[Not really allotment stuff]
I have been giving the issue of automatic watering systems some thought. I have some resources and restrictions. I have two large water butts which will have water in all the time. They are not very high (they are below the shed gutter to collect the water) so there is not much pressure. There is no mains electricity. There is a shed and a greenhouse. I have a spare car battery and a solar panel to charge it.
I have searched t'internet for pumps and motorised valves. I can find pumps, including 12v pumps for water supplies in caravans and 12v pumps for garden fountains. I have had no success with any kind of low voltage motorised valve.
I have wondered how to deliver a fixed amount of water to a grow bag or pot. I have tried making a simple syphon with a drinks bottle and some piping, which works as expected, but how to fill it?
As a simple stop-gap I'm going to build a simple two step timer. This will trigger a few times per day and each time it will switch a pump on for a fixed time.