From: Joerg Hansmann (info_at_jhansmann.de)
Date: 2001-12-17 23:05:51
Hi Doug,
----- Original Message -----
From: Doug Sutherland <wearable_at_earthlink.net>
To: <buildcheapeeg_at_yahoogroups.com>
Sent: Monday, December 17, 2001 5:03 PM
Subject: [buildcheapeeg] ModularEEG Parts Questions
> Guys,
>
> I'm placing an order at digikey for building the
> ModularEEG.
You are aware that it is not tested and that
it might require some patches to get it running ?
BTW. use 100pF ceramic Capacitors instead of 1nF C25,C26 for
input HF blocking.
> I have a few questions about the parts:
>
> 1) Should I be ordering DIP packaging for the ICs?
Yes.
> 2) There are two DIP versions of TLC277 op-amps,
> TCL277CP
C stands for commercial temperature range 0..70 Celsius
> and TLC277IP.
I stands for industrial temperature range -40..85 Celsius
> Which do I need?
C should be enough.
> And
> what is the difference? The IP are cost more.
>
> 3) There are two versions of AT90S4438P uCs,
Should it not be AT90S4433 ?
> AT90S443-8PC and AT90S443-8PI. Which do I need?
Same as above. AT90S4433-8PC should be enough.
> 4) Assuming I make the programming cable per the
> schematic, I don't need a flash tool or one of
> those $80 Atmel kits, is that right?
Right. You only need to download the SP12 programmer freeware.
> 5) There are bunch of different 7.3728 Mhz crystals,
> packaging is either cylinder, HC49,
IIRR I have used a HC49 Type with flat hight.
(Hey Frans ! If you read this, could you please have a
look on the RS232EEG-Prototype board ?)
> or 2-DIP, and
> load capacitance of 18pF or 20pF. I'm wondering
> if CA-301 7.372M-C 7.3728 MHZ CYL XTAL CA-301 TYPE
> is appropriate?
I did not find any hints in the datasheet.
> 6) Is an LM340T-5.0 1A 5V TO-220-3 Regulator okay?
TO-220-3 pins have twice the spacing of the 7805 regulator.
It will not fit.
> 7) The schematic lists MAX232E. Is that extended
> temp version? There is MAX232CPE and MAX232EPE.
MAX232E is +-15kV ESD protected. But that is not really
necessary.
MAX232CPE (0..70 Celsius) should be OK.
> 8) There are Fairchild and Toshiba 6N139s. Which
> ones do you recommend, or does it matter?
I used one from Agilent (HP) , but I think it does not matter.
> 9) The only part I can't find at digikey is the
> TMA0505S. There sure doesn't seem to be many
> pages about this DC/DC converter. Is there an
> alternate part that would be suitable? I found
> the data http://www.fse-power.com/html/pdf/tma.pdf
> but where do I get these things?
e.g. From RS-components
> 10) I will be connecting this EEG to an embedded
> PC running off NiMH batteries and powered by
> a PT6302A regulator. This is a 5V 3A reg with
> high efficiency (~90%). Do you think it would
> be safe to power both the PC and EEG from
> this single regulator?
Yes.
> If so, can I avoid the
> TMA0505S
No.
If you omit the DCDC you can also omit the optocouplers
and have no isolation. That might be OK if your embedded PC
is battery powered _and_ has no peripheral connections -
but think of the risk if it is connected to a faulty battery charger
or a badly isolated peripheral device...
> and 7805?
Yes. But only the 7805. If you have regulated 5V you do not need it.
> If not, how can I run both
> the PC and EEG off single battery source? It
> would be a PITA to have two sets of batteries.
>
> Thanks,
> Doug
>
> PS. Sorry for my ignorance on packaging and IC
> versions. Some of these data sheets leave
> a lot to be desired.
I _have_ the infos from the datasheets (mostly downloaded as pdf-files
from the manufacturers).
But you are right: Sometimes the infos are hard to find.
Regards,
Joerg
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