Article on ModularEEG + alternate circuit

Hi,

Asking, What consequences can changes in circuit have on output quality.

I will be mentioning quickly about some alterations and changes in parts,
please answer to them.If you think the part of the circuit is important and
should be kept unaltered please mark it as NA.

Developers please skip to *Questions>>*
Moderators please stay with me.

*Questions to Moderators of openEEG*
*
*

> I will be writing in the article about openEEG community and I would like
> to know from moderators that can we publish and use content given on
> openEEG website.
> Content which I will be utilizing is as follows :
>
>    - Design Documentation
>
>
>    - Building Guide
>
>
>    - Testing Tips
>
> Our magazine is associated with a community of DIYers and they would like
> to know more about moderators of modularEEG and openEEG. I agree that this
> is a collaborative project but it all starts some where.
> If the moderators can reply with their names and current salutation it
> will be really helpful.


*Questions to Developers*

I am a Technical Editor at a publishing house and my aim of making the
> prototype is to make a cheaper version using IC and other components which
> are commonly available in an average electronic market.
> I have started building a prototype of Modular EEG.But some of the
> components are hard to found and I began to look out for alternate parts.
> I am also writing my understanding of the purpose of device.Please append
> it If you think it doesn't looks correct.
>
> *Design Modification Questions**
> **1) Changing DC-DC converter.**
> **Function
> *DC-DC converter is an important part of the design.It separates noise
> from supply section and provides an isolated ground to Digital Circuit.
> *Question
> **If we power with a 12 v battery and use a laptop to monitor the output
> will the isolation be still required ?*
> (PS:There is a lot of noise coming from PC-SMPS to COM port if we don't
> use opto-isolators and use PC instead of laptop.)
> *Possible Solutions :
> *Currently the main source of noise appears to be Serial Cable and other
> devices (SMPS , UPS etc..) connected to same wall socket. The main headache
> is to provide an isolated supply and GND to MAX232.
> Can we do it by using a separate battery for MAX232E supply.
> 5V for MAX232E. (ESD Protected)
> 12V for digital circuit.*
> **In the above configuration if we use MAX232(E) instead of MAX232 will
> we still need Opto isolators ?*
> *If we use separate battery will the noise from PC-smps be removed ?*
> It appears that the ground will be still common between MAX232-PC-Digital
> Circuit.Only the supply side will be separate. But really is there no
> other way of doing this without TMV0505 and two opto isolators.
> 2) *Changing Op-amps on Analog Board.*
> What other Op-amps can we use Instead of TLC-277 P.
> a)MCP607
> b)TLO62
> what other options can we look into ?
> With TLO62 we are getting 2.4 volts instead of 2V on IC205A 1st pin on
> analog board, Is this bad ?
> 3) *Debugging Circuit**
> *If I do not use the third filter on digital board,I see a 14 Hz square
> wave (2V) with a signal riding on positive side of the pulse. The amplitude
> of the signal varies If we control P202 (8.2K POT).
> Is this a good sign , What wrong do you see here?
> Because If I connect the filter circuit ( 7.5 K and 220 nf) between Analog
> board and ADC points there is no signal output.
> For me this is definitely a bad sign,but I would to know from others ?
> 4) *Connecting the Calibration Signal**
> *I get the 14 Hz wave (0-4V), which is connected to U_cal through two
> 1Meg resistors and one 10K resistor.
> I can see some signal between the two resistors, but there is nothing but
> noise after the 10K resistance which is connected to U_cal.
> *Questions *
> Where should the calibration signal be seen , Should it be seen on the
> positive side of the pulse output before the Bessel Worth filter on digital
> board ?
>
> If that is correct, Either the noise is too much on my board or something
> else is wrong. I have checked all the following test points,and only on IC205 pin 1 I find +2.4V instead of 2V which might be because I am using
> TLO62.

 Checkpoint Voltage

 VGND +2V

 IC201 pin 1 +2V

 IC202 pin 6 +2V

 IC203 pin 6 +2V

 IC205 pin 1 +2V

 IC205 pin 7 +2V

 IC206 pin 1 +2V

 IC206 pin 7 +2V

 pad204 +2V

 pad203 +2V



Kindly answer to the questions because I think other diyers who are short
of components might want to know about these problems.

Whoa I have written a long email , lets see who all sees it to the end :)


Thanks and Regards,
-- 
Divyansh Gupta
*--*
*
*
*Academy Of Embedded Technology*
Website : www.aet-embedtech.com
Skype : gupta.divyansh
gmail: divyu.gups

------------------------------------------------------------------------------
Learn the latest--Visual Studio 2012, SharePoint 2013, SQL 2012, more!
Discover the easy way to master current and previous Microsoft technologies
and advance your career. Get an incredible 1,500+ hours of step-by-step
tutorial videos with LearnDevNow. Subscribe today and save!
http://pubads.g.doubleclick.net/gampad/clk?id=58041391&iu=/4140/ostg.clktrk