Description:  The main chip of this item is GY-213V-HTU21D.  The HTU21D is a low-cost, easy to use, highly accurate, digital humidity and temperature sensor.  This sensor is ideal for environmental sensing and data logging and perfect for a weather stations or humidor control systems.  All you need is two lines for I2C communication and you'll have relative humidity readings and very accurate temperature readings as a bonus   There are only four pins that need to be hooked up in order to startusing this sensor in a project, one for VCC, one for GND, and two data lines for I2C communication.  This board has built in 4.7k pull up resistors for I2C communications.  If you're hooking up multiple I2C devices on the same bus, you may want to disable these resistors.  Dimensions: 0.6 x 0.6".     Package included:  3 x I2C GY-213V-HTU21D Temperature Humidity Sensor