Re: EEG-SMT modding

And of course, I'd be really grateful for sharing the files or links with
me.

On 24 Jul 2017 12:58 a.m., "Damián Filo" <[email protected]> wrote:

> 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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