sensor disconnection and counting steps with multiple sensors

Comments

• Eric

  November 2016

  What board are you using and how fast are you streaming the data?
• zz3d

  November 2016

  Hello Eric. The Board is BMI160. Sample Frequency is 50.  Scale: -2/+2
• zz3d

  November 2016 edited November 2016

  Metawear RG
• Eric

  November 2016 edited November 2016

  The bmi160 has a step counter built into its firmware.  You can utilize that instead to avoid streaming larges amounts of acceleration data to your ios device.

  
  

  If you are intent on processing the raw data yourself, take a look at the fitness tracker app which has a step counter approximation using the rms values.

  https://github.com/mbientlab-projects/iOSFitnessTracker
  
• trt

  January 2017

  Hello,

  
  

  I
  have written the code for collecting combined data at the same from the
  2 sensors connected to the iOS device.
  
  The Board is BMI160. Sample Frequency is 50.  Scale: -2/+2
  As per your suggestion to zz3d, I also update framework of Metawear SDK and try to get step counter/ steps from sensors.
  but I am not able to get proper steps from each sensor. Please help me to get out of this.
  
  Here is the following code:
  
  for( MBLMetaWear *device in self.aDevices ) {
          NSLog(@%@",[device.accelerometer class]);
          @weakify( device );
         
          // start accelerometer
          [self.aStreamingEventsAccel addObject:device.accelerometer.dataReadyEvent];
          [device.accelerometer.dataReadyEvent startNotificationsWithHandlerAsync:^(MBLAccelerometerData* accel, NSError *error) {
  
              @strongify( self );
              @strongify( device );
  
              if( !error ) {
  
                  if( [self.delegate respondsToSelector:@selector(gotAccelerometerDeviceData:xVal:yVal:zVal:timestamp:)] ) {
  
                      NSLog(@xVal = %f, yVal = %f, zVal = %f, timestamp = %@",accel.x,accel.y,accel.z,accel.timestamp);
                      [self.delegate gotAccelerometerDeviceData:[self getDeviceIndex:device] xVal:accel.x yVal:accel.y zVal:accel.z timestamp:accel.timestamp];
                  }
              }
              else {
  
                  _ALOG( @%@", error.localizedDescription );
              }
          }];
         
          if ([device.accelerometer isKindOfClass:[MBLAccelerometerMMA8452Q class]])
            {
              MBLAccelerometerMMA8452Q *accelerometerMMA8452Q = (MBLAccelerometerMMA8452Q *)device.accelerometer;
              [self.streamingEvents addObject:accelerometerMMA8452Q.tapEvent];
              [accelerometerMMA8452Q.tapEvent startNotificationsWithHandlerAsync:^(MBLDataSample * _Nullable obj, NSError * _Nullable error) {
                  if (obj) {
                      NSLog(@Tap Count: %d, ++self.tapCount);
                  }
              }];
          }
          else if ([device.accelerometer isKindOfClass:[MBLAccelerometerBMI160 class]])
            {
       MBLAccelerometerBMI160 *accelerometerBMI160 = (MBLAccelerometerBMI160 *)device.accelerometer;
             
              [self.stepsSreamingEvents addObject:accelerometerBMI160.stepEvent];
              [accelerometerBMI160.stepEvent startNotificationsWithHandlerAsync:^(MBLNumericData * _Nullable obj, NSError * _Nullable error) {
                  @strongify( self );
                  @strongify( device );
                 
                  if (obj) {
                      if( !error ) {
                          if( [self.delegate respondsToSelector:@selector(gotstepsFromDeviceData:stepVal:timestamp:)] )
                            {
                              steps = ++self.accelerometerBMI160StepCount;
                              NSUInteger deviceIndex = [self.aDevices indexOfObject:device];
                              [self.delegate gotstepsFromDeviceData:[self getDeviceIndex:device] stepVal:steps timestamp:obj.timestamp];
                            }}
                      else{
                      _ALOG( @%@", error.localizedDescription );
                      }}}];}}
  
  
  self.aDevices = contains connected MetaWear sensors array
  in delegate method m just using step value to display for Left steps/Right steps.
  
  Challenge 1: Sometimes my sensors gets step events while they are steady on table.
  Challenge 2: Also step events count from 2 steps per sensors, sometimes it gives 4 steps in one reading or more. I'm getting stuck to minimize this. is it kind of Firmware issue?

  What would be your suggestion for accurately counting steps with two sensors (left and right)? 

  Thank you in advance for your time.
• Eric

  January 2017

  How frequently are you reading the step counter?  Also, have you tried using the step counter by itself and with only one device?  That is, no acceleration streaming and no tap detection.
• trt

  January 2017 edited January 2017

  Hello Eric,
  Thanks for reply.
  
  I had tried both way to read step counter.
  1. I had add step event after connect sensor successful and write below code,
   self.stepEvent = [[accel.stepCounter periodicReadWithPeriod:500] differentialSampleOfEvent:60000];
          [self.stepEvent startLoggingAsync];
  
  than I used to download data in every 1 min of time interval.
  
  2. I had add step event after getting accel data from device ,after loop through each device I had added step event and read data at a time. here is code.
  
  for( MBLMetaWear *device in self.aDevices ) {
  
  MBLAccelerometerBMI160 *accelerometerBMI160 = (MBLAccelerometerBMI160 *)self.device.accelerometer;
      [self.streamingEvents addObject:accelerometerBMI160.stepEvent];
      [accelerometerBMI160.stepEvent startNotificationsWithHandlerAsync:^(MBLNumericData * _Nullable obj, NSError * _Nullable error) {
          if (obj) {
              self.accelerometerBMI160StepLabel.text = [NSString stringWithFormat:@Step Count: %d, ++self.accelerometerBMI160StepCount];
          }
      }];
  }
  
  where, self.aDevices = Array of connected sensor.
  
  Also, have you tried using the step counter by itself and with only one device?
  - Yes, I had tried it with only one device also, but I'm getting twice steps. I don't know why, but I though it refresh setting.
   accel.tapType = (int)0; (MBLAccelerometerTapTypeSingle)
  
  Let me know where I'm wrong or doing mistake to read step counter?
  
  I need accurate step counter because my app is based on only that. Help me to get out of this.
  
  again, Thank you so much for your time.
  
• stephen

  January 2017

  One thing that may be causing confusion is that the stepCounter on counts when stepEvent is activated.

  
  

  Aside from that, can you erase the app from your iOS device just to confirm a clean start and then try out the stepEvent on just one device:

  [accelerometerBMI160.stepEvent startNotificationsWithHandlerAsync:^(MBLNumericData *obj, NSError * error) {

  NSLog(@%@", obj);

  }];
     
  
• trt

  January 2017 edited January 2017

  Hello stephen,
  Thanks for reply
• stephen

  January 2017

  Also, can you confirm if you are using two devices, one mounted on the right leg and one of the left?  The step detector is sensitive enough to register a step taken by either leg, so maybe this could explain your "getting twice steps"?  If not, can you explain your exact configuration and experiment where double steps are being recorded?

  
  

  Thanks!

  -Stephen
• trt

  January 2017

  Hello Stephen,
  
  Let me explain my scenario, I'm using two Metawear sensor at a time and get connected one by one. (this devices are stored in my global array). Currently I'm assume that index=0 is Left leg sensor and index=1 is Right leg sensor (though i can not figure out which one is right/left sensor at a time). Than I add step event while getting Accel data for a device within For loop, and calculating offset.
  
  Regarding twice steps, it's happen when I'm using startNotificationsWithHandlerAsync, but whenever I disconnect device i'm not using stopNotificationsAsync. I think this is the problem where data are stored on flash memory of sensor. M I right?
  
  one more confusing thing happen, whenever I check device.accelerometer, sometimes it gives me MBLAccelerometerMMA8452Q and sometimes it gives me MBLAccelerometerBMI160.
  
  Thanks for figure out issues and help me to get out of this situation. I'll let you know what happen or what result I get after add stopNotificationsAsync.
  stopNotificationsAsync and
  
• trt

  January 2017

  Hello Stephen,
  
  Step event give me always +1 interval which is right as per documentation. Is it possible that I'm using for loop  to print a step of each sensor along with delegate method to another class. So is there any possibility of loop hole in code to get twice steps per sensor at a time?
  
  Waiting for your suggestion.
  Thanks for co-ordination.
  
  
  Thanks!
  - Trupti
  
• stephen

  February 2017

  - Not calling stopNotificationsAsync:

  This is okay, we understand that unexpected disconnects occur and so the SDK will take care of cleaning up any un-used notifications next time you connect.

  
  

  - MBLAccelerometerMMA8452Q vs MBLAccelerometerBMI160:

  This is odd, the type shouldn't change, is it possible you are connecting to different types of MetaWears?  If you can reproduce this let me know.

  
  

  It's hard for me to comment further on the "twice steps per sensor", since it appears the the event itself is producing the correct data.  It could likely be some issue with the for loop or delegate methods as you suggested.

  
  

  Thanks,

  -Stephen