Forcing Arduino to Only Boot from an External Supply

We are using an Arduino Micro and need to have it (only) boot from an external supply. It cannot boot from USB power. We need this because the Arduino must preset an IC on power up that is connected to the same external supply. If the USB cable stays connected to the Arduino, the Arduino receives power from the bus and will not reboot to preset the IC.

Our attempt was to pull the resettable fuse in series with the USB power line on the Arduino Micro board. With that "fix" we were unable to upload to the Arduino or even see the Arduino on a com port.

Any suggestions would be appreciated.


What you are trying to do is not possible without as you have found buggering up the loading of code into the device. Because if you can load code it has to have booted up, if it has not booted up you can not load code.

Grumpy, not sure I understand. We first supply power to the Arduino with our external supply, supposedly this should boot up the Arduino. Then we try to upload. The Arduino is not recognized.

So you want it NOT powered from USB? Then either damage the Arduino circuit board or open up a USB cable and "cut the red wire!"

When it's time to upload, manually press the reset button on the Arduino. (While it's powered from the external source.)

MorganS: or open up a USB cable and "cut the red wire!"

A less drastic option may be to communicate with the PC using an FTDI cable (USB-TTL cable). Then you can choose which "wires" should be connected to the Arduino. All you need for comms is Rx Tx and GND.


Cut the track in the USB socket and program it using a stand alone programmer.

Sounds like the XY problem to me!