I'm planning to use barrels full of water to make a drip watering system. I can make the water controls from a pretty easy toilet fill&flush valves and balance it so it needs a very light push on the vertical axis to open/shut.
I need the plants to be watered at night only. Not strictly so it can spill a bit into the morning. So basically it has to be at one position during the day and another during the night.
I'm not an English native and my tech terminology is lacking, so I don't really know what to ask google to find me.
I don't know if light detection or a timer on it would be cheaper.
Failing electronics I guess I can make something with a parabolic mirror or Fresnel lens a metal plate feeding into a sterling engine.