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As of 2025-07-24

How to Write Files to ESP32

How to write files to the ESP32 mounted on TWELITE SPOT

This guide explains how to write files (the files under the data/ folder) to the ESP32 mounted on TWELITE SPOT.

This article introduces an advanced topic (how to treat the flash area of the ESP32 mounted on TWELITE SPOT as a file system and write files such as HTML).

For example, if you do not need to write HTML files to TWELITE SPOT to behave as a web server (implemented in the spot-server sample) or write encryption key files to TWELITE SPOT, you can ignore the contents of this article.

This article uses third-party open-source software.

We cannot provide detailed instructions on third-party software usage. Also, we assume no responsibility for any damages caused by using third-party software.

The method introduced in this article requires Arduino IDE 1.x. Due to technical constraints, as of May 2023, Arduino IDE 2.x is not supported.

Because the plugin used here is written in Java, it does not work with Arduino IDE 2.x, which is not Java-based unlike Arduino IDE 1.x. For more details, see the Arduino IDE GitHub issue (Missing support for external tools / plugins · Issue #58 · arduino/arduino-ide) (in English).

Installing the Plugin

Install the Arduino plugin (arduino-esp32fs-plugin) to write files to the ESP32 flash area.

Downloading the Plugin

Download esp32fs.zip from the following page:

Release Update to support Big Sur · lorol/arduino-esp32fs-plugin

The original arduino-esp32fs-plugin is me-no-dev/arduino-esp32fs-plugin, but here we use the forked version lorol/arduino-esp32fs-plugin which supports the latest LittleFS file system.

Installing the Plugin

Extract the downloaded esp32fs.zip.
If there is no tools folder in your Arduino sketchbook location (set in Arduino IDE preferences, e.g., C:\Users\foo\Documents\Arduino), create it.
Create the folder ESP32FS/tool inside the tools folder and place the esp32fs.jar file extracted from the zip there. (Example path: C:\Users\foo\Documents\Arduino\tools\ESP32FS\tool\esp32fs.jar).
The plugin will be available the next time you start Arduino IDE.

Connecting to the Host

Connect TWELITE R3 / R2

Connect TWELITE R3 / R2 to the 7P interface side labeled ESP32.

Connect Power

Supply 5V power to the USB-C connector on the side.

Always connect TWELITE R3 / R2 to TWELITE SPOT in the same orientation as shown above. Connecting in the wrong orientation may damage TWELITE SPOT or TWELITE R3 / R2.

Arduino IDE Operations

Open the Sketch

Start Arduino IDE and open the sketch.

Place Files to Write

Open Sketch -> Show Sketch Folder.
Create a data folder at the same level as the sketch file (.ino).
Place the files to write inside the data folder.

The directory structure inside the data folder is preserved in the flash area.

Select Serial Port

From the Tools -> Port menu, select the port for TWELITE R3 / R2.

On Windows, serial ports are named like COM?, and on macOS/Linux, like /dev/tty?.

Boot ESP32 in Programming Mode

Press the ESP32 reset switch EN(RST) and the ESP32 boot switch BOOT on TWELITE SPOT, then release them in the order EN(RST) -> BOOT.

Resetting while holding BOOT switches ESP32 into programming mode.

Execute Writing

Click Tools -> ESP32 Sketch Data Upload.
At Select FS for /data folder, select LittleFS.

Click OK.

When writing completes, Hard resetting via RTS pin... is displayed at the bottom of the screen.

Depending on your environment, writing may fail with a message like this (confirmed on macOS):

`Error: esptool not found!`

In that case, placing esptool.py in the Arduino15 folder/packages/esp32/tools/esptool_py/<version>/esptool.py might resolve the issue.

For example, on macOS, obtain esptool.py and create a symbolic link as follows:


/usr/bin/pip3 install esptool
ln -s ~/Library/Python/3.9/bin/esptool.py ~/Library/Arduino15/packages/esp32/tools/esptool_py/4.5.1/esptool.py

Note: Specify /usr/bin/pip3 to avoid installing in the Homebrew directory.

Reset ESP32

After writing completes, press and release the ESP32 reset switch EN(RST) on TWELITE SPOT to reset ESP32.