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Flash ESP32

Download Firmware

The pre-compiled binary files can be found on the GitHub Releases Page (the right column on the projects start page). Currently there are pre-compiled binaries for ESP32 and ESP32-S3 MCUs.

Overview of pre-compiled binaries

Binary MCU Device Profile mandatory First Flash / OTA Comment
opendtu-generic.bin ESP32 No OTA Deprecated!
opendtu-generic.factory.bin ESP32 No First Flash Deprecated!
opendtu-generic_esp32.bin ESP32 Yes OTA
opendtu-generic_esp32.factory.bin ESP32 Yes First Flash
opendtu-generic_esp32s3.bin ESP32-S3 Yes OTA For boards with usb-uart bridge
opendtu-generic_esp32s3.factory.bin ESP32-S3 Yes First Flash For boards with usb-uart bridge
opendtu-generic_esp32s3_usb.bin ESP32-S3 Yes OTA For boards with integrated usb connection
opendtu-generic_esp32s3_usb.factory.bin ESP32-S3 Yes First Flash For boards with integrated usb connection


All pre-compiled binaries require a mandatory Device Profile. You have to upload one after flashing the firmware!

Flash ESP32


When flashing OpenDTU onto the ESP32 for the first time, you need to flash it over serial using the factory firmware binary file. You need to write the factory binary to the ESP32 flash chip at address 0x0.

The factory binary also contains a bootloader and partition scheme needed to properly boot the ESP32.

Before starting the flash process you have to put the ESP into flash mode. Most boards are able to do this automatically but sometimes it's not working:

  1. Connect GPIO0 to GND before booting the device
  2. Power-on or reset the ESP32 while GPIO0 is connected to GND
  3. Start the flash process

The actual procedure to flash the ESP32 depends on the tool used. Click on the tab below that matches your flash tool.

OpenDTU Web Flasher

The easiest, platform independent method. Requires Chrome based browser.

Espressif provides their own Flash Download Tools for Windows.

Flash Downloda Tool

Change COM9 to the correct port on your computer.

  • On startup, select Chip Type --> ESP32 and WorkMode -> Develop
  • Prepare all settings (see picture). Make sure to uncheck the DoNotChgBin option. Otherwise you may get errors like "invalid header".
  • Press "Erase" button on screen. Look into the terminal window, you should see dots appear. On some boards, the automatic bootloader selection does not work. In this case you have to manually press the "Boot" button on the ESP32 board. Wait for "FINISH" to see if flashing/erasing is done.
  • To program, press "Start" on screen, then the "Boot" button (if required).
  • When flashing is complete (FINISH appears) then press the Reset button on the ESP32 board (or powercycle ) to start the OpenDTU application.
4 --port COM1 erase_flash --port COM1 --chip esp32 --before default_reset --after hard_reset \
    write_flash --flash_mode dout --flash_freq 40m --flash_size detect \
    0x0 opendtu-generic*.factory.bin

Change COM1 to the correct port on your computer. If you get an error at the end of the flash procedure, you can try with a lower the baudrate eg. 460800.

Users report that ESP_Flasher is suitable for flashing OpenDTU on Windows.