This module allows you measure moisture via analog output pins and it provides a digital output when a threshold of moisture is exceeded.
The module is based on the LM393 op amp.
It includes the electronics module and a printed circuit board that “collects” the rain drops. As rain drops are collected on the circuit board, they create paths of parallel resistance that are measured via the op amp.
The lower the resistance (or the more water), the lower the voltage output. Conversely, the less water, the greater the output voltage on the analog pin. A completely dry board for example will cause the module to output five volts.