Arduino to Android – Turning an LED On and Off

This example shows you how to program an Android device to communicate with an Arduino over bluetooth and turn on or turn off an LED.

The Android device connects via the bluetooth to the Arduino which is running in a loop waiting for data from the bluetooth inteface. The data is read from the bluetooth interface using the software serial library. If the Arduino reads a 1 it turns an LED on pin 13 on. If it finds a 0 then it turns the LED off. If it reads anything else it doesn't change the state of the LED.

If you are using the Sparkfun Bluetooth Mate when you successfully connect to it from your Android program the Red Stat LED will turn off and the Green Connect LED will turn on solid.

For this example I used the same setup as I did for my earlier Arduino to Android tutorial: Arduino to Android – Basic Bluetooth Connectivity with the addition of an LED connected to pin 13 on the Arduino.

Download Zip Archive of Android Source Files

Arduino Sketch

#include <SoftwareSerial.h>

SoftwareSerial mySerial(6, 5);
int dataFromBT;

void setup() {
  Serial.begin(57600);
  Serial.println("LEDOnOff Starting...");

  // The data rate for the SoftwareSerial port needs to 
  // match the data rate for your bluetooth board.
  mySerial.begin(115200);
  pinMode(13, OUTPUT);   
}

void loop() {
  if (mySerial.available())
    dataFromBT = mySerial.read();

  if (dataFromBT == '0') {
    // Turn off LED
    digitalWrite(13, LOW);
  } else if (dataFromBT == '1') {
    // Turn on LEFD
    digitalWrite(13, HIGH);
  }
}

LEDOnOFF.java
goes in <ProjectRoot>\src\com\example\ledonoff\

package com.example.ledonoff;

import java.io.IOException;
import java.io.OutputStream;
import java.util.UUID;

import com.example.ledonoff.R;

import android.app.Activity;
import android.bluetooth.BluetoothAdapter;
import android.bluetooth.BluetoothDevice;
import android.bluetooth.BluetoothSocket;
import android.content.Intent;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.Toast;

public class LEDOnOff extends Activity {
  private static final String TAG = "LEDOnOff";
  
  Button btnOn, btnOff;
  
  private static final int REQUEST_ENABLE_BT = 1;
  private BluetoothAdapter btAdapter = null;
  private BluetoothSocket btSocket = null;
  private OutputStream outStream = null;
  
  // Well known SPP UUID
  private static final UUID MY_UUID =
      UUID.fromString("00001101-0000-1000-8000-00805F9B34FB");

  // Insert your server's MAC address
  private static String address = "00:00:00:00:00:00";
  
  /** Called when the activity is first created. */
  @Override
  public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    Log.d(TAG, "In onCreate()");

    setContentView(R.layout.main);

    btnOn = (Button) findViewById(R.id.btnOn);
    btnOff = (Button) findViewById(R.id.btnOff);
    
    btAdapter = BluetoothAdapter.getDefaultAdapter();
    checkBTState();

    btnOn.setOnClickListener(new OnClickListener() {
      public void onClick(View v) {
        sendData("1");
        Toast msg = Toast.makeText(getBaseContext(),
            "You have clicked On", Toast.LENGTH_SHORT);
        msg.show();
      }
    });

    btnOff.setOnClickListener(new OnClickListener() {
      public void onClick(View v) {
        sendData("0");
        Toast msg = Toast.makeText(getBaseContext(),
            "You have clicked Off", Toast.LENGTH_SHORT);
        msg.show();
      }
    });
  }
  
  @Override
  public void onResume() {
    super.onResume();

    Log.d(TAG, "...In onResume - Attempting client connect...");
  
    // Set up a pointer to the remote node using it's address.
    BluetoothDevice device = btAdapter.getRemoteDevice(address);
  
    // Two things are needed to make a connection:
    //   A MAC address, which we got above.
    //   A Service ID or UUID.  In this case we are using the
    //     UUID for SPP.
    try {
      btSocket = device.createRfcommSocketToServiceRecord(MY_UUID);
    } catch (IOException e) {
      errorExit("Fatal Error", "In onResume() and socket create failed: " + e.getMessage() + ".");
    }
  
    // Discovery is resource intensive.  Make sure it isn't going on
    // when you attempt to connect and pass your message.
    btAdapter.cancelDiscovery();
  
    // Establish the connection.  This will block until it connects.
    Log.d(TAG, "...Connecting to Remote...");
    try {
      btSocket.connect();
      Log.d(TAG, "...Connection established and data link opened...");
    } catch (IOException e) {
      try {
        btSocket.close();
      } catch (IOException e2) {
        errorExit("Fatal Error", "In onResume() and unable to close socket during connection failure" + e2.getMessage() + ".");
      }
    }
    
    // Create a data stream so we can talk to server.
    Log.d(TAG, "...Creating Socket...");

    try {
      outStream = btSocket.getOutputStream();
    } catch (IOException e) {
      errorExit("Fatal Error", "In onResume() and output stream creation failed:" + e.getMessage() + ".");
    }
  }

  @Override
  public void onPause() {
    super.onPause();

    Log.d(TAG, "...In onPause()...");

    if (outStream != null) {
      try {
        outStream.flush();
      } catch (IOException e) {
        errorExit("Fatal Error", "In onPause() and failed to flush output stream: " + e.getMessage() + ".");
      }
    }

    try     {
      btSocket.close();
    } catch (IOException e2) {
      errorExit("Fatal Error", "In onPause() and failed to close socket." + e2.getMessage() + ".");
    }
  }
  
  private void checkBTState() {
    // Check for Bluetooth support and then check to make sure it is turned on

    // Emulator doesn't support Bluetooth and will return null
    if(btAdapter==null) { 
      errorExit("Fatal Error", "Bluetooth Not supported. Aborting.");
    } else {
      if (btAdapter.isEnabled()) {
        Log.d(TAG, "...Bluetooth is enabled...");
      } else {
        //Prompt user to turn on Bluetooth
        Intent enableBtIntent = new Intent(btAdapter.ACTION_REQUEST_ENABLE);
        startActivityForResult(enableBtIntent, REQUEST_ENABLE_BT);
      }
    }
  }

  private void errorExit(String title, String message){
    Toast msg = Toast.makeText(getBaseContext(),
        title + " - " + message, Toast.LENGTH_SHORT);
    msg.show();
    finish();
  }

  private void sendData(String message) {
    byte[] msgBuffer = message.getBytes();

    Log.d(TAG, "...Sending data: " + message + "...");

    try {
      outStream.write(msgBuffer);
    } catch (IOException e) {
      String msg = "In onResume() and an exception occurred during write: " + e.getMessage();
      if (address.equals("00:00:00:00:00:00")) 
        msg = msg + ".\n\nUpdate your server address from 00:00:00:00:00:00 to the correct address on line 37 in the java code";
      msg = msg +  ".\n\nCheck that the SPP UUID: " + MY_UUID.toString() + " exists on server.\n\n";
      
      errorExit("Fatal Error", msg);       
    }
  }
}

strings.xml
goes in <ProjectRoot>\res\values\

<?xml version="1.0" encoding="utf-8"?>
<resources>

    <string name="app_name">LED On Off</string>

</resources>

main.xml
goes in <ProjectRoot>\res\layout\

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:orientation="vertical" >

    <TextView
        android:layout_width="fill_parent"
        android:layout_height="wrap_content" />

    <Button
        android:id="@+id/btnOn"
        android:layout_width="100dp"
        android:layout_height="wrap_content"
        android:text="Turn LED On" />

    <Button
        android:id="@+id/btnOff"
        android:layout_width="100dp"
        android:layout_height="wrap_content"
        android:text="Turn LED Off" />

</LinearLayout>

AndroidManifest.xml
goes in <ProjectRoot>

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.ledonoff"
    android:versionCode="1"
    android:versionName="1.0" >

    <uses-sdk android:minSdkVersion="15" />

    <application
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name" >
        <activity
            android:name=".LEDOnOff"
            android:label="@string/app_name" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>
    
    <uses-permission android:name="android.permission.BLUETOOTH" />
    <uses-permission android:name="android.permission.BLUETOOTH_ADMIN" />

</manifest>

Screen Capture from Acer A100

Notes:

1. As the SDK Emulator doesn’t emulate bluetooth and probably wouldn't be able to make a connection even if it did this example will not run in the emulator.
2. This example is built upon the work of others. I post it here not as an example of original work but rather as a complete working example for reference. If I didn't appropriately credit you for your work please let me know and I will add you.