Burning question:

So, I'm trying to burn the Arduino Leo bootloader onto a ATmega32U4 that's on 3.3V and the internal 8MHz clock. Do I have to modify and rebuild the bootloader to set the fuses correctly, and can this be done with AVR Studio?

All of the references on doing this are dated. The folder structure for the Arduino IDE has changed. I've done it in the past with 5V 16MHz 32U4s using an Arduino as ISP, but never with the AVRISP mkII on the Arduino IDE.

On the good side, I do have it up and running with Atmel Studio.


  • Are you planning to run the ATmega32U4 at 8 MHz?
    – Nick Gammon
    Commented Sep 2, 2015 at 5:21
  • Yes I am. I have both the RC version and the non-RC with an external 8MHz xtal. Commented Sep 4, 2015 at 5:23
  • Update: So I have tried several different methods, each with their own issues. The latest was to use the AVR ISP mkII on a Mac, as there are driver problems with Windows. It seems to have burnt the Lilypad USB bootloader on, but when I plug in the USB, nothing shows up on my PC. This is quite the rabit hole for something I thought was going to be trivial. Commented Sep 5, 2015 at 1:22
  • Where did you get this Lilypad USB bootloader? The Lilypad has an Atmega328V and no USB interface.
    – Nick Gammon
    Commented Sep 5, 2015 at 3:21
  • @NickGammon link The bootloader is in the Arduino folder hardware > arduino > avr > bootloaders > caterina-LilyPadUSB. Commented Sep 6, 2015 at 4:01

1 Answer 1


If you have an appropriate crystal attached then you can do this in the Arduino IDE. Select your board and programmer in the IDE menu, connect the programmer to the board, and choose Burn Bootloader from the menu. This will both burn the prebuilt bootloader image and set the fuses in a single operation.

Note that you cannot use USB on the '32U4 if you are running off either a ceramic resonator or the internal oscillator, and so you should not attempt to use the Leonardo bootloader in either case.

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