Arduino Pro mini 3.3V/5V adjustable?

I bought a 5V Pro mini from here:

I expected it to put out 5V on the Vcc pin when RAW and GND are connected to an external power supply (thei is example is a 9V battery, but I’ve tried others, same result).

I checked it with my meter, and it puts out ~3.3V (3.28/9). I was sure they sent me the wrong version, but then I checked when connected to an FTDI board, with RAW and GND not connected, and it puts out 5V on Vcc.

Google revealed this: – an adjustable. I looked at my board, and there is something labeled “SW4” to the right of the pins for FTDI connection (if the board is oriented face up with the FTDI pins on the left).

I have tried to slide the switch in either direction, and it will not move. I do not want to put more force on it in fear of breaking something (not a huge financial loss, but I don’t have another–more on order, but it takes 3-4 weeks).

Should I force it? Is there another approach? Is this really adjustable or is it an anomaly?


Can you make a photo of your switch ?

It’s at the link I provided, but see attached. Thanks.

It’s “S4” not SW4 and in this pic it’s on the right.

Firstly, S4 is a diode, not a switch!

There are many variations of the Pro Mini, I think the one you have is not adjustable. In the original Sparkfun design, although the chip will run with VCC = 3.3V or 5V, the onboard regulator is 3.3V if you run from the RAW input.

I’ve found the third-party sellers can be quite vague about the version they are selling, and never found schematics for them.

I think you have a 3.3V 8MHz version. Can you have a close look at the crystal or resonator with a magnifier, is there something on it with "16" or with "8" ?

The adjustable version you mentioned is with a solder blob, not a switch.

S4 is marked as if it’s a diode.
I think you were sent a 3.3V model.
The FTDI connects to Vcc, it does not go thru the regulator. If the FTDI is set for 5V output, the promini will have 5V on its Vcc.

Thank you all.

It appears that my 1st suspicion was correct: I have a 3.3V model.

There is something on the crystal, it appears to be 2 characters, but I cannot read it..need a stronger magnifier.

The diode is in the same place as the solder blob on the adjustable, so I jumped to the conclusion that it must be a switch (and the "s" in s4 helped lead me there).

Hopefully, the replacements I get (from a different supplier) will be what I ordered.

I contacted the supplier, and they admitted that they sent me the wrong version--because that's all they have. To their credit, they offered a refund while letting me keep the 3.3V. They say that's what they got from the factory and it's possible that they did not know when they sent it. I've had it for 4 months and didn't realize the difference until I cared.