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July 24, 2013
about 4 years ago
If anyone is interested, here is the response I received from Sparkfun Tech Support:
“Yeah, the only difference is between the two are the voltage regulators, external crystal oscillator, jumper J1 next to the microB USB connector (closed for the 5V version). The ATMega32U4 chips are the same that is used for each of the boards but they are uploaded with VID in the bootloader. This is why the board is not recognized in the device manager after uploading code with the wrong board selection. Somewhere when programming the board with the bootloader, there’s a line of code that needs to be changed. Our engineer hasn’t looked at it in a while but it there is a line where it has "PLR CSR.” The reason why is because the 3.3V and the 5V have different PIDs. They are indicated in the boards.txt in the SF32u4_boards folder for the board definitions. Looking at the boards.txt file, it looks like the extended bits are also different. You should keep that in mind when programming the ATMega32U4 microcontroller.
I think it would be easier to just buy a 3.3V Pro Micro board than to mess around with the firmware and rework the board.“
Please let me know if anyone finds this information helpful- Thanks!
Turning a Pro Micro 5V board into a 3.3V board:
Does anyone know if it is possible to turn a Pro Micro 5V board into a 3.3V board (by changing the voltage regulator and the crystal)? I assumed that since the schematics are the same for each version of the boards, except the mentioned parts, that it would work once resetting the bootloader. However, I can’t get it to work. When I try to program the modified board (even after doing the device reset thing), my PC keeps indicating that the USB port is not recognized. I know the board still functions, because I had the Pro Micro blink sketch programmed in before the modification, and the LEDs still blink but at half the freq (crystal is now 8MHz instead of 16MHz).
My only assumption at this point is that the actual ATMega 32U4 chips are somehow different between the 5V and the 3.3V boards, though I couldn’t find any info on the ATMega32U4 datasheet to support this.
Any ideas would be helpful! Thanks!
what is the oscillator used on the 3.3V 8MHz board? I’d like to find a part on digikey.
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