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  • I understand the need for a 9V battery to activate the relay coil, but is the battery also powering the Arduino? this would mean that there is no need for the Arduino’s wall plug correct? (Im refering as Wall Plug to the Black charger type input on the bottom left hand side). Also by the circuit portrayed this is a NPN transistor correct? Would it make a difference if I use a PNP transistor?, other than the wiring of course.

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