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Thread: Problem with INPUT_PULLUP on pins 3 and 9

  1. #1
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    Problem with INPUT_PULLUP on pins 3 and 9

    Hello to all of you, I'm Luca, electrical and electronic technician 53 years old and this is my first post.

    After Arduino UNO, i recently started with Teensy 4.1 and unfortunately I already have a problem trying to use the QuadEncoder library.
    When I set pins 2 and 3 as channels A and B with the PULLUP option active, the encoder on that channel does not work correctly.

    Below I have verified that the problem exists even without the library. I wrote this simple program:

    enc_teensy.ino


    where I simply set all pins as pullUp inputs on setup(). Loop() is empty.

    All pins of Teensy are left unconnected. I connect only microUSB cable.

    With the tester I read that the voltage on all pins is 3.21 Volt. On pins 3 and 9 it is 0.3 Volt and on pin 13 it is 1.69 Volt.
    With teensy not powered and unconnected from all... Measuring with ohmmeter beetwin gnd and pins, I have value arround 56KOhm for all pins. For pin 3 i have 3.9KOhm for pin 9 I have 16 Ohm

    Now I can understand the voltage on pin 13, since there is the LED, but those on 3 and 9 are strange to me.
    Do I already have to think that my Teensy 4.1 was born badly? Or there are reasons that explain this. Note that if I program pin 3 or 9 for are Output they work correctly when i set I have 3.21 Volt and if reset I have 0 Volt.

  2. #2
    Senior Member+ Frank B's Avatar
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    I've tested your sketch.. can't confirm this.

    Not good.


    Your ohmmeter.. which voltage does it use for measuring Ohm?
    Last edited by Frank B; 01-21-2021 at 03:05 PM. Reason: lol... volt<-->ohm

  3. #3
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    Under 3Volt. Is a common multimeter model HT25N tester from firma HT.
    I never connect my teensy with nothing before today and I only try to test with simple wire connected to pin GND and pins, but i buy them on Amazon and i begin to tink that is not a good idea!

  4. #4
    Senior Member+ Frank B's Avatar
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    At least, Amazon makes it easy to return parts...

  5. #5
    Senior Member+ KurtE's Avatar
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    Works on the T4.1 I just tried... Pin 3 and 9 are fine.

  6. #6
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    Thanks.
    Now I arrange to have him replaced.

  7. #7
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    Quote Originally Posted by tecno67 View Post
    Under 3Volt. Is a common multimeter model HT25N tester from firma HT.
    I never connect my teensy with nothing before today and I only try to test with simple wire connected to pin GND and pins, but i buy them on Amazon and i begin to tink that is not a good idea!
    3V is possibly not safe on low voltage CMOS chips. Many standard multimeters use 0.2V full-scale except on diode mode.
    The 56k you see on the powered down chip is because you are back-driving the power through the protection diodes from that 3V
    source.

  8. #8
    Senior Member+ Frank B's Avatar
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    I measured mine (cheap but good) - it uses 0.13V
    In "diode measure" mode it uses 3.8V

    Note, the i.mx.rt uses much less than 3.3V internally. I *think* absolute max is 1.6V (only when overclocking)

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