Many thanks for help - today I made it work Here are my steps that worked for me:

• I used MYSController 1.0.0 beta, took bootloader MYSBootloaderV13pre.hex and uploaded to Arduino Mini Pro with AVRDUDESS and USBasp programmer
• then uploaded serial gateway sketch to another Mini Pro
• attached nR24L01+ radios to both
• connected MYSController, configured serial connection and all just started to work
• then uploaded simple DHT sketch, edited csv file in MYSController and selected it for OTA FW update

After less than minute new FW was already at the node and it started to send data. I am very happy I played with Arduino projects for several years, but this stuff you have made is absolutely amazing! Now time for some real nodes - first one will be stepper controller for telescope focuser.

It still works fine - however I have one more question, maybe stupid About RF channels. I use nR24L01+ radios at default channel 76, however for final solution I would like to switch to some higher freq. Does precompiled bootlader work only at this default channel 76? So if I would like to switch to channel 101 I need to compile bootloader with this setting? Or there is some magic behind that makes it work some other way?

Many thanks for help - today I made it work Here are my steps that worked for me:

• I used MYSController 1.0.0 beta, took bootloader MYSBootloaderV13pre.hex and uploaded to Arduino Mini Pro with AVRDUDESS and USBasp programmer
• then uploaded serial gateway sketch to another Mini Pro
• attached nR24L01+ radios to both
• connected MYSController, configured serial connection and all just started to work
• then uploaded simple DHT sketch, edited csv file in MYSController and selected it for OTA FW update

After less than minute new FW was already at the node and it started to send data. I am very happy I played with Arduino projects for several years, but this stuff you have made is absolutely amazing! Now time for some real nodes - first one will be stepper controller for telescope focuser.

Ok, what I've done so far according to https://www.mysensors.org/about/ota:

• connected USBasp to Arduino Pro Mini and set fuses to 16MHz external oscillator (using AVRDUDESS)
• then tried to upload MYSbootlader using Arduino IDE (versions 1.6.11 and 1.8.1) but it failed with some "cannot set sck period"
• so I uploaded bootloader with AVRDUDESS
  Question is - at this stage should I be able to program Arduino Pro Mini with serial programmer, or now it can be done only using OTA? Because I am not able to do it with serial programmer and Arduino IDE.
  Burning bootloader with AVRDUDESS works fine because I changed it many times from original to MYSbootlader, also programming Arduino with precompiled sketch works fine.
  I will describe my project little bit later, when I will have more nodes working Currently I am on stepper motor controller node.

This is my first post in this forum - so hello everyone! And many kudos for all developers and contributors.
I am on my way of building distributed sensors and actuators system for astroimagers, and would love to have OTA firmware update possibility. I use nR24L01 radio and each node will be based on Atmega328 working at internal 8MHz and 3V, and have two questions:

• which bootlader hex should I write?
• does MYSbootloader support programming via serial? I tried several hex files with several fuses combinations and never succeeded to program Atmega328P via serial