1. CIS 470 Mobile App Development
Lecture 24
Wenbing Zhao
Department of Electrical Engineering and Computer Science
Cleveland State University
11/17/2018
CIS 470: Mobile App Development

2. Step Counting (Pedometer)
Taken from Android Sensor Programming By Example, Packt Publishing, 2016
Step detector and step counter sensors
A custom algorithm using the accelerometer sensor’s data to detect walking, jogging, and fast running activities
11/17/2018
CIS 470: Mobile App Development

3. CIS 470: Mobile App Development
Step Counter Sensor
The step counter sensor is used to get the total number of steps taken by the user since the last reboot of the phone
The value of the step counter sensor is reset to zero on reboot
In the onSensorChanged() method, the number of steps is given by event.value[0]
The event timestamp represents the time at which the last step was taken
This sensor is especially useful for those applications that don't want to run in the background and maintain the history of steps themselves
This sensor works in the batch and continuous modes. If we specify 0 or no latency in the SensorManager.registerListener() method, then it works in continuous mode, otherwise, if we specify any latency, then it groups the events in batches and reports them at a specified latency
11/17/2018
CIS 470: Mobile App Development

4. CIS 470: Mobile App Development
Step Counter APIs
protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.stepcounter_layout); mStepsSinceReboot = (TextView)findViewById(R.id.stepssincereboot); mSensorManager = (SensorManager) this.getSystemService(Context.SENSOR_SERVICE); if(mSensorManager.getDefaultSensor(Sensor.TYPE_STEP_COUNTER) != null) { mSensor = mSensorManager.getDefaultSensor(Sensor.TYPE_STEP_COUNTER); isSensorPresent = true; } else { isSensorPresent = false; } }
public void onSensorChanged(SensorEvent event) { mStepsSinceReboot.setText("Steps since reboot:" + String.valueOf(event.values[0])); }
11/17/2018
CIS 470: Mobile App Development

5. CIS 470: Mobile App Development
Step Detector Sensor
The step detector sensor triggers an event each time a step is taken by the user
The value reported in the onSensorChanged() method is always one, the fractional part is always zero, and the event timestamp is the moment that the user's foot hits the ground
The step detector sensor has lower accuracy and produces more false positives compared to the step counter sensor
The step counter sensor is more accurate, but it has more latency in reporting the steps, as it uses extra time after each step to remove any false positive values
The step detector sensor is recommended for those applications that want to track the steps in real time and maintain their own history of each and every step with their timestamp
11/17/2018
CIS 470: Mobile App Development

6. CIS 470: Mobile App Development
Step Detector APIs
public void onCreate() { super.onCreate(); mSensorManager = (SensorManager) this.getSystemService(Context.SENSOR_SERVICE); if(mSensorManager.getDefaultSensor(Sensor.TYPE_STEP_DETECTOR) != null) { mStepDetectorSensor = mSensorManager.getDefaultSensor(Sensor.TYPE_STEP_DETECTOR); mSensorManager.registerListener(this, mStepDetectorSensor, SensorManager.SENSOR_DELAY_NORMAL); mStepsDBHelper = new StepsDBHelper(getApplicationContext()); } }
public void onSensorChanged(SensorEvent event) { mStepsDBHelper.createStepsEntry(); }
onSensorChanged() is called for every step
11/17/2018
CIS 470: Mobile App Development

7. Custom Step Counting and Activity Detection
Step counting: count number of peaks/valleys
Types of activities: highest peak values
private static final int WALKINGPEAK = 18; private static final int JOGGINGPEAK = 25; private static final int RUNNINGPEAK = 32;
Green circle: true peak
Red circle: valley
Yellow circle: false peak (to be filtered out)
11/17/2018
CIS 470: Mobile App Development

8. CIS 470: Mobile App Development
Detect Peaks
public void findHighPeaks() { //Calculating the High Peaks boolean isAboveMeanLastValueTrue = false; int dataSize = mRawDataList.size(); for (int i = 0; i < dataSize; i++) { if(mRawDataList.get(i).value > WALKINGPEAK) {
// add all continuous data points that are bigger than WALKINGPEAK to the array
// One of these points include both the true peak and the false peaks, and many other points that are not peaks mAboveThresholdValuesList.add(mRawDataList.get(i)); isAboveMeanLastValueTrue = false; } else {
// Once we see a point that is below the threshold, we are falling out of the peak region
// Now time to find the peaks if(!isAboveMeanLastValueTrue && mAboveThresholdValuesList.size()>0) {
// Sort the temporary data array. The last one in the array has the biggest value, which is the peak
// which could be true or false peak Collections.sort(mAboveThresholdValuesList,new DataSorter()); mHighestPeakList.add(mAboveThresholdValuesList.get(mAboveThresholdValuesList.size()-1)); mAboveThresholdValuesList.clear(); } isAboveMeanLastValueTrue = true; } } }
11/17/2018
CIS 470: Mobile App Development

9. CIS 470: Mobile App Development
public void removeClosePeaks() { for (int i = 0; i < mHighestPeakList.size()-1; i++) { if(mHighestPeakList.get(i).isRealPeak) { if(mHighestPeakList.get(i+1).time - mHighestPeakList.get(i).time < 400) { if(mHighestPeakList.get(i+1).value > mHighestPeakList.get(i).value) { mHighestPeakList.get(i).isRealPeak = false; } else { mHighestPeakList.get(i+1).isRealPeak = false; } } } } }
Observation: false peaks are very close to the true peak. Use this fact to filter them out
11/17/2018
CIS 470: Mobile App Development

10. CIS 470: Mobile App Development
The Pedometer app
Create an app and name it MyPedometer
Replace existing manifests, activity_main.xml, styles.xml, strings.xml, MainActivity.java with the source code provided in the course webpage
Add the following java files: AccelerometerData.java, CustomAlgoResultsActivity.java, DateStepsModel.java, ListAdapter.java, StepsCounterActivity.java, StepsDBHelper.java, StepsHistoryActivity.java, StepsService.java, StepsTrackerDBHelper.java, StepsTrackerService.java
Add the following xml files: capability_layout.java, list_rows.xml, pedomesterlist_layout.xml, stepcounter_layout.xml, list_raw_divider_gradient.xml
11/17/2018
CIS 470: Mobile App Development

11. CIS 470: Mobile App Development
The Pedometer app
11/17/2018
CIS 470: Mobile App Development

12. CIS 470: Mobile App Development
Exercise
If you compare the step count using the API and that from the custom algorithm, you will see they are different depending on where you place the phone
Make the three parameters for activity detection for walking, jogging, and running (18, 25, 32) customizable in the app itself dynamically, e.g., by adding three TextEdits and a button, so that the result from the custom algorithm is similar to result from the APIs
11/17/2018
CIS 470: Mobile App Development