There are several ways of controlling relays from atrduino:
-Using transistor, diode and resistor (and having a common ground)
-Using Optoisolator (I have found 4 channels IC, may be there are 8 channels)
-Using relay driver, like ULN2803A
-Using SSR and connecting it directly to arduino’s pin without. This looks like the simplest solution, but SSRs are not cheap and usually SPST. The also require heatsinks
-Using relay module
If I understand correctly, I need external power supply since all 8 relays could be activate at the same time.
If this is the case I will probably use some 12V LED driver. I’m not sure do I really need a complete isolation in this case?
Further, I’m planning to control relays using I2C port expander, so I probably will need to take into account input line power requirement.
So, my question is how do I choose the right option?