Marker mode is poorly implemented in GUI v4. Also, after discussion, it should really be named “Trigger mode” instead or something different.

http://openbci.com/forum/index.php?p=/discussion/1928/timestamps-to-sync-stimulus-and-eeg-vs-external-hardware-trigger/p1

Can you mention the source of your "stimulus marker"? Is it an external device that can output a digital / binary leading edge at the mark? That is the case where you would use the optoisola

I recommend using external trigger with the OptoIsolator solution. https://docs.openbci.com/docs/02Cyton/CytonExternal#optoisolation

If you are doing P300 / ERP, "timestamped stimulus markers" will not be sufficient accuracy. Instead the recommendation is to use what is called an external trigger signal, recorded simultan

Are you still sending external trigger digital signals from your Arduino to Cyton? (Corresponding to audio high or low tone?) I thought that used TWO of the input pins. Are you using the opto-isolator

Glad you found Irene's post. Your original question mentioned ERP / P300, which requires a precise external trigger aligned with the presented stimuli. Irene's page is oriented toward a Motor Imagery

https://openbci.com/forum/index.php?p=/discussion/2107/external-audio-triggers-oddball-paradigm-increase-sampling-frequency

Usually ERP / P300 is done with an opto isolator / external trigger, shown later on the same page. P300 needs very precise timing to do signal averaging to increase signal to noise level. Operator inp

seeing square, want to trigger one push button and seeing triangle another push button. But not sure how to connect with the board ? Is it same as using digital pin D17, D18 ?

Are you sure you want Marker Mode, or are you more looking to record an external trigger signal in one of the three Aux channels?

I still don't understand how you can be doing "post processing steps to find P300", without using a trigger and averaging.

If you don't use the signal averaging, aligned by the trigger, your P300 pulse will be subject to all the random noise that accompanies EEG. This is how (your quote) "the normal range of eeg in e

The P300 is a weak signal at the scalp, as shown in Jeremy's paper. This is why multiple trials must be averaged to improve signal to noise ratio. (Separate averages for normal and odd-ball cases.) I

(2) Well for P300 I must use trigger. My question was for confirming that I am getting the right eeg range value. Because eeg are so sensitive. For any movement sometimes peak changes. I wanted to k

How can you do P300 at all without some kind of trigger to align your recordings for averaging? Why are you not using the trigger?

N.B. my enquiries are for without external trigger. So that I could be sure that my measurements are right.

Well, actually you could do the external photo trigger on Ganglion, by sacrificing one of the 4 EEG channels, as the trigger channel. In this case you would need a 2 resistor voltage divider network t

You may be able to use an area on your (tablet?) output screen as an optical trigger source. This DOES use a hardware photo detector, but that detector is only connected to the Cyton, not to any exter

Please examine your trigger creation / detection, as to why timing differs from standard P300.