Re: Data Acq. Concept Help

Hi Michael,

Gentlemen, thanks for the ideas! I'm a EE that's been doing software
for the past 10+ years so I really appreciate the advice. If I do a
good job with this I may get more HW projects :-)

I was thinking 8 to 12 ch. ADC chips I2C or SPI controlled. The larger
mux/single ADC might be easier, but possibly less reliable; if it fails
I'll loose a larger group of channels. That's probably why you
elaborated on the protection required, which I will surely provide
regardless. Maybe the more stringent pcb requirements for the ADG731
mux would make a stronger case for the 8 to 12 channel devices as well?
I will think further on the tradeoffs--I think it's a good idea.

I don't believe I can combine all signals on a single board for the
following reason. The signals into the module are from a string of 2+
VDC battery cells so I have a high common mode issue that requires some
isolation so not all channels be on the same board. For e.g. 64ch per
board (64 x 2.75 V = 175 V), which I will handle by using difference
amp front end and isolating between boards. (210 x 2.75 V = 578 V) This
was probably overlooked from my original post.

The Lantronix XPorts are ~ $50 each so for 4 boards is 200.00 bucks.
I don't think I can get away with 1 board. Not to mention the required
hubs for the network.

On the other hand, Cypress USB on the PSoC is ~ $2.00/chip, or the
EZ-USB (8051 on board) probably similar price. I'll still need a
PC-104 board to interface with the USB based boards, and ethernet
interface to a central data collection computer. USB enables easy
bench tests of the boards with LabView and any PC, and seems to provide
quite a flexible product. I'm seeing advantages with my original
concept.

I would like to avoid the PC-104 boards: Maybe one XPort put somewhere
in a module could take it's place and provide the ethernet interface to
a central computer, but then how do I collect the data off the boards
via USB? PC-104 does seem like overkill, but would enable data
formatting and preprocessing i.e. averaging (not required) and possibly
diagnostic functions (are required).

All in all, I'll have 9 modules (to clarify, each module acquires data
from 210 high common-mode inputs, some temperature measurements, etc.
225 signals, plus a few spares) into the 4? boards we're discussing,
with some type of ethernet access to a central computer that collects
all the measured data from each of the modules (9 x 225+ signals total)

.

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