circuitry.
Might be the ideal use for a PIC, get everything into two ICs, one
PIC and one OP-AMP.

> Given a sufficient kick I may even bother to dig up the reference.

I will save you the trouble, they live in my navigation file.

The First Article appeared in September 1991 Electronics World +
Wireless World

The second in January 1992 issue

Last contact I have for Telcon is
  Telcon metals Limited
  Napier Way
  Crawley
  West Sussex
  RH10 2RB
  UK

  +44 (293) 28800
  +44 (293) 36904  (fax)

They did not sell direct to the public at the time I looked into this
project.  They have a distributor in South Africa called Spectratech
or more commonly these days Elvey International but I don't think the
cores recommended for the flux gate are any common part though I may
be wrong now.  I managed to get a similar core from Spectratech in 1992
but never did more than drive it with 50 Hz signal to look at the outputs
and watch in awe as the wave shapes on the sence coild changed as one
moved a screwdriver in the vicinity.

There is also a British Standard BS5935 or the IEC 635 that is titled
  Torroidal strip-wound cores made of magnetically soft material.
This makes for pretty weak reading but it does have one or two
formulas for calculating the window area and such.  Also mentions
the recommemded core aspect ratios but little else that is usefull.

> M. Harrison                                     TEL 44 1235 445288

Perhaps you could find out if Telcon have a UK or US retail outlet.

Cheers
--
Kalle Pihlajasaari   kallespamKILLspamip.co.za   http://www.ip.co.za/ip
Interface Products   P O Box 15775, DOORNFONTEIN, 2028, South Africa
+ 27 (11) 402-7750   Fax: 402-7751    http://www.ip.co.za/people/kalle

DonTronics, Silicon Studio and Wirz Electronics uP Product Dealer

1997\08\05@110546 by Pioneer Microsystems

flavicon
face
I have stumbled onto the thread on the Fulxgate compas, which is an
interesting subject.  Might I impose on you, Kalle, to scan and E-mail the
articles that you have?  I know it is a bit of a pain, but European
magazines are not very common over here.  Thanks!

Chris Eddy, PE
Pioneer Microsystems, Inc.
Pittsburgh, PA

1997\08\05@142537 by Harold Hallikainen

picon face
       All this fluxgate compass stuff is real interesting, but a little
too late for me.  When in high school I was intrigued with the automatic
pilot on my father's boat.  It had a floating magnet compass with a card
with a flag on it.  The base of the compass had lamp and photocell
assembly that could rotate so the flag on the card would block half the
light from the lamp to the photocell.  The rotation of the base was
connected to the motor that would steer the rudders.  There was a clutch
between the motor and the rudders.  The clutch served a couple purposes.
One was that it let you turn the autopilot off!  The second was that if
the clutch was off, the autopilot continued to adjust the compass base so
the flag half covered the photocell.  When you turned the clutch back on,
the boat would keep going in the current direction.
       Anyway, I wanted to make a fluxgate automatic pilot.
Unfortunately, my father's boat sank last November when it hit a sandbar
going into Tamales Bay in fog.


Harold

1997\08\05@144226 by John Shreffler

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face
part 0 1224 bytes
-----Original Message-----
From:   Harold Hallikainen [SMTP:.....haroldhallikainenKILLspamspam.....JUNO.COM]
Sent:   Tuesday, August 05, 1997 12:08 PM
To:     EraseMEPICLISTspam_OUTspamTakeThisOuTMITVMA.MIT.EDU
Subject:        Re: PIC: fluxgate compass

       All this fluxgate compass stuff is real interesting, but a little
too late for me.  When in high school I was intrigued with the automatic
pilot on my father's boat.  It had a floating magnet compass with a card
with a flag on it.  The base of the compass had lamp and photocell
assembly that could rotate so the flag on the card would block half the
light from the lamp to the photocell.  The rotation of the base was
connected to the motor that would steer the rudders.  There was a clutch
between the motor and the rudders.  The clutch served a couple purposes.
One was that it let you turn the autopilot off!  The second was that if
the clutch was off, the autopilot continued to adjust the compass base so
the flag half covered the photocell.  When you turned the clutch back on,
the boat would keep going in the current direction.
       Anyway, I wanted to make a fluxgate automatic pilot.
Unfortunately, my father's boat sank last November when it hit a sandbar
going into Tamales Bay in fog.


Harold

1997\08\05@211015 by Harold Hallikainen

picon face
On Tue, 5 Aug 1997 14:34:56 -0400 John Shreffler <johnsspamspam_OUTAVENUETECH.COM>
writes:
>------ =_NextPart_000_01BCA1AC.BF945EF0
>Content-Type: text/plain; charset="us-ascii"
>Content-Transfer-Encoding: 7bit
>
>Was the boat on autopilot at the time?
>


       Nope!

1997\08\11@185639 by johnb

picon face
> > Re: Various messages such as:

> > In all the excitement regarding magnetic direction devices, has anyone
> > mentioned fluxgate devices with arc-minute accuracy? (specious claim -
> > indefensible really).
> > I read Electronics and Wireless World 5 years back now, got the kit and
> > built one sensitive to micro-gauss for monitoring the earths magnetic field
> > for incipient aurorae.
> > The company supplying the coil, Telcon metals, still exists as far as I know
> > and thus so should the supplier of the kit. It strikes me as being the
> > perfect thing for a PIC project. What's more it has a follow-up article
> > using it as the core of an electronic compass.
************************************************************
For anybody following the discussion about the electronic compass:
I have tried to tie all this info together, by telephoning all the
companies and people concerned.

Electronics World (EW) is a UK magazine published by Reed-Elsevier, at:
http://www.reedbusiness.com

They have a US distributor but this is not mentioned on the Web site
which is poor. All one can do is email the editor of EW magazine, and
ask
him about EW back issues, which won't please him. I found them in my
local
Public Library.

The article by Richard Noble in the Sept 91 issue of Electronics World
is called "Fluxgate Magnetometry" is a very good introduction to the
subject of detecting and measuring very tiny magnetic fields. The second
article (Jan 92) is called "Electronic Fluxgate Compass" and shows that
a device for compass use can be much simpler. Both describe a simple but
elegant synchronous detector circuit (also known as a "lock-in"
detector)
that permits the measurement of signals buried deep in noise. However,
this
is an analog technique and is a world away from Pic-Chips.

The circuits specify the Telcon Metals Type HCR alloy core type 7a. I
have
phoned Telcon, and they still make them. They are made to order only,
and
there is a minimum order charge of UKP 200.

The more recent articles (March 97 - "True Orientation" and August 97 -
"Self-calibrating compass") show that Telcon cores are still used but a
different measuring method is used. The core now forms part of an
oscillator
whose period is a measure of the applied field. The sensor gives a large
output pulse that is easily measured by a Pic-chip. It functions
in a similar way to the Precision Navigation Inc (PNI) Vector 2X
sensors.

Kits of parts are available for Richard Noble's designs. I phoned him,
and
was referred to Speake and Co Ltd (SCL), a company in Wales that
produces them.

First, the 1991/92 parts are no longer available. They are "all in the
past"
according to Mr. Speake. He sent me a catalog of all the modules
available.

The interesting one is the FGM2 sensor plus SCL004 processor (a 40-pin
device that is clearly a Pic-chip), priced at UKP 30.55 ("EW reader
offer").
It offers RS232 output (eg, to a PC) in degrees or "raw XY", I2C link to
EEPROM to store calibration data, synchronous serial link to a digital
LED
display, and many other features.

The March 97 article ("true orientation") is well worth reading because
it
explains the very advanced maths that are needed to turn a fluxgate
sensor
into a practical compass. The effect of large nearby magnetic objects
can
be completely nulled out by their calibration system. Both the SCL and
PNI
devices offer this feature; these companies are offering very similar
devices. However, if Ford decided to fit a compass in every car, I doubt
if either company would get the contract at their current prices.

Telcon Metals are at 01293 528 800
Speake and Co are at 01873 811 281 Fax 01873 810 958

John Blackburn,
London UK.

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