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Modbus RTU to REST API Gateway for ESP32 Ethernet Systems

An ESP32-based gateway that centralizes RS485/RS232 Modbus RTU access and exposes it through REST, WebSocket, web UI, and CLI.

josephsr

Published June 04, 2026

144 UCC

15 WCC

11 VAR

Original author: Jan Green · DenmarkOriginal source (new tab)

Modbus RTU to REST API Gateway for ESP32 Ethernet Systems

Components

Hardware components
W5500

WIZnet - W5500

x 1

ESP32

Espressif - ESP32

x 1

WIZnet parts

Project description

Overview This project implements a Modbus API Gateway that connects RS485/RS232 Modbus RTU devices to Ethernet-based software systems through a REST API. Instead of allowing multiple clients to access a Modbus RTU bus directly, the gateway places an ESP32 at the center of the system. The ESP32 becomes the controlled access point for Modbus communication. External clients such as Node-RED, SCADA software, HMI panels, browser tools, scripts, or automation servers communicate with the gateway over HTTP, while the gateway handles the actual Modbus RTU transactions through RS485 or RS232. The…

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