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I've got an Leonardo board, it seems to be official, in that it has the Arduino branding and Made In Italy on the bottom.

However I cannot get anything to run with external power supply. Everything when powered via the USB from the computer runs fine. As soon as I use any sort of external power, and I've tried both the barrel jack with 4x AA batteries, 6x AA batteries, 9v square battery and a Shield with 2x 3.7v lithium batteries - it turns on but doesn't do anything - the USB device doesn't even appear to the computer at all unless I pull the external power out again.

Is this a faulty board? Do I need to change the jumper arrangement on the board so it'll run with external power?

  • I have just tested all combinations of power plugging and unplugging on my Leonardo. No problem with anything. – Majenko Jan 11 at 14:13
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    And what "jumper arrangement" are you on about? There's no jumpers on a Leonardo. – Majenko Jan 11 at 14:19
  • The ICSP section - I thought it might have something to do with it. I guess i've just got a dud board then. It's a Leonardo R3 by the way. – Danny Shepherd Jan 11 at 14:29
  • The ICSP is a header for a connector, not for jumpers! This question is related to your previous question: arduino.stackexchange.com/questions/60405/… With a new question please show us also the sketch. I think a arduino board with seperated usb-serial chip and removed the reset via the dtr signal is better for your project. But I don't know the ideal combination that can do it all. You are in uncharted waters. – Jot Jan 11 at 14:32
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    @Pylon While a voltage lower than 6.6V will cause the USB's P-fet to get turned on when it's not desirable. It won't affect the operation of the sketch at all. Worst case scenario the computer will disable the USB port completely to isolate the external power. And it would alert you to that fact (Windows would pop up a bubble, linux / OS X would put it in dmesg, etc). – Majenko Jan 11 at 23:08

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