opto-splitter

aka "opto," "opto-isolator." A DMX data-distribution device, used when more than one data stream is required, or when the number of devices on a single line exceeds the maximum of 32. Required as the protocol does not permit "Y" cables. The "opto" part is short for "optically isolated," a desirable feature so that a fault on one output cannot propagate to other outputs.

Some opto-splitters just provide electrical isolation between the input and the outputs, but the best types have a separate transformer-isolated power supply or DC-to-DC converter for the input and each of the outputs. This provides isolation between each and every data link entering the unit. A quick way to tell if a unit has this type of isolation: With the unit unplugged from power and data links, run a dc continuity check with a VOM between pin 1 on each of the data links. If it's an open circuit to all other pin 1's, the link has full isolation.