External Trigger with photodiode connected to analog pins of Cyton
Hello,
I wanted to explore the option of external triggers for visual stimuli, we show images to participants and want to have a trigger exactly when image is displayed on the monitor.
I was wondering if it would be a good idea to connect photodiode connected to analog pin of the cyton and update firmware code to check for photodiode readings and somehow put marker on data stream?
is it possible? how precise the markers would be?
Shyamal
Comments
Shyamal, hi.
Did you see the External Trigger page:
https://docs.openbci.com/Cyton/CytonExternal/
When the "board mode" is set to "Analog Board Mode" (with the corresponding GUI Widget), it will simultaneously record the external signal IN SYNC with the EEG samples.
https://www.google.com/search?as_q=photodiode+trigger&as_sitesearch=openbci.com
William
https://github.com/OpenBCI/OpenBCI_Experiment
https://openbci.com/forum/index.php?p=/discussion/3055/external-trigger-question-on-photodiode-resolved
https://openbci.com/community/measuring-stimulus-timing-with-a-photoresistor/
I think I want to do something like this, however, it will only give me the of the sensor values and simply not make a marker in the data stream itself. Later, I have to see, at which timestamp the values are significantly different than rest and then will have to put marker at that time.
Have I understood it properly?
NO
The analog sensor data stream is recorded SIMULTANEOUSLY with the data samples. EXACT synchronization. NO 'time-stamps' involved. No 'markers' needed. You just measure the two white vs black analog values, and perform a threshold (greater than or less than) test on the analog (board mode) value stream to determine where your on-screen trigger block appeared.
https://github.com/OpenBCI/OpenBCI_Experiment
William
Understood! Thank you. I'm going to give it a try!