Convert the cheap, ubiquitous solenoid valve to servo-actuation so your arduino plant waterer doesn't need its own power station. Requires: SG90 servo 10mm disc magnet One of them polypropylene solenoid valves that are dead cheap Carefully bust off the solenoid part then slot this together and pop it on top. Update: Now controls 2 valves. Files with "double" in the name for that. The main block has breakaway support built into the model. Split and remove that if it's not your thing. There's a bit of wiggle room to get the servo lined up just right, so don't push it all the way in and screw it down tight right away.