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Modbus Data Logger

A modular ESP32-based Modbus RTU data logger with support for SD card logging, JSON configuration, real-time clock (RTC), and dynamic scaling of transformer-based values.

🔧 Features

  • Reads data from Modbus RTU devices (e.g., EM-07 meters)
  • Dynamically configurable via config.json
  • Logs data to SD card in JSON or CSV format
  • Timestamped data using DS3231 RTC
  • Interactive RTC setup via Serial
  • Easy to extend with additional registers or logic

📂 File Structure

File Purpose
config.json Main configuration file for registers
main.ino Arduino entry point
SystemManager.* Startup and runtime orchestration
RtcManager.* RTC time handling
ConfigManager.* Loads config.json
ModbusManager.* Handles Modbus requests & scaling
StorageManager.* Logging to SD card
DataLogger.* Ties together config, Modbus, and logs

🗂️ config.json

A human-readable file that defines Modbus registers to read, how to scale them, and logging settings.

See config_json_documentation for full format description.

Example:

{
  "device": "EM-07",
  "transformers": {
    "VTR": 100,
    "CTR": 200
  },
  "logging": {
    "interval_ms": 1000
  },
  "registers": [ ... ]
}

📌 Hardware Requirements

  • ESP32 board (tested on DOIT ESP32 DEVKIT V1)
  • DS3231 RTC module (I2C)
  • RS485 module for Modbus communication
  • SD card module (SPI)

⚠️ Pinout must be set in code. Not all hardware pins are defined in config.json.

Check these inside ModbusManager.cpp, StorageManager.cpp, or main.ino

Example for RS485:

static const int MODBUS_RX_PIN = 17;
static const int MODBUS_TX_PIN = 16;
static int deRePin = 4; // <- manually set here

🔌 Setting the RTC Time

Option A: Automatically Prompted on First Boot

If the RTC returns an invalid time (e.g., 1970 or 2000), the system prompts you via Serial to enter the correct datetime.

Format required:

YYYY-MM-DD HH:MM:SS

Example:

2025-07-03 14:30:00

Option B: Force via setup pin (optional)

You can connect a button to GPIO (e.g. GPIO0) to trigger setup mode manually.

🖥️ serialSetupMenu() [optional]

An interactive serial console with basic setup/testing features:

  • [1] Set RTC Time
  • [2] Show current config
  • [3] Print register test read
  • [0] Exit

Add this menu to loop() if needed:

if (Serial.available()) {
    serialSetupMenu();
}

🚀 Getting Started (Arduino IDE)

1. Install dependencies:

  • ESP32 board support via Board Manager
  • Libraries:
    • RTClib
    • ArduinoJson
    • ModbusMaster
    • SD

2. Flashing

  • Open main.ino in Arduino IDE
  • Select correct board + COM port
  • Flash the project

3. Initial Setup

  • Insert SD card with config.json
  • Connect device via Serial Monitor (baud 115200)
  • If prompted, enter current date/time

📎 Notes

  • Ensure your Modbus slave responds correctly to the register map.
  • Double-check length field in registers (1 = 16-bit, 2 = 32-bit)
  • Use scaling expressions like val * 0.1 * VTR

📃 License

MIT License