start and pause codes

schmidtjoseph · Post by **schmidtjoseph** » Wed Sep 08, 2010 5:32 pm

Hello,
I am trying to run an experiment that will integrate eye tracking and eeg. I am currently using SR research experiment builder to send TTL pulses to the eeg at specific events. The codes are being recognized properly, however I am having a problem getting the equipment to properly start and pause. I can manually do this but I would like to have this be a more automatic process that starts at the beginning of each trial and pauses at the end of each trial to minimize the file size and for ease of data analysis. Our configuration file is set to start with an 254 code and pause with a 255 code. It would appear that actiview sees the 254/255 codes (it shows it in the window) but it does not trigger the recording to start or pause. Does the pulse need to be of a specific length or are there any other parameters that I need to set to trigger this properly? Any help / ideas why this might not be working would be greatly appreciated. Thanks.
Joe

Post by **Coen** » Thu Sep 09, 2010 11:15 am

The pulse need to be longer than one sample period (e.g. > 0.5 millisecond on 2 kHz sample rate). The triggers should be visible with the correct code in the trigger display (monopolar tabpage, use decimal display mode for the triggers).

Best regards, Coen (BioSemi)

schmidtjoseph · Post by **schmidtjoseph** » Thu Sep 09, 2010 2:48 pm

Hello,
Thanks for your reply. Currently I am sending a 20ms pulse and we do see the correct code (according to the configuration file) in the trigger display page, however it does not start the recording. From your reply it was a little unclear, should the pulse be 1 sample or can it just be as short as 1 sample (longer should work equally well)? Any idea what could be the problem? Thanks again for all the help.

Post by **Coen** » Thu Sep 09, 2010 5:20 pm

The pulse should be at least 1 sample period, longer than that is no problem. So, your 20 ms pulses are fine. Anyway, if there is a problem with the pulse length, then this is reflected by the displayed triggers. So, if you see the numbers 254 and 255 at the proper moments, then all is well.

Please note that the the triggers only control the release and press of the PAUSE control. You have to push the START FILE button first, and enter the BDF file information. ActiView will then start, with the saving paused, waiting for either a manual or trigger input to release the pause button and start streaming to disk.

Best regards, Coen (BioSemi)