Hi, Firstly I should point out that the "Shimmer Display" application, and the associated firmware, are deprecated and should not be used for new projects. These have been replaced by ShimmerConnect, the Labview library and the Matlab drivers, all using the BoilerPlate firmware.
That said, even if you do switch to BoilerPlate you will get timestamps in the same format. These timestamps are relative, not absolute and is not based on "wall" time. Instead it is based on the ticks of the 32.768kHz clock on the Shimmer. This timestamp value starts at zero when the Shimmer is turned on/reset. If using a 16-bit value for the timestamp, as these applications are, then it will roll around every two seconds (2^16 / 32768). This timestamp is useful for a number of things, such as detecting missed packets, determining sampling rate, etc. For example, if sampling at 51.2Hz (and not exactly 50Hz as you mention), then the difference between two subsequent packet's timestamps should be 640 (32768/51.2). Mike On Fri, Mar 16, 2012 at 6:33 AM, Yeoh Wee Soon (I2R) <[email protected]> wrote: > Hi, > > > > I am using Shimmer Display Application (shDisplay.exe) for data collection, > and the sampling rate selected for the acceleromter is 50Hz using the > firmware “AccelGyro_shimmer2_50Hz_6G.ihex”. To end data collection, I click > the “Stop” button and a dialogue popped up, using the default filename > associated with the “Stop” date and time. Let say the default file name of > "20120309_000446" reviews that this data collection starts on 09 March 2012 > at 00:04:46 Hrs. > > > > When I opened up the data file, the first entry of the TimeStamp is "21885". > It looks to me that "21885" is an offset from 00:04:46 Hrs, may I know is it > to be interpreted? > > > > I have prepared a document contains 3 screen shots to illustrate my > question. Please help in clarifying my doubt! > > > > Thank you. > > Institute for Infocomm Research disclaimer: "This email is confidential and > may be privileged. If you are not the intended recipient, please delete it > and notify us immediately. Please do not copy or use it for any purpose, or > disclose its contents to any other person. Thank you." > > _______________________________________________ > 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
