Re: Arduino development possibility

On Fri, Apr 12, 2013 at 12:13 PM, Aaron Silber <[email protected]> wrote:

> Chuck,
>
> Thanks for your input. Sorry about the multiple send. I'm going to stop
> using Thunderbird.
>
and I didn't get them.  Did you have some other remarks that weren't in
this email?

It's a little embarrassing. So, apologies to everyone who I just
> irrevocably sent several duplicate posts.
>
> You make some good points about the sampling rate for EEG. I forget I'm
> not building a logic analyzer here :P
>
> Best,
> Aaron
>
I love good design problems--and it's always good to define the problem
well from the beginning.  If you had a lot of adc's chained together over
SPI, you might be able to get large numbers of channels on a
microcontroller.  At low enough frequencies, you'd be able to have them all
communicating serially over a relatively small number of pins.

It's clear that it won't scale ideally.  It might be a valuable exercise to
see how many channels you can scale up to with an arduino (whose
programming is much less labor intensive than with FPGAs)





> On Apr 12, 2013 12:58 PM, "Charles Z Henry" <[email protected]> wrote:
>
>> Hi Aaron
>>
>> I also wanted to talk about things that aren't easy, for a few minutes
>> here :)
>>
>> I have been looking at FPGA programming for building a open source sound
>> card architecture that scales to large numbers of channels ( a similar
>> problem to recording EEG signals).
>>
>> At first, I was thinking of using the FPGA to talk to ADC's over SPI or
>> I2C... However, this approach has a definite cost (and intellectual
>> property) drawback.  I now think that a better idea is to build sigma-delta
>> ADC arrays on an FPGA itself.
>>
>> At very low sampling frequencies (as in EEG recording), you can build a
>> 1st-order or 2nd-order converter with low-enough noise.
>> THAT kind of hardware project could get you to 192 channels without being
>> prohibitively expensive.
>>
>> I'm just getting started reading for the adc designs (and who knows if
>> I'll ever get it off the ground), but I'd be glad to have your thoughts on
>> it.
>>
>> Chuck
>>
>>
>> On Fri, Apr 12, 2013 at 7:59 AM, Aaron Silber <[email protected]>wrote:
>>
>>>  Welcome to the OpenEEG list. I apologize that I cannot read or
>>> pronounce your name, as I only speak English.
>>>
>>> You're very right when you acknowledge that it won't be easy :) The
>>> "typical" Arduino (ATMega8/168/322) only has less than 30 total GPIO pins,
>>> closer to 20. Processing the 4 or so channels we have is difficult enough
>>> to perform analog/digital conversions and all the serial communications in
>>> real time. An ATMega168 is only rated to 20MHz, after all (and often gets
>>> run at 16MHz).
>>>
>>> 192 electrodes! That's a whole lot of electrodes, a whole lot of paste,
>>> and a whole lot of data. I guess if you need that many then you really need
>>> that many.
>>>
>>> So, I think that working on modifying the modularEEG design to
>>> accommodate that many inputs would need in some regards a complete
>>> reworking. There are some good parts of the project such as the way DRL and
>>> active probes are handled that can be used to your advantage. They have
>>> already been designed and tweaked, so I would imagine it better to not
>>> "reinvent the wheel" there.
>>>
>>> A faster processor and enough I/O are two requirements. You will not
>>> necessarily need 192 GPIO as this can be very expensive to find in a
>>> microcontroller - utilizing discrete circuitry such as dedicated ADC's and
>>> multiplexers can reduce this number greatly. Atmel, manufacturer of the
>>> ATMega line, also makes other processors all the way up through FPGA's. The
>>> ARM architecture is also a possible route. The Cortex series can achieve
>>> good speeds and versatility at good prices. Think of mobile devices and how
>>> much power they can get with relatively little expense.
>>>
>>> I wish you good luck! Keep in touch.
>>>
>>> -Aaron
>>>
>>>
>>> On 04/12/2013 07:20 AM, ΓΛΥΚΑΣ, ΣΩΤΗΡΙΟΣ wrote:
>>>
>>> Hello to everyone and I hope I'm in the right place.
>>> I'm thinking of expanding the current openEEG capabilities to be able to
>>> be used for lab purposes, professional use etc. for a project at my
>>> university. I was thinking of 192 electrodes with enough analog arduino
>>> inputs and a usb or serial exit to PC with all the data needed by the
>>> currently existing openEEG software.
>>> I know it won't be easy but I'm willing to study, work and learn.
>>> I'll probably have to build my own arduino board, I don't think that any
>>> with the specifications I need already exists.
>>> This is where you guys come in, do you think it's possible with
>>> something like this or is it not powerful enough? Should I use something
>>> else?
>>> Also, currently there are analog and digital boards, do you think it
>>> would be easier if I used 2 arduinos? One for processing the analog and one
>>> for the digital signals?
>>> Thank you in advance.
>>>
>>>
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>>
>>
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>
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