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Thread: Teensy 3.1 Logic Level 5V tolerance

  1. #1

    Teensy 3.1 Logic Level 5V tolerance

    I am using a 5V IBM TrackPoint module as a HID mouse. I am connecting the TrackPoint's PS/2 RESET, DATA, and CLK to digital pins 13, 9, 3 via a Logic Level Converter. All works well. The TrackPoint is powered via the Teensy 3.1's 5V VUSB.
    I am using the GND pin next to the RESET button.

    I've been told that the Teensy 3.1 digital pins are 5V tolerant, so I removed the Logic Level Converter, and connect directly to the Teensy, but nothing works.
    Do I have to set anything to enable 5V tolerance? or am I mistaken in its use?

    Can anyone suggest what to try next, please

    Here is a link to the setup thread on the thinkpad forum:
    http://forum.thinkpads.com/viewtopic.php?f=12&t=111143

    And a link to the library on Github:
    https://github.com/feklee/arduino-trackpoint
    Last edited by rootScript; 05-05-2014 at 03:57 PM. Reason: updated related threads

  2. #2
    Here is a diagram, that should help explain what I doing:
    Click image for larger version. 

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    TrackPoint, Logic Level Converter, Teensy 3.1.

  3. #3
    Senior Member+ MichaelMeissner's Avatar
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    IIRC, the 5v tolerance only applies when you are doing a digitalRead. If you are doing an analogRead, you need to make sure the voltage is not higher than 3.3v.

  4. #4
    Senior Member PaulStoffregen's Avatar
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    The pins with both analog and digital functionality (pins 14 to 23) are 5V tolerant, even when operating as analog inputs.

    But anything over the reference voltage, which is 3.3V by default but can be configured for 1.2V, will read as the maximum value (1023 in the default 10 bit mode). Applying 3.4 to 5.0 volts to those pins will not damage the chip, but you can't read the voltage other than knowing it's over 3.3V.

    Pins A10, A11, A12, A13 and A14 are NOT 5V tolerant. Applying more than 3.3V to any of those pins can result in damage.

  5. #5
    I have moved over to the pin ranges suggested:
    Code:
    Trackpoint trackpoint(
    17, //TrackPoint DATA
    16, //TrackPoint CLK
    14); //RESET
    But the TrackPoint doesn't respond (without the Logic Level Converter (LLC)).

    So I tried removing the LLC from either the DATA or CLOCK, separately.
    It seems that the TP_CLK only works through the LLC, to Teensy pin 16.
    The TP_DATA is ok to connect straight to the Teensy pin 17.

    But anything over the reference voltage, which is 3.3V by default but can be configured for 1.2V, will read as the maximum value (1023 in the default 10 bit mode). Applying 3.4 to 5.0 volts to those pins will not damage the chip, but you can't read the voltage other than knowing it's over 3.3V.
    So do you mean that the pins 14-23 won't be damaged by 5V, but I can't read the values if over the reference voltage of 3.3V (other than know the value is over 3.3V (in my case the voltage across GND & pin 16 is 4.4V))?
    You mentioned the reference voltage can be configured for 1.2V, I am guessing that 5V ref is not possible.

    Paul:
    I as understand it (I could be misinterpreting) - you are saying pins 14-23 are tolerant (no damage) of 5V, but not capable of being used with 5V Logic. Is that correct?
    Last edited by rootScript; 05-05-2014 at 03:50 PM.

  6. #6
    Senior Member+ KurtE's Avatar
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    I know others probably have better guesses.

    I am only guessing, but I had an issue several years ago with an XBee connecting up to an Atmega based board (Axon II), and with some XBee adapters including early sparkfun one, it would not work. Finally figured out that the DOUT from the XBee was not being level shifted and it's high voltage was not high enough to register as a high on the Axon... Wonder if maybe you are running into something similar here?

    Kurt

  7. #7
    With the LLC connected, the voltage before the LLC across GND & TP_CLK (TrackPoint CLK) is 4.1V, the voltage after the the LLC is 2.7V. This is when the TrackPoint works, with TP_CLK on Teensy pin 16 (via the LLC).

    Without the LLC the voltage across GND & TP_CLK is 4.4V, but the TrackPoint doesn't respond.

    With or without the LLC, the Teensy shows up in the USB device tree as a USB 3.0 HiSpeed Bus > Serial/Keyboard/Mouse/Joystick

  8. #8
    Senior Member Jp3141's Avatar
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    Quote Originally Posted by PaulStoffregen View Post
    The pins with both analog and digital functionality (pins 14 to 23) are 5V tolerant, even when operating as analog inputs.

    But anything over the reference voltage, which is 3.3V by default but can be configured for 1.2V, will read as the maximum value (1023 in the default 10 bit mode). Applying 3.4 to 5.0 volts to those pins will not damage the chip, but you can't read the voltage other than knowing it's over 3.3V.

    Pins A10, A11, A12, A13 and A14 are NOT 5V tolerant. Applying more than 3.3V to any of those pins can result in damage.
    Paul -- it might be helpful (and avoid latent failures) if the pinout card indicated this.

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