Any way to distinguish between the 3.3v and 5v Arduino Pro Mini?

Hi all,

I've recently bought an Arduino Pro Mini locally and was told it was a 5v/16Mhz version. However, I can't confirm that for myself as the checkboxes on the back of the pcb (5v, 3.3v, 20Mhz, 16Mhz, 10Mhz, 8Mhz) are all unchecked / unmarked. I have already hooked it up to my Uno R3 since i didn't bother buying a FTDI just yet, I might still do that since I can't be bothered to remove the chip from the Uno all every time I want to program the Mini.

When I plugged the USB cable into my Mac the LED's seemed quite bright to me which is when I really started to doubt whether or not it wasn't a 3.3v still. It can be programmed (tried it quickly with a modified blink sketch) but those LED's are bright!

Also, I've seen Youtube video's where the power LED is red and the LED on pin 13 is green, mine is reversed? Maybe that is an indicator?

I've already searched the SparkFun website for answers but the only difference i can spot between their two versions is the number on the Atmel chip. Their 5v version has a "Mega 328P AU 1137" and the 3.3v has a "Mega 328P AU 1110". Mine is a "Mega 328P AU 1243". I've also searched for that number and came up with the datasheet which lists voltages between 1.8v and 5.5 with speeds ranging from 0Mhz to 20Mhz, so that doesn't really help me either.

Any and all help would be appreciated greatly as i'd rather not fry the board before i even get a decent sketch on it =)

Can you measure the VCC pin when power is applied to Raw? If its 3.3V, then you've got a 3.3V/8MHz board.
The chip itself will happily run at 3.3V or 5V.
Maybe you can read some marking on the regulator?

Just checked, on the regulator are 3 letters, PLS. I supplied USB 5v to RAW and got 4.8v on VCC. I'm guessing that's the exact same as i put in with the USB 5v. Does that mean this is actually a 5v board?

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RAW goes thru the regulator.
USB does not, it connects to VCC more directly. Or directly. Need to check the promini schematic on the Products page (and my fine browser dumps me out of the forum and gets all fouled up when I try, so am not going to look now).

CrossRoads:
RAW goes thru the regulator.
USB does not, it connects to VCC more directly. Or directly. Need to check the promini schematic on the Products page (and my fine browser dumps me out of the forum and gets all fouled up when I try, so am not going to look now).

I think i read something about that but i wasn't quite sure. I thought i'd better ask and make sure then to fry the Mini on my first powerup.

JohnLincoln:
I think that the last 4 digits of the number on the Atmel IC might just be the date code for the week of manufacture, i.e. week 43 of 2012 for yours.

That could explain it, but i can't really see the value of that information let alone value it that much that i'd physically put it on the chip itself. A revisionnumber would make more sense.

Havng the data code on the chips helps with parts traceability - and also lets you check the errata section of the datasheet to see which sections apply to the chip.

I can see how that makes sense. Thanks =)

I have 5V promini's and they work perfectly at 3.3V if that's what you need. - At least in all my musings they have! :smiley:

Skywatch

Technically you are running them out of spec tho - the datasheet indicates ~3.8V is needed for 16 MHz operation.