I want to be able to use my HC-05, currently on Serial3 to download code to on my 2560 from a connected android tablet. I'm currently running MegaCore, which has optiboot on it.

I've looked for examples of this and can't find one. Surely someone is doing this and the optiboot documentation says you can do it.

I am currently planning on downloading the hex file, but let me know if there's a better approach.


  • download from where over HC-05? what format? hex or bin? or you want to make a Serial upload with avrdude over HC-05 on Serial3? then you need the bootloader to listen at that Serial
    – Juraj
    Jul 12, 2021 at 17:14
  • @Juraj What format should I use? I was planning on bin, but what format to write to the flash? Download from a tablet in the field that has the internet connection. That's kind of what I'm asking. How do I get the bootloader to listen to Serial3?
    – Thom
    Jul 12, 2021 at 17:20
  • you want to use InternalStorage of my ArduinoOTA library to store and apply the updated sketch binary?
    – Juraj
    Jul 12, 2021 at 17:23
  • @Juraj That would be great! Will that let me read from the Serial port?
    – Thom
    Jul 12, 2021 at 17:27
  • 1
    yes, the examples in the Advanced section
    – Juraj
    Jul 12, 2021 at 17:33


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