MQTT EMQX MQTT Integration

Connect LINK485 devices to EMQX for scalable, enterprise-grade MQTT messaging

⏱️ Setup Time: 15-20 minutes | 📚 Prerequisites: EMQX broker installed, LINK485 gateway configured | 🔒 Security: TLS/SSL optional, Username/Password authentication

Overview

EMQX is a highly scalable, open-source MQTT broker that supports millions of concurrent connections. This guide demonstrates how to connect LINK485 gateways to EMQX for reliable industrial IoT data collection, supporting both cloud and on-premise deployments.

Why EMQX?

⚡ High Performance

Supports 5M+ concurrent connections and millions of messages per second

🔄 Clustering

Built-in clustering for high availability and horizontal scaling

🔐 Security

TLS/SSL, authentication plugins, ACL, and rate limiting

📊 Dashboard

Built-in web dashboard for monitoring, metrics, and client management

Architecture

LINK485 Gateway
Modbus Devices
→
EMQX Broker
MQTT Pub/Sub
→
Applications
SCADA, Databases, Analytics

LINK485 publishes Modbus data to EMQX via MQTT. EMQX handles message routing, persistence, and distribution to multiple subscribers including databases, analytics platforms, and custom applications.

Prerequisites

  • EMQX Broker: Version 5.0+ installed and running (Download here)
  • LINK485 Gateway: Firmware v2.0+ with MQTT support
  • Network Access: LINK485 can reach EMQX on port 1883 (MQTT) or 8883 (MQTTS)
  • EMQX Dashboard Access: Default at http://broker-ip:18083 (admin/public)

Step 1: Install EMQX (Optional)

If you don't have EMQX installed yet, here's a quick Docker setup:

# Pull EMQX Docker image
docker pull emqx/emqx:5.3

# Run EMQX container
docker run -d --name emqx \
  -p 1883:1883 \
  -p 8883:8883 \
  -p 8083:8083 \
  -p 18083:18083 \
  emqx/emqx:5.3

Ports:

  • 1883: MQTT (unencrypted)
  • 8883: MQTTS (TLS/SSL encrypted)
  • 8083: WebSocket
  • 18083: EMQX Dashboard (web UI)

💡 Production Tip: For production deployments, use docker-compose or Kubernetes for clustering and persistence.

Step 2: Configure EMQX Authentication (Optional)

For secure deployments, configure authentication in EMQX:

  1. Open EMQX Dashboard: http://broker-ip:18083 (login: admin/public)
  2. Navigate to: Authentication → Create
  3. Select Mechanism: Built-in Database (Username/Password)
  4. Add User: Create credentials for LINK485
    • Username: link485_gateway
    • Password: (create a strong password)
    • Is Superuser: No
  5. Click "Create"

⚠️ Security Note: Always use authentication and TLS in production environments. Never use default credentials.

Step 3: Configure Access Control (ACL)

Restrict which topics LINK485 can publish to:

  1. In EMQX Dashboard: Go to Authorization → Create
  2. Select Type: Built-in Database
  3. Add ACL Rules:
    • Username: link485_gateway
    • Permission: Allow
    • Action: Publish
    • Topic: link485/data/${clientid}
  4. Add another rule for status messages with topic: link485/status/${clientid}

This ensures each gateway can only publish to its own topics.

Step 4: Configure LINK485 Device via Mobile App

For Link485 Air (WiFi)

  1. Power on your Link485 Air device
  2. Download Link485 App:
  3. Open App and Add Device: Tap "Add New Device"
  4. Enter WiFi Credentials:
    • SSID: Your WiFi network name
    • Password: Your WiFi password
  5. Choose Integration Type: Select "EMQX" from dropdown
  6. Enter EMQX Broker Details:
    • Broker Address: Your EMQX broker IP or hostname
    • Port: 1883 (or 8883 for TLS)
    • Username: link485_gateway (if authentication enabled)
    • Password: Your password (if authentication enabled)
    • Use TLS: Toggle ON if using port 8883
  7. Tap "Connect" - Device will configure and connect automatically

For Link485 4G (Cellular)

  1. Power on your Link485 4G device with SIM card inserted
  2. Download Link485 App (same as above)
  3. Optional: Enter WiFi credentials if you want WiFi as backup connectivity
  4. Choose Integration Type: Select "EMQX"
  5. Enter EMQX Broker Details (same as above)
  6. Tap "Connect" - Device uses 4G for primary connection

💡 Pro Tip: The mobile app automatically handles QoS, keepalive, and reconnection settings. You just need to provide broker credentials!

Understanding Data Flow & Topics

1. Data FROM Device (Telemetry)

Device publishes Modbus data to:

{broker_address}/{app_name}/telemetry

Your application should subscribe to:

mosquitto_sub -h broker-ip -p 1883 \
  -t "link485/+/telemetry" \
  -u link485_gateway -P your_password

2. Commands TO Device

Device subscribes to commands at:

{broker_address}/{device_mac}/commands

Your application should publish commands to:

mosquitto_pub -h broker-ip -p 1883 \
  -t "link485/AA:BB:CC:DD:EE:FF/commands" \
  -m '{"command":"read_holding_registers","address":0,"count":10}' \
  -u link485_gateway -P your_password

📝 Note: Replace {device_mac} with your device's MAC address (visible in Link485 mobile app). The app configures these topics automatically during setup.

Step 5: Verify Connection in EMQX Dashboard

  1. Open EMQX Dashboard: http://broker-ip:18083
  2. Go to Monitoring → Clients: You should see your LINK485 gateway listed
  3. Check Connection Details:
    • Client ID: link485-gateway-001
    • Status: Connected (green)
    • IP Address: Gateway's IP
  4. Monitor Messages: Go to Monitoring → Topic Metrics to see message rates

Expected Dashboard View:

Client ID Username Status IP Address
link485-gateway-001 link485_gateway ● Connected 192.168.1.100

Step 6: Subscribe to Data with MQTT Client

Test receiving data using the EMQX WebSocket client or MQTT.fx:

Option A: EMQX WebSocket Client

  1. In EMQX Dashboard, go to Tools → WebSocket Client
  2. Keep default settings and click Connect
  3. In the Subscribe section, enter topic: link485/data/#
  4. Click Subscribe
  5. You should see JSON messages arriving with Modbus data

Option B: MQTT.fx or Mosquitto Client

# Using mosquitto_sub (Linux/Mac)
mosquitto_sub -h broker-ip -p 1883 -t "link485/data/#" -u link485_gateway -P your_password

# Using MQTTX CLI
mqttx sub -h broker-ip -p 1883 -t "link485/data/#" -u link485_gateway -P your_password

Data Format

LINK485 publishes JSON-formatted messages to EMQX:

{
  "device_id": "link485-gateway-001",
  "timestamp": "2025-10-29T10:45:23Z",
  "slaves": [
    {
      "slave_id": 1,
      "name": "Energy Meter 1",
      "type": "energy_meter",
      "registers": {
        "voltage": 230.5,
        "current": 12.3,
        "power": 2835.15,
        "energy": 1234.56,
        "frequency": 50.02
      },
      "quality": "good",
      "last_poll": "2025-10-29T10:45:22Z"
    },
    {
      "slave_id": 2,
      "name": "VFD Pump",
      "type": "vfd",
      "registers": {
        "speed": 45.6,
        "current": 8.2,
        "status": "running"
      },
      "quality": "good",
      "last_poll": "2025-10-29T10:45:22Z"
    }
  ],
  "gateway_info": {
    "uptime": 86400,
    "rssi": -65,
    "firmware": "2.1.4"
  }
}
Field Type Description
device_id string Unique gateway identifier (matches Client ID)
timestamp ISO8601 UTC timestamp when data was collected
slaves array Array of Modbus slave devices
slaves[].slave_id integer Modbus slave address (1-247)
slaves[].name string Human-readable device name
slaves[].registers object Key-value pairs of register data
gateway_info object Gateway health and status information

Advanced: EMQX Rule Engine

EMQX Rule Engine allows real-time data processing, filtering, and forwarding:

Example 1: Forward High Power Readings to Webhook

SQL Rule:

SELECT
  device_id,
  timestamp,
  slaves[1].registers.power as power
FROM
  "link485/data/#"
WHERE
  slaves[1].registers.power > 5000

Action: Webhook → POST to https://alerts.example.com/high-power

Example 2: Store Data in TimescaleDB

SQL Rule:

SELECT
  *
FROM
  "link485/data/#"

Action: TimescaleDB → Insert into timeseries table

Example 3: Republish to Separate Topics per Device Type

SQL Rule:

SELECT
  *
FROM
  "link485/data/#"

Action: Republish → devices/${slaves[1].type}/${device_id}

Troubleshooting

❌ Connection Failed

  • Verify EMQX broker is running: docker ps or check service status
  • Ensure firewall allows traffic on port 1883/8883
  • Test connectivity: telnet broker-ip 1883
  • Check EMQX logs: docker logs emqx

❌ Authentication Failed

  • Verify username/password are correct in both EMQX and LINK485
  • Check authentication is enabled in EMQX Dashboard
  • Ensure user exists in EMQX authentication database
  • Try connecting without authentication first to isolate issue

❌ Client Keeps Disconnecting

  • Check for duplicate Client IDs (must be unique per connection)
  • Verify network stability between LINK485 and EMQX
  • Increase keepalive interval in LINK485 settings (default: 60s)
  • Check EMQX max connections limit hasn't been reached

❌ Not Authorized to Publish

  • Check ACL rules in EMQX Dashboard → Authorization
  • Verify topic pattern matches what LINK485 is publishing to
  • Ensure authorization is properly configured and enabled
  • Try disabling ACL temporarily to isolate issue

❌ No Data in WebSocket Client

  • Verify LINK485 shows "Connected" status in its dashboard
  • Check Modbus slaves are configured and responding
  • Ensure subscription topic includes wildcard correctly: link485/data/#
  • Check EMQX dashboard for incoming message rates

Performance Tuning

For High-Volume Deployments

  • Increase Max Connections: Edit emqx.conf - set listeners.tcp.default.max_connections = 100000
  • Enable Clustering: Deploy multiple EMQX nodes for horizontal scaling
  • Use Persistent Sessions: Enable session persistence for guaranteed delivery
  • Message Batching: Configure LINK485 to batch messages if publishing frequently
  • QoS Strategy: Use QoS 0 for non-critical telemetry, QoS 1 for important data
  • Monitoring: Enable Prometheus metrics for production monitoring

Next Steps

📊 Integrate with InfluxDB

Use EMQX Rule Engine to forward data to InfluxDB for time-series storage

📈 Visualize with Grafana

Create real-time dashboards by connecting Grafana to your time-series database

🔄 Node-RED Integration

Subscribe to EMQX topics from Node-RED for visual workflow automation

☁️ EMQX Cloud

Use EMQX Cloud for fully managed, scalable MQTT service

Need Help with EMQX Integration?

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