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Two sources at the same time

Posted: 11 Oct 2011, 08:02
by bcip3

I am interested in using two amplifiers at the same time (EEG signals from two different cards provided by the same subject) because they only have 16 channels and I would need 32 channels. Would it be possible?

Signal source: NIDAQ_mx_Source.exe

Thanks in advance.

Re: Two sources at the same time

Posted: 11 Oct 2011, 11:41
by mellinger

this is not possible with the current version of the NIDAQ source module.

Provided that two NI boards can be hardware-synchronized, and provided that the NIDAQ-MX API allows acquisition from from more than one board at a time, the required modification to the code might be relatively straightforward, and would be a welcome addition to the NIDAQ source module, so you might give it a try.


Re: Two sources at the same time

Posted: 13 Oct 2011, 04:23
by bcip3
Hi Juergen,

Thanks for your response. I will have a look to it in order to update NIDAQ source module functionality. We are thinking in purchasing a new NI board with 32 channels for future experiments.


Re: Two sources at the same time

Posted: 13 Oct 2011, 07:15
by gschalk

If you would like to expand the functionality of the NI module such that it supports acquisition from more than one device, you need to think about synchronization. Unless you somehow synchronize the data acquisition clock in both boards, they will simply sample signals at different times. Even if you are then able to pick up data from both boards, and put them in one BCI2000 signal, the data will not be very useful. What you would need to do is to synchronize the boards in hardware. E.g., set one board to produce a counter, wire the lowest bit of the counter to the A/D clock input of each board, set each board to use that external A/D clock input rather than the internally generated clock, and then acquire and merge data from both devices. This is done in the DTADC Source Module, which supports two boards. You would also then need to check whether the boards only have one sample-and-hold for all channels, or one for each channel. Then, you would need to change the AlignSamples (or so) parameter, which sets whether or how samples from different channels are aligned in time, accordingly.


Re: Two sources at the same time

Posted: 03 Nov 2011, 08:40
by bcip3
Hi Schalk,

Thanks for the details. We have decided to purchase a new digital amplifier with 32 channels, therefore, the idea of increasing the functionability of NIDAQ source module is stopped.