From: Joerg Hansmann (jhansmann_at_g...)
Date: 2000-12-21 14:47:38
Hi,
----- Original Message -----
From: <yaniv_vi_at_yahoo.com>
To: <buildcheapeeg_at_egroups.com>
Sent: Wednesday, December 20, 2000 7:22 AM
Subject: [buildcheapeeg] to jeorg - about the infrared com ?
> hi joerg
> did you checked the irx board (and schematic ) for cheap efficent
> irda comm ?
Yes. I took a look at it.
The IS1U20 irda receiver utilized in the circuit is very interesting, because
it performs pulse stretching for direct interfacing to a normal uart-input.
However SHARP writes in their datasheet, that IS1U20 is not recommended
for new design.
The irda-Transmitter side is the worst part: A simple IR-emitter-LED has to
be pulsed with 3/16 of the baud-rate and that is obviously done by
the pic16f84 per software.
Lets assume baud=115200
XTAL=10Mhz -> PIC instruction cycle time = 400 nSec
A 3/16 baudrate pulse would be 1.628uSec and that would be only 4 instructions
on the PIC. For processing one complete bit 21 instructions would be used.
That means timing is very critical and the communication could probably
be only half-duplex.
The AT90S4433 at ca. 7Mhz is nearly 3 times faster than the PIC at 10Mhz,
however I make use of about 3 interrupts and want to use full duplex
communication. So generating irda pulses in software is a concept
I do not like very much.
> when comparing it to the other alternative - take in nthe option that
> is the irx board you can use the irda c code in the ateml processor .
C code for PIC/Atmel will not be very portable because it is very
machine dependent.
> here's the address :
>
> http://www.media.mit.edu/~r/projects/picsem/irx2/
>
>
> and another thing :
> maybe now is the time to start integration check (of crrent version)
> with a biofeedback practicioner ?
Perhaps a biofeedback practitioner could give some hints about
feedback-protocols etc.
> to ask him what he think of the sw and hw ?
sw: that is the part of Rob.
hw: It is still a raw pcb with some cables lying on my desktop.
How should the integration check look like ?
> 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.
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.
> it may be possible to get somebody to help you , would you like it ?
Yes of course.
Regards,
Joerg
This archive was generated by hypermail 2.1.4 : 2002-07-27 12:28:28 BST