ESP32 RS485 Modbus RTU Sniffer for Solar Guardian & Epever Tracer 1210A

This project is designed to sniff Modbus RTU traffic between a Solar Guardian and an Epever Tracer 1210A solar charge controller using an ESP32. Data is captured by ESP32 and sent to the PC, where it's saved as a Wireshark-compatible .pcapng file by Python code. The data file is opened by Wireshark and decoded in a human-readable format.

Hardware Used

• ESP32 DevKit v1
• Waveshare TTL TO RS485 (C)
• Waveshare USB TO RS485
• Epever Tracer 1210A solar charge controller
• Small solar panel
• 12V battery

Below is a photo of the test setup:

Features

• ESP32 firmware (main.c):
  • Listens to RS-485 Modbus RTU traffic via UART2 (RX GPIO16).
  • Detects Modbus RTU frame boundaries using UART idle detection.
  • Validates CRC and timestamps each frame.
  • Forwards raw frames with metadata to the PC over USB serial (UART0).
• Conversion to Wireshark compatible file (sniffer_to_pcapng_raw.py):
  • Data from UART0 is saved as a Wireshark compatible .pcapng format.
• Wireshark Lua script (modbus_register_names.lua):
  • Decodes Modbus register numbers and values for Epever Tracer 1210A.
  • Displays register names, scaling, and units for easy analysis.
  • Adds human-readable info to Wireshark's packet details and Info column.

How It Works

1. Sniffing: The ESP32 listens passively on the RS-485 bus, capturing all Modbus RTU frames between the Solar Guardian and the Epever Tracer.
2. Logging: Captured frames are sent to the PC via USB serial and saved as a .pcapng file.
3. Analysis: Open the .pcapng file in Wireshark with the provided Lua script enabled. The script decodes register values and presents them with descriptive names and units.

File Overview

• main/main.c: ESP32 firmware for sniffing and forwarding Modbus RTU frames.
• sniffer_to_pcapng_raw.py: Python script for receiving RTU frames and saving as a Wireshark .pcapng format.
• modbus_register_names.lua: Wireshark Lua script for decoding Epever Tracer 1210A Modbus registers.

Usage

1. Flash the ESP32 with the firmware in main.c.
2. Connect ESP32 USB to your PC and use the SolarGuardian for communication to the Epever Tracer.
3. Connect the ESP32 to the RS-485 bus (RX to data line, GND to ground), it will automatically capture the communication and send to PC
4. Start python sniffer_to_pcapng_raw.py for saving the data as a .pcapng file.
5. Open the capture in Wireshark. Enable the Lua script (modbus_register_names.lua) in Wireshark.
6. Analyze: Human-readable register names and values will appear in the packet details and Info column (see screenshot for example).

Example (Wireshark)

Requirements

• ESP32 development board
• RS-485 transceiver (for ESP32 UART RX)
• Wireshark (with Lua enabled)

References

• ESP-IDF UART documentation
• rosswarren/epevermodbus — Python driver and register map for Epever charge controllers

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Project Status

This project enables detailed, real-time monitoring and reverse engineering of Modbus RTU traffic between solar controllers, with protocol decoding in Wireshark.

Work in progress - to be continued one day...