So there have been some questions about similar relay modules before.
This particular one is titled “3.3V/5V 16A Relay Module for Arduino Nano Due Raspberry Pi ESP8266 + Optocoupler”.
But not much info on the 3.3V trigger option and the seller is providing no information and a web search provide little information.
So I decided to draw an electrical schematic from visual inspection of the components and PCB tracks and a bit of logic where I could not see the PCB tracks (See attached image).
WARNING Other modules might use different components and there is no guarantee that this schematic is correct.
As it was by visual inspection can anybody see flaws in the schematic?
I’ve added some text about possible powering and triggering options for 5v and 3.3v, again anybody see any problems with these statements?
Note I did not like adding the option of powering the DC with 5V and a 3.3V low level trigger option because this would have put 5v to 3.3v across the optocoupler and pushing a small current in to a 3.3v Arduino output and it might or might not work/damage the Arduino