The voltage input on microcontroller is usually a range, something like 3V-12V. If you power it with 3.3V, does that mean the digital output voltage is 3.3? On an Uno board, if I power it with 3.3, can I use the digital output to power up 3.3V modules?
The Uno is designed to operate at 5v.
You can power it through the power connector with a power supply between 7.5v and 12v because it has an onboard voltage regulator to provide a stable 5v supply.
You CAN'T supply an Atmega328 chip with more than 5v and at lower voltages it needs to operate at a lower frequency than 16 MHz. Read the Atmel datasheet to get all the details.
The Uno has a 3.3v output that could be used to power some low current external devices. Check the Arduino specifications.
Generally if you connect an Arduino Uno pin with 5v output to an external device that requires a 3.3v signal you will damage the device. You must reduce the voltage. However an Uno seems to read the 3.3v output from an external device correctly.
...R
arusr:
The voltage input on microcontroller is usually a range, something like 3V-12V. If you power it with 3.3V, does that mean the digital output voltage is 3.3? On an Uno board, if I power it with 3.3, can I use the digital output to power up 3.3V modules?
The AVR chip on an Arduno Uno can run at 3.3V, yes.
But... an "Uno" is more than just the AVR chip. The Uno board has many components on it that are designed to run at 5V.
The Uno has a 3.3V power output that you can use to power 3.3V devices but the digital I/O pins at at 5V so they might damage devices that aren't 5V tolerant. If in doubt use a level shifting chip like the cd4050 to convert the 5V signals from the Arduino to 3.3V.