It may be possible to wire the sensor to the sensor port on OpenSprinkler and use it as if it’s a rain sensor. So when the sensor is activate, it disables watering. Though your sensor seems a analog sensor (you said the output is 0 to 5V), it can still be used as a digital switch — generally, microcontrollers detect digital switches by using a pullup resistor. So when the switch is open, it reads a high (e.g. 5V), and when the switch is closed it reads a low (0V). Depending on the logic of your sensor, you configure the sensor as normally open or normally closed.