From: Jim Meissner (jpmeissner_at_mindspring.com)
Date: 2002-01-11 23:25:44
Dear Joerg:
>years. I know how they can fail.
> I would like to hear more on this...
I think I addressed the important part in the other Email. Normally the primary and secondary are wound on to of each other. The picture you sent shows that the design of your DC/DC transformer is very good. It would take several layers of tape under each winding and vacuum impregnation make it really good.
> The primary side of the DCDC (where the batteries would be) is
> still connected via RS232 to the PC.
No I had intended to separate the two. The PC side of the opto isolator should be powered by the PC or a separate power supply. The DC/DC converter would be completely separate when hooked up to a battery and insulated fromground. That should work safely. Or if you trust the DC/DC then power itfrom a power supply rather than the battery. That should satisfy both?
> (BTW) I noticed the filter in front of the A/D converter. Do you
> really mean a 20 K ohm and a 100 nf cap.
It seemed like a pretty low frequency with a 100 nf.
> the ADC-input pins in order to reject HF that might find its way
> into the cable connecting the analog pcbs with the digital pcb.
I agree that that is the correct location for the filter.
> The schematics are in eagle CAD file-format.
> If you download a freeware eagle CAD version
> from www.cadsoft.de
> you can view the files.
Thank you I will try that. Is that what you draw your schematics with?
> If you are interested I can alternatively convert the *.sch and
> *.brd files to *.pdf or *.png
After looking at your last pdf file my computer crashed. I could read it but not print it. After that nothing worked. I had to run scandisk from DOS to get it back.
I hope that my comments are helpful. Sometimes another head and a new lookat things helps.
Juergen P. (Jim) Meissner
Check out my Website at www.MeissnerResearch.com
Read about the benefits of the Brain State Synchronizer sounds for improving your life and health.
----- Original Message -----
From: Joerg Hansmann
To: buildcheapeeg_at_yahoogroups.com
Sent: Friday, January 11, 2002 4:26 PM
Subject: Re: [buildcheapeeg]Patient Safety and Input protection
Hi Jim ,
----- Original Message -----
From: Jim Meissner <jpmeissner_at_mindspring.com>
To: <buildcheapeeg_at_yahoogroups.com>
Sent: Friday, January 11, 2002 9:39 AM
Subject: Re: [buildcheapeeg]Patient Safety and Input protection
...
>transformer. BTW My company manufactured transformers for a few
>years. I know how they can fail.
I would like to hear more on this...
...
> I have a compromise proposal.
> If the source that drives the DC/DC
> converter were to be a 6 or 12 volt battery, it would be safe.
Why ?
The primary side of the DCDC (where the batteries would be) is
still connected via RS232 to the PC. If the PC power supply
fails (and protection earthing too) you have 230V / 120V
on the RS232 lines.
So where is the difference between 230V from a defective
PC or 230V from a defective AC-adaptor ?
> Then
> the opto isolators are the weak link.
> So "you" can use an AC power supply to drive the DC/DC converter.
I would like to use +5V from the PC gameport instead.
> Why not give others the option to use batteries.
Yes. You are right.
> (BTW) I noticed the filter in front of the A/D converter. Do you
> really mean a 20 K ohm and a 100 nf cap.
Yes.
> What frequency does that
> roll off at?
It is the 5th pole of a 5pole 75 Hz cutoff Bessel filter.
(The other 4 poles are on the amplifier pcb).
I have decided to put the 5th pole directly in front of
the ADC-input pins in order to reject HF that might find its way
into the cable connecting the analog pcbs with the digital pcb.
>
> Is this board a working design? Have you actually built these?
It is more or less the digital section of the RS232EEG
(downloadable at http://www.jhansmann.de\eeg )
Because the RS232EEG prototype worked, I assume that
the modularEEGdigital pcb will work too.
The schematics are in eagle CAD file-format.
If you download a freeware eagle CAD version
from www.cadsoft.de
you can view the files.
If you are interested I can alternatively convert the *.sch and
*.brd files to *.pdf or *.png
Regards,
Joerg
To unsubscribe from this group, send an email to:
buildcheapeeg-unsubscribe_at_egroups.com
Your use of Yahoo! Groups is subject to the Yahoo! Terms of Service.
This archive was generated by hypermail 2.1.4 : 2002-07-27 12:28:36 BST