In518 - Ic Datasheet

Are you trying to this IC with a different model?

Your circuit with an IN518 is failing. Fix: If it’s an opto-isolator, test the LED side with a 1.2V source (use a 220Ω resistor with 5V). The output side should switch a low-current load. If not, replace with a PC817 (verify pin 1 location – it may have a dot or notch). in518 ic datasheet

Have a photo of your IN518 part? Post it below for a precise ID. Are you trying to this IC with a different model

I can provide a circuit diagram or a list of equivalent ICs if needed. in518 ic datasheet