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Thread: Can i power a MIDI in/out circuit with the teensy alone?

  1. #1
    Junior Member
    Join Date
    May 2021
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    15

    Can i power a MIDI in/out circuit with the teensy alone?

    I am planning on building a teensy 4.0 midi circuit, and have been looking at the info at https://www.pjrc.com/teensy/td_libs_MIDI.html.

    However, i wanted to ask about the power supply. In the schematics, it looks like an external 5V source is required to be connected to Vin and pin 8 on the opto ic (apparently the 3.x and the 4.x versions share the same schematics):

    Click image for larger version. 

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    What's confusing me is that - judging by the photos of the finished circuit - the power supply seems to come from the teensy alone.

    I'm asking because - ideally - i'd like to build the circuit in a fashion that allows tapping power from the teensy alone. It would be nice to have the sole USB connection power everything.

    Could someone please clarify? Thanks in advance!

  2. #2
    Senior Member PaulStoffregen's Avatar
    Join Date
    Nov 2012
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    25,085
    Yes, USB power is fine.

    When Teensy is powered by the USB cable, and if you haven't cut the VUSB-VIN pads apart on the bottom side, then the USB power will appear at the VIN pin. It is easily capable of powering the 6N138 or similar optocouplers.

  3. #3
    Junior Member
    Join Date
    May 2021
    Posts
    15
    Thanks for your quick reply!

    So by default Vin is an 5V output? No wonder i'm confused .

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