From: sleeper75se (sleeper75se_at_yahoo.se)
Date: 2002-01-17 23:02:55
--- In buildcheapeeg_at_yahoogroups.com, "Jim Meissner" <jpmeissner_at_mindspring.com> wrote:
> Dear Andreas:
>
> I just downloaded your latest work. Wonderful, Wonderful,
Wonderful!
Hi Jim,
Thanks! But it's not tested yet. There are probably some bugs here
and there, or worse critters. ;o)
>
> Think the SMT TinyEEG board is great because you can use one board
for a single channel machine, or two boards for right and left
hemisphere.
>
> My interest would be to add several more boards for EKG, GSR,
temperature, respiration rate, etc.
The idea is to use these as plugin-boards, similar to the PCI-cards
in a PC. The ADC module would be the motherboard. Still working on
that. One drawback for the first version will be that the AC/DC
jumpers can only be changed by physically removing the amplifier
card, change the jumper and then put it back. But, digitally
controlled, analog switches of good quality are so very expensive and
probably not good enough.
You may not have noticed it, but I've removed the ESD resistors from
the amplifier board. These will be on the "motherboard" instead. My
main reason for this was to reduce the size and make it cheaper to
experiment with different ESD/patient-protection circuits.
The 100uF caps are also relocated to the motherboard, because you
just need one pair for all 8 channels, right?
>
> The eight channel 12 bit board looks good. I would guess that this
is bipolar input so the TinyEEG input-boards hook directly to the A/D
board.
Yes, there is no biasing for this version. Of course this limits the
range of power supply voltages. The full 12-bit input range of the
ADC is +/- 4.096V and it must be powered with +/-5V, so the optimal
power supply for the amplifiers is 5 volts as well. If one exploits
the fact that the filter-opamps aren't rail-to-rail, you could use +/-
6 volts maximum for the amplifier.
For people who wants reduced voltages (say +/-2.5V), the ADC-board
must be changed, but it's a start...
> Can you make the TinyEEG boards in your kitchen?
Actually, I'll be making them at the university's electronics club.
That's basically a kitchen, (but not very clean) with better
ventilation (chemistry-lab-grade). If this works well, I'll create
gerber-files and let someone make more professional-looking PCB's.
> What can I do to help with the project.
>
> I would be willing to build and test.
>
Sure, that would be great! But as you know, there are no guarantees
it will work. This is my first microvolt design ever, so in the worst
case I expect having to redesign the whole PCB. :-p. I'd appreciate
it if you took a closer look at the layout and looked for rough spots
(such as large current loops). I know this is pretty difficult to do,
and perhaps it is unnecessary with a board this size, and the low
frequencies involved?
By the way, there is a place on the PCB with very tight tolerances,
that probably will have to be patched after etching. The inputs of
the in-amp must be guarded so I routed a guard ring that's only 8
mils wide when it passes *between* the pads of the SO-8 package. I've
never done that before. It's going to be interesting. :-)
> I would be willing to "try" to make boards if you send me
the "negatives".
Hmm, you want me to send you hard copies? I wonder if they would
survive the transatlantic journey. :-) You could ask a print shop to
help you with the PDF. Since the file is online, you wouldn't even
have to download it, just tell them where the it is... If they have
1200-dpi printers and thin paper, chances of success are greater.
By the way, I will upload a slightly cleaned-up version of the
amplifier-masks soon, so don't start anything yet! :o)
Regards,
Andreas
This archive was generated by hypermail 2.1.4 : 2002-07-27 12:28:36 BST