I would like to know if I am using an Opto-isolated relay board, in any of the following cases, will I lose the isolation? If one could also explain why, that would be even greater!
1) Using a single 5V power supply. Connect it to JD-VCC (jumper removed) and to GND. Bring out another wire from the same power supply to power up an arduino. Connect arduino's VCC to relay board's VCC and digital pin to IN pin of relay (Arduino's GND is not connected to anything). Will connecting board's VCC to arduino which is powered by the same power supply that powers the relay coils means I lose isolation?
2) Using a AC-DC buck converter to convert 220V AC to 5V DC, from the buck converter bring 2 wires: one to the JD-VCC and one to power an arduino which then connects to relay's board VCC (jumper removed) (same as 1 but instead of power supply I am using a single buck converter to power relay coils and to power an arduino.
3) Using 2 different AC-DC buck converter to convert 220V AC to 5V DC. From one converter I power relay board. From the other converter I power arduino which is connected to board's VCC (jumper removed) and IN pin
I have a feeling that only the third option gives isolation while the other two means my arduino is not isolated from the relay coils, but if the reason for that is because the arduino is powered by the same circuit which powers the coils (same power supply / same buck converter circuit) I would argue that even in the third option, the 2 different buck converters are connected to the same AC source (in this case, my house electricity) and therefore, the arduino and the coils are not really isolated.
Would be very interesting to hear your opinion about this one...
Thanks in advance!