How long should bluetooth downloading sensor data from a Metaware sensor take in the Metabase App?
Hello,
I just got a pair of metaware sensors for my lab, and I'm trying to figure out whether they'll be useful for our next grant.
I did a short test of one of the sensors at 800 Hz for accelerometer and gyroscope with some magnetometer at 20 Hz, for a total of three minutes. I then downloaded the data from it to a Samsung Galaxy S6 using the Metabase app. The data (attached) took over ten minutes to transfer from the metaware, which seems slow - is there something obvious I should be doing differently, or is that just the maximum transfer speed using bluetooth?
I physically set the sensor onto the phone's screen while it was downloading, so I wouldn't expect it to be a wireless connectivity problem.
Comments
This is entirely correct. Unfortunately BluetoothLE is slow so if you max out the memory it will take 15 minutes to download.
Ah, okay. Looks like we're probably have to do streaming instead of batching. Based on the calculator, it seems like if I'm collecting data at 200Hz on the accelerometer and gyroscope, the download time will last for 75% of the subject's test duration, which would introduce a lot of waiting before the next subject can start (or require us to buy twice as many sensors so we can rotate them out in shifts). Our current system downloads via USB, which means we can get everything off of it in under a minute, or grab all the data off at the end of the day if needed.
So I guess my next question is, how does the streaming setup deal with intermittent bluetooth connection?
If it loses contact with the hub device for a couple of seconds (since in our movement tasks, the subjects have to turn around), are those datapoints lost forever, or does streaming mode use an internal buffer to ensure the full dataset gets transmitted? I noticed a warning about using 200 Hz causing issues; is that because it can't transmit fast enough to clear the buffer if it ends up falling behind?
Also, in your experience, are all bluetooth interfaces basically equal, or does the hardware in the hub device matter for how strong the connection is (that is, can I avoid the signal strength issues of low energy bluetooth by just using something with a bigger/better antennae)?
Finally, and perhaps this is veering a little offtopic, but can I just click a button and simultaneously activate the vibration function on MetaMotionR+ sensors from the stock Metabase app? I'm not seeing any way to do it, but I'm not super familiar with the app and it's possible I'm just missing something.
Thanks!
In streaming mode, if you disconnect, you lose data.