Count steps with acceleration data from your Apple or Android mobile device

You can use the accelerometer in your mobile device to count steps in MATLAB.

Connect to the mobile device

Use the sensorgroup object to create a connection to your mobile device. In this case, we're using an Apple iPhone 3GS, but you can use an Android device by passing AndroidMobile instead

obj = sensorgroup('AppleMobile');
Waiting for data...
To configure your mobile device:
1.  Open the Sensor Monitor app.
2.  Select the Network tab.
3.  For Host, enter 172.28.152.88, 192.168.228.1, or 192.168.22.1
4.  For Port, enter 50000
5.  Choose one or more sensor.
6.  Set Current Send Mode to Binary.
7.  Tap Start Send.

Collect the acceleration data

Walk around for 30 seconds, then retrieve the data from the Acceleration log

pause(30)
accelVector = accellog(obj);

Stop collecting data by clearing the variable from the workspace

clear obj

Analyze the acceleration data

The acceleration data is captured in an [n x 3] array, where the 3 columns represent the x, y, and z acceleration values.

plot(accelVector) Transform the vector data into a scalar, and subtract gravity.

accelScalar = sqrt(sum(accelVector.^2, 2));
accelScalarNoGravity = accelScalar - 9.8;
plot(accelScalarNoGravity) Assume that we count a step whenever the acceleration goes from negative to positive value. Find the indexes of these zero crossing events

aboveZero = accelScalarNoGravity > 0;
zeroCrossing = diff(aboveZero) == 1;
zeroCrossingIndex = find(zeroCrossing);

Plot those events

hold on
plot(zeroCrossingIndex, zeros(size(zeroCrossingIndex)), 'r', 'Marker', 'v', 'LineStyle', 'none')
hold off The number of steps is equal to the number of zero crossing events

numberOfSteps = numel(zeroCrossingIndex)
numberOfSteps =

32