Hi Matthias, >From your two emails I'm unsure what firmware you are running on the Shimmers and what application you are using on the PC side to capture the data (is it custom?).
This looks more like a software problem (on one side of the link) rather than a hardware or communication problem (remember Bluetooth is a "reliable" protocol). If you are using one of the example Shimmer apps then I can rule out the suggestion that "the AD-conversion on the Shimmer device itself that is still changing values when the data is already being transmitted to the application" as all these apps perform double buffering on the shimmer to prevent this exact problem. If you are using custom code on the shimmer or the PC the one suggestion I do have is to use the standard BoilerPlate image with either ShimmerConnect or one of the Labview sample applications to see if the same thing happens. Mike On Tue, May 22, 2012 at 9:58 PM, Matthias Van Gysel < [email protected]> wrote: > Hi again, > > I've noticed that the AccelGyro firmware sends a CRC code along with its > data. > How do I use this checksum to verify the authenticity of my data packet? > And does the BoilerPlate firmware provides some sort of check? > > I want to know this because I have noticed that when I receive an error > (data-peak) in my logfile, > the corresponding package has all its data shifted 2 places back. But it > seems as if the checksum is still in its original place. > If I can show that the checksum is ok for the corrupted package then its > probably the fault of the sensor itself right? > > I've made a screenshot of the corrupted data-package so you can see for > yourself. > > I hope someone can help me out! > > Matthias Van Gysel > > > 2012/5/22 Leonid Ivonin <[email protected]> > >> Hi Matthias, >> >> In our lab we have recently experienced a problem that is very similar to >> the one you described. We recorded ECG signal with Shimmer sensor and the >> C# application provided by Shimmer. The data collected with this sensor for >> 10 our of 36 participants was corrupted by a strong noise with high >> amplitude. We are pretty sure that this noise was not caused by external >> factors, because during the measurement our participants were instructed to >> sit still and also we made sure that the connection of electrodes to their >> skin was good. Moreover we were not able to find any pattern in this >> problem, it happened randomly. We assume that at some point of measurement >> something went wrong in the sensor, but we have no idea what caused it. >> >> I have attached a sample screenshot. On the left side of the picture you >> can see normal ECG signal, then at some point of time it just becomes a >> high amplitude noise. Filters do not help to eliminate this noise. >> >> That is our experience :) >> >> Regards, >> >> Leonid >> >> >> On Tue, May 22, 2012 at 6:09 PM, Matthias Van Gysel < >> [email protected]> wrote: >> >>> Hi, >>> >>> I'm currently working on a project that streams data over a Bluetooth >>> connection from a Shimmer2r sensor to a C# application. >>> I record this data, but when I open the recorded data-file, lots of the >>> data seems to be corrupted or something like that. >>> Data peaks that go as high as 60, when actually the data is normalised >>> to change its value between -1.5 and 1.5. >>> >>> I have tried to test whether it is the sensor, the connection or the >>> application that is causing these errors to the data but I can't work it >>> out. >>> Does anyone ever had the same type of problems? Or knows what this data >>> means and where it comes from? >>> >>> I have talked about this to one of my supervisors and he said that it >>> might be the AD-conversion on the Shimmer device itself that is still >>> changing values when the data is already being transmitted to the >>> application. >>> >>> I don't have a single clue anymore so I really hope someone can help me >>> out here. >>> >>> I inserted a screenshot of the corrupted data into this mail. The >>> screenshot shows the corrupted data and what it normally should be. >>> >>> >>> Matthias Van Gysel >>> >>> >>> >>> _______________________________________________ >>> Shimmer-users mailing list >>> [email protected] >>> https://lists.eecs.harvard.edu/mailman/listinfo/shimmer-users >>> >>> >> > > _______________________________________________ > Shimmer-users mailing list > [email protected] > https://lists.eecs.harvard.edu/mailman/listinfo/shimmer-users > >
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