The document discusses using accelerometers and other sensors in Java ME applications for Nokia Series 40 phones. It covers the available sensor APIs, how to access acceleration and other sensor data, performance considerations, and ensuring compatibility across devices. Code examples are provided to demonstrate reading accelerometer values and handling sensor input in games and other apps.

1. USING ACCELEROMETERS AND OTHER
SENSORS IN JAVA ME ON SERIES 40
Attila Csipa [@achipa]
Technology Wizard, Nokia
1 © 2012 Nokia Using accelerometers and other sensors in Java ME on Series 40 v1.1 October 23, 2012 Attila Csipa

2. 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

3. 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
3 © 2012 Nokia Using accelerometers and other sensors from Java ME on Series 40 v1.1 October 23, 2012 Attila Csipa

4. DP 2.0 – NEW APIS
Full touch Sensors & Multipoint
UI Orientation Touch APIs
Gestures: Virtual
...
Pinch Keyboard
4 © 2012 Nokia Using accelerometers and other sensors from Java ME on Series 40 v1.1 October 23, 2012 Attila Csipa

5. 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.
5 © 2012 Nokia Using accelerometers and other sensors from Java ME on Series 40 v1.1 October 23, 2012 Attila Csipa

6. 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
–…
6 © 2012 Nokia Using accelerometers and other sensors from Java ME on Series 40 v1.1 October 23, 2012 Attila Csipa

7. SENSORS: JSR-256
JSR page at http://bit.ly/VdZDlG
• 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)
7 © 2012 Nokia Using accelerometers and other sensors from Java ME on Series 40 v1.1 October 23, 2012 Attila Csipa

8. 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
8 © 2012 Nokia Using accelerometers and other sensors from Java ME on Series 40 v1.1 October 23, 2012 Attila Csipa

9. 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
• Ideal for games!
9 © 2012 Nokia Using accelerometers and other sensors from Java ME on Series 40 v1.1 October 23, 2012 Attila Csipa

10. 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)
10 © 2012 Nokia Using accelerometers and other sensors from Java ME on Series 40 v1.1 October 23, 2012 Attila Csipa

11. 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) { }
11 © 2012 Nokia Using accelerometers and other sensors from Java ME on Series 40 v1.1 October 23, 2012 Attila Csipa

12. 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
12 © 2012 Nokia Using accelerometers and other sensors from Java ME on Series 40 v1.1 October 23, 2012 Attila Csipa

13. 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;
}
}
13 © 2012 Nokia Using accelerometers and other sensors from Java ME on Series 40 v1.1 October 23, 2012 Attila Csipa

14. 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
14 © 2012 Nokia Using accelerometers and other sensors from Java ME on Series 40 v1.1 October 23, 2012 Attila Csipa

15. 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?)
15 © 2012 Nokia Using accelerometers and other sensors from Java ME on Series 40 v1.1 October 23, 2012 Attila Csipa

16. COMPATIBILITY
16 © 2012 Nokia Using accelerometers and other sensors from Java ME on Series 40 v1.1 October 23, 2012 Attila Csipa

17. 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
17 © 2012 Nokia Using accelerometers and other sensors from Java ME on Series 40 v1.1 October 23, 2012 Attila Csipa

18. 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)
18 © 2012 Nokia Using accelerometers and other sensors from Java ME on Series 40 v1.1 October 23, 2012 Attila Csipa

19. 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
19 © 2012 Nokia Using accelerometers and other sensors from Java ME on Series 40 v1.1 October 23, 2012 Attila Csipa

20. RESOURCES & TIPS
22 © 2012 Nokia Using accelerometers and other sensors from Java ME on Series 40 v1.1 October 23, 2012 Attila Csipa

21. NOKIA IDE FOR JAVA ME
Integrated SDK + Toolchain JAD Editor
App Templates Device SDK Manager
23 © 2012 Nokia Using accelerometers and other sensors from Java ME on Series 40 v1.1 October 23, 2012 Attila Csipa

22. 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
24 © 2012 Nokia Using accelerometers and other sensors from Java ME on Series 40 v1.1 October 23, 2012 Attila Csipa

23. CODE EXAMPLES SHOWN TODAY
• Wiki
• aMaze
• Racer
• Cottage360 (episode 19)
25 © 2012 Nokia Using accelerometers and other sensors from Java ME on Series 40 v1.1 October 23, 2012 Attila Csipa

24. 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/
27 © 2012 Nokia Using accelerometers and other sensors from Java ME on Series 40 v1.1 October 23, 2012 Attila Csipa

25. THANK YOU! QUESTIONS?
Want to learn more?
www.developer.nokia.com
Attila Csipa [@achipa]
Technology Wizard, Nokia
28 © 2012 Nokia Using accelerometers and other sensors from Java ME on Series 40 v1.1 October 23, 2012 Attila Csipa