How could a computer system help to keep the soil damp?

[Open Intelligence]

Use a water sensor to measure the water content of the soil and then pass these measurements via an analogue to digital converter to a computer which had stored upper and lower levels for these measurements. If the measurement is too low, the computer, via a digital to analogue converter controls an activator which turns on a sprinkler. If the measurement is too high, the computer turns the sprinkler off.