EEG-SMT test protocol?

[blackcoat]

Hi All,

I have just purchased the EEG-SMT with four active electrodes and one passive electrode, but I am failing to get any sensible results. Can you point me to a test protocol (if possible including all settings) that I can run through to make sure the device and the electrodes are behaving properly?

Also, I am not quite sure I am successfully identifying the active vs the passive electrodes. Can someone give me a hint there?

Cheers,
Rob

[LubOlimex]

Hey Rob,

The passive electrode lacks any electronic elements on the back of the contact plate. The active ones have more "parts" on the same back side.

A good explanation on how to use and test the EEG-SMT starts on page 7 of the user's manual: https://www.olimex.com/Products/EEG/OpenEEG/EEG-SMT/resources/EEG-SMT.pdf.

Few pointers: make sure DRL is passive electrode; make sure you hold this DRL electrode firmly in your hand; make sure to start with only 1 channel (2 active electrodes) connected to channel 1 for example, before using 2 channels (4 active electrodes) simultaneously; start with ElecGuru software since it is simpler to use

It is impossible to perform the full routine of test procedures at home since this requires:

1. to open the case which would break the warranty seal
2. additional AVR programmer
3. custom-made hardware for testing each pin

Best regards,
Lub/OLIMEX

[blackcoat]

Hi Lub,

Thank you for your response. I have done all the installing, connecting as per manual, but I think there is something wrong with my device. I'll show a couple of screenshots to demonstrated.

All screenshots are captured after approx 20 seconds of equilibration, during which the signal often fluctuates wildly to start but then settles.

1. EEG-SMT, with no electrodes attached.


2. Only channel 1 and DRL electrodes connected to device, but not attached to my head.


3. Same as (2), but now attached to my head.


4. Only channel 2 and DRL electrodes connected to device. No difference of attached to my head or not.


To me there seems to be something wrong with the device. I cannot say yet if there is anything wrong with the electrodes yet.

Kind regards,
Rob

[LubOlimex]

Hey Rob,

Let's speak about the second picture where you say "2. Only channel 1 and DRL electrodes connected to device, but not attached to my head.".

You should have two electrodes connected to CH1+ and CH1- and they are situated symmetrically on your head (preferably over the temples, at the forehead sides). Also you should have a passive electrode connected to DRL and you should hold it firmly in your hand. Was that so when you took the screenshot?

Can you do exactly the above setup with the same electrodes for channel two (CH2+ and CH2-) and again post the screenshot?

Ideally, if you stay calm with everything installed as mentioned above and not moving your head (just looking at the screen) you should see a relatively flat line and then if you roll your eyes right or left you should see peaks.

Tell me if this happens and whether it happens on one of the channel or both.

Best regards,
Lub/OLIMEX

[blackcoat]

Hi Lub,

Those were the conditions of images 3 and 4, exactly as you described.

To be precise, referring to the images in the previous post:
1: no electrodes connected.
2: one electrode connected to CH1-, one to CH1+, one to DRL, electrodes hanging over desk.
3: one electrode connected to CH1-, one to CH1+, one to DRL, electrodes attached to my head, above temples, in calm state.
4: one electrode connected to CH2-, one to CH2+, one to DRL (electrodes on head or not, no difference.)

Cheers,
Rob

[LubOlimex]

Hello Rob,

Unfortunately, if you do as described (and the DRL is a passive electrode and makes a good contact) and you receive such readings, and you have cycled the active electrodes (to ensure it is no electrode issue), this indicates one of two hardware problems:

1. The board wasn't properly washed and it has soldering residue left over. It might have gotten dust or other hard particles which cause signal issues.
2. The board's electrode connectors (audio jacks) got damaged this might be due to weak solder or improper transportation handling

If you have purchased the board directly from our web shop I advise you to write an e-mail to support@olimex.com that contains a link this forum thread (and copy-paste conclusion) so we can formally accept the return. Warranty conditions might be found here: https://www.olimex.com/wiki/GTC#Warranty.

If you have purchased the board from a retailer or official distributor please contact that person/company for the warranty.

Best regards,
Lub/OLIMEX