How can I tell if my arduino mini pro is 3.3V or 5v?

[BulldogLowell]

Measure the voltage between Vcc and ground while powered by USB.

The output will be either 5V or3V3.

[andriej]

you can also see the output on board.
if it stays 5V it's 5V and 3.3V... just guess ;-)

[korttoma]

Power them on the "raw" pin with 9V or something. Then measure the voltage on the Vcc pin. If it measures 5V it is a 5V board and if it measures 3.3V it is a 3.3V board.

[axillent]

if you can recognize the marking on xtal you will find 5v with 16Mhz and 3.3V with 8mhz

[Alco van Neck]

Oh en not 100% waterproof visual: all my 3.3 V arduino mini pro's do have a RED reset switch on it. the 5V arduino's got a white reset button

ebay 3.3 arduino with red button
ebay 5v white button

[axillent]

@Alco-van-Neck said:

Oh en not 100% waterproof visual: all my 3.3 V arduino mini pro's do have a RED reset switch on it. the 5V arduino's got a white reset button

this criteria has nothing to do with an official arduino pro mini :)
http://www.arduino.cc/en/Main/ArduinoBoardProMini

[Alco van Neck]

@axillent said:

this criteria has nothing to do with an official arduino pro mini :)
http://www.arduino.cc/en/Main/ArduinoBoardProMini

very true but it's a way.. and yes I used a lot of cloned nano's....

[DrJeff]

@BulldogLowell Thanks your determining way is the best way to check a Pro mini with no USB! You can just use the programming cable connected to RAW and check the VCC it will be slightly less like 4V7 or 3V2 but close enough.

[Alexandre Magno]

@Alco-van-Neck said:

ebay 5v white button

I am searching the schematic of this board. Someone here have it?

[NickBuilder]

@Alexandre-Magno

Hi!

Look here: https://www.arduino.cc/en/Main/ArduinoBoardProMini
Check the documentation/schematics section.