Electronic – arduino – Are these two Arduino Pro Micros jumpered correctly


I picked up a couple of cheap Pro Micro's off eBay a while back. Both are blue, and have no brand identifier on them (ie, Adafruit, Sparkfun, etc.). The ebay ad. directly copies the text from SparkFun's Pro Micro – 5V/16MHz product page, where I got the schematic.

My challenge here is that I couldn't seem to get them to be identified by the IDE, so I'm trying to figure out just which they are. I know they are Pro Micro, but still not sure about the 3.3V vs. 5V part.

Here's a summary of what I know…

  • The product description says 5V
  • The boards are marked "V11"
  • The voltage regulator on the board is a mic5219 labeled LG50 (which is 5v)
  • The spot on the back where one can mark "5V" or "3.3V" on the circuit is not marked
  • The schematic states for the jumper "Closed for 5V version"
  • The J1 jumper is NOT bridged, which would imply it's configured for 3.3V (?)
  • The main chip is an ATMEL MEGA32U4.

So there's the quandry. 5V regulator, but J1 not bridged as for 3.3V? 3.3V?

Here are some photos…
The two boards
Closeup of un-bridged J1 and voltage regulator (LG50, a 5V one)
Back of board showing unmarked 3.3V/5V and V11

Any suggestions on how I can precisely identify the boards or at least know if they in fact are 5V but should have J1 bridged? It seems based on the voltage regulator that it's 5V, but then J1 should be bridged if this was the case.

Best Answer

At a glance, the operating frequency of the XTAL on board may tell the operating voltage of your Arduino.

If the XTAL is 16MHz, the device is probably 5V. If the XTAL is 8MHz, the device is probably 3.3V.

Make sure to use a multimeter and trace the power pins to the jumper / LDO. Also measure voltage at LDO output to see if LDO is active or not.