Arduino Pro Mini 3V3 with TTL-232R-3V3 gives 5V

Hello, I use an FTDI TTL-232R-3V3 cable to connect my PC to my Arduino Pro Mini 3V3. Problem that I found was that the cable is not providing 3V3 but 5V on the VCC connection ! So in this combination the Arduino is powered by 5V instead of 3V3 that should be....

Or is it me doing something wrong ? Anyone using the same configuration ?

Thanks paddy

Some more background information from the Arduino Pro Mini Quickstart Guide :

The board comes without built-in USB circuitry, so an off-board USB-to-TTL serial convertor must be used to upload sketches. This can be a FTDI TTL-232R USB - TTL Level Serial Converter Cable for the 5V Arduino Mini Pro), or a FTDI TTL-232R-3V3 USB - TTL Level Serial Converter Cable or the SparkFun FTDI Basic Breakout Board for a 3.3V Arduino Mini Pro. One convenient way to connect these is by inserting a six-pin 0.1" male pin header into the end of the FTDI cable or breakout board, and pressing it against the six hole programming header on the Mini Pro.

The TTL-232R-3V3 cable is wired for 3V3 signal levels, but it brings out 5V on the VCC line. To use this with a Pro-Min-3V3, you should connect VCC (from the cable) to the RAW input on the Pro-Mini-3V3. Power will then pass through the Pro-Mini regulator and supply the required 3V3.

If you connect VCC from FTDI to VCC on the Pro Mini, you run the risk of damaging the FTDI chip embedded in the cable. Your Pro-Mini should not suffer from this, but you may harm peripheral devices attached to the Pro-Mini that expect 3V3 logic and power.


I've been puzzling over the voltage question also, since I plan to use a TTL-232R 3V3 with a Pro Mini 328 3.3V, so I was glad to find this thread. Oddly, a few suppliers of the FTDI 3V3 cable indicated the VCC supplies 3.3V instead of 5V, which greatly confused this hardware-challenged programmer. Would plugging the cable's 6-pin connector directly and cleanly into the Pro Mini (using a 6-pin male pin header) connect it VCC to VCC? If so, how would I split off the VCC line individually and route it to the Pro Mini's RAW input? Also, I wonder why SparkFun doesn't carry the TTL-232R 3V3?

Datapoint: I have an FTDI Basic, is marked 3.3V, has worked just fine for lots of programming of 5V Promini’s and 3.3v Promini.
Outut measures 3.23V when connected USB port.
Vcc on Promini measures the same with both prominis (but then there there is nothing to take it higher either).

How are you guys getting 5V out of the FTDI? Have you blown the regulator on the FT232RL chip?

I bought 10 cables directly at FTDI; TTL-232R-3V3. They all give 5V output for the supply and 3V3 levels for TTL. Could it be that FTDI changed it since than ? I bought them about 1,5 year ago


The cables have always supplied 5v, it's just passed straight through from the usb power lines.

The FTDI chip provides a regulated 3v3 supply on one of its pins. It can only supply a small amount of current so is of limited use.

Different adapters can obviously break different pins out.

This topic refers to a specific product (a cable) from Future Technology Devices International (what a name) or FTDI for short.

The FTDI cables bring out USB 5V to Vcc irrespective of logic level. Another issue to note is that DTR (used for auto reset on Arduino) is not available (they have RTS and CTS brought out).

These cables (the real thing if you like) have been around for a long time, but they've been copied and modified by other companies to meet different requirements. It is somewhat confusing because the 6 pin connector is the same (and they often trade by the same or similar name), but pins to signal mapping is different.

Se, check before buying and make sure you order something that fit your requirements.

Uh-oh -- now I gots the heebie-jeebies about connecting the TTL-232R 3V3 to my Pro Mini. I also have an FTDI Basic Breakout board that does provide 3.3V, but I'd sure like to use the FTDI cable instead. Not at the cost of frying my little Pro Mini, however.

You're cool - check the specs from the hardware web page:

Microcontroller ATmega168 -> now 328s actually Operating Voltage 3.3V or 5V (depending on model) Input Voltage 3.35 -12 V (3.3V model) or 5 - 12 V (5V model) (on the RAW pin)

Just a slightly different regulator between the 2 parts. The 8MHz promini will work just fine at 5V as well - check 28.3 of the atmega spec.

Hey, that's great news, CrossRoads. I was afraid I had blown $25 (incl. shipping) at Digi-Key on the wrong cable. I'm looking for it to arrive tomorrow. A tip of the hat to you, sir.