From: Jim Meissner (jpmeissner_at_mindspring.com)
Date: 2002-01-07 18:17:54
Dear Andreas: (and welcome back Doug)
Since you asked for some comments, here are a few. These are not in any order. They are meant to be constructive!
1) The RF bypass caps (C1 and C53) must go to a good solid ground like chassis or pc board ground plane.
2) The inductor L2 and R56 must go in the (-) power bus. I am not convinced the inductors are needed if you are running from batteries.
> It runs on four 1.5V batteries.
Do you intend to run the op amps from +/- 3 volts and then float the processor? That could be big trouble!
The processor power will take some extra care and may need the inductors toisolate the power glitches. A separate battery for the processor would beideal. The digital and analog ground should be connected together at one star ground point.
3) The .1 uf bypass caps C27-37 etc need to be distributed with resistors throughout the various op amp stages. As Joerg shows in his schematics, they must be on each op amp power pin to ground.
4) With such a small board, keeping the processor noise out of the input will be take some careful design and layout. This should be breadboarded first before committing to a pc board layout. You might think of this as two projects, the preamp, and rest of the circuit. The circuit after pin 6 of U2 and U3 can be built with confidence and possibly gamble with a pc board layout without a breadboard stage. The preamp will take more tweaking. This design may change several times. Consider a shielded box for the input stage 1NA114 and associated components.
5) The Bessel filter may be an enormous overkill. I found no significant brain wave frequencies above 60 Hz.
6) Your input protection diodes should also go to a good ground. I used a2N3904 for a reason. Don't arbitrarily change transistors unless you knowwhy.
7) What is your decision to use the 1NA114 rather than the lower noise LT1012.
8) Have you or Joerg actually used the left leg drive? I have had no experience using it. I do know why it is used for ECG. Do you have any information that it works better than the traditional circuit ground reference for EEG.
> It uses a LED for data transmission into a plastic
> fiber. I've posted a schematic for the receiver
> previously.
Could you tell me the date when you posted it, so I can look at it?
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: Monday, January 07, 2002 3:33 AM
Subject: [buildcheapeeg] TinyEEG
Here's what I've been working on for a while. It still
needs a lot of adjustments. A surface-mount PCB-design
for the current schematic is 90% done - it fits in
less than 1/2 a euro-board. Don't expect the
through-hole version to be that small.
The LT1012 design got put on hold a bit - its only
advantage was that it can use larger resistors at the
inputs (though not large enough).
Please read the design notes on the schematic and
comment on what I've done so far.
Various stuff:
It runs on four 1.5V batteries.
It uses a LED for data transmission into a plastic
fiber. I've posted a schematic for the receiver
previously.
I've cut away everything non essential, so forget
about expandability...
/Andreas
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This archive was generated by hypermail 2.1.4 : 2002-07-27 12:28:36 BST