Because many people say NE555 does not work, now we have changed to TL555,This analog capacitive soil moisture sensor measures soil moisture levels by capacitive sensing, rather than resistive sensing like other types of moisture sensor It is made of a corrosion resistant material giving it a long service life Insert it into soil and impress your friends with the real-time soil moisture data This module includes an on-board voltage regulator which gives it an operating voltage range of 3.3 ~ 5.5V This sensor is compatible 3-pin "Gravity" interface, which can be directly connected to the Gravity I/O expansion shield