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'[EE] Compass (magnetic sensor)'
2005\02\11@190133 by Padu

face picon face
Quick question, I'm selecting a "magnetic heading" solution for my autonomous vehicle platform. I've already searched the pic archives and some robotics sites on the internet, and here are the main suppliers that I found:

-Honeywell HMR line - too expensive, although they have one model under $100
-Dinsmore - bad resolution or bad frequency (2.5s update rate)
-Devantech - I liked this one, is not too expensive (around $50), 1Hz update and 0.1 deg resolution (5deg acc)

Do you have any other pointers?

What is important to me: 1) cost 2) update rate (2Hz is desireable, 1Hz is ok) 3) resolution (1 degree is fine already) 4) accuracy (5 deg is ok I guess)

And of course, easy to integrate with a PIC

Thanks
.--. .- -.. ..-

2005\02\11@201527 by Josh Koffman

face picon face
If your unit is always moving and has a line of sight to the sky, you
could use GPS. Not an ideal solution, I know. There used to be a bunch
of compass sensors, but at most they gave you 16 cardinal points I
believe.

Josh
--
A common mistake that people make when trying to design something
completely foolproof is to underestimate the ingenuity of complete
fools.
       -Douglas Adams

On Fri, 11 Feb 2005 15:59:39 -0800, Padu <spam_OUTpaduTakeThisOuTspammerlotti.com> wrote:
{Quote hidden}

2005\02\11@203017 by Robert Rolf

picon face
Mass market retail compass? $20 or so.
The version I saw was a vehicle/human compass and had
3 M/R sensors. Used a standard SPI interfaced chip to a
COB (chip on board) micro driving the LCD.

R

Padu wrote:

{Quote hidden}

2005\02\11@205353 by Vic Fraenckel

flavicon
face
Padu,

May I suggest you look at:

http://www.robot-electronics.co.uk/shop/Compass_CMPS032004.htm

This is a digital compass with an I2C interface
Search google for "cmps03" for many hits

or

https://www.pnicorp.com/

this is a digital compass with an SPI interface.
search google for "Vector 2x compass" for many hits

Both compasses are widely used in the robotics field.

HTH

Vic
________________________________________________________

Victor Fraenckel - The Windman
victorf ATSIGN windreader DOTcom
KC2GUI

     Home of the WindReader Electronic Theodolite
                              Read the WIND

"Dost thou not know, my son, with how little wisdom the world is governed?"
-Count Oxenstierna (ca 1620) to the young King Gustavus Adolphus

"People sleep peacefully in their beds at night only because rough
men stand ready to do violence on their behalf."
-George Orwell

"When a true genius appears in the world you may know him by this sign: that
all the dunces are in confederacy against him."   -Jonathan Swift



2005\02\11@234035 by michael brown

picon face
Some linear Hall sensors arranged around a decent magnetic (needle type)
compass.  You should be able to calculate sin and cos of the needle end
position.  From that you should be able to calculate a heading.  Perhaps
a bit Rube Goldberg, but I don't see why it wouldn't work.  Of course it
probably won't meet your needs, but it might be fun anyway. ;-)

Padu wrote:
{Quote hidden}

2005\02\11@234535 by Padu

picon face
The rover will have a gps unit, but I'd like to have two sources of
direction

----- Original Message -----
From: "Josh Koffman" <.....joshybearKILLspamspam@spam@gmail.com>
To: "Microcontroller discussion list - Public." <piclistspamKILLspammit.edu>
Sent: Friday, February 11, 2005 5:15 PM
Subject: Re: [EE] Compass (magnetic sensor)


{Quote hidden}

autonomous vehicle platform. I've already searched the pic archives and some
robotics sites on the internet, and here are the main suppliers that I
found:
> >
> > -Honeywell HMR line - too expensive, although they have one model under
$100
> > -Dinsmore - bad resolution or bad frequency (2.5s update rate)
> > -Devantech - I liked this one, is not too expensive (around $50), 1Hz
update and 0.1 deg resolution (5deg acc)
> >
> > Do you have any other pointers?
> >
> > What is important to me: 1) cost 2) update rate (2Hz is desireable, 1Hz
is ok) 3) resolution (1 degree is fine already) 4) accuracy (5 deg is ok I
guess)
> >
> > And of course, easy to integrate with a PIC
> --

2005\02\11@234948 by Padu

picon face
Vic,

Thank you for your suggestions, the first link you gave me is the 3 option
on my list, but indeed my first choice so far. It compares (at least
specifications) with the honeywell but almost half of price.

padu
{Original Message removed}

2005\02\12@021454 by Robert Rolf

picon face
How about three? Rate gyros. Murata and others make them.
They were used in 'Gyropoint' mice which are now long
off the market, but which I sometimes see at garage sales.

If you have a couple hundred to spend, you can get
a quite accurate fiber optic 3 axis gyro system from
Rockwell??

You can also make your own ultrasonic rate gyro.
If I recall correctly, and article it Nuts and Volts
2 years ago spelled out exactly how (1" length of 1"
aluminum tubing, transucer crystals, some analog
and micro.

R

Padu wrote:

> The rover will have a gps unit, but I'd like to have two sources of
> direction
>
> {Original Message removed}

2005\02\12@081755 by Dan Crews

picon face
Padu,

One thing I'd like to mention is an experience a friend had with one
such sensor suite.  He found it worked a bit erratically and after a
lot of head scratching from the entire lab, someone hit on the old
problem:

too much metal near the compass.  

It seemed the device was extremely sensitive (like dragged off 50+
degrees at times)  to metal in the environment -- like rebar in the
floor and pipes in the wall or under the asphalt . . .   Long story
short, it was neat to watch it follow magnetic iso-lines, but, um, it
never really worked well as a navigation tool.

Granted, this was a small autonomous agent, and was always close to
the ground.  I don't know the details of your design, but it's
something to consider.  All said, think the idea of GPS coupled with
gyro and some good signal processing would profit you more in function
. . .  but there's no substitute for your own hands on learning.  If
you've got the time/money/inclination to play, have fun!

Dan Crews, E.I.T.
(EraseMEcrews.danspam_OUTspamTakeThisOuTgmail.com)  <><

2005\02\12@092852 by Vic Fraenckel

flavicon
face
I believe both the CMP03 and the Vector 2x mentioned in my previous post
have provisions in their firmware to allow user to do soft iron calibration
to handle the problem of near-by iron objects. I suggest RTFM for each.
These devices have be successfully used to assist robots in navigating. I
strongly suggest googling to see some of the applications that have/are
being done with them.

HTH

Vic
________________________________________________________

Victor Fraenckel - The Windman
victorf ATSIGN windreader DOTcom
KC2GUI

     Home of the WindReader Electronic Theodolite
                              Read the WIND

"Dost thou not know, my son, with how little wisdom the world is governed?"
-Count Oxenstierna (ca 1620) to the young King Gustavus Adolphus

"People sleep peacefully in their beds at night only because rough
men stand ready to do violence on their behalf."
-George Orwell

"When a true genius appears in the world you may know him by this sign: that
all the dunces are in confederacy against him."   -Jonathan Swift


2005\02\12@151208 by Dan Crews

picon face
On Sat, 12 Feb 2005 09:27:15 -0500, Vic Fraenckel
<victorfspamspam_OUTwindreader.com> wrote:
> I believe both the CMP03 and the Vector 2x mentioned in my previous post
> have provisions in their firmware to allow user to do soft iron calibration
> to handle the problem of near-by iron objects. I suggest RTFM for each.

Don't remember who made my friend's compass -- wasn't my money spent
-- but it did indeed have an ambient magnetic calibration routine.  It
worked great for the motors, wires, batteries, etc,  but when the
robot moved ten feet, the magnetic profile of the rebar underneath it
had changed (can we say recalibrate?  Oh, wait, we need a reference to
North to do that -- Foiled again!)

Yes, datasheets are created for a purpose, and the more you read, the
more you savor the really good ones . . .  but they don't always solve
inherent problems.  the calibration is good for cutting out, say, the
frame of a car or a nearby engine block/motor, but if this is a small
vehicle (again, I havn't seen Padu's design)  or mounted near the
ground, then metal moving relative to the compass may strongly affect
the measurements -- something we desire independance from!


Dan Crews, E.I.T.
(@spam@crews.danKILLspamspamgmail.com)  <><

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