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Thread: External power supply for USB to Gamecube adapter (Teensy 3.6)

  1. #1
    Junior Member
    Join Date
    Aug 2019

    External power supply for USB to Gamecube adapter (Teensy 3.6)

    For my first project, I am building an adapter to use a USB game controller (a Switch Pro Controller in this case) with a Gamecube console.
    I got everything working using the USBHost_t36 library and with the Teensy connected to my laptop.

    Now, since this adapter is meant to be used on the go, I would like to use the Gamecube cable to power the Teensy from the console instead of my laptop USB port.

    The Gamecube console provides these pins:
    - 3.3v data (used to communicate with the console both ways)
    - 3.3v GND
    - 3.3v power
    - 5v GND
    - 5v power

    I am already using the 3.3v data and 3.3v GND pins to communicate with the console.

    Click image for larger version. 

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    Here come the newbie questions!
    1) Are the pins provided by the console enough to power the Teensy 3.6 (96Mhz) + USB host port/guest device?
    2) Is it safe for me to connect the 5v pin to Vin and 5v GND to the Teensy, even though I already have the 3.3v data and 3.3v GND connected?
    3) I read that it is not safe to have both USB and external power at the same time, how can I work around this on the Teensy 3.6?

    Thank you for reading and for your help!

  2. #2
    Senior Member+ MichaelMeissner's Avatar
    Join Date
    Nov 2012
    Ayer Massachussetts
    We can't answer #1, since we have no idea how much power the gamecube provides (or if you've hooked up anything else to the Teensy). It likely has enough power, but until you test it out, you won't know.

    (Note, I am a software guy, if somebody answers with more EE grounding, believe them and not me).

    Yes, you can connect the 5v to VIN and ground to ground. Note, use the regular ground pins (such as the pin next to pin 0), and not the analog ground pin (between VIN and 3.3v).

    The way you prevent using both USB and external power is to cut the solder pad underneath the Teensy so there is no connection between the USB power and VIN. See the back of the card that came with your 3.6 for the location of this pad. Here is an old post about doing this:

    If you cut connection between VIN and VUSB, when you program your Teensy, you will need to supply 5v power to VIN. One way to do this is to solder a jumper wire (or female header) to the inner hole for VIN, and then connect VIN to VUSB if you are programming the Teensy and don't have Gamecube adapter attached and turned on.

    Alternatively, you can just disconnect the Gamecube when you program the Teensy. After the program has been loaded, unplug the USB cable and plug in the Gamecube. But this requires you to not use both power systems at the same time.

  3. #3
    Junior Member
    Join Date
    Aug 2019
    Thank you for the thoughtful and useful reply Michael! I'm also from a software background, trying to take my electronics skills to the next level

    I tried connecting the 5v + GND from the Gamecube console to Vin and GND and the Teensy is booting up.
    Using a logic analyzer, I can see that it does successfully communicate with the console.

    However, it does not seem to be communicating with the USB controller, I'm guessing because the port is considered "inactive".
    This causes the Teensy to send a "neutral" controller state to the console regardless of what buttons I press.
    Using a multimeter, it seems that the "5v" pin actually provides ~4.5v, not sure if that matters.

    1) At this point, it seems impossible to power the Teensy AND the controller from the Gamecube cable, or am I missing something?

    2) The USB controller does however have a battery, and it would be fine to just use the USB cable for data communication.
    Is there a way to "trick" the USB host module to turn on and communicate with the controller, without providing power?

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