From: Joerg Hansmann (info_at_jhansmann.de)
Date: 2001-12-21 11:36:47
Hi Sade R. M.,
----- Original Message -----
From: sademade <sademade_at_yahoo.com>
To: <buildcheapeeg_at_yahoogroups.com>
Sent: Thursday, December 20, 2001 7:08 AM
Subject: [buildcheapeeg] Re: modularEEG input stage prototype ... Some Ideas :
...
> Well, I just wanted to say that would like to see those who do not
> contribute to the hw or sw design, to contribute $ donations to
> Joerg for making pcb prototypes
Until now all EEG-Prototypes were single sided with
0.016 inch traces and 0.015 inch clearance. I could print
the pcb layouts on a 300dpi printer and process and etch them in
my kitchen sink in tupperware boxes.
So the pcbs were not really a cost factor until now.
...
> I have used BBrown ADS1211 4 diff channel A/D part in some projects,
A nice chip (with an awful reset option that I have never got working).
I have used it in a project too recently (16 channel pH controller)
> and would think that such part would allow using just single stage
> of the INA114's, and make the analog section much smaller, and
> perhaps boost the noise-performance,
Maybe it is possible to get below 1uVp-p noise.
> provided someone better than
> me routed the guardings/shieldings, though, I would like to learn
> more of how to route high-quality low-noise analog microvoltage
> input stages.
> I used ADS1211 in interfacing to pressure sensors
> and RTD's that provide very low voltage when driven with precision
> constant current generators, and it just is superior to many other
> A/D parts.
However a bit costly (at least at RS Components here in Germany).
> I am sure that combining it with something like INA114
> and good routing techniques could somehow boost the analog section
> yet, and not cost much more to speak off.
>
> Then, would consider optical isolation layer right after the
> ADS1211, and operate it trough the optosisolated SPI port
> signals, taking total 2 isolator packages to accomplish, if
> using some nice doubles and quads that are out there these days,
> smt, go to very small space.
These isolators would have a much higher data rate than the RS232 lines
I suppose ?
Moritz and I have had big trouble to get a CNY64 (which is rated for IEC601-1)working at 115200 baud.
So I see some problems...
> After that, would throw in possibly either some small risc
> flash microcontroller with hw multiplier, or, consider
> some of the nicer versions of the TI flash DSP's, combined
> with a USB controller chip from some company FTDI,
...
I think these are good ideas. However at the moment
we (or at least I )should focus on getting the modularEEG
analog part working.
Regards,
Joerg
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