Review on 🔌 Enhance Arduino Projects with Channel Module Trigger Optocoupler by Michael Finnegan

Typically an optocoupler is used to isolate the input signal from other signals on both the high and low side. This circuit uses a common ground between input and relay power, which doesn't make sense to me. So the optocoupler protects the input signal from the back EMF of the relay, but I can use a 0.1 cent diode for that. I modified the circuit so that the input side of the optocoupler is isolated from this circuit, then I am driving a circuit that does not share a common ground with this circuit. This allows me to get the ground loop isolation I need for my control circuit and still get the benefit of this device. sensitive circuits. My guess is that the designers making these circuits don't really know what opto-isolators are for in general circuit sense and just make them because they're sold as is. Just a guess.