pro mini programming



  • So for a while now I have mainly been using 5 volt pro minis for my projects. I recently purchased a batch of 10 3.3v pro minis. My question is, for the 3.3v pro minis, do I have to use an FTDI set for 3.3v or can I use the one that I have set for 5 volts? Obviously I would want to do it with the pro mini disconnected from the rest of the circuit so as to not damage things like the radio, but I was wondering if it would hurt the pro mini in any way?


  • Hardware Contributor

    According to the schematic
    https://www.arduino.cc/en/uploads/Main/Arduino-Pro-Mini-schematic.pdf
    the ftdi header is attached to vcc and is not regulated. High level of cpu is then 5V.

    According to the specs 2.7 up to 5.5 V should be ok @ 8 MHZ
    http://www.atmel.com/Images/Atmel-42735-8-bit-AVR-Microcontroller-ATmega328-328P_Summary.pdf

    I usually do it the other way round: use a 16Mhz pro mini @ 3.3 V to use RFM69 without level shifters. This is out of specification but working fine.



  • @FotoFieber So programming your 5 volt pro minis with a 3.3v FTDI works? Maybe I'll just do that to be safe. The FTDI that I typically use for programming has a solder pad for 5v and one for 3.3v. Right now it is connected to 5v. I'll just move it to the 3.3v pad.

    Thanks for the help.


  • Hardware Contributor

    @dbemowsk
    Yes, I do program my 5V arduino pro mini with 3.3V
    As long as the serial levels of rx/tx are the same as vcc, it should work with both voltages. As you have written, you have to take care of the attached sensors/actuators.


  • Hardware Contributor

    Programming 5V devices with 3.3V should (nearly always) work as 3.3 > 5/2 (so its a logical 1). I think I also programmed some 3.3V pro minis with 5V and it worked too. As FotoFieber said the atmega works with 5V. I think as long as you disconnect other components first, there should be no problem.



  • It works okey, if other components are disconnected. Pro mini board and atmega for 3.3 and 5 v versions are identical (except xtal) and capable to work in either voltage level. My pro mini and voltage selectable ftdi never caused problem. (Just keep nrf out of circuit, supplying 5v isn't good for it)



  • @Talat-Keleş that is good to know, but I think @FotoFieber has the right idea to switch to programming with 3.3v. That way I am safe in the event that I forget to remove the radio prior to programming. I should be able to keep everything in circuit and still program it.



  • @dbemowsk solder pins, and use a jumper block?



  • @wallyllama I have that on one of my FTDI adapters. This one is built into the USB connector housing and there is not really any room to do that. I am okay with just soldering it to the 3.3v output and going with that. The only thing I really use it for is programming.


  • Hero Member

    I vote for the 3.3V all the time rule. I have a jumper on my ftdi adapter but I don't touch it anymore, too dangerous when you forget to put it back.



  • @dbemowsk
    indeed 3v3 is always safest setting Just set and forget it.



  • Just a word of warning:

    I've been using a cheap FTDI-USB adapter from China (ebay) that has a 5V-3.3V jumper on it. With the jumper set to 3.3V, I connected my 3.3V pro-mini to it with the nRF24L01 module still attached. I spent a few minutes with it hooked up that way, trying to get my node to talk to my gateway, and suddenly my nRF24L01 module stopped responding altogether. I swapped it out with another one, and after a few minutes that one stopped responding too. I double and triple checked my all wiring, then I started poking at it with a multi-meter...

    ...and I discovered that the FDTI-USB adapter was giving me 5V on the VCC pin! It didn't matter which way I set the jumper, VCC was always at 5V. Then I checked another FTDI-USB adapter I had lying around. That one had a switch instead of a jumper, and it turned out the labels on the board were reversed - setting it to 3.3V was actually 5V and vice-versa!

    So just be aware, and double check the voltage before you trust those things.


  • Mod

    China quality strikes again :-(


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