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Re: pot verse optical encoder

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  • Bruce
    jownzie, There are rotary pots made specifically for that application, they can be expensive though. Mechanical rotary encoders, RVDTs (Rotary Variable
    Message 1 of 2 , Jan 1, 2005
      jownzie,

      There are rotary pots made specifically for that application, they can
      be expensive though.

      Mechanical rotary encoders, RVDTs (Rotary Variable Displacement
      Transformers), and synchros and resolvers are also used to measure
      angular position.

      I picked up a handful of Grayhill mechanical encoders from
      Allelectronics a couple years ago. I think they were 4 bit gray code
      encoders. You haven't mentioned your accuracy, resolution or range
      requirements.

      I wonder if you could hack a synchro together by taking a stepper, run
      A/C or pulsing DC (NRZ) into the rotary element and picking the
      strongest signal off the secondary?

      Folks also put together DIY optical encoders using reflective painted
      (black/white) pinwheel designs and optically coupled elements.

      Bruce

      --- In home_electronics@yahoogroups.com, "jownzie" <smjones1969@s...>
      wrote:
      >
      >
      > I am working on a device that needs to monitor the position of
      > something. It is an angular displacement and I have geared the pot
      to
      > go almost one full turn giving me maximum resolution. I like using
      > this method becuase of its simplicity but there are a couple of
      flaws.
      > The first is I suspect the POT could potential give bad readings as
      it
      > is sliding around, even with a filter capacitor in place. I have not
      > witnessed this but have not conducted any tests. Even if the
      feedback
      > ocasionally bounced, it probably wouldn't be too bad since the
      > sampling and calculations would be happening one right after
      another.
      > The other concern is that pots have a rated life. I am thinking of
      > manufacturing this project and can't deal with something that would
      > expire after a year or whatever. So the best next idea I think is to
      > use an optical encoder in place of the pot. I don't like using the
      > encoder for a couple of reasons. The first is it is a bit more
      complex
      > than simply reading an A to D conversion. The second is that is
      always
      > relative to a reference, while a pot gives you true position. And
      the
      > encoder, from what I have saw, are easily 30 dollars even for a
      small
      > basic one. So I guess my question is this? Would I be able to get
      away
      > with a pot in this application. How long do pots last? Can I ensure
      > the pot will give true readings as it is sliding around? I know you
      do
      > not know all the specifics, but basically the pot would be simply
      > sweeping full range back and forth driven by a small DC motor,
      meaning
      > the speeds would not be incredibly fast.
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