@OldSurferDude I use this. https://www.homedepot.com/p/Orbit-Solenoid-for-Battery-Operated-Timer-57861/203151515
Instead of having to hold the valve open, i can just pulse it. I use a simple motor controller to pulse it and when i need to close it, pulse it in "reverse". That way I could use a battery and if it only opens once or twice a day it's only a half a second or so of draw off the battery.
@4994james or just use internal vcc measurement as described on the same page. That saves you the voltage divider.
I wrote a convenient library to measure vcc internally : https://github.com/Yveaux/Arduino_Vcc
