5Pcs 3-5V Optocoupler Isolation Board Optoelectronic Isolator EL817 PC817 Card Rail Bracket Input 3-5 V Optocoupler Isolation Module 1 Channel Opto PNP NPN Signal Converter

Very Good

Update: I'm a dummy -In my original 'I'm not sure what's happening' review, I failed to take resistance into account.After testing both Gnd-Out and Gnd-VCC resistances (with input triggered), I found readings of around 300 and 10k, respectively.Retested with 5v supply and appropriate load between ground and out (white LED with forward voltage ~ 2.75v) - worked like a charm. See last 2 photos.Original review:***I was able to get this EL817 based opto to trigger instantly with 3-5v input, but have not had success closing a circuit consisting of a 6v power source and ~ 5v load via any combination of the output terminals, including tying input/output grounds together.The boards appear well manufactured, and the components I've tested give consistent readings, so I'm certain that I'm missing something.Will continue tinkering and update this review with my eventual outcome.

I have used optocouplers all my life, but typically only in breadboards or as part of a larger printed circuit. These little modules let me add optical isolation off-board and after design lock, so if I need isolation for just one or a few signals I can add it after the fact. I find uses for these all the time. Recommended.