The Atmel ATmega32U4 microcontroller on the Arduino Micro board has an operating voltage range (Vcc) from 2.7 to 5.5 volts. In addition, there is a 3.3 volt regulator on the board (presumable for powering other devices). Has anyone had modified the board to run the microcontroller on 3.3 volts? Doing this makes it a easier to interface to digital devices that can't tolerate I/O voltage higher than their supply voltage. I would prefer not to fool around with level-shifters, resistor dividers, etc. for lower voltage devices.
The Micro has a USB interface which may not (probably won't) work with only 3.3V.
However apart from that I don't see any major objection to just putting 3.3V into the "5V" pin on the board (bypassing the voltage regulator) and thus running it at 3.3V. Not sure if the voltage regulator is designed for that, it may not be. You can make a level converter out of a transistor and a couple of resistors, if you need to keep it at 5V.
Seeedstudio has one, and it will work off the USB as well as its been my test board for the past long while. I believe it will regulate down the 5V from the USB to 3.3V. The uC will most definitely work at 3.3V.
Sorry for the late response. Thanks for the replies. I'll study the options mentioned. I would like to use the USB, at least initially. since a logic high is >=2.8 volts and low <=0.3 volts for the Data+ and Data- signals, I believe the uC should be able to drive the bus successfully (if marginally).