Re: Source Sealed Potentiometers?


Frnak McKenney wrote:
On 9 Oct 2006 12:15:19 -0700, Robert Adsett <sub2@xxxxxxxxxxxxxxxxxxxxx> wrote:
Frnak McKenney wrote:
--snip--
http://www.taosinc.com/downloads/pdf/encoderdesign4b.pdf
http://www.taosinc.com/downloads/pdf/IOSDN1.pdf
--snip--
I'm also having trouble translating the "tracked" approach out of
the optical domain and into the magnetic... um, "field" (oooog!)
to satisfy the OP's concerns regarding outdoor use. It's not that I
think that this translation _couldn't_ be done, it's that I get
stuck at the part where I picture _my_ rather clumsy fingers trying
(for the third time) to glue 256 magnets of two different widths
around the circumference of the OP's platform in the correct
pattern.

Hm. What if I wrapped _one_ flexible magnetic strip around the
platform's rim and then covered it with a carefully punched strip of
metal? Will enough of the strip's magnetic field get through so
that a linear Hall Effect sensor can tell the difference between a
narrow and a wide slit? I suspect I can print-and-paste-and-punch a
pattern more reliably than I can glue individual itsy-bitsy
magnets... I need to think about this.

Reverse the set up a bit, put the magnet on the sensor and just leave
the punched pattern on the table. That's essentially how gear tooth
detecting hall sensors work, at least some of them incorporate the
magnet into the sensor assembly. Building an array of them to achieve
the desired resolution I'll leave to you ;)

By "leave the punched pattern on the table" did you mean not use it?
Or that I should attach my oh-so-laboriously punched metal strip to
the rim of the platform ("table")?

The latter, sometimes English is just too flexible :)

Oh, and just to stir the pot a bit more, in my search for an array
of Hall Effect sensors I ran across the Honeywell HMC1512 magnetic
sensor:

I've usually used Allegro sensors (linear sensors to measure current)
The one time I used a Honeywell sensor it had entirely too much drift.
Linear hall sensors in general are rather inaccurate and need
calibration before use. I think you'd need a rather gross pattern to
use them.

Ah, well... It's been fun, but I have to go do some RealWork(tm).
Sigh.

Well, that's no fun!

Robert

.

Relevant Pages

  • Re: Hall effect sensor
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  • Re: Source Sealed Potentiometers?
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