I²C opto/relay card:

The popularity of our series on I²C devices is still growing, and that is why we venture to propose a real-world interface for the I²C bus. The eight channels on the interface described here are electrically isolated by optocouplers or relays, and operate under the control of I²C bus commands. If you need more than eight channels, it is possible to put up to seven more cards on to the bus.