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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