Can't Upload after 32u4 Bootloader

Hi there,

I have an ATmega32u4 running at 3.3V with an 8MHz resonator and I'm able to burn the Arduino bootloader onto it using an Arduino as ISP by selecting "Arduino Leonardo" and clicking "Burn Bootloader" with the SPI connected and a 10uF cap between RESET and GND on the Arduino. During the process it verifies that it's a 32u4 chip, writes, reads, etc and finishes.

However, the problem is that after successfully burning the bootloader I try loading the blink sketch to it and it just goes through the port search and never finds the 32u4 when I press the 32u4's RESET button during that search. The Arduino IDE also doesn't detect any USB ports. And yes, I have 22 Ohm resistors on D+ and D- and I'm certain that my hardware is good.

Any ideas what's going wrong here?


I also tried selecting "Adafruit Feather 32u4" which uses 3.3V/8MHz and successfully burned the bootloader but same thing, no luck with uploading code via USB afterward.

Found the problem. V_USB on the 32u4 was connected to 3.3V instead of the micro USB voltage.