Creating Activity for Visualizing Recorded Sensor Data from List Items

In previous blog Using RealmRecyclerView Adapter to Show Recorded Sensor Experiments[2], I  have created a DataLoggerActivity in PSLab Android app containing RecyclerView showing a list having all the recorded experiments where every list item shows the date, time and the sensor instrument used for recording the data, but there arises below questions:-

  • What if the user wants to see the actual recorded data in form of a graph?
  • How the user can see the location recorded along with the data on the map?
  • How can the user export that data?

There is no way I could show all of that information just on a list item so I created another activity called “SensorGraphViewActivity” the layout of that activity is shown in the figure below:

Figure 1 shows the layout of the Activity as produced in Android editor

The layout contains three views:-

  1. At the top there is graph view which I created using Android MP chart which will show the recorded data plotted on it forming the exact same curve that was created while recording it, this way it is useful to visualize the data and also there is also a play button on the top which simulates the data as it was being plotted on the graph in real time.
  2. In the middle, there is a Card view containing two rows which will simply show the date and time of recording.
  3. At the bottom, there is a Map view which shows the location of the user which would be fetched when the user recorded the data.

This is the gist of the layout file created for the activity.

But now the question arises:-

How to show the data in the activity for the item that the user wanted?

For that, I implemented click listener on every list item by simply adding it inside the onBindViewHolder() method

public void onBindViewHolder(@NonNull final ViewHolder holder, int position) {
   SensorLogged temp = getItem(position);
   Date date = new Date(temp.getDateTimeStart());
   holder.cardView.setOnClickListener(new View.OnClickListener() {
       public void onClick(View view) {

and inside the click listener I performed following three steps:-

  1. First I stored the position of the item clicked inside a variable.

    int positionVar = holder.getAdapterPosition();
  2. Then I used that position from the variable to fetch related data from the Realm database by simply using getItem() method which returns the SensorLogged[1] RealmObject at that position as I used a special type of RecyclerView Adapter called as RealmRecyclerViewAdapter[2].

    int positionVar = holder.getAdapterPosition();
  3. Then I created an Intent to open the SensorGraphViewActivity and passed the related data (i.e., sensortype, foreignkey, latitude, longitude, timezone, date, time) from SensorLogged[1] object to activity in form of extras.
    Intent intent = new Intent(context, SensorGraphViewActivity.class);
    intent.putExtra(SensorGraphViewActivity.TYPE_SENSOR, item.getSensor());
    intent.putExtra(SensorGraphViewActivity.DATA_FOREIGN_KEY, item.getUniqueRef());

And, in the SensorGraphViewActivity, I used getIntent() method to fetch all those extra data in the form of Bundle.
For showing the data in the graph I used the foreign key fetched from the intent and queried all the LuxData[1] RealmObject containing that foreignkey in the form of RealmResult<LuxData>[2] ArrayList and used that list to populate the graph.

Long foreignKey = intent.getLongExtra(DATA_FOREIGN_KEY, -1);
Realm realm = Realm.getDefaultInstance();
entries = new ArrayList<>();
RealmResults<LuxData> results = realm.where(LuxData.class).equalTo(DATA_FOREIGN_KEY, foreignKey).findAll();
for (LuxData item : results) {
   entries.add(new Entry((float) item.getTimeElapsed(), item.getLux()));

For the map, I fetched the latitude and longitude again from the intent and used the coordinates to show the location on the open street view map.

Thread thread = new Thread(new Runnable() {
   public void run() {
       IMapController mapController = map.getController();
       mapController.setZoom((double) 9);
       GeoPoint startPoint = new GeoPoint(latitude, latitude);

For map purposes, of course, I used a separate thread as it is a heavy and time-consuming process and it could lead the app to lag for a long time which could hamper the User Experience.

Thus after the data being plotted on the map and coordinated being plotted on the map, we can see the layout of the activity as shown in Figure 2.

Figure 2 shows the layout of the activity after being populated with data.

I also created the export button in the toolbar that will use the CSVLogger[3] class implemented inside the PSLab android app to export the data in the form of CSV file and save it in the external storage directory.


  1. Storing Recorded Sensor Data in Realm Database – My blog where I created the Realm Model classes to store recorded data.
  2. Using RealmRecyclerView Adapter to Show Recorded Sensor Experiments – My previous blog where I created the RecyclerView.
  3. Saving Sensor Data in CSV format – Blog by Padmal storing the data in CSV format.

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Export Sensor Data from the PSLab Android App

The PSLab Android App allows users to log data from the sensors connected to the PSLab hardware device. Sensor Data is stored locally but can be exported in various formats. Currently the app supports exporting data in .txt and .csv (comma-separated values) format. Exported data can be used by other users or scientists to study or analyze the data. Data can also be used by other softwares like Python, GNU octave, Matlab to further process it or visualise it in 3D. In this post, we will discuss how to export the locally stored realm data in .txt or .csv format. We will take the data of MPU6050 sensor as an example for understanding how locally logged data is exported.

Query Local Realm Data

We have attached a long click listener to sensor list view that detects which list item is selected. Clicking any sensor from sensor list for slightly longer than usual would result in a dialog popping up with the option to

  • Export Data: Results in exporting data in a format which is selected in App settings
  • Share Data: Shares sensor data with other users or on social media (yet to be implemented)
Source: PSLab Android App

As soon as the Export Data option is selected from the dialog, sensor data of the corresponding sensor is queried. The data model of the sensor and how it’s saved in the local realm database is discussed in the post Sensor Data Logging in the PSLab Android App.

RealmResults<DataMPU6050> results = realm.where(DataMPU6050.class).findAll();

Once we get the required data, we need to write it in .txt or .csv format depending on what the user has selected as a preference in App Settings.

Getting User Preference from App Settings

The format in which the sensor data should be exported is presented to the user as a preference in App Settings. Currently the app supports two formats .txt and .csv.

Source: PSLab Android App
private String format;
SharedPreferences preferences = PreferenceManager.getDefaultSharedPreferences(this);
String formatValue = preferences.getString("export_data_format_list", "0");
if ("0".equals(formatValue))
   format = "txt";
   format = "csv";

Export Data in .txt Format

To export the sensor data in .txt format, we need to create a .txt file in the external storage. folder variable is a path to PSLab Android folder in the external storage. If the folder doesn’t exist, it will be created.

File folder = new File(Environment.getExternalStorageDirectory() + File.separator + "PSLab Android");

After getting reference of the app folder in the external storage, we would create a text file in the PSLab Android folder. As soon as the text file is created, we initialize the FileOutputStream object to write data into the text file. The sensor data that was queried in the previous section is written into the text file just created. Finally after the complete sensor data is written, the stream is closed by stream.close() method.

FileOutputStream stream = null;
File file = new File(folder, "sensorData.txt");
try {
   stream = new FileOutputStream(file);
   for (DataMPU6050 temp : results) {
       stream.write((String.valueOf(temp.getAx()) + " " + temp.getAy() + " " + temp.getAz() + " " +
               temp.getGx() + " " + temp.getGy() + " " + temp.getGz() + " " + temp.getTemperature() + "\n").getBytes());
} catch (IOException e) {
} finally {
   try {
       if (stream != null) {
   } catch (IOException e) {

Export Data in .csv Format

Writing data in .csv format is similar to that in .txt format. As CSV stands for Comma Separated Values, which means each data value is separated by “,” (comma). It is similar to an excel sheet. The first row consists of labels that denote the type of value in that particular column. The other rows consist of the sensor data, with each row corresponding to a sample of the sensor data.

File file = new File(folder, "sensorData.csv");
PrintWriter writer;
try {
   writer = new PrintWriter(file);
   StringBuilder stringBuilder = new StringBuilder();
   for (DataMPU6050 temp : results) {
} catch (FileNotFoundException e) {


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