From: Joerg Hansmann (info_at_jhansmann.de)
Date: 2002-01-13 18:44:33
Dear Jim:
----- Original Message -----
From: Jim Meissner <jpmeissner_at_mindspring.com>
To: <buildcheapeeg_at_yahoogroups.com>
Sent: Saturday, January 12, 2002 12:25 AM
Subject: Re: [buildcheapeeg]Patient Safety and Input protection
> ...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.
So this could be a safe option ?
I have just emailed traco power products, the manufacturer
of the tmv-en DCDC converter series, if their TMV-EN DCDCs are
IEC601-1 compliant.
> 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 from ground. That should work safely.
Then I do not see the point for using the DCDC at all for battery operation.
A LDO regulator would perform better.
Perhaps the pcb layout could be done in a way, that alternatively
for battery operation a LDO could be used, and for DCDC powered
operation a TMV-EN DCDC.
So each user could decide what degree of safety he needs.
> Or if you trust the
> DC/DC then power it from a power supply rather than the battery. That
> should satisfy both?
Could be an option.
>> (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.
f-3dB should be 1/(2*PI*R*C) = 79.6 Hz
>> 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?
Have you had success with eagle-freeware ?
>> 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.
Sorry to hear that.
Seems to me like you ran out of memory on win9x.
To avoid such problems in future I need some more infos:
1)Operating system used ? (win95, win98, win98se , WINME , NTxx, win2000, etc.)
2)RAM ?
3)Free space on HD (for swapping)
4)pdf viewer used ? (Acrobat reader Vx.x?)
> I hope that my comments are helpful. Sometimes another head and a new
> look at things helps.
Getting a design revised often will certainly improve the
quality. This is the same with GNU licensed open software
design.
Regards,
Joerg
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