Re: Source Sealed Potentiometers?


Frnak McKenney wrote:
The documents mentioned in the other thread:

http://www.taosinc.com/downloads/pdf/encoderdesign4b.pdf
http://www.taosinc.com/downloads/pdf/IOSDN1.pdf

describe a somewhat<grin!> less sensor-hungry approach to using a
single-track encoder pattern to determine absolute position, in
their case to 1/4096 of a full turn (0.088 degrees). They use a
single sensor (really, 128 photodiodes in a single package) with a
single-track 256-element pattern to accomplish this; I'm on my
third reading, and it's starting to make sense.

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 ;)

Robert


Anyway, if I misunderstood your comment, I apologize. Please give it
another "whack".


Frank McKenney, McKenney Associates
Richmond, Virginia / (804) 320-4887
Munged E-mail: frank uscore mckenney ayut minds pring dawt cahm (y'all)
--
"We don't just borrow words; on occasion, English has pursued other
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pockets for new vocabulary." -- James D. Nicoll
--

.

Relevant Pages

  • Re: Source Sealed Potentiometers?
    ... to glue 256 magnets of two different widths ... pattern more reliably than I can glue individual itsy-bitsy ... Reverse the set up a bit, put the magnet on the sensor and just leave ...
    (comp.arch.embedded)
  • Re: Hall effect sensor
    ... You gotta worry about the magnetic field strength dropping with time and temperature (I forget if the magnets get weaker as temperature goes up or down, ... If you have a rotating thingy, and the environment is rugged, you may need to mount the sensor & magnet rather far apart to allow for vibration, knocks, misalignment etc. ... However a year or two ago that mine had a fire and temporarily closed down, so the price of neodymium magnets shot up. ...
    (sci.electronics.basics)
  • Re: Which one to buy: Tamron SP 180mm F/3.5 Di Macro or Sigma EX 180mm F/3.5 DG Macro
    ... The "mush" is the right thing to do. ... resolving detail in the image projected on the sensor, ... Seven randomly incorrect lines is 7 more mistakes than no incorrect lines. ... And they really are randomly incorrect: the test pattern has equal-width ...
    (rec.photo.digital.slr-systems)
  • Re: Shimmed Mounts and Extension Tubes
    ... Wolfgang Weisselberg wrote: ... sensor already had a pattern it could use to calculate the required focus? ... It's plausible to me that at the instant when the squirrel disappeared, the lens was racking to find a pattern that the AF sensors could use. ... The fact that the camera moves the focussing motor until it gets a signal from the AF sensor is what makes it a closed-loop process. ...
    (rec.photo.digital.slr-systems)
  • Re: Minimal encoder patterns (was: Source Sealed Potentiometers?)
    ... "Absolute" optical encoder wheel patterns ... pattern into a two-track pattern. ... array sensor to determine the encoder wheel's position. ... Frank McKenney, McKenney Associates ...
    (comp.arch.embedded)