Timer

Controller is most often used by an irrigation professional. Timer is viewed as a retail DIY term. 

The controller is the part of an automatic sprinkler system that determines when a valve will turn on and how long it will operate. The timer sends a low voltage signal to the valve, which will then open for a predetermined amount of time allowing water to flow to the sprinklers. The size of the timer to purchase is determined by how many zones are in the sprinkler system. Controller is most often used by an irrigation professional. Timer is viewed as a retail DIY term.