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Thread: 5v pin on the 3.6

  1. #1
    Junior Member
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    5v pin on the 3.6

    Not getting a voltage out of this pin. Is this a known issue? Do I need to write some sort of code to enable this pin?

  2. #2
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    Which pin do you mean, the VIN pin next to AGND or the 5V pad on the bottom? How are you powering the Teensy?

  3. #3
    Senior Member KurtE's Avatar
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    My guess is he is talking about the +5v pin on the USB Host...

    If you look at the schematic: https://www.pjrc.com/teensy/schematic.html

    You will see that that pin that power is routed through TPD3S014 chip, which I believe is controlled by the PTE6 pin on the Teensy processor, which has an external pull down resistor and it is a high enable... So probably something has to pull that pin high.

    My guess is something that is part of the USB Host would need to do it... But if you were to want to try doing it outside of USB port, you might get away with hacking a few registers to set that pin in Digital Pin mode (ALT1), as an output pin and with a high value...

    Not sure if anyone has tried this.

  4. #4
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    Yes the USB host port 5V hole. Not really sure what it's for, I thought it might supply 5V. Thanks for the link to the schematic, I have a lot to learn but I like the looks of this board a lot. New to microcontrollers and electronics, just stepping outside the arduino sphere. Thanks for the help.

  5. #5
    Senior Member PaulStoffregen's Avatar
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    Quote Originally Posted by FerengiOrFoe View Post
    Yes the USB host port 5V hole. Not really sure what it's for,
    It's for powering up USB devices.... in a glorious but distant future when we have a mature USB host library.

    Currently this very early test code is all that exists.

    https://github.com/PaulStoffregen/k66_usbhost

    The code which turns on the USB host power is in USBHost::begin() in ehci.cpp.


    I thought it might supply 5V.
    It does indeed do that, or almost 5V, but only under software control. By default it's turned off.

    This isn't just any ordinary 5V. The special hardware is meant to support hot-plugging USB devices. Without this circuitry, if you just hot-plug a USB device to Teensy, which is itself a USB device with it's initial hot-plug capacitive loaded limited, the sudden current flow to charge the capacitors in the new device could momentarily drain Teensy's power too low, cause it to crash or reboot.

    The power switch is also meant as a measure to allow applications to deal with poorly behaved USB devices. If they go very wrong, it'll always be possible to hard reboot them by power cycling.


    New to microcontrollers and electronics, just stepping outside the arduino sphere. Thanks for the help.
    Also new to forums? You duplicated this question from your other thread, in the process annoying one the more helpful regulars here who was trying to help you. A simple rookie mistake, but not the best way to get help...

  6. #6
    Junior Member
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    Yes, also new to the forums. My mistake fellas. I appreciate the help and apologize for the bad form. Thanks again for another detailed answer.

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