EEG-SMT noise

Started by Shizof, February 12, 2013, 11:43:23 pm

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Shizof

Hi, I just bought EEG-SMT, 4 active and 1 passive electrodes. I tried OpenVibe, Brainbay and ElectricGuru but in every program, I get constant noise from both channels, when I disconnect them, the noise goes away, I took a screenshot with only passive and channel 1 + and - electrodes connected. Note that electrodes are not touching me, they are just hanging far away from each other, which I think should not give any readings.



If I put the passive one on my ear and ch1+ and ch1- to my forehead, it's almost the same except some gaps between. What should I do, this is not supposed to be like this right?

LubOlimex

Hello Shizof,

This is abnormal reading, and probably is caused either by a hardware fault or by dust/leftover soldering flux. Now, the question is whether the problem is in the EEG-SMT or in the active electrodes.

Please, tell me what the device shows if the electrodes are disconnected. If it does show the same with no electrodes connected then the problem is in the EEG-SMT and the board would probably need cleaning. If it shows a straight line then the problem is in the electrodes most probably.

Best regards,
Lub/OLIMEX
Technical support and documentation manager at Olimex

Shizof

Hi, in the screenshot channel 2 electrodes are disconnected and as you can see it gives straight line, this happens the same with channel 1, if I disconnect all of them, it gives straight line in all programs.

Last night as I was struggling to get good reading I connected a long f-m usb cable and got the device away from my computer. During that time the electrodes were attached and when I was standing in the middle of the room, I was watching computer monitor from afar, both channels gave straight lines for a while, and I thought that was it, but when I hang them on a chair, they started to give me these noisy readings again, and when I hold them again standing, they kept giving me noisy, so I disconnected channel 2 and took this screenshot for you.

LubOlimex

Please ensure the electrodes are fully inserted in EEG-SMT. Ensure that the DRL electrode (the passive one) has a good contact (maybe hold it in hand).

Can you also try cleaning the contact area of the electrodes with some alcohol? Also how did you place the electrodes in the situation shown in the manual? Is it possible to do testing rotating the active electrodes?

Tell me how it goes.

Best regards,
Lub/OLIMEX
Technical support and documentation manager at Olimex

Shizof

Ok I'll try again this evening, and buy alcohol on the way home. As far as I know the jacks were fully inserted.

First time I tried, I put the passive one on my left earlobe and attached it tight with a rubber band. Then I attached ch1+ to FP1 and ch1- to FP2. ch2+ to F7 and ch2- to F8. But all I got was this amazingly noisy readings (in openvibe it gave pure black readings until I rescaled the window to see that it is constant noise).

Then I detached them one by one and the noise continued until I disconnected the electrodes on that channel. Then I realized there is constant noise.

Rotating the electrodes might be the answer to irregular readings, but currently it gives me constant noise even if I don't attach them on me or make them only touch thin air. I read the forum topics and made a search on internet to find a solution, but I couldn't solve it.

I did try to hold the passive electrode on my hand to eliminate the noise but that didn't work either.

LubOlimex

Hey Shizof,

By rotating I meant what happens if you switch the places of the active electrodes (use different electrode for different +/- hole)? Does the readings change? Does this show on channel 2 also ?

Best regards,
Lub/OLIMEX
Technical support and documentation manager at Olimex

Shizof

Yes, I actually tried that when I was browsing this forum for answers too, but both channels are giving the same noise so I don't think there is a problem with electrode sockets. I'll post extensive screenshots with different setups tonight.

Shizof

Ok. I took a lot of screenshots. After cleaning the electrodes, nothing changed, I tried using ch1+ and ch2+ etc. combinations and there is definitely nothing wrong with channels. if i plug something on ch2 it is showing on channel 2. As somebody said somewhere on this forum, touching the usb port helps for a while but after 3-4 seconds max, it gives the same noisy readings.


Here are the screenshots:

Both channels plugged, not touching usb metal:


Only channel 1 is plugged, touching usb metal:


But after 3-4 seconds, the reading goes bad again:


Only channel 2 is plugged, touching usb metal:


But after 3-4 seconds, the reading goes bad again:


Both channels plugged, touching usb metal:


Not all touchs are good:



Ok, what do you suggest I should do? I got my first close to real readings from this device but only for 2 seconds, and now I can't even get them again.


LubOlimex

Hey Shizof,

Please return the device for a repair. If you have purchased directly from us e-mail the details mentioned in the Warranty Policy quoted below to info@olimex.com. Please make sure to include a link to this forum post and write also your forum name (just to avoid confusion about the problem).

QuoteWarranty and returns:

Our boards have lifetime warranty against manufacturing defects and components.

During the development work it is not unlikely that you can burn your programmer or development board. This is normal, we also do development work and we had damaged a lot of programmers and a lot of boards during our daily job so we know how it works. If our board/programmer has worked fine then stopped, please check if you didn't apply over voltage by mistake, or shorted something in your target board where the programmer was connected etc. Sometimes boards may be damaged by ESD shock voltage or if you spill coffee on them during your work when they are powered.


Please note that the warranty does not cover problems caused by improper use, short-circuiting, over-voltages, ESD shock etc.

If the board have warranty label it should be not broken. Broken labels void the warranty, same apply on boards with intervention by customer like additional components soldered or removed components, such boards will be not subject of our warranty.

If you are positive that the problem is due to manufacturing defect or component you can return the board back to us for inspection. When we receive the board we will check and if the problem is by us we will repair/replace free of charge, otherwise we can quote on the repair cost.

Note that all shipping back and forth is to be covered by the customer.

Before you ship anything back you need to ask for RMA.

When you ship back please attach to it your shipping address, phone, e-mail, RMA# and a brief description of the problem. All boards should be sent back in antistatic package and should be well-packed to prevent damage during transportation.


If you bought it from a distributor they should replace it.

Best regards,
Lub/OLIMEX
Technical support and documentation manager at Olimex

Shizof

February 14, 2013, 08:49:50 am #9 Last Edit: February 14, 2013, 08:53:43 am by Shizof
Ok. I bought it from your Turkey distributor: www.embeddedtrading.com

Do you think I should send them the electrodes too? Or just the device?

LubOlimex

Just the EEG-SMT. Electrodes seems to work correct. As I said the problem is not major it seems as excessive soldering flux was left after washing(the board seems to work correct but in specific conditions if flux is left after washing the boards it acts as conductor and might compromise the connections), but I don't want you to repair a brand-new device yourself.

Regards,
Lub/OLIMEX
Technical support and documentation manager at Olimex

gustux

Hi Lub,

I think i have the exact problem as Shizof.

I tried with 3 sets of electrodes, 2 AE and 1 PE.

In my case it differs of that is being run on a WinXP VirtualBox PC, because of the programming environment. That could be a problem?

And it does the same as with Shizof, but sometimes it works and sometimes not, like in the pictures shown below:

https://www.dropbox.com/s/qjcijcxzust7gl7/2013-02-18%2018.41.15.jpg [AE with conductive paste]

https://www.dropbox.com/s/ptyhwddoh4vopoo/2013-04-04%2008.55.07.jpg [CH1 no connection, CH2 FP1-T3 working fine]

https://www.dropbox.com/s/dwnqe02cxipomva/2013-04-04%2009.10.10.jpg [Headband showing the AE positions]

https://www.dropbox.com/s/mxdcnnzqf9c5gc4/2013-04-04%2009.07.20.jpg [CH1 with noise, same problem as with Shizof, CH2 noisy but working]

I really would like this system to work on the first try, becase i had a really bad time on my final work presentation, the EEG-SMT didnt worked at all!

Can you help me with this?

I tried using a metal case for the EEG-SMT, changed to KY Lub for the electrodes, cleaned the skin/electrodes with alcohol, even shaved my head in the FP1/2 and T3/4, and nothing seemed to work.

Thank you,

Gustavo



LubOlimex

Hi Gustavo,

1. Where did you place the passive DRL electrode?
2. Was the device working in the beginning?
3. Can you place the DRL on the right ear?
4. Is it possible to make an EKG reading instead of EEG just to check if there is a hardware problem with the device? First test one channel then the other place one electrode on infront left elbow the other infront of right elbow and the DRL either hold in hand or on the right leg.
5. Try to clean the electrodes.
6. Sometimes dust and mechanical particles (sand, etc) get in the box of the device and might deteriorate the signal; might need a cleaning with a soft cloth and some alcohol. Though I don't recommend opening the device since that might compromise the warranty. However, if you are tight on schedule...

Best regards,
Lub/OLIMEX
Technical support and documentation manager at Olimex

gustux

Hi Lub,

Those are my answers:

1. Where did you place the passive DRL electrode?
to my wrist, im using an antistatic band instead of the PE from Olimex (as in the picture below), i might say it worked fine in previous tests


2. Was the device working in the beginning?
yes, it worked fine, using 4 AE and my DRL wrist band

3. Can you place the DRL on the right ear?
yes, i tried that and nothing (i also tried using an Olimex PE, instead of my wrist band)

4. Is it possible to make an EKG reading instead of EEG just to check if there is a hardware problem with the device? First test one channel then the other place one electrode on infront left elbow the other infront of right elbow and the DRL either hold in hand or on the right leg.
i will try it tonight

5. Try to clean the electrodes.
everytime im cleaning them with alcohol, to remove the conductive paste used in the previous session

6. Sometimes dust and mechanical particles (sand, etc) get in the box of the device and might deteriorate the signal; might need a cleaning with a soft cloth and some alcohol. Though I don't recommend opening the device since that might compromise the warranty. However, if you are tight on schedule...
can i use a contact cleaner, compressed air or dust remover spray can?


I was testing it today and i got nothing while using the 4 AE, but then i tried changing the CH2 AE electrodes to PE, leaving the AE in CH1 connected to the EEG-SMT but NOT on my scalp, it worked on Electric Guru showing me a small amplitude signal, i could see the muscular movements generated from my eyes, eyebrows and masseter muscle.

I then changed the same PA to the other channel (CH1) and again the signal disrupted like in this picture:
https://www.dropbox.com/s/wyqiqjzjop9ngpm/Error_AE_Grupo1.jpg

Then when i disconnected all electrodes from the EEG-SMT, i got this noise only in CH1:
https://www.dropbox.com/s/vws95ahcwvbdfpr/sin%20conexion.jpg

Thank you for all the help,

Gustavo


gustux

Hi Lub,

I was trying again the EEG-SMT using only one channel (CH1) and 2 PE, and it worked fine! but... some minutes later, 10 minutes i think, it started to catch noise and as i read here i gave a try by touching the USB case, and yep, the signal quality got better:



Regards,

Gustavo