Schematics for a small breakout board PCA9540BD component (http://www.nxp.com/documents/data_sheet/PCA9540B.pdf).
The PCA9540BD is a 2-channel I2C-bus multiplexer.
Let's say that you want to get data from 2 components through I2C but they both have the same I2C address. The PCA9540BD allows you to redirect the SCA and SDA pins to (SCA0, SDA0) or (SCA1, SDA1).
The PCA9540BD pins have a pitch of 0.05 inches making the component difficult to connect to your arduino. This breakout board allows you to connect the PCA9540BD component to a classical prototype board.
It can conveniently be connected in the middle of the board. Unlike a DIP8 connector, the order of the pins are altered so that all pins connected to your arduino are on one side, and all pins connected to your devices are on the other side.
You can see below how the pins are ordered:
The schematics are under the GPLv3+ license.
I have implemented a driver for arduino allowing you to control the component. It is available in this repository.