BLE Telemetry Lite

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Firmware for ESP32-C3, ESP32-S3, and similar microcontrollers, enabling telemetry broadcast from Crossfire and ELRS radio systems over Bluetooth or Wi-Fi.

Features

• Transmits Crossfire/ELRS telemetry from RC transmitters to phones, tablets, or laptops via Bluetooth or Wi-Fi
• Compatible with transmitters using Aux-serial output as well as direct connection to internal modules (e.g. Jumper RC up to T15)
• Telemetry display supported via TelemetryViewer, WebTelemetry, or the built-in web interface

Hardware

Development boards ESP32-C3-SuperMini (recommended) or ESP32-S3-SuperMini. Other ESP32-based boards with BLE and Wi-Fi support may also work, but compatibility is untested and not guaranteed.

These boards are compact, affordable, and free from unnecessary components. If using a different ESP32-C3 or ESP32-S3 board, note that pin numbering may differ from the microcontroller's internal pin numbers. Refer to your board’s datasheet to identify correct pin mappings.

Wiring

The module connects to the transmitter’s SerialAUX interface using 4 wires:

• 5V
• GND
• TX → to pin 3 (module RX)
• RX → to pin 4 (module TX) (optional)

Wiring to a RadioMaster Pocket transmitter example

If the transmitter lacks SerialAUX, connect the ELRS/Crossfire internal module’s TX pin directly to the module’s RX (pin 3).

Connection to internal TX on a Jumper T20 transmitter example

Flashing

Download the archive matching your board from Releases and unpack it. It contains bootloader.bin, partitions.bin, boot_app0.bin, firmware.bin, and merged.bin (all four files as a single image).
The bootloaders differ between boards - use the archive for your chip only.

Firmware via web interface

Switch between BLE and Wi-Fi modes by pressing the Boot button on the module.

In Wi-Fi mode, connect to the BLE Telemetry Lite access point using the password: 12345678.
The web interface is accessible at http://192.168.4.1.
Open the web interface, go to the Update tab and upload firmware.bin from the release ZIP matching your chip (esp32c3-supermini-*.zip for ESP32-C3, esp32s3-supermini-*.zip for ESP32-S3).
OTA updates the application only and preserves your settings. The remaining files in the ZIP (bootloader.bin, partitions.bin, boot_app0.bin, merged.bin) are only needed for wired flashing of a blank chip or one that needs recovery.

Firmware via Flash Download Tool

Download Flash Download Tool, set the settings as shown in the screenshot and don't forget to specify your COM port.

Flashing via esptool

Option 1: browser, nothing to install

1. Open esp.huhn.me in Chrome, Edge, or Opera.
2. Select merged.bin, connect the board via USB, pick the serial port, and click Connect.
3. Click Erase (full chip erase), then Program.

Option 2: esptool, single file

pip install esptool
esptool --chip esp32c3 write_flash 0x0 merged.bin

Option 3: esptool, separate files

esptool --chip esp32c3 write_flash 0x0 bootloader.bin 0x8000 partitions.bin 0xE000 boot_app0.bin 0x10000 firmware.bin

For the S3 board use --chip esp32s3 instead of --chip esp32c3. In esptool 4.x and older the command is called esptool.py.

If the board was running other firmware before, erase the flash first:

esptool --chip esp32c3 erase_flash

Flashing merged.bin (or erasing the flash) resets device settings (mode, baudrate, name) to factory defaults - this is normal when flashing for the first time.

License

This repository's source code is available under the MIT License.