Additional Trigger Question

[MalloryHall]

Is there a way to send triggers to be incorporated into the .bdf file by using something like function keys? We were looking into a way to document closed eyes vs open eyes for resting EEG, among other things. We were also wondering if there is a way if it would work while tasks are sending triggers via the reciever.

[Coen]

On ActiView 5.14 and higher, the function keys F1-F8 are by standard coupled to trigger lines 9-16. A key press makes the respective trigger line high. Make sure that the trigger inputs 9-16 are pulled low at the trigger port of the USB receiver (by connecting pin 9-16 to pin 37). If trigger inputs 9-16 are left unconnected, they will be constantly high due pull up resistors in the USB receiver (and the function key presses are not recorded).

Best regards, Coen (BioSemi)

[max]

Dear Coen,

I'm sorry, but after reading lots of forum entrys and the relevant webpages on your website I still do not understand how it is realisable to send external triggers and function key triggers simultaneously.


[quote="Coen"]Make sure that the trigger inputs 9-16 are pulled low at the trigger port of the USB receiver (by connecting pin 9-16 to pin 37). If trigger inputs 9-16 are left unconnected, they will be constantly high due pull up resistors in the USB receiver (and the function key presses are not recorded).[/quote]

How can I connect pin 9-16 to pin 37? By soldering? How do I know which pin on my trigger cable refers to which number?

Seems like I'm the only one not understanding, as no one else asked.

Thanks in advance

[Coen]

The connection of pin 9-16 to pin 37 is indeed done by soldering a short wire. The pin layout can for example be found on http://pinouts.ru/connector/37_pin_D-SU ... ctor.shtml (pin 1 is also seen inside the connector).

Best regards, Coen (BioSemi)

[max]

Dear Coen

I did some test measurements do learn more about the triggers, and I noticed the following:

First of all it is possible to send external triggers and function key triggers simultaneously without soldering. I always tried the function keys without the trigger cable connected - and then it wasn't working - or with the trigger cable connected to the computer on which ActiView is running - then it was working fine. So I wondered how I'm able to connect an external computer for stimulus presentation at the same time.

But the function key triggers work perfectly with the trigger cable connected to the USB-receiver and the other end unconnected to anything. So I tried the function keys with the trigger cable connected to an extra computer sending external triggers and it was als working perfectly fine (Don't know, why I never tried this before)
However, sending internat and external triggers works without soldering.

The other thing I noticed was a strange behavior of the trigger within the first second of every saved measurement. The trigger value starts with a rather “high” value of maybe -6356990 and then falls down by 2^16 (65536) integers to -6422526 (in this case). This happens in every measurement, even if no trigger cable is connected at all. The exact time of the drop always differs but each time it happens within the first second. The same happens when restarting the saving after it has been paused. Can you give me any explanation for this phenomenon? I could't find any on your websites or in the forum.

Thanks a lot.

[Coen]

The trigger cables as currently delivered by BioSemi already have triggers 9-16 grounded (connected to pin 37). This is not true for our older cables (delivered before 2007), were triggers 9-16 are floating (and pulled high by the pull-ups in the receiver).

The change of the 24-bit value in the first second after start or resume after pause is caused by the "start epoch" bit (bit 16, see http://www.biosemi.com/faq/trigger_signals.htm). In your review software, you should separate the trigger bits (bits 0-15) from the system status bits (bits 16-23).

Best regards, Coen (BioSemi)

[max]

Thanks for these answers