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()as described further in Chapter 7,"Hardware Interface"):

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.

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