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Thread: >1Mohm impedance on Teensy 3.2 analog inputs?

  1. #1
    Junior Member
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    >1Mohm impedance on Teensy 3.2 analog inputs?

    The datasheets for these resistive position sensors say that impedance needs to be >1Mohm for accurate performance:

    https://www.murata.com/~/media/webre...tion/r51e.ashx

    https://industrial.panasonic.com/cdb.../ARE0000C1.pdf

    Do I need to add anything to the connection from position sensor to Teensy 3.2 analog input pin to achieve >1Mohm impedance? Capacitors, resistors, inductors?

    If it makes a difference, the wire lengths from position sensor to Teensy will be 5-20cm.

    Thanks.

  2. #2
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    What resolution and sample rate or bandwidth do you need? You could simply put a 1M resistor in series, that would make your sensor happy, but the Teensy ADC unhappy (either extremely high noise, and/or slow response with a filter capacitor, due to RC time constant). Normally with such a high impedance requirement you would use an active device, like a buffer opamp between the sensor output and the ADC input.

  3. #3
    Senior Member+ Frank B's Avatar
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    It's more in the range of 100k.

  4. #4
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    Quote Originally Posted by JBeale View Post
    What resolution and sample rate or bandwidth do you need? You could simply put a 1M resistor in series, that would make your sensor happy, but the Teensy ADC unhappy (either extremely high noise, and/or slow response with a filter capacitor, due to RC time constant). Normally with such a high impedance requirement you would use an active device, like a buffer opamp between the sensor output and the ADC input.
    Thanks for mentioning opamps. With that hint I found this article which goes into more detail about the tradeoffs involved in driving an MCU ADU with a resistive voltage divider:

    https://www.embeddedrelated.com/showarticle/110.php

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