Re: EEG-SMT

Hi Alexandre,

No worries. If you want some more insurance if the device is working
properly then you could do the "CAL_GND" test. Look it up in the list and
here: http://openeeg.sourceforge.net/doc/modeeg/modeeg_building.html. It's
a test built into the device whereby a squarwave signal gets looped with
the electrode inputs and then should be seen on the electricguru screen.
It's used for trimming the device by Olimex (or other builder). I believe
it's possible with the smt kit also because I saw the CAL signal output one
time when I opened the housing. You will have to make a little cable to do
the test though. Another more simple test is the DRL test: Short all the
electrodes to the DRL and that should render a "flat" line on both
channels. I'm not an electrical engineer so I don't know if positive
results on the test cancel out the possibility that the device isn't
working properly but it should at least give you some extra reinsurance.
Also I think you shouldn't have to filter out the mains hum completely. A
good indicator of good electrode connections is a low amplitude of the
mains hum frequency in a spectrum graph. So when it's too high you know
something is up.

Kind Regards,

Niels

On Tue, May 28, 2013 at 8:30 AM, Alexandre Dubreucq <
[email protected]> wrote:

> Hi niels,
>
> Thanks for your answer, actually it helps (comforts?) a lot, I'll try this
> right away.
> I had noticed the problem of interferences caused by AC but this should
> not be a problem using a filter on frequencies lower than 50Hz as shown at
> http://bakerdh.wordpress.com/2013/01/31/a-first-look-at-the-olimex-eeg-smt/
> .
>
> Thanks again
> Le 28 mai 2013 01:10, "Niels Samuels" <[email protected]> a écrit :
>
> Hi Alexandre,
>>
>> I've managed to get a good signal with the device but only with all four
>> (if using both channels) of the active electrodes on the forehead using a
>> "fairly tight" headband and holding the DRL in my hand or stuck under the
>> headband as well. Also I can only work with the device using a laptop
>> running on the battery (no mains) and using a high quality usb cable. I'm
>> then able to obtain a signal with fairly low mains interference.
>>
>> Hope this helps.
>>
>> Kind Regards,
>>
>> Niels
>>
>> On Mon, May 27, 2013 at 9:27 PM, Alexandre Dubreucq <
>> [email protected]> wrote:
>>
>>> Hello everyone,
>>>
>>> I got myself a OLIMEX EEG-SMT device, and i can't get it to work
>>> properly : the signal is very messy, and if i take off one electrode,
>>> nothing changes on the signal in the software (using brain bay or
>>> elecguru for example).
>>>
>>> Has someone already managed to have some results using OLIMEX EEG-SMT
>>> ? If yes, how did u fix the electrodes on your head ?
>>>
>>> Thanks
>>>
>>>
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