From: Doug Sutherland (wearable_at_earthlink.net)
Date: 2001-12-13 06:13:52
Hi Moritz,
> The MAX232 has to be powered separately from the EEG. The
> easiest way would be to use some of the RS232 handshaking
> lines as a power supply. Unfortunately these don't deliver
> enough power for a MAX232.
There are ways ...
http://www.hut.fi/Misc/Electronics/circuits/rspower.html
> What we could do is make a discrete transistor design
> replacing the MAX232 and powering it from the serial port.
Are you sure that powering either from the PC serial port
is safe? It sounds kind of strange considering that we are
trying to isolate the EEG from the PC. What happens if
there is a problem with the PC handshake lines?
> The disadvantage is maybe not 100% compatibility to RS232.
I doubt that many products are actually 100% compliant
these days. This old standard has been bent way out of
shape. Parallel port standards are even worse.
> This solution is also cheaper, because the MAX232 is quite
> expensive.
I use DS275 level converters these days. They are small
8-pin DIPs and require no external capacitors.
>> Is the irDa idea better or is it really overkill?
> It would allow our device to pass medical norms and it's
> not much more expensive then RS232 with MAX232.
But it does require and irDA transceiver on the PC.
So many option/issues ... the question is ... who decides?
Who is the Linus of OpenEEG? Ultimately somebody has to
make decisions one way or another ...
-- Doug
This archive was generated by hypermail 2.1.4 : 2002-07-27 12:28:33 BST