Advanced sensors in Series 40 Java ME apps

ADVANCED EXAMPLES OF SENSOR
USAGE IN JAVA ME ON SERIES 40

Attila Csipa [@achipa]
Technology Wizard, Nokia

1 © 2012 Nokia Advanced examples of sensor usage in Java ME on Series 40 v1.2 February 19, 2013 Attila Csipa

CONTENTS
• Introduction
– Platforms & Versions
• Sensors
– Physical vs virtual
– JSR-256
– Measurables
– Accelerometers
– Usage
– UI considerations
– Performance
– App Compatibility
• Resources

2 © 2012 Nokia Using accelerometers and other sensors from Java ME on Series 40 v1.1 October 23, 2012 Attila Csipa

PLATFORMS
API Differences: bit.ly/S40Apis

5th Ed., FP1 6th Ed., Lite 6th Ed. 6th Ed., FP1 DP 1.0 DP 1.1 Developer Platform 2.0

http://www.developer.nokia.com/Devices/Device_specifications/Comparison.xhtml?dev=Asha_306,Nokia_Asha_309,Asha_311


DP 2.0 – NEW APIS

Full touch Sensors & Multipoint
UI Orientation Touch APIs

Gestures: Virtual
...
Pinch Keyboard


SENSORS
Etymology
Originated 1925–30 from sense + -or.

Noun
sensor (plural sensors)
A device or organ that detects certain external stimuli and responds in a
distinctive manner.


SENSORS: PHYSICAL VS VIRTUAL
• Physical sensors (physical values, g or m/s, mbar, etc)
– Acceleration
– Light
– ...
• Virtual sensors (combined or interpreted values, %, enum-s)
– Battery level
– Orientation
–…

SENSORS: JSR-256
JSR page at Nokia Developer JSR docs

• JSR 256 Sensor API
– Generic: designed also for temperature, blood pressure, etc.
– Support on Series40 from DP2.0 (Asha Full Touch)
– Also available on Symbian (from S60 5th edition onwards)
• Two packages
javax.microedition.sensor (read information)
javax.microedition.sensor.control (settings, start/stop)

SENSORS: WHAT TO LOOK FOR
• Currently supported
– Battery Charge: 0 .. 100, charge percentage
– Network Field Intensity: 0 .. 100, signal strength
– Charger State: 0 .. 1, charger connected
– Acceleration: –2g .. +2g, x / y / z axis
– Double Tap: 1 .. 63, phone sides
– Orientation: 0 .. 6, phone orientation


SENSORS: ACCELEROMETERS ARE COOL
• Enrich user interaction
– Doesn’t suffer from finger size limits
– Doesn’t suffer from screen size limits
– Doesn’t interfere with what the user sees on the screen
– Natural interaction (language/culture independent)
• Ideal for games!


SENSORS: UNDERSTANDING ACCELEROMETERS
• Acceleration is CHANGE of the speed vector
• Standstill normalized value is 1.0, why? GRAVITY
• Nitpick - accelerometers measure translation not rotation
• Rotation can still be measured indirectly (we measure
gravity vector hopping from one axis to the other)


Example:
SENSORS: API AVAILABILITY Racer, aMaze

• No System property for the API version?
– Check Class availability
– ClassNotFoundException? → API not supported
// Virtual keyboard support
try {
// Check if class is available
Class.forName("javamicroedition.sensor.SensorConnection");
// SensorManager.findSensors("acceleration", null);
useSensors = true;
} catch (ClassNotFoundException e) {
// Class not available: -> no Sensor API support.
useSensors = false;
} catch (Exception e) { }


Example:
SENSORS: DYNAMIC DISCOVERY SensorBrowser

• Sensors can be discovered dynamically!
private List sensorsList;
private SensorInfo[] sensorInfos;

public SensorBrowser() {
display = Display.getDisplay(this);

sensorsList = new List("Sensors list:", List.EXCLUSIVE);
sensorInfos = SensorManager.findSensors(null, null);
for (int i = 0; i < sensorInfos.length; i++) {
sensorsList
.append(constructVisibleSensorName(sensorInfos[i]), null);
}
sensorsList.addCommand(CMD_LIST_DETAIL);
sensorsList.addCommand(CMD_EXIT);
sensorsList.setCommandListener(this);
}


Example:
SENSORS: CAN SAY WHO/WHAT THEY ARE SensorBrowser

• A wealth of inspectable information available
SensorInfo sensorInfo = sensorInfos[currentSensorId];
sensorDetail =
new Form("Sensor detail: "
+ constructVisibleSensorName(sensorInfo));
sensorDetail.append(new StringItem("Quantity:", sensorInfo
.getQuantity(), StringItem.LAYOUT_LEFT));
sensorDetail.append(new StringItem("Context type:", sensorInfo
.getContextType(), StringItem.LAYOUT_LEFT));
sensorDetail.append(new StringItem("Connection type:",
connectionTypeToString(sensorInfo.getConnectionType())));
sensorDetail.append(new StringItem("URL:", sensorInfo.getUrl(),
StringItem.LAYOUT_LEFT));
String[] properties = sensorInfo.getPropertyNames();
for (int i = 0; i < properties.length; i++) {
Object value = sensorInfo.getProperty(properties[i]);
sensorDetail.append(new StringItem(properties[i] + ":", value
.toString(), StringItem.LAYOUT_LEFT));
}


Example: MovingBall
SENSORS: USING THEM – ROLL YOUR OWN
• Establish sensor connection
// Find all acceleration sensors, the contextType is left undefined
SensorInfo[] sensorInfos = SensorManager.findSensors("acceleration", null);
// Find an acceleration sensor that returns double values
for (int i = 0; i < sensorInfos.length; i++) {
if (sensorInfos[i].getChannelInfos()[0].getDataType() == ChannelInfo.TYPE_DOUBLE) {
accSensor = (SensorConnection) Connector.open(sensorInfos[i].getUrl());
}
}

• Check data in game loop
// Use 1 as a buffer size to get exactly 1 value for each axis
Data[] data = accSensor.getData(1);
speedX = -data[0].getDoubleValues()[0]; // data[0] => x-axis
speedY = data[1].getDoubleValues()[0]; // data[1] => y-axis


SENSORS: USING THEM – COPY WITH PRIDE
• Use the wrapping classes from Nokia Developer examples
private void enableSensors() {
if (accelerationProvider != null) {
accelerationProvider.close();
}
accelerationProvider = AccelerationProvider.getProvider(
new AccelerationProvider.Listener() {
public void dataReceived(double ax, double ay, double az) {
if (isSensorTurning()) {
tilt = (int) ay;
}
}
});
if (accelerationProvider != null) {
Main.sensorsSupported = true;
} else {
Main.sensorsSupported = false;
}
}


SENSORS: IT‘S A CONDITION (INTERFACE)
• Operators temperature.addCondition(listener, new LimitCondition(50,Condition.GREATER_THAN));

– OP_EQUALS
– OP_GREATER_THAN
– OP_GREATER_THAN_OR_EQUALS
– OP_LESS_THAN
– OP_LESS_THAN_OR_EQUALS
• Three Conditions and isMet()
– LimitCondition – a value and an operator
– RangeCondition – two operators, two values
– ObjectCondition – compares to Objects (Strings, etc)


SENSORS: UI CONSIDERATIONS
• Calibrate! (see aMaze example)
• Look for change, not particular values
• Which axis is which (portrait vs landscape)
• Anticipate noise in readings (average values if needed)
• Don’t force accelerometer usage if it doesn’t add to the
user experience


SENSORS: PERFORMANCE
• Filter (LimitCondition) for values you’re really interested in
• Separate from mainloop – use Threads (see Cottage360
video and source)
• Responsiveness is more critical than with keyboard input
• Choose right frequency (is 100 reads/sec really needed?)


COMPATIBILITY


COMPATIBILITY? CODE CONSIDERATIONS
• Source & binary compatible
– xx years old Java ME apps run on
full touch phones (and vice versa)!
• Downwards compatibility
– Check API support of target phones
– Lowest common denominator:
→ Nokia Java SDK 2.0 compiled app
runs on old phones


COMPATIBILITY? USE-CASE CONSIDERATIONS
• Input type
– Sensors complementing buttons (universal)
– Discrete input CAN be easier with buttons (f.ex Snake)!
– Sensors complementing touch controls (touch&type)
– Most common
– Accelerometer only (no pre-DP2.0)
– Rarer than you think, but possible! (f.ex wire loop game)


DYNAMIC API USAGE
• Single code base for different phones
– Code that uses new APIs
– Externalize to extra class
– Check API support at runtime
– Instantiate class if supported
– Different methods for checking available


RESOURCES & TIPS


NOKIA IDE FOR JAVA ME
Integrated SDK + Toolchain JAD Editor

App Templates Device SDK Manager


CODE EXAMPLES
• Nokia IDE
– Nokia Hub → Nokia Series 40
Code Examples
• Online
– bit.ly/JavaMeExamples
• Emulator
– Help → MIDlet Samples
• Maps & LWUIT
– C:NokiadevicesNokia_SDK_2_0_Javaplugins


CODE EXAMPLES SHOWN TODAY
• Wiki
• aMaze
• Racer
• Cottage360 (episode 19)


GET STARTED
• Overview
– www.developer.nokia.com/Develop/Java/Getting_started/
• Downloads
– SDK: www.developer.nokia.com/Develop/Java/
– LWUIT: projects.developer.nokia.com/LWUIT_for_Series_40
• Guides
– Design & User Experience
– Porting from Android
– www.developer.nokia.com/Develop/Java/Documentation/
– Training Videos: www.developer.nokia.com/Develop/Java/Learning/
– Code Examples: www.developer.nokia.com/Develop/Java/Code_examples/


THANK YOU! QUESTIONS?
Want to learn more?
www.developer.nokia.com

Attila Csipa [@achipa]
Technology Wizard, Nokia


Advanced sensors in Series 40 Java ME apps

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