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Intefacing ARM A/D with 5V sensors

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  • gkicomputers
    Hi, What would be the best way to interface a 5V sensor (say a Analog Devices gyro) to the 2.5V ARM A/D? The gyro s output is already buffered, would a simple
    Message 1 of 2 , Mar 4, 2005
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      Hi,

      What would be the best way to interface a 5V sensor (say a Analog
      Devices gyro) to the 2.5V ARM A/D? The gyro's output is already
      buffered, would a simple voltage divider work to drop the output to
      2.5 V? What values and resistor types would I use? Do I pick the
      lowest resistor value that the sensor can drive (to minimize the
      input impedance seen by the a/d), or do I need to use another opamp
      with a .5 gain stage.

      Also, I understand the ARM A/D spec is guarantee at full core speed,
      but do you think the performance of the A/D vary with speed? I heard
      some microcontrollers a/d performance has peaks and valleys as a
      function of speed.

      thanks for any help the ADuC is a nice chip!

      joe pierson
    • good_roots_in_germany
      ... speed, ... heard ... Well, your question is already one year old, but maybe still valid. I recomend to do a voltage divider e.g. 2 x 1 kOhm resistor and
      Message 2 of 2 , Jul 17, 2006
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        --- In ADuC_ARM@yahoogroups.com, "gkicomputers" <gkicomputers@...>
        wrote:
        >
        >
        >
        > Hi,
        >
        > What would be the best way to interface a 5V sensor (say a Analog
        > Devices gyro) to the 2.5V ARM A/D? The gyro's output is already
        > buffered, would a simple voltage divider work to drop the output to
        > 2.5 V? What values and resistor types would I use? Do I pick the
        > lowest resistor value that the sensor can drive (to minimize the
        > input impedance seen by the a/d), or do I need to use another opamp
        > with a .5 gain stage.
        >
        > Also, I understand the ARM A/D spec is guarantee at full core
        speed,
        > but do you think the performance of the A/D vary with speed? I
        heard
        > some microcontrollers a/d performance has peaks and valleys as a
        > function of speed.
        >
        > thanks for any help the ADuC is a nice chip!
        >
        > joe pierson
        >

        Well, your question is already one year old, but maybe still valid. I
        recomend to do a voltage divider e.g. 2 x 1 kOhm resistor and buffer
        this with an Op-Amp (+ to resistor chain, - to output). Analog
        recomends a 10 Ohm resistor between output and ADC input. More
        details are found at ADuC datasheet rev. A, page 41, figure 47.

        Guenther
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