From: Jim Meissner (jpmeissner_at_mindspring.com)
Date: 2002-01-13 19:00:49
Dear Andreas:
Nice post!
As you know I was questioning your "simple" two transistor receiver circuit. Sometimes "too" simple and "too" cheap can be "too" expensive in the long run. There is very little use of saving pennies if the result is a project not working or not getting done. I love your LT1671 comparator solution.
Please post the rest of the circuit, the 5 volt regulator and where that power comes from. Will the RS232 port have enough power?
Please post the DS275 circuit and power source.
The circuit that I used for years that worked well was the "simple opto coupler" using the 4N35 ( see my drawing http://www.MeissnerResearch.com/Upload/Iso01.gif )
The improvement that I would like to see is something that would be safe for 5 or 10 KV. A separated transmitter-receiver with 1 or 2 inch air spacing mounted on separated boards would be enough and not require going to fiber optics. I think that means that I voted for #2 or #3.
What is the difference between the DS275 and the 4053?
The data rate I used was 9600 Baud. Joerg keeps asking about 56 K Baud? What do "you" need for the TinyEEG project?
Juergen P. (Jim) Meissner
Check out my Website at www.MeissnerResearch.com
Read about the benefits of the Brain State Synchronizer sounds for improving your life and health.
----- Original Message -----
From: Andreas Robinson
To: buildcheapeeg_at_yahoogroups.com
Sent: Sunday, January 13, 2002 10:48 AM
Subject: [buildcheapeeg] Re: optical coupler
--- In buildcheapeeg_at_yahoogroups.com, michalchik_at_aol.com wrote:
> I was wondering if anyone has thought about using
> a simple electro-optical coupler to isolate the EEG
> from the computer. That seems simpler than try to
> go through an IR. port.
Hi,
if you are referring to an IC with a led and a
photo-diode, the answer is yes. But there are safety
issues, so other solutions are also interesting.
Since the topic has been brought up, I'm attacing a
new serial-port-powered fiber-optic receiver I'm
considering for the TinyEEG. It is based on a
micropower (0.47 mA) comparator that is very fast
(60ns).
The increased speed and reliability comes with
increased cost. I've made some calculations below,
going from high end to low end with various solutions:
1. Fiber LED & photodiode + comparator + DS275: $18.50
2. Regular LED & photodiode + comparator + DS275: $10
3. Regular LED & photodiode + comparator & 4053: $6
4. Regular LED & photodiode + transistor driver: $2
No 1 is intended for fiber while no 2, 3 and 4 are
useful for wide-spacing optocouplers. 2-4 can be used
for fiber as well, but you would have to make your own
connectors.
Option 1 relies on these parts (available at Digikey):
FB134-ND - Plastic Fiber Optic IR-LED (7ns): $5.25
FB128-ND - Plastic Fiber Optic Red LED (100ns): $4.88
FB120-ND - Plastic Fiber Optic Photodiode (5ns):
$4.18
So, the question is now: Which option does the people
of the group prefer?
/Andreas
PS. The PCB is coming along nicely. DS.
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