HIgh GPIO LOGIC with optocoupler

Question

I want to know if my high side logic from 3.3 volt esp32 is right about linking a led on a gpio output to an optocoupler

Answer 1

This Answer might not be 100% complete, but here are 2 things I'd change:

According to the PCF817 datasheet, the nominal forward current is 20 mA with a forward voltage of 1.2 V. That means R11 is way too large. The drop at R11 is 3.3 V - 1.2 V = 2.1 V @ 20 mA, so R11 should be ~ 105 Ohm.

The way you wired up the output side will probably not work correctly. When the optocoupler is off, your transistor's base is floating, which should be avoided. I'd probably do something like this:

^{simulate this circuit – Schematic created using CircuitLab}

That way the Relay should be default on and triggering the opto pulls Q5's base to GND -> state switches to off.

Be aware though, I haven't tried/tested/simulated this, so it might not work perfectly, but that's where I'd start.