where does MMR get the time info?

I have 2 MMR sensors and I grouped them in the MetaBase application to start data (acc & gyro) logging. After downloading the log files, I see data entry like the following:

epoc (ms),timestamp (+0800),elapsed (s),x-axis (g),y-axis (g),z-axis (g)
1610504506670,2021-01-13T10.21.46.670,0.000,-0.035,-0.140,1.007
1610504506680,2021-01-13T10.21.46.680,0.010,-0.036,-0.140,1.017

I want to know from where the sensor gets the time information. Does it have an internal clock or if it retrieves from the smart phone when it communicates with the phone through MetaBase app?

Comments

  • The time is synched when the MetaWear board downloads the data to the phone.

    The internal clock in the MetaWear is just a counter (in ms). It is not a world clock (date + time / epoch).
    In the metaWear, the data looks like this:
    time = 1 ms, data = 0.10
    time = 2 ms, data = 0.11
    time = 3 ms, data = 0.15

    The world clock (date + time / epoch) is from the phone.
    So when I download that data on my phone:
    epoch (time+date) = 1610555890001, data = 0.10
    epoch (time+date) = 1610555890002, data = 0.11
    epoch (time+date) = 1610555890003, data = 0.15

  • Laura, thank you for the answer.
    Can help me confirm the following: the starting time point t of data logging is the time when the phone issues command to start a new session.
    Why I am asking is because we want to combine MetaWear with other sensors in our application; so the data point synchronization is crucial.

  • I have another question:
    My Windows computer cannot find MMR either in Bluetooth setting when I try to add new Bluetooth device or in MetaBase when I try to add Device. I have tried Ble 4 and 5 dongles. Both not successful. What could be the problem?
    I have ordered MetaHub which includes a Bluetooth USB dongle. How is it different from those Bluetooth dongles in the market? I guess it should not be, right?

  • Hey @dji2r,
    Some bad news, we are going to stop supporting Windows because of reliability issues.

    You can still use it but it will take some development/bluetooth skills as you have already guessed (we just won't support it - our users are reporting too many issues because Windows is notoriously bad with BLE).

    Now, the MetaHub dongles might not work on Windows (Windows might not have the drivers for that dongle). We sell a Windows specific dongle that will work for you. You should buy a Windows specific dongle with good reviews if you can (amazon has many).

    Can you use your smartphone in the meantime?

  • Hi @Laura,

    I am OK with smartphone, however we want to combine MetaWear with other sensors in our application; so the data point synchronization is crucial. If we want to use smartphone, we have to move all my other sensors data collection to the same smartphone, which is not an easy task.

    1. Can help me confirm the following: the starting time point t of data logging in MetaBase is the time when the phone issues command to start a new session.
    2. If Windows is not supported, can I assume Linux like Ubuntu is still a good option, which you still support?
    1. Yes.
    2. Ubuntu is highly recommended!
  • I got notification from mbientlab that MMS has been released.
    I assume all the Smartphone apps like MetaBase provided by mbientlab would work with MMS as well.
    I wonder if all my current code (most Python), which works with MMR, will work with MMS.

  • Yes and Yes.

  • edited March 30

    In the email, it says "Now you can gather data for 46.5 hours non-stop when logging sensor fusion data at 100Hz (that's 67,108,864 data entries, over 67million data points!)".
    Consider this case: first I started logging; one hour later, I stopped it; forgot to download; then started logging again for one hour and stopped. If I tried to download, would I get 2 hours' logging data or 1 hour only because the new logging always replace the old one?

  • You get 2 hours, old data does not get replaced with new data unless the log memory is full.

  • Thx Laura.
    Then I have another question: since there are so much data in the memory, what if I only want to download some part of it? My experience with MMR: it takes me 40 minutes to download data from 2 MMR at the same time. Since MMS memory is much bigger, downloading time will be too long.

  • edited April 1

    We used to support partial downloads but we no longer support it at this time (the API was too confusing for users).
    You should download everything at once.

    We are adding USB download support on MMS since it will be too long to download over BLE. This is coming out in a few weeks.

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