Re: EEG-SMT modding

Thanks for reply.

So, the cutoff frequency, do you know how exactly should I set the resistor
and capacitor values for 50Hz?

EEG-SMT is using ATMega16, so 8 channels shouldn't be problem, but I'm
worried about the firmware capabilities and I think, that it allows only up
to 6 channels. So I need to check this thoroughly.

About the INA129, it is better, when I checked the datasheets, it is
cheaper and better, but the inner resistor values are different, so I'm not
sure if I shouldn't change some resistors or capacitors around it. Do you
have any idea how can I check it?

On 23 Jul 2017 6:57 p.m., "Greg Feneis" <[email protected]> wrote:

>
> ​See reply inline below​
>
>
>
>
>
> Kind regards,
>
> Greg Feneis
>
>
>
>
>
> On Sun, Jul 23, 2017 at 4:32 AM, Damián Filo <[email protected]> wrote:
>
>> Hello, I am building my own modded EEG SMT, and I noticed, that there and
>> also in original OpenEEG is "3rd order Besselworth filter" with  Fc=59Hz. I
>> am not sure what Fc stands for, but if it is something like cut-off
>> frequency, it won't filter 50Hz electrical hum in europe. Shouldn't it be
>> then set to 49 Hz, or something like that?
>>
> ​Yes, either cutoff or corner frequency or some such.  It's a low-pass
> filter that attempts to block frequencies higher than 59Hz.  You can tune
> the filter to suite your particular needs.  Keep in mind that some EEG
> signals are near 50Hz.  As you lower the cutoff frequency to reject power
> line noise, you also begin to reject EEG signals.  This is not a problem if
> you are only interested in lower frequency EEG signals.  ​
>
>
>>
>> I am making my own version of EEG-SMT mainly because of being able to
>> make the PCB at school conditions (It's a school project) and also usage of
>> lower cost newer parts like INA129 instead of INA114, different 3,5"
>> jacks... Also I'm making it scalable, so it would be possible to connect
>> extension module through 14pin idc connector (up to 8 channels would be
>> then possible). It would be also possible to connect bluetooth module
>> instead of USB/UART and the power would be supplied through microUSB
>> connector.
>>
> ​Regarding 8 analog channels into a single microcontroller's ADC, there is
> likely a limit to the number of analog channels you can successfully record
> simultaneously with the original processor.  I don't know what that is.  As
> you may know, each conversion of a channel's analog sample takes some
> time.  Add to that, changing analog channels input to the ADC, add to that
> time required for the microprocessor to fetch the conversion from the ADC
> and save it or send it somewhere.​
>
>
>>
>> I'd be glad to send schematics and PCB design in Eagle to anyone who
>> would ask for it. Now (23.7.2017) I'm at 60%.
>>
>> Also I have one more question, will there be a problem when I use INA129
>> instead of INA114? I've noticed, that INA129 creates less noise and is
>> almost the same as 114 and it is cheaper.
>>
> ​Please review the datasheets of both parts and use the part with better
> specifications, even if it is more expensive.  Unless the cost difference
> is extreme, I would only be concerned with lowering cost if I were going to
> go into production for sale.  In that case, I would get the system working
> exactly as shown in the schematic first, then I would experiment with
> tuning and changing parts to suite my needs.  ​
>
>
>>
>> Thanks for replies.
>> --
>> Damián Filo
>>
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