Re: EEG-SMT modding

I am grateful, for you pointing the direction where I should look. That's
what I need. I didn't want exact values of components, but rather what
topics or which threads I need to research to get those values.

On 23 Jul 2017 9:03 p.m., "Greg Feneis" <[email protected]> wrote:

> This is a school project, so you will benefit most by investigating and
> studying various theories and learning how this works rather than if I just
> tell you what you need to do and you do it.
>
> I recommend you assemble the kit as specified and get it working
> correctly.  Then improve it as you see fit.  If you want to lower the
> cutoff frequency of the filter, study active filters.  There are many web
> sites about this.  Regarding substituting the instrumentation amplifier, I
> recommend using the original part and getting everything to work correctly
> first.  If you want to substitute better parts to improve the design, do so
> after you get the original working.  To help you convert to a new
> instrumentation amp. study instrumentation amplifier applications.  All of
> the analog IC manufacturers have plenty of info on this.
>
> Good luck!
>
>
>
>
>
> Kind regards,
>
> Greg Feneis
>
>  <http://www.linkedin.com/in/electromechanical>
>
>
>
>
> On Sun, Jul 23, 2017 at 11:25 AM, Damián Filo <[email protected]> wrote:
>
>> 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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>>>
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>
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