|
| 1 | +page.title=Environment Sensors |
| 2 | +parent.title=Sensors |
| 3 | +parent.link=index.html |
| 4 | +@jd:body |
| 5 | + |
| 6 | +<div id="qv-wrapper"> |
| 7 | + <div id="qv"> |
| 8 | + <h2>In this document</h2> |
| 9 | + <ol> |
| 10 | + <li><a href="#sensors-using-temp">Using the Light, Pressure, and Temperature |
| 11 | +Sensors</a></li> |
| 12 | + <li><a href="#sensors-using-humid">Using the Humidity Sensor</a></li> |
| 13 | + </ol> |
| 14 | + <h2>Related samples</h2> |
| 15 | + <ol> |
| 16 | + <li><a href="{@docRoot}resources/samples/AccelerometerPlay/index.html">Accelerometer |
| 17 | + Play</a></li> |
| 18 | + <li><a |
| 19 | +href="{@docRoot}resources/samples/ApiDemos/src/com/example/android/apis/os/RotationVectorDemo.html"> |
| 20 | +API Demos (OS - RotationVectorDemo)</a></li> |
| 21 | + <li><a |
| 22 | +href="{@docRoot}resources/samples/ApiDemos/src/com/example/android/apis/os/Sensors.html">API Demos |
| 23 | +(OS - Sensors)</a></li> |
| 24 | + </ol> |
| 25 | + <h2>See also</h2> |
| 26 | + <ol> |
| 27 | + <li><a href="{@docRoot}guide/topics/sensors/index.html">Sensors</a></li> |
| 28 | + <li><a href="{@docRoot}guide/topics/sensors/sensors_overview.html">Sensors Overview</a></li> |
| 29 | + <li><a href="{@docRoot}guide/topics/sensors/sensors_position.html">Position Sensors</a></li> |
| 30 | + <li><a href="{@docRoot}guide/topics/sensors/sensors_motion.html">Motion |
| 31 | + Sensors</a></li> |
| 32 | + </ol> |
| 33 | + </div> |
| 34 | +</div> |
| 35 | + |
| 36 | +<p>The Android platform provides four sensors that let you monitor various environmental properties. |
| 37 | +You can use these sensors to monitor relative ambient humidity, illuminance, ambient pressure, and |
| 38 | +ambient temperature near an Android-powered device. All four environment sensors are hardware-based |
| 39 | +and are available only if a device manufacturer has built them into a device. With the exception of |
| 40 | +the light sensor, which most device manufacturers use to control screen brightness, environment |
| 41 | +sensors are not always available on devices. Because of this, it's particularly important that you |
| 42 | +verify at runtime whether an environment sensor exists before you attempt to acquire data from |
| 43 | +it.</p> |
| 44 | + |
| 45 | +<p>Unlike most motion sensors and position sensors, which return a multi-dimensional array of sensor |
| 46 | +values for each {@link android.hardware.SensorEvent}, environment sensors return a single sensor |
| 47 | +value for each data event. For example, the temperature in °C or the pressure in hPa. |
| 48 | +Also, unlike motion sensors and position sensors, which often require high-pass or low-pass |
| 49 | +filtering, environment sensors do not typically require any data filtering or data processing. Table |
| 50 | +1 provides a summary of the environment sensors that are supported on the Android platform.</p> |
| 51 | + |
| 52 | +<p class="table-caption" id="table1"> |
| 53 | + <strong>Table 1.</strong> Environment sensors that are supported on the Android platform.</p> |
| 54 | +<table> |
| 55 | + <tr> |
| 56 | + <th scope="col" style="white-space:nowrap">Sensor</th> |
| 57 | + <th scope="col" style="white-space:nowrap">Sensor event data</th> |
| 58 | + <th scope="col" style="white-space:nowrap">Units of measure</th> |
| 59 | + <th scope="col" style="white-space:nowrap">Data description</th> |
| 60 | + </tr> |
| 61 | + <tr> |
| 62 | + <td>{@link android.hardware.Sensor#TYPE_AMBIENT_TEMPERATURE}</td> |
| 63 | + <td><code>event.values[0]</code></td> |
| 64 | + <td>°C</td> |
| 65 | + <td>Ambient air temperature.</td> |
| 66 | + </tr> |
| 67 | + <tr> |
| 68 | + <td>{@link android.hardware.Sensor#TYPE_LIGHT}</td> |
| 69 | + <td><code>event.values[0]</code></td> |
| 70 | + <td>lx</td> |
| 71 | + <td>Illuminance.</td> |
| 72 | + </tr> |
| 73 | + <tr> |
| 74 | + <td>{@link android.hardware.Sensor#TYPE_PRESSURE}</td> |
| 75 | + <td><code>event.values[0]</code></td> |
| 76 | + <td>hPa or mbar</td> |
| 77 | + <td>Ambient air pressure.</td> |
| 78 | + </tr> |
| 79 | + <tr> |
| 80 | + <td>{@link android.hardware.Sensor#TYPE_RELATIVE_HUMIDITY}</td> |
| 81 | + <td><code>event.values[0]</code></td> |
| 82 | + <td>%</td> |
| 83 | + <td>Ambient relative humidity.</td> |
| 84 | + </tr> |
| 85 | + <tr> |
| 86 | + <td>{@link android.hardware.Sensor#TYPE_TEMPERATURE}</td> |
| 87 | + <td><code>event.values[0]</code></td> |
| 88 | + <td>°C</td> |
| 89 | + <td>Device temperature.<sup>1</sup></td> |
| 90 | + </tr> |
| 91 | +</table> |
| 92 | + |
| 93 | +<p class="note"><sup><strong>1</strong></sup> Implementations vary from device to |
| 94 | +device. This sensor was deprecated in Android 4.0 (API Level 14).</p> |
| 95 | + |
| 96 | +<h2 id="sensors-using-temp">Using the Light, Pressure, and Temperature Sensors</h2> |
| 97 | + |
| 98 | +<p>The raw data you acquire from the light, pressure, and temperature sensors usually requires no |
| 99 | +calibration, filtering, or modification, which makes them some of the easiest sensors to use. To |
| 100 | +acquire data from these sensors you first create an instance of the {@link |
| 101 | +android.hardware.SensorManager} class, which you can use to get an instance of a physical sensor. |
| 102 | +Then you register a sensor listener in the {@link android.app.Activity#onResume |
| 103 | +onResume()} method, and start handling incoming sensor data in the {@link |
| 104 | +android.hardware.SensorEventListener#onSensorChanged onSensorChanged()} callback method. The |
| 105 | +following code shows you how to do this:</p> |
| 106 | + |
| 107 | +<pre> |
| 108 | +public class SensorActivity extends Activity implements SensorEventListener { |
| 109 | + private SensorManager mSensorManager; |
| 110 | + private Sensor mPressure; |
| 111 | + |
| 112 | + @Override |
| 113 | + public final void onCreate(Bundle savedInstanceState) { |
| 114 | + super.onCreate(savedInstanceState); |
| 115 | + setContentView(R.layout.main); |
| 116 | + |
| 117 | + // Get an instance of the sensor service, and use that to get an instance of |
| 118 | + // a particular sensor. |
| 119 | + mSensorManager = (SensorManager) getSystemService(Context.SENSOR_SERVICE); |
| 120 | + mPressure = mSensorManager.getDefaultSensor(Sensor.TYPE_PRESSURE); |
| 121 | + } |
| 122 | + |
| 123 | + @Override |
| 124 | + public final void onAccuracyChanged(Sensor sensor, int accuracy) { |
| 125 | + // Do something here if sensor accuracy changes. |
| 126 | + } |
| 127 | + |
| 128 | + @Override |
| 129 | + public final void onSensorChanged(SensorEvent event) { |
| 130 | + float millibars_of_pressure = event.values[0]; |
| 131 | + // Do something with this sensor data. |
| 132 | + } |
| 133 | + |
| 134 | + @Override |
| 135 | + protected void onResume() { |
| 136 | + // Register a listener for the sensor. |
| 137 | + super.onResume(); |
| 138 | + mSensorManager.registerListener(this, mPressure, SensorManager.SENSOR_DELAY_NORMAL); |
| 139 | + } |
| 140 | + |
| 141 | + @Override |
| 142 | + protected void onPause() { |
| 143 | + // Be sure to unregister the sensor when the activity pauses. |
| 144 | + super.onPause(); |
| 145 | + mSensorManager.unregisterListener(this); |
| 146 | + } |
| 147 | +} |
| 148 | +</pre> |
| 149 | + |
| 150 | +<p>You must always include implementations of both the {@link |
| 151 | +android.hardware.SensorEventListener#onAccuracyChanged onAccuracyChanged()} and {@link |
| 152 | +android.hardware.SensorEventListener#onSensorChanged onSensorChanged()} callback methods. Also, be |
| 153 | +sure that you always unregister a sensor when an activity pauses. This prevents a sensor from |
| 154 | +continually sensing data and draining the battery.</p> |
| 155 | + |
| 156 | +<h2 id="sensors-using-humid">Using the Humidity Sensor</h2> |
| 157 | + |
| 158 | +<p>You can acquire raw relative humidity data by using the humidity sensor the same way that you use |
| 159 | +the light, pressure, and temperature sensors. However, if a device has both a humidity sensor |
| 160 | +({@link android.hardware.Sensor#TYPE_RELATIVE_HUMIDITY}) and a temperature sensor ({@link |
| 161 | +android.hardware.Sensor#TYPE_AMBIENT_TEMPERATURE}) you can use these two data streams to calculate |
| 162 | +the dew point and the absolute humidity.</p> |
| 163 | + |
| 164 | +<h4>Dew point</h4> |
| 165 | + |
| 166 | +<p>The dew point is the temperature at which a given volume of air must be cooled, at constant |
| 167 | + barometric pressure, for water vapor to condense into water. The following equation shows how you |
| 168 | +can calculate the dew point:</p> |
| 169 | + |
| 170 | +<pre class="no-pretty-print classic"> |
| 171 | + ln(RH/100%) + m·t/(T<sub>n</sub>+t) |
| 172 | +t<sub>d</sub>(t,RH) = T<sub>n</sub> · ------------------------------------ |
| 173 | + m - [ln(RH/100%) + m·t/(T<sub>n</sub>+t)] |
| 174 | +</pre> |
| 175 | + |
| 176 | +<p>Where,</p> |
| 177 | + |
| 178 | +<ul type="none"> |
| 179 | + <li>t<sub>d</sub> = dew point temperature in degrees C</li> |
| 180 | + <li>t = actual temperature in degrees C</li> |
| 181 | + <li>RH = actual relative humidity in percent (%)</li> |
| 182 | + <li>m = 17.62</li> |
| 183 | + <li>T<sub>n</sub> = 243.12</li> |
| 184 | +</ul> |
| 185 | + |
| 186 | +<h4>Absolute humidity</h4> |
| 187 | + |
| 188 | +<p>The absolute humidity is the mass of water vapor in a given volume of dry air. Absolute |
| 189 | + humidity is measured in grams/meter<sup>3</sup>. The following equation shows how you |
| 190 | + can calculate the absolute humidity:</p> |
| 191 | + |
| 192 | +<pre class="no-pretty-print classic"> |
| 193 | + (RH/100%) · A · exp(m·t/(T<sub>n</sub>+t) |
| 194 | +d<sub>v</sub>(t,RH) = 216.7 · ------------------------------------ |
| 195 | + 273.15 + t |
| 196 | +</pre> |
| 197 | + |
| 198 | +<p>Where,</p> |
| 199 | + |
| 200 | +<ul type="none"> |
| 201 | + <li>d<sub>v</sub> = absolute humidity in grams/meter<sup>3</sup></li> |
| 202 | + <li>t = actual temperature in degrees C</li> |
| 203 | + <li>RH = actual relative humidity in percent (%)</li> |
| 204 | + <li>m = 17.62</li> |
| 205 | + <li>T<sub>n</sub> = 243.12 degrees C</li> |
| 206 | + <li>A = 6.112 hPa</li> |
| 207 | +</ul> |
| 208 | + |
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