Set Up Your Mobile Device

In order to receive data from a mobile device in MATLAB®, you will need to install and set up the MATLAB Mobile™ app on your mobile device.

Log in to the MathWorks® Cloud from the MATLAB Mobile Settings.

Create a Connection to Your Mobile Device

On theCommandsscreen of MATLAB Mobile, use themobiledevcommand to create an object that represents your mobile device.

m = mobiledev;

The displayed output should showConnected: 1, indicating that themobiledevobject has successfully established a connection to the app.

Prepare for Data Acquisition from Multiple Sensors

Use the appropriatemobiledevproperties to enable sensors on the device.

m.AngularVelocitySensorEnabled = 1; m.OrientationSensorEnabled = 1;

Start Acquiring Data

After enabling the sensors, theSensorsscreen of MATLAB Mobile will show the current data measured by the sensors. TheLoggingproperty allows you to begin sending sensor data tomobiledev.

m.Logging = 1;

The device is now transmitting sensor data.

At the start of logging, the device is lying flat on a table with the screen facing up. The positive Y-axis of the angular velocity sensor is defined to extend out from the top of the device. Positive roll of the orientation sensor is defined as a clockwise rotation about the Y-axis when facing the positive direction of the axis.

During logging, the device is turned face-up and face-down a few times about its Y-axis. This generates Y-axis changes in angular velocity and roll changes in orientation.

Stop Acquiring Data

TheLoggingproperty is used again to have the device stop sending sensor data tomobiledev.

m.Logging = 0;

Retrieve Logged Data

Each sensor's data can be accessed from themobiledevobject. Two different timestamp variables are created because the angular velocity and orientation data may not be recorded by the device at the same time.

[av,tav] = angvellog(m); [o,to] = orientlog(m);

Plot Raw Sensor Data

The data of interest from the sensors are isolated into separate variables and plotted.

yAngVel = av(:,2); roll = o(:,3); plot(tav,yAngVel,to,roll); legend('Y Angular Velocity','Roll'); xlabel('Relative time (s)');

The data is plotted in seconds relative tomobiledev'sInitialTimestampproperty. This property provides the absolute time of the first data point recorded by a sensor and sent to MATLAB. It acts as the reference point for the timestamps of all sensor data accessed using functions such asangvellogandorientlog, which are given in seconds relative toInitialTimestamp.

Convert to Absolute Timestamps

To convert all sensor timestamps into absolute timestamps, theInitialTimestampvalue is converted into adatetimeobject. The individual sensor timestamps, which are in units of seconds, are converted intoseconds. This simplifies the date arithmetic of turning relative timestamps into absolute timestamps.

tInit = datetime(m.InitialTimestamp,“InputFormat”,'dd-MM-yyyy HH:mm:ss.SSS'); tAngVel = tInit + seconds(tav); tOrient = tInit + seconds(to);

Plot Multiple Sensors Over Absolute Time

Both sensors now have absolute timestamps represented usingdatetime. This makes it easy to visualize the actual time that significant events occurred in sensor readings.

The orientation sensor uses units of degrees, while the angular velocity sensor uses units of radians per second. Before plotting again,yAngVelis converted to degrees per second.

yAngVelDeg = yAngVel * 180/pi; plot(tAngVel,yAngVelDeg,tOrient,roll); legend('Y Angular Velocity','Roll'); xlabel('Absolute time (s)');

Clean Up

Turn off the enabled sensors and clearmobiledev.

m.AngularVelocitySensorEnabled = 0; m.OrientationSensorEnabled = 0; clearm;