Android accelerometer sampling rate/delay stabilization

Question

I'm trying to detect the force strength of a tap by using the data from the accelerometer and with the method onTouch.

As far as I know, the fastest sampling frequency for the accelerometer is 200-202Hz, but this variability is giving me problems when trying to match the timestamps for the onTouch event and the peak in the accelerometer data.

Is there a way to stabilize the readings of the accelerometer to avoid this problem? Like controlling the specific thread or something?

Answer 1

If you want to match the hardware-provided time (event.timestamp) and the System time you can do this by adjusting the times.

Usually the times are not the same, but they just differ by a constant amount of milliseconds. I suggest you to print out both times and compare them. You will then notice what the offset is:

In my question, Ormi734 suggested to use the following code:

private long timeDiff = 0l; // this will be used to adjust the offset between the times
private boolean offsetDetermined = false;

@Override
public void onSensorChanged(SensorEvent event) {

    // just determine the offset once, since it should remain constant
    // you could also adjust it every n samples if it needs to be really accurate
    if (!offsetDetermined) {
        long MiliTime = System.currentTimeMillis();
        long NanoTime = event.timestamp;
        timeDiff = MiliTime - NanoTime / 1000000;

        log.info("Synchornizing sensor clock. Current time= " + MiliTime+ ", difference between clocks = " + timeDiff);

        offsetDetermined = true;
    }

    float x = event.values[0];
    float y = event.values[1];
    float z = event.values[2];
    long ts = event.timestamp / 1000000 + timeDiff;

    // do your stuff here   
}

Accelerometer logger: experiencing occasional long delays between frames