Hello,
I would like to create a custom PCB to incorporate the Sparkfun Micro 3.3V. We used an ATmega32U4 running at 3.3V and a 16MHz crystal. However, when I flash the chip with the Sparkfun Micro 3.3v bootloader, it is not recognized by my computer. When it is flashed with the 5V bootloader, it is able to communicate to the computer.
Can you please advise on why this issue would occur? Should the fuses be changed?
Hello bershadm,
Yes there will be a problem. The 3.3V bootloader was configured for the 3.3V/8MHz Pro Micro. The 5V bootloader will work since you’re using a 16MHz crystal. I think you might be able to program if you change timing settings or the crystal itself.
Just be aware of [bootloader behavior changes for future development as well.](https://cdn.sparkfun.com/datasheets/Dev/Arduino/Boards/32U4Note.pdf)
Thanks for that reply! The schematic for the 3.3V Micro shows a 16MHz crystal, why would there be an issue with this configuration?
When I use the 5V bootloader, the chip can be programmed and appears to be working properly. I’m able to communicate via the Serial port and blink TX/RX LEDs. However, I’m also trying to use the same chip to communicate to 2 different battery gauges, one using I2C and the other one using UART. Neither of these communications are working at the moment, would this be related to the fact that we are using a 16MHz crystal or do you think it’s a completely different issue. I have tested the UART battery gauge using both 3.3V and 5V Micros and the code worked on those devices.
Thanks in advance for your help!
Mike