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Thread: Necessity of Level Shifter for Teensy 3.2 I2C Functionality

  1. #1
    Junior Member
    Join Date
    Mar 2019
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    2

    Necessity of Level Shifter for Teensy 3.2 I2C Functionality

    I've read just about everything on this forum I can find about using Teensy 3.2 and I2C. I have successfully gotten a Teensy slave working with a Teensy master using I2C protocol for testing purposes.

    I am now attaching the Teensy 3.2 to a 5V logic I2C bus within another system but haven't succeeded in I2C SCL or SDA to the Teensy. I want to rule out the necessity of a level shifter for the Teensy 3.2.

    Is a level shifter needed for I2C functionality of a Teensy 3.2 on a 5V logic bus? I believe the answer is no since I2C pulls down the line, but I want to double check here as well and ensure I don't need extra hardware to get this working. I know Teensy's are 5V tolerant on digital pins and just need to rule this possibility out so I can continue debugging more into software perhaps.

    Thank you for the time!

  2. #2
    Hi, try putting two pullup resistors 4k7 on sda and scl
    https://www.pjrc.com/teensy/td_libs_Wire.html

  3. #3
    Junior Member
    Join Date
    Mar 2019
    Posts
    2
    I've got 2 pullups on there now and they work great with another Teensy as a Master. The issue is when I am putting the Teensy slave on a 5V I2C bus though and whether a level shifter isn't actually needed since I2C pulls the line down?

  4. #4
    theoretically there is no need, teensy 3.2 is 5v tolerant.

  5. #5
    Senior Member
    Join Date
    Feb 2017
    Posts
    279
    Why not just use the level shifter and remove all doubt? Here: https://www.adafruit.com/product/757

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