A Optocoupler also called a photocoupler, optical isolator or opto-isolator is a small chip that transfers signals between two isolated circuits using light. A basic optocoupler uses a led and a phototransistor, the brighter the led the more current is allowed to pass through the phototransistor.
The PS2501-1 are optically coupled isolators containing a GaAs light emitting diode
and an NPN silicon phototransistor.
The PS2501-1 are in a plastic DIP (Dual In-line Package)