[sdiy] Magnetic field

[Ian Fritz]

At 05:48 AM 8/2/2004, WeAreAs1 at aol.com wrote:


>I do agree with Harry, though.  I think optical would be more reliable,
>predictable and consistent.  There wouldn't be as great a variability as 
>to the
>position of the light sources or sensors as there would be with the magnetic
>system.  I'm guessing that there's a lot of variability in magnetic feild 
>strength
>with those tiny magnets, which would require a lot of futzing, I think.

Think and guess what you like.  :-)

I've worked with both.  Photo sources and detectors have a lot of part-to 
part variability.  Also a large temperature dependence.  You can find some 
discussion of this at my website, where I show a servo compensated photo 
system used for an opto-based breath-pressure sensor.

Magnets don't have any significant temperature drift, and the Hall sensors 
you get nowadays have built-in compensation.  I like the idea of having a 
software calibration. Mechanical adjustment of this stuff is a pain, 
especially if you have to do a full keyboard.

Good luck!

   Ian