DFRobot Gravity Expansion Shield and Sensors for Arduino - DFRobot SEN0193, This sensor measures soil moisture levels by capacitive sensing, rather than resistive sensing like other common types of moisture sensor. It is made from a corrosion-resistant material giving it a long service life. Simply insert it into the soil and impress your friends with the real-time soil moisture data!The sensor includes an on-board voltage regulator which gives it an operating voltage range of 3.3 to 5.5V. It is compatible with low-voltage MCUs (both 3.3V and 5V logic). To make it compatible with a Raspberry Pi, an ADC converter is required. The sensor is compatible with the DFRobot 3-pin 'Gravity' interface, so it can be directly connected to the Gravity I/O Expansion Shield. DFRobot SEN0193 Gravity Analog Capacitive Soil Moisture Sensor