System Diagram
Figure 1 shows how a conventional automated sprinkler control system works. The microprocessor uses a bank of relays to control electrically operated valves, one valve per sprinkler circuit, and one relay per valve.When a relay closes, the corresponding valve opens and water flows. The valves all share a common ground line that, if interrrupted, disables all the valves. Some controllers come with wiring terminals in the ground line designed to support a rain sensor that opens the circuit.
FIGURE 1: Conventional automated sprinkler controls
As in most control systems, an automated sprinkler controller has processing and actuators; it lacks the sensors and related processing it needs to be smart. Figure 2 shows how we modified the conventional system, adding moisture and weather forecast sensors, more capable processing (a PC), and one or more new actuators.
You could implement the system without a PC, using a standalone processor such as the Javelin Java processor, but we found it convenient to have the greater hardware resources and Internet connectivity of a PC available. The standalone processor can directly support an interface to read the moisture sensors, and you could still use the X-10 actuators we’ve used with a standalone processor if you interfaced it through its own interface module, such as an X-10 TW523 or CM11A.
FIGURE 2: Modified automated sprinkler control system