Particle Core based project in charge of taking care of my green plants.
The water pump will not work with a voltage under 5V. In order to power it, I soldered a wire straight on the VUSB pin of the USB header. The following picture illustrates where to solder the wire on the former Arduino Nano. You can do the same with the Particle Core diode (black component between the USB header and the VIN pin).
SmartWatering – Arduino plant watering – [Link]