> > 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.