I'm trying to design an SSVEP scenario and wondering if there are any ways to cross-check if the stimulus frequency is displaying accurately on the LCD screen.
It may seem weird but this is what we did. If you have access to a P300 Speller (BCI2000 or OpenVibe) configure the standard 6x6 matrix to use 250 ms ISI. This will give you four stimulations per second. On OpenVibe you can use the standard p300 sample that comes with the installation bundle. You just put somebody to wear you cap or headset and instruct them to pay attention to all the letters. You get the signals from O1 and O2. If you extract all the epochs and average all of them you must see the four bumps. Now what you can do is to go step by step and reducing that value, lower and lower. You can repeat this all over until you have two good differentiable frequencies by counting the number of bumps on the averaged segments. 60 ms and 80 ms work good. You can bound gradually if you LCD screen refreshing works. Keep in mind that if you run this on Windows, it is not a RTOS, so you can have sometimes weird behavior with the timing. You need a faster computer btw.
Second option: pick an Arduino UNO and LDR light sensor with a couple of resistances. You can write a very easy code to get the light values continuously and transmit them to a serial connected computer. You put the sensor very close to the monitor, and program some UI application to generate the flashing at whatever frequency you want. If everything is OK you will see exact same frequency on the signal obtained from the Arduino and check if the LCD refreshing is OK (https://maker.pro/arduino/tutorial/how-to-use-an-ldr-sensor-with-arduino)
Finally, the attached paper proposed a very detailed procedure to verify exactly all the frequencies from the stimulation and to check if the synchronization is OK.
Hope it helps and good luck !
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