[Tinyos-help] question about magnetometer sensor

Tian He tianhe at cs.virginia.edu
Mon Jan 26 09:24:20 PST 2004

> Hello,
>     I just began to use magnetometer sensor on the platform of MICA2.
> Since we have some experiences to do with MICA, I am now able to get
> sensing values. But my problem is that the magnetometer sensor seems to
> only can detect moving magnetic field! What I mean is that when the
> magnet is still, the sensor value we get from ADC is always 0 (or
> almost 0) no matter how close and how strong the magnet is. But as
> long as it moves, the sensor can provide values reflecting the
> change of magnetic field strength. Does anybody have the same problem?
> If you once had the same problem and have solved it, please tell me
> your solution. If you haven't, welcome to send me email to discuss it.

Please take a look at the magnet sensing component.  The output of  this
compoent is the changes of the sensor values.
Not absolute value.  You need rewrite the code, if you want to detect the
absolute values.  It is not a hardware issue.

>     Another problem is about the sensitivity of the magnetometer
> sensor. I use a powerful magnet ring to give a magnetic field. But the
> sensor only can detect it within about 1 foot (so weak, isn't it?). I
> hear for others that some people claimed they can do measurement with
> the distance of 2 meters. If you do, please tell me how and what kind
> of magnet you use and other measuring condition.

Depends on the size of the targets. We can detect car at about 2~3 meters.
Your result is normal.

> Q. Zhou
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