Whoopsied a Pro Micro V/MHz Chip Selection

Had a Sparkfun Pro Micro ATmega32u4 5V/ 16MHz working just dandy, had it wired up to an LED matrix.

Uploaded the same code with some minor adjustments, but I accidentally had the 3.3V/8MHz chip option selected in the IDE when I did the upload.
Upload completed, display is running twice as fast (moving LED), but now Windows doesn’t recognize the USB device. “Unknown USB Device (Device Descriptor Request Failed)” in the device manager, so the IDE doesn’t even see the board to reupload with correct settings.

No idea where to start with fixing this problem. Help, please. :frowning:

If you press reset, I think you’ll find that it briefly appears. You might be able to time pressing of reset just right (you want to be releasing reset right about when it finishes compiling and starts trying to upload).

What’s happening is that once the sketch starts running, it falls off USB because the sketch was compiled for the wrong speed, so it configures the USB based on that.

The brute force solution is to reburn bootloader with an ISP programmer. This will wipe the currently installed sketch.

No reset button, have tried starting upload and then plugging in, no bueno. The 32u4 wonkiness with turning off and on itself during USB transfers is probably making it a bigger mess.

I'm guessing I have to do the bootloader thing. I don't have an Uno with a DIP though, just SMD, but I'll go do some reading and see what I can do.

Got it fixed, somehow I missed this page before. Took a few tries with the double reset business but it finally works.

https://learn.sparkfun.com/tutorials/pro-micro--fio-v3-hookup-guide/troubleshooting-and-faq#ts-reset

This... is... gold!!! Thanks for sharing INTP!!! :slight_smile: