How to Connect Any PLC to MQTT in 10 Minutes

Connecting PLC data to MQTT is the first step in modern industrial digitalization. As a lightweight messaging protocol, MQTT has become the de facto standard for Industrial IoT—it handles unstable network environments well, supports real-time data streaming, and is natively supported by almost all cloud platforms, data analytics tools, and MES systems.

However, in real factory environments, connecting PLC data to MQTT is far more complex than imagined. PLCs from different manufacturers use different communication protocols (Modbus, OPC UA, Siemens S7, Ethernet/IP...), and traditional solutions require writing driver code for each protocol, resulting in high deployment and maintenance costs.

This article demonstrates how to connect any PLC to MQTT in 10 minutes using EMQX Neuron, without writing any code.

Why is PLC to MQTT So Difficult?

Protocol Fragmentation

Equipment in factory workshops comes from different eras and manufacturers:

Each protocol has its own data format, addressing method, and communication mechanism. Traditional solutions require developing and maintaining independent drivers for each protocol.

Inconsistent Data Formats

Even after successfully collecting data, different PLCs have vastly different data formats:

• Register addresses: 40001 (Modbus) vs DB1.DBD0 (Siemens) vs N7:0 (Allen-Bradley)

• Data types: INT16, FLOAT, BOOL, STRING...

• Byte order: Big-endian vs Little-endian

These data need to be standardized before being sent to MQTT.

Deployment and Maintenance Costs

Traditional access solutions often rely on dedicated hardware gateways, which not only have high initial procurement costs but also incur a series of hidden expenses: deployment and debugging of hardware gateways require professional engineers to operate on-site, which is time-consuming and labor-intensive; driver adaptation for different PLC protocols, firmware upgrades, and troubleshooting all require additional technical service fees.

EMQX Neuron: Industrial Edge Gateway Software

EMQX Neuron is an industrial edge gateway software designed specifically for industrial scenarios. It integrates protocol conversion, data processing, and MQTT publishing into a lightweight software solution.

Core Advantages

1. 100+ Industrial Protocols Out of the Box

   • Modbus TCP/RTU, OPC UA, Siemens S7, Ethernet/IP, BACnet, IEC 60870-5-104, DNP3...

   • Complete protocol list: Data Collection Plugin List

2. Flexible & Lightweight Deployment

   • Docker container: One-click deployment, cross-platform operation (runs with 256MB memory)

   • Kubernetes: Cloud-native deployment

   • Bare-metal installation: Supports Ubuntu, CentOS, Debian

   • Edge hardware: Raspberry Pi, Industrial PC, ARM gateways

3. Zero-Code Configuration

   • Visual configuration via Web interface

   • Complete PLC to MQTT pipeline in 10 minutes

4. Powerful Edge Computing Capabilities

   • SQL stream processing: 160+ built-in functions, supports filtering, transformation, aggregation

   • AI algorithm integration: Supports Python, ONNX, external HTTP services

   • Real-time alerts: Millisecond-level response, supports complex rules

5. Enterprise-Grade Features

   • High performance: Single node supports 100,000+ data points

   • Security: TLS/SSL encryption, user permission management

   • Observability: Complete logs, metrics, and monitoring

10-Minute Hands-On: Modbus PLC to MQTT

Let's demonstrate the entire process through a complete hands-on case.

Architecture Overview

Prerequisites

• PLC or simulator: This example uses a Modbus TCP simulator (PeakHMI Slave Simulators)

• EMQX Neuron: Quick deployment via Docker

• MQTT Broker: Use public broker broker.emqx.io

• MQTT client: Use MQTTX to verify data

Step 1: Start EMQX Neuron

docker pull emqx/neuronex:latest
docker run -d --name neuronex -p 8085:8085 --log-opt max-size=100m --privileged=true emqx/neuronex:latest

Access http://localhost:8085 and log in with default credentials: Username: admin, Password: 0000

Step 2: Add Southbound Device (Data Source)

Southbound devices are connections between NeuronEX and PLCs.

1. Go to "Data Collection" → "Southbound Devices"

2. Click "Add Device"

3. Configure device parameters:

   • Name: modbus-tcp-1

   • Plugin: Select "Modbus TCP"

   • IP Address: Enter the simulator's IP (e.g., 192.168.1.100)

   • Port: 502 (Modbus TCP default port)

   • Keep other parameters as default

4. Click "Add Device"

Step 3: Create Collection Group and Tags

Collection groups are used to group data points, and each group can have an independent collection frequency.

3.1 Create Collection Group

1. Click on the modbus-tcp-1 device card you just created

2. Click "Create Group"

3. Configure group parameters:

   • Group Name: group-1

   • Collection Interval: 1000 (milliseconds, i.e., collect once per second)

3.2 Add Data Tags

1. Click "Tag List" for the group-1 group

2. Click "Add Tag"

3. Configure tag parameters:

Address format explanation:

• 1!40001, where 1 is the station number and 40001 is the holding register address

• 1!00001:1, where 1 is the station number and 00001 is the coil address

4. Click "Create"

After completing tag creation, the device status will automatically change to "Connected".

Step 4: Verify Data Collection

1. Go to "Data Collection" → "Data Monitoring"

2. Select southbound device: modbus-tcp-1

3. Select group: group-1

4. View real-time data

You will see the real-time values of each tag.

Step 5: Configure Northbound Application (MQTT Publishing)

Northbound applications are used to send collected data to external systems.

5.1 Create MQTT Application

1. Go to "Data Collection" → "Northbound Applications"

2. Click "Add Application"

3. Configure application parameters:

   • Name: mqtt-broker

   • Plugin: Select "MQTT"

5.2 Configure MQTT Connection

1. Fill in the application configuration page:

   • Server Address: broker.emqx.io (public MQTT Broker)

   • Server Port: 1883

   • Client ID: neuron-client-001 (optional)

   • Username/Password: Leave blank (public broker requires no authentication)

2. Click "Submit", and the application status will change to "Running".

5.3 Subscribe to Southbound Data Group

1. Click "Add Subscription" for the mqtt-broker application

2. Configure subscription parameters:

   • Topic: factory/line1/modbus-tcp-1/data (custom topic)

   • Subscribe to Southbound Driver Data: Select modbus-tcp-1 → group-1

3. Click "Submit"

Step 6: Verify MQTT Data

Use the MQTTX client to verify that data is successfully published to the MQTT Broker.

1. Open MQTTX and create a new connection:

   • Name: TestConnection

   • Host: broker.emqx.io

   • Port: 1883

2. Add subscription:

   • Topic: factory/line1/modbus-tcp-1/data

3. View received data:

{
  "timestamp": 1706745600000,
  "node_name": "modbus-tcp-1",
  "group_name": "group-1",
  "values": {
    "temperature": 23.3,
    "pressure": 88,
    "motor_status": 1
  }
}

Congratulations! You have completed the complete data pipeline from Modbus PLC to MQTT in 10 minutes.

Advanced: Support for More PLC Protocols

The example above uses a Modbus simulator for data collection. EMQX Neuron supports 100+ industrial protocols. For a complete tutorial on collecting data from Siemens S7-1200 PLC using EMQX Neuron and sending it to MQTT, please refer to: Connecting Siemens S7-1200 PLC to MQTT in 10 Minutes

Advanced: Edge Data Processing

EMQX Neuron can not only collect and forward data but also perform real-time data processing at the edge.

Use Cases

• Data filtering: Only upload data exceeding thresholds (e.g., temperature > 80°C)

• Data transformation: Unit conversion (PSI → Bar), value calculation (+1, ×0.9)

• Data aggregation: Calculate average, maximum, minimum values

• Alert triggering: Real-time anomaly detection and alert sending

Quick Example: Temperature Over-Limit Alert

Scenario: When temperature exceeds 80°C, send an alert to a separate MQTT topic.

1. Subscribe data to the data processing module

   In "Data Collection" → "Northbound Applications", find the default DataProcessing application and add a subscription: the group-1 collection group of the modbus-tcp-1 driver.

   Data will automatically flow into the neuronStream data stream of the data processing module.

2. Create processing rule

   Go to "Data Processing" → "Rules", click "New Rule":

SELECT
  timestamp,
  node_name,
  values.temperature as temp
FROM neuronStream
WHERE values.temperature > 80

3. Configure action (Sink)

   Click "Add" in the "Actions" module, select "MQTT":

   • Server Address: broker.emqx.io:1883

   • Topic: factory/alerts/high-temperature

   • Data Template:

{
  "alert_type": "high_temperature",
  "device": "{{.node_name}}",
  "temperature": {{.temp}},
  "timestamp": {{int64 .timestamp}}
}

4. Verify alert

   Subscribe to factory/alerts/high-temperature in MQTTX. When the temperature exceeds 80°C, you will receive an alert message.

Summary

Connecting PLCs to MQTT should not be a complex, expensive, and time-consuming project. EMQX Neuron simplifies the entire process in the following ways:

✅ 100+ protocols out of the box: No need to write drivers for each PLC

✅ Zero-code configuration: Visual Web interface operations, complete configuration in 10 minutes

✅ Lightweight deployment: Docker container, 200MB+ image, 256MB memory

✅ Edge computing capabilities: SQL stream processing + AI algorithm integration

Start your industrial digitalization journey today and let data flow.