Universal Edge IoT Modbus RTU/TCP to MQTT Gateway

The Industrial Modbus RTU/TCP to MQTT Gateway is a rugged edge device built to bridge legacy Modbus field equipment with modern MQTT-based IoT platforms and cloud dashboards. It reads data from Modbus RTU (RS485) and Modbus TCP (Ethernet) devices, converts raw register values into clean engineering values, and publishes them to your MQTT broker — while simultaneously acting as a Modbus TCP server so SCADA, PLC, or HMI systems can read and write the same data over Ethernet.

Everything is configured through a local, password-protected web interface, reachable over the gateway’s own Wi-Fi access point. No cloud dependency, no proprietary software, and no complex toolchain — just connect, configure, and deploy.

This is a fully customizable solution. Register counts, device limits, tag structures, topic formats, and data handling policies are tailored to your project. Contact us with your requirements and we will customize the gateway to match.

Key Features

Dual Protocol Support — Modbus RTU & Modbus TCP

• One RS485 port for Modbus RTU field devices

• One RJ45 Ethernet port for Modbus TCP devices, MQTT, and internet access

• Acts as Modbus master to poll field devices, and as Modbus TCP server for SCADA/PLC/HMI access

• Supports Coils, Discrete Inputs, Holding Registers, and Input Registers

• Wide datatype support including INT16/32/64, UINT16/32/64, FLOAT32/64, UNIX time, and BCD formats

• Configurable byte/word order, scaling, offset, and engineering units per register

MQTT Publishing with Flexible Topic Structures

• Publishes to any standard MQTT broker over Ethernet

• Three topic structures available: topic-per-register, JSON object per device, or a single JSON object for the entire gateway

• Configurable topic prefix, per-tag QoS, retain flags, and unit inclusion

• Short tag keys auto-generated from register names, with duplicate detection

• Last Will message for gateway online/offline status

• Automatic reconnection with backoff when the broker becomes unavailable

USB Offline Buffering

• USB port enables local data buffering when the network or MQTT broker is unavailable

• Ensures no data loss during connectivity interruptions

• Buffered data is forwarded once the connection is restored

Smart Send Policies

• Periodic, on-change, or on-change with heartbeat publishing modes

• Configurable deadband (absolute and/or percentage) to reduce redundant traffic

• Minimum and maximum send intervals per tag

• Immediate publish on device recovery, with optional full snapshot after reconnect

• Offline markers published when a device goes offline

Local Wi-Fi Configuration & Web Portal

• Password-protected Wi-Fi access point for on-site setup

• Admin web login with changeable credentials

• Configure devices, registers, MQTT settings, and network parameters from any laptop or phone browser

• No special software or cloud account required

Device & Register Discovery

• Automatic device scan across multiple baud rates, parities, and slave addresses

• Register scan reads address ranges and displays incoming data in multiple datatypes

• Bulk register addition with selected datatype and scaling

• Discovered devices and registers saved directly to the configuration

Modbus TCP Server for SCADA/PLC/HMI

• Serves cached polled values without adding load to the RS485 line

• Configurable TCP port, idle timeout, and read-only mode

• Transparent unit-ID mode or flat gateway address map

• Function codes 01, 02, 03, 04, 05, 06, 15, and 16 supported

• Standard Modbus exception codes on failure

• Writes accepted only for writable registers within configured limits, then forwarded to the RS485 bus

• Per-client and global diagnostic counters

Modbus TCP Client

• Each device can independently use RTU or TCP as its transport

• Configurable IP, port, unit ID, timeouts, retries, poll interval, and keep-alive per device

• TCP devices share the same register model and decoding as RTU devices

• Polled independently so TCP traffic never affects the RS485 cycle

• Automatic reconnection with backoff, plus per-device connection status and latency monitoring

Industrial Hardware Design

• Metal enclosure with screw fitting for harsh environments

• 12 V to 24 V DC wide input range

• Real-time clock with battery backup for accurate timekeeping during power loss

• Factory reset button restores defaults while preserving configured devices and registers

• Protected memory handling and power-loss-safe configuration storage

• Automatic recovery from network and device faults

• Dual-core processor running RTOS-based firmware, with network handling and Modbus engine kept separate for full-load responsiveness

Network & Time Management

• Ethernet supports DHCP or static IP

• NTP time synchronization when internet access is available, or manual date/time entry

• Automatic reconnection after network or internet interruptions

Firmware Update via Web Portal

• Upload firmware directly from the local web page

• Gateway installs and restarts automatically

• No special tools, no site visit, no downtime complexity

Customization Available

Every deployment is different. We offer full customization on:

• Number of supported Modbus slave devices

• Total register count

• Tag naming conventions and topic structures

• Register mapping and datatype handling

• Send policies and deadband logic

• MQTT payload format and JSON structure

• Modbus TCP server address mapping

• Branding and enclosure labeling

Tell us your project requirements and we will tailor the gateway to fit.

Typical Applications

• Factory automation and machine monitoring

• Energy monitoring and sub-metering

• Water and wastewater treatment plants

• Building management systems (BMS)

• Solar and renewable energy installations

• Oil and gas remote monitoring

• Cold chain and environmental monitoring

• Legacy Modbus equipment modernization for Industry 4.0

Why Choose This Gateway

• No cloud lock-in — works with any MQTT broker (AWS, Alibaba or your own Custom MQTT broker)

• No data loss — USB offline buffering keeps every reading safe

• No load on RS485 — SCADA reads come from cache, not the field bus

• No special tools — configure everything from a browser over Wi-Fi

• No compromise — industrial metal casing, wide DC input, battery-backed RTC

• Fully customizable — registers, tags, topics, and policies built around your project

Ordering & Customization

This gateway is available as a customizable platform. Share your Modbus device list, register map, MQTT broker details, and topic requirements, and we will deliver a configured unit ready for deployment.

Contact us to discuss your project.