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Thread: USB + External Power on 3.2

  1. #1
    Member
    Join Date
    Dec 2018
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    Toronto Canada
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    24

    USB + External Power on 3.2

    I have cut the V-USB line on the bottom of my 3.2 and confirmed with a continuity checker it is disconnected. When I power the circuit ONLY externally using this example everything works as expected. When I disconnect the ext. power and plug in the USB the circuit also works. Is this right?

    I figured with the VIN cut the pins wouldn't be outputting.

    For context, the circuit is for stepper motors with drivers and 24v lines plugged into the drivers (separated from the circuit). The drivers apparently need extremely low power to run so maybe something odd is working by fluke?

  2. #2
    Senior Member
    Join Date
    Jan 2013
    Posts
    184
    Quote Originally Posted by jingleby View Post
    When I disconnect the ext. power and plug in the USB the circuit also works. Is this right?
    No.

    First, two nits:

    What is meant by "the circuit also works"? How are you testing this? FYI, the Blink example sketch is a good simple test.

    The link you provided is to PJRC's How-To Tips: Using External Power and USB. It's not clear what example you are referring to.

    Also, be aware that the pictures all show a Teensy 2 on that page. The Teensy 3.2 will look slightly different where you are to cut the trace, but the idea is similar.

    I found Paul's forum post addressing another user's issue that sounds similar to what you have. Executive Summary: The trace was not really cut.

    Best regards. I hope this helps.
    Last edited by markonian; 01-18-2019 at 06:39 PM. Reason: Added suggestion of Blink example code

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