From: Jim Meissner (jpmeissner_at_mindspring.com)
Date: 2002-01-14 15:21:14
Dear Andreas:
> Hmm, at this distance, regular diodes facing each other, shielded
> with a piece of plastic tube painted black (a straw perhaps) might
> work just as well.
Yes, I know that! The only reason I suggested going with the fiber is thatit will work with no fussing around! Yes, I know $10 can be saved, but lets do that on the next phase. Right now lets "bolt together" something that is guaranteed to work the first time. There will be plenty of adventure when we get to the electrodes, conductive paste, shielding, etc, so save your strength!
+++++++++++++++++++++++++++++++++++++++++++++++++++++
> I'm also considering changing to a different microcontroller and
> possibly use an external ADC for higher precision, like these.............
I have used the LT1294, talking to it from the PC with Quick Basic. Makes you wonder whether you need a micro processor at all?
BUT, seriously, having written the PC program for the Com port, FFT, VGA display for Waterfall and waveform, etc there probably is not enough time to "handhold" the A/D converter.
My preference would be the HC11 ( $9 ) because I know the code and I use itin one of my products. The BrainMaster also uses it. Would compatibilitywith the BrainMaster be important?
I would like to address the question of 8, 12, 16 bit converter choices.
Having used an 8 bit converter for years, I can tell you the frustration with that limited range. I actually had to install a manual gain pot in order to get the signal within the range. During deep meditations I would haveto increase the gain in order to see the signal. At that gain, the eye blinks would overload the amp and cause clipping which causes havoc with the FFT analysis. Talk about data distortion! This is why I cautioned you about multiple AC coupling capacitors. These will create false frequency datato the FFT and take a long time to settle. Since you and Joerg love to dosimulations, look at the step response of an overload signal into an FFT. I don't know it your software can do transient analysis.
I would rather spend an extra $10 for the 12 bit converter.
As a matter of fact I would be willing to spend an extra $50 for a 16 bit converter and have DC coupling throughout.
Is your design flexible enough to give these options?
Keep up the good work!
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: sleeper75se
To: buildcheapeeg_at_yahoogroups.com
Sent: Monday, January 14, 2002 7:58 AM
Subject: [buildcheapeeg] Re: optical coupler
--- In buildcheapeeg_at_yahoogroups.com, "Jim Meissner" <jpmeissner_at_mindspring.com> wrote:
> Dear Andreas:
>
> Thanks for the reference pages.
>
> Unless I read it wrong, the max rate of the DS275 is 19 KBaud and
> it still needs a power source larger than +5 volts ( a 9 volt
> battery )?
Hi Jim,
where did you see the 19kbaud figure? I must have missed that one.
+12V can be taken from one of the status lines. Anyway DS275 is
looking less and less attractive at the moment.
> The cleanest solution seems to be
> the Fiber-optic IR-LED feeding a short piece of fiber ( 2-3 inches )
> into a fiber-optic Photodiode feeding the
> LT1671 comparator driving a MAX232A.
Hmm, at this distance, regular diodes facing each other, shielded
with a piece of plastic tube painted black (a straw perhaps) might
work just as well.
> That would get a reliable 120 KBaud or better.
> An external 5 volt wall wart power supply may be needed
> which is OK with me.
+5V can also be taken from the mouse or keyboard ports.
Ok, in the name of flexibility what do you think of making room for
several different solutions? Then one can try all of them and pick
whatever is most suitable.
These are the options right now:
Transmission: either fiber (the receiver would be external) or
an "extra-wide" opto coupler.
Reception: Comparator with either a MAX232, a 4053 or nothing at all
Power: RS232-powered or external power (5-12V)
I'm also considering changing to a different microcontroller and
possibly use an external ADC for higher precision, like these:
http://www.linear.com/prod/datasheet.html?datasheet=324
http://www.linear.com/prod/datasheet.html?datasheet=326
> This solution may be more expensive than wished for, but it
> would get the project up and running. ( Very Important! )
Agreed. There are 200+ people waiting... :-)
Regards,
Andreas
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This archive was generated by hypermail 2.1.4 : 2002-07-27 12:28:36 BST