Bosch Accelerometer

With the exception of our first ever board, the MetaWear R, all other MbientLab boards use a Bosch accelerometer, represeted by the AccelerometerBosch interface. This interface is an extension of the Accelerometer interface providing methods and classes specific to Bosch accelerometers.

Currently, we support both the BMI160 and BMA255 sensors and they share much of their functionality with only a few differences enumerated in their respective interfaces.

import com.mbientlab.metawear.module.AccelerometerBosch;

AccelerometerBosch accBosch = board.getModule(AccelerometerBosch.class);

Low/High Detection

Low/High-g detection is an algorithm on the sensor that detects when the measure acceleration falls below a low bound or rises above a high bound. Before enabling the algorithm, first configure the algorithm parameters using the LowHighConfigEditor interface. For low-g detection, set the low threshold, select which type of low-g criteria to use, and enable low-g detection.

// enable low-g detection, use sum criteria,
// detect when sum < 0.333g
accBosch.lowHigh().configure()
        .enableLowG()
        .lowThreshold(0.333f)
        .lowGMode(AccelerometerBosch.LowGMode.SUM)
        .commit();

And, for high-g detection, set the high threshold and enable which axes to monitor.

// enable high-g detection on z-axis,
// detect when acc > 2g
accBosch.lowHigh().configure()
        .enableHighGz()
        .highThreshold(2f)
        .commit();

After configuring the algorithm, add a route for the low/high data represented by the LowHighResponse.

import com.mbientlab.metawear.module.AccelerometerBosch.LowHighResponse;

accBosch.lowHigh().addRouteAsync(new RouteBuilder() {
    @Override
    public void configure(RouteComponent source) {
        source.stream(new Subscriber() {
            @Override
            public void apply(Data data, Object... env) {
                Log.i("MainActivity", data.value(LowHighResponse.class).toString());
            }
        });
    }
}).continueWith(new Continuation<Route, Void>() {
    @Override
    public Void then(Task<Route> task) throws Exception {
        accBosch.lowHigh().start();
        accBosch.start();
        return null;
    }
});

Flat Detection

Flat detection checks when the sensor enters or leaves a horizontal position i.e. laying on a table. Data is interpretted as a boolean where true signifies the sensor is laying horizontally.

accBosch.flat().addRouteAsync(new RouteBuilder() {
    @Override
    public void configure(RouteComponent source) {
        source.stream(new Subscriber() {
            int i = 0;
            @Override
            public void apply(Data data, Object... env) {
                Log.i("MainActivity", "Flat? " + data.value(Boolean.class));
            }
        });
    }
}).continueWith(new Continuation<Route, Void>() {
    @Override
    public Void then(Task<Route> task) throws Exception {
        accBosch.flat().start();
        accBosch.start();
        return null;
    }
});

Orientation Detection

The orientation detector alerts you when the sensor’s orientation changes between portrait/landscape and front/back. Data is represented as a SensorOrientation type.

import com.mbientlab.metawear.data.SensorOrientation;

accBosch.orientation().addRouteAsync(new RouteBuilder() {
    @Override
    public void configure(RouteComponent source) {
        source.stream(new Subscriber() {
            @Override
            public void apply(Data data, Object... env) {
                Log.i("MainActivity", "Orientation = " + data.value(SensorOrientation.class));
            }
        });
    }
}).continueWith(new Continuation<Route, Void>() {
    @Override
    public Void then(Task<Route> task) throws Exception {
        accBosch.orientation().start();
        accBosch.start();
        return null;
    }
});

Tap Detection

The tap detection algorithm checks if the difference in acceleration exceeds a threshold. To detect double tap, a second tap must be registered within the quiet delay but before the double tap window ends. The shock duration is a period of time where the direction of the first tap is locked; the quiet delay starts after the shock duration ends. Use a TapConfigEditor to set the aforementioned parameters and to select which tap types to detect.

Data from the tap detection algorithm is represented as a Tap type.

import com.mbientlab.metawear.data.TapType;
import com.mbientlab.metawear.module.AccelerometerBosch.TapShockTime;

// enable single tap detection
accBosch.tap().configure()
        .enableSingleTap()
        .threshold(2f)
        .shockTime(TapShockTime.TST_50_MS)
        .commit();
accBosch.tap().addRouteAsync(new RouteBuilder() {
    @Override
    public void configure(RouteComponent source) {
        source.stream(new Subscriber() {
            @Override
            public void apply(Data data, Object... env) {
                Tap tap = data.value(Tap.class);
                switch(tap.type) {
                    case SINGLE:
                        Log.i("MainActivity", "Single tap");
                        break;
                    case DOUBLE:
                        Log.i("MainActivity", "Double tap");
                        break;
                }
            }
        });
    }
}).continueWith(new Continuation<Route, Void>() {
    @Override
    public Void then(Task<Route> task) throws Exception {
        accBosch.tap().start();
        accBosch.start();
        return null;
    }
});

Motion Detection

The motion detection algorithms on the Bosch chips use the difference in consecutive acceleration data samples to determine different types of motion.

Motion	Description
Any	Difference exceeds threshold for N consecutive samples
No	Difference doesn’t exceed the threshold for a period of time
Slow	Same as any motion but axis and direction information is not retained

The different motion detection algorithms are accessed with the motion method and only one algorithm can be active at any time.

import com.mbientlab.metawear.module.AccelerometerBosch.NoMotionDataProducer;

final NoMotionDataProducer noMotion = accBosch.motion(NoMotionDataProducer.class);

// configure no motion detection
// difference < 0.1g for 10 seconds before interrupt is fired
noMotion.configure()
        .duration(10000)
        .threshold(0.1f)
        .commit();
noMotion.addRouteAsync(new RouteBuilder() {
    @Override
    public void configure(RouteComponent source) {
        source.stream(new Subscriber() {
            @Override
            public void apply(Data data, Object... env) {
                Log.i("MainActivity", "No motion detected");
            }
        });
    }
}).continueWith(new Continuation<Route, Void>() {
    @Override
    public Void then(Task<Route> task) throws Exception {
        noMotion.start();
        accBosch.start();
        return null;
    }
});