Hi Lucas,
Some question need to be answered first.
What is the maximum distance between your sensor?
How many modules you need?
Could you use something else than ethernet?
And of course what kind of voltage input you need?
- If everything could be centralized, a simple I2C expander and some Raspberry Add-on board will do the trick.
- If it is around different buildings, maybe an arduino with ethernet shield will be better.
-if it is on different location in the same building then you could use simple PLC controller , like some cheap ethernet modbus PLC at Automation Direct.
I was on the same road and I made myself a board. It is not ethernet but it could use the same cable.
Please check this post.
http://www.raspberrypi.org/forums/viewt ... 06#p618006
This is about a small board I made with 10 I/Os that could be set to different mode.
The cost is just a little more expensive than aduino UNO but at least I do have a plastic box and terminals with screw.
The github contains the Gerber and you could just send directly to iteadstudio.com. The pcbs will cost around $20 (for 10) with shipping.
https://github.com/danjperron/PIC_MULTI_10_IO
If you are not afraid to build the board, this is the cheapest way.
Daniel