Android Devices

 

 Android Devices

Hardware Differences on Android Devices

The hardware available on each Android device varies, as seen in Table 1.1. In general, most of the differences are transparent to the developer and not covered further here. However, a few hardware differences are important to understand to assist in writing device-independent code. Screens, user input methods, and sensors are discussed here.

Screens

Two technologies used for displays are liquid crystal displays (LCD) and light-emitting diodes (LED).The two specific choices in Android phones are thin-film transistor (TFT) LCDs and active-matrix organic LED displays (AMOLED).A benefit of TFT displays is a longer lifetime. A benefit of AMOLED displays is no need for backlighting and therefore deeper blacks and lower power.

Overall,Android devices are categorized into small, normal, and large screens and low-, medium-, and high pixel density. Note that the actual pixel density might vary but will be chosen as one of these.A summary of currently available device screens is shown in Table.

Summary of Device Screens Supported by Android

Screen Type	Low-Density (~120ppi), ldpi	Medium-Density (~160ppi), mdpi	High-Density (~240ppi), hdpi
Small screen	QVGA (240x320), 2.6-inch to 3.0-inch diagonal
Normal screen	WQVGA (240x400), 3.2-inch to 3.5-inch diagonal FWQVGA (240x432), 3.5- inch to 3.8-inch diagonal	HVGA (320x480), 3.0- inch to 3.5-inch diagonal	WVGA (480x800), 3.3-inch to 4.0-inch diagonal FWVGA (480x854), 3.5-inch to 4.0-inch diagonal
Large screen		WVGA (480x800), 4.8-inch to 5.5-inch diagonal FWVGA (480x854), 5.0-inch to 5.8-inch Diagonal

           

User Input Methods

Touchscreens enable users to interact with the visual display.There are three types of touchscreen technology:

• Resistive—Two resistive material layers sit on top of a glass screen.When a finger, stylus, or any object applies pressure, the two layers touch together and the location of the touch can be determined. Resistive touchscreens are cost-effective, but only 75 percent of the light shows through, and until recently, multitouch was not possible.

• Capacitive—A charged material layer is overlaid on a glass screen.When a finger or any conductive object touches the layer, some charge is drawn off, changing the capacitance, which is measured to determine the location of the touch. Capacitive touchscreens allow as much as 90 percent of the light through, although accuracy can be less than resistive.

• Surface Acoustic Wave—This uses a more advanced method that sends and receives ultrasonic waves.When a finger or any object touches the screen, the waves are absorbed.

The waves are measured to determine the location of the touch. It is the most durable solution, but more suitable for large-scale screens such as automatic bank tellers.

All Android devices use either resistive or capacitive touchscreen technology, and with a few early exceptions, all support multitouch.

In addition, each Android device needs an alternative method to access the screen.This is through one of the following methods:

• D-pad (directional pad)—An up-down-right-left type of joystick

• Trackball—A rolling ball acting as a pointing device that is similar to a mouse

• Trackpad—A special rectangular surface acting as a pointing device

Sensors

Smartphones are becoming sensor hubs in a way, opening a rich experience for users. Other than the microphone that every phone has, the first additional sensor introduced on phones was the camera. Different phone cameras have varying capabilities, and this is an important factor for people in selecting a device.The same type of diversity is now seen with the additional sensors.

Most smartphones have at least three basic sensors: a three-axis accelerometer to measure gravity, a three-axis magnetometer to measure the ambient magnetic field, and a temperature sensor to measure the ambient temperature. For example, the HTC Dream (G1) contains the following sensors (which can be displayed using getSensorList()

AK8976A 3-axis Accelerometer

AK8976A 3-axis Magnetic field sensor

AK8976A Orientation sensor

AK8976A Temperature sensor

The AK8976A is a single package from Asahi Kasei Microsystems (AKM) that combines a piezoresistive accelerometer, Hall-effect magnetometer, and temperature sensor. All provide 8-bit precision data.The orientation sensor is a virtual sensor that uses the accelerometer and magnetometer to determine the orientation.

For comparison, the Motorola Droid contains the following sensors:

LIS331DLH 3-axis Accelerometer

AK8973 3-axis Magnetic field sensor

AK8973 Temperature sensor

SFH7743 Proximity sensor

Orientation sensor type

LM3530 Light sensor

The LIS331DLH is a 12-bit capacitive accelerometer from ST Microelectronics. It provides much more accurate data and can sample up to 1kHz.The AK8973 is an AKM package with an 8-bit Hall-effect magnetometer and temperature sensor.

In addition, the Droid contains two more sensors.The SFH7743 is an Opto Semiconductor’s short-range proximity detector that turns the screen off when an object (such as the ear) is within about 40mm distance.The LM3530 is an LED driver with a programmable light sensor from National Semiconductor that detects ambient light and adjusts the screen backlight and LED flash appropriately.

One other example of sensors available on an Android device is the HTC EVO 4G, which has the following sensors:

BMA150 3-axis Accelerometer

AK8973 3-axis Magnetic field sensor

AK8973 Orientation sensor

CM3602 Proximity sensor

CM3602 Light sensor

The BMA150 is a Bosch Sensortec 10-bit accelerometer which can sample up to 1.5kHz.The CM3602 is a Capella Microsystems, Inc., short distance proximity sensor and ambient light sensor combined into one.

Overall, it is important to understand each Android model has different underlying hardware.These differences can lead to varying performance and accuracy of the sensors.

Features of Android

The detailed features of Android and how to take advantage of them provide a main theme throughout this book. On a broader level, some key features of Android are major selling points and differentiators. It is good to be aware of these strong points of Android and utilize them as much as possible.

Multiprocess and App Widgets

The Android OS does not restrict the processor to a single application at a time.The system manages priorities of applications and threads within a single application.This has the benefit that background tasks can be run while a user engages the device in a foreground process. For example, while a user plays a game, a background process can check stock prices and trigger an alert as necessary.

App Widgets are mini applications that can be embedded in other applications (such as the Home screen).They can process events, such as start a music stream or update the outside temperature, while other applications are running.

Multiprocessing has the benefit of a rich user experience. However, care must be taken to avoid power-hungry applications that drain the battery.These multiprocess .

Touch, Gestures, and Multitouch

The touchscreen is an intuitive user interface for a hand-held device. If utilized well, it can transcend a need for detailed instructions. After a finger touches the screen, drags and flings are natural ways to interact with graphics. Multitouch provides a way to track more than one finger down at the same time.This is often used to zoom or rotate a view.

Some touch events are available transparently to the developer without the need to implement their detailed behaviors. Custom gestures can be defined as needed. It is important to try to maintain a consistent usage of touch events as compared to other applications.These touch events are discussed further in other Chapter.

Hard and Soft Keyboards

One feature on a pocket device that galvanizes users is whether it should have a physical (also called hard) keyboard or software (also called soft) keyboard.The tactile feedback and definite placement of keys provided by a hard keyboard tends to make typing much faster for some, whereas others prefer the sleek design and convenience offered by a software- only input device.With the large variety of Android devices available, either type can be found.A side effect for developers is the need to support both. One downside of a soft keyboard is a portion of the screen needs to be dedicated to the input.This needs to be considered and tested for any user interface (UI) layout.