From: Joerg Hansmann (info_at_jhansmann.de)
Date: 2001-12-05 15:23:35
Hi,
----- Original Message -----
From: tralad <ldean_at_metrowerks.com>
To: <buildcheapeeg_at_yahoogroups.com>
Sent: Wednesday, December 05, 2001 5:31 AM
Subject: [buildcheapeeg] Analog board
> I found the biosemi design Joerg's circuit is based on... blaming
> temporary blindness :)
>
> I have one comment/question, and I hope I am not displaying
> overwhelming ignorance (wouldn't be the first time).
>
> Joerg wrote:
>
> 8) IC3A, IC3B forms a 5-pole Sallen Key Butterworth Low Pass
> with 75Hz cutoff frequency. (5th pole is on the digital board)
>
> Now, I am wondering why the 5th pole should be on a separate
> board?
The 5th pole is a simple RC lowpass very close to the ADC-inputs
of the AT90S4433.
My intention was to reject noise and HF that might be radiated
into the ribbon cable connecting the analog and the digital part.
> It seems that if the analog part of the circuit could all be
> kept together, then it could hook to any microprocessor.
Are you thinking of uC eval-boards ?
In this case you would have to build a connector from the
modEEG ribbon cable to the eval board and could easily place the
RC lowpass there.
> This
> would mean we could test just the analog board with our 6811s
> which would significantly reduce development cost.
No problem.
> Was it a lack
> of space on the board, or is there some other reason? Would it
> be possible to isolate all the analog circuitry to one board fo
> increase modularity?
Possible: Yes, but I think this would decrease noise and HF rejection.
Regards,
Joerg
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