In-Wall Junction Box Compatible Modbus Output Module
Designed to fit inside standard junction boxes, this compact Modbus-enabled output module provides a general-purpose solution suitable for lighting control as well as various automation applications. The main goal is to offer a distributed and centrally controllable output module without the need for large control panels.
Thanks to its small form factor, the module can be integrated directly into existing installations without adding visible hardware.
Technical Overview
Microcontroller: STM8S series
Communication: Modbus RTU over RS485
Supply Voltage: 12–36V DC
PCB Size: 3 cm × 2.4 cm
Output Type: Relay-based digital output
Installation: Compatible with standard junction boxes
The compact PCB design allows direct installation inside the junction box, eliminating the need for an external enclosure.
Application Scenarios
The Modbus-controlled output can be used in a wide range of applications:
Lighting on/off control
Fan or small motor control
Valve, contactor, or solenoid triggering
General-purpose digital outputs for automation systems
Smart building and industrial control applications
The module integrates easily with PLCs, HMIs, SCADA systems, and PC-based Modbus master software.
Communication and Control
The system operates as a Modbus RTU slave. Output control is handled via:
Holding registers
or Coil registers
This ensures stable and reliable communication with standard Modbus infrastructures.
General Evaluation
The resulting module offers:
A compact form suitable for limited spaces
Industrial communication compatibility
Flexible usage beyond lighting applications
A cost-effective and scalable design
Such in-wall distributed modules provide a clean and practical solution for smart building and distributed automation systems.