Hi! First of all I would like to stress that I am still new to Arduino, and English isn’t my first language. And if this is the wrong place to post, I apologize.
I am currently working on an exam project along with 1 group member, where we are working with the topic “Sleep and REM-stage detection”.
Theory
Since the eyes of a sleeping person in the REM stage move rapidly, the impulses sent through the muscles should be able to be picked up by electrodes on the temples.
Product
So we created a small product, using an Arduino Uno, a INA106KP differential amplifier (called “DA” from now on), 2x capacitors of 4.7 uF (In the datasheet of the DA, there were examples, where the most simple one had capacitors to regulate the power from the arduino) and 2x 500 Ohm resistances to create a voltage divider, so we can get a voltage of 2.5V on the V- pin and 5V on the V+ port. On an analog port we measure the output of the DA. See picture 1 and 2 for a very poor reference.
The problem
As of right now, we are not really sure if we have set everything up correct. The reason for this, is because no matter what we do with the electrodes (made by copper, because we wanted a reusable material), we keep getting the same signal (see picture 3).
I hope that anyone can spot potential mistakes and give some insight on what we are doing wrong.
"what is the frequency of the peaks? "
Approx 3 seconds
"is it related to heart beat or something else?"
No, because these peaks occur even when no electrodes are connected to a person, and at the same rate. The only difference between when the electrodes are on or off, is the height of the peaks.
"What are you trying to measure?"
Nerve impulses, our theory, like said in the main post, was that we would be able to see a difference in the voltage between the tempels, when we moved our eyes, due to the impulses.
My first suspicion from looking at the images is you are picking up something from the keyboard or touchpad scanning. Try moving your hardware away from there. I know they do measure eye movement with electrodes like you are doing - I have sleep apnea and have had to have several "sleep studies" where they wire you up with about 20 wires (heart rate, breathing, eye movement etc.) and then have you sleep the night away - in the morning they review the data and will show you where REM was etc. One thing you might want to check out is the gel electrodes they use for stuff like that. I suspect there is a fair amount of DSP and other filtering that goes on to get rid of ambient noise too.