GPIO streaming timestamp not accurate

udi_o

Hi,

Running the Metawear-SampleAndroidApp with GPIO ADC streaming generates CSV file with time column that is incremented every 33ms: 

0

0.033

0.066

0.099

0.132

0.165

etc.

However, capturing 1 minute of data reaches only ~40 seconds

Any suggestions?

Eric

I do not see any issues exporting data past 1 minute on my Nexus 6 (Android M) and Nexus 7 (Android 5.1.1).

Just to be clear, you can see 1 min worth of data on the graph but when you export the CSV file, you only receive ~40 seconds?

udi_o

Yes, I'm streaming 1 minute measured with external stop-watch, then I stop the streaming and save+email. 

The final entries on the CSV file are:

40.722

40.755

40.788

40.821

40.854

40.887

40.92

The file consists in total 1242 rows of data which match ~40 seconds: 1242 X 0.033 = ~40

Eric

Does the graph show 1 minute worth of data?

udi_o

The graph shows 40 seconds but the actual duration was 60 seconds.

It looks like the sampling rate is actually 0.050 and not 0.033

Eric

The sampling rate is 0.033s (30Hz).  If you run the sampling for longer, say 120 seconds, does the graph stop at 40 seconds?  If not, then it seems like your device is not capturing all data packets.

udi_o

1) Why should the graph stop at 40 seconds?

2) Is the time-stamp calculated by the SampleAndroidApp regardless missing packets?

3) The same fault occurred both with LG 5.5 and Samsung 4.3 devices, any suggestions / workaround?

Eric

1. It shouldn't so if it does, something is seriously wrong with the app
2. Time stamps are based on number of samples received.  The were originally based on when the mobile device received the data but high frequency streams results in multiple data being received at the same time.
3. You can try lowering the sampling frequency to 1Hz and increasing it until you see this error.