SparkFun-32u4 power

Are we talking about this product?

Yes, that is the board I am referring to.

If your board looks different from the pictures on the product page, then I suggest you make a picture and show what’s on yours. On the product page I clearly see solderjumper pad in the forward corner showing the 5 volt side containing a solderbridge. If you would remove that, and solder the middle to the 3.3 volt side then the microcontroller would operate on 3.3 volt basis. It still gets the 5 volt from the USB connector though, or whatever you connected to the 5 volt input.

Thank you - I see it more clearly now. There are 3 pads and the solder blob “jumpers” 2 of them. On my actual piece the solder blob obscured the fact that it was covering two pads and I didn’t clue in.

The USB connector is followed by a PTC-fuse before it is labeled as 5 volt in the schematic. So you won’t have that protection if you power it at the 5 volt point with your own powersupply. Also, you loose the serial port connection if you don’t use the USB connection. Quite a drawback in the testing and developing phase.

I see what you mean about the fuse. However I don’t quite understand your last remark regarding the serial connection?

Thanks for your help.