coupler Coupler is also called the adapter photoelectric coupler is light to medium transmission signals of a electric a light electric conversion device.It consists of two parts, light source and by light.The light source coupler and by light assembly in the same sealed casing, with transparent insulation isolation between each other.Light source of the pin as input, the optical device pins for the output side, common light source for light emitting diode, the light apparatus for photosensitive diode, light activated triode, etc.Photoelectric coupler sort is more, common have a photodiode, photoelectric triode, photosensitive resistance, optically controlled thyristor, photoelectric darlington, integrated circuits, etc.