Sometimes I2C addresses can over lap, or maybe you need to use more than one of the same device. The I2C multiplexer shield is a way to control 8 I2C buses from a single I2C peripheral on a microcontroller. Voltage translation is also handled by the multiplexer chip. It was built on an Arduino shield protoboard from the Schmartboard people.
To test how well this board is suited for prototyping, I decided to build an eight channel I2C shield with a TI PCA9548A 8 channel I2C switch. This chip allows voltage-level translation between 2.5V/3.3V and 5V buses and can communicate with up to eight I2C devices. These features make it very useful to interfacing I2C devices that may require different logic levels.