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Topic: Scalar, Float and OpenBCI
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StabMe



Joined: Jul 29, 2016
Posts: 34

PostPosted: Jan 21, 2023 4:37 AM    Post subject: Scalar, Float and OpenBCI

I have a design that uses all scalar elements that i want to modify and use OpenBCI board in it as a source. I tried two different elemetns: DeviceSet with OpenBCI selected in the menu and OpenBCI element with FTDISerialPort element connected to its input. Both produce a degraded signal, as if sampling frequency is seriously lowered.

So i decided to isolate the issue and created a simple design that uses all scalar version of: FTDI->OpenBCI, Filter (to remove DC and 60Hz line frequency), Oscilloscope with auto range connected. It produced same degraded signal:

https://i.ibb.co/dW8fTLy/Scalars.jpg

Then i created a replica of the design with all floats. Signal looked fine:

https://i.ibb.co/QjnYrKw/Floats.jpg

Then i used a float version of OpenBCI element and captured a few minutes of data into and EDF file.

I then created two simple chains of signal: a Scalar EDF reader and Filter->Oscilloscope in Scalar and in Float version. Scalar version degraded the signal. it seemed.


https://i.ibb.co/whw5rPN/Two-Chains.jpg


So, is there any way i can use Scalar OpenBCI element and be able receive signal from in it high fidelity?
jarek



Joined: Oct 22, 2007
Posts: 983

PostPosted: Jan 21, 2023 10:08 AM    Post subject:

Scalar elements require more thoughtful configuration. But they are older and more tested than the float equivalent, so they should work. Float elements were added later in order to simplify their use and I would recommend using them whenever possible.

In your scalar example try to change the Filter element configuration. Go to "Advanced features" tab and set "Output bits" to 24 (from the default 16) and see if it helps.
StabMe



Joined: Jul 29, 2016
Posts: 34

PostPosted: Jan 21, 2023 12:24 PM    Post subject:

Jarek,

When i right click on the Filter and go to Advanced Parameters, there is no option named 'Output bits' neither in setting, nor in signal parameters. Am i looking in the wrong place?
jarek



Joined: Oct 22, 2007
Posts: 983

PostPosted: Jan 21, 2023 1:06 PM    Post subject:

This is different than usual, because Filter is one of the first ever elements created for BioEra.

Look for this tab on the main properties.
StabMe



Joined: Jul 29, 2016
Posts: 34

PostPosted: Jan 21, 2023 1:46 PM    Post subject:

Jarek,

I feel very dumb to post this, but here are all possible tabs containing all possible options and 'Output bits' is not one of them:

https://i.imgur.com/A6uf9es.png
jarek



Joined: Oct 22, 2007
Posts: 983

PostPosted: Jan 21, 2023 2:24 PM    Post subject:

This option is only available in the Scalar version of the Filter. You are showing Float version.
StabMe



Joined: Jul 29, 2016
Posts: 34

PostPosted: Jan 21, 2023 3:44 PM    Post subject:

My bad!

Seems like changing the Output bits parameter fixed the issue. Thank you!
Any other element types that should be set to 24bit in order to work correctly with OpenBCI?
jarek



Joined: Oct 22, 2007
Posts: 983

PostPosted: Jan 21, 2023 4:06 PM    Post subject:

If I remember correctly then there is only 1 other element like that: FFTTransform.

But using scalar elements may lead you to other problems. Make sure you read about signal scaling in the manual (advanced).
StabMe



Joined: Jul 29, 2016
Posts: 34

PostPosted: Jan 22, 2023 1:30 AM    Post subject:

This helps a lot.

Thank you!
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