CoreS3 RS232 Serial Server

ESPHome-based serial-to-TCP bridge running on M5Stack CoreS3 with RS232 Module 13.2.

Exposes an RS232 serial port as a TCP socket using esphome-stream-server. Clients connect to the device's IP on port 6638 and get transparent bidirectional serial data relay.

Hardware

• M5Stack CoreS3 (ESP32-S3, 240MHz, 16MB flash, PSRAM)
• RS232 Module 13.2 stacked on the CoreS3 bus
  • TX: GPIO17
  • RX: GPIO18
  • Baud rate: 115200 (default, changeable at runtime)

Prerequisites

• pixi package manager

Building and Flashing

# Install dependencies
pixi install

# Compile firmware
pixi run compile

# Compile, upload and show logs (device connected via USB)
pixi run run

# Upload pre-compiled firmware
pixi run upload

# View device logs
pixi run logs

# Clean build artifacts
pixi run clean

WiFi Setup

On first boot (or when no saved WiFi network is available), the device starts a captive portal AP. Connect to it with your phone or laptop, then configure your WiFi credentials through the portal. The credentials are saved and used on subsequent boots.

The AP and captive portal should be also started if the device fails to connect to the saved WiFi network (e.g. due to network not available), after 90 seconds. You can use it to reconfigure WiFi settings.

The Improv via serial is also supported for WiFi configuration. To use it, connect to the serial port (provided via USB) and use ESPHome Web tool to change WiFi settings.

Connecting to the Serial Port

Once the device connects to WiFi, connect any TCP client to <device-ip>:6638. Data sent over TCP is forwarded to the RS232 port and vice versa.

Some settings related to processing of the data (like echo, line endings, special characters, clipboard handling, etc.) depend on the device connected to the serial port of the RS232 port and the client software used to connect to the TCP port. The serial server itself is a transparent bridge and does not modify the data in any way.

Below are example connection instructions for common TCP client software and usual connected devices (like serial consoles of network equipment, microcontrollers, etc.):

socat

# escape allows terminating the session with Ctrl+D
socat -,rawer,escape=0x04 TCP:<device-ip>:6638

PuTTY / KiTTY

1. Set Connection type to Raw
2. Enter the device IP as Host Name
3. Set Port to 6638
4. Go to Terminal category and change Local echo and Local line editing to Force off
5. Click Open

Web Server

The device runs a web server on port 80 (http://<device-ip>/). It provides:

• Device status overview
• Baud rate selector — change the RS232 baud rate at runtime (2400, 4800, 9600, 19200, 38400, 57600, 115200). The selected value is saved and persists across reboots.
• Client connected — whether a TCP client is currently connected to the serial server
• Number of connections — count of active TCP connections
• WiFi signal strength, IP address, SSID, and MAC address
• Device uptime
• Debug info (heap free, loop time, internal temperature)
• OTA firmware update capability

Configuration

Main config: cores3-serialserver.yaml

Shared packages in packages/common/: wifi.yaml, uptime.yaml, debug.yaml