Ardulink-MQTT: IoT Ready Arduino Communication

The ardulink-mqtt module bridges Ardulink-2 with MQTT brokers, enabling IoT-style communication between Arduino boards and any MQTT-compatible system.

What It Does

ardulink-mqtt acts as a translator:

  • Connects to your Arduino via any Ardulink link (serial, Bluetooth, etc.)
  • Exposes the Arduino’s pins as MQTT topics
  • Publishes pin changes from Arduino to MQTT
  • Subscribes to MQTT topics and forwards commands to Arduino
┌──────────┐  Serial   ┌──────────────┐  MQTT  ┌─────────────┐
│  Arduino │ <───────> │ ardulink-mqtt│ <────> │ MQTT Broker │
│  (FW)    │           │ (bridge)     │        │ (Mosquitto) │
└──────────┘           └──────────────┘        └─────────────┘
                                                      │
                                             ┌────────┴─────────┐
                                             │  Java / Node-RED │
                                             │  / Any MQTT app  │
                                             └──────────────────┘

Quick Start

1. Start the Bridge 

java -jar ardulink-mqtt-2.3.1.jar \
    -connection "ardulink://serial?port=/dev/ttyACM0" \
    -broker "tcp://localhost:1883"

For testing without hardware:

java -jar ardulink-mqtt-2.3.1.jar \
    -connection "ardulink://virtual-console" \
    -broker "tcp://localhost:1883"

2. Subscribe to Arduino Events

Using mosquitto_sub:

# Subscribe to all Arduino messages
mosquitto_sub -t "ardulink/#"

# Subscribe to pin 13 digital changes
mosquitto_sub -t "ardulink/digital/13"

3. Send Commands to Arduino 

# Turn on LED on pin 13
mosquitto_pub -t "ardulink/digital/13" -m "true"

# Set analog pin A0 to 512
mosquitto_pub -t "ardulink/analog/0" -m "512"

Maven Dependency

For programmatic MQTT link usage (not the standalone bridge):

<dependency>
    <groupId>org.ardulink</groupId>
    <artifactId>ardulink-link-mqtt</artifactId>
    <version>2.3.1</version>
</dependency>

try (Link link = Links.getLink("ardulink://mqtt?broker=tcp://localhost:1883&topic=arduino1")) {
    link.switchDigitalPin(Pin.digitalPin(13), true);
}

Command Line Options

Option Description
-connection <url> Ardulink connection URL (e.g., ardulink://serial?port=...)
-broker <url> MQTT broker URL (e.g., tcp://localhost:1883)
-topic <name> Base topic prefix (default: ardulink)
-username <user> MQTT authentication username
-password <pass> MQTT authentication password
-separatedTopics <bool> Use separate topics per pin type

MQTT Topic Structure

By default, topics follow this pattern:

Topic Direction Description
ardulink/digital/<pin> Both Digital pin read/write
ardulink/analog/<pin> Both Analog pin read/write
ardulink/tone/<pin> Java → Arduino Play a tone
ardulink/custom Both Custom messages

Integration with Node-RED

Ardulink-MQTT works seamlessly with Node-RED. See the Node-RED Sample for a complete walkthrough including Docker Compose setup.

Integration with Home Automation

Since MQTT is a standard IoT protocol, Ardulink-MQTT integrates with:

  • Home Assistant — MQTT sensor/switch entities
  • OpenHAB — MQTT binding
  • Node-RED — Flow-based visual programming
  • Grafana — Via MQTT data source
  • Custom dashboards — Any MQTT client

Next Steps