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This relay module can switch high voltage / high current with a 3V logic signal from a microcontroller. There's an optocoupler on the PCB to isolate and protect your circuit from noise. Works well with 3.3V devices like a Raspberry Pi and esp8266. Rated Relay voltage / current: 240VAC / 10ALogic signal voltage: 3V
This sensor has a series of exposed traces connected to ground and other traces connected to the signal with a pull up resistor. The resistor will pull the sensor trace value high until a drop of water shorts the sensor trace to the grounded trace.