Arduino Android Serial Communication

4 min readJun 8, 2019

In this tutorial, I would show you how to establish a serial communication channel between Android and Arduino through USB cable and send data bidirectionally.

Requirements

Hardware:

Android Phone
Arduino (theoretically from any type, but I’ll be using Arduino Uno)
USB 2.0 Cable Type A/B (for Arduino)
OTG Cable (On The Go)
Normal USB Cable (for transferring the data from Android Studio to your phone)

Software:

Wiring and Setup

Wiring must be established in the following way:

Working on the Android Side

We would be using a simple and powerful Omar Aflak’s - Arduino Library for establishing serial communication.

1. Adding the dependency:

a) Add the following line of code to your module build.gradle file.

implementation 'me.aflak.libraries:arduino:1.3'

b) Add jitpack to your project.build.gradle file.

allprojects {
    repositories {
        jcenter()
        maven { url "https://jitpack.io" }
    }
}

2. Understanding the API:

Given below are the most useful methods and callbacks which would serve the required purpose.

a) Constructor: This is used to create a new Arduino instance (Essentially, as you can guess, its a requisite for implementing further methods and callbacks).

Arduino arduino = new Arduino(Context);

b) Arduino Listener: There is a listener which you can set this way.

arduino.setArduinoListener(new ArduinoListener(...))

The listener implements the following methods:

onArduinoAttached(UsbDevice device) // arduino plugged in. Here you should call arduino.open(device)onArduinoDetached() // arduino plugged outonArduinoMessage(byte[] bytes) // arduino sent a message through Serial.print()onArduinoOpened() // connection with arduino openedonUsbPermissionDenied() // when user denies the USB permission

c) Method for Sending Data: For sending messages to Arduino use the following method:

String msg = "Hello Arduino! This is Android.";
arduino.send(msg.getBytes());

3. Implementation:

Here is the complete implementation of a full-fledged application for arduino-android communication.

a) MainActivity.java

<your package name>import android.hardware.usb.UsbDevice;
import android.os.Handler;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.text.method.ScrollingMovementMethod;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;import me.aflak.arduino.Arduino;
import me.aflak.arduino.ArduinoListener;public class MainActivity extends AppCompatActivity implements ArduinoListener {    private Arduino arduino;
    private TextView displayTextView;
    private EditText editText;
    private Button sendBtn;@Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);        displayTextView = findViewById(R.id.diplayTextView);
        editText = findViewById(R.id.editText);
        sendBtn = findViewById(R.id.sendBtn);        displayTextView.setMovementMethod(new    ScrollingMovementMethod());        sendBtn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                String editTextString =   editText.getText().toString();
                arduino.send(editTextString.getBytes());
                editText.getText().clear();
            }
        });        arduino = new Arduino(this);
    }@Override
    protected void onStart() {
        super.onStart();
        arduino.setArduinoListener(this);
    }@Override
    protected void onDestroy() {
        super.onDestroy();
        arduino.unsetArduinoListener();
        arduino.close();
    }@Override
    public void onArduinoAttached(UsbDevice device) {
        display("arduino attached...");
        arduino.open(device);
    }@Override
    public void onArduinoDetached() {
        display("arduino detached.");
    }@Override
    public void onArduinoMessage(byte[] bytes) {
        display(new String(bytes));
    }@Override
    public void onArduinoOpened() {
        String str = "arduino opened...";
        arduino.send(str.getBytes());
    }@Override
    public void onUsbPermissionDenied() {
        display("Permission denied. Attempting again in 3 sec...");
        new Handler().postDelayed(new Runnable() {
            @Override
            public void run() {
                arduino.reopen();
            }
        }, 3000);
    }private void display(final String message){
        runOnUiThread(new Runnable() {
            @Override
            public void run() {
                displayTextView.append(message);
            }
        });
    }
}

b) activity_main.xml

<?xml version="1.0" encoding="utf-8"?><LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    tools:context=".MainActivity"><TextView
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_margin="5dp"
        android:text="Enter the text below:" /><EditText
        android:id="@+id/editText"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_margin="5dp" /><Button
        android:id="@+id/sendBtn"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_margin="5dp"
        android:text="Send" /><TextView
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="Received Messages From Arduino:"
        android:layout_marginTop="5dp"
        android:layout_marginLeft="5dp"
        android:layout_marginRight="5dp"/><TextView
        android:id="@+id/diplayTextView"
        android:layout_width="match_parent"
        android:layout_height="0dp"
        android:layout_margin="5dp"
        android:layout_weight="1"
        android:background="@android:color/darker_gray"
        android:textColor="@android:color/black"
        android:textSize="16sp"
        android:scrollbars = "vertical" /></LinearLayout>

Working on the Arduino Side

Arduino code is relatively simple. It simply echoes back whatever it receives on the serial port.

void setup() {
  // initialize serial communication at 9600 bits per second:
  Serial.begin(9600);
}void loop() {
  char incomingByte;
   // If there is a data stored in the serial receive buffer, read it and print it to the serial port as human-readable ASCII text.
  if(Serial.available()){  
    incomingByte = Serial.read();
    Serial.print(incomingByte);  
  }
}

That's it! You are good to go 😉. Communication has been established bidirectionally. The data sent from Android will be echoed back by Arduino. I have added the screenshots below so that you see the visual imprint of the above code without running it (if you are lazy enough like me 😛).