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Thread: Teensy 4.0,4.1 web pages need a warning about INPUT_DISABLE on Analog Inputs

  1. #1
    Junior Member
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    Oct 2019
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    Tucson
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    Teensy 4.0,4.1 web pages need a warning about INPUT_DISABLE on Analog Inputs

    The Teensy 4.0 and 4.1 analog inputs require the digital inputs to be disabled, otherwise they have a weak pullup/pulldown circuit active that causes a small glitch around the midpoint, ~1.67V.
    The cure is this statement in the setup() section:
    pinMode(<pin>, INPUT_DISABLE);

    The Teensy 4.0 and Teensy 4.1 product pages, in the Analog Input section, need to state this important fact.

    I wasted a couple hours before I finally figured out the right Google search terms to find the forum discussion in which this is revealed.

  2. #2
    Senior Member
    Join Date
    Jul 2020
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    I think its the bus-keeper functionality, and there is somewhere a thread about this.

    Note the description on the product page:
    Digital Input Pins
    Digital pins may be used to receive signals. Teensy 4.0 pins default to INPUT most with a "keeper" resistor. Teensy 4.0 pins accept 0 to 3.3V signals. The pins are not 5V tolerant. Do not drive any digital pin higher than 3.3V.
    This issue could be regarded as simply a bug in analogRead() for the T4. The T4 is the most recent Teensy so there are still issues like this.

    [ here's that thread: https://forum.pjrc.com/threads/34319...+INPUT_DISABLE ]

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