This is an optocoupler manufactured by Everlight, a Taiwanese optoelectronics company. The EL817S1(D)(TU)-F is a surface-mount device (SMD-4) optocoupler, composed of an infrared light-emitting diode (LED) and a photosensitive device. The optocoupler is designed for isolated signal conversion between a low level output signal and a high level transfer signal. The optocoupler is compliant with the RoHS directive and is RoHS-certified, meaning that it does not contain any hazardous substances. It is capable of operating within a wide temperature range of -40°C to 100°C. The optocoupler also features an isolation voltage of 5.2kVrms.