From: michalchik_at_aol.com
Date: 2001-12-11 21:59:33
Hi All,
I still find myself disagreeing with the majority that feels that optical
isolation is necessary for safety. I posted the following message to
sci.electronics.design to get a second opinion on this issue. I will post the
replies I get.
Hi all,
I am in a list-serve on do it yourself EEG building. The devices we make need
to be hooked directly to a persons skull via conductive electrodes. The
consensus in the group seem to be that to avoid the possibility of
electrocution the actual recorder needs to be separated from the computer and
powered by a battery. Date would be transferred between the two with an IR.
link.
Personally I think this is daft and overkill. EEG's have been around for
going
on a century and I have never heard of an electrocution death. Since the
recorder is passive and the signals we are picking up are less than 1 volt, I
would think it would be easy to build a cut off circuit that would ground
itself out or short out is the potential between electrodes or the electrode
and ground ever exceeded 1 volt.
I had in mind either using zener diodes in series with opposed biases or
setting up some threshold switch using an op-amp and a reference voltage from
a
dry cell to cut off power if it exceeds the safety threshold. Or maybe both.
Also this device is going to be hooked into either the microphone, serial or
parallel port of a computer so the computer power supply is going to also
keep
the voltages very low.
2 questions:
1) Do the safety circuits I described sound sufficient to you guys?
2) Do you know where I can look up the accepted standards for safety ci
rcuits
in medical equipment hooked up directly people.
I have surfed UL's website and have not found any useful information yet.
Thanks,
Michael Michalchik
This archive was generated by hypermail 2.1.4 : 2002-07-27 12:28:33 BST