This was my first prototype of the hub that will allow the user to connect and disconnect sensors as they please. I was in China this summer, and picked up several mini-USB ports at a component store. I figure that most people are already familiar with how to connect and disconnect these pieces, so I decided to try them out. They have 5 pins, not including the metal casing.
I am using pin 1 for power, pin 2 for the analog signal, and the casing itself for ground. I have already planned the next prototype which will use the last three pins as identification pins, so that the Arduino knows what sensor is plugged in which port, and will record this in the data file on the SD card, along with the data itself.
This iteration of the sensor hub is made completely by hand on Perf Board. The next iteration will be a homemade PCB, for size and consistency reasons. One of the images shows a carbon monoxide sensor connected.