Re: Data Acq. Concept Help
- From: martin griffith <martingriffith@xxxxxxxxxxxxx>
- Date: Tue, 19 Jul 2005 23:59:28 +0200
On 19 Jul 2005 13:29:52 -0700, in sci.electronics.design "schmoester"
<to_schmoe@xxxxxxxxx> 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 µC or the
>8051 µC 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
.
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