Android硬件开发------传感器介绍

在Android手机中，内置了很多传感器，最常见的就是重力传感器，我们最常用的，比如说在玩游戏时，使用手机控制移动的方法，还有一些其他的传感器，像温度传感器、湿度传感器、光传感器、加速度传感器等，我们在日常使用中，一般是用不到的，但是如果在开发过程中使用到这些传感器，还是要知道这些传感器的使用方法。

1、传感器管理类

在手机内置的传感器，有统一的管理类SensorManager

SensorManager sensorManager = (SensorManager) getSystemService(Context.SENSOR_SERVICE);

在SensorManager中，有getSensorList方法，这个方法返回所有的传感器。

public List<Sensor> getSensorList(int type) {
        // cache the returned lists the first time
        List<Sensor> list;
        final List<Sensor> fullList = getFullSensorList();
        synchronized (mSensorListByType) {
            list = mSensorListByType.get(type);
            if (list == null) {
                if (type == Sensor.TYPE_ALL) {
                    list = fullList;
                } else {
                    list = new ArrayList<Sensor>();
                    for (Sensor i : fullList) {
                        if (i.getType() == type) {
                            list.add(i);
                        }
                    }
                }
                list = Collections.unmodifiableList(list);
                mSensorListByType.append(type, list);
            }
        }
        return list;
    }

在List集合中有一个Sensor类，在Sensor类中有很多传感器的类型：

TYPE_ACCELEROMETER	加速传感器
TYPE_ORIENTATION	方向传感器
TYPE_PRESSURE	压力传感器
TYPE_PROXIMITY	临近传感器
TYPE_TEMPERATURE	温度传感器
TYPE_GRAVITY	重力传感器
TYPE_LINEAR_ACCELERATION	线性加速传感器
TYPE_ROTATION_VECTOR	旋转向量传感器
TYPE_RELATIVE_HUMIDITY	湿度传感器
TYPE_AMBIENT_TEMPERATURE	温度传感器
TYPE_MAGNETIC_FIELD_UNCALIBRATED	磁场传感器
TYPE_GAME_ROTATION_VECTOR	游戏旋转向量传感器
TYPE_GYROSCOPE_UNCALIBRATED	陀螺仪传感器
TYPE_STEP_DETECTOR	计步器传感器
TYPE_STEP_COUNTER	计步器传感器
TYPE_HEART_RATE	心率传感器
TYPE_WAKE_GESTURE	手势唤醒传感器
TYPE_GLANCE_GESTURE	掠过手势传感器
TYPE_HEART_BEAT	心跳传感器
TYPE_LIGHT	光线传感器

还有很多传感器，就不在此一一列举出来，标注黑体的传感器就是比较重要的传感器，可能会在开发中使用到的传感器。

List<Sensor> sensorList = sensorManager.getSensorList(Sensor.TYPE_ALL);
        for (Sensor sensor :
                sensorList) {
            Log.e("TAG","sensor==="+sensor);
        }

通过getSensorList可以查看当前手机支持的传感器有哪些，因为不是每个手机都可以支持所有的传感器。

2020-02-10 20:11:56.710 13572-13572/? E/TAG: sensor==={Sensor name="ICM20690 Accelerometer", vendor="InvenSense", version=1, type=1, maxRange=78.4532, resolution=0.0023956299, power=0.325, minDelay=5000}
2020-02-10 20:11:56.710 13572-13572/? E/TAG: sensor==={Sensor name="ICM20690 Accelerometer Uncalibrated", vendor="InvenSense", version=1, type=35, maxRange=78.4532, resolution=0.0023956299, power=0.325, minDelay=5000}
2020-02-10 20:11:56.710 13572-13572/? E/TAG: sensor==={Sensor name="AK09916C Magnetometer", vendor="AKM", version=1, type=2, maxRange=4911.9995, resolution=0.14953613, power=1.1, minDelay=20000}
2020-02-10 20:11:56.710 13572-13572/? E/TAG: sensor==={Sensor name="AK09916C Magnetometer Uncalibrated", vendor="AKM", version=1, type=14, maxRange=4911.9995, resolution=0.14953613, power=1.1, minDelay=20000}
2020-02-10 20:11:56.711 13572-13572/? E/TAG: sensor==={Sensor name="ICM20690 Gyroscope", vendor="InvenSense", version=1, type=4, maxRange=34.906586, resolution=0.0010681152, power=2.5, minDelay=5000}
2020-02-10 20:11:56.711 13572-13572/? E/TAG: sensor==={Sensor name="ICM20690 Gyroscope Uncalibrated", vendor="InvenSense", version=1, type=16, maxRange=34.906586, resolution=0.0010681152, power=2.5, minDelay=5000}
2020-02-10 20:11:56.711 13572-13572/? E/TAG: sensor==={Sensor name="TMD2620 PROX", vendor="ams AG", version=2, type=8, maxRange=5.000305, resolution=1.0, power=0.1, minDelay=0}
2020-02-10 20:11:56.711 13572-13572/? E/TAG: sensor==={Sensor name="BMP285 Pressure", vendor="BOSCH", version=1040700, type=6, maxRange=1100.0, resolution=0.0018005371, power=0.025, minDelay=38461}
2020-02-10 20:11:56.711 13572-13572/? E/TAG: sensor==={Sensor name="ICM20690 Accelerometer -Wakeup Secondary", vendor="InvenSense", version=1, type=1, maxRange=78.4532, resolution=0.0023956299, power=0.325, minDelay=5000}
2020-02-10 20:11:56.711 13572-13572/? E/TAG: sensor==={Sensor name="ICM20690 Accelerometer Uncalibrated -Wakeup Secondary", vendor="InvenSense", version=1, type=35, maxRange=78.4532, resolution=0.0023956299, power=0.325, minDelay=5000}
2020-02-10 20:11:56.712 13572-13572/? E/TAG: sensor==={Sensor name="AK09916C Magnetometer -Wakeup Secondary", vendor="AKM", version=1, type=2, maxRange=4911.9995, resolution=0.14953613, power=1.1, minDelay=20000}
2020-02-10 20:11:56.712 13572-13572/? E/TAG: sensor==={Sensor name="AK09916C Magnetometer Uncalibrated -Wakeup Secondary", vendor="AKM", version=1, type=14, maxRange=4911.9995, resolution=0.14953613, power=1.1, minDelay=20000}
2020-02-10 20:11:56.712 13572-13572/? E/TAG: sensor==={Sensor name="ICM20690 Gyroscope -Wakeup Secondary", vendor="InvenSense", version=1, type=4, maxRange=34.906586, resolution=0.0010681152, power=2.5, minDelay=5000}
2020-02-10 20:11:56.712 13572-13572/? E/TAG: sensor==={Sensor name="ICM20690 Gyroscope Uncalibrated -Wakeup Secondary", vendor="InvenSense", version=1, type=16, maxRange=34.906586, resolution=0.0010681152, power=2.5, minDelay=5000}

通过getDefaultSensor传入传感器的类型可以得到某个特定类型的传感器：

public Sensor getDefaultSensor(int type) {
        // TODO: need to be smarter, for now, just return the 1st sensor
        List<Sensor> l = getSensorList(type);
        boolean wakeUpSensor = false;
        // For the following sensor types, return a wake-up sensor. These types are by default
        // defined as wake-up sensors. For the rest of the SDK defined sensor types return a
        // non_wake-up version.
        if (type == Sensor.TYPE_PROXIMITY || type == Sensor.TYPE_SIGNIFICANT_MOTION
                || type == Sensor.TYPE_TILT_DETECTOR || type == Sensor.TYPE_WAKE_GESTURE
                || type == Sensor.TYPE_GLANCE_GESTURE || type == Sensor.TYPE_PICK_UP_GESTURE
                || type == Sensor.TYPE_WRIST_TILT_GESTURE
                || type == Sensor.TYPE_DYNAMIC_SENSOR_META) {
            wakeUpSensor = true;
        }

        for (Sensor sensor : l) {
            if (sensor.isWakeUpSensor() == wakeUpSensor) return sensor;
        }
        return null;
    }

比如说，我想使用温度传感器，那么就使用温度传感器的TYPE类型得到温度传感器，发现手机里没有温度传感器，我的是小米6手机，不知道其他的手机有没有，小米6已经好几年了，不知新代的手机有没有温度传感器。

Sensor temSensor = sensorManager.getDefaultSensor(Sensor.TYPE_AMBIENT_TEMPERATURE);
Log.e("TAG","tem==="+temSensor);

2020-02-10 20:22:17.740 14165-14165/com.example.sensor E/TAG: tem===null

那就挑一个加速传感器，这个在手机里是有的，我们测试一下返回的数据。
要想测试传感器返回的数据，需要注册监听器registerListener，要注意一点是，要在onResume方法中注册。

 public boolean registerListener(SensorEventListener listener, Sensor sensor,
            int samplingPeriodUs, int maxReportLatencyUs) {
        int delay = getDelay(samplingPeriodUs);
        return registerListenerImpl(listener, sensor, delay, null, maxReportLatencyUs, 0);
    }

registerListener有很多构造方法，还包括Handler字段，说明可以做回调，线程切换；除了这个，还有一个delay字段，这个字段是数据采集频率。

private static int getDelay(int rate) {
        int delay = -1;
        switch (rate) {
            case SENSOR_DELAY_FASTEST:
                delay = 0;
                break;
            case SENSOR_DELAY_GAME:
                delay = 20000;
                break;
            case SENSOR_DELAY_UI:
                delay = 66667;
                break;
            case SENSOR_DELAY_NORMAL:
                delay = 200000;
                break;
            default:
                delay = rate;
                break;
        }
        return delay;
    }

SENSOR_DELAY_FASTEST返回的delay = 0，说明采集的信息立刻返回，非常灵敏，后续的依次减慢，SENSOR_DELAY_NORMAL是最慢的。

 @Override
    protected void onResume() {
        super.onResume();
        sensorManager.registerListener(new SensorEventListener() {
            @Override
            public void onSensorChanged(SensorEvent event) {

            }

            @Override
            public void onAccuracyChanged(Sensor sensor, int accuracy) {

            }
        },accSensor,SensorManager.SENSOR_DELAY_GAME);
    }

在注册监听的时候，需要实现SensorEventListener监听器，当中两个方法：onSensorChanged和onAccuracyChanged，分别在数据发生变化时回调，以及精度变化时回调。

在SensorEvent类中，只有这几行代码：

 public final float[] values;

    /**
     * The sensor that generated this event. See
     * {@link android.hardware.SensorManager SensorManager} for details.
     */
 public Sensor sensor;

    /**
     * The accuracy of this event. See {@link  android.hardware.SensorManager
     * SensorManager} for details.
     */
 public int accuracy;

    /**
     * The time in nanosecond at which the event happened
     */
 public long timestamp;

    @UnsupportedAppUsage
 SensorEvent(int valueSize) {
      values = new float[valueSize];
 }

values数组保存的就是数据的变化值，数组中三个值，分别代表x,y,z三个方向的加速度值。

 sensorManager.registerListener(new SensorEventListener() {
            @Override
            public void onSensorChanged(SensorEvent event) {
                float[] values = event.values;
                tv_x.setText(Float.toString(values[0]));
                tv_y.setText(Float.toString(values[1]));
                tv_z.setText(Float.toString(values[2]));
            }

            @Override
            public void onAccuracyChanged(Sensor sensor, int accuracy) {

            }
        },accSensor,SensorManager.SENSOR_DELAY_NORMAL);