Supported Target	ESP32-C3

ESP32-C3 UART Bridge

The ESP32-C3 UART Bridge is an ESP-IDF project. This makes the ESP32-C3 act as USB to serial UART interface like FT232R or CP210x. The communication is transferred in both directions between the Computer and the target MCU through the ESP32-C3 UART Bridge.

NOTE: Firmware tested on ESP32-C3. But it may work in other ESP32 family.

See diagram below:

 COMPUTER            ESP32-C3             MCU
┌────────┐     ┌────────┬────────┐     ┌────────┐
│        │     │        │        │     │        │
│        │     │        │        │     │        │
│        │     │        │        │     │        │
│        │     │        │        │     │        │
│  USB   │◄───►│  CDC   │  UART  │◄───►│  UART  │
│        │     │        │        │     │        │
│        │     │        │        │     │        │
│        │     │        │        │     │        │
│        │     │        │        │     │        │
└────────┘     └────────┴────────┘     └────────┘

Hardware Required

The example can be run on ESP32-C3 based development board connected to a computer with a single USB cable for flashing and bridging. The target MCU interface should have 3.3V logic.

Setup the Hardware

Connect the target MCU serial interface to the ESP32-C3 as follows.

---

ESP32-C3 chip	Kconfig Option	ESP32-C3 Pin	Target MCU UART Pin
Transmit Data (TxD)	UBRIDGE_UART_TXD	GPIO21	RxD
Receive Data (RxD)	UBRIDGE_UART_RXD	GPIO20	TxD
Ground	n/a	GND	GND

See connection diagram below:

 ESP32-C3           MCU
┌────────┐       ┌────────┐
│        │       │        │
│        │       │        │
│ GPIO21 ├──────►│  RxD   │
│        │ 3.3v  │        │
│        │ logic │        │
│ GPIO20 │◄──────┤  TxD   │
│        │       │        │
│        │       │        │
└────────┘       └────────┘

How to Compile the Project

ESP-IDF v5.0.1 or newer can be used to compile the project. Please read the documentation of ESP-IDF for setting up the environment.

• idf.py menuconfig can be used to change the default configuration. The project-specific settings are in the "ESP32 Uart Bridge Configuration" sub-menu.
• idf.py build will build the project binaries.
• idf.py -p PORT flash will flash the ESP32-C3. The PORT is the serial port created by an ESP32-C3 USB-CDC profile connected to the USB D+/D- pins of the ESP32-C3. This serial connection has to be established to upload firmware into the ESP32-C3 and it also used to act as bridge.

The initial flashing can be done by using other methods, see this guide.

Configure the project

Use the command below to configure project using Kconfig menu as showed in the table above. The default Kconfig values can be changed such as: UBRIDGE_UART_BAUD_RATE, UBRIDGE_UART_PARITY, UBRIDGE_UART_PORT_NUM (Refer to Kconfig file).

idf.py menuconfig

NOTE: The default baud rate is 57600 and port number 0

WARING: The parity setting by default selected none. If you are going to flash STM32 using the ST serial bootloader you MUST select even parity.

Build and Flash

Build the project and flash it to the board:

idf.py set-target esp32c3
idf.py build
idf.py -p PORT flash