Reading Digital and Analog Pins

Ardulink-2 supports event-driven communication with Arduino. Instead of polling pins, you can subscribe to changes and react when they happen.

Listening for Pin Changes 

import org.ardulink.core.Link;
import org.ardulink.core.pin.Pin;
import org.ardulink.core.pin.Pin.DigitalPin;
import org.ardulink.core.pin.Pin.AnalogPin;
import org.ardulink.core.events.PinChangedEvent;
import org.ardulink.core.events.FilteredEventListenerAdapter;
import org.ardulink.core.convenience.Links;

public class PinReader {
    public static void main(String... args) throws Exception {
        try (Link link = Links.getDefault()) {

            // Digital pin 2 (e.g., a button)
            DigitalPin buttonPin = Pin.digitalPin(2);
            link.addListener(FilteredEventListenerAdapter.filter(
                PinChangedEvent.class, buttonPin,
                e -> System.out.printf("Button: %s%n", e.getValue())
            ));
            link.startListening(buttonPin);

            // Analog pin A0 (e.g., a potentiometer)
            AnalogPin sensorPin = Pin.analogPin(0);
            link.addListener(FilteredEventListenerAdapter.filter(
                PinChangedEvent.class, sensorPin,
                e -> System.out.printf("Sensor: %s%n", e.getValue())
            ));
            link.startListening(sensorPin);

            System.out.println("Listening for pin changes...");

            // Keep running
            Thread.sleep(Long.MAX_VALUE);
        }
    }
}

How It Works

  1. FilteredEventListenerAdapter.filter(...) — Creates a listener that only fires for changes on the specified pin
  2. link.addListener(...) — Registers the filtered listener
  3. link.startListening(pin) — Tells the Arduino firmware to report changes on this pin
  4. The Arduino firmware monitors the pin and sends a message when it changes
  5. The Java side receives the message and fires the event callback

Pin Types

Digital Pins 

DigitalPin pin = Pin.digitalPin(13);  // Digital pin 13
link.startListening(pin);

Digital values are boolean — true (HIGH) or false (LOW).

Analog Pins 

AnalogPin pin = Pin.analogPin(0);  // Analog pin A0
link.startListening(pin);

Analog values are int — 0 to 1023 (10-bit resolution).

Stopping Listeners 

// Stop listening to a specific pin
link.stopListening(Pin.digitalPin(2));

// Remove the event listener
link.removeListener(myListener);

Practical Example: Button + LED 

import org.ardulink.core.Link;
import org.ardulink.core.pin.Pin;
import org.ardulink.core.pin.Pin.DigitalPin;
import org.ardulink.core.events.PinChangedEvent;
import org.ardulink.core.events.FilteredEventListenerAdapter;
import org.ardulink.core.convenience.Links;

public class ButtonLED {
    public static void main(String... args) throws Exception {
        try (Link link = Links.getDefault()) {
            DigitalPin led = Pin.digitalPin(13);
            DigitalPin button = Pin.digitalPin(2);

            // When button changes, toggle LED — filtered to pin 2 only
            link.addListener(FilteredEventListenerAdapter.filter(
                PinChangedEvent.class, button,
                e -> {
                    boolean pressed = Boolean.TRUE.equals(e.getValue());
                    link.switchDigitalPin(led, pressed);
                    System.out.println(pressed ? "LED ON" : "LED OFF");
                }
            ));

            link.startListening(button);
            System.out.println("Press the button to toggle LED...");
            Thread.sleep(Long.MAX_VALUE);
        }
    }
}

Reading Current Pin State

To read the current value of a pin without waiting for changes, you can send a custom message request. See Custom Messages for the protocol details.

Next Steps