From: Joerg Hansmann (jhansmann_at_g...)
Date: 2000-12-22 16:39:34
Hi,
----- Original Message -----
From: <yaniv_vi_at_yahoo.com>
To: <buildcheapeeg_at_egroups.com>
Sent: Friday, December 22, 2000 2:13 PM
Subject: [buildcheapeeg] Re: to jeorg - about the infrared com ?
...
> > However SHARP writes in their datasheet, that IS1U20 is not
> > recommended
> > for new design.
> what does this mean ?
It is a friendly warning by SHARP , that they intend to
discontinue the production of this device.
> is there a problem to reuse this tested design ,you think ?
see discussion below...
> > That means timing is very critical and the communication could
> >probably
> > be only half-duplex.
> comm is only half duplex .
> is it a problem ? your protocol isn't half duplex ?
At the moment the protocol _is_ only half-duplex, however
the next protocol will utilize full-duplex for sending
commands and data streams from the PC to the EEG-device
(setting sample rate, flashing LEDs, playing arbitrary waveforms
over pwm-output ) without interrupting the EEG-datastream
from the EEG-device to the PC.
I have done a little search for irda specifications and datasheets
and realized, that irda _never_ has been full-duplex
(at least not on the physical layer).
In fact all transceiver circuits I saw, shut down their input
during transmission.
At the moment I see following solutions:
1) EEG-light: Communication is only one-directional.
con: No changes of sample frequency etc. will be possible,
no LED-flashing for hemisync-devices etc.
pro: Cheap and easy to implement (some time critical code
on the At90S4433, but that does not matter because there
will be no need to receive data and implement other features)
2) EEG-irda: Communication is bidirectional half-duplex and
assigned to interleaving time-slots.
con: Very time critical windows-driver required to manage the
interleaving.
pro: Easy to implement with some additional hardware
on AT90S4433. Virtual full-duplex communication
with full features.
3) EEG-RS232: Communication is full duplex over cable.
con: Isolation is done with opto-couplers and is not as safe
as an airgap of 1 metres with irda.
pro: Easy. Cheap. Full features. No data loss/change or
bit-errors on transmission line.
...
...
> > How should the integration check look like ?
> let's assume for a minute you have a box and laptop is safe .
> you or maybe rob (does he have a bfb machine )
AFAIK Rob has a BM.
> should go to
> bfb practicioner
I dont know anyone here in Germany who is professionally
working with brain waves feed back.
> willing to help.
> and use maybe basic software , but talk to him / check
> with him about all aspects of h.w. - what does he think of
> them - especially for personal use .
> but i don't think it's need overstressing , because first
> version won't be 100% - the next ones will be better with alot of
> user feedback .
> and also taLK WITH him about safety .
Here in Germany safety is not a matter of practitioners
but of institutions like TÜV, VDE etc.
Putting medical devices on the market without licence
could result in high fines or up to one year in jail.
(And that is something I am definitely _not_
interested in ;-) )
> > > and in paralellel work on remaining h.w. subjects .
> >
> > A problem is safety.
> > Recently there was a thread about bio-signal amplifiers on
> de.sci.electronics
> > One question was, wheather a battery powered laptop connected to an
> EEG
> > with optocouplers would be safe:
> > The answer was : NO.
> > Because in a Laptop high voltages are generated for display
> background
> > illumination. Under worst case conditions those voltages can kill a
> test subject
> > connected to the EEG.
> >
> o.k. so first we should make irda . but all the
> devices i know use optocouplers and have fda approval .
> so what's the reliability of this info ?
Many authors on de.sci.electronics are very competent.
But to be sure, the papers of the responsible authority
should be checked (e.g. FDA etc.)
> maybe it's depends on breakdown voltage of the optocouplers ?
The manufacturer of the optocoupler must guarantee the fitnes of his product
for medical applications.
All datasheets I have seen have a disclaimer for medical fitnes at the at
the end.
An other thing is pcb design and casing. The best optocoupler
will not have much use, if the pcb - design is bad or it is badly
manufactured. Also casing could corrupt isolation.
> but that's not so important because we'll make irda one .
> and btw - i don't heard of anybody hhurt from this kind
> of mallfunction yet .(just btw - not as rule)
Sometimes is always the first time... (could be from Murphys laws...)
> > Even if the EEG is fully battery powered, the battery voltage of
> let us assume 12VDC
> > could lead to severe health damage if connected with low impedance
> electrodes
> > (like EEG-Electrodes) to the test subject.
> > 10uA is the maximum current allowed under any condition.
> > The existing design can not guarantee this and must therefore be
> revised.
> there 's one thing i dont' know
> 1. is this one of the things the fcc checks ?
I do not have papers about the FCC checking procedures.
> 2. what's exatly needs to be changed to make it safe and how hard it
> will be ?
One proposal was to put 1 meg resistors in series with each eeg-input.
However I assume that this will increase noise.
> 3. it seem that in life there are many potential 10UA sources ,
> so this claim seem very very strict .
Yes. But in normal life you are not connected with low impedance
electrodes.
Regards,
Joerg
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