From: Joerg Hansmann (info_at_jhansmann.de)
Date: 2001-12-19 15:08:07
Hi Andreas,
----- Original Message -----
From: sleeper75se <sleeper75se_at_yahoo.se>
To: <buildcheapeeg_at_yahoogroups.com>
Sent: Wednesday, December 19, 2001 3:55 AM
Subject: [buildcheapeeg] Re: modularEEG input stage prototype
> Hi Joerg,
>
> sorry to hear that it didn't work. Does this mean we don't have a
> working input stage at the moment?
We could use the RS232EEG input stage instead (first stage gain reduced to 10
and one additional stage) and add the DRL and guarding
circuit.
However then we have no user protection against INA114 worst case failure
(inputs internally shorted to supply lines)
> A couple of questions:
>
> How is the input stage realized? A double sided board with ground
> planes and guards is much closer to how it should look than a
> breadboarded setup.
It is a single sided board (the gameport-EEG PCB) heavily patched
(traces removed, wires added)
Interference as a possible cause for the bad result has been one of my
ideas too, and I have soldered copper foil for shielding below the input
stage and finally shielded the whole pcb. This has removed 50Hz line noise
completely but not the 0.1 Hz noise.
Further I have changed all AGNG lines to star topology
to avoid possible current coupling - but that has changed nothing.
> The schematic says the protection diodes are 1N4148.
It should have been BAT48 shottkey diodes - but these I have
removed right in the beginning because they picked up voltage
variations from the DC supply line and thereby caused the whole
circuit to oscillate from rail to rail.
> What happens if
> you cover them with a piece of electricians tape?
> (They're light sensitive)
>
> Is the noise reduced/changed if you cool the input circuit (not the
> INA114) with cold-spray or something similar? I realize this is a
> shot in the dark...
I could test it.
Regards,
Joerg
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