I'm building an automatic dog water bowl filler powered by solar panels. It includes two voltage regulators one 7805 for the arduino and a 7812 for the solenoid that turns the water on and off, using a automatic sprinkler valve and some PVC pipe. The arduino controls a relay that turns on the 7812 circuit to power the solenoid. I need help at certain times during the day there is not enough power coming from the solar panels to power the device, I need a circuit that will take very little voltage and current to run, and check the power coming in. when the circuit is at the minimum required voltage and current, turn the main circuit on. Then turn off when it gets to a low voltage and current.
Much Help is need here