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Re: "Tilt" Sensor

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  • John
    ... I would go with an accelerometer if you can, it has the big advantge of no moving parts. I appreciate your price concern, but would have thought that the
    Message 1 of 7 , Apr 11 3:11 AM
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      --- In Electronics_101@yahoogroups.com, "Chuck Hackett" <egroupscdh@...> wrote:

      > I am currently experimenting with an Analog Devices ADXL202
      > Tilt/Accelerometer (+/- 2g) but I fear that it will not give me the
      > resolution I need.
      >
      > There are some real nice ones out there for chips in the $30-$50 range but
      > I'd like to keep it closer to $5-$15 ...
      >
      > Suggestions?
      >  

      I would go with an accelerometer if you can, it has the big advantge of no moving parts. I appreciate your price concern, but would have thought that the cost of even the best accelerometer would be a very small proportion of the cost of the entire machine.

      John.
    • Chuck Hackett
      ... Or ... Disadvantages of pendulum: - Takes lots of room - Required critical damping to settle it quickly after a disturbance (i.e.: vehicle moves, vehicle
      Message 2 of 7 , Apr 11 6:31 PM
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        > From: AlienRelics
        >
        > Plumb bob with capacitive proportional sensing of differential position?
        Or
        > LVDT sensing of position of same?

        Disadvantages of pendulum:
        - Takes lots of room
        - Required "critical" damping to settle it quickly after a disturbance
        (i.e.: vehicle moves, vehicle stops, hydraulics tilts vehicle towards
        "level", etc.). This probably requires placing the pendulum, or parts of
        it, in oil to dampen it, and the oil bath must be enclosed to avoid
        spilling, etc., etc.
        - Still must build a "pickoff" device/sensor which adds complication

        > From: John
        > ....
        > I would go with an accelerometer if you can, it has the big advantage of
        no
        > moving parts. I appreciate your price concern, but would have thought that
        > the cost of even the best accelerometer would be a very small proportion
        of
        > the cost of the entire machine.

        I have added caps to the accelerometer I have to drastically lower its
        bandwidth (down to about 10 hz) and as the bandwidth goes down the
        resolution goes up (or the ability to detect the 'real' value out of the
        'noise'). It looks like I will be able to achieve a sensitivity of a bit
        more than 0.2 degrees.

        In my search I uncovered several nice devices at SparkFun.com, even a nice
        unit that combines a 3-axis accelerometer with a tilt-corrected compass in
        the same chip.

        BTW: The "cost of the entire machine" is pretty low considering that its
        parts (including solenoid valves, hyd pump, motors, steel, etc.) came from
        my "scrap box" :-)
         
        Cheers,

        Chuck Hackett
        "Good judgment comes from experience, experience comes from bad judgment"
        7.5" gauge Union Pacific Northern (4-8-4) 844
        http://www.whitetrout.net/Chuck
      • John Beaty
        Hi Chuck, I have been mulling over a somewhat related project with a 2g accelerometer. That range of resolution would work very well.   How many bits of
        Message 3 of 7 , Apr 12 7:17 AM
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          Hi Chuck,

          I have been mulling over a somewhat related project with a 2g accelerometer.
          That range of resolution would work very well.  

          How many bits of resolution do you use for an A/D converter to successfully read at that level?
          How much time is needed between readings to "see" the 0.2 deg change?

          Thanks

          John


          ________________________________
          From: Chuck Hackett <egroupscdh@...>
          To: Electronics_101@yahoogroups.com
          Sent: Thursday, April 11, 2013 9:31 PM
          Subject: RE: [Electronics_101] Re: "Tilt" Sensor



           
          > From: AlienRelics
          >
          > Plumb bob with capacitive proportional sensing of differential position?
          Or
          > LVDT sensing of position of same?

          Disadvantages of pendulum:
          - Takes lots of room
          - Required "critical" damping to settle it quickly after a disturbance
          (i.e.: vehicle moves, vehicle stops, hydraulics tilts vehicle towards
          "level", etc.). This probably requires placing the pendulum, or parts of
          it, in oil to dampen it, and the oil bath must be enclosed to avoid
          spilling, etc., etc.
          - Still must build a "pickoff" device/sensor which adds complication

          > From: John
          > ....
          > I would go with an accelerometer if you can, it has the big advantage of
          no
          > moving parts. I appreciate your price concern, but would have thought that
          > the cost of even the best accelerometer would be a very small proportion
          of
          > the cost of the entire machine.

          I have added caps to the accelerometer I have to drastically lower its
          bandwidth (down to about 10 hz) and as the bandwidth goes down the
          resolution goes up (or the ability to detect the 'real' value out of the
          'noise'). It looks like I will be able to achieve a sensitivity of a bit
          more than 0.2 degrees.

          In my search I uncovered several nice devices at SparkFun.com, even a nice
          unit that combines a 3-axis accelerometer with a tilt-corrected compass in
          the same chip.

          BTW: The "cost of the entire machine" is pretty low considering that its
          parts (including solenoid valves, hyd pump, motors, steel, etc.) came from
          my "scrap box" :-)
           
          Cheers,

          Chuck Hackett
          "Good judgment comes from experience, experience comes from bad judgment"
          7.5" gauge Union Pacific Northern (4-8-4) 844
          http://www.whitetrout.net/Chuck




          [Non-text portions of this message have been removed]
        • Chuck Hackett
          ... In my case the accelerometer puts out two signals for each (x & Y) axis. One is the raw analog signal and the other is a PWM signal. I ll be using the
          Message 4 of 7 , Apr 14 1:26 PM
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            > From: John Beaty
            >
            > Hi Chuck,
            >
            > I have been mulling over a somewhat related project with a 2g
            > accelerometer.
            > That range of resolution would work very well.
            >
            > How many bits of resolution do you use for an A/D converter to successfully
            > read at that level?

            In my case the accelerometer puts out two signals for each (x & Y) axis. One is the raw analog signal and the other is a PWM signal. I'll be using the PWM signals and feeding it to a timer pin on the ATMega to measure the pulse width.

            The data sheet seems to say that using the PWM you get a bit more resolution than what is available in the analog signal but it's not clear to me why.

            The part I'm using (ADXL202) is no longer available (at least I don't see it at Mouser or Digikey) but I'm sure there are newer chips that would work for you.

            Also check out http://SparkFun.com as they have several with eval/breakout boards. (they also gave gyros and compasses if you need them).

            > How much time is needed between readings to "see" the 0.2 deg change?

            With the added low-pass filters to reduce the response frequency and increase resolution the settling time is still well under sub-1/4 second which works for my application.

            Cheers,

            Chuck Hackett
            "Good judgment comes from experience, experience comes from bad judgment"
            7.5" gauge Union Pacific Northern (4-8-4) 844 http://www.whitetrout.net/Chuck
          • John Beaty
            The manufacturer s website suggests the ADXL212 which looks to be very similar and looks like it uses the PWM interface. Haven t studied it in detail, but is
            Message 5 of 7 , Apr 15 6:08 AM
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              The manufacturer's website suggests the ADXL212 which looks to be very similar and looks like it uses the PWM interface.
              Haven't studied it in detail, but is is an interesting approach that I had not seen.

              Thanks for the information and suggestions.

              John.


              ________________________________
              From: Chuck Hackett <egroupscdh@...>
              To: Electronics_101@yahoogroups.com
              Sent: Sunday, April 14, 2013 4:26 PM
              Subject: RE: [Electronics_101] Re: "Tilt" Sensor



               
              > From: John Beaty
              >
              > Hi Chuck,
              >
              > I have been mulling over a somewhat related project with a 2g
              > accelerometer.
              > That range of resolution would work very well.
              >
              > How many bits of resolution do you use for an A/D converter to successfully
              > read at that level?

              In my case the accelerometer puts out two signals for each (x & Y) axis. One is the raw analog signal and the other is a PWM signal. I'll be using the PWM signals and feeding it to a timer pin on the ATMega to measure the pulse width.

              The data sheet seems to say that using the PWM you get a bit more resolution than what is available in the analog signal but it's not clear to me why.

              The part I'm using (ADXL202) is no longer available (at least I don't see it at Mouser or Digikey) but I'm sure there are newer chips that would work for you.

              Also check out http://SparkFun.com as they have several with eval/breakout boards. (they also gave gyros and compasses if you need them).

              > How much time is needed between readings to "see" the 0.2 deg change?

              With the added low-pass filters to reduce the response frequency and increase resolution the settling time is still well under sub-1/4 second which works for my application.

              Cheers,

              Chuck Hackett
              "Good judgment comes from experience, experience comes from bad judgment"
              7.5" gauge Union Pacific Northern (4-8-4) 844 http://www.whitetrout.net/Chuck




              [Non-text portions of this message have been removed]
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