RAK812 RX TX pin with Arduino Pro Mini 3,3V


I’m on a project with P2P between two RAK812 that work perfectly on Arduino Uno. Now, i want to use Arduino Pro Mini in 3,3V to reduce power consumption, but i’m not able to communicate with the RAK812 module anymore ! Nothing. I guess i have to bypass the 5V to 3,3V UART converter, but i don’t don’t where i have to put my RX-TX signal …

Someone can help me ?

Thank you very much,


Welcome to our community!

The version of RAK812 is ancient and RAKwisnode has achieved low power consumption up to 9.7 μA. You can email us and send a WisNode for testing to you.

E-mail address: [email protected]

Thank you for your answer,

I know RAK812 are obsolete, but I only have them for the moment to achieve my proof of concept ! In the futur, I will buy RAK811 of course.
The power consumption of the RAK812 is very low, but the power consumption of Arduino Uno is not (like 45mA !!) ! That’s why i use a 3,3V Arduino Pro Mini (less than 1mA).

So can you tell me if it’s possible to communicate with a RAK812 by the UART but in 3,3V instead of 5V ?

(sorry if I made mistakes in my sentences, etc, i’m french :wink: )


You can remove the figure jumper cap, and then through TXD, RXD data transfer, so you can use 3V3!
Hope help you!!!

What a very kind offer - is that open to all of us :wink:

Thank you very much ! It works !

Just a last question, maybe not on the same subject but whatever ! Is it possible to communicate between RAK811 and RAK812 on P2P ? I guess yes, but just to be sure !
As I told you, for the moment I’m doing a proof of concept in the company where i work, but in the futur, we will make an entiere PCB dedicated to our connected objet, and we will certainly use RAK811.

Hi !

I still have troubles… but this time … very weird troubles ! I pass trought the TXD and RXD pins, and I can send AT commands to the RAK and it works, but the RAK doesn’t answers to my Arduino ! This is incredible… like, it’s just 2 wires, and i have troubles !

I know that AT commands works because I can send message and data, and receive them perfectly with another RAK module which is connected to my computer.

So … Why the TX Arduino to RXD RAK works, and TXD RAK to RX Arduino doesn’t works ? :frowning_face:
Do you have something to help me ?

Thank you,


It may well be that the Arduino is struggling with a fast baud rate. Due to clocking errrors/drift, 115200baud is too fast for an Arduino - so you could use a serial adapter to change the baud rate of the RAK module to something slower - I use 9600 but I hear that up to 57600 is OK.

Yes, as @ nmccNick McCloud said,You can fix it by modifying the baud rate.

Thank you for yours answers !

When i saw yours answers I was so happy !
But now… go back to reality ! I’m trying to set the bauderate at 9600 ! But impossible, no success … even with RAK Serial Port Tool.

I send “at+uart=9600,8,0,0,0” ( /r/n is no needed) and it give me “ERROR-1”
I tried many times with arduino and now with Rak Serial Port Tool, but nothing i’m stuck. I always use RAK811 datasheet to know AT commands, but I have RAK812… Is there something different between the two RAK ?

Sorry for asking you more help, but i’m still stuck !


As mentioned before, this version is old, I suggest you replace RAK811, so that we can help you better!
PS:If you do not need /r/n, you need to change other serial port tools to send try.

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