Modbus RTU Relay Controller

This Express.js application provides a REST API to control Modbus RTU relays through RS485 via USB.

Setup

1. Connect your USB-RS485 converter to your computer
2. Install dependencies:

   npm install

3. Update the serial port in app.js if needed (default is /dev/ttyUSB0)

Running the Application

npm start

The server will start on port 3000.

API Endpoints

Get Relay State

• GET /relay/:number
• Returns the state of a specific relay
• Example: GET http://localhost:3000/relay/1

Set Single Relay State

• POST /relay/:number
• Sets the state of a specific relay
• Body: { "state": true } or { "state": false }
• Example: POST http://localhost:3000/relay/1

Set Multiple Relay States

• POST /relays
• Sets multiple relay states at once
• Body: { "states": [true, false, true] }
• Example: POST http://localhost:3000/relays

Configuration

Default Modbus RTU settings:

• Baud Rate: 9600
• Data Bits: 8
• Stop Bits: 1
• Parity: None
• Device ID: 1

Adjust these settings in app.js if your device requires different parameters.