This I²C extender board from SJTbits enables the operational range of an I²C bus to be extended significantly. By transparently converting the data and clock lines to differential signals and back, they allow I²C devices to communicate at distances of over a hundred feet.
This I²C extender board from SJTbits greatly expands the operational distance of an I²C (TWI) bus by transparently bridging the connection between individual I²C devices with differential signaling. The board takes the two I²C signals, data (SDA) and clock (SCL), and divides them into inbound and outbound signals (four signals). Each of these unidirectional signals is connected to either a differential line receiver or differential line transmitter, thus forming four sets of differential pairs (eight signals). By using differential signals, the extender boards can increase the range and noise immunity of an I²C bus, and isolating each I²C device helps avoids problems caused by excessive bus capacitance.
More technical information at Pololu.
This product has been discontinued.