Android Sensor Programming. Weihong Yu

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Android Sensor Programming

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Sensors Overview

• The Android platform is ideal for creating

innovative applications through the use of

sensors.

• These built-in sensors measure motion,

orientation, and various environmental

conditions.

• These sensors are capable of providing raw

data with high precision and accuracy, and are

useful if you want to monitor three-dimensional

device movement or positioning, or you want to

monitor changes in the ambient environment

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Android Sensors Overview

•Android Sensors:

– MIC – Camera – Temperature – Location (GPS or Network) – Orientation – Accelerometer – Proximity – Pressure – Light

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Sensors

• hardware-based sensors

– physical components built into a handset or tablet device – They derive their data by directly measuring specific

environmental properties, such as acceleration, geomagnetic field strength, or angular change

• software-based sensors

– not physical devices, although they mimic hardware-based sensors

– Software-based sensors derive their data from one or more of the hardware-based sensors and are sometimes called virtual sensors or synthetic sensors

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categories of sensors supported by

Android platform

• Motion sensors :measure acceleration forces and rotational forces along three axes

– accelerometers, gravity sensors, gyroscopes, etc.

• Environmental sensors: measure various

environmental parameters, such as ambient air

temperature and pressure, illumination, and humidity

– barometers, photometers, and thermometers.

• Position sensors: measure the physical position of a device

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Sensor Coordinate System

• When a device is held in its

default orientation

– the X axis is horizontal and points to the right

– the Y axis is vertical and points up

– and the Z axis points toward the outside of the screen face

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Android sensor framework

• The sensor framework provides several classes

and interfaces that help you perform a wide

variety of sensor-related tasks

– Determine which sensors are available on a device. – Determine an individual sensor's capabilities, such

as its maximum range, manufacturer, power requirements, and resolution.

– Acquire raw sensor data and define the minimum rate at which you acquire sensor data.

– Register and unregister sensor event listeners that monitor sensor changes.

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Sensor Framework-sensor Manager

• You can use this class to create an instance of

the sensor service

• This class provides various

methods

for

accessing and listing sensors, registering and

unregistering sensor event listeners, and

acquiring orientation information.

• This class also provides several sensor

constants

that are used to report sensor

accuracy, set data acquisition rates, and

calibrate sensors.

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Sensor Framework---Sensor

• You can use this class to create an

instance of a specific sensor. This

class provides various

methods

that let

you determine a sensor's capabilities.

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Sensor Framework---SensorEvent

• The system uses this class to create a sensor

event object, which provides information about

a sensor event.

• A sensor event object includes the following

information:

– the raw sensor data

– the type of sensor that generated the event – the accuracy of the data

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Sensor Framework---SensorEventListener

• You can use this interface to create two

callback methods that receive notifications

(sensor events) when sensor values change or

when sensor accuracy changes.

– onAccuracyChanged(Sensor sensor, int

accuracy) :Called when the accuracy of a sensor has changed.

– onSensorChanged(SensorEvent event) :Called when sensor values have changed.

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Basic Steps for Programming

• Step 1--access a SensorManager via

getSystemService(SENSOR_SERVICE).

• Android supports several sensors via the SensorManager

• Step 2--access the Sensor via the

sensorManager.getDefaultSensor() method

• Step 3--Once you acquired a sensor, you can register a SensorEventListener object on it. This listener will get informed, if the sensor data changes.

• Step 4--To avoid the unnecessary usage of battery you register your listener in the onResume() method and de-register it in the onPause() method.

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Example 1:List all sensors

• Step 1--- get a reference to the sensor service

private SensorManager mSensorManager;

mSensorManager = (SensorManager)

getSystemService(Context.SENSOR_SERVI

CE);

• Step2---get a list of all sensors on a device

List<Sensor> deviceSensors =

mSensorManager.getSensorList(Sensor.TYP

E_ALL);

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Example 2:Use Accelerometer

• Step 1---get an instance of SensorManager

and Sensor

mSensorManager = (SensorManager)

getSystemService(Context.SENSOR_SERVIC

E);

mAccelerometer =

mSensorManager.getDefaultSensor(Sensor.T

YPE_ACCELEROMETER);

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Example 2:Use Accelerometer

• Step 2---register a sensor event listener

mSensorManager.registerListener(this,

mAccelerometer,

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Example 2:Use Accelerometer

• Step 3---override

onSensorChanged(SensorEvent event) and

use event.values[] to get the co-ordinates

@Override

public void onSensorChanged(SensorEvent

event) { float x = event.values[0]; float y =

event.values[1]; float z = event.values[2]; }

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Codes for Using Accelerometer

• Get the Sensor Service and Sensor

public void onCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState); setContentView(R.layout.activity_acc_main); mytx=(TextView)this.findViewById(R.id.tx); myty=(TextView)this.findViewById(R.id.ty); mytz=(TextView)this.findViewById(R.id.tz); sm=(SensorManager)this.getSystemService(Context.SE NSOR_SERVICE); mysensor=sm.getDefaultSensor(Sensor.TYPE_ACCELE ROMETER); }

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Codes for Using Accelerometer

• Define an instance of SensorEventListener

private final SensorEventListener mysensorlistenr=new

SensorEventListener(){

public void onAccuracyChanged(Sensor sensor, int accuracy) {

// TODO Auto-generated method stub }

public void onSensorChanged(SensorEvent event) {

// TODO Auto-generated method stub

mytx.setText(String.valueOf(event.values[0])); myty.setText(String.valueOf(event.values[1])); mytz.setText(String.valueOf(event.values[2])); } };