Others > Biofeedback - EEG, ECG, EKG

Noise only on the first channel of the SMT?

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Kris:
Hello everyone, I get a lot of noise (50hz I think) on the channel 1, and ONLY on the first channel (it's not related to the electrodes, when I permute the 2 channels I get the same result).

I tried to plug the SMT on a laptop, disconnected every electrical device around . The only way I found to get rid of that noise and get a crisp wave is touching with my finger the ground part of the USB plug of the SMT.




What is the cause? CheapUSB cable? bad connection somewhere? faulty SMT?

Thanks

LubOlimex:
Hello Kris,

This is the usual reading of the device when the DRL is not attached properly or not connecting properly. Make sure the DRL connects to a proper place on your body as far from the other electrodes as possible. Make sure the DRL is a passive electrode. Sometimes (especially if using gel) cleaning the electrodes with alcohol can improve the readings.

Additionally, it is possible that the DRL cable has malfunctioned.

In the original design there wasn't DRL electrode and users were supposed to touch the GND part to get a clear graph (like you did with the GND of the USB).

Best regards,
Lub/OLIMEX

Kris:
Thanks for your quick support  :D

I tried to clean the electrodes, tried different electrodes (olimex and DIY electrode, passive of course), different places on the body, gel, no gel and I get the same result:



but why only on one channel? that's odd


LubOlimex:
Hey Kris,

What kind of electrodes you use for the two channels? Active ones or passive ones, Olimex-made or made by others?

May I also ask you to make an EKG reading instead of EEG this time and again post the pictures? First take a screenshot of the readings of channel one then a screenshot of the readings of channel two. Place the electrodes on both hands (in front of the elbow area) and the DRL on your right leg.

Regards,
Lub/OLIMEX

Kris:
I've re-done an EEG reading with a set of active electrodes and I don't get that noise with them, this means that the other set of passive electrodes is the cause, sorry  :-X.

Could you help me finding what's wrong with my passive electrodes ? (the Olimex active electrodes are nice but not easily usable on every location on the scalp).

They are made of an AgCl electrode, a shielded coaxial cable and a 3.5 stereo jack

electrode side: "hot" wire is connected to the electrode (not in contact with the shield)
jack side: "hot" wire is connected to the middle ring of the jack and the shield to the ground (largest pin), the tip (5v?) is not used


thanks again for your quick support  :)

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