Relays and Arduino November 21, 2010 Here I will try to show how to connect a relay to an arduino, with a TIP102 transistor. Related Posts Read serial from an Arduino 2 minute Optocoupler Green Energy About The Author Mikey One Comment Jorge Gamez 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. May 28, 2018 Reply Add a Comment Cancel reply Your email address will not be published. Required fields are marked *Comment Save my name, email, and website in this browser for the next time I comment.