diff --git a/android/ConductorsSensor/app/build.gradle b/android/ConductorsSensor/app/build.gradle
index 8b1a7ce..f34dab1 100644
--- a/android/ConductorsSensor/app/build.gradle
+++ b/android/ConductorsSensor/app/build.gradle
@@ -4,7 +4,7 @@ android {
     compileSdkVersion 26
     defaultConfig {
         applicationId "de.tonifetzer.conductorssensor"
-        minSdkVersion 21
+        minSdkVersion 24
         targetSdkVersion 26
         versionCode 1
         versionName "1.0"
@@ -34,5 +34,5 @@ dependencies {
     api 'com.mbientlab:metawear:3.4.0'
     implementation 'com.android.support:preference-v7:26.1.0'
     implementation 'com.android.support:preference-v14:26.1.0'
-    compile 'com.github.wendykierp:JTransforms:3.1'
+    implementation 'com.github.wendykierp:JTransforms:3.1'
 }
diff --git a/android/ConductorsSensor/app/src/main/AndroidManifest.xml b/android/ConductorsSensor/app/src/main/AndroidManifest.xml
index 08c7f1b..03f66a3 100644
--- a/android/ConductorsSensor/app/src/main/AndroidManifest.xml
+++ b/android/ConductorsSensor/app/src/main/AndroidManifest.xml
@@ -4,6 +4,8 @@
 
     <uses-permission android:name="android.permission.BLUETOOTH"/>
     <uses-permission android:name="android.permission.BLUETOOTH_ADMIN"/>
+    <uses-permission android:name="android.permission.ACCESS_FINE_LOCATION"/>
+    <uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION"/>
 
     <application
         android:allowBackup="true"
diff --git a/android/ConductorsSensor/app/src/main/java/de/tonifetzer/conductorssensor/MainActivity.java b/android/ConductorsSensor/app/src/main/java/de/tonifetzer/conductorssensor/MainActivity.java
index 9b76dda..fb8bcc9 100644
--- a/android/ConductorsSensor/app/src/main/java/de/tonifetzer/conductorssensor/MainActivity.java
+++ b/android/ConductorsSensor/app/src/main/java/de/tonifetzer/conductorssensor/MainActivity.java
@@ -1,14 +1,24 @@
 package de.tonifetzer.conductorssensor;
 
+import android.Manifest;
+import android.app.AlertDialog;
+import android.content.DialogInterface;
+import android.content.pm.PackageManager;
+import android.graphics.Color;
+import android.os.Build;
+import android.os.Handler;
+import android.os.Looper;
 import android.support.v4.app.Fragment;
 import android.support.v4.app.FragmentActivity;
 import android.support.v4.app.FragmentTransaction;
 import android.os.Bundle;
 import android.support.v7.widget.PopupMenu;
+import android.util.Log;
 import android.view.MenuInflater;
 import android.view.MenuItem;
 import android.view.View;
 import android.widget.CompoundButton;
+import android.widget.TextView;
 import android.widget.Toast;
 import android.widget.ToggleButton;
 
@@ -18,11 +28,14 @@ import de.tonifetzer.conductorssensor.estimation.Estimator;
 import de.tonifetzer.conductorssensor.sensor.ConnectFragment;
 import de.tonifetzer.conductorssensor.settings.SettingsFragment;
 
-public class MainActivity extends FragmentActivity implements PopupMenu.OnMenuItemClickListener, ToggleButton.OnCheckedChangeListener{
+public class MainActivity extends FragmentActivity implements PopupMenu.OnMenuItemClickListener, ToggleButton.OnCheckedChangeListener, Estimator.OnEstimationListener{
+
+    private static final int PERMISSION_REQUEST_COARSE_LOCATION = 1;
 
     ConnectFragment mConnectFragment;
     Stack<String> mFragmentStack;
     ToggleButton mStartStopToggle;
+    TextView mBpmTextView;
 
     Estimator mEstimator;
 
@@ -35,9 +48,19 @@ public class MainActivity extends FragmentActivity implements PopupMenu.OnMenuIt
         mStartStopToggle= (ToggleButton) findViewById(R.id.startBtn);
         mStartStopToggle.setOnCheckedChangeListener(this);
 
+        //textview to show the bpm estimation
+        mBpmTextView = (TextView) findViewById(R.id.bpmText);
+
+        mEstimator = new Estimator();
+        mEstimator.addListener(this);
+
         // ensures the connection to the bt sensor board
         mConnectFragment = new ConnectFragment();
         mFragmentStack = new Stack<>();
+
+        //check for ble permissions
+        checkForBlePermissions();
+
     }
 
     @Override
@@ -135,21 +158,78 @@ public class MainActivity extends FragmentActivity implements PopupMenu.OnMenuIt
 
         if (isChecked) {
             if(mConnectFragment.getSensorBoard() != null && mConnectFragment.getSensorBoard().isConnected()){
-                mConnectFragment.getSensorBoard().startAccelerometer();
 
-                //todo: estimator classe mit start und stop funktion. board bei start durchreichen.
+                mBpmTextView.setTextColor(Color.parseColor("#EE693F"));
+                Toast.makeText(this, "Start estimation", Toast.LENGTH_SHORT).show();
+                mEstimator.start(mConnectFragment.getSensorBoard());
+
+                //todo: metronom
 
             } else {
+
                 Toast.makeText(this, "Please connect a sensor!", Toast.LENGTH_SHORT).show();
                 mStartStopToggle.setChecked(false);
             }
 
         } else {
             if(mConnectFragment.getSensorBoard() != null){
-                mConnectFragment.getSensorBoard().stopAccelerometer();
+
+                mBpmTextView.setTextColor(Color.parseColor("#158b69"));
+                Toast.makeText(this, "Stop estimation", Toast.LENGTH_SHORT).show();
+                mEstimator.stop();
             }
 
         }
 
     }
-}
+
+    @Override
+    public void onNewEstimationAvailable(double bpm) {
+
+        runOnUiThread(new Runnable() {
+            @Override
+            public void run() {
+                mBpmTextView.setText(String.valueOf(Math.round(bpm)));
+            }
+        });
+    }
+
+
+    private void checkForBlePermissions(){
+        if(this.checkSelfPermission(Manifest.permission.ACCESS_COARSE_LOCATION) != PackageManager.PERMISSION_GRANTED) {
+            final AlertDialog.Builder builder = new AlertDialog.Builder(this);
+            builder.setTitle("This app needs location access");
+            builder.setMessage("Please grant location access so this app can detect the Sensor over Bluetooth.");
+            builder.setPositiveButton(android.R.string.ok, null);
+            builder.setOnDismissListener(new DialogInterface.OnDismissListener() {
+                @Override
+                public void onDismiss(DialogInterface dialogInterface) {
+                    requestPermissions(new String[]{Manifest.permission.ACCESS_COARSE_LOCATION}, PERMISSION_REQUEST_COARSE_LOCATION);
+                }
+            });
+            builder.show();
+        }
+    }
+
+    @Override
+    public void onRequestPermissionsResult(int requestCode, String permission[], int[] grantResults){
+        switch(requestCode){
+            case PERMISSION_REQUEST_COARSE_LOCATION: {
+                if(grantResults[0] == PackageManager.PERMISSION_GRANTED) {
+                    Log.d("MainActivity", "coarse location permissin granted");
+                } else {
+                    final AlertDialog.Builder builder = new AlertDialog.Builder(this);
+                    builder.setTitle("Functionality limited");
+                    builder.setMessage("Without permission, this app is not able to connect to a sensor.");
+                    builder.setPositiveButton(android.R.string.ok, null);
+                    builder.setOnDismissListener(new DialogInterface.OnDismissListener() {
+                        @Override
+                        public void onDismiss(DialogInterface dialogInterface) {
+                        }
+                    });
+                    builder.show();
+                }
+            }
+        }
+    }
+}
\ No newline at end of file
diff --git a/android/ConductorsSensor/app/src/main/java/de/tonifetzer/conductorssensor/estimation/BpmEstimator.java b/android/ConductorsSensor/app/src/main/java/de/tonifetzer/conductorssensor/estimation/BpmEstimator.java
index 55cb641..8ac4a2f 100644
--- a/android/ConductorsSensor/app/src/main/java/de/tonifetzer/conductorssensor/estimation/BpmEstimator.java
+++ b/android/ConductorsSensor/app/src/main/java/de/tonifetzer/conductorssensor/estimation/BpmEstimator.java
@@ -27,7 +27,7 @@ public class BpmEstimator {
     //private SimpleKalman mKalman;
 
 
-    public BpmEstimator(AccelerometerWindowBuffer windowBuffer, double sampleRate_ms, int resetAfter_ms){
+     BpmEstimator(AccelerometerWindowBuffer windowBuffer, double sampleRate_ms, int resetAfter_ms){
         mBuffer = windowBuffer;
         mSampleRate_ms = sampleRate_ms;
 
@@ -46,6 +46,14 @@ public class BpmEstimator {
         //mKalman = new SimpleKalman();
     }
 
+    public void reset(){
+        mResetCounter = 0;
+        mBpmHistory_X.clear();
+        mBpmHistory_Y.clear();
+        mBpmHistory_Z.clear();
+        mBpmHistory.clear();
+    }
+
     //TODO: we use the buffer from outside.. this buffer is continuously updated.. not good!
     public double estimate(AccelerometerWindowBuffer fixedWindow){
 
diff --git a/android/ConductorsSensor/app/src/main/java/de/tonifetzer/conductorssensor/estimation/Estimator.java b/android/ConductorsSensor/app/src/main/java/de/tonifetzer/conductorssensor/estimation/Estimator.java
index c4d80f1..16eec0b 100644
--- a/android/ConductorsSensor/app/src/main/java/de/tonifetzer/conductorssensor/estimation/Estimator.java
+++ b/android/ConductorsSensor/app/src/main/java/de/tonifetzer/conductorssensor/estimation/Estimator.java
@@ -1,6 +1,5 @@
 package de.tonifetzer.conductorssensor.estimation;
 
-import android.hardware.Sensor;
 import android.util.Log;
 
 import java.util.LinkedList;
@@ -20,14 +19,14 @@ public class Estimator implements SensorBoard.OnSensorBoardDataListener {
 
     private Timer mTimer = new Timer();
 
-    Estimator(){
+    public Estimator(){
 
         mAccelerometerWindowBuffer = new AccelerometerWindowBuffer(6000, 750);
         mBpmEstimator = new BpmEstimator(mAccelerometerWindowBuffer, 0, 5000);
     }
 
     public void start(SensorBoard sensorBoard){
-        if(mSensorBoard != null){
+        if(sensorBoard != null){
             mSensorBoard = sensorBoard;
             mSensorBoard.addListener(this);
             mSensorBoard.startAccelerometer();
@@ -45,6 +44,7 @@ public class Estimator implements SensorBoard.OnSensorBoardDataListener {
             mSensorBoard.stopAccelerometer();
 
             mAccelerometerWindowBuffer.clear();
+            mBpmEstimator.reset();
 
         } else {
             Log.i("Estimator","Cant stop estimator. SensorBoard is null.");
@@ -97,7 +97,7 @@ public class Estimator implements SensorBoard.OnSensorBoardDataListener {
                     Utils.removeOutliersZScore(bpmList, 3.4);
                     //Utils.removeOutliersHeuristic();
 
-                    //Log.d("BPM: ", bpmList.toString());
+                    Log.d("BPM: ", bpmList.toString());
 
                     double bpm = -1;
                     if(!bpmList.isEmpty()) {
@@ -160,7 +160,7 @@ public class Estimator implements SensorBoard.OnSensorBoardDataListener {
     }
 
     private List<OnEstimationListener> mEstimationListeners = new CopyOnWriteArrayList<>();
-    public void add(OnEstimationListener listener){mEstimationListeners.add(listener);}
-    public void remove(OnEstimationListener listener){mEstimationListeners.remove(listener);}
+    public void addListener(OnEstimationListener listener){mEstimationListeners.add(listener);}
+    public void removeListener(OnEstimationListener listener){mEstimationListeners.remove(listener);}
 
 }
diff --git a/android/ConductorsSensor/app/src/main/java/de/tonifetzer/conductorssensor/sensor/SensorBoard.java b/android/ConductorsSensor/app/src/main/java/de/tonifetzer/conductorssensor/sensor/SensorBoard.java
index c11d45b..9e6ab2f 100644
--- a/android/ConductorsSensor/app/src/main/java/de/tonifetzer/conductorssensor/sensor/SensorBoard.java
+++ b/android/ConductorsSensor/app/src/main/java/de/tonifetzer/conductorssensor/sensor/SensorBoard.java
@@ -211,7 +211,6 @@ public class SensorBoard implements ServiceConnection {
                     source.stream(new Subscriber() {
                         @Override
                         public void apply(Data data, Object... env) {
-                            Log.i("MainActivity", data.value(Acceleration.class).toString());
 
                             for(OnSensorBoardDataListener listener : mDataListeners){
                                 listener.onAccelerometerChanged(new AccelerometerData(