From: Joerg Hansmann (info_at_jhansmann.de)
Date: 2002-03-04 12:03:35
Hi,
----- Original Message -----
From: Andreas Robinson <sleeper75se_at_yahoo.se>
To: <buildcheapeeg_at_yahoogroups.com>
Sent: Saturday, March 02, 2002 6:43 PM
Subject: [buildcheapeeg] Re: My project - status report
...
> > For 20MHz you need 10nF ceramics (with very short
> > wires) very near to the DCDC outputs.
>
> Unfortunately is the cable is not detachable and the
> supply looks very difficult to open without breaking
> something (there are no screws). However I can try
> shortening the cable to 5-10 cm.
What cables ? I thought your DCDC were pcb mounted ?
(at least I had this impression from the pcb layout)
And don't get me wrong: I did not want you to break anything
open...
> I've attached a switcher-CAD schematic of a filter I
> hope will work. The 10uF tantalums are there to
> attenuate a 500kHz resonance peak caused by the 10uH +
> 10nF LC-combination. Please tell me what you think, is
> it "realistic"?
It looks good.
BTW: The thing with putting the 10nF C close to the output (with X
shaped traces) assumes that the DCDC has some output impedance
(should be listed in the datasheet of the DCDC)
...
>
> Oops. I already knew that, yet somehow failed to
> implement it (for the 2200uF capacitor anyway). :-p
It is somewhat questionable to me what sense makes a
2200uF C in a device with switching frequencies of
many 10 to 100kHz anyway.
...
> > amplifier:
...
> Hmm, maybe I was unclear. The filter is not performing
> well,
In theory or in practical experiments ?
Perhaps with better electrodes the offset handling
capacity is enough ?
> because the high-gain stage (G=100) in front of
> it will cause saturation of the output (after both
> gain stages) for fairly low offsets (15mV). Lowering
> the gain before the filter and increasing it after,
> will produce better results. G=20 is the equivalent of
> what you are using now and your design handles 100mV
> offsets.
I would like to know, what DC offset the Abhayamudra unit
can handle:
Excerpt from the article about the Abhayamudra unit
(http://www.pocket-neurobics.com/)
that Doug has posted some days ago:
"...
We also include a number of features to try to ensure eeg sessions are
successful (with these big amplifications required, there's lots of
scope for things to go wrong). We have constant monitoring of the
"offset potential" - probably the most common cause of eeg signals
going 'flat-line'.
..."
Regards,
Joerg
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