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[Reply #90 on:]

Possible, but will require additional logics.

As indeed does option 1, it's just that the logic is called an "Arduino"

I'm inclined to say use two Arduinos, the comms between them is simple (depending on the speed required) where as muxing the SD and Ethernet will I think be harder.

So one Arduino does nothing but sniff the SPI and forward the data to the other.

The other handles that as well as the sensors and ethernet.   

As long as the average data rate of the SPI data is < the rate the 2nd Arduino can offload the data to the ethernet that will work.

So I think it boils down to the average data rate on the SPI. We've determined that the bit rate is 4MHz, how long are the bursts and how frequent?

______
Rob

[Reply #91 on:]

Could try this approach for dual control of the SD card
http://arduino.cc/forum/index.php?topic=71523

[Reply #92 on:]

I've found a setup that is working: A standalone AVR, a crystal and two capacitors in slave mode for eavesdropping the SPI line and then I2C communcation to an Arduino Ethernet board that transfers the data to a webservice. Have it wired and working on my desk. Will solder it onto a protoshield. Will clean up the code and examine the SD library to find out the pattern to look for in the block write to find the last line of text since it looks like that the bytes I'm after are not always at exactly the same position. Thanks for all help and ideas! An additional AVR was even cheaper than the buffer logics required in two masters sharing the same SD card aproach.