From: Jim Meissner (jpmeissner_at_mindspring.com)
Date: 2002-02-06 04:54:43
Dear Andreas:
Thank you for your clear reply. What you say makes sense. Too bad about windows!
Would this method work with my old Boland C++ DOS version?
I like the idea of being able to look at any channel at any time. The two EEG channels need to be sampled at a 128 Hz rate. The EKG could be much slower. And the temperature and skin resistance data could be every second or less.
If you do this with an external microprocessor transmitting through the RS232, you now have to provide channel information or have a set order that has to be decoded. Seems more complicated to me.
Under windows do you have an interrupt driven comm port so that you do not loose data while spooling to the hard drive. With DOS that was not a problem.
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: Tuesday, February 05, 2002 7:57 PM
Subject: [buildcheapeeg] Re: Hardware Question
--- In buildcheapeeg_at_yahoogroups.com, "Jim Meissner" <jpmeissner_at_mindspring.com> wrote:
> Dear Group: especially Andreas, Joerg, Jim Peters, Doug Sutherland
Hi Jim,
>
> Digging through my files while looking for the Mind Mirror stuff,
> I found a 12 bit analog to digital converter I had built. The
> application note from 1990 is for an LT1290 from Linear
> Technology. What I liked about it is that I could talk to it in
> Quick Basic. I know that you software snobs will turn up your
> noses, but I have a lot of wonderful programs running in Quick
> Basic. It could also be addressed in C, but I have not found C to
> run much faster than compiled Basic. I don't want to be a
> programmer, I just want my answer on the CRT display or printer,
> don't care how it gets there. Sorry about the little rant about
> all the fancy languages like Java, Linux etc.
Well, actually, I've written a lot of code in Quick Basic before
switching to C++/Windows. It's a very nice language, so my nose
remains where it is. :o)
...
>
> What are the pro and cons?
>
> How about the interrupt driven comm port software vs. directly
addressing the chip.
Ok, this is what I know:
In a multitasking system, your application might be suspended for
several milliseconds at a time while the CPU is busy working with
another process, so direct addressing will give you tons of of clock
jitter distortion in your data.
You could perhaps use a system timer routine, but it would only help
a bit, because its precision is probably a lot worse than 1 ms.
While sampling, you must also disable all interrupts. If you don't,
your application can be interrupted by another process or an
interrupt handler. In DOS, that's no problem, but in Windows it can
take 50ms or more before your program regains control. During that
time the sample and hold capacitor in the ADC will lose some charge,
and you get distortion that way. Unfortunately, you can't disable the
interrupts, only the OS-kernel and kernel-drivers can.
I think talking to the ADC directly (from Basic for instance) is a
good way to test a design, but it won't work well in a modern
multitasking OS, so I have to recommend the microcontroller option.
I hope this answers your question.
Regards,
Andreas
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This archive was generated by hypermail 2.1.4 : 2002-07-27 12:28:38 BST