PicDude wrote:

>>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.

  Not really, cost of a bottom end GPS unit would be on par with a
quality compass.

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

  The only built-in compass I've seen in cars is similar to what you've
outlined, with out eight direction combinations.
  What type of sensor are you using?  Only type I've seen offer some
calibration adjustments.  Yours sounds like a sealed unit with only
power input, and position output.

>>  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!

  Yes, I was impressed...  Not.

>>  Now, if I need backup, I carry two GPS recievers.

> So I wonder what sensor the compass in newer American vehicles use?

  Pretty much similar to what you're doing now.

>  I've
> driven quite a number of these and played with (evaluated?) the compasses
> quite a bit.  Seemed to work quite decently.

  They too don't have very high directional accuracy, and since they're
working with known vehicles, it's easy to implement.  They know exactly
where they stand, the calibration offsets are fixed, there's virtually
no guesswork on the production line.

  As an after-market thing, it's a different story.

  I've never bothered with it, because accuracy and more specifically,
resolution was next to useless for my purposes.

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