1. Lecture 4: Sensors Topics: Motion, Position, and Environmental Sensors
Date: Feb 7, 2017

2. References (study these)

3. Sensors Overview
Motion Sensors
Position Sensors
Environmental Sensors

4. Examples Motion Sensors Position Sensors Environmental Sensors
Measure acceleration and rotational forces.
e.g., accelerometers, gravity sensors, gyroscopes, and rotational vector sensors.
Position Sensors
Measure the physical position of a device
e.g., orientation sensors and magnetometers
Environmental Sensors
Measure various environmental parameters
e.g., barometers, photometers, and thermometers.

5. Types of Sensors Sensor HW/SW Notes Use TYPE_ACCELEROMETER HW
(Ax, Ay, Az) + g; ms2
Shake, Tilt
TYPE_AMBIENT_TEMPERATURE 0C
TYPE_GRAVITY
SW/HW
g = (gx, gy, gz); ms2
TYPE_GYROSCOPE
ω = (ωx, ωy, ωz) rad/s
Spin, Turn
TYPE_LIGHT
Illumination; lx
Brightness control
TYPE_LINEAR_ACCELERATION
(Ax, Ay, Az); no g; ms2
TYPE_MAGNETIC_FIELD
(Bx, By, Bz) µT
Compass
TYPE_ORIENTATION SW
3 axis rotation; matrix
Device position
TYPE_PRESSURE
hPa or mbar
Air pressure
TYPE_PROXIMITY
cm; distant from screen
Phone position
TYPE_RELATIVE_HUMIDITY
humidity (%)
Dew point
TYPE_ROTATION_VECTOR
Device’s rotation vector
TYPE_TEMPERATURE

6. Android Sensor Framework
Check Availability
What sensors do I have?
Get Information
e.g., maximum range, manufacturer, power requirements, and resolution.
Get Values
e.g., raw sensor data, minimum rate.
Register/unregister for Sensor Events

7. Four Relevant Classes SensorManager: Sensor:
Create an instance of the sensor service.
Accessing and listing sensors.
Registering and unregistering sensor event listeners.
Acquiring orientation information.
Report sensor accuracy, set data acquisition rates, and calibrate sensors.
Sensor:
Create an instance of a specific sensor.
Determine a sensor's capabilities.

8. Four Relevant Classes SensorEvent SensorEventListener
Carries information about a sensor event:
Raw data, sensor type, accuracy, timestamp
SensorEventListener
Two callback methods that receive notifications:
onSensorChanged() and onAccuracyChanged()

9. Working with Sensors
Step 1: Get the SensorManger from system services. Step 2: Get the Sensor (or a list) from the manager.
private SensorManager sm; private Sensor s; private List<Sensor> l;
sm = (SensorManager) getSystemService
(Context.SENSOR_SERVICE);
l = sm.getSensorList(Sensor.TYPE_ALL);
s = sm.getDefaultSensor(Sensor.TYPE_LIGHT);
Returns “null” if no proximity sensor

10. Working with Sensors
Step 3 (optional): Get information about a Sensor.
s.getName(); s.getMaximumRange(); s.getResolution(); s.getMinDelay(); s.getPower(); s.getVendor(); s.getVersion();

11. Working with Sensors
Step 4: Implement and Register SensorEventListener
public class MainActivity extends AppCompatActivity implements SensorEventListener{ private SensorManager sm; private Sensor s; private List<Sensor> l; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); sm = (SensorManager) getSystemService(Context.SENSOR_SERVICE); l = sm.getSensorList(Sensor.TYPE_ALL); s = sm.getDefaultSensor(Sensor.TYPE_LIGHT); sm.registerListener(this, s, ); } @Override public void onSensorChanged(SensorEvent event) { } @Override public void onAccuracyChanged(Sensor sensor, int accuracy) { } }

12. Code Practice: Show a list of available sensors on the device.
Get Gravity Sensor readings.
Report them at 1 second interval.
Now, add another sensor, e.g., Light Sensor.
Report light sensor at 0.5 second interval.

13. Good Practices: Check sensor before using.
Declare <uses-feature> in the manifest.
Unregister at onPause(), register at onResume().
if(sm.getDefaultSensor(Sensor.TYPE_LIGHT) == null) { //Display sensor not available message. }
<uses-feature android:name="android.hardware.sensor.accelerometer" android:required="true" />
@Override protected void onPause() { super.onPause(); sm.unregisterListener(this); protected void onResume() { super.onResume(); sm.registerListener(this, s, ); }

14. Good Practices: Don’t block onSensorChanged()
Choose sensor delays carefully.
@Override public void onSensorChanged(SensorEvent event) { //Not a place to solve an NP-hard problem here*. }
*it’s a joke