Data Acq. Concept Help

[schmoester]

Hi,

I've got ~220 low-freq. (0 to 4V max) signals to measure and send to
another computer (over ethernet).

This group of signals will be handled by a single data acq. module
physically separate (20 meters) from identical others, all connected by
an ethernet bus.

Module Concept & Reqmts:
--PC-104 CPU board with USB and Ethernet interfaces. Ethernet to other
modules, USB to custom DAQ boards, described below.
--Want to divide-up the 220 inputs into ~50 per board, -> ~ 5 boards,
spare channels good.
--High Common-Mode voltage (< 200VDC) on some inputs, -> difference amp
front end on some channels. (LTC1990)
--Digitize signals (12-bit) with I2C ADC's (thinking MAX1238)
--Offload data from boards to local PC via USB. Would like to use the
Cypress EZ-USB or the Cypress PSoC with USB onboard (CY8C24794). This
would be the I2C to USB bridge. I want to keep the USB interface and
not use only I2C controlled by PC-104 board.

Questions:
--How do I buffer the data on the DAQ boards until I can read it off
with the USB interface? Will the CY8C24794 PSoC with an M8 ľC or the
8051 ľC on the EZ-USB interface with external memory (onboard flash on
the PSoC has too few read cycles to use continuously). Perhaps the
8051 is more suitable than the M8 for interfacing with external memory.

Any PSoC experts that wouldn't mind some additional questions down the
road if I go that route?

Thanks for sharing your insights!
Omar

 

[martin griffith]

On 19 Jul 2005 13:29:52 -0700, in sci.electronics.design "schmoester"
<to_schmoe@yahoo.com> wrote:

Hi,

I've got ~220 low-freq. (0 to 4V max) signals to measure and send to
another computer (over ethernet).

This group of signals will be handled by a single data acq. module
physically separate (20 meters) from identical others, all connected by
an ethernet bus.

Module Concept & Reqmts:
--PC-104 CPU board with USB and Ethernet interfaces. Ethernet to other
modules, USB to custom DAQ boards, described below.
--Want to divide-up the 220 inputs into ~50 per board, -> ~ 5 boards,
spare channels good.
--High Common-Mode voltage (< 200VDC) on some inputs, -> difference amp
front end on some channels. (LTC1990)
--Digitize signals (12-bit) with I2C ADC's (thinking MAX1238)
--Offload data from boards to local PC via USB. Would like to use the
Cypress EZ-USB or the Cypress PSoC with USB onboard (CY8C24794). This
would be the I2C to USB bridge. I want to keep the USB interface and
not use only I2C controlled by PC-104 board.

Questions:
--How do I buffer the data on the DAQ boards until I can read it off
with the USB interface? Will the CY8C24794 PSoC with an M8 ľC or the
8051 ľC on the EZ-USB interface with external memory (onboard flash on
the PSoC has too few read cycles to use continuously). Perhaps the
8051 is more suitable than the M8 for interfacing with external memory.

Any PSoC experts that wouldn't mind some additional questions down the
road if I go that route?

Thanks for sharing your insights!
Omar
Seems an utterly horribly complicated method for getting a slow

speed DAQ system into an ethernet connection.

Ignoring the input conditioning, I'd start with say 64 NS's adcs7478
spi adcs per board. Poll them with a 8051, (since I never did get
around to learning the msp430) That 64*2 bytes per board times your
sample rate, say 50s/sec. A massive 6.4KB/sec.
Might have to put 8K of external ram on the 8051, dammit

Feed them into a Lantronix Xport or eqiuvalent, and give them
individual IP addresses

Whats the software budget for this?
Or am I missing something?



martin

 

[schmoester]

Hi Martin,

Thanks for the reply. That's a great concept.

I have just a couple issues:
I've got nine of these modules, each of which have to send their data
to a central computer. To have each board have it's own ip address (5
bds x 9 modules = 45) seems like too many for the central computer to
talk to, versus say nine. I'm sure it can be done, but what do i use
for a hub? One per module and another to collect the modules I guess.

If I were to use an single Xport per module, how would I get the data
to it from the 5 daq boards in each module? I was thinking USB--maybe
just replace my PC-104 board with a custom board with an XPort on it?

You're right, there's a lot of software to be done. I'm very much
interested in simpifying, and I agree, my concept seems overly
complicated. I also thought USB on the cards would also facilitate
bench testing them.

Thanks again for your help!

martin griffith wrote:

On 19 Jul 2005 13:29:52 -0700, in sci.electronics.design "schmoester"
to_schmoe@yahoo.com> wrote:

Hi,

I've got ~220 low-freq. (0 to 4V max) signals to measure and send to
another computer (over ethernet).

This group of signals will be handled by a single data acq. module
physically separate (20 meters) from identical others, all connected by
an ethernet bus.

Module Concept & Reqmts:
--PC-104 CPU board with USB and Ethernet interfaces. Ethernet to other
modules, USB to custom DAQ boards, described below.
--Want to divide-up the 220 inputs into ~50 per board, -> ~ 5 boards,
spare channels good.
--High Common-Mode voltage (< 200VDC) on some inputs, -> difference amp
front end on some channels. (LTC1990)
--Digitize signals (12-bit) with I2C ADC's (thinking MAX1238)
--Offload data from boards to local PC via USB. Would like to use the
Cypress EZ-USB or the Cypress PSoC with USB onboard (CY8C24794). This
would be the I2C to USB bridge. I want to keep the USB interface and
not use only I2C controlled by PC-104 board.

Questions:
--How do I buffer the data on the DAQ boards until I can read it off
with the USB interface? Will the CY8C24794 PSoC with an M8 ľC or the
8051 ľC on the EZ-USB interface with external memory (onboard flash on
the PSoC has too few read cycles to use continuously). Perhaps the
8051 is more suitable than the M8 for interfacing with external memory.

Any PSoC experts that wouldn't mind some additional questions down the
road if I go that route?

Thanks for sharing your insights!
Omar
Seems an utterly horribly complicated method for getting a slow
speed DAQ system into an ethernet connection.

Ignoring the input conditioning, I'd start with say 64 NS's adcs7478
spi adcs per board. Poll them with a 8051, (since I never did get
around to learning the msp430) That 64*2 bytes per board times your
sample rate, say 50s/sec. A massive 6.4KB/sec.
Might have to put 8K of external ram on the 8051, dammit

Feed them into a Lantronix Xport or eqiuvalent, and give them
individual IP addresses

Whats the software budget for this?
Or am I missing something?



martin

 

[martin griffith]

On 20 Jul 2005 07:08:45 -0700, in sci.electronics.design "schmoester"
<to_schmoe@yahoo.com> wrote:

martin griffith wrote:
On 19 Jul 2005 13:29:52 -0700, in sci.electronics.design "schmoester"
to_schmoe@yahoo.com> wrote:

Hi,

I've got ~220 low-freq. (0 to 4V max) signals to measure and send to
another computer (over ethernet).

This group of signals will be handled by a single data acq. module
physically separate (20 meters) from identical others, all connected by
an ethernet bus.

Module Concept & Reqmts:
--PC-104 CPU board with USB and Ethernet interfaces. Ethernet to other
modules, USB to custom DAQ boards, described below.
--Want to divide-up the 220 inputs into ~50 per board, -> ~ 5 boards,
spare channels good.
--High Common-Mode voltage (< 200VDC) on some inputs, -> difference amp
front end on some channels. (LTC1990)
--Digitize signals (12-bit) with I2C ADC's (thinking MAX1238)
--Offload data from boards to local PC via USB. Would like to use the
Cypress EZ-USB or the Cypress PSoC with USB onboard (CY8C24794). This
would be the I2C to USB bridge. I want to keep the USB interface and
not use only I2C controlled by PC-104 board.

Questions:
--How do I buffer the data on the DAQ boards until I can read it off
with the USB interface? Will the CY8C24794 PSoC with an M8 ľC or the
8051 ľC on the EZ-USB interface with external memory (onboard flash on
the PSoC has too few read cycles to use continuously). Perhaps the
8051 is more suitable than the M8 for interfacing with external memory.

Any PSoC experts that wouldn't mind some additional questions down the
road if I go that route?

Thanks for sharing your insights!
Omar
Seems an utterly horribly complicated method for getting a slow
speed DAQ system into an ethernet connection.

Ignoring the input conditioning, I'd start with say 64 NS's adcs7478
spi adcs per board. Poll them with a 8051, (since I never did get
around to learning the msp430) That 64*2 bytes per board times your
sample rate, say 50s/sec. A massive 6.4KB/sec.
Might have to put 8K of external ram on the 8051, dammit

Feed them into a Lantronix Xport or eqiuvalent, and give them
individual IP addresses

Whats the software budget for this?
Or am I missing something?



Thanks for the reply. That's a great concept.

I have just a couple issues:
I've got nine of these modules, each of which have to send their data
to a central computer. To have each board have it's own ip address (5
bds x 9 modules = 45) seems like too many for the central computer to
talk to, versus say nine. I'm sure it can be done, but what do i use
for a hub? One per module and another to collect the modules I guess.

If I were to use an single Xport per module, how would I get the data
to it from the 5 daq boards in each module? I was thinking USB--maybe
just replace my PC-104 board with a custom board with an XPort on it?

You're right, there's a lot of software to be done. I'm very much
interested in simpifying, and I agree, my concept seems overly
complicated. I also thought USB on the cards would also facilitate
bench testing them.

Thanks again for your help!
Please don not top post a reply, it annoys many people, and wars

start!

The limit seems to be the size of the board. The data rate is slow
enough that a single 8051 micro could handle the complete number ADC
channels.
I'm confused between by what you mean by modules. But having an 8051
board with 64 ADCs would mean only 4 boards to give 255 ADCs and would
only use 4 web servers like the lantronixs, that is one per board.
That is 4 ip adresses.

This USB stuff. Just another layer of confusion for me. Many micros
already have a UART internally, I'd just put on a max232 driver and
talk to it via an old fashioned terminal program. I still use procomm
from 20 years ago on occasion, or window$ terminal. I avoid
hyperterminal. This makes debugging very easy.

If you put a double pole change over switch between the microprocessor
TX and RX uart lines that switches between RS232 and the lantronixs
xport, you can bypass all the ethernet "layer of confusion" for
testing.

I suggested SPI over I2C, for 2 reasons
1) you may run out of I2C adresses
2) SPI is easier to write code for (my opinion),


martin

 

[MK]

"martin griffith" <martingriffith@XXyahoo.co.uk> wrote in message
news:d3ssd1l4l4qif8nvraps00euri0n7ev1uk@4ax.com...

On 20 Jul 2005 07:08:45 -0700, in sci.electronics.design "schmoester"
to_schmoe@yahoo.com> wrote:



martin griffith wrote:
On 19 Jul 2005 13:29:52 -0700, in sci.electronics.design "schmoester"
to_schmoe@yahoo.com> wrote:

Hi,

I've got ~220 low-freq. (0 to 4V max) signals to measure and send to
another computer (over ethernet).

This group of signals will be handled by a single data acq. module
physically separate (20 meters) from identical others, all connected
by
an ethernet bus.

Module Concept & Reqmts:
--PC-104 CPU board with USB and Ethernet interfaces. Ethernet to other
modules, USB to custom DAQ boards, described below.
--Want to divide-up the 220 inputs into ~50 per board, -> ~ 5 boards,
spare channels good.
--High Common-Mode voltage (< 200VDC) on some inputs, -> difference
amp
front end on some channels. (LTC1990)
--Digitize signals (12-bit) with I2C ADC's (thinking MAX1238)
--Offload data from boards to local PC via USB. Would like to use the
Cypress EZ-USB or the Cypress PSoC with USB onboard (CY8C24794). This
would be the I2C to USB bridge. I want to keep the USB interface and
not use only I2C controlled by PC-104 board.

Questions:
--How do I buffer the data on the DAQ boards until I can read it off
with the USB interface? Will the CY8C24794 PSoC with an M8 ľC or the
8051 ľC on the EZ-USB interface with external memory (onboard flash on
the PSoC has too few read cycles to use continuously). Perhaps the
8051 is more suitable than the M8 for interfacing with external
memory.

Any PSoC experts that wouldn't mind some additional questions down the
road if I go that route?

Thanks for sharing your insights!
Omar
Seems an utterly horribly complicated method for getting a slow
speed DAQ system into an ethernet connection.

Ignoring the input conditioning, I'd start with say 64 NS's adcs7478
spi adcs per board. Poll them with a 8051, (since I never did get
around to learning the msp430) That 64*2 bytes per board times your
sample rate, say 50s/sec. A massive 6.4KB/sec.
Might have to put 8K of external ram on the 8051, dammit

Feed them into a Lantronix Xport or eqiuvalent, and give them
individual IP addresses

Whats the software budget for this?
Or am I missing something?



Thanks for the reply. That's a great concept.

I have just a couple issues:
I've got nine of these modules, each of which have to send their data
to a central computer. To have each board have it's own ip address (5
bds x 9 modules = 45) seems like too many for the central computer to
talk to, versus say nine. I'm sure it can be done, but what do i use
for a hub? One per module and another to collect the modules I guess.

If I were to use an single Xport per module, how would I get the data
to it from the 5 daq boards in each module? I was thinking USB--maybe
just replace my PC-104 board with a custom board with an XPort on it?

You're right, there's a lot of software to be done. I'm very much
interested in simpifying, and I agree, my concept seems overly
complicated. I also thought USB on the cards would also facilitate
bench testing them.

Thanks again for your help!
Please don not top post a reply, it annoys many people, and wars
start!

The limit seems to be the size of the board. The data rate is slow
enough that a single 8051 micro could handle the complete number ADC
channels.
I'm confused between by what you mean by modules. But having an 8051
board with 64 ADCs would mean only 4 boards to give 255 ADCs and would
only use 4 web servers like the lantronixs, that is one per board.
That is 4 ip adresses.

This USB stuff. Just another layer of confusion for me. Many micros
already have a UART internally, I'd just put on a max232 driver and
talk to it via an old fashioned terminal program. I still use procomm
from 20 years ago on occasion, or window$ terminal. I avoid
hyperterminal. This makes debugging very easy.

If you put a double pole change over switch between the microprocessor
TX and RX uart lines that switches between RS232 and the lantronixs
xport, you can bypass all the ethernet "layer of confusion" for
testing.

I suggested SPI over I2C, for 2 reasons
1) you may run out of I2C adresses
2) SPI is easier to write code for (my opinion),


martin

Hello all,

This doesn't need zillions of boards or 64ADCs.

Try 8 x ADG731 or ADG732 multiplexers (32 in 1 out, 7mm square package) and
1 Silabs 8051F005 (8051 core, 12 bit, 100kHz ADC with 8 channel mpx).

Talk to the Lantronix thingy using the uart on the 8051 and you have the
whole shooting match in 10 chips and it will all fit on a 100mm square board
quite easily.

Dont forget to protect the silicon with resistors and transient stoppers of
some kind. You can get these in 4 wide arrays in 0805 size packages so the
64 - 128 you are going to need will still fit on the board. RC filters are a
good idea as well.

I think you may need 6 layers and 0.006" design rules to cope with the 7mm
chip scale packages on the multiplexors but one high tech board is much
easier to deal with than loads of bits all trying to talk to each other.


Michael Kellett

www.mkesc.co.uk

 

[martin griffith]

On Thu, 21 Jul 2005 08:02:51 +0100, in sci.electronics.design "MK"
snip

Hello all,

This doesn't need zillions of boards or 64ADCs.

Try 8 x ADG731 or ADG732 multiplexers (32 in 1 out, 7mm square package) and
1 Silabs 8051F005 (8051 core, 12 bit, 100kHz ADC with 8 channel mpx).

Talk to the Lantronix thingy using the uart on the 8051 and you have the
whole shooting match in 10 chips and it will all fit on a 100mm square board
quite easily.

Dont forget to protect the silicon with resistors and transient stoppers of
some kind. You can get these in 4 wide arrays in 0805 size packages so the
64 - 128 you are going to need will still fit on the board. RC filters are a
good idea as well.

I think you may need 6 layers and 0.006" design rules to cope with the 7mm
chip scale packages on the multiplexors but one high tech board is much
easier to deal with than loads of bits all trying to talk to each other.


Michael Kellett

www.mkesc.co.uk


Thats very true, I was very slow in thinking, thanks for waking me up!

martin

 

[schmoester]

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)

 

[MK]

"schmoester" <to_schmoe@yahoo.com> wrote in message
news:1121969322.755745.250510@g49g2000cwa.googlegroups.com...

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)

Hello,

You never told us about the hard bit !

(I remember an earlier thread about this and I think the suggestions were
relay multiplexors).

You'll have trouble if you try and float the boards at different DC
voltages - just imagine trying to debug some 3.3V logic with 500V DC on
top.

I don't think that any of the difference amplifiers like TI INA117 (only
200V) can cope with 600V common mode so you end up with an isolation
amplifier, which is expensive or making your own difference amps (with
precision resistor issues like drift and trimming).

If you can steal power from the cells you are measuring then there are
little AVR processors which will run from 2V and have built in voltage
references and 10 bit A-D converters. You could use one per cell and let
them talk to a central processor via an opto-coupler. You would have to
expect to steal an average current of perhaps 50uA from the cell which may
not be possible.


Michael Kellett

 

[schmoester]

Thanks Michael,

I plan to use linear optocouplers for the isolation, and need to figure
out how to use the difference amp to linearize them with the feedback
output from the optocoupler. There are app notes on this.

I want to minimize load on the batteries. Also, some inputs to the daq
module are from sensors other than the batteries, but output a similar
voltage level. If I avoid dependence on the battery voltages, I can
put any input on any channel for flexibility.

Ideally, I'd like to disconnect inputs from the unit when it's not in
use, but don't want to use (many!) mechanical relays. The spec sheets
on the difference amps show a resistor network from the inputs to
ground, lowering the input impedance from whats seen on a typical
opamp, so there will be current draw. I guess we're stuck with
manually removing the connectors from the module chassis to disconnect
the inputs, unless I can think of something clever to do this.

I noticed on your web site you've worked alot with USB. Is it
difficult to write driver code on the embedded side? I'd like mine to
conform to the test and measurement class standard. Could you offer
any advice? Have you worked with the Cypress chips? I'm still not
clear on how the data from the ADC's will be accumulated and then read
off the board from the USB port. I believe I need to interface
external memory to some MCU device. Maybe the USB fifo memory will
suffice? This is all new to me. The Cypress EZ-USB has an 8051, I'm
thinking I can use this.

Much thanks!