, leave the jumper in. Having an optoisolatar and the relay seems like overkill to me. Most applications just drive the transistor to drive the relay.
Oh, to this point: Do you mean relay module VCC or JD-VCC? My plan to set it up like in the schema you postet: VCC gets the Arduino 3.3V, JD-VCC gets the 5V from the buck converter.
Neither is correct.Please consider carefully and follow my explanation above.
The only difference I can find is, that you said GND and 5V should run from the buck converter to the relay.
But because the same buck converter Powers the Arduino and the relays, GND is at all interconnected and so it should make no difference in my eyes if GND comes from Arduino or directly from the Buck converter? Is there one more difference?
The second of my drawing is in my eyes the same as the one you shared. Only difference: 3.3V from Arduino instead of 5V.
The first one gets 5V to the logical side of the relay. Here I would be afraid that the Arduino gets damaged when logical pins are low and get 5V through it.
The VCC on the relay board pairs with the "IN" lines which go from the relay board to the Arduino, so it should travel with them and and back to the "Raw" pin on the Arduino or at least alongside the 5 V line from the "Raw" pin back to the buck converter, not with the "JD-VCC" power line.
You will note the two LEDs in series, which means that until the voltage between VCC and IN reaches 2.6 V or so, no current will flow so it could never pull the Arduino pin higher than 5 - 2.6 or 2.4 V, which is much less than 3.3 V.
So just leave the JD-VCC jumper on and eliminate a wire.
Davidking8811 please don't hijack someone else's thread.