Bluetooth and Wireless Connections

Ardulink-2 supports wireless Arduino communication through Bluetooth, MQTT, and NodeMCU/ESP8266 modules.

Bluetooth

Hardware Requirements

  • Arduino board with a Bluetooth module (HC-05, HC-06, or similar)
  • Bluetooth-enabled computer (or USB Bluetooth adapter)

Setup

  1. Connect the Bluetooth module to Arduino (typically TX/RX pins)
  2. Pair the module with your computer via OS Bluetooth settings
  3. Add the dependency:
<dependency>
    <groupId>org.ardulink</groupId>
    <artifactId>ardulink-link-bluetooth</artifactId>
    <version>2.3.1</version>
</dependency>
  1. Connect using the Bluetooth MAC address:
import org.ardulink.core.Link;
import org.ardulink.core.pin.Pin;
import org.ardulink.core.convenience.Links;

public class BluetoothExample {
    public static void main(String... args) throws Exception {
        try (Link link = Links.getLink("ardulink://bluetooth?address=00:11:22:33:44:55")) {
            link.switchDigitalPin(Pin.digitalPin(13), true);
        }
    }
}

Replace 00:11:22:33:44:55 with your Bluetooth module’s actual MAC address.

MQTT

MQTT is ideal for IoT deployments where Arduino and Java run on different machines, or when you need broker-based communication.

Setup 

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

Using the Standalone MQTT Bridge

The ardulink-mqtt module provides a standalone JAR that bridges an Arduino connection to an MQTT broker:

# Download from Maven Central or use the standalone jar
java -jar ardulink-mqtt-2.3.1.jar \
    -connection "ardulink://serial?port=/dev/ttyACM0" \
    -broker "tcp://localhost:1883"

Connecting via MQTT in Java 

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

MQTT Configuration Options

Parameter Default Description
broker — MQTT broker URL (e.g., tcp://localhost:1883)
topic ardulink Base topic for messages
username — MQTT authentication username
password — MQTT authentication password
separatedTopics false Use separate topics per pin type

NodeMCU / ESP8266

Ardulink-2 has dedicated support for NodeMCU boards, which can connect via serial or MQTT.

Setup 

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

Serial Connection 

try (Link link = Links.getLink("ardulink://nodemcu?port=/dev/ttyUSB0")) {
    link.switchDigitalPin(Pin.digitalPin(2), true);
}

MQTT Connection 

try (Link link = Links.getLink("ardulink://nodemcu?broker=tcp://localhost:1883")) {
    link.switchDigitalPin(Pin.digitalPin(2), true);
}

When using MQTT with NodeMCU, the firmware includes a Lua init.lua script (available in the distribution) that connects the NodeMCU to the MQTT broker.

Raspberry Pi

The Raspberry Pi link adapter controls GPIO pins directly on the Pi (no Arduino needed):

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

try (Link link = Links.getLink("ardulink://raspberry")) {
    link.switchDigitalPin(Pin.digitalPin(7), true);
}

Choosing a Transport

Use Case Recommended Transport
Direct USB connection Serial (JSSC)
Short-range untethered Bluetooth
IoT / remote access MQTT
ESP8266 projects NodeMCU
Raspberry Pi GPIO Raspberry Pi
Testing without hardware Virtual

Next Steps