For controllers without rain sensor port, it’s typically to use a normally closed rain sensor connected in series on the COM (common) wire. That way, the rain sensor is normally closed, allowing valve actions; when it rains, the rain sensor becomes open circuit and disables watering. OpenSprinkler has a rain sensor port and allows software-defined rain sensor actions. The only thing you have to make sure is that the sensor should be a simple on/off switch, not an analog switch. The one that you posted: I am not sure what type of rain sensor it is.