Modbus TCP IO Module

A flexible Ethernet-based Modbus TCP IO module built on the Wiznet W5500-EVB-Pico board (RP2040). Features a modern web interface for configuration and real-time monitoring with support for configurable I2C sensors.

Features

Network Configuration

• DHCP support with fallback to static IP
• Configurable network settings via web interface
• Custom hostname support
• Real-time IP address display
• Built-in LED indicates Modbus client connection status

IO Capabilities

• Digital Inputs: 8 channels (GP0-GP7)
  • Configurable pullup resistors
  • Input inversion option
  • Latching capability (inputs remain ON until reset)
  • Latch reset via web interface or Modbus
• Digital Outputs: 8 channels (GP8-GP15)
  • Toggle outputs directly from web interface
  • Configurable initial state (ON/OFF at startup)
  • Output inversion option
  • Real-time status updates
• Analog Inputs: 3 channels (GP26-GP28)
  • 12-bit resolution (0-4095)
  • 3.3V reference voltage
  • Values displayed in millivolts (0-3300mV)
  • Real-time trend graphs

I2C Sensor Support

• Configurable I2C sensors via web interface
• EZO sensor support (pH, DO, EC with calibration commands)
• Temperature compensation for pH measurements
• Dynamic sensor configuration and calibration
• Sensor data available via Modbus and web interface

Modbus Server

• Protocol: Modbus TCP
• Default Port: 502
• Register Map:
  • Discrete Inputs (FC2): 16 inputs
    • 0-7: Digital input states
  • Coils (FC1/FC5): 128 coils
    • 0-7: Digital output control
    • 100-107: Digital input latch reset
  • Input Registers (FC4): 32 registers
    • 0-2: Analog input values (millivolts)
    • 3+: Available for I2C sensor data
  • Holding Registers (FC3/FC16): 16 registers

Web Interface

• Modern, responsive design
• Live IO status updates
• Interactive digital output control
• Digital input latch reset functionality
• Configuration management
  • Network settings (DHCP toggle, IP configuration)
  • IO configuration with table-based layout
  • I2C sensor configuration and calibration
• Real-time monitoring
  • Digital input/output states
  • Analog input values with trend graphs
  • Connected Modbus clients
  • I2C sensor data
• Sensor management
  • Add/edit/delete I2C sensors
  • EZO sensor calibration interface
  • Compact register usage summary

Hardware

Board

• Module: Wiznet W5500-EVB-Pico
• Processor: RP2040 (Dual-core ARM Cortex-M0+)
• Ethernet: W5500 with lwIP stack
• Power: USB or PoE (requires PoE module)
• USB: Custom VID/PID for unique device identification

IO Pin Assignments

Digital IO

Function	GPIO Pin	Description
DI1	GP0	Digital Input 1
DI2	GP1	Digital Input 2
DI3	GP2	Digital Input 3
DI4	GP3	Digital Input 4
DI5	GP4	Digital Input 5
DI6	GP5	Digital Input 6
DI7	GP6	Digital Input 7
DI8	GP7	Digital Input 8
DO1	GP8	Digital Output 1
DO2	GP9	Digital Output 2
DO3	GP10	Digital Output 3
DO4	GP11	Digital Output 4
DO5	GP12	Digital Output 5
DO6	GP13	Digital Output 6
DO7	GP14	Digital Output 7
DO8	GP15	Digital Output 8

Analog Inputs

Function	GPIO Pin	ADC Channel	Range
AI1	GP26	ADC0	0-3300mV
AI2	GP27	ADC1	0-3300mV
AI3	GP28	ADC2	0-3300mV

Ethernet Interface

Function	GPIO Pin
CS	GP17
IRQ	GP21
SCK	GP18
MOSI	GP19
MISO	GP16

I2C Interface

Function	GPIO Pin	Description
SDA	GP24	I2C Serial Data
SCL	GP25	I2C Serial Clock

Note: I2C bus is initialized and ready for sensor connections. Sensors can be configured dynamically via the web interface.

Development

Environment

• PlatformIO
• Framework: Arduino
• Board: Raspberry Pi Pico
• Core: Earlephilhower's Arduino core

Dependencies

• Arduino Framework
• W5500lwIP Ethernet Library
• ArduinoModbus
• ArduinoJson
• LittleFS for file system operations

Building and Flashing

1. Clone the repository
2. Open in PlatformIO
3. Build and upload to the board

Configuration

Default Network Settings

• DHCP: Enabled
• Fallback Static IP: 192.168.1.10
• Subnet: 255.255.255.0
• Gateway: 192.168.1.1
• Modbus Port: 502

Memory Layout

• Configuration stored in LittleFS
• Version control for config structure
• Automatic migration of settings

Usage

1. Power up the board via USB or PoE
2. Connect to network via Ethernet
3. Access web interface via IP address
4. Configure network settings if needed
5. Configure IO settings as required:
   • Set digital input pullup, inversion, and latching options
   • Configure digital output initial state and inversion options
6. Control digital outputs via web interface or Modbus
7. Monitor inputs and outputs in real-time
8. Reset latched inputs via web interface or by writing to Modbus coils 100-107

Debugging

• Serial debug output (115200 baud)
• Web interface status indicators
• Modbus client connection monitoring
• Built-in LED indicates Modbus client connection

Sensor Configuration

Supported Sensors

EZO Sensors (Atlas Scientific)

• EZO-pH: pH measurement with temperature compensation
• EZO-DO: Dissolved oxygen measurement
• EZO-EC: Electrical conductivity measurement
• EZO-RTD: High-precision temperature measurement

EZO sensors include built-in calibration routines accessible via the web interface.

Adding Custom Sensors

To add support for new I2C sensor types:

1. Add Sensor Library (if needed) to platformio.ini:

   lib_deps = 
       # Existing libraries...
       your/sensor-library@^1.0.0

2. Implement Sensor Reading Logic in src/main.cpp:

   // Add to the sensor reading loop around line 810
   else if (strcmp(configuredSensors[i].type, "YOUR_SENSOR") == 0) {
       // Add your sensor reading code here
       float sensorValue = yourSensor.readValue();
       // Store or process the value as needed
   }

3. Configure via Web Interface: Use the sensor configuration page to add your sensor with appropriate I2C address and Modbus register mapping.

Web-Based Configuration

1. Access Web Interface: Connect to the device IP address
2. Navigate to Sensor Configuration: Scroll to the sensor configuration section
3. Add New Sensor: Click "Add Sensor" and fill in:
   • Name (descriptive label)
   • Type (sensor model/type)
   • I2C Address (in hex format, e.g., 0x48)
   • Modbus Register (starting from register 3)
4. Calibration: Use built-in calibration tools for supported sensors
5. Save Configuration: Click "Save & Reboot" to apply changes

Troubleshooting

• Check I2C Wiring: Verify SDA (GP24) and SCL (GP25) connections
• Verify I2C Address: Ensure the sensor address matches configuration
• Power Requirements: Most sensors require 3.3V power supply
• Serial Monitor: Check debug output for sensor initialization messages
• Pull-up Resistors: Some sensors may need external 4.7kΩ pull-ups on SDA/SCL