On Monday 19 April 2004 08:21 pm, John Tserkezis scribbled:
>   Short answer:  Use GPS, you need to be moving, but it's a small price=
 to
> pay.

Way beyond what I wanted/needed, at far higher cost.


>   Longer answer:
>   Basically, it should be mounted anywhere where it will work within th=
e
> calibration limits of the compass.  If it doesn't have calibration
> adjustments (mechanical or electronic) don't even try using it.

Well, I made the compass with a PIC, some LEDs and a sensor.  The sensor =
has 4=20
digital outputs, which with overlap, can indicate 8 different locations. =
=20
Best I can hope for in terms of calibration is to rotate the sensor.  But=
=20
with a resolution of only 8 points, precision is not a problem (or even a=
=20
requirement :-)


>   My magnetic compass came with instructions to point the vehicle to no=
rth
> (using other known methods) some distance from any surrounding metal,
> overhead wires etc, then go though the calibration adjustment (point NS=
E &
> W) till it reads correctly.
>
>   I had it down to within a few degrees.
>
>   In use, it was a different story.  Every time you remove or install a
> piece of equipment in your vehicle, you have to check it doesn't interf=
ere
> with the compass, and re-calibrate if it does.

Sort like like how aircraft compasses get re-calibrated every time any=20
equipment is changed.  They just add a little card with correction factor=
s=20
(degrees) for major points.


>   While sitting at traffic lights, the adjacent lane (if moving) would
> cause the compass to swing back and forth each time a car passed me.

Ugh!


>   While driving in a steady straight line on the freeway (no other
> surrounding cars) the compass would sometimes swing back and forth due =
to
> surrounding steel barriers and such.
>
>   In the end, I found it so useless (because I couldn't guarantee the
> "purity" of my environment where I needed it) that I relied on GPS only=
=2E=20
> The compass was for backup just in case GPS went down.
>
>   Now, if I need backup, I carry two GPS recievers.

So I wonder what sensor the compass in newer American vehicles use?  I've=
=20
driven quite a number of these and played with (evaluated?) the compasses=
=20
quite a bit.  Seemed to work quite decently.


Cheers,
-Neil.

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