No signal from g.USBamp anymore

[dominic_reichl]

Hello everyone,

we're currently facing problems with receiving a signal in OpenVibe and running out of ideas of how to solve them.

We use OpenVibe on two different computer systems (Windows 7 and Windows 8.1) and our acquisition device is g.USBamp (drivers: g.USBamp_Driver_3.12.00_Win32 and g.USBamp_Driver_3.12.00_Win64).

For several weeks we didn’t have any problems with displaying EEG signals in OpenVibe. Last week we had a minor issue with the 16-channel g.GAMMAbox, which was fixed simply through recalibration. Since then, however, the signal display in OpenVibe looks like this:


These are our settings for the acquisition server:


Which OpenVibe scenarios we use - be it signal monitoring for motor imagery (picture above) or the simplest case of "Acquisition client" connected to "Signal display" - makes no difference either. It's also not a matter of scaling: Best Fit vs. manual scaling changes nothing. Nor does auto-calibration help.

Further indicators that something is wrong are (1) that the device drift is higher than it was on the weeks before (when we had no problems with the signal), i.e., it now fluctuates between 0 and -4ms, and (2) that whenever the button "Disconnect" is pressed in the acquisition sever, the amplifier and gammabox have to be powered off and on before reconnection, otherwise the impedance check will show 0.00k ohms for all channels.

It doesn't seem to be a hardware problem because we've tried two functioning g.GAMMAboxes, and other signal display software (g.Recorder) shows a perfectly normal signal!
However, it also doesn't seem to be a software problem because we haven't changed anything in the software since when it was still working, and after trying various solutions in vain, we reinstalled and recompiled the entire OpenVibe platform on one computer as well as the g.USBamp driver, but this made no difference either.

Do you have any further ideas for getting a proper EEG signal?

Thanks,
Dominic

[jtlindgren]

Hi Dominic, sorry to hear about your problem - these are the most difficult ones to trace, as they may depend on
the whole system configuration. We have a gusbamp/gammabox combo here and do not have this problem,
although at the moment our gtec driver seems to be 3.14.

With gusbamp, the driver bits should match the OS bits. The CAPI bits should always be 32bit though.

Guess 1

You don't mention which openvibe version you are using? In 0.18, there are some issues when gusbamp
impedance check is enabled if you press play when the check is running. What if you do the following: disable
AS impedance check. close it. turn the gusbamp off and on. restart AS with the impedance check disabled.
Do you still get zeroes when you connect+press play?

Speculation 2

I remember once our system went to a state where I couldn't get meaningful signal from the gusbamp and turning off/on
the amp didn't help - this was 'fixed' by rebooting the computer. But in our case, I think the gtec demo tool also returned
meaningless data [ a bit off topic: at home, I have an external USB audio interface which sometimes stops working on Win7,
and turning the device off and on doesn't help. In that case, rebooting the computer helps, but I narrowed it down a bit:
restarting the Windows audio service is sufficient... ]

Option 3

If all above fails, I'd start by really trying to narrow down where the issue is coming from, for example
by installing official 0.18 or earlier OpenViBE and to see if the problem is still there, and/or possibly trying
this on some new computer. If you reinstall on an old one, rename Users/you/AppData/Roaming/openvibe
folder (modified configs are there and not affected by reinstall) to something else so ov will be in default state.


Best,
Jussi

[dominic_reichl]

Thanks for your reply, Jussi!

We're using OpenVibe version 0.18.0 on both systems and yes the driver bits match the OS bits.
I'll try to update the driver, test your suggested solutions and report back on Tuesday.

Best,
Dominic

[dominic_reichl]

The problem was indeed caused by the impedance check.
At first I got again no signal, then I deactivated the impedance check, still no signal, then I rebooted the system and tried again without impedance check and everything worked perfectly fine.
Thank you so much, Jussi!

[jtlindgren]

Thanks for the confirmation! The impendance check seems to put the device to a special state, and we needed to
restore this to the proper state in the driver code again, before acquisition starts. If you're interested, you can
try our git master where this has already been fixed. We'll put it to the next release as well (due this month or the next).


Best,
Jussi