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Thread: Newbie: What is meant by "not 5 volt tolerant"

  1. #1
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    Newbie: What is meant by "not 5 volt tolerant"

    Hi, I'm a newbie to physical projects such as teensy, but a long time programmer (iOS)

    I have just received my first teensy, a 3.6

    It says "Teensy 3.6 pins are not 5 volt tolerant. Do not apply more than 3.3 volts"

    Yet when I do the "tutorial 4" project,on this site, I install a button, and that button feeds 5 volts to a pin. The same goes for the next tutorial with a potentiometer. This is because the power coming from the Teensy itself (actually the USB connected to it) is 5 volts.

    https://www.pjrc.com/teensy/tutorial3.html
    https://www.pjrc.com/teensy/tutorial4.html

    So this leaves me a bit confused as to the instruction not to apply more than 3.3 volts to a pin.

    Sm I not meant to be doing these tutorials? Or am I missing something obvious?

    Can someone explain this to me?

    Thanks

  2. #2
    Senior Member+ KurtE's Avatar
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    It means that this board does not support +5v going to the IO pins, and doing so could easily damage the board.

    Some of these tutorials have not been updated to work properly on those boards which do not support +5v.
    But in the Tutorial 3, you could easily modify it to instead bring the +3.3v signal from the board to the rail instead of the +5v and things should work fine. Obviously looking at volt meter will only show 3.3v instead of 5, but...

  3. #3
    Senior Member+ defragster's Avatar
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    to add - hopefully usefully - to KurtE's note:

    The original Arduino UNO and Teeny 2's were designed as 5 volt devices to interface to other things with 5 volt signals.

    As processors moved to 32 bit and faster speeds 3.3V has become the norm as exemplified by Teensy 3.x's and the LC. Some devices could tolerate 5v signals to some degree - though they only required and provided 3.3V outputs.

    The chip for T_3.2 was specifically chosen for broad 5V tolerance to prevent damage interfacing to 'older' signals. The T_3.5 was made because of digital pin 5V tolerance - at the cost of reduced performance over the T_3.6 which for performance sake cannot tolerate 5V - or in fact anything over 3.3 V will at some point likely damage the processor.

    For tutorials from Teensy 2 times - exchanging 3.3 V power for 5V would be required and should work with buttons and LED's and potentiometers.

  4. #4
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    Thanks guys, that makes sense.

    So i'm meant to use the 3.3V (250 mA max) pin for power.

    I did read somewhere that the baud rate (?) is slower when set to 3.3volt, but I can't find that reference again. Is there anything else I have to do, other than use the 3.3 volt pin (and use appropriate circuit design)?

    Cheers
    Last edited by narco; 03-17-2019 at 04:25 AM.

  5. #5
    Senior Member+ defragster's Avatar
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    Yes that pin or the one in the middle carries a second copy of the same 3.3V - also same as the 3.3V on the opposite edge on the T_3.6. That should work for tutorial #4

    <edit>: Just read the baud rate? If the device is a 3.3V UART device then the baud rate will not be a factor - probably up to whatever the device supports.

  6. #6
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    <edit>: Just read the baud rate? If the device is a 3.3V UART device then the baud rate will not be a factor - probably up to whatever the device supports.
    I would add: in all other cases there seems to be a relation:the higher the speed the lower the voltage and the denser the connector

  7. #7
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    Thanks. Everything seems to be working well now (other than my cheap breadboard not being very reliable in its connections!)

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