I have never been happy that my first version of the drop controller had 2 different power supplies; a 12 volt supply for the solenoid valves and a second 5 volt supply for the Arduino, so I looked for a way to share the 12 volt supply. After a short search I came across Derek Molloy’s video on Youtube. This describes making a 5 volt power supply from a mains adaptor.
Full video after the break