The Si7021 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 build a weather stations or humidor control system. All you need are 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 start using this sensor in a project. One for VCC, one for GND, and two data lines for I2C communication. This breakout board has built-in 4.7KΩ pullup 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"
Image and content credit : Sparkfun