The raindrop sensor module is used for rain detection. It is also for measuring rainfall intensity. The module includes a rain board and a control board that are separate for more convenience. It has a power indicator LED and an adjustable sensitivity though a potentiometer. The module is based on the LM393 op amp. It includes a printed circuit board(control 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.