From: sleeper75se (sleeper75se_at_yahoo.se)
Date: 2002-02-28 16:09:30
--- In buildcheapeeg_at_yahoogroups.com, "Suttons_Bay" <suttons_bay_at_yahoo.com> wrote:
> Hi guys,
Hi Steve, welcome to the group!
>
> I'm new to this group. I'm a professional biomedical engineer. I
> have experience with all the standards, and have just gotten
> approval from TUV for use of one of my projects in Europe.
Sounds like you have come to the right place. :-)
>
> I'm not sure where to start or what your group could
> use my skills on best. I develop hardware, I design
> analog electronics, use uPs, I do clinical testing...
> you name it... so....
>
> What would you like me to help on...?
There are lots of ways you can help. There are quite a few unanswered
questions to begin with if you would like?
First let me explain who the hardware folks are, and what we do.
There are two people actively designing hardware here, Joerg Hansmann
(electrical engineer) and myself (engineering student). We have two
separate, slightly different projects, and we are aided by Jim
Meissner, who is a retired electrical (analog) engineer.
Joerg is designing a two-channel (expandable to six), device called
ModularEEG, that runs on mains power, and uses virtual ground
techniques to lower costs. It uses a microcontroller with an internal
10-bit ADC.
It is supposed to be a through hole design (unless his plans have
changed), so that hobbyists can assemble it easily.
He has also designed a fairly elaborate patient protection circuit
attached to the input stage to limit the current through the patient
at all times, even if the preamplifiers fail.
I am designing a two-to-eight channel device called TinyEEG (surface
mount). It will run on batteries so I can use a real split power
supply. The resolution is 12-bits, using an ADC separate from the
microcontroller.
There is no protection circuitry on the preamplifiers except ESD
protection, assuming that as long as the amplifier is protected, it
won't fail.
Both devices use a driven right-leg circuit to supress line hum, and
communicates with a PC over a standard RS232 serial port, optically
isolated.
That's how it is supposed to be anyway. We've not finished building
them yet. :-)
---Now for the questions:
First:
A while back, we had a discussion about patient safety, and different solutions. Then Joerg designed his protection circuit that diverts any overcurrents away from the patient, using bipolar transistors.
I'm wondering... what does a circuit (if any) that sits between the patient and the instrumentation amplifier inputs in professional (FDA/IEC compliant) equipment look like?
Several application notes for instrumentation amplifiers only depicts a box attached to the inputs that says "protection" without any further explanation... :-(
Second:
Some EEG-devices in the biofeedback-category claim to have very high input impedance, on the order of 20 gigahoms or more that simplifies the preparation of the skin.
But adding small (100pF) capacitors between the amplifier-inputs and ground, necessary for EMC-reasons will cause the impedance to drop quite significantly, down to 10-50megaohms around 10-20Hz I think it was. My question: What do they know that we don't? Are they "lying" or ignoring EMI-protection to get high impedance or using the Secret Design Technique (tm)?
Third:
Are you aware of any single-chip EEG input stages (instrumentation amplifier + aliasing filter, possibly several channels) available on the open market for a reasonable price? Or is everyone designing their own chips for internal use only?
Fourth:
Do you know what steps must be taken and what the costs are, for getting an FDA approval, or its european counterpart?
Any answers to these questions, however brief, is greaty appreciated...
Regards,
Andreas
PS. If you have a good EEG/EMG/ECG design that you can share, feel free to do so! ;o) DS.
> > Steve
This archive was generated by hypermail 2.1.4 : 2002-07-27 12:28:39 BST