Question

I’m trying to code a very basic lightmeter application for use with my old 35mm cameras using my Galaxy S2 as the sensor.

I should point out first of all that there is a hidden/test mode available on this phone selected by entering star hash zero star hash, on the dialller keypad then selecting ‘sensor’. This makes available the light sensor which shows a range of Lux values varying between 5 and over 2000 in steps of 5 as I vary the light level.

The very simple proof of concept code I have written will only show me three values, namely 10, 100 and 1000 over the same range of lighting condtions. My code is:

public class LightMeterActivity extends Activity implements SensorEventListener {

    private SensorManager mSensorManager;
    private Sensor mLightSensor;
    private float mLux = 0.0f;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        mSensorManager = (SensorManager) getSystemService(SENSOR_SERVICE);
        mLightSensor = mSensorManager.getDefaultSensor(Sensor.TYPE_LIGHT);
    }

    @Override
    protected void onResume() {
        super.onResume();
        mSensorManager.registerListener(this, mLightSensor,
                SensorManager.SENSOR_DELAY_FASTEST);
    }

    @Override
    protected void onPause() {
        mSensorManager.unregisterListener(this);
        super.onPause();
    }

    @Override
    public void onAccuracyChanged(Sensor arg0, int arg1) {}

    @Override
    public void onSensorChanged(SensorEvent event) {
        if (event.sensor.getType() == Sensor.TYPE_LIGHT) {
            mLux = event.values[0];
            String luxStr = String.valueOf(mLux);
            TextView tv = (TextView) findViewById(R.id.textView1);
            tv.setText(luxStr);
            Log.d("LUXTAG", "Lux value: " + event.values[0] );

        }
    }
}

Can anybody suggest why this might be?

I have seen the question Light sensor on Nexus One returns only two distinct values
which didn’t help at all. I can’t understand how the built in test mode can see the full range and my code can’t.

Answer 1

I only tested this on the Galaxy S2 but the only way I could see the true value was to get it directly the system device file:

#cat "/sys/devices/virtual/lightsensor/switch_cmd/lightsensor_file_state"

or in java:

Scanner st = new Scanner(new File("/sys/devices/virtual/lightsensor/switch_cmd/lightsensor_file_state"));
int lux = st.nextInt();
st.close();