Re: [buildcheapeeg] Re: Is it time yet?

From: Joerg Hansmann (info_at_jhansmann.de)
Date: 2002-01-29 04:29:37


Hi Andreas,

----- Original Message -----
From: sleeper75se <sleeper75se_at_yahoo.se>
To: <buildcheapeeg_at_yahoogroups.com>
Sent: Sunday, January 27, 2002 8:59 AM
Subject: [buildcheapeeg] Re: Is it time yet?
...
>
> Joerg, how is your version coming along?

At the moment I have conflicting ideas regarding the
digital part of the modularEEG.
What would be most useful for me were an IEC601-1 conformal
design with DCDC converter (TRACO THI series) and fiber
optical RxD and TxD line or two wide spacing optocouplers.
PC side RS232 could easily have an MAX232 output and does not
require power stealing from the PCs RS232 status lines. Thus
long RS232 cables with only GND,TxD,RxD could be used.
The 6000V isolated PC-side of the interface could be
safely powered with an wall plug in transformer.
Battery operation would also be possible, but were
quite power consuming because the DCDC draws 100mA
just for itself.

On the other hand the same pcb should be turned into
a battery friendly version without DCDC and RS232 power
stealing by just putting some other components on the pcb
and changing some jumpers.

However I fear that these are two rather different designs
that cannot be changed easily into each other.

The analog part of the modularEEG needs some changes
too:

Now as the virtual ground problem is solved, the next
thing is to decide about is the differential mode DC-handling
capability respectively if the input stage should stay at
G=10 or should better be G=100 (less DC handling possible, but
some noise enhancements).
I would like to do some experiments before deciding what is better.

Then some SPICE simulations should be done to see if the
DRL circuit is stable under all possible conditions.

When all this is done, the resulting changes will be
inserted in the eagle schematic and a modified pcb layout
will be done. After that the first modularEEG prototype
can be built.

Regards,

Joerg



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