Integrating Stock Sensors with PSLab Android App

A sensor is a digital device (almost all the time an integrated circuit) which can receive data from outer environment and produce an electric signal proportional to that. This signal will be then processed by a microcontroller or a processor to provide useful functionalities. A mobile device running Android operating system usually has a few sensors built into it. The main purpose of these sensors is to provide user with better experience such as rotating the screen as he moves the device or turn off the screen when he is making a call to prevent unwanted screen touch events. PSLab Android application is capable of processing inputs received by different sensors plugged into it using the PSLab device and produce useful results. Developers are currently planning on integrating the stock sensors with the PSLab device so that the application can be used without the PSLab device.

This blog is about how to initiate a stock sensor available in the Android device and get readings from it. Sensor API provided by Google developers is really helpful in achieving this task. The process is consist of several steps. It is also important to note the fact that there are devices that support only a few sensors while some devices will support a lot of sensors. There are few basic sensors that are available in every device such as

  • “Accelerometer” – Measures acceleration along X, Y and Z axis
  • “Gyroscope” – Measures device rotation along X, Y and Z axis
  • “Light Sensor” – Measures illumination in Lux
  • “Proximity Sensor” – Measures distance to an obstacle from sensor

The implementing steps are as follows;

  1. Check availability of sensors

First step is to invoke the SensorManager from Android system services. This class has a method to list all the available sensors in the device.

SensorManager sensorManager;
sensorManager = (SensorManager) getSystemService(Context.SENSOR_SERVICE);
List<Sensor> sensors = sensorManager.getSensorList(Sensor.TYPE_ALL);

Once the list is populated, we can iterate through this to find out if the required sensors are available and obstruct displaying activities related to sensors that are not supported by the device.

for (Sensor sensor : sensors) {
   switch (sensor.getType()) {
       case Sensor.TYPE_ACCELEROMETER:
           break;
       case Sensor.TYPE_GYROSCOPE:
           break;
       ...
   }
}

  1. Read data from sensors

To read data sent from the sensor, one should implement the SensorEventListener interface. Under this interface, there are two method needs to be overridden.

public class StockSensors extends AppCompatActivity implements SensorEventListener {

    @Override
    public void onSensorChanged(SensorEvent sensorEvent) {

    }

    @Override
    public void onAccuracyChanged(Sensor sensor, int i) {

    }
}

Out of these two methods, onSensorChanged() method should be addressed. This method provides a parameter SensorEvent which supports a method call getType() which returns an integer value representing the type of sensor produced the event.

@Override
public void onSensorChanged(SensorEvent sensorEvent) {
   switch (sensorEvent.sensor.getType()) {
       case Sensor.TYPE_ACCELEROMETER:
           break;
       case Sensor.TYPE_GYROSCOPE:
           break;
       ...
   }
}

Each available sensor should be registered under the SensorEventListener to make them available in onSensorChanged() method. The following code block illustrates how to modify the previous code to register each sensor easily with the listener.

for (Sensor sensor : sensors) {
   switch (sensor.getType()) {
       case Sensor.TYPE_ACCELEROMETER:
           sensorManager.registerListener(this, sensorManager.getDefaultSensor(Sensor.TYPE_ACCELEROMETER), SensorManager.SENSOR_DELAY_UI);
           break;
       case Sensor.TYPE_GYROSCOPE:
           sensorManager.registerListener(this, sensorManager.getDefaultSensor(Sensor.TYPE_GYROSCOPE), SensorManager.SENSOR_DELAY_UI);
           break;
   }
}

Depending on the readings we can provide user with numerical data or graphical data using graphs plotted using MPAndroidChart in PSLab Android application.

The following images illustrate how a similar implementation is available in Science Journal application developed by Google.

Resources